Can mass spectrometry work on liquids and solids?

[ASidd]

I am researching mass spectrometry for my school assignment and I seem to be getting contradictory answers. Some websites say that the sample used in mass spectrometry is definitely vaporized before use but other websites state that it can work on liquids e.g. in liquid chromatography/ mass spectrometry units? Which one is correct?

 

[gadong]

The key point to recognise is that mass spectrometric measurements are carried out under vacuum conditions. In order to perform the analysis, the sample must somehow be turned into gaseous fragments.

Mass spectrometry of solids can most easily be achieved by bombarding the sample with energetic ions (e.g. Ar⁺). This causes the solid to emit so-called "secondary ions" (ionised fragments of the solid) which are then mass-analysed in a conventional mass spectrometer. This technique is known as secondary ion mass spectrometry or SIMS. SIMS is widespread in all kinds of applications, e.g. geology, semiconductors, and is known for its high sensitivity (<< 1 atomic layer).

Liquids are usually volatile enough to be analysed as gases (e.g. by allowing a small sample to expand in the ionization chamber). This is the approach used in gas chromatography (liquid is injected onto a hot filament, and vaporises). A technique related to SIMS, fast atom bombardment, is also used for mass spectral analysis (liquids of interest are mixed with the relatively involatile glycerine, for example).

 

[ASidd]

But what happens in liquid chromatography? Are the molecules being analyzed not liquids?

 

[Yanick]

Mass spectrometry relies on many different ionizing techniques to get a charged species. You should look into the different ionization methods to get more information. What works for certain compounds isn't necessarily the best technique for others.

I found this by googling mass "spectrometry ionization methods"
http://www.research.uky.edu/core/massspec/jeolioniz.pdf

 

[gadong]

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2643089/

The above link describes the principles of liquid chromatography mass spectrometry. In a nutshell, the analyte is ionized by a technique known as electrospray ionization (http://en.wikipedia.org/wiki/Electrospray_ionization). This involves pumping it through a capillary, and pulling out the meniscus using using high voltage. No bombardment is involved - the extracted molecules and clusters ionize by themselves.

 

[DrDu]

But what happens in liquid chromatography? Are the molecules being analyzed not liquids?

In LC-MS when the dissolved substances leave the liquid chromatography unit, they are vaporized and then further ionized and analyzed in the MS.