Flow injection spectrophotometric determination of total carbonyls in hydrocarbons by reaction with vanillin

The determination of total carbonyls in hydrocarbons by flow injection is based on the condensation reaction between the carbonyl group and vanillin in a strongly alkaline sodium hydroxide medium. The carbonyls, in an organic phase, were introduced into an aqueous carrier stream, mixed and extracted in a phase separator before the reaction product in the aqueous phase was detected spectrophotometrically at 414 nm. Parameters affecting the performance of the robust analyser were studied. The proposed analyser is fully computerised and is able to monitor total carbonyls in samples at a frequency of 15.3 samples per hour with a relative standard deviation < 2.5% at ca 500 mg l−1. The calibration graphs are linear between 100 and 1000 mg l−1 for acetone and between 250 and 1000 mg l−1 for other carbonyl compounds. The detection limits for the individual carbonyl compounds are given. The proposed system is suitable for the determination of total carbonyl compounds in organic solvents in the range 0.025 – 0.1% m/v calculated as acetone.