Determination of Urinary Citrate by Ion Chromatography

Abstract Ion chromatography was used to determine urinary citrate concentration. The technique is simple, requiring a 100-fold dilution of urine and 35 minutes at most for each analysis. The technique does, however, have the disadvantage that it requires a rather expensive automated system. The minimum detectable limit for citrate was 0.5 μ g./ml. in a standard solution, and the regression line for the standard curve from 0.5 to 50  μ g./ml. citrate had a significant correlation coefficient (lnY = 1.048 × lnX-2.755, r = 0.997). The intra-run coefficient of variation was 0.9 per cent. The overall intra-run and inter-run coefficients of variation, including the sampling and dilution of urine, were 4.8 and 8.3 per cent respectively. There is a possibility that another ion is close enough to the citrate peak to interfere; however, this problem can be solved by the treatment of the sample with citrate lyase. When the present method was compared with the conventional enzyme method, a significant correlation between the results was obtained in both human and rat urine. The 24-hour urinary citrate excretion in eight normal human males was 73.8 to 378.4 mg./day (mean, 174.7 mg./day), while that in male Wistar-strain rats (approximately 150 gm.) was 1.5 to 18.6 mg./day (mean, 9.5 mg./day), as measured in more than 50 consecutive rat urine samples.