Test strips for the determination of the ionic strength or specific gravity of an aqueous sample

A test strip capable of determining the ionic strength or specific gravity of an aqueous test sample containing cations, said strip comprising a porous absorbent carrier matrix impregnated with a test reagent comprising

• a pH chromogenic indicator selected from the group consisting of dibromothymolsulfonphthalein and thymolsulfonphthalein, and
• a reagent selected from the group consisting of
• 1-hydroxyethlidene-1,1-diphosphonic acid,
• aminotris(methylenephosphonic acid),
• 2-(phthalimidoethyl)phosphonic acid,
• a first inorganic phosphate having a structural formula ##STR4## the first inorganic phosphate having been titrated by an acid or base to achieve its metal complexing and buffering capacity, and wherein M stands for one equivalent of an alkali metal, ammonium, lower alkyl ammonium, or hydrogen ion, and x is an integer ranging from zero to two, and
• a second inorganic phosphate having a structural formula, ##STR5## the second inorganic phosphate having been titrated by an acid or base to achieve its metal complexing and buffering capacity, and wherein M stands for one equivalent of an alkali metal, ammonium, lower alkyl ammonium, or hydrogen ion, and y is an integer ranging from zero to one.