A stable colorimetric assay to measure toxin elevation of inorganic phosphate in bile

A modified assay for the measurement of nanomole amounts of Pi in 50 microliters of bile is described. The assay is based on the formation of a complex between malachite green dye and phosphomolybdate under acidic conditions. Only three simple steps are required to produce a colored complex which remains stable for at least 3 h; these steps are precipitation with acid, addition of color reagent containing dye and surfactant, and incubation at 37 degrees C. Analysis of bile samples collected from a rat given the toxin 1,1-dichloroethylene demonstrated that the assay is well suited to routine assays of biliary Pi as an endogenous indicator of aberrant hepatobiliary function.