Supplies and Services for Mass Spectrometers, Gas Chromatographs
and Liquid Chromatographs
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28 | Last Update: 01/31/00 |
INTRODUCTION
Headspace GC is a well established technique for the analysis of volatiles in solid and liquid samples. It is widely used for applications such as blood alcohol analysis and arson analysis. Headspace GC can often be used in place of thermal desorption techniques. The main advantage over thermal desorption is the ability of the headspace technique to be automated. Its main disadvantage is its lack of sensitivity in comparison to thermal desorption. However, for applications in which large quantities of samples need to be analyzed and the volatiles are present in the samples at concentrations above the ppb level, headspace GC is an excellent technique.
The GC Cryo-Trap is a useful accessory to expand the capabilities of the headspace GC technique. The GC Cryo-Trap consists of a small heating/cooling chamber which surrounds the front 4 inches of the capillary or guard column. It is installed inside the GC oven, just under the GC injection port to permit the trapping of volatile organics at the front of the column. Liquid Nitrogen is utilized to permit the trapping of volatiles down to -180 degrees C. The GC Cryo-Trap permits the injection of large gas sample volumes via techniques such as Headspace and Thermal Desorption. It eliminates the need to cool the entire GC oven for cryo-focusing samples on column. During the entire injection process, the volatiles in the gas sample when injected into the GC injection port are concentrated in a narrow band at the front of the GC capillary column. When the GC Cryo-Trap is subsequently heated, the trapped volatiles are released in a narrow band to be chromatographed via the GC capillary column. This results in the generation of sharp, well resolved GC peaks for large gas volume injections. It also permits the injection of multiple samples when weak concentrations of volatiles are present in the samples to be analyzed.
The purpose of this study was to evaluate the usefulness of the GC Cryo-Trap in conjunction with the headspace injection technique for the analysis of volatile organics in water based latex paints utilizing capillary GC columns. Water based latex paints contain a large number of volatile organics at concentrations in the ppm level. The combination of the headspace GC technique with the GC Cryo-Trap is a practical method for the analysis of these samples.
