Formaldehyde (HCHO) is a highly irritating, toxic and presumably carcinogenic chemical widely used in industry and the health-care sector. Exposure to formaldehyde in the workplace is hence an important health concern. Occupational health legislation requires employers to monitor workforce HCHO exposure at regular intervals. Methods for formaldehyde monitoring currently endorsed by the regulatory bodies are essentially laboratory based and as such, time and labor intensive. Development of simpler, more cost-effective methods which can be used in-the-field has so far been limited by the fact that most known detection techniques are not specific for formaldehyde or dependent on either exotic equipment or hazardous chemicals. This thesis describes the development of a new colorimetric method which can be used to detect formaldehyde in the 0.03 to 2ppm range. Unlike available techniques, this method is selective for HCHO and also easy and safe to use. It was discovered that 6-amino-1-napththol-3-sulfonic acid (j-acid) reacts with formaldehyde under relatively mild aqueous conditions and at room-temperature to form the easily detectable yellow dye 2,2'-bis(6-amino-1-napththol-3-sulfonic acid)methane. Dye formation was found to be specific for HCHO. Reaction with higher aldehydes and other substances is prevented sterically by the sulfonic acid groups in the C-3 position of j-acid. The kinetics of this reaction were investigated and optimal reaction conditions regarding j-acid concentration, pH and temperature were determined. It was discovered that the mechanism of the reaction is complicated by a reversible side-reaction which is competing for available HCHO. Ways to improve the j-acid reaction were investigated. Eight j-acid derivatives were synthesised and tested. None of these compounds was found to be reactive at the same mild conditions used with j-acid. Two compounds, however, 6-N-acetylamino-1-naphthol-3-sulfonic acid and 6-N-methyl-amino-1-naphthol-3-sulfonic acid where identified which can be used in acid (1M HCl and above). With those compounds, dyes with a higher extinction coefficient are formed. Based on the j-acid reaction a new analytical device for the detection of gaseous HCHO was developed. This device utilises an optical technique called attenuated reflection spectroscopy and was built using solid state optoelectronics.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599295 |
| Date | January 2000 |
| Creators | Gandenberger, F. U. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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