Colorimetric methods of determination of menthol in air.

Menthol vapours are irritant to eyes, nose and throat, and ingestion of this chemical has been reported by Von Oetingen (1958)1) to cause abdominal pain, vomiting, staggering gait and sopor. The workers exposed to high concentrations of menthol vapours in an industry manufacturing menthol crystalls from the plant extracted mentha oil complained of drowsiness, headache, nausea and vomiting. Till 1979 no TLV2) has been assigned to menthol. In order to conduct industrial hygiene survey in such a plant with a view towards establishing a TLV, there is need of simple, sensitive and reliable methods for determination of menthol in air. There is qualitative method of detection of menthol in British Pharmocopia (1973)3) based on the development of a purple colour on dilution of the reaction product of menthol and vanillin in concentrated sulphuric acid medium with water in the ratio of 2 : 1 (v : v). The other method described by Masamune (1933)4) is based on the visual colorimetric estimation of the red colour developed by heating menthol with DMAB in (1.6 : 1) sulphuric acid : water (v : v) medium. Guerin (1905)5) and Ekkert (1928)6) stated that the higher alcohols and phenols dehydrated by concentrated sulphuric acid combine with aromatic aldehydes such as DMAB to give colour. According to Snell and Snell (1957)7) the factors increasing colour intensity in addition to amount of higher alcohol are ; increase in aldehyde, increase in sulphuric acid, heating and time. In the present paper it was intended to study the various factors influencing the sensitivity of DMAB and Vanillin methods so that the analytical techniques of determination of menthol are optimised. To find out a suitable