Abstract
AbstractA colorimetric method is described allowing convenient and rapid estimation of 5–15 μg Ca in 0.1 ml of blood serum. N‐hydroxy‐naphtalene‐1,8‐dicar‐boxylic acid imide forms an insoluble salt with Ca, which is brought into solution by the addition of ethylene diamine tetra‐acetic acid in excess. N‐hydroxy‐naphtalene‐1,8‐dicarboxylic acid imide has an absorption maximum at 338 mμ in alkaline solution; the optical density of the EDTA solution is therefore measured at this wavelength. Two moles of N‐hydroxy‐naphtalene‐1,8‐dicarboxylic acid imide will be equivalent to one mole of Ca. Tartaric acid, low concentrations of citric acid, phosphate, magnesium, zinc, and ferrous or ferric ions will not interfere in the determinations of Ca by this method. Higher concentrations of citric acid as well as the presence of manganese, strontium, and barium, are harmful and must be avoided.
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