Pesticide/PCB Analysis Using LVSL

Introduction
Today, many laboratories face the challenge of accurately analyzing pesticides and polychlorinated biphenyl (PCB) residues. In addition, the need for lower detection limits of these compounds forces labs to find ways to attain results in the pg/µL range. By combining a large volume splitless (LVSL) injection with full scan GC/MS system, low-level samples can be analyzed with very little preparation time.

A large-volume splitless injection technique was developed that exploits a unique injection port design. This injection port design eliminates problems typically associated with large solvent volumes. The technique was optimized using a special software tool and then it was evaluated using standards containing pesticides and PCBs at concentrations ranging from 1.25 ? 250 ppb in hexane.

Correlation coefficients for standards in this evaluation were greater than 0.99 for all components (Figure1). Reproducibility data was obtained through repeated injections of seven standards at 2.5 ppb. Chrysanthemum tea extracts were also analyzed, both spiked and blank. Large volume splitless injection proved to be a rugged technique that offers the environmental laboratory an additional option in the effort to decrease detection limits.

Experimental Conditions
The analysis was performed using a TRACE DSQ^TM equipped with a 250 L/s turbomolecular pump and Ion Bright^? source, a TRACE GC Ultra^TM equipped with a modified split/splitless inlet, an AS 2000 autosampler, and Xcalibur? 1.4 (Thermo Scientific, Austin, TX and San Jose, CA). Also used were a 30m x 0.25mm i.d. x 0.25 µm of Rtx®-5MS analytical column and a Siltek® Press-Tight® union (Restek Corporation, Bellefonte, PA). Pesticide and PCB standards were obtained from Supelco (Bellefonte, PA) at concentrations of 500 µg/mL. Internal standard solution was obtained from Cerilliant Corporation (Round Rock, TX).

The GC/MS system was set up with a 5 m pre-column connected to a 30 m x 0.25 mm x 0.25 µm Rtx-5MS column. The inlet liner was a splitless liner with glass wool. The injection volume was 35 µL, and the splitless duration and initial oven temperature and time were optimized for the LVSL technique. Run time was less than 20 minutes for all compounds. The mass spectrometer acquired data in full scan mode, from 35-550 amu at a scan rate of 1500 amu/sec.

Results and Conclusions
Pesticide and PCB analysis was easily accomplished using the LVSL technique. This technique simplifies sample preparation by minimizing evaporation and concentration techniques. The system modifications that enable the use of the LVSL technique are easily reversible, which provides flexibility when this technique is used in conjunction with the SSL technique. Additionally, the Ion Bright source was found to enhance system performance with very little maintenance.

References

1. "Concurrent Solvent Recondensation Large Sample Volume Splitless Injection" by T. Porzano Magni. Journal of Separation Science. In press.
2. "25^th Int. Symp. On Capillary Chromatography: by T. Porzano Magni. Riva del Garda. 2002.
   

Figure 1 (TOP image) Data for hexachlorocyclopentadiene at 1.25 pg/µL, showing an extracted ion chromatogram (m/z 237) and (BOTTOM image) calibration curve from 1.25-250 pg/µL (r2=0.9990).

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