Location
- Research Support Building (CACTUS)
- Rúa de Constantino Candeira, 1. Campus Vida , 15782Santiago de Compostela
- Phones
- 881 816 242
In case of impure samples, the GC-MS technique would separate all components of the impure sample and we would obtain the mass spectrum of each of the components that are separated.
Mass spectrometry techniques that can be combined with gas chromatography are Electronic Impact, Chemical Ionisation and APCI (Atmospheric Pressure Chemical Ionisation). The first two consist of a quadrupole analyser (low resolution), while APCI has a TOF (Time of Flight) as an analyser (high resolution).
Types of analysis that can be performed:
- Qualitative: analysis of known or unknown compounds for the identification of compounds from a list of known compounds or from a search in a library of spectra.
- Quantitative: quantitative determination of one or more analytes of known structure in a sample.
Sample introduction methods that can be performed:
- Liquid sample injection:
- Split: uses a flow divider at the entrance of the column and only a part of the sample enters the column, the rest is removed outside through the Split line. Recommended for majority analysis.
- Splitless: the entire sample volume is injected. Recommended for minority and trace analysis.
- Large volumes, for ultra-trace analysis. Up to a maximum of 10 ul.
- Headspace injection: In this method, the liquid or solid sample is placed in a closed vial with a divider and heated for a set time at a set temperature. During this operation, most of the volatile compounds are transferred to the air in the flask, called headspace. It is heated long enough to reach equilibrium. An aliquot of the air in the bottle is then taken with a syringe and injected into the gas chromatograph.
- SPME (solid phase micro-extraction): Solid-phase micro-extraction (SPME) is a simple technique that brings together the extraction and concentration steps, uses no solvents, and allows automation in the pre-concentration and analysis steps. Small sample volumes can be used without loss of sensitivity. This extraction-pre-concentration technique, coupled on-line to gas chromatography-tandem mass spectrometry (GC-MS/MS), is a very powerful analytical tool for trace analysis of aqueous samples.
SPME employs a coated fibre with a phase used for extraction, which can consist of a liquid polymer or a solid sorbent. This coating can extract different types of molecules, volatile or non-volatile, from different types of liquid or gas phase media. The number of molecules extracted by the fibre is proportional to their concentration in the sample, provided that an aerothermodynamic equilibrium is reached.
The type of fibre used depends on the molecular weight and polarity of the analytes.
Available fibre types:
|
Stationary/thickness phase |
Maximum operating temperature |
Polarity |
Recommended use |
|
Polydimethylsiloxane (PDMS) § 100µm, unbound phase § 7 µm, bonded phase |
280°C. 340°C. |
Non-polar |
Aromatics, esters, pesticides... -100 microns: Used for volatiles -7 microns: Used for heavy compounds (PAHs) |
|
Polyacrylate (PA) § 85 µm, partially cross-linked phase |
320°C. |
Polar |
Used for phenols. |
Mass Spectrometry and Proteomics Unit
- Research Support Building (CACTUS)
- Rúa de Constantino Candeira, 1. Campus Vida , 15782Santiago de Compostela
- 881 816 242