Sensitive formaldehyde determination with Nash's reagent and a 'tryptophan reaction'.

The widely applied Nash-method and its modifications have unsatisfactory specificity and restricted sensitivity for the determination of small amounts of formaldehyde. A method using small volumes of reaction mixtures with low background absorbance is described; this method avoids dilution during the protein denaturation step by the use of trichloroacetic acid. Alternatively a 'tryptophan-sulfuric acid-iron' reaction takes advantage of high specificity for formaldehyde detection. A more economical and sensitive variant is described including trichloroacetic acid precipitation of protein. The sensitivity and specificity of the colour development reaction of the 'tryptophan-sulfuric acid-iron' reaction appears to be superior to the Nash-modification. However the detection of formaldehyde by the NASH method can also be amplified by subsequent extraction and concentration of the reaction product diacetyl-dihydrolutidine into n-amyl alcohol so that a formaldehyde amount of few nanomoles can be determined. The application of these methods is recommended in cases of formaldehyde formation in small amounts such as in cell cultures or when kinetic data at low substrate concentrations and slow turnover rates have to be measured.