Simultaneous determination of potassium, calcium, sodium and magnesium ions in urine by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) was applied for the simultaneous determination of potassium (K+), calcium (Ca2+), sodium (Na+) and magnesium (Mg2+) ions in human urine samples. Separations were carried out in a pH 4.2 carrier electrolyte containing 10 mM imidazol, 5 mM 2-hydroxy-iso-butyric acid, 2 mM 18-crown-6, and 0.2% acetic acid. Indirect UV detection was conducted at 215 nm. An aliquot (100 mu l) of urine specimen with precipitate was diluted 1: 100 with distilled water (9.9 ml), filtered through a 0.2 pm membrane filter, degassed using an ultrasonic generator, and then injected directly into the capillary. Twenty-four hours (24-h) urine samples were collected from 110 Japanese men and women aged 18-74 years. The four cations were well separated in less than six minutes. The mean values of the cation concentrations in mg/l were K+=1,372, Ca2+=88, Na+=3,072 and Mg2+=62. The concentrations of K+, Na2+ and Mg2+ were in agreement with those obtained in urine samples using an ion selective electrode meter for K+ and Na+ determination, and a colorimetric reaction method with xylidil blue for Mg2+ determination. The proposed method is simple, rapid, and does not require any preliminary treatment of the urine samples except diluting.