var textForPages = ["MASARYKOVA UNIVERZITA                                                Přírodovědecká fakulta                                                                                         Letní                                                elektrochemická                                                                                             škola                                                Summer                      electrochemical                      school","2                         Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009                     Spolupořadatelem  a  sponzorem akce je firma Metrohm                                                                                            http://www.metrohm.cz/                                             © 2014 Masarykova univerzita                ISBN 978-80-210-6827-8                                                         Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","3                   Úlohy pro letní elektrochemickou školu                      1.  POTENCIOMETRICKÁ TITRACE (Iveta Pilařová, Romana Ševčíková)                              Stanovení protonačních konstant adeninu                                    str. 4                    2.  VOLTAMETRIE NA SOLID STATE ELEKTRODÁCH (Rudolf Navrátil, Mehdi                        Ravandeh)                              Elektrochemická  detekce  purinových  derivátů  na  pencil  grafitové                               elektrodě                                                                                           str. 10                    3.  ELIMINAČNÍ VOLTAMETRICKÁ PROCEDURA (EVP) (Libuše Trnková, Libor                       Gurecký)                               Aplikace  různých  eliminačních  funkcí  na  vybrané  voltametrické                               křivky                                                                                                  str. 15                    4.  KOROZE (Libor Gurecký, Libuše Trnková)                              Stanovení korozní rychlosti pro vzorky oceli Tafelovou metodou                                                                                                                                            str. 20                    5.  ELEKTROCHEMICKÁ  IMPEDANČNÍ  SPEKTROSKOPIE  (EIS)  (Peter  Barath,                       Vimal Sharma)                               EIS  adeninu  na  nemodifikovaných  a  modifikovaných  grafitových                               elektrodách                                                                                       str. 26                   Summer electrochemical school tasks                          1.  POTENTIOMETRIC TITRATION (Iveta Pilařová, Romana Ševčíková)                                  Determination of protonation constants of adenine               p. 4                       2.  VOLTAMMETRY ON SOLID STATE ELECTRODES (Rudolf Navrátil,                           Mehdi Ravandeh)                                  Electrochemical detection of purine derivatives on pencil                                  graphite electrode                                                                        p. 10                        3.  ELIMINATION VOLTAMMETRIC PROCEDURE (EVP) (Libuše Trnková,                           Libor Gurecký)                                  The application of  different elimination functions to chosen                                  voltammetric curves                                                                     p. 15                       4.  CORROSION (Libor Gurecký, Libuše Trnková)                                   Determination of corrosion rate of chosen steel samples    p. 20                       5.  ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY  (EIS) (Peter Barath                           Vimal Sharma)                                  EIS of adenine on unmodified and modified graphite electrodes                                                                                                                                           p. 26                                                  Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","4                                       POTENTIOMETRIC TITRATION                            Determination of protonation constants of adenine                            Potentiometry  is  one  of  the  most  simple  electroanalytical  techniques,  being                primarily used for pH measurements in different samples and for the determination of ionic                 constituents  in  biological  fluids  (e.  g.  blood,  urine),  but  also  as  a  transduction  mode  in                 monitoring  selective  interactions  in  molecular  sensor  devices  or  in  the  course  of  chemical                reactions. One of the major types of potentiometry, potentiometric titration is based on the                 monitoring of the working electrode potential change as a function of the reagent addition to                the sample. Potentiometric methods are used for different types of titration (e.g. acidobasic                 titrations, complexing, redox, precipitation). The result is the potentiometric titration curve of                the characteristic sigmoidal shape and the titration endpoint is determined by using different                 mathematical methods, such as second derivative of titration points, linearization of titration                 curve (Gran’s method), calculation of polynom (Samsonk’s method)[1,2].                        Potentiometric  titration  is  suitable  method  for  the  investigation  of  protonation  –                 deprotonation  equilibrium  of  biologicaly  important  compounds  (purine  derivatives,                cytokinins, etc.) and it enables very precisely determination of protonation constants pK a.                         Adenine  (6-aminopurine)  is  one  of  the  two  most  commonly  occurring  purines  in  a                 ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), and thus is involved in the process                of  protein  synthesis  and  transmission  of  genetic  information.  The  knowledge  of  its                 protonation  equilibrium  is  very  important  not  only  in  biochemical  processes  and  in                electroanalysis, but also for the study of metal complexes in which adenine takes the role of                 the ligand. Adenine exhibits two dissociation constants (pK a1 = 4.12 and pK a2 = 9.83) [3]                                                  Fig.1: Protonation-deprotonation of adenine                  APPARATUS, ACCESSORIES AND REAGENTS                        automatic titrator Titrando 835 (Metrohm, Switzerland), thermostat Julabo F25 – EH                        Tiamo 01/02 software (Metrohm, Switzerland)                       combined ion – selective electrode LL Ecotrode plus                                                   Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","5                         potentiometric vessel                        argon                       factorized NaOH; HCl; NaCl; milli Q water (18.2 MΩ·cm, 25 °C)                        adenine                 SOLUTIONS                Stock solutions                                                                                                  -3                c (NaOH) = 0.1 mol/L; c (HCl) = 0.1 mol/L; c (NaCl) = 1 mol/L; c (adenine) = 1·10  mol/L                The LL Ecotrode plus electrode calibration                  5 mL of HCl + 4.5 mL of NaCl + 40.5 mL of milli Q water                  Sample measurement                 0.5 mL of HCl (0,1mol/L) + 5 mL of adenine (mmol/L) + 4.95 mL of NaCl (1 mol/L) + 39.55                mL of milli Q water                 EXPERIMENT                 The LL Ecotrode plus electrode calibration                 5 mL of HCl (0.1mol/L); 4.5 mL of NaCl (1mol/L) + 40.5 mL of milli Q water                Sample measurement                  0.5 mL of HCl (0.1mol/L) + 5 mL of adenine (mmol/L)  + 4.95 mL of NaCl (1 mol/L) +39.55                mL of milli Q water                 PARAMETERS                 1) Electrode calibration: the addition of standard titrant solution (0.1M NaOH) = 0.01 mL ;                 the total volume of 0.1M NaOH = 10 mL; the dosing rate is “maximal” and the titration mode                is set as “optimal”. Other parameters are “0” or “off”                  2) Sample measurement: the addition of 0.1M NaOH = 0.001 mL; the total volume of 0.1M                NaOH = 1 mL; the dosing rate is “maximal” and the titration mode is set as “optimal”. Other                 parameters are “0” or “off”                  Inert atmosphere ensured by bubbling with  argon (99.999%) and stirring (magnetic stirrer,                speed 3); temperature 25 °C.                  MEASUREMENT                 a) Start  PC, open Tiamo 1.2 software (see manual  below) and clean the automatic burette                system with standard titrant solution (10 mL of 0.1 mol/L NaOH).                                                   Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","6                  b) Prepare measured solution (for electrode calibration or sample measurement) in the vessel,                 put LL Ecotrode and dosing capillary into the vessel. Ensure inert atmosphere (bubbling and                stirring). c) Set titration parameters in the selected method.                  d) Start the measurement.                 e) Record the titration curve and export data.                  Note: LL Electrode plus is filled by 3M KCl, the filing hole should be opened during the                measurement. After measurement don´t let the electrode for long time in basic solution, clean                 it and  put it in stock solution (3M KCl).                  POTENTIOMETRIC CURVE EVALUATION                        The  acidic  part  of  calibration  curve  is  used  for  determination  the  slope  (q)  and                                        0                equilibrium  potential  (E )  by  linear  regression.  The  equivalence  point  allows  to  calculate                concentration of HCl. The basic part of calibration curve help to calculate pK w (should be for                               o                temperature  25 C  about  13.78).  All  these  values  are  important  for  calculation  of  pH  and                degree of titration z  and subsequently of pKa value based on these equations:                                             z                                               1 z                 pKa      log H      log         log   A                  pKa  log H   log         log  A                     1                                                 2                                          1 z         HA                                     z          A                                              c NaOH  V ekv  c NaOH  V  H       OH                                                   V       V                                      z            celk                                                              c                                                               L                                                          V celk  V                                                             Adenine                                      250                                      200                                      150                                      100                                    E/mV  50 0                                      -50 0     0.2     0.4    0.6     0.8     1      1.2                                     -100                                     -150                                     -200                                     -250                                     -300                                                              V/mL                           Fig.1: An example of measured data - titration curve of adenine in water                                                   Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","7                  RESULTS AND REPORT                                         Calibration                      Measuring                                     slope q        E 0                 pK a1       pK a2                                                                1.                                                                2.                                                                3.                  REFERENCES                 [1]    Mermet J.-M., Kellner R. et al, Analytical Chemistry, Wiley-VCH, 2004                 [2]    Zýka J., Analytická Příručka, SNTL, 1980                 [3]    D.D.  Perrin,  Dissociation  Constants  of  Organic  Bases  in  Aqueous  Solution,                       Butterworths, London, 1965                 [4]    Lippert  B.,  Gupta  D.,  Promotion  of  rare  nucleobase  tautomers  by  metal  binding,                       Dalton Transactions, 2009                                                                               Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","8                  DISCUSSION AND REMARKS                                                                                                         Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","9                  DISCUSSION AND REMARKS                                                                                                         Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","10                         VOLTAMMETRY ON SOLID STATE ELECTRODES                     Electrochemical detection of purine derivatives on the pencil                                                  graphite electrode                        Linear  sweep  voltammetry  (LSV)  is  one  of  most  used  electrochemical  methods.  It                requires a good potentiostat and three electrode set, which consists of a working electrode, an                auxiliary electrode, and a reference electrode. The current is measured between the working                and an auxiliary electrode while the potential between the working electrode and a reference                electrode is swept linearly in time. The slope of the potential vs. time is called the scan rate v                and the polarization process can be described by the equation: E = E initial + vt. The oxidation                or reduction processes of electro-active species are registered as current maxima (peaks I p)                providing the determination of  their concentration in solutions.                                                         5                                                                    1/2                                                               1/2                                                                 I p=2.99·10 n(αn a) AD cv 1/2        (Delahay equation)                Where: I p stands for the current peak, n stands for the number of electrons participating in                reaction and n a  for the number of electrons participating in a rate determining step, α is the                electron transfer coefficient, A is the effective area of electrode, D is the diffusion coefficient,                c is the concentration,  v is the scan rate.                        Purines provide on the pencil graphite electrode (PeGE) in voltammetry well readable                oxidation  signals.  Our  research  showed  that  the  oxidation  response  of  purines  can  be                increased by using an electro-catalytical effect of monovalent copper ions. Cu(I)ions, obtained                by  the  reduction  of  Cu(II)  in  situ  on  PeGE  surface,  are  capable  to  form  a  Cu(I)-purine                complex and this  complex increases surface concentration of the purine  studied. Thus, the                electroanalysis of adenine, guanine  or xanthine with the use of monovalent copper are based                on: 1) the electrochemical reduction of Cu(II) at potential -0.1 V, 2) the formation of Cu(I)-                purine complex, 3) the oxidation of complex at potentials closed to 0.5 V, 4) the oxidation of                purine whose signal is higher than one without the presence of copper ions. The application of                copper ions in voltammetric experiments contributes to significant decrease of the detection                limit of purine [1-3].                APPARATUS, ACCESSORIES AND REAGENTS                        AUTOLAB PGS30 Analyzer (EcoChemie, Netherlands)                       NOVA software (Metrohm, Switzerland)                        Electrodes (working - PeGE with leads Tombow, 0.5 mm, reference – Ag/Ag Cl/3M                       KCl, counter electrode – Pt); voltammetric vessel                       argon                       phosphate-acetate buffer pH 5.5; c (CH 3COOH) = 0.4 mol/L, c (H 3PO 4) = 0.4 mol/L,                       c(NaOH) = 2 mol/L                       adenine,  guanine  or  other  purine  derivative,  copper  sulphate;  miliQ  water  (18.2                       MΩ·cm)                                                      Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","11                  SOLUTIONS                 Supporting electrolyte                       phosphate-acetate buffer pH 5.5; c (CH 3COOH) = 0.4 mol/L, c (H 3PO 4) = 0.4 mol/L,                                                         -3                       c(NaOH) = 2 mol/L; CuSO 4 = 1·10  mol/L                Samples                                                                         -3                        adenine, guanine or xanthine (stock solution = 1·10  mol/L)                EXPERIMENT                        Voltammetric experiment  of  purine derivate in the absence of copper ions                       2 mL supporting electrolyte + 8 mL miliQ H 2O + 100 µL purine                       Voltammetric experiment of purine derivative in the presence of copper ions                       2 mL supporting electrolyte + 8 mL miliQ H 2O + 100 µL of purine  + 100 µL Cu(II)                 PARAMETERS (CV OR LSV - CYCLIC OR LINEAR SWEEP VOLTAMMETRY)                        LSV measurement                        Start potential -0.1 V; stop potential -0.2 V; upper vertex potential 1.4 V; lower vertex                       potential -0.1 V; scan rate 200 (400, 800) mV/s; time of accumulation 120 s, room                       temperature                 MEASUREMENT                     a)  Clean  voltammetric  vessel  (diluted  nitric  acid,  than  miliQ  water);  add  2  mL  of                       supporting electrolyte, 8 mL miliQ H 2O and 100 µL of Adenine or Guanine.                    b)  Insert working electrode into pencil and connect all electrodes.                    c)  Perform three electrode set into the measuring vessel with solution of sample.                    d)  Record the voltammogram with the specified voltammetric parameters.                    e)  Smooth voltammetric curves by Savitzky-Golay filter (level 2).                    f)  Save the smoothed curves.                    g)  Add 100 µL of Cu(II) solution into solution of sample and record LSV curves with the                       specified parameters.                    h)  Smooth voltammetric curves by Savitzky-Golay filter (level 2).                    i)  Save the smoothed curves.                    j)  Load overlay total voltammograms from all experiments and compare them.                 CURVE EVALUATION                Evaluate the peak potential and the peak height of the purine derivative (adenine, guanine or                xanthine) in the absence and in the presence of Cu(II) ions.                             200                                         LSV xanthin                           150                                                                           Fig.  1:  Real  voltammogram  of                           I[uA]   100                                     purine  (Xan  in  the  absence                                                                           (dashed line) and in presence (full                            50                                                                           line) of Cu(II) ions                             0                                 -100    400   E[mV]  900      1 400                                                 Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","12                      a)  The evaluation of CV peak height and peak potential for both measurements (with and                       without Cu(II) ions) for different scan rates (from 50mV/s to 800 mV/s per 50 mV/s).                    b)  The  assessment  of  the  influence  of  scan  rate  and  Cu(II)  ions  on  peak  height  and                       potential.                    c)  The determination of  rate determining step in  oxidation  of adenine or guanine (see                       Delahay equation).                    d)  The evaluation of oxidation process of purine derivative without Cu(I) and with Cu(I)                 RESULTS                                     without Cu                                with Cu                            scan rate       E (V)      I(A)         scan rate       E (V)      I(A)                           (mV/s)                                  (mV/s)                            REFERENCES                 [1]        Kounaves, Samuel P. Voltammetric Techniques. Handbook of Instrumental                              Techniques for Analytical Chemistry. pp. 709–725.                 [2]    Aladag N., Voltammetric Study of Aminopurines on a Pencil Graphite Electrode in the                       Presence of Copper Ions, Electroanalysis, 2010                 [3]    Farias P.A.M., Ultratrace Determination of Adenine in the Presence of Copper by                       Adsorptive Stripping Voltammetry, Talanta, 2001                 [4]    Jelen. F., Voltammetric Study of Adenine Complexes with Copper on Mercury                       Electrode, Electroanalysis, 2009                                                                 Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","13                  DISCUSSION AND REMARKS                                                                                                       Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","14                  DISCUSSION AND REMARKS                                                                                                       Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","15                       ELIMINATION VOLTAMMETRIC PROCEDURE (EVP)                      The application of different elimination functions to chosen                                                 voltammetric curves                         The  elimination  voltammetric  procedure  (EVP)  is  a  mathematical  processing  of                voltammetric data enabling achievement of better sensitivity and detection limits of studied                compounds compared to voltammetric methods on which it relies. It works with elimination                voltammetric functions (EVF), eliminating or conserving some chosen partial currents. EVP                is based on different dependences of these partial currents on scan rate. In other words, the                variable parameter is  the scan rate and  EVF are presented as linear combinations of total                currents measured at different scan rates. In EVP must be satisfied two necessary conditions:                       1)  An eliminated current can be expressed as a product of two independent functions -                         the scan rate function and electrode potential function.                                                         I  j  Y  j (E ) W j (  )                       where  Y j(E) is potential function and W j(ν) is scan rate function.                       2)  A total voltammetric current is expressed as a sum of partial currents.                                                         n                                                   I      I  j  I d  I c  I k  ...                                                       j  1                 where I d is the diffusion current, I c the charging current and I k the kinetic current.                Advantages of the approach consist in simplicity and availability.  EVP is not time consuming                procedure  and  it  is  able:  (i)  to  provide  better  sensitivity,  (ii)  uncover  of  minor  processes                hidden in major processes, (iii) to extend potential range and (iv) to yield new information                about electrode processes. The interaction of partial currents can be  considered as a partial                drawback. This disadvantage is sometimes reflected in an elimination signal distortion, as for                example in the case of strongly adsorbed electroactive substances. Then the disadvantage is                changed in  the advantage because the elimination signal  is  much more  higher  and has  the                form (peak-counterpeak) which does not need a baseline correction [1].                                                                                   peak-counterpeak                                    Fig.1: A substance transported                Fig.2: A totally  adsorbed                       to  an electrode only by diffusion            electroactive substances                                                 Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","16                  I ref – reference current,  f (I) – the aplication of the elimination function E4                (I k +I c   elimination and I d conservation), the values on the axe x are dimensionless.                  elimination function E4:     f (I) = a 1I  (v1/2) + a 2I  (v) + a 3I (v2)                                                        f(I) = – 11.657I 1/2 + 17.485I – 5.8284I 2                        Export data from NOVA 1.10 (or GPES) to Excel.                       Use elimination voltammetric procedure EPV  E4 for measured data                 PARAMETERS                        Scan rates with integer 2:   e.g., 100, 200, 400 and 800 mV/s                       Elimination voltammetric functions with calculated coefficients                           f(I)          Characteristics                     EVLS equation                         E1       I d≠0; I k=0 (I c dist. By 1.707)   f(I) = -3.4142·I 1/2 + 3.4142·I                        E2       I d≠0; I c=0 (I k dist. By 2.414)    f(I) = 4.8284·I 1/2 - 2.4142·I                        E3       I k≠0; I d=0 (I c dist. By -0.707)   f(I) = 3.4142·I 1/2 - 2.4142·I                         E4            I d≠0; I k=0; I c =0      f(I) = -11.657·I 1/2 + 17.485·I - 5.8284·I 2                        E5            I k≠0; I d=0; I c =0       f(I) = 6.8284·I 1/2 - 8.2426·I + 2.4142·I 2                         E6            I c≠0; I d=0; I k =0       f(I) = 4.8284·I 1/2 - 8.2426·I + 3.4142·I 2                  CURVE EVALUATION                        Evaluate the EVP curves of the adenine in the absence and in the presence of Cu(II)                       ions                                                f ( I)                                 EVP                                        I                             Fig. 3:Dependence of elimination current coefficient  EVP on scan rate coefficient x for EVFs                                                     Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","17                  RESULTS                                 without Cu                                        with Cu                     method                I(A)                       method                I(A)                    CV (LSV)                                        CV (LSV)                       EVP                                              EVP                     REFERENCES                [1]  Trnková  L.,  Elimination  Voltammetry  with  Linear  Scan,  J.  Electroanal.  Chem.,  582                       (2005) 258.                 [2]  Trnková  L.,  Application  of  Elimination  Voltammetry  with  Linear  Scan  in                      Bioelectrochemistry, Reasearch Signpost, 2007                                                                                    Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","18                  DISCUSSION AND REMARKS                                                                                                        Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","19                  DISCUSSION AND REMARKS                                                                                                         Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","20                                                      CORROSION                      Determination of corrosion rate of steel samples in different                    environments by linear polarization assessed by Tafel equation                 The simplest definition of corrosion is: It is the process of a metal returning to the material’s                thermodynamic state. Most of the materials form the oxides or sulfides from which they were                originally in the earth. In the other words, corrosion is the gradual destruction of materials                (usually metals) by reduction-oxidation reactions:                                                          n+                                               o                              Anode:         M  - ne→ M                                                            -                                                                     -                              Cathode:       O 2 + 2H 2O + 4e  → 4OH  (in alkaline solutions)                                                                                          +  -                                             O 2 + 4H  + 4e  → 2H 2O (in acidic solutions)                                                      +                                                                 2H  + 2e→ H 2                                                                   Fig. 1: The combination of anodic                                                                  polarization curve with current density j a                                                                  (metal  ionization)  and cathodic                                                                  polarization curve with current density j c                                                                  (cation reduction and hydrogen                                                                  depolarization). The bold line represents                                                                  the sum of both processes.                        Most  corrosion  phenomena  are  of  electrochemical  nature  and  consists  of  two  (or  more)                electrode  reactions  on  the  surface  of  corroding  material.  One    possible  reaction  is  the                oxidation of metal (e.g., metal or steel dissolution) refers to anodic partial reaction and the                other one is the reduction reaction (e.g., reduction of oxygen) which refers to cathodic partial                reaction.  Non-electrochemical  reaction  between  products  of  these  reactions  forms  the  final                product (e.g., rust). To determine the corrosion rate, depending on kinetics of both cathodic                and anodic reactions, we obey Faraday’s law, where the linear relationship exists between the                metal  dissolution  rate  at  some  potential  and  the  partial  anodic  current  density  for  metal                dissolution.  If  there  is  no  external  polarization,    the  metal  spontaneously  gains  a  certain                potential (corrosion potential – E corr) in contact with an oxidizing electrolytic environment.                The partial anodic current density at the E corr refers to the corrosion current density i corr.                                                        E corr=i corr/nF                 Where n is the chargé number (number of electrons exchanged in dissolution reaction), F is                the Faraday’s constant (F = 96.485 C/mol). The E corr can be obtained between the equilibrium                potentials  of  the  anodic  and  cathodic  partial  reactions,  which  could  be  predicted  by                electrochemical thermodynamics [1-3].                To slow down the corrosion rate we use several types of inhibitors. We distinguish these types                of  inhibitors:  anodic,  cathodic,  mixed  and  volatile  corrosion  inhibitors  (VCI).  Anodic                inhibitors  usually  form  the  protective  oxide  film  on  the  metal  surface.  Cathodic  inhibitors                                                 Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","21                  slower  the  cathodic  reaction  or  selectively  precipitate  on  the  surface  area  to  decrease  the                diffusion of reducing substances to the surface. Mixed inhibitors reduce both cathodic and                anodic reactions via film forming compounds. VCI (also called Vapor Phase Inhibitors) are                compounds transported in a closed environment to the site of corrosion by vaporizing from                the source [4].                Steel materials are subject to corrosion and loose some attributes caused by their oxidation                depending on time. Studied material is subjected to linear polarization (LSV - Linear Sweep                Voltammetry)  and  LSV  curves  are  processed  using  the  Tafel  slope  analysis  providing  not                only  a  corrosion  rate,  but  also  a  corrosion  potential,  a  current  density  and  a  polarization                resistance.  These  results  enable  to  compare  different  corrosive  materials  and  effects  of                corrosion accelerators or inhibitors in different environment.                Linear   polarization   evaluation   and   Tafel    slope   analysis   are   described   on                http://www.ecochemie.nl/Applications/.                 CALCULATION OF CORROSION RATES                 The corrosion rate depends on the kinetics of both anodic (oxidation) and cathodic (reduction)                reactions. According to Faraday's law, there is a linear relationship between the metal                dissolution rate or corrosion rate, R M, and the corrosion current  density i corr:                                                       M                                                                      R  i                                                  M                                                      nF    corr                The relationship between current density and potential of anodic and cathodic electrode                reactions under charge transfer control is given by the Butler-Volmer equation:                                                    2 .303     2 .303                                                        i  i corr (e  b a  e  b c  ) , where    E  E corr                 In the above equation E is the applied potential and i corr the measured current density. The                overpotential,  η,  is  defined  as  the  difference  between  applied  potential  and  the  corrosion                potential  E corr. The corrosion potential, is the open circuit potential  (OCP) of a corroding                metal. The corrosion current, i corr, and the Tafel constants b a, and b c can be measured from the                experimental data.                  APPARATUS, ACCESSORIES AND REAGENTS                        AUTOLAB PGSTAT101 (Metrohm Switzerland); Corrosion cell 400 ml (Metrohm,                       Switzerland), Thermostat F12 Julabo (Julabo, Germany)                       Software NOVA 1.10.2 (Metrohm, Switzerland)                       Electrodes (WE – sample (steel); RE – Ag/AgCl/3 M KCl; AE – Stainless steel or Pt)                       NaCl solution, c 1(NaCl) = 0.15 mol/L, c 2(NaCl) = 0.6 mol/L; mild steel sample (M r =                       55,585)                                                                      -3                       Corrosion inhibitor:  Adenine or caffeine  (1*10 mol/L)                 SOLUTIONS                Supporting electrolyte                0.15 M NaCl solution pH 5,75                0.6 M NaCl solution pH 5,88                Inhibitor solution :1m M adenine or caffeine                                                  Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","22                  EXPERIMENT                 Measuring method: Linear sweep voltammetry (LSV), procedure in NOVA: linear                polarization (with  open circuit  potential - OCP determination)                 PARAMETERS                 Measuring method: Linear sweep voltammetry (LSV)                 Start potential -0.3 V, stop potential 0.3 V, scan rate 5 or 10 m V/s, temperature 25 °C                Make sure that there is no bubble at the end of the salt bridge after supporting electrolyte is                poured inside the corrosion cell!                 MEASUREMENT                    a)  There are sample of mild steel circuits available. Clean them by scratching the                       measuring side with sandpaper 21111 2/0 than wash it in acetone.                    b)  Insert mild steel circuit into measuring cell and connect as working electrode                    c)  Pour the supporting electrolyte (400 mL) into the corrosion cell and plug reference                       electrode and auxiliary electrode                    d)  Set the temperature on the thermostat to 25 °C and wait until the temperature inside                       the corrosion cell is stabilized.                    e)  Record the linear polarization voltammogram with the specified parameters. Save the                       voltammogram together with method parameters                    f)  Repeat step a) to e) with all samples.                 CURVE EVALUATION                                                Fig. 2: Real voltammograms comparison of mild steel samples in different                       environments: Saline solution (blue), 0.1 M H 2SO 4 (red).                                                          Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","23                  RESULTS                                 Ecor     icor      jcor    Polarizationresistence      Corrosion rate                  Solution                                 [V]     [A]     [A/cm2]             [Ω]                 [mm/year]                  0.9 % NaCl                    3.5 % NaCl                  0.9 % NaCl                  + inhibitor                 3.5 % NaCl                  + inhibitor                 0.9 % NaCl                  + inhibitor                 3.5 % NaCl                  + inhibitor                  REFERENCES                [1]    Schweitzer P.A., Fundamentals of Metallic Corrosion, CRC Press, 2007                 [2]    Kaesche H., Corrosion of Metals, Springer-Verlag Berlin Heidelberg, 2003                 [3]    Fontana M.G., Corrosion Engeneering, McGrawe-Hill Book Company, 1987                 [4]    Sastri V.S., Green Corrosion Inhibitors, John Wiley \& Sons, Inc, 2011                                                                            Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","24                  DISCUSSION AND REMARKS                                                                                                           Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","25                  DISCUSSION AND REMARKS                                                                                                           Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","26                   ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY (EIS)                   EIS of guanine on modified and unmodified graphite electrodes                  Electrochemical  Impedance  Spectroscopy  (EIS)  is  a  powerful  technique  for  the                characterization  of  electrochemical  systems.  The  promise  of  EIS  is  that,  with  a  single                experimental procedure encompassing a sufficiently broad range of frequencies, the influence                of the governing physical and chemical phenomena may be isolated and distinguished at a                given applied potential.                 In  recent  years,  EIS  has  found  widespread  applications  in  the  field  of  characterization  of                materials.  It  is  routinely  used  in  the  characterization  of  coatings,  batteries,  fuel  cells,  and                corrosion  phenomena.  It  has  also  been  used  extensively  as  a  tool  for  investigating                mechanisms in electro–deposition, electro–dissolution, passivity, and corrosion studies. It is                gaining popularity in the investigation of diffusion of ions across membranes and in the study                of semiconductor interfaces.                 Principles of EIS measurements                 The fundamental approach of all impedance methods is to apply a small amplitude sinusoidal                excitation  signal  to  the  system  under  investigation  and  measure  the  response  (current  or                voltage or another signal of interest1). In the following figure, a non-linear i-E curve for a                theoretical electrochemical system is shown in Figure 1.                                           Fig. 1: Potential and current modulation recorded during an impedance measurement                  A low amplitude sine-wave ∆E·sin(ωt), of a particular frequency ω, is superimposed on the                DC polarization voltage Eo. This results in a current response of a sine wave superimposed on                the  DC  current  ∆i·sin(ωt+φ)  .  The  current  response  is  shifted  with  respect  to  the  applied                potential (see Figure 2).                                                          Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","27                                      Fig. 2: Time domain plots of the low amplitude AC modulation and response                  The Taylor series expansion for the current is given by:                                                 di             d  2 i                                           i             E                E  2  .....                                                dE             dE 2                                                    E o  ,i o                                                                    E o  ,i o                If the magnitude of the perturbing signal ∆E is small, then the response can be considered                linear in first approximation. The higher order terms in the Taylor series can be assumed to be                negligible.   The impedance of the system can then be calculated using Ohms law as:                                                                E (  )                                                         ( Z  )                                                                ( i  )                  This  ratio  is  called  impedance,  Z(ω),  of  the  system  and  is  a  complex  quantity  with  a                magnitude  and  a  phase  shift  which  depends  on  the  frequency  of  the  signal.  Therefore  by                varying the frequency of the applied signal  one can  get  the impedance  of the system as a                function of frequency. Typically in electrochemistry, a frequency range of 100 kHz – 0.1 Hz                is  used.  The  impedance  Z(ω),  as  mentioned  above  is  a  complex  quantity  and  can  be                represented in Cartesian as well as polar coordinates. In polar coordinates the impedance of                the data is represented by:                                                      Z(   )   Z(   )  e                  Where |Z(ω)| is the magnitude of the impedance and  is the phase shift.  In Cartesian                coordinates the impedance is given by:                                                     ( Z  ) Z  (  ) j Z  (  )                  Where Z'(ω) is the real part of the impedance and Z\"(ω) is the imaginary part and     .                 Data presentation                  The plot of the real  part of impedance  against the imaginary part  gives a  Nyquist plot, as                shown in Figure 3. The advantage of Nyquist representation is that it gives a quick overview                of  the  data  and  one  can  make  some  qualitative  interpretations.  While  plotting  data  in  the                Nyquist format the real axis must be equal to the imaginary axis so as not to distort the shape                                                Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","28                  of the curve. The shape of the curve is important in making qualitative interpretations of the                data.  The  disadvantage  of  the  Nyquist  representation  is  that  one  loses  the  frequency                dimension of the data. One way of overcoming this problem is by labeling the frequencies on                the curve.                 The absolute value of impedance and the phase shifts are plotted as a function of frequency in                two  different  plots  giving  a  Bode  plot  in  Figure  4.  This  is  the  more  complete  way  of                presenting the data.                                                     Fig. 3: A typical Nyquist plot                                            Fig.4: A typical Bode plot                 A third data presentation mode involving a 3D plot, is available. In this presentation mode the                real  and  imaginary  components  are  plotted  on  the  X  and  Y  axis,  respectively  and  the                logarithm of the frequency is plotted on the Z axis (see Figure 5).                                                                        Fig.5: 3D plot                 The relationship between the two ways of representing the data is given by:                                                                                        Z                                                    2                                        Z  2  Z  2  (  Z )                                       tg(  )                                                                                      Z                 Alternatively, the real and imaginary components can be obtain from:                                      Z     Z  cos             and           Z  Z  sin                                                     Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","29                  APPARATUS, ACCESSORIES AND REAGENTS                        AUTOLAB PGSTAT20 Analyzer (Metrohm AUTOLAB, Netherlands)                       NOVA software 1.10                       Electrodes (working - PeGE with leads Tombow, 0.5 mm, reference – Ag/Ag Cl/3M                       KCl, counter electrode – Pt); voltammetric vessel                       argon                       phosphate-acetate buffer pH 5.5;  c (CH 3COOH) =0.4 mol/L, c  (H 3PO 4)=0.4 mol/L,                       c(NaOH)=2 mol/L                       adenine; copper sulphate; miliQ water (18.2 MΩ·cm)                   SOLUTIONS                 Supporting electrolyte                        phosphate-acetate buffer pH 5.5; c (CH 3COOH) =0.4 mol/L, c (H 3PO 4)=0.4 mol/L,                                                          -3                        c(NaOH)=2 mol/L, c(CuSO 4)=1·10 mol/L                 Samples                                      -3                       adenine = 1·10  mol/L;  (or guanine)                EXPERIMENT                          EIS  experiment  for  adenine  in  the  absence  of  copper  ions  –  2  mL  supporting                       electrolyte + 8 mL miliQ H 2O + 100 µL adenine (guanine)                  PARAMETERS                        Measuring method potentiometric electrochemical impedance spectroscopy                       Start 0.1 V, End potential 1.2V, logarithmic step 0.2V                       Frequency 10 000- 0.1 Hz, 50 steps (logarithmic)                       RPM 0.1V                 MEASUREMENT                     a)  Clean voltammetric vessel (diluted nitric acid, than miliQ water). Than we added in                       the vessel 2 mL of supporting electrolyte, 8 mL miliQ H 2O and 100 µL of adenine                       (guanine)                    b)  Insert working electrode into pencil and connect all electrodes.                    c)  Start potentiometric EIS                    d)  Save data                    e)  Data analysis, Fit and Simulation                    f)  Insert equivalent circuit and Fit data                    g)  Export results                                                           Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","30                  Measured data                 Equivalent circuit                                           Results                              Element         Parameter             Value                            R1             R                   83.613                           R2             R                   9.4724                           Q1             Y0                  9.2585E-06                                          N                   1.0198                            Q2             Y0                  6.8726E-06                                          N                   0.94971                                           χ²                  0.033201                  REFERENCES                  [1]  Metrohm Autolab,  Application note EIS01                 [2]  Barsoukov  E.,  Macdonald  J.  R.:  Impedance  spectroscopy.  Theory,  Experiment,  and                    Applications. J. Wiley, New Jersey 2005.                                                            Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","31                  DISCUSSION AND REMARKS                                                                                                       Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","32                  DISCUSSION AND REMARKS                                                                                                       Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","33                                              ACKNOWLEDGEMENT                    (a) CEITEC  –  Central  European  Institute  of  Technology  Project                    CZ.1.05/1.1.00/02.0068                  (b) MUNI/A/0972/2013 project                (c) KONTAKT II (LH13053) of the Ministry of Education, Youth and Sports of                      the Czech Republic                 (d)  Project  POSTDOC  I,  reg.  No.  CZ.1.07/2.3.00/30.0009,  The  project  is  co-                     financed  by  the  European  Social  Fund  and  the  state  budget  of  Czech                     Republic                                                                                      Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","34                          • Founded in 1986                  • Based in Utrecht, The Netherlands                  • Since 1999  part of the Metrohm Group                 • Introduced the first computer controlled potentiostat/galvanostat                  • Develops and produces the high quality Autolab range of products                  • Strong background in electrochemistry                 • Supported by the worldwide Metrohm distribution network                  • Three years factory warranty on all instruments                  • Dedicated to research                  Eco Chemie – Metrohm  Autolab                 Eco Chemie was  founded  in 1986  and  is since 1999  a member  of the  Metrohm  group  of                companies.  In  2009  the    company  name    changed    to    Metrohm    Autolab  to  reflect  the                customer oriented combination of the world- wide Metrohm  sales and  support  organization                 and  the  high  quality  Autolab  series  of  instruments  developed  by  Eco Chemie.  Metrohm                Autolab  is  an  ISO9001  certified  company..  Metrohm    Autolab  based    in  Utrecht,    The                Netherlands, designs and  manufactures  Autolab instruments,  acces- sories, and software for                electrochemistry.  Known  for  innovation,  the  Autolab  was  the  first  commer­  cial  digital                 potentiostat/galvanostat,  that  was  completely  computer  controlled.  Our  latest  software                package NOVA has again set a high standard for powerful electrochemical research software.                With  our  background  and  knowledge  in  electrochemistry  and  our  worldwide  distributor                network,  our  mission  is to  serve the  research  community  all over the  world  by supplying                 state  of  the  art  instruments  and  unrivalled support.  All  Metrohm  Autolab instruments  are                covered by a three year factory warranty.                                                                Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009","35                        Všechna práva vyhrazena. Žádná část této elektronické knihy nesmí                 být reprodukována nebo šířena v papírové, elektronické či jiné podobě                  bez předchozího písemného souhlasu vykonavatele majetkových práv                 k dílu, kterého je možno kontaktovat na adrese – Nakladatelství                 Masarykovy univerzity, Žerotínovo náměstí 9, 601 77 Brno.                                  Letní elektrochemická škola                 Summer electrochemical school                   Kolektiv autorů: Libuše Trnková, Peter Barath, Mehdi Ravandeh, Vimal                 Sharma,  Iveta Pilařová, Romana Ševčíková, Rudolf Navrátil, Libor Gurecký                   Grafická úprava: Romana Ševčíková, Libor Gurecký                 Vydala Masarykova univerzita, Brno                 Vydání první, 2014                   ISBN 978-80-210-6827-8                                                          Zpracováno za přispění CEITEC, CZ. 1.05/1.1.00/02.0068,                                                projektů: MUNI/A/0972/2013 a LH 13053 KONTAKT II  od                                               MŠMT ČR,  POSTDOC I, No. CZ.1.07/2.3.00/30.0009"];