Determination of Therapeutic Levels of Gamma-hydroxybutyric Acid (GHB) in Plasma/Urine by Gas Chromatography-Mass Spectrometry (GC-MS) (CAT#: STEM-CT-2702-CJ)

Gas chromatography mass spectrometry (GC-MS) consists of two different analytical techniques: gas chromatography (GC) and mass spectrometry (MS). Usually, the analytical instrument consists of a gas chromatograph that is hyphenated via a heated transfer line to the mass spectrometer, and the two techniques take place in series. Data from a GC-MS is three-dimensional, providing mass spectra that can be used for identity confirmation or to identify unknown compounds plus the chromatogram that can be used for qualitative and quantitative analysis.

Biochemistry; Biopharmaceuticals; Biomedical

The sample mixture is first separated by the GC before the analyte molecules are eluted into the MS for detection.
1. The sample is first introduced into the GC manually or by an autosampler and enters the carrier gas via the GC inlet. If the sample is in the liquid form, it is vaporized in the heated GC inlet and the sample vapor is transferred to the analytical column.
2. The sample components, the “analytes”, are separated by their differences in partitioning between the mobile phase (carrier gas) and the liquid stationary phase (held within the column), or for more volatile gases their adsorption by a solid stationary phase. In GC-MS analyses, a liquid stationary phase held within a narrow (0.1-0.25 mm internal diameter) and short (10-30 m length) column is most common.
3. After separation, which for GC-MS analyses doesn’t require total baseline resolution unless the analytes are isomers, the neutral molecules elute through a heated transfer line into the mass spectrometer.
4. Within the mass spectrometer, the neutral molecules are first ionized, most commonly by electron ionization (EI).
5. The next step is to separate the ions of different masses, which is achieved based on their m/z by the mass analyzer.
6. After the ions have been separated by the mass analyzer based on their m/z, they reach the ion detector where the signal is amplified by an electron multiplier (for most low resolution MS) or a multi-channel plate (for most HRMS instruments). The signal is recorded by the acquisition software on a computer to produce a chromatogram and a mass spectrum for each data point.

• Sample: Environmental pollutants; Industrial by-products; Drugs; Food contaminants; Bodily fluids; Blood; Saliva; Serum; Plasma; Other secretions containing large amounts of organic volatiles; Pesticide; Metabolites of illicit and synthetic drugs; Liquid; Soil; Air; Fragrance; Plastic & More
• Equipment: Gas Chromatography-Mass Spectrometry (GC-MS) Instrument
• (Optional): Gas Chromatography (GC) Columns

1. GC alone is limited in that it isn't possible to identify unknown compounds using standard GC detectors, but this is possible when paired with MS. Conversely, direct analysis of samples using MS produces mixed mass spectra that can be difficult to deconvolute and interpret, especially when there are more than a few compounds in the sample. But pairing with GC gives the ability to separate the mixture.
2. GC-MS is used in many industries for routine analysis looking for volatile contaminants with a molecular weight of usually less than 700 amu, for example in the food, environmental, forensics, anti-doping and consumer products industries.
3. GC-MS is also used in research to identify unknown volatile compounds, including in food and flavors, space, petrochemical, chemical, agriculture, tobacco, pharmaceutical, healthcare, energy, mining, environmental and forensics to name but a few.