Gas Chromatography Mass Spectrometry and Fourier Transform Infrared Spectrometry

Gas Chromatography Mass Spectrometry (GCMS)

When gas chromatography is coupled to mass spectrometry, the resulting technique is referred to as GC-MS. After complex mixtures are separated on the GC column, they are detected by mass spectrometry, which generates a characteristic mass spectrum for each compound which may be used as a “fingerprint” for identification purposes. Measured mass spectra may be screened against a NIST mass spectral libraries for identification. In addition, the characteristic fragmentation pattern for each compound allows for a highly specific and sensitive method to be developed for quantitation of a compound in a complex matrix.

Fourier Transform Infrared Spectroscopy (FTIR)

Fourier transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectral range. This confers a significant advantage over a dispersive spectrometer, which measures intensity over a narrow range of wavelengths at a time. The term Fourier transform infrared spectroscopy originates from the fact that a Fourier transform (a mathematical process) is required to convert the raw data into the actual spectrum.

Fourier transform spectroscopy technique shines a beam containing many frequencies of light at once and measures how much of that beam is absorbed by the sample. Next, the beam is modified to contain a different combination of frequencies, giving a second data point. This process is rapidly repeated many times over a short time span. Afterwards, a computer takes all this data and works backward to infer what the absorption is at each wavelength.

An infrared microscope allows samples to be observed and spectra measured from regions as small as 5 microns across. Images can be generated by combining a microscope with linear or 2-D array detectors. The spatial resolution can approach 5 microns with tens of thousands of pixels. The images contain a spectrum for each pixel and can be viewed as maps showing the intensity at any wavelength or combination of wavelengths. This allows the distribution of different chemical species within the sample to be seen.