An aqueous reagent for determining inorganic phosphate in a protein-containing liquid biological sample comprises a molybdate salt, an acid capable of reacting with the molybdate salt to form molybdic acid for complexation with phosphate to form phosphomolybdate complexes, a ferric salt in an amount sufficient to inhibit turbidity in the sample, and a nonionic surfactant reagent in an amount sufficient to further inhibit turbidity in the sample, the molybdate salt and the acid being present in amounts sufficient to form an amount of molybdic acid sufficient to produce a detectible color change when complexed with phosphate in the sample.

A complex of a long chain cationic surfactant and an organic anionic dye is useful in demonstrating the presence of and determining the concentration of fatty acids, compounds which hydrolyze to liberate fatty acids, or the activity of hydrolaze enzymes which produce fatty acids from a substrate.

A reagent of the type comprising an acid, a molybdate salt, a non-ionic surfactant, and polyvinylpyrrolidone (PVP). The reagent is characterized in that it further comprises an enhancing amount of at least one sugar alcohol. Also, a method for assaying inorganic phosphorus of the type which comprises mixing a sample of biological fluid with a reagent and measuring the absorbance of the resulting solution. The method is characterized in that the above reagent is employed therein. The method can further be characterized in that the measurement can be made via a rate technique.

A quantitative colorimetric or spectrophotometric method of determining analyte albumin using a specie specific dye-based color reagent is disclosed. The method utilizes a standard solution comprising an aqueous solution of albumin of different specie than that of the analyte and a water soluble surfactant containing at least one hydrophobic group of contiguous carbon atoms. The surfactant is of a type and present in an amount such that the standard solution mimics, with respect to spectrophotometric response, an aqueous solution of the analyte when the standard solution and the analyte solution contain the same concentrations of albumin and color reagent.

A reagent for determining quantitatively the amount of phosphorous in bodily fluids which comprises a surface active agent, a strong acid, ammonium molybdate, a heavy metal chelating compound, and anti-oxidant, and deionized water is described. A method of using such a reagent is also described.