Use of artificial neural networks for the evaluation of electrochemical signals of adenine and cytosine in mixtures interfered with hydrogen evolution

Quantitative determination of tocopherols in edible vegetable oils using electrochemical ultra-microsensors combined with chemometric tools

We have developed an electroanalytical method to quantify different isomers of tocopherols in edible vegetable oils. The method uses the square wave voltammetry on a carbon fiber disk ultramicroelectrode in benzene/ethanol+0.1 mol L(-1)H2SO4. Because the oxidation peaks of these natural antioxidants show an important overlapping, we have used two chemometric tools to obtain the multivariate calibration model. One method was the multivariate curve resolution-alternating least square (MCR-ALS), which assumes a linear behavior, i.e., the total signal is the sum of individual signals of components, and another nonlinear method such as artificial neuronal networks (ANNs). From the accuracy and precision analysis between nominal and estimated concentrations by both methods, we could infer that the ANNs method was a good model to quantify tocopherols in edible oil samples. Recovery percentages were between 94% and 99%. In addition, we found a difference of 1.4-6.8% between the total content of tocopherols in edible oil samples and the vitamin E content declared by the manufacturers.

Does chemometrics enhance the performance of electroanalysis?

This review explores the question whether chemometrics methods enhance the performance of electroanalytical methods. Electroanalysis has long benefited from the well-established techniques such as potentiometric titrations, polarography and voltammetry, and the more novel ones such as electronic tongues and noses, which have enlarged the scope of applications. The electroanalytical methods have been improved with the application of chemometrics for simultaneous quantitative prediction of analytes or qualitative resolution of complex overlapping responses. Typical methods include partial least squares (PLS), artificial neural networks (ANNs), and multiple curve resolution methods (MCR-ALS, N-PLS and PARAFAC). This review aims to provide the practising analyst with a broad guide to electroanalytical applications supported by chemometrics. In this context, after a general consideration of the use of a number of electroanalytical techniques with the aid of chemometrics methods, several overviews follow with each one focusing on an important field of application such as food, pharmaceuticals, pesticides and the environment. The growth of chemometrics in conjunction with electronic tongue and nose sensors is highlighted, and this is followed by an overview of the use of chemometrics for the resolution of complicated profiles for qualitative identification of analytes, especially with the use of the MCR-ALS methodology. Finally, the performance of electroanalytical methods is compared with that of some spectrophotometric procedures on the basis of figures-of-merit. This showed that electroanalytical methods can perform as well as the spectrophotometric ones. PLS-1 appears to be the method of practical choice if the %relative prediction error of approximately +/-10% is acceptable.

Flow injection determination of adenine at trace level based on luminol–K2Cr2O7 chemiluminescence in a micellar medium

A novel flow injection chemiluminescence (CL) analysis method for the determination of adenine in the presence of sodium dodecylbenzene sulfonate (SDBS) surfactant micelles is described. This method is based on the luminescent properties of the luminol-K2Cr2O7-adenine in alkaline medium sensitized by SDBS. The optimized experimental conditions were evaluated and the possible mechanism was discussed by examining CL emission spectrum and the effect of various free radical scavengers on CL emission intensity. The CL increase is linearly related to the concentration of adenine in the range of 2.92x10(-6) to 4.38x10(-10) mol l-1 with a detection limit of 2.46x10(-10) mol l-1 (S/N=3). The relative standard deviation for 2.92x10(-7) mol l-1 samples was 1.67% (n=12). The proposed method has been applied to the determination of adenine in human serum.

Elimination voltammetry of adenine and cytosine mixtures

The elimination voltammetry with linear scan (EVLS) was used to study adenine and cytosine reduction signals at the mercury electrode. In comparison with the linear scan voltammetry (which provides only one unresolved peak), two elimination functions provide good resolution of individual peaks and significant increase of sensitivity. The first elimination function eliminates the kinetic current (I(k)) and conserves the diffusion current (I(d)). The second elimination function eliminates kinetic and charging currents (I(k) and I(c)) simultaneously and conserves the diffusion current (I(d)). Both functions give two well-resolved peaks of adenine and cytosine in a wide concentration range, while the linear sweep voltammetry gives badly resolved peaks due to hydrogen evolution. The best resolution of peaks is observed in acetate buffer at pH 3.8 and the detection limit for both substances is 500 nM. The concentration dependence of EVLS peak heights for one substance at the constant concentration of the other substance is linear. The peak potentials differ in these elimination functions. The difference in EVLS peak potentials gives the possibility to evaluate alpha n(a). Elimination voltammetry with linear scan contributes to the resolution of cathodic signals of purine and pyrimidine bases at very negative potentials near supporting electrolyte discharge.