Potassium concentration differences in the vitreous humour from the two eyes revisited by microanalysis with capillary electrophoresis

This paper presents a study of the variability of potassium concentrations in the vitreous humour of the two eyes of the same body at identical postmo rtem interval. The study was carried out by collecting microsample amounts (50 mul) of vitreous humour and by using an original method of capillary el ectrophoresis with indirect detection. The electrophoretic separations were carried out in a pH 4.5 running buffer composed of 5 mmol/l imidazole, 5 m mol/l 18-crown-6 ether and 6 mmol/l alpha -hydroxybutyric acid. Detection w as by indirect UV absorption at 214 nm. Vitreous humour samples were collec ted from 57 medico-legal autopsies or external examinations of cases of sud den natural or violent deaths. All samples prior to analysis were diluted 1 :20 with a 40 mug/ml aqueous solution of barium, the used internal standard , and finally injected by nitrogen pressure. The mean concentrations of pot assium measured in the two eyes of all the cases included in the present st udy ranged from 4.1 to 23.5 mmol/l with the postmortem interval values vary ing from 7 to 144 h. A highly significant (P <0.0001) linear correlation wa s found between these two parameters as described by the equation: y=0.1698 x+2.3587, r=0.89. The intra-eye variability of potassium concentrations was low with an average RSD of 3.89% (+/-1.83 SD) (48 eyes, five samples per e ye). No statistically significant difference was found between the potassiu m concentrations in the two eyes of the same subject in a group of 24 cases , excepting a single case. (C) 2001 Elsevier Science B.V. All rights reserv ed.