MASS SPECTROSCOPY

- Meesha Singh

IntroductionBasic Principle: Mass spectrometer converts molecules to ions under

vacuum so that they can be moved about and manipulated by external electric and magnetic fields.

These ions are then separated and determined. Separation is achieved on different trajectories of moving ions in electrical and/or magnetic fields.

Associated components:i. A small sample of compound is ionized, usually to

cations by loss of an electron- The lon Sourceii. The ions are sorted and separated according to their mass

and charge. - The Mass Analyzeriii. The separated ions are then detected and tallied, and the

results are displayed on a chart.- The Detector

Instrumentation

Soft Ionization TechniquesElectrospray Ionization (ESI)Spray sample solution from a needle into an orifice in the

interface across a high potential difference.Heat and gas flows: to desolvate the ions existing in the

sample solution. It can produce multiple charged ions with the number of

charges tending to increase as the molecular weight increases.

Extremely useful for accurate mass measurement, particularly for thermally labile, high molecular mass substances (ie. proteins, oligonucleotides, synthetic polymers, etc.)

Matrix-Assisted Laser Desorption/Ionization (MALDI)

Dissolve analyte in a solution containing an excess of a matrix such as sinapinic acid or dihydroxybenzoic acid.

Such matrix has a chromophore that absorbs at the laser wavelength.

Place a small amount of this solution is placed on the laser target.

The matrix absorbs the energy from the laser pulse and produces a plasma that results in vaporization and ionization of the analyte.

Rapid and convenient molecular weight determination.

Time-of-Flight (TOF) Mass AnalyzerFor an ion accelerated by voltage V, the resulting

velocity is proportional to the mass-to-charge ratio. In a Time-of-flight (TOF) mass spectrometer, ions are detected on the basis of the time needed to travel a path L.

Ions of very high mass-to-charge (several hundreds of kD) may be recorded after an appropriate length of time.

Fastest available MS analyzer Well suited for pulsed ionization methodsHighest practical mass range of all MS analyzers.

Recent advances in the application of mass spectrometry in food-related analysis

•Led to automation of various procedures in food analysis.

•Structure elucidation of sugars •Elucidate metabolism of vitamins

LC-MS coupling techniques

•Lipid analysis•for e.g. characterization of the

acylglycerol and sterol fraction•Analyze food samples such as

breakfast cereal and concentrated beef and vegetable extract.

•Analysis of polyphenolic compounds

HPLC-MS coupling

techniques

•Rapid and accurate evaluation of the authenticity of milk

•Helpful in evaluating the presence of cow milk in buffalo milk samples and detecting the addition of powdered milk to fresh raw milk samples.

•Analysis of trypsin-digested peptides of lectin

MALDI-TOF-MS

•Mass determination of milk proteins•Detection of modifications in

proteins caused by insertion, deletion or modification of amino acids

•Identification of genetic variants and post-translational modifications

ESI-MS

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