Capillary ion analysis of potassium concentrations in human vitreous humor

Capillary ion analysis (CIA) is a form of capillary electrophoresis which uses the differential electrophoretic mobility of ions to perform a separation of an ionic mixture. Application of this technique for direct detection of potassium concentrations in human vitreous humor was the purpose of this investigation. CIA was performed using a Waters Quanta 4000 Capillary Electrophoresis System with a 745 Data Module using a 75 microm x 60 cm capillary and a run electrolyte of 67.7 mg hydroxyisobutyric acid (HIBA), 52.8 mg 18-crown-6-ether and 64 microL UV-CAT-1 reagent (4-ethylbenzylamine) in a volume of 100 mL water (18 Mohm) with a voltage of 20 kV using ultraviolet absorption detection at 214 nm. Migration times were: ammonium ion, 2.86 min; potassium, 3.24 min; calcium, 3.84 min; sodium, 3.98 min; barium (internal standard), 4.68 min; and lithium, 4.79 min. Correlation coefficients (r) between peak area ratios and concentration ranges of 2.5-144 mmole/L (100-1000 ppm) were from 0.9855 to 0.9999. Coefficients of variation (CV) ranged from 1.45 to 13.8% between days and from 1.38 to 9.43% within-day. Application of this methodology to twenty-five vitreous humor specimens from forensic cases was compared to analysis by ion-specific electrode for potassium concentration. Comparison of CIA to ion-specific electrode analysis of vitreous humor potassium concentrations revealed a correlation coefficient of 0.9642. CIA is applicable to forensic analysis of potassium concentration in forensic vitreous humor specimens. Quantitation of numerous cation concentrations is possible by direct CIA of vitreous humor.