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Add-On System Detects Hazardous VOCs

Tue, 02/07/2012 - 5:53am

An analytical system used in conjunction with a GCMS unit can provide enhanced results in the detection of air toxins in canister air samples.

by Nicola Watson, Markes International, Llantrisant, United Kingdom

Figure 1: Total ion chromatogram for a 1 L standard containing 1 ppb air toxics, analyzed splitless, cryogen-free and in full-scan mode using TD/GCMS (quad).
Figure 1: Total ion chromatogram for a 1 L standard containing 1 ppb air toxics, analyzed splitless, cryogen-free and in full-scan mode using TD/GCMS (quad).

As evidence grows indicating the harmful effects of low-level exposure to hazardous air pollutants such as air toxics, there is an increasing need for analytical laboratories employing canisters to detect ever-lower levels of analytes, while maintaining high standards of analysis and application flexibility.

This article describes how Markes’ CIA Advantage satisfies this need, having been designed to allow a wide range of sample concentrations to be analyzed without the need for dilution. Using a combination of loop sampling, large volume sampling and the ability to split sample flows, component concentrations ranging from ppt to low percent levels can be handled on one instrument. CIA Advantage systems comply with U.S. EPA Method TO-15 for air toxics. Up to 27 canisters can be accommodated, allowing round-the-clock automated operation without need for cryogen.

Experimental and results

The experimental setup employed a CIA Advantage instrument in conjunction with GCMS. The experiment found that air toxics comprise various compounds with a range of volatilities from C3 hydrocarbons to polysubstituted benzenes. They often have low concentrations, which frequently require that the whole sample is transferred to the GC (a splitless analysis) to ensure maximum sensitivity. Figure 1 shows the total ion chromatogram for a splitless analysis of a 1 L standard containing 1 ppb air toxics, according to U.S. EPA Method TO-15. A very good peak shape can be seen for the more volatile compounds, which is important when carrying out splitless analyses.

A key benefit of the CIA Advantage for the analysis of these challenging samples is the backflush focusing trap (i.e. the analytes are injected into the GC in the opposite direction in which they are absorbed). This makes it possible to use more than one sorbent, allowing analysis of a wide range of compounds in a single run, as shown in Figure 1, where a three-bed sorbent trap was employed.

Ambient air samples can contain air toxics at a wide range of concentrations. The CIA Advantage-HL model can easily deal with such situations because it can sample at both low volumes (using a sample loop) and high volumes (using a mass flow controller). Both low-volume and high-volume samples can be compared using the same calibration curve for seven example compounds from the TO-15 standard.

Carryover and peak shape

Figure 2: Chromatogram of a 40 mL sample of a 1 ppm 62-component TO-15 standard. Inset: Expansion of the peaks for 1,2,4-trichlorobenzene and hexachlorobuta-1,3-diene, with the chromatogram of a subsequent 500 mL nitrogen blank added.
Figure 2: Chromatogram of a 40 mL sample of a 1 ppm 62-component TO-15 standard. Inset: Expansion of the peaks for 1,2,4-trichlorobenzene and hexachlorobuta-1,3-diene, with the chromatogram of a subsequent 500 mL nitrogen blank added.
If a system is to be suitable for analyzing both trace- and high-concentration samples, it is absolutely essential that sample carryover is minimal. Otherwise, significant time can be spent cleaning the system or, more seriously, the concentration of target compounds in low-concentration samples can be over-estimated. Figure 2 demonstrates that the CIA Advantage recovers immediately after being subjected to an overloaded sample of TO-15 air toxics. Taking the stickiest and highest-boiling compound in the list, 1,2,4-trichlorobenzene, just 185 pg was present in the subsequent blank run, compared to 303 ng in the original. Carryovers for the 62 compounds were in all cases <0.07%, with 82% of the compounds not being detected at all in the blank run.

It is also important that the system can analyze samples without a split to guarantee maximum sensitivity for low-concentration samples. The CIA Advantage can do this without any reduction in the quality of the peak shape.

As shown, the CIA Advantage provides excellent results over the full range of air toxics sampled from canister air. Cryogen-free operation reduces running costs, while the heated internal lines and efficient purge steps combine to avoid the problem of carryover, even with less volatile analytes.

This negligible carryover means that canister analysis can be confidently undertaken on samples of unknown concentration, facilitating automation and therefore increasing productivity.

For more information, contact Markes International at www.markes.com, or call +44 0 1443 230935.

 

 

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