Development of a fully buffered molybdate electrolyte for capillary electrophoresis with indirect detection and its use for analysis of anions in Bayer liquor

A new counterion-buffered molybdate electrolyte was developed and optimized for simultaneous quantitative determination of up to eight anions (chloride, sulphate, oxalate, fluoride, formate, malonate, succinate, and acetate) in Bayer liquor by capillary electrophoresis with indirect detection at 214 nm. The separation parameters were optimized in respect to separation of the critical analyte group fluoride - formate - malonate, with the optimal electrolyte prepared from molybdic trioxide containing 5.0 mmol/L MoO3, 1.3 mmol/L cetyltrimethylammonium bromide (CTAB), and buffered with diethanolamine (DEA) to pH 9.2 (ca. 20mM DEA). Total length of separation capillary was 80 cm, resulting in run time of under 4 min. The method is suitable for a wide concentration range of the analytes (1-50 mg/L) with linear calibration plots (R2= 0.9983-0.9999). Relative standard deviations were 0.05%-0.07% for migration times and 0.67%-2.04% for peak areas. The detection limits were in the range of 0.17-0.51 mg/L or 2-10 μmol/L (hydrostatic injection of 30 s of 1000 x diluted sample). Due to its good buffering capacity, the electrolyte exhibited an excellent ruggedness and good tolerance to the alkaline samples. Consequently, Bayer liquor samples could be diluted as little as 100 x which allows more sensitive determination of minor components over previous methods. The method was successfully applied to analysis of Bayer liquor samples with recoveries in the range of 95-105%. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.