SPECTROPHOTOMETRY
Spectrophotometer method
Nash mehod: The very early basis of a spectro-photometric procedure proposed by Nash (1953) is the Hantzsch reaction between acetylacetone, ammonia and formaldehyde to form 3,5-diacetyl-1,4-dihydrolutidine (λmax = 412 nm). To complete the reaction, the procedure requires pH adjustment with ammonium acetate and heating. But under strongly acidic conditions, it may be used in the presence of trioxan and other compounds, which degrade to formaldehyde. The sensitivity may be increased by measuring the fluorescence spectrum. These methods are relatively sensitive and selective for formaldehyde and it is useful on account of the mild conditions employed. However, the procedure needs long reaction times and cannot be simply adopted for an automatic analysis. In order to develop a simple and automated method of analysis for formaldehyde, a Flow Injection Analysis (FIA) system with an incorporated gel-filtration chromatography column is proposed and have been applied to determine formaldehyde in fish (Benchman, 1996).