A colorimetric procedure for the determination of aldehydes in seawater and in cultures of methylotrophic bacteria

A spectrophotometric procedure for the determination of aldehydes was optimized for use in seawater, it involves the sequential reaction of aldehydes with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and FeCl₃ to produce a colored compound which is soluble in 50% acetone. The standard curve obeyed Beer's law to 90 μM formaldehyde in 0.7 m NaCl. The molar absorptivity of 21 800 absorbance units μM^?1 cm^?1 at 635 nm was not affected by changes in salinity. The limit of detection was 180 nM HCHO l^?1 when a pathlength of 1 cm was used, and 72 nM HCHO l^?1 when a pathlength of 5 cm was used.The MBTH procedure was used to compare formaldehyde production in cultures of the marine methanotroph, Methylomonas pelagica, growing on methane or methanol. The average rate of formaldehyde production, normalized to cell number, was almost 20 times greater in cultures grown on methanol than in cultures grown on methane.A depth profile of aldehyde concentrations from a station in the Peru upwelling region (10°S, 79°W) showed one peak in the oxygen gradient in the photic zone (80 m), two in the oxygen minimum (200 and 300 m), and one in the oxygen gradient below the minimum (800m). Aldehyde concentrations ranged from 0.6 to 8.8 μM formaldehyde equivalents l^?1. Except for the maxima where the aldehydes account for 13–15% of expected DOC concentrations, the background level of aldehydes was approximately 1% of DOC.