QUANTITATIVE-DETERMINATION OF IONIZED CALCIUM AND TOTAL CALCIUM IN HUMAN SERUM BY CAPILLARY ZONE ELECTROPHORESIS WITH INDIRECT PHOTOMETRIC DETECTION

We have developed a new method to quantitatively determine ionized cal cium and total calcium by using high performance capillary electrophor esis (HPCE) with indirect photometric detection. Other cations such as Na+, K+, and Mg+ can also be quantitatively determined. A 70 cm x 50 mum i.d. fused silica capillary was used for the separation. The detec tion window was located 25 cm from the cathodic end, and the detection wavelength was set at 214 nm. A 100 mM imidazole solution at pH 7.4 ( adjusted with 5 % H2SO4) containing 0.1 % hydroxypropylmethylcellulose (HMC, 4000 centipoise) was used as background electrolyte. Whole seru m was injected for 5 s at 15 kV for the determination of ionized calci um. The total calcium levels in a number of human serum samples were d etermined by HPCE and compared with the NIST reference method (atomic absorption), and the results agree with each other within 95 % confide nce. Two NIST standards were analyzed by HPCE, and the results fit eac h other perfectly. The ionized calcium levels in sera by this HPCE met hod have been compared with those obtained with ion-selective electrod e (ISE) method, and the results were lower than those of ISE, which wa s what we anticipated. The effects of sample temperature and buffer pH were studied.