A Colorimetric Method for the Estimation of Free Formaldehyde and Hexa- Methylenamine
نویسنده
چکیده
It has previously been ascertained] that the phloroglucinol or Jorissen test is among the most sensitive color tests for free formaldehyde. The advantages claimed for it are: (1) simplicity; (2) great sensitivity; (3) it reacts with free or liberated formaldehyde only, and does not itself liberate formaldehyde from such compounds as hexamethylenamine; (4) finally, with the phloroglucinol test there is a gradation of colors, from pink to deep red, depending on the concentration of formaldehyde, which suggested to us the possibility of its application in a quantitative manner. However, the colors are not permanent. Their maximum intensity is reached within 3 minutes and then they gradually change to a violet and finally disappear altogether. This is particularly true with the high dilutions. Therefore we sought for a substance, or mixture of substances, which would give us the same quality of color as in the phloroglucinol test, and yet be permanent when used in making a set of standards. After considerable experimentation with metallic salts and different dyes, a mixture of Congo red (0.025 per cent in water containing 5 per cent alcohol) and methyl orange (0.01 per cent in water) was found to be satisfactory. A mixture of these in the proper proportions is only necessary in matching the reds of phloroglucinol in the lower concentrations of formaldehyde. For the higher concentrations Congo red alone suffices.
منابع مشابه
Estimation of nitrogenase using a colorimetric determination for ethylene.
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