Method and system for low temperature detection of semi volatile organic compounds
A sample analysis method includes directing a sample that contains one or more SVOC components to a GC column to temporally separate components present in the sample. Output gas from the GC column is expanded into a sample cell. The sample cell is held at a temperature and pressure that are lower than the temperature and pressure at an outlet of the GC column. The volume of the sample cell is sufficiently large for maintaining the one or more SVOC components in a gaseous phase. Infrared spectra of the components in the sample cell are obtained using a Fourier transform infrared spectrometry system.
1. A sample analysis method, comprising:
directing a sample that includes one or more SVOC components to a GC column to temporally resolve components present in the sample;
expanding output gas from the GC column into a sample cell,
wherein the sample cell is held at a temperature lower than the temperature of an outlet of the GC column and has a pressure lower than the pressure at the outlet of the GC column,
and wherein the sample cell has a volume sufficiently large for maintaining the one or more SVOC components in a gaseous phase; and
obtaining infrared spectra of the components in the sample cell with a Fourier transform infrared spectrometry system.
2. The sample analysis method of claim 1 , further comprising maintaining background infrared spectra that include infrared spectra from previously eluted components and analyzing currently eluting components with reference to the background infrared spectra.
3. The sample analysis method of claim 1 , wherein spectral responses of the components are acquired over time and current spectral responses are compared to a background that changes with time and comprises previously acquired spectral responses.
4. The sample analysis method of claim 1 , further comprising collecting the one or more SVOC components on a concentrating device.
5. The sample analysis method of claim 4 , wherein the concentrating device is a thermal desorption tube packed with a material that does not trap water or volatile organic compounds.
6. The sample analysis method of claim 1 , wherein the outlet of the GC column is at a temperature that is at least about 200° C. higher than the temperature of the sample cell.
7. The method of claim 1 , wherein the volume of the sample cell is at least about 200 times higher than an initial volume available to the gas before emerging from the outlet of the GC column.
8. The method of claim 1 , wherein the one or more SVOC is present in an air, water or solid sample.
9. The method of claim 1 , wherein the sample contains a pesticide, a herbicide, an insecticide, a plasticizer, a flame retardant, a phthalate, a mycotoxin, a PCB, an illicit drug, an explosive or an accelerant.
10. The method of claim 1 , wherein the one and more SVOCs are not concentrated by solvent extraction.
11. The method of claim 1 , wherein IR calibration spectra are established at an initial temperature of the sample cell.
12. The method of claim 11 , wherein the sample cell is heated from the initial temperature to an intermediate temperature, wherein the intermediate temperature is lower that the temperature of the outlet of the GC column.
13. The method of claim 12 , wherein additional IR calibration spectra are obtained at the intermediate temperature.
14. The method of claim 1 , wherein the sample cell is fitted with gold-coated optics and the temperature of the sample cell is sufficiently low to substantially preserve IR reflectivity of the gold-coated optics.
15. The method of claim 1 , wherein detection levels for the one or more SVOCs are as low as parts per trillion.
16. The method of claim 1 , wherein the sample cell is evacuated prior to expanding the output gas from the GC column.
17. The method of claim 1 , wherein the sample cell is a flow cell held at a pressure that is lower than atmospheric pressure.