Mobile phase.

GC is used for analyzing volatile organics, and generally separating by boiling points. GCMS indicates that a mass spectrometer is used as the detector for the GC. GCMSMS, indicates that the instrument is capable of isolating and fragmenting a desired molecular weight, and the resulting fragments can then be analyzed by mass spectrometry. LC is a separation performed in the liquid phase and is generally used for larger more polar molecules which are incompatible with GC. When a mass spectrometer is used as a detector, you have LCMS. There really are significant differences, but in terms of which one is best, it simply depends on the application. They each have their uses.

Thank you

GC (gas chromatography) is based on the volatility of the molecule at various temperatures while LC (liquid chromatography) is based on its solubility in various solvents (water, methanol, acetonitrile, isopropyl alcohol, hexane...).

In both cases the chromatographic separation is based on its selective retention. MS, UV, RI, ELSD is just a tool to detect the molecule. It is the column that is the 'heart' of the separation.

Gas Chromatography is a separation technique for volatile and thermally stable compounds. An inert gas is used as the mobile phase. Liquid Chromatography is a separation technique for high molecular weight and non-volatile samples. A combination of liquids is used as the mobile phase. Hence the requirement for a sample to be analyzed by GC is it's volatility and thermal stability while in LC it is the solubility in the mobile phase. MS is a detector that is added to either GC or LC. MS provides a mass spectrum which will be useful for characterizing the compound. In GCMS, the compound is fragmented only once. In GC/MS/MS, a fragment from the compound is further fragmented by colliding it with a gas like Argon to produce daughter ions. This will produce an MS/MS spectrum which will enable the user to precisely quantify the target by eliminating any possible matrix interference. There are different scan modes available in GC/MS/MS.

LC is preffered in most laboratories because it is more universal then GC (it is estimated that only approx. 20-30 % of compounds can be analysed by GC). However, mobile phases in LC (organic solvents) are source of pollutants (waste) and are toxic for human health and the environment (their utlilization is required). In GC we have gases as mobile phase (in most cases hydrogen or hellium). Therefore, GC stends out in terms of green chemistry.

Very good answers. I would like to add that for each of these techniques you need a specific, dedicated instrument and they are quite expensive instruments...

GC-MS/MS and LC-MS/MS are much more expensive than (single quadrupole) GC-MS and LC-MS. You need to know well your application!

Dear Dhia,

While gas chromatography–mass spectrometry (GC–MS) has beenwidely recognized as the " gold standard " in forensic testing, use of liquid chromatography–tandem mass spectrometry (LC–MS-MS) is be-coming more common. This is because LC–MS-MS offers several ad-vantages over GC–MS such as quicker and less extensive extraction procedures and the ability to identify and measure a broader range of compounds.

Both LC-MS and GC-MS are methods to separate chemicals in a mixture or a sample. Both methods separate the chemicals by chromatography first, then further examine and identify them by the mass spectrometer. Additionally, both methods require a mobile phase and a stationary phase. The only difference is that LC-MS uses a solvent as its mobile phase, while GC-MS uses inert gases (like helium) in the same capacity.

Sincerely yours, Homayoon.

While GC-MS and LC-MS differ fundamentally by mobile phase, GC-MS has the advantage of NIST library which can predict the compounds qualitatively based on the mass spectra matching. Without standard, predicting/quantifying the compounds is not possible in LC-MS and both the instruments cannot be used for quantification.

GC-MS/MS is a quantitative equipment which needs standard for calibration and quantification. The limit of detection in GC-MS/MS is ppt level and it is ppm in case of GC-MS and ppb on LC-MS.

So, LC-MS and GC-MS/MS needs standard for doing any kind of analysis.

In LC-MS, solvent i.e: Water, Acetonitrile, Methanol, Ethanol, Propanol, Isopropanol are used as mobile phase where in GC-MS, gas i.e: He, H have been used as mobile phase.

Both LC-MS and GC-MS are methods to separate chemicals in a mixture or a sample. Both methods separate the chemicals by chromatography first, then further examine and identify them by the mass spectrometer. Additionally, both methods require a mobile phase and a stationary phase. The only difference is that LC-MS uses a solvent as its mobile phase, while GC-MS uses inert gases (like helium) in the same capacity

Both LC-MS and GC-MS are methods to detect the compounds in crude from fungi, plant, bacteria, and others.

GC-MS = for volatile compounds

LC-MS = for non volatile compounds