Abstract: This disclosure relates to a method and reagents for determining amphetamine and methamphetamine in a biological fluid such as urine. In particular, this disclosure relates to a fluorescence polarization immunoassay procedure for determining the presence of amphetamine and methamphetamine in a single assay and to a novel class of tracer compounds employed as reagents in such procedures. The procedure described includes pretreatment of the biological sample to eliminate cross-reactants such as .beta.-hydroxyphenethylamine by preincubating the sample solely with an aqueous periodate solution having a pH from about 4.0 to about 7.5 without adjustment to an alkaline pH.

Abstract: A vertical beam spectrophotometer for measuring the light absorption of an assay prepared using standard wet chemistry procedures and conventional solid phase coated bead technology is disclosed. The spectrophotometer measures the absorption of the assay in a conventional reaction cuvette with the bead remaining in the cuvette. The light source of the spectrophotometer illuminates the bead, which diffuses the light into the surrounding assay solution. A lense projects the diffused light onto a photocell which converts it into an electrical signal having magnitude related to the light absorption of the assay. The signal is processed in a known manner by conventional processing circuitry to obtain an absorption value.

Abstract: Interfering proteins are precipitated and digoxin extracted in a fluorescence polarization immunoassay for digoxin with a protein precipitating reagent. The reagent contains about 3 to 4% 5-sulfosalicyclic acid in an aqueous solution including about 40 to 60% of a straight or branch chained organic alcohol having from 1 to 4 carbon atoms.

Abstract: A reduced dinucleotide, preferably nicotinamide adenine dinucleotide (NADH), is stabilized in an aqueous base liquid containing propylene glycol, boric acid and a buffer capable of buffering within a pH range of 8-11. The stabilized liquid contains greater than 50% (v/v) water. The remaining volume contains propylene glycol which has been chemically treated to remove oxidants. This reagent may be used by itself or in conjunction with an assay reagent system for use in the clinical laboratory.