Simultaneous analysis of nitro compounds by Voltammetric method combined with the principal component regression (PCR)
Abstract
The ability to simultaneously determine 6 nitro compounds including nitrobenzene (NB), 2-nitrophenol (2-NP), 3- nitrophenol (3-NP), 4-nitrophenol (4-NP), 2,4- dinitrophenol (DNP) and trinitrophenol (TNT) in the same samples was investigated by differential pulse Voltammetry on hanging mercury drop electrodes (HMDE), in acetate buffer of pH 4.6. It was found that peak potentials of voltammetric reduction waves of NB, 2-NP, 3-NP and 4-NP appeared at - 0.297, - 0.251, - 0.267 and - 0.337 V respectively. Under the same conditions there are three peak potentials at -0.076, - 0.161, - 0.267 V for TNT and two peaks at tại - 0.176, - 0.282V for DNT. The peaks of these compounds are very close together. Due to the serious overlapping of Voltammetric peaks of these compounds in the mixtures, so that by a conventional Voltammetry it not possible to individually determine each compound. In this study, the linear multivariate regression method such as principal component regression (PCR) was used to resolve the overlapped Voltammograms. The obtained relative standard error (RSEt) of method is less 10%. The percent of recoveries were within ± 10% of the target value. The developed method was then applied to the analysis of these nitro-substituted aromatic compounds in field samples with similar satisfactory results.
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Introduction
The simultaneous determination methods of the nitro - compound mixtures in the environmental samples have received considerable attention, because they are widely used to in industries to control the pollution of individual pollutants present in waste water. The high level toxicity of nitro- compounds and their propagation through environment are capable of polluting land, water, air and affecting on human, animal health, fish, aquatic organism and other life forms [7]. There is a variety of analytical methods applied to determine these compounds including performance liquid chromatography (HPLC), UV-vis spectrophotometry and electrochemistry. These methods are often complex and time consuming and requiring sample pretreatments involving separation, extraction before analyzing [3,4,5]. For the Voltammetric methods, due to the serious overlapping of their reductive peak potentials caused by the general structural formula, the nitro-compounds cannot be quantitatively determined individually. Therefore these methods are usually limited to analyzing a single chemical composition or determining the sum of the nitro compounds in the mixtures [6-8].
In this study, linear multivariable regression method which is principal component regression (PCR), (applying mathematical, statistical, graphics methods, etc) were applied for experimental planning, optimization of obtained experimental data used to resolve the overlapped Voltammograms of nitro-compounds [3]. Based on the PCR model, each nitro compound such as NB, 2-NP, 3-NP, 4-NP, DNT and TNT was simultaneously determined from Voltammograms of their mixtures. In order to eliminate background effect, multivariable regression equation using the measured signal when carry out the experiment on the sample base instead of only using distilled water.
Conclusion
The multivariate regression using principle component regression (PCR) was successfully applied to simultaneously determine all 6 compounds: TNT, DNT, 2-NP, 3-NP, 4-NP and NB by Voltammetric using hanging mercury drop electrodes. Good validation results were obtained: RSE less 10%; recoveries (%) within 10%). As such, PCR method can be used to simultaneously analyze TNT, DNT, 2-NP, 3-NP, 4-NP and NB in the same mixture without separating them. The developed method was then applied to the analysis of the nitro-substituted aromatic compounds in field samples with similar satisfactory results.