Proteomic analysis ionization state

In addition to protein identification and characterization, another major goal of proteomics research is to quantify protein expression levels. However, MS is not inherently quantitative. Thus, the intensity of a peptide ion introduced to the mass spectrometer via ESI or MALDI does not reflect necessarily the amount of peptide present in the sample, due to the strong dependence of ionization on the physical and chemical nature of the analyte. To overcome this challenge, numerous quantitative analysis strategies have been developed to measure the differences in protein abundances between two different cellular states of a biological system (for example, normal and diseased cells). 

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