Application Of Capillary Electrophoresis On-line Concentration Methods In Food Analysis

Capillary electrophoresis(CE)is a new analytical technology having many advantages,such as high efficiency,high automation,and low consumption of samples and reagents.However,due to the low sample amount and short detection optical path,the detection sensitivity of CE is one order of magnitude lower compared to HPLC,which made it diffcult to satisfy the requarements in the trace analysis.In order to improve the detection sensitivity of capillary electrophoresis and more widely apply it to the analysis of trace components,several on-line concentration methods were introduced to real sample analysis in this study.The mainly content of this study is as follow.1.A very simple,sensitive,and reliable method for the routine determination of riboflavin in cereal grains by capillary electrophoresis with laser-induced fluorescence detection(CE-LIF)was established for the first time in this study.Two on-line concentration techniques,namely,stacking in reverse migrating micelles(SRMM)and sweeping,were examined to enhance the detection signal.The optimum separation buffer consisted of 20 mM phosphoric acid and 140 mM sodium dodecyl sulfate(SDS),and a hydrodynamic injection of 30 s at 0.5 psi was confirmed for the introduction of a sample.In addition,it was found that salt in sample matrix influenced the performance of SRMM,showing the standard addition method was required for the quantitative analysis.The linearity of the method was good with a range of 0.5-500 ng/mL(r=0.9990).The limit of detection(LOD)was 0.29 ng/mL at a signal-to-noise ratio of 3.This procedure presented was successfully applied to determine riboflavin in 18 samples of 9 types of cereal grains.The recovery rates varied from 94%to 98%,and the relative standard deviation(RSDs)was less than 4.1%.2.Two new on-line concentration methods based on stacking in reverse migrating micelles-anion selective exhaustive injection(SRMM-ASEI),stacking in reverse migrating micelles-anion selective exhaustive constant current electrokinetic injection,stacking in reverse migrating micelles-anion selective exhaustive constant voltage electrokinetic injection were established to analyse the bisphenol A(BPA)in PC bottles.The optimal injection condition of SRMM-ASEI using a constant current electrokinetic injection:pressure injection,3 psi×45 s;electrokinetic injection,20 μA×2 min.The best injection condition of SRMM-ASEI using a constant voltage electrokinetic injection:pressure injection,3 psi×40 s;electrokinetic injection,10 kv×0.8 min.Other electrophoretic conditions:separation voltage,-10 kv;the sample matrix of pressure injection,20 mM NaH2PO4;the sample matrix of electrokinetic injection,20 mM NaH2PO4+10 mM SDS,pH=2.7;buffer,25 mM NaH2PO4+100 mM SDS+ 15%acetonitrile,pH=2.7.A definite concentration of BPA was found in all the three kinds of PC bottle after baking under 100℃ for 12 h and 36 h.3.A reversed-phase dispersive liquid-liquid microextraction(RP-DLLME)procedure coupled to micellar electrokinetic chromatography(MEKC)was established for the extraction and determination of bisphenol A(BPA)in edible oils.The optimized extraction conditions for 1.5 g of the edible oil sample were:volume of diluent(n-hexane),6 mL;extractant mixture,120 μL 0.2 M NaOH-methanol(2:8,v:v);extraction time,2 min;centrifugation time,3 min.The optimum electrophoretic conditions:separation voltage,-15 kv;pressure injection,3 psi×35 s;separation buffer,60 mM NaH2PO4 and 120 mM SDS-acetonitrile(80:20,v:v,pH 2.5).The linearity of the method was good in the range of 0.01-5 μg/g(r>0.99).The limit of detection(LOD)was 0.9 ng/g at a signal-to-noise ratio of 3.This procedure presented was successfully applied to the determination of BPA in 10 edible oil samples,and from 7 out of it BPA was detected.The average recovery rates ranged from 86.0%to 100.6%,and the RSDs were less than 4.6%.