Isotope Dilution Analysis in the Quantitative Study of Proteins

4 Isotope Dilution Analysis in the Quantitative Study of Proteins 

In recent years, a remarkable trend can be observed i.e. the utilization of inductively coupled plasma-mass spectrometry (ICP-MS) as an attractive complement for protein quantification. If the heteroatom-containing proteins are known and the standards are available, the absolute quantification of proteins can be easily obtained via element analysis by ICP-MS. However, when ICP-MS is interfaced to a separation system, such as HPLC, the organic solution and inorganic salts introduced into ICP-MS usually decrease the instrumental stability and detection limits. To overcome the problems, isotope dilution analysis is introduced to an ICP-MS-based linked system.  

As and Ajp are the number of atoms in the sample and spike, respectively A s and sp are the abundance of isotope b in the sample and spike. 

Isotope dilution analysis for protein quantification with ICP-MS is usually performed by linked techniques based on the coupling to an effective separation method, such as HPLC or CE. Generally, proteins to be analyzed should contain ICP-MS-detectable elements, including both naturally occurring and artificially labeled. After introduction of the spike that has different isotopic composition from the analyte, the elemental isotope ratio can be measured in ICP-MS and thus the detectable elements can be absolutely quantified by use of the isotope dilution equation. If proteins have been identified with biological mass spectrometry, or the elemental stoichiometric ratios of proteins have been known, the amount of proteins can be deduced from the elemental concentration of the proteins. 

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