Field-amplified Sample Stacking Coupled With Capillary Electrophoresis In Phenylenediamines And Artifical Pigments Detection

Capillary electrophoresis (CE), because of its high separation efficiency, lowsample consumption, easy operation, low experimental costs, has been acknowledgedas a highly efficient separation technique in the field of analytical chemistry. However,due to its low sensitivity of the commonly used UV detector, coupled with the smallinjection volumes and the short detection optical path, make the limit of CE detectionis relatively higher, which can not meet the analysis of the trace substances detection.The techniques of CE on-line sample enrichment can effectively avoid thephenomenon of target components loss which is caused by the off-line samplepreconcentration methods. On-line sample preconcentration techniques haveenrichment efficiency and a variety of selection modes. The technique of fieldamplified sample injection (FASI) is simpler to the other stackings and was firstlyreported by Mikkers. This technique is based on the different migration speeds of theanalyte particles in two different conductivity solutions. The accumulation is formedon the interface. The injection mode of FASI is based on the voltage which can introduce the same ion charges. Because the sample and the background aresimultaneously introduced into the tube, so the mode don’t exist the sample volumerestriction which is produced through pressure injection. The technology of FASI hasbeen widely used in pharmaceutical analysis, food analysis, cosmetics analysis,environmental analysis, bio-analysis and other fields. In this paper, we choose theFASI online enrichment method which is combined with capillary electrophoresisseparation technology, analyse the compounds of the hair dye and jelly. Theexperimental study contains the following two sections:1. A method for the determination of three phenylenediamine isomers in hairdyes has been developed using CZE coupled with FASI. Factors that affect theaccumulation efficiency, such as the ionic strength of the background electrolytesolution, buffer pH, the length and composition of the pre-column of water, thesample matrix, the amount of sample electrokinetic injection were examined andoptimized. The optimum experimental conditions are as follows:+16kV voltageanalysis,60mmol/L disodium hydrogen phosphate solution, pH5.5, the waterpre-column (30μmol/L phosphoric acid)30mbar5s, electrokinetic injection:+6kV16s. Under the optimal conditions, the enrichment factors were:60.4,193.4,858.3;the linearity range from0.03mg/L to1mg/L with the correlation coefficient (r)ranging from0.997to0.998. Detection limits varied from0.9μg/L to4.8μg/L. Theinter-day and intra-day precisions of peak area are lower than3.2%and5.5%respectively. Three kinds of hair dyes were investigated and spiked at the levels of0.1mg/L,0.5mg/L,1.0mg/L. Recoveries range from70.3%to102.3%, demonstratingthat the proposed method is effective for the determination of phenylenediamineisomers in hair dyes.2. The method FASI-CZE to analyse five kinds of synthetic pigment has beendeveloped. Experiment study is carried out with a negative high voltage in order tomeet the requirement of FASI mode. Because the five pigment ions in the solutionexists in anionic form. Factors that affect the accumulation efficiency, such as theionic strength of the background electrolyte solution, buffer pH, the length of thepre-column of water, the amount of sample electrokinetic injection were examined and optimized. The optimum experimental conditions are as follows:-25kV voltageanalysis,80mmol/L disodium hydrogen phosphate solution, pH4.7, the waterpre-column25mbar8s, electrokinetic injection:-6kV10s. Under the optimalconditions, the enrichment factors were:160.4,91.3,101.2,86.2,82.5, the linearityrange was0.002mg/L~10mg/L with the correlation coefficient (r) ranging from0.993to0.999. Detection limits varied from0.018mg/L to0.039mg/L. The inter-dayand intra-day precisions of peak area are lower than6.9%and4.6%respectively.Three kinds of jelly were investigated and spiked at the levels of0.1mg/L and0.5mg/L. Recoveries range from72.6%to109.2%, demonstrating that the proposedmethod is effective for the determination of synthetic pigments in jelly.