Alizarin Red S, pH 7.0, is an aqueous solution of Alizarin Red S (C.I. 58005), a synthetic azo dye. In addition, potassium dihydrogen phosphate, di-sodium hydrogen phosphate dihydrate and sodium azide are included in the formulation.

Applications for this solution are mainly in histology and cytology, where it is used to stain and visualize biological specimens, specifically to identify calcium deposits in tissues. The solution can also be used in water analysis to determine total hardness, calcium and magnesium content in water samples.

The chemical mode of operation is based on the reaction of the azo dye alizarin red S with calcium ions in a complexation reaction that results in a color change. The buffer components included, potassium dihydrogen phosphate and di-sodium hydrogen phosphate dihydrate, adjust the pH to 7.0, while sodium azide acts as a preservative. At a pH of 7.0, the sensitivity and selectivity of the solution to calcium ions may be lower than at a pH of 9.0.

The special suitability of Alizarin Red S, pH 7.0, solution is demonstrated by its application in biomedical research and water analysis. However, it should be noted that the sensitivity to calcium ions may be reduced at a pH of 7.0, compared to a solution at pH 9.0.