A comparison of the performance of ammonium phosphate,titan yellow and edta methods for the determination of magnesium in blood serum

Detailed analyses were carried out on 3 specimens of serum to compare the precision and accuracy of 4 typical chemical methods for magnesium, and to determine whether wet-ashing or deprotemisation with trichloroacetic or acetic acid affected the results. Two ammonium phosphate precipitation methods involving spectrophotometry of phosphate in the precipitate, a spectrophotometric method with Titan Yellow and a visual EDTA titration method were studied. The analyses were designed to reveal systematic errors and the results were analysed statistically.One ammonium phosphate method on untreated and wet-ashed samples and the EDTA method gave concordant and relatively precise results, which were used to estimate the true values. On this basis, another ammonium phosphate method involving overnight precipitation, gave consistently high results. The Titan Yellow method gave large random errors, particularly when proteins were not removed. The preliminary treatment of the samples did not appear to have any consistent effect.