Indirect capillary electrophoretic detection methods of cations and anions

[摘要] ENGLISH ABSTRACT:Capillary electrophoresis (CE) has recently attracted considerable attention as apromising analytical technique for the separation of cations and anions in complexmatrices. Determination of ions in aqueous samples using capillary electrophoresiscan be accomplished with indirect UV detection. Most inorganic ions have weakabsorption profiles in the UV-Vis wavelength range. These mostly non-absorbingspecies are commonly detected by indirect UV absorbance through addition of anabsorbing co-ion (chromophore) into the electrolyte. Inorganic cations most oftenrequire an additional complexing agent to selectively alter their similar mobilities andproper separation.For optimal determination of alkali, alkaline, and transition metal ions, severalelectrolytes systems were studied. These include pyridine, imidazole and 4-aminopyridine as UV-absorbing species and glycolic acid, a-hydroxyisobutyric acidand their mixture were used as complexing reagents. A mixture of 10 metal ions (K+,Na+,Ca2+, Mg2+, Mn2+, Fe2+, Cd2+, Pb2+, Ni2+and Zn2+) was successfully separated.Detectionwas performed at 210,214 and 254 nm.In the anion determination chromate and 2, 6 pyridine dicarboxylic acids (PDC) wereused as back ground electrolytes for inorganic ions(F-, CI- en SO₄² ̄ ) and organicacids (tartaric acid, malic acid, succinic acid and citric acid) separations respectively.Electroosmotic flow (EOF) was reversed in the direction of the anode by addingCetyltrimethylammonium bromide (CTAB) to the electrolyte. Highly alkalineconditions were used to confer a negative charge on inorganic and organic anions to promote their migration towards the anode. The detection wavelength was 200 nm.All peaks were completely resolved and well separated. The limit of detection (LOD)of cations and anions were in the range of 0.5 - 3 ppm and 2 - 3.5 ppm respectively.The described methods were used successfully in routine analysis of real samples.This includes the qualitative and quantitative analysis of an environmental watersamples from the areas surrounding Stellenbosch, beverages and orange juice.

[发布机构] Stellenbosch University