Determination of methanol concentrations in legally and locally distilled alcohol found on the market using UV/VIS spectrophotometry

Abstract

The objective of this study was the evaluation of the levels of methanol in alcoholic beverages using the visible spectrophotometric technique. In this study were taken 15 samples of various alcoholic beverages around Kampala. Alcoholic beverages are defined as drinks, whose main ingredient (except water) is ethyl alcohol. Other components of alcoholic beverages are other alcohols, acids, aldehydes, esters, etc. It is believed that higher methanol content may be present in some alcoholic drinks produced by traditional distilleries or some alcohol brewing companies. As a result of this, there could be a higher risk of methanol concentration in products. Therefore, this research focused on quantifying the amount of methanol in some alcoholic beverages using a Visible- Scanning Spectrophotometer model 7310 JENWAY. This method was simple, fast and reliable giving satisfactory results. The results showed some level of methanol in many of the studied local and foreign alcoholic drinks between the ranges of 217.2 to 2061.7 ppm. A good linear relationship of the concentration of methanol versus absorbance is observed with a linear range of 0.02-6.0 mg mL-1. The detection limit (3σ/S) is 90 ppm, the limit of quantitation is 300 ppm, while its Relative Standard Deviation (R.S.D) is 113.8 % and the recovery rate is 97.5%. The equation of the calibration line was A = 0.0011C – 0.2219, with a linear correlation coefficient of 1. The results showed that the levels of methanol observed in many of the analyzed drinks pose a health threat to the human body when consumed. This was based on the World Health Organization (WHO) and the Uganda National Bureau Of Standards (UNBS) limits which are 500 ppm and 300 ppm respectively.