Phenol interference in the mercury-free pararosaniline method and the chromotropic acid method for formaldehyde

The modified pararosaniline method for formaldehyde which uses no poisonous mercury reagent is not affected by phenol/formaldehyde ratios ranging from 1 to 100, whereas such ratios caused almost total inhibition of the chromotropic acid method, even if water, 1% sodium bisulfite or 0.01 N H2SO4 were used to simulate different collection media. No influence of phenol also occurred even for 11 days of storage at room temperature before analysis.