Final answer:
Mass spectrometry is the technique used for protein sequencing but not for protein purification; it identifies and analyzes protein structure, making it essential in proteomics.
Step-by-step explanation:
The technique used for protein sequencing and not for protein purification is mass spectrometry. Mass spectrometry is primarily used to identify and determine the characteristics of molecules, including the sequencing of proteins. Unlike other methods like High-Performance Liquid Chromatography (HPLC), isoelectric focusing, and affinity chromatography which are employed for purification, mass spectrometry does not purify proteins but rather helps to analyze their structure after they have been separated and purified using other techniques.
Advances in mass spectrometry have enabled the analysis of very small samples of proteins determining their amino acid sequence, modifications, and structure. This is essential for identifying proteins and understanding their function and role in biological processes. It is particularly helpful in proteomic analysis for the detection of proteins even in small quantities, making it a powerful tool for disease state analysis and biomarker discovery in complex biological samples.