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GC/MS
is a highly sensitive and specific technique used for both the identification
of unknown substances and the quantification of known substances. The technique
can be applied to compounds in the molecular weight range of 30 – 750,
provided the compound, or a derivative of it can be volatilised without decomposition.
Detection sensitivity is compound-dependent but is in the region of 50ng
for qualitative determinations and 500pg for quantitation.
The gas chromatograph in use is an HP5890 equipped with both split/split less and on-column injectors. The mass spectrometer is a VG TRIO1, which can provide both electron impact (EI) and chemical (positive and negative) ionisation (CI) techniques.
Examples of quantitative assays in current use are:
- Methylmalonic acid in plasma and urine
- N14/N15 ratios in urinary nitrates and nitrites
- Tetrahydrocannabinol, cannabidiol and metabolites in plasma
- Nandrolone, norandrostenedione and norandrostenediol in dietary supplements and their metabolites norandrosterone and noretiocholanolone in urine
- In vitro metabolism of estradiol
- Glycerol in plant extracts
Contact tel: +44 (0)1224 551131 (GA Cameron)
The
section has recently taken delivery of a Thermo Finnigan Surveyor liquid chromatograph
interfaced directly to a Thermo Finnigan Quantum triple
quadropole
mass spectrometer, facilitating the analysis of polar thermolabile compounds
up to molecular weigh 1500. Selected ion monitoring (SIM) on the first quadropole
or selected reaction monitoring (SRM) on the third quadropole is used for
quantification. The latter is more sensitive and a limit of quantitation of
1fg on column has
been obtained for some compounds. The instrument is equipped with both electrospray
(ESI) and atmospheric pressure chemical ionisation (APCI) sources and spectra
can be generated in both positive and negative modes. Full parent scan and selected ion monitoring is performed on the first
quadropole, whereas the third quadropole is used for full scan, product ion
scans (MS+MS/MS), SRM and neutral loss scanning.
Examples of quantitative assays in current use are:
- Glutathione conjugates of gliotoxin
- Simvastatin and metabolites in plasma
- Anandamide
Contact tel: +44 (0)1224 551131 (GA Cameron)
Sample preparation
The section provides full sample preparation capabilities:
- Solid phase extraction
- Normal/reversed phase, ion exchange, mixed mode
- Liquid/liquid extraction
- Derivatisation
Contact tel: +44 (0)1224 551131 (GA Cameron)
Mass Spectrometry Section · Division of Applied Medicine
University of Aberdeen · Polwarth Building · Foresterhill · Aberdeen
AB25 2ZD
Tel: +44 (0)1224 552487· Fax: +44 (0)1224 554761