SPECTROPHOTOMETRIC FLOW-INJECTION ANALYSIS OF FORMALDEHYDE IN AQUEOUS-SOLUTIONS USING 3-METHYL-2-BENZTHIAZOLINONE HYDRAZONE

A flow injection method for the determination of formaldehyde was deve loped. It is based on its reaction with 3-methyl-2-benzthiazolinone hy drazone (MBTH) to yield a blue formazan anion. Typically 180 mul sampl es are injected into a buffered carrier stream with a frequency of 30 per hour. This sample line merges with the reagent stream containing M BTH, whereupon an azine is formed. After merging with a second stream containing an acidic solution of FeCl3 as reagent, MBTH is oxidized to an intermediate that attacks the azine yielding the formazan dye with an epsilon(max) at 635 nm. The method was applied to formaldehyde con centrations in the range from 0.15 mg/l to 15 mg/l. The relative stand ard deviation was 2.3% for 3 mg/l formaldehyde, and 5.1% for 0.3 mg/l, respectively. Strong reducing agents like nitrite interfere seriously . Out of the family of carbonyl compounds only acetaldehyde and propio naldehyde cause strong positive interference.