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 thesame body at identical postmortem interval. The study was carried out by collecting microsample amounts (50 ml) ofvitreous humour and by using an original method of capillary electrophoresis with indirect detection. The electrophoreticseparations were carried out in a pH 4.5 running buffer composed of 5 mmol/ l imidazole, 5 mmol/ l 18-crown-6 ether and 6mmol/ l a-hydroxybutyric acid. Detection was by indirect UVabsorption at 214 nm.Vitreous humour samples were collectedfrom 57 medico–legal autopsies or external examinations of cases of sudden natural or violent deaths. All samples prior toanalysis were diluted 1:20 with a 40 mg/ml aqueous solution of barium, the used internal standard, and finally injected bynitrogen pressure. The mean concentrations of potassium measured in the two eyes of all the cases included in the presentstudy ranged from 4.1 to 23.5 mmol/ l with the postmortem interval values varying from 7 to 144 h. A highly significant(P,0.0001) linear correlation was found between these two parameters as described by the equation: y50.1698x12.3587,r50.89. The intra-eye variability of potassium concentrations was low with an average RSD of 3.89% (61.83 SD) (48 eyes,five samples per eye). No statistically significant difference was found between the potassium concentrations in the two eyesof the same subject in a group of 24 cases, excepting a single case.