Which method yields reliable quantification of ethanol in the presence of isopropanol?

Which method yields reliable quantification of ethanol in the presence of isopropanol?

• A. Reaction with permanganate and chromotropic acid
• B. Conway diffusion followed by dichromate reaction
• C. Alcohol dehydrogenase reaction
• D. Gas-liquid chromatography

Answer: (D)

Quantifying ethanol reliably when another volatile alcohol like isopropanol is present depends on separating the two substances before measurement. Gas-liquid chromatography accomplishes this because the sample is vaporized and carried through a column whose stationary phase interacts differently with ethanol and isopropanol. Each alcohol travels through the column at its own rate and exits at a distinct time, producing separate peaks. The detector then measures the ethanol peak independently of any isopropanol peak, so the ethanol concentration is quantified accurately even in a mixture. Other approaches either rely on reactions that aren’t highly specific to ethanol or don’t separate components. For example, enzymatic methods use alcohol dehydrogenase to produce a detectable change, but these can be affected by the presence of isopropanol or other substances, leading to interference. Colorimetric or diffusion-based methods may react with multiple species and fail to distinguish ethanol from isopropanol, reducing accuracy in mixed samples. Gas-liquid chromatography avoids these issues by providing a physical separation prior to detection, making it the most reliable choice here.

Quantifying ethanol reliably when another volatile alcohol like isopropanol is present depends on separating the two substances before measurement. Gas-liquid chromatography accomplishes this because the sample is vaporized and carried through a column whose stationary phase interacts differently with ethanol and isopropanol. Each alcohol travels through the column at its own rate and exits at a distinct time, producing separate peaks. The detector then measures the ethanol peak independently of any isopropanol peak, so the ethanol concentration is quantified accurately even in a mixture.

Other approaches either rely on reactions that aren’t highly specific to ethanol or don’t separate components. For example, enzymatic methods use alcohol dehydrogenase to produce a detectable change, but these can be affected by the presence of isopropanol or other substances, leading to interference. Colorimetric or diffusion-based methods may react with multiple species and fail to distinguish ethanol from isopropanol, reducing accuracy in mixed samples. Gas-liquid chromatography avoids these issues by providing a physical separation prior to detection, making it the most reliable choice here.