A Rapid Formaldehyde Assay Using Purpald Reagent: Application under Periodation Conditions

Measurement of formaldehyde is encountered in a broad range of applications including the wine and alcohol industry and environmental pollution surveillance. In carbohydrate structural chemistry, frequent use is made of formaldehyde by periodate oxidation of terminal vicinal diols. Popular methods for the detection of formaldehyde use reagents such as chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) or acetylacetone. The chromotropic acid method requires heating of the sample under strongly acidic conditions, which is undesirable in many applications. The acetylacetone method yields a yellow color product, and is less specific and sensitive (Mimura et al., J. Hyg. Chem. 22, 39-41, 1976). The reaction of formaldehyde with Purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole) works under alkaline conditions at room temperature, and the sensitivity is superior to other methods. The color development by this reagent, however, requires oxidation of the adduct with hydrogen peroxide, air oxygen, or dilute periodate. We found that low levels of periodate, commonly used to oxidize specifically terminal vicinal diols to yield formaldehyde, are compatible with color development with the Purpald reagent. We have investigated the conditions required for use of the Purpald reagent, especially in conjunction with periodate oxidation reactions. We have used the assay either in test tubes or with microplates, attaining sensitivity of as little as 1 nmol formaldehyde.