A rapid and sensitive spot test amenable to visual or spectrophotometric quantitation has been developed for a wide variety of biochemical reagents by utilizing the transition metal salt cupric chloride and its large number of related colored compounds. This assay is potentially a widely applicable multipurpose test for rapidly detecting the presence of unknown substances. Combination of the test sample with the working reagent results in the immediate formation of a distinctive colored product that may be precipitable. Some compounds require the further addition of sodium hydroxide in order to generate the distinctively colored product. Distinctive reactions occur with the following reagents, and their limit of visual detection is indicated in parentheses: ammonium bicarbonate (12.5 mm), ammonium acetate (25 mm), ammonium hydroxide (0.1%), ammonium sulfate (2%), ammonium persulfate (0.02 mm), l-(+)-cysteine (0.07 mM), dithiothreitol (DTT) (1.25 mM), EDTA (0.6 mM), ethylene glycol bis(β-aminoethyl ether) N,N′-tetraacetic acid (5 mm), d-glucose (6 mm), glycerol (0.3%), imidazol (12.5 mm), dl-methionine (100 mm), mercaptoethanol (0.05%), sodium azide (19 mm, 0.1%), sodium dithionite (0.25%), sodium metabisulfite (25 mm), sodium nitrite (6.2 mm), sodium periodate (3.1 mm), sodium sulfite (12.5 mm), sodium thiosulfite (12.5 mm), sucrose (6 mm), and N,N,N′,N′-tetramethylethylenediamine (0.05%). A distinctive exothermic reaction occurs with hydrogen peroxide, but without color change. Compounds reacting insignificantly include 50 mm Tris buffer, urea, N,N′-methylene bisacrylamide, sodium dodecyl sulfate, isopropyl alcohol, sodium fluoride, trichloroacetic acid, phenol, mannose, K2HPO4, guanidine HCl, chloramine-T, magnesium chloride, and boric acid, where the solids were tested at approximately 10 mg/ml. Spectrophotometric standard curves were developed for DTT and sodium azide utilizing the clear supernatants resulting from these reactions. Combinations of at least four reagents could be discriminated, as demonstrated with mixtures of glucose, sodium azide, EDTA, and DTT. In addition ammonium sulfate could be detected to a limit of 4% in the presence of protein, DTT, and EDTA in a 50 mm Tris buffer. Spot tests were developed which utilized reagent-impregnated filter paper and gave distinetive colored products on addition of 5 μl of test sample. © 1986.
Fleming, N., & Nixon, R. A. (1986). A versatile transition metal salt reaction for a wide range of common biochemical reagents: An instantaneous and quantifiable color test. Analytical Biochemistry, 154(2), 691–701. https://doi.org/10.1016/0003-2697(86)90048-5