4. Conclusions
The methods developed in this paper are simple and reliable for the determination of formaldehyde and sulfur dioxide. With a reference color card, the developed methods can be used as a qualitative or semi-quantitative method for on-site analysis of samples containing formaldehyde and sulfur dioxide. The developed method as a new field screening tools was used to test samples at the point of sale for the supervisor of the government or the consumer. Moreover, the present method is sensitive, time saving, require no complicated instruments and consumes a small amount of reagent, and the reagent itself is of low toxicity. This method is applied with success to the analysis of formaldehyde or sulfur dioxide in the foods or Chinese herbals and the results agree well with those obtained by the standard method.