Without the aid of chromatographic techniques, quantification of bio-ethanol in fermentation-broth distillate becomes inconvenient. Potassium permanganate is preferable over potassium dichromate because of the latter well-known toxic properties, it is common used in ethyl alcohol determination either by visible determination of Cr(III) green optical density, a consumed Cr(VI) determination in strong acid medium by measuring band absorbance decrease at 267 nm or the unreacted Cr(VI) determination iodometrically after alcohol oxidation. Nevertheless, these titre methods arise difficulties experience analysts from multiple solutions preparation, standardization that should be carried out every day and to successful end point detection in the presence of Cr(III) green color which leads to a significant ethanol quantification error. Noteworthy permanganate-iodometrydrawbacks as same as titre dichromate difficult practical procedures and multiple reagents employed.
In this laboratory a self colorimetric method was developed in neutral medium as alcohol-specific oxidizing agent precludes both of its undesirable high oxidizing properties and difficult titrimetric methodologies for bio-ethanol quantification. It is based on unreacted permanganate optical density difference between a non ethanol-containing sample as a blank and ethanol-containing sample is directly proportional to the consumed permanganate amount in ethanol red-ox reaction and consequently directly proportional to ethanol content. This optical density difference versus ethanol concentration 1-6% v/v obeys Beer-Lampert law provides limit of detection, limit of quantification and correlation coefficient equal 0.17%, 0.56% and 0.999 respectively.