A method of applying an organic acid reagent having limited transolubility in organic solvents, aqueous solvents, and mixtures thereof to a component of a diagnostic test device by mixing an organic acid reagent and an amine to form a salt complex, dissolving the salt complex in a solvent to release the organic acid reagent into the solvent, and applying the solvent to the component of the diagnostic test device such that the organic acid reagent present in the solvent becomes integrated into the diagnostic test device. The amine is represented by the formula H.sub.mNR.sub.n wherein m is 0, 1, or 2; n is 1, 2, or 3; the sum of m and n is 3; and R is an independently selected group which renders the salt complex soluble in aqueous solvents, organic solvents, or mixtures thereof. The amine is also represented by the formula NR.sub.4.sup.+ wherein R is an independently selected group which renders the salt complex soluble in aqueous solvents, organic solvents, or mixtures thereof. The organic acid reagent is selected from a carboxylic acid, a sulfonic acid, a phosphoric acid, and mixtures thereof. Preferred reagents are dyes like pyragallol red. In a specific embodiment the diagnostic test device is a paper test strip.