EPA Method 8260C is used to determine volatile organic compounds in a variety of solid waste matrices. It is applicable for nearly all types of samples, including air sampling trapping media, ground and surface water, aqueous sludges, caustic liquors, acid liquors, waste solvents, oily wastes, mousses, tars, soil, sediments and more. The compounds can be introduced into gas chromatography-mass spectrometry systems with purge and trap being the most common technique.
A major component of any purge and trap system is the analytical trap, which is responsible for retaining the VOCs during the purge cycle and releasing them upon heating. The VOCs are then transferred to the GC/MS for separation and detection. Teledyne Tekmar completed a study that compares four traps commonly used for purge and trap analysis using an automated VOC sample prep system and USEPA Method 8260C.
Standard methods such as USEPA Method 8260C define the dimensions of analytical traps, as well as recommend packing material. Traps are packed with multiple beds of adsorbent materials, to allow for differentiation of a broad range of compounds. The weaker adsorbent bed is placed on the topside of the trap, while the stronger adsorbent bed is placed below the weaker adsorbent bed. The stronger adsorbent material does not effectively desorb the less volatile analytes; rather they are retained in the weaker adsorbent bed. In turn the less volatile analytes fail to reach the stronger adsorbent bed, so only the most volatile analytes reach the stronger adsorbent bed due to the volatility. Desorption is carried out by back-flushing the analytical trap using the Gas Chromatograph (GC) carrier gas flow (Helium).
Teledyne Tekmar used its Atomx automated VOC sample prep system in conjunction with the Agilent 7890/5975 GC/MS to evaluate each trap for USEPA Method 8260C.
For additional details on the experiment conditions, instrument parameters, and calibration-minimum detection limits (MDL), download the associated Application Note.
Results and Chromatograms Highlights
- Gaseous Compounds – When comparing the analytical traps for the gaseous compounds, i.e.: dichlorodifluoromethane, chloromethane, vinyl chloride, bromomethane, chloromethane and trichloromonofluoromethane, there were clear differences between the four analytical traps. The biggest difference observed when utilizing the #3 analytical trap is that the low level (0.5ppb) is hindered by the water front.
- Polar Compounds – The hardest group of compounds to recover in the Purge and Trap analysis is the polar compound group. The hydrogen bonding associated with these compounds makes them difficult to purge out of water.
- Halogens – The most reactive compounds on the USEPA 8260C list are generally the chlorinated and brominated compounds. Typically, these compounds can be used to monitor the performance of the analytical trap.
- Aromatic compounds – These are the most stable in the USEPA Method 8260C compound list due to their structures. Since the trapping materials employed for these compounds are similar there are no clear advantages between the traps for these compounds.
- High Boiling Point/Late Eluting Compounds and Carry Over – One key difference between all four traps is carry over. Heavier compounds such as Napthalene, 1,2,4 and 1,2,3-Trichlorobenzene exhibit the highest amount of carry over. This is due in part to incomplete desorption and cause a gradual rise in the bake back-pressure.
For a complete results and a study conclusion, download the associated Application Note.