Measurement of organic substances in the gas phase using on-line electrochemical techniques

Aniline was chosen as an atmospheric pollutant which might be monitored using an electrochemical sensor. The effect of pH and of different organic solvents on electrode poisoning was investigated for the analysis of aniline by voltammetry and it was concluded that it was not possible to prevent poisoning of the electrode by the reaction products. The analysis of aniline by flow injection analysis (fia) with DC (constant potential) and pulsed (double pulse) amperometric detection also suffered from electrode poisoning and the latter had a relatively high detection limit. Secondary and tertiary substituted anilines with similar volatilities to aniline at room temperature were examined as suitable alternatives to aniline using voltammetry. Dimethyl-p-toluidine poisoned the electrode to a small extent when analysed by voltammetry. Detection of this compound by fia with pulsed amperometric detection showed improved electrode stability but was not judged suitable for long term monitoring of atmospheric samples of the amine. A satisfactory method for monitoring aniline on line was developed using fia with triple pulse amperometric detection (PAD). The PAD waveform was optimised with respect to a low detection limit and a degree of selectivity towards possible atmospheric interferents for the detection of aniline in dilute aqueous acid at a platinum electrode. A wall jet cell was designed for the analysis of aniline vapour in air which was continuously trapped in dilute acid and periodically injected into a fia system. The cell was not affected by small gas bubbles and was reasonably portable [continued]...