Use of Quinizarin as a Spectrophotometric Reagent for MgO Content Analysis of Portland Cement and Cement Clinker

A new direct spectrophotometric method for the determination of magnesium oxide in Portland cement and cement clinker is proposed. The method is based on a reaction with quinizarin (QUIN, 1,4-dihydroxyanthraquinone) in ethanol-water (50% v/v) solution at pH=9.5–10.3. Under optimum conditions, the determination of 0.5–3.9 μgċml−1 of magnesium is possible. The method is rapid and selective and possesses good accuracy and precision. The analysis of cement materials of variable magnesium content is feasible over the concentration range of 0.85–3.2 μgċml−1 Mg; the detection limit is 25.3 ngċml−1 Mg. Under the given conditions, no constituents normally present in Portland cement materials interfer. The procedure was tested by analyzing several standard reference materials and real samples of Portland cement and has been found to give satisfactory results. It has been satisfactorily applied to the determination of magnesium in clay and raw meal.