Mass Spectrometry

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Discuss the advantages, disadvantages and limitations of mass spectrometry for the analysis of both small molecules and proteins.

Mass spectrometers. They are a powerful tool used to evaluate analytes such as single atoms, molecules, whole proteins, or the simple peptide chains that make them up. Using the mass to charge ratio (m/z) of these analytes, we can differentiate one or many entities (such as one particular peptide fragment, or a panel of them) from everything else in a complex sample [X1]. This method had truly had a revolutionary impact on science with the sensitivity, resolution and the range of masses able to be measured [X12].

Most mass spectrometers are made up of a few different parts: an ion source (which
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We can determine detailed structural information about a protein using one type of MS, or minute changes in quantity with another. We can measure many things at once, or one thing with great sensitivity [X12]. Proteins which previously were present in very low concentrations can be studied much more efficiently with this tool.

Protein Additionals:
Studying proteins using MS can be difficult. There are two major ways to study them, using a Bottom-Up or Top-Down approach. The bottom-up approach involves enzymatically digesting a sample, to yield a complex mixture of smaller peptide chains which can be more managable. This problem with this approach is that higher information such as structure is lost while some parts of the protein may also be unmeasureable due to unexpected modification, or too small a size [X1]. The top-down approach is when the entire protein is ionized, fragmented and measured at once inside the MS (Without the need for prior digestion). The entire protein can then be studied fully, providing means of studying proteins and their modifications without having to worry about degradation during sample processing [X1]. One of the drawbacks of this approach the need for a simple, relatively pure sample (Which usually means extra offline processing before analysis can begin)
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Although the ESI and MALDI methods are substantially better than the previous methods, they still have their weaknesses, and so new methods have been created in an attempt to advance [X16]. All in all, these newer non-vacuum methods that are able to analyse non-volatile compounds still use either the ESI, sonic-spray ionization (SSI) or MALDI principles [X16]. These atmospheric methods are quicker (No need to wait evacuation) but there is a loss of recovery rate and therefore sensitivity due to unwanted analyte ion-gas interactions [X16].

The more recent inlet techniques (Lasterspray ionization inlet [LSII], matrix-assisted ionization inlet [MAII], and solvent-assisted ionization inlet [SAII]) are sensitive, useful at both high and low mass range and can be used at ambient pressure or with a vacuum (With liquid or tissue specimens too) [X16]. These inlet techniques are functionally similar to ESI in the spectra they produce, these techniques also inherit the delicate treatment of proteins from ESI too

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