Mass Spectrometry (MS)

Contributors: Catherine H. Stephens, Eric Monroe

Overview

Technique: Mass Spectrometry (MS)
Formal name: Mass Spectrometry
Sample image of the data

What this techniques measures (compound classes, physical structures, etc): Mass spectrometers measure the molecular mass of compounds via a mass to charge ratio (m/z). This ratio can be indicative of the chemical/molecular/atomic composition of a sample via measurement of an intact compound or its fragments. Mass spectrometers cover a wide range of instruments and serve as the detector for numerous hybrid techniques. As such, other methods (liquid and gas chromatography) are often used to separate complex mixtures and numerous methods of producing ionized forms of the compounds from samples. Many mass spectrometers exist with different methods of separating and measuring m/z at different resolutions, sensitivities, level of analyte fragmentation and price point. In essence, a mass spectrometer is just one box (the end detector) that relies on other components in order to define the experimental parameters and capabilities of the complete hybrid instrument – one could think of a mass spectrometer as one Lego piece that snaps onto additional components to become a complete scientific instrument.
Limitations of this technique: The type of mass spectrometer often introduce certain limitations in the m/z range that an instrument can detect. Other limitations are a result of individual mass spectrometers or the hybrid techniques that utilize mass spectrometry as a detection strategy. The wide range of options on the market and in use can largely adapt to individual experimental needs. No one mass spectrometer will be able to adapt to all samples but addressing each potential issue would be beyond the scope of this page.
Can/how can this technique be made quantitative? Mass spectrometry can be quantitative and semi-quantitative under certain analysis protocols and is largely dependent upon the hybrid methodologies used and/or the availability of standards. Ionization reproducibility is often a limiting factor for quantification.

Samples

Phases it can be used to examine (gas, liquid, solid) Solids, liquids, and gasses may be examined under certain conditions as the mass spectrometer is the detector of hybrid experiments. Ionization and sample introduction can be performed in many different mechanisms (some select options will be detailed in other sections of this wiki).
Is this technique non-destructive? Broadly no. Mass spectrometry requires some sample to be introduced into the instrument so these methods would not meet the most conservative definition of non-destructive. Some techniques such as the ambient ionization methods may be used in a minimally invasive manner such that no visible sampling/damage the may be produced.
How invasive is this technique? Mass spectrometry can be minimally invasive due to high sensitivity measurements but, with the many arrangements of mass spectrometers in hybrid instruments, the level of invasiveness is often dependent upon the sample introduction method. Some methods can sample in a minimally invasive manner from a solid object or collect gasses produced from a material.
Minimum size of sample necessary to use this technique? This is highly dependent upon the needs of the hybrid method and sample complexity. Most modern mass spectrometers have detection limits in the sub-nanogram scale for individual compounds. Samples often need to be much larger due to sampling limitations/practicalities of the sample introduction and ionization method of an individual instrument set up.
Sample preparation methods Sample preparation is performed outside of the mass spectrometer and is dependent upon the hybrid instrumentation used as the mass spectrometer is a detector. It requires that an analyte be presented in an ionized form via an additional mechanism, as will be discussed in other portions of this wiki.

Applications

Examples of how this technique is used in the field? Mass spectrometers serve as a detector with many capabilities. A non-exhaustive list would include trace metals analyses, molecular identification of compounds, speciation of biological products, volatiles analyses, etc.
Risks associated with using this technique? Some sampling is required even with minimally invasive methodologies. Results can be complex and in some cases requires extensive data interpretation.

Budgetary Considerations

Approximate cost to purchase equipment for this technique? Mass spectrometers can range from ~$50k to > $1 million depending on the type of mass spectrometer and the associated sample introduction methods.
Annual cost to maintain this equipment? Annual service coverage costs are often in the 5-10% of the cost of the instrument. Consumable costs vary widely on the techniques that are used with the mass spectrometer.
Sample analysis costs? Commercial labs would be expected to have a sample charge in the $100-$1000 range, highly dependent upon the specifics of the method and instrumentation required.

==Case Studies== [provide description and links]

Additional Information

Complementary Techniques [describe and link]
Variations of this technique [describe and link]

References

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