Determination of microgram amounts of calcium in small biological samples by EDTA titration using Patton and Reeder's indicator

Abstract

An EDTA titration method has been developed for the determination of calcium in small biological samples. Fresh or dried material is extracted with 1 N nitric acid and the extract is alkalinised to pH 13.4 and titrated with EDTA in the presence of Patton and Reeder's indicator and sodium tartrate. Barium, magnesium, manganese, iron, lead, zinc, oxalate, phosphate and sulphate do not interfere owing to the high pH and the presence of tartrate. Copper interferes, but up to 5 µg of copper can be masked with cyanide if the copper concentration does not exceed one tenth the calcium concentration. This method permits the quantification of calcium in the range 0.5–40 µg and with a reproducibility of ±2.5% or better.