ISO 6920:1984

Crude sodium borates for industrial use — Determination of total and alkali-soluble calcium and magnesium contents — Titrimetric method

The calcium content is determined by titration of an aliquot portion of the test solution with ethyleneglycol-bis-(2-aminoethyl)-N,N,N’,N’-tetra acetic acid, disodium salt (EGTA) solution using 2-carboxy-2′-carboxy-2′-hydroxy-5′-sulphoformazylbenzene (Zincon) as indicator. The combined magnesium and calcium contents are determined by titration of a further aliquot portion of the test solution with ethylenediaminetetra-acetic acid, disodium salt (EDTA) solution, using Mordant black 11/potassium chloride as indicator, after addition of triethanolamine solution and buffer solution. The magnesium content is calculated by difference.