Photometric assay of methanol and formaldehyde in industrial waste-waters using alcohol oxidase and 3-methyl-2-benzothiazolinone hydrazone

An enzymo-chemical method using alcohol oxidase (AO) and 3-methyl-2-benzothiazolinone hydrazone (MBTH) for the simultaneous analysis of methanol and formaldehyde in mixtures, including industrial waste-waters, is described. The enzyme oxidizes methanol to formaldehyde, while MBTH plays a double role: (1) in the first step of the reaction, it forms a colourless azine adduct with pre-existing and enzymatically formed formaldehyde and prevents its further oxidation by AO; (2) in the second step, non-enzymatic oxidation of azine product to cyanine dye occurs in the presence of ferric ions in acid medium. Pre-existing formaldehyde content is evaluated by a colorimetric reaction with MBTH before sample treatment with AO, and methanol content is determined by the increase in a coloured product after enzymatic oxidation of methanol to formaldehyde. The possibility of a differential assay of methanol and formaldehyde by the proposed method has been proved for model solutions, for real samples of technical formalin and real industrial waste-waters from the Pustkow plant for phenol-formaldehyde resins (Poland). The sensitivity of the assay for both analytes approaches 30 ng of analyte per millilitre of reaction mixture, that is 3.2-fold higher than with the chemical method with the use of permanganate and chromotropic acid. The linearity of the calibration curve is significant (p < 0.0001), and the standard deviation does not exceed 7%.