The capillary electrophoretic separation of Fe 2+ , Co 2+ , Zn 2+ and Ni 2+ in a phosphate buffer solution by complexing with 4 (2 thiazolylazo)resorcinol was investigated. The influences of some crucial parameters that included chelating ligand in the electrophoretic running buffer and sample solution, pH value and concentration of buffer were examined. Under optimum conditions (10mmol·l -1 NaH 2PO 4 Na 2HPO 4 buffer containing 1×10 -4 mol·l -1 TAR, pH 7 5), a baseline separation of these metals was accomplished within 3 min. The detection limits (S/N=3) ranged from 0 013—0 14 μg·ml -1 . The method was applied to analyze trace metal ions in the environmental samples.
This work describes the simultaneous deter- mination of catechins and caffeine in green, black tealeaves and canned tea-drink using micellar electrokinetic chromatography. The catechins analyzed include (+)-catechin, (-)- epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate. Using UV absorption method at 280 nm, the limits of detections of catechins and caffeine are 10-6 mol/L, which is suitable for the real sample determination. Using this analytical method, the extraction of these compounds from the tealeaves with hot water is compared under different temperatures. The effects of temperature on the amount of catechins and caffeine extracted are evident, showing that (-)-epigallocatechin gallate is the most easiest to be extracted at 100℃. The stability of catechins and caffeine in stocking solution of tea-drink at 4℃ is also compared on five consecutive days. The contents of catechins and caffeine in green and black teas are discussed and the difference of the content between different tealeaves can provide a reference for the assessment of tea quality.
