Analytical & Bioanalytical Electrochemistry
Volume:1 Issue: 3, Sep 2009

Cytochrome c (Cyt c) was absorbed on gold electrode modified with a mixture (1:3) of 11-mercapto-1-undecanol and 11-mercaptoundecanoic acid (C11) solutions. The Cyt c/C11/Au electrode thus prepared showed a well-defined quasi reversible voltammetric peak with electron transfer rate constant of 234 s-1. The surface coverage of Cyt c oriented on the surface of C11-modified electrode was determined to be 4.73×10-11 mol cm-2. The Cyt c/C11/Au electrode linearly responded to H2O2 in the concentration range from 90 to 500 μM with a correlation coefficient of 0.9973. Using the reciprocal plot of the steady state current versus hydrogen peroxide concentration, apparent Michaelis constant for the Cyt c was estimated to be 759 μM. In addition, voltammetric analysis was used to study the in situ denaturation of the immobilized Cyt c by gradual addition of either urea up to 8 M or dimethyl formamide (DMF) up to 55%. It was revealed that the mechanism of Cyt c denaturation depends on media (organic or aqueous) were used. So that in the presence of DMF it follows a two-phase process, whereas in urea containing buffer solution, it pursues a single-phase course.

The H-point standard addition method (HPSAM), partial least squares (PLS) and principal component regression (PCR) were used, during the present study, for the simple, accurate and simultaneous determination of two oxidants of hydrogen peroxide (H2O2) and peracetic acid (PAA) using the kinetic data from novel potentiometric method. The methods are based on the difference observed in reaction rate of iodide ion with PAA and H2O2 in the presence of Mo(VI) in acidic media. Therefore, the reaction rate of iodide ion with PAA and H2O2 was monitored by an iodide ion-selective electrode (IISE). Results have demonstrated that the simultaneous determination of H2O2 and PAA can be done in the concentration ranges of 0.5-14.0 and 0.05-2.0 μg mL-1, respectively. The total relative standard error for applying the PLS and PCR methods to 8 synthetic samples in the concentration ranges of 2.0-11.0 μg mL-1 for H2O2 and 0.3-1.9 μg mL-1 for PAA, were 2.70 and 3.24, respectively. The effects of certain foreign ions, upon the reaction rate, were determined for assessing the selectivity of the method. The proposed methods (HPSAM, PLS and PCR) were evaluated, using a set of synthetic sample mixtures, and applied for the simultaneous determination of H2O2 and PAA in water samples.

Quantitative structure-electrochemistry relationship (QSER) model has been used to predict and explain half-wave reduction potentials (E1/2). This method allows for the prediction of E1/2s in a variety of organic compounds based on their structures alone. Stepwise multiple linear regression (MLR) was performed to build the model. The proposed methodology was validated using leave-one-out and leave-group-out cross validation using division of the available data set into training and test sets. The results illustrated that the linear techniques such as MLR combined with a successful variable selection procedure are capable to generate an efficient QSER model for predicting the E1/2s of different compounds. A model with low prediction error and good correlation coefficient was obtained (R2 calibration=0.883, R2 prediction=0.836, Q2 LOO=0.825,Q2 LGO=0.806, REP(%)=-12.98, RMSEP=0.203). This model was used for the prediction of the E1/2 values of some organic compounds which were not used in the modeling procedure.

Molecularly imprinted polymer (MIP), having recognition sites for parathion, was used for carbon paste electrode fabrication and then used as a voltammetric sensor for parathion determination. Different factors including electrode composition, conditions of parathion extraction in the electrode and electrochemical measurement parameters were evaluated and then optimized by using various techniques of screening and response surface experimental design. After optimization, very high sensitivity and sub-nanomolar detection limit were obtained successfully. It was shown that the sensor response for parathion concentration was linear in the range of 0.3-710 nM. Detection limit of designed sensor was calculated equal to 0.07 nM. It was shown that the application of multivariate optimization method instead of traditional optimization method led to considerable improvement in the final sensor performance.

The fast Fourier transform square-wave voltammetry (FFTSWV) was used for determination of adrenaline as a new detection technique based on measurements of electrode admittance. The working electrode was a poly(1-methylpyrrole) modified glassy carbon electrode (GCE) that exhibited stable and sensitive current responses towards adrenaline. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on the electrode. The response is generated by admittance of the redox process of adrenaline. The support electrolyte that provided a more defined and intense peak current for adrenaline determination was at 0.1 M phosphate buffer solution (PBS) at pH 4.5 at modified glassy carbon electrodes. The linear response was obtained in the range of 3.0×10-9M to 2.0×10-8M with a detection limit of 8.68×10-10 M for adrenaline by this method. The modified electrode has been successfully applicable for the determination of adrenaline in pharmaceuticals. The proposed method showed excellent stability and reproducibility.