Which technique is widely used for identifying and quantifying proteins based on mass-to-charge ratios?

• A. Western blot is used for protein identification.
• B. RT-qPCR is used for quantifying proteins.
• C. Mass spectrometry is used for protein identification and quantification based on mass-to-charge ratio.
• D. ELISA detects nucleic acids.

Answer: (C)

Mass spectrometry measures ions by their mass-to-charge ratio, making it ideal for identifying and quantifying proteins in complex samples. In practice, proteins are usually chopped into peptides, then ionized and analyzed to determine their masses. The resulting spectra, especially from tandem MS, reveal peptide sequences that can be matched to proteins, enabling identification. For quantification, the intensity of peptide ions is compared across samples, and can be done with label-free methods or with isotopic labeling and targeted approaches to achieve relative or absolute measurements. Techniques that rely on antibodies or nucleic acids don’t use mass-to-charge information for identification and quantification, so they don’t fit the basis of this question.