Gas Chromatography - Tandem Techniques - Examples of GC/MS Spectrometry Applications > Analysis of Waxes and Lipid Type Materials > Page 77
It is seen that there are a number of low-level contaminants in the crude material, and by the use of single ion monitoring, very small traces of contaminants can easily be identified. The chromatogram obtained by single ion monitoring at a m/z value of 76 discloses the presence of arsine at a level of 4 ppb in the original sample.
GC/MS has also been extensively used in environmental analysis. Hiatt et al. (24) developed a vacuum distillation procedure for the isolation of volatile materials from natural sources, such as water, soil, oil, fish samples etc. The layout of their sample collection apparatus is shown in figure 63. The samples were placed in a flask which was connected in sequence to two valves, the first valve connected a pump to the sample vessel either directly, or by a second valve and through a cryo-trap. The sample chamber valve was closed and the condenser, cryo-trap, and gas lines were evacuated. The sample flask was then cooled to the required temperature (usually -5ūC and the pump valve was then rotated so that the vapors were drawn through the first valves to the cryo-trap, which was cooled to -196ūC with liquid nitrogen. The volatile materials from the sample were condensed and collected in the trap. When collection was complete, the sample valve was again rotated, the cryo-trap warmed, and the contents eluted onto the GC column by a stream of helium.