Colorimetric enzymatic determination of serum total carbon dioxide, as applied to the Vickers Multichannel 300 discrete analyzer.

Phosphoenolpyruvate carbosylase (EC 4.1.1.31) has been used in developing a simple, inexpensive colorimetric assay for serum total carbon dioxide in an open system. The oxaloacetate formed by the action of the enzyme on bicarbonate and phosphoenolpyruvate is measured by use of the diazonium salt of Fast Violet B. Interferences from billirubin, pyruvate, and drugs are negligible. Acetoacetate interference is significant only in highly ketotic samples, and a serum blank corrects for it. Serum protein interference is equivalent to 3.3 plus or minus 1.25 mmol of CO2 per liter and hence is sufficiently constant to be corrected for by use of a serum standard or serum blank. The method has been applied to the Vickers M-300 and D-300 systems and within-batch standard deviations of plus or minus 0.1 to plus or minus 0.6 mmol/liter have been observed. Excellent correlation with orthodox techniques has been obtained.