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 calcium and total calcium by using high performance capillary electrophoresis (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 detection 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 serum was injected for 5 s at 15 kV for the determination of ionized calcium. The total calcium levels in a number of human serum samples were determined by HPCE and compared with the NIST reference method (atomic absorption), and the results agree with each other within 95 % confidence. Two NIST standards were analyzed by HPCE, and the results fit each other perfectly. The ionized calcium levels in sera by this HPCE method have been compared with those obtained with ion-selective electrode (ISE) method, and the results were lower than those of ISE, which was what we anticipated. The effects of sample temperature and buffer pH were studied.