Determination of calcium in urine by the chloranilate method.

Evidence is presented that the colorimetric chloranilate calcium method can be accurately applied to urine provided that elimination of interfering substances, which include magnesium, is performed prior to the determination. Isolation of calcium as the oxalate, followed by perchioric acid digestion, has been shown to be an acceptable method whereby urinary calcium can be put in a suitable state for analysis. Allowing the urine to stand for 1 hr. at pH 2 prior to the oxalate precipitation has been shown to be a simple means of eliminating the sampling error due to calcium precipitates.