On-line Preconcentration Methods Research Of Electrokinetic Chromatography And Application In Detection Of Glucocorticoids

Glucocorticoids belonging to the steroids make the skin tender and white. But the use fora long term can have many side effects on human body. The paper established3methods ofmicroemulsion electrokinetic chromatography with on-line preconcentration techniques toseprate and enrich glucocorticoids in cosmetics. These methods have effectively solved theproblem of low detection sensitivity of conventional separation methods, and can meet therequirement of trace detection. Preconcentrations realize the sensitive, simple and efficientdetection of glucocorticoids in cosmetics and it is of great significance for cosmetic qualitycontrol. The main contents are shown as follows:1．A sensitive assay was established by reverse migration microemulsion electrokineticcapillary chromatography with sweeping (sweeping-MEEKC) to detect6glucocorticoids incosmetics. The analysis of different microemulsion microstructures and electrical propertieson the enrichment and the effect of ionic liquids were studied, and optimized the compositionand pH value of background buffer, pH value of sample matrix and so on. The buffer iscomposed of2.0%(w/w) sodium dodecyl sulfate (SDS),6.6%(w/w) butanol,0.8%(w/w)octane,20mmoL/L NaH2PO4buffer (pH2.4). Seperating voltage is-20kV. The conditionsof sample injection is hydrodynamic injection of5kPa×70s. Detection wavelength is at240nm. Under the optimum conditions, the preconcentration reach120~236folds and linearrelationship is favorable in0.05~10.0mg/L (r=0.9989~0.9998). LODs are at the range of20.0~60.5μg/L (S/N=3) and the recoveries are87.9%~110.6%. The ionic liquid can improvethe effect of concentration but extend analysis time. This sweeping-MEEKC method hasmake it more significantly simple and sencetive that test6glucorticoids in the cosmetics.2．A reverse migration microemulsion electrokinetic capillary chromatography methodwith field-amplified sample stacking (FASS-MEEKC) has been developed and validated fordetection of6glucocorticoids in cosmetics. The composition and pH value of backgroundbuffer, the injection voltage and time, water plug injection were discussed. The optimizedmicroemulsion buffer is composed of2.8%(w/w) SDS,6.6%(w/w) butanol,0.6%(w/w)octane,20mmoL/L NaH2PO4buffer (pH2.5). Seperating voltage is-20kV. The conditionsof sample injection and water plug are-20kV×54s and15kPa×40s. Detection wavelengthis at240nm. Under the optimum conditions, the preconcentration reached100~186folds andLODs are20.0μg/L~60.5μg/L (S/N=3). The recoveries are83.9%~108.5%. Favorable linearrelationship is from0.05to10.0mg/L (r=0.9986~0.9997) and RSD＜5.8%. This proposedFASS-MEEKC method is successfully applied for determing of6neutral glucorticoids in thereal cosmetic samples.3．For the first time, a method that combines two preconcentration techniques, samplestacking and sweeping, was used to determine8trace glucocorticoids in cosmetics by reverse migration MEEKC (stacking-sweeping-MEEKC). The method using hydrodynamic sampleinjection, the pH value of sample matrix was as the same as the background buffer. Thebackground buffer is composed of2.4%(w/w) SDS,6.6%(w/w) butanol,0.6%(w/w) octane,20mmoL/L NaH2PO4buffer (pH2.4). Seperating voltage is-20kV. The conditions ofsample injection is5kPa×90s. Detection wavelength is at240nm. Under the optimumconditions,122~280folds incrase in sensitivity could be obtained as compared with normalMEEKC.The linear range is0.05to10.0mg/L with the square of the correlation coefficientsranging from0.9986to0.9997. LODs are at the range of20.0~60.5μg/L.The recoveries arebetween83.9%and108.5%. RSD are all below4.7%. This method is user-friendly andsensitive with high efficiency enrichment to realize the trace detection of8glucorticoids incosmetics.