DETERMINATION OF METAL CATIONS BY CAPILLARY ELECTROPHORESIS - EFFECT OF BACKGROUND CARRIER AND COMPLEXING AGENTS

The determination of trace metals in aqueous samples can be readily accomplished by capillary electrophoresis (CE) via indirect absorbance detection. Methods for simultaneously determining alkali, alkaline earth and transition metal ions and Group IB, IIB and IVA metals ions were developed. Imidazole, benzylamine, ephedrine or pyridine was used as the carrier buffer and the background absorbance provider. Glycolic acid, alpha-hydroxyisobutyric acid or succinic acid was used as the complexing agent. The elements determined were Li, Na, K, Cs, Mg, Ca, Sr, Ba, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ag, Al and Pb. All ions could be separated in less than 15 min. In most instances reported here, more than a dozen ions could be separated in 5-10 min. All peaks were well separated and baseline resolved (i.e., no peaks overlapped), except Ag and Al, which required a separate and additional analysis. The detection limit was in the range 0.02 (Na)-208 ppb (Cr) with the electrokinetic injection mode (10 kV, 5 s). The reproducibility was 1% for the migration time and better than 5% for the peak height for most metal ions. The calibration graphs were linear for most ions in the concentration range 10(-5)-10(-3) M (R(2)=0.9995-0.9999) using the hydrodynamic injection mode. Concentrations lower than 10(-5) M can be determined using the electrokinetic injection mode, but the calibration graph is not linear. The methods developed here are well suited for determining metal ions in a variety of real samples.