you most definitely can. But i would suggest you use Thermal desorption (TD-GC/MS) to make sure you detect even VOCs present in trace level.

Yes you can. In this method, the volatile compounds are introduced into the gas chromatograph by the purge-and-trap method or by other methods. There are various techniques by which these compounds may be introduced into the GC/MS system. Purge-and-trap is the most commonly used technique for volatile organic analytes. Other techniques including direct injection following dilution with hexadecane for waste oil samples; automated static headspace for solid samples; direct injection of an aqueous sample or injection of a sample concentrated by azeotropic distillation and closed system vacuum distillation for aqueous, solid, oil and tissue samples. For air samples, technique involving headspace trap system and desorbing volatile organics from trapping media is applied. In addition, direct analysis utilizing a sample loop is used for sub-sampling. The analytes are introduced directly to a wide-bore capillary column or cryofocussed on a capillary pre-column before being flash evaporated to a narrow-bore capillary for analysis. The column is temperature-programmed to separate the analytes, which are then detected with a mass spectrometer (MS) interfaced to the gas chromatograph (GC). Analytes eluted from the capillary column are introduced into the mass spectrometer via a jet separator or a direct connection. (Wide-bore capillary columns normally require a jet separator, whereas narrow-bore capillary columns may be directly interfaced to the ion source). Identification of target analytes is accomplished by comparing their mass spectra with the electron impact (or electron impact-like) spectra of authentic standards. Quantitation is accomplished by comparing the response of a major (quantitation) ion relative to an internal standard using a five-point calibration curve.

Dear YOGESH TRIPATHI

How about internal standard. As I do not know what is the composition of my sample, can I add any general internal standard into my samples?

One thing to keep an eye on : moisture. U do not specify 'human samples' so I suppose it will be breath or liquid (blood?). They have water in common breath samples are even over saturated as the collection temperature is lower then the production temperature. If you use a system witch relies on cryo whatever ( trapping, focusing,...) the present water will start to freeze and block the trap or column resulting in very weird gcms behavior. On trap systems like TD-GC/MS water may change the sorption properties of the trap material even if this is hydrofobe (film buy condensation), In extremes water may create breakthrough pathway's. An other effect of water on the column is variation in retention time even on a water friendlily column like a corsslinked bounded wax. Removing water without loosing VOC's is a hard job drying the sample trap or using LiCl are the best options but far from ideal. Collectiong an breath sample in a special plastic bag an putting it in a freezer is also done.

About the Internal standard(IS).

The generalIS in GC/MS is not a good idea. It will give You a false sense of security. In GC/MS the only good IS is a dueterated compound if this is not avaiable choose a related compound with a retention time close to the compound of interest. You can find more explanation for this in:

Analytical Chemistry (Impact Factor: 5.7). 08/2010; 82(15):6480-6. DOI:10.1021/ac100780s

"Characterization and improvement of signal drift associated with electron ionization quadrupole mass spectrometry"

On top of this if you use a preconcentration system like trapping then the IS should behave in this process similar to your analyte.

But do you really need an IS (and thus quantification) ? For profiling it should be possible to normalize your chromatograms to the highest peak and use the same approach as the search algorithms in the MS databases

Since composition of your sample is unknown, using general IS would not be a correct approach. Identification of target analytes can be done by comparing their mass spectra with the that of authentic standards or reported data.