Capillary zone electrophoresis of potassium in human vitreous humour: validation of a new method

The analysis of potassium in the vitreous humour has long been regarded as an important tool in medicolegal and forensic toxicological investigation, particularly for the determination of the post-mortem interval. The present work was aimed at the optimisation and validation of a reliable, simple an d fast capillary electrophoresis method for potassium analysis in the human vitreous humour with indirect UV detection at a wavelength of 214 nm, Elec trophoretic separations were carried out in a running buffer comprising 5 m M imidazole, 5 mM 18-crown-6 ether and 6 mM D,L alpha-hydroxybutyric acid ( HIBA), adjusted to pH 4.5. Constant voltage runs were carried out by applyi ng a voltage of 500 V/cm at 25 degrees C. The samples were injected in the hydrodynamic mode at the anodic end of the capillary (0.5 p.s.i. for 10 s; 1 p.s.i.=6894.76 Pa). The method showed good linearity in the concentration range from 6.5 mM to 16.25 mu M, with an r(2) value of 0.9994. The limit o f detection, based on a signal-to-noise ratio of three, was 9.0 mu M. Absol ute intra-day RSDs of migration times were <0.40%, while the day-to-day val ues were less than or equal to 1.72%. Absolute peak area reproducibility wa s always better than 2.50%. A comparison of capillary electrophoresis with flame photometry on twelve real autopsy samples showed an excellent correla tion with an r(2) value of 0.9333. A preliminary application to real cases (20 subjects) was carried out plotting vitreous humour potassium vs. post-m ortem interval with a resulting r(2) of 0.904 and a Y-intercept of 4.75 mM, in agreement with the existing literature. (C) 1999 Elsevier Science B.V. All rights reserved.