Maximum error of visual water testing using indicator reagent papers

Based on metrological documents in force using the uniform color space as a system of color measurements, the maximum error of visual semiquantitative determination of iron(II, III), cadmium, calcium, cobalt, magnesium, coppe r, mercury, lead, and zinc; total of iron(II, III), cadmium, cobalt, copper , nickel, mercury, and zinc; total of the above metals and manganese, silve r, lead, and lanthanum; and nitrate, nitrite, sulfate, phosphate, active ch lorine, chloride, and chromate ions in water, as well as pH of aqueous solu tions was estimated. Determinations were performed using comparators with r eference color scale and corresponding concentration scales, in which the c oncentration increased in geometrical series with the ratio 2 or 3. The res ults of calculations and the experimental data indicated that visual testin g can be used for the semiquantitative determination of trace components wi th a maximum relative error of 33 or 50% on condition that the entire color scale chosen according to the standard color gamut is divided into no more than six or seven grades. With color scales divided into more grades, the determination becomes qualitative. Twenty rapid test procedures for the sem iquantitative determination of ions in water were certified.