Thermal Desorber

8690-1088

The SRI Thermal Desorber permits volatile and semi-volatile compounds in soil, or other solid matrices, to be injected and analyzed with little or no sample preparation, and with very high sensitivity. With the thermal desorber, no solvent extraction is required. This is a major convenience for field operations and helps save on costs. Little operator skill is needed, and 4-10 analyses can be run per hour, depending on specific requirements.

Because of the large sample size of up to one gram, an analyte present in the soil at 1 ppm desorbs 1000 nanograms onto the GC column. This results in detection limits in the ppb range for most compounds. Sandy soil can typically be desorbed with no sample preparation at all. Clay soil is first mixed with sodium sulfate granules to break the clay into a fine powder coating the granules, then the clay and sodium sulfate mix is desorbed.

This chromatogram on the right is from a GC with a thermal desorber and an FID detector. Synthetic diesel range samples like this are used to verify complete desorption. Sample: 2000 ng synthetic diesel range organics desorbed from the soil.

Up to one gram of soil is loaded into a reusable glass tube, and secured in place with plugs of glass wool. The tube is then inserted into the hot (275°C) thermal desorber fitting, which is mounted in the heated valve oven compartment on the 8610C.

Soil samples can typically contain 20-50% water. FID or FID/DELCD detectors are commonly used with the thermal desorber because the SRI FID automatically re-lights the flame after a large water peak. The thermal desorber + FID/DELCD configuration is perfect for detecting PCBs, pesticides, PAHs, JP-4, kerosene, and diesel in soil. Due to the extreme selectivity of the DELCD detector, PCBs can be discriminated against even in the presence of massive hydrocarbon contamination.

These two chromatograms on the left show the analysis of PCB 1254 standard in diesel oil with our PCB GC system, which is equipped with a thermal desorber and an FID/DELCD combination detector. The FID shows the diesel hydrocarbons and the PCBs, but the PCB peaks are obscured by the diesel peaks. In contrast, the DELCD shows the PCBs only, revealing what was essentially hidden in the FID chromatogram.

This set of chromatograms shows the analysis of a real-world standard: 0.3 grams of soil from a contaminated site. This real-world standard is certified by NIST to contain 1.34 ppm PCBs. The FID shows a large hydrocarbon matrix which is pre-combusted in the FID flame before reaching the DELCD, which shows a clean PCB 1254 chromatogram. Pre-combustion of the sample by the FID protects the DELCD from hydrocarbon contamination.

8690-1088 Thermal desorber

8690-1087 10-pack reusable ground glass desorber tubes