Selective flow-injection determination of methanol using immobilized enzyme reactors

A flow-injection procedure is described for the determination of methanol based on its alcohol oxidase-catalysed conversion to formaldehyde, which is then oxidized to formic acid by NAD+ in the presence of formaldehyde dehydrogenase. The concentration of NADH produced is measured by fluorimetry. Both enzymes and catalase, which is added to improve enzyme stability and the extent of the overall enzymatic reaction, are immobilized or coimmobilized on controlled-pore glass. Concentrations of methanol ≥ 1.2 × 10−6 M can be analysed. The proposed procedure has a linear application range of 4.0 × 10−6–8.0 × 10−5 M (fluorescence = −3.81 + 1.67 × 106 [methanol]; r = 0.998, n = 6), an R.S.D. of 1.8% at 2.4 × 10−5 M methanol, and a sampling frequency of 30 h−1. Enzyme reactors keep their catalytic properties for 3–4 months and can be reused for 400 determinations on average.