Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Which option is not a method of water purification?

1. Gas chromatography

2. Double distillation

3. Ion exchange column

4. Reverse osmosis

The correct answer is: Gas chromatography

Gas chromatography is primarily an analytical technique used to separate and analyze compounds that can be vaporized without decomposition. It is generally employed in laboratories for the qualitative and quantitative analysis of substances in various samples, including environmental samples, food products, and biological fluids. However, it does not function as a method for water purification, as it does not remove impurities or contaminants from water. In contrast, double distillation, ion exchange columns, and reverse osmosis are all methods designed specifically to purify water. Double distillation involves heating water to create vapor, which is then cooled to collect pure water, effectively removing many impurities. Ion exchange columns work by exchanging ions in water with ions present in the resin within the column, removing dissolved salts and other ionic contaminants. Reverse osmosis uses a semi-permeable membrane to separate water from contaminants, allowing only water molecules to pass through while filtering out larger molecules and impurities. Understanding these distinctions highlights why gas chromatography does not belong in the group of water purification methods.