Rapid determination of methanol in herbaceous distillates for their safety evaluation by a new modified chromotropic acid method

Document Type : Research article


1 Department of Immunology, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.

2 Department of Nursing & Midwifery, Faculty of Nursing & Midwifery, Islamic Azad University, Rasht Branch, post code: 4147654919, Rasht, Iran.


All sophisticated methods for direct determination of methanol require advanced instruments and high technical knowledge which preparing them is very expensive in none developed and developing countries. This work reports a simple and efficient qualitative technique for semi determination of methanol content in herbal distillates by a new modified chromotropic acid method. The technique is based on the indirect detection of methanol after its oxidation and transforming to formaldehyde by chromotropic acid (formaldehyde specific color indicator). To measure methanol level in herbal distillates, a water diluted sample were mixed with 50µl of sulfuric acid and potassium permanganate and after 5 minutes, followed by addition sodium bi-sulfite, chromotropic acid and concentrated sulfuric acid in two separated steps and finally, eye comparing with four color standard tubes which gives a range of amount of methanol in the sample. The method has a good precision and accuracy and its Limit of Detection is 25 mgL-1. It is particularly suitable for semi quantitative measurement of methanol in herbal distillates not only in the production process quality control of workshops or small companies with no laboratory equipment and adequate financial properties but also the quality check of point of-sale samples from commercial markets. To the best of our knowledge, there isn’t any report about such method.