Which of the following techniques is more commonly used to measure vitamins?

• A. High-performance liquid chromatography
• B. Spectrophotometry
• C. Nephelometry
• D. Microbiological

Answer: (A)

Vitamins are small organic molecules that are best quantified by separating them from other substances in a sample and then measuring them precisely. High-performance liquid chromatography provides the precise separation needed to resolve different vitamins and their derivatives, and it can be paired with detectors like UV, fluorescence, or mass spectrometry for accurate quantitation. This combination makes it versatile enough to measure many vitamins in one run with high specificity and sensitivity, which is why it is the most commonly used technique for vitamin analysis.

Spectrophotometry depends on how strongly a substance absorbs light, but many vitamins don’t have unique or sufficiently strong spectra in complex samples, leading to potential interferences. Nephelometry targets light scattering from particles or immune complexes and is mainly used for proteins and similar analytes, not vitamins. Microbiological assays measure vitamin activity through biological response, but they are slower, more variable, and less suited to routine quantification.

For these reasons, high-performance liquid chromatography is the preferred method for measuring vitamins.