Demystifying the Process of Calibrating Your Thermal Desorption Gas Chromatography System Using Compressed Gas Standards
Oral Presentation
Prepared by J. Brown, O. Shimelis
Supelco/Sigma-Aldrich, 595 North Harrison Road,, Bellefonte, PA, 16823, United States
Contact Information: [email protected]; 814-359-5917
ABSTRACT
To accurately determine the concentration of the VOCs in the sample, a representative calibration curve has to be established with the thermal desorption gas chromatography system. To develop the calibration curve, a series of thermal desorption (TD) tubes are spiked with increasing concentrations of a known chemical standard. Injecting the chemical standard directly into the GC is not representative or possible, since the transfer line of the Thermal Desorber is connected directly to GC column (thus by-passing the GC Inlet).
As more laboratories switch to using multi-bed TD tubes to collect a broader range of VOC’s; a better technique in the preparation of spiked calibration tubes needs to be considered. Multi-bed TD tubes usually contain a bed of stronger adsorbent such as Carbosieve and/or Carboxen. When liquid phase calibration standards are used for spiking, the solvent is retained by these stronger absorbents and is subsequently desorbed into the gas chromatograph causing separation issues and detection of early eluting analytes.
This study investigates the technique of using gas phase standards to spike TD tubes for the analysis of Hazardous Air Pollutants (HAPS) when using EPA Compendium Method TO-17. The presentation will show how to accurately obtain the correct volumes of the gas mix that covers the calibration range without complicated dilutions. Also discussed is the importance of equilibrating the gas mix to atmospheric pressure in order to obtain correct mass per volume concentration. This study also examined the effects of moisture by using a humidified gas stream when preparing spiked TD tubes for system calibration in preparation of TO-17 analysis.
Oral Presentation
Prepared by J. Brown, O. Shimelis
Supelco/Sigma-Aldrich, 595 North Harrison Road,, Bellefonte, PA, 16823, United States
Contact Information: [email protected]; 814-359-5917
ABSTRACT
To accurately determine the concentration of the VOCs in the sample, a representative calibration curve has to be established with the thermal desorption gas chromatography system. To develop the calibration curve, a series of thermal desorption (TD) tubes are spiked with increasing concentrations of a known chemical standard. Injecting the chemical standard directly into the GC is not representative or possible, since the transfer line of the Thermal Desorber is connected directly to GC column (thus by-passing the GC Inlet).
As more laboratories switch to using multi-bed TD tubes to collect a broader range of VOC’s; a better technique in the preparation of spiked calibration tubes needs to be considered. Multi-bed TD tubes usually contain a bed of stronger adsorbent such as Carbosieve and/or Carboxen. When liquid phase calibration standards are used for spiking, the solvent is retained by these stronger absorbents and is subsequently desorbed into the gas chromatograph causing separation issues and detection of early eluting analytes.
This study investigates the technique of using gas phase standards to spike TD tubes for the analysis of Hazardous Air Pollutants (HAPS) when using EPA Compendium Method TO-17. The presentation will show how to accurately obtain the correct volumes of the gas mix that covers the calibration range without complicated dilutions. Also discussed is the importance of equilibrating the gas mix to atmospheric pressure in order to obtain correct mass per volume concentration. This study also examined the effects of moisture by using a humidified gas stream when preparing spiked TD tubes for system calibration in preparation of TO-17 analysis.
