Calibrating Gasoline Range Organics (GROs) Using an Automated Dilution Scheme with the Atomx Concentrator/Multi-Matrix Autosampler

Tyler Trent and Nathan Valentine, Teledyne Tekmar

In developing the Atomx automated sample prep system, Teledyne Tekmar integrated both a P&T concentrator and a multi-matrix autosampler into a single platform system that can be used in the analysis of soil, water, and soils requiring methanol extraction. This "all-in-one" setup has allowed for greatly increased throughput and efficiency through the built in features it provides.

Table I: MDL and calibration %RSD for target and surrogate compounds

In this study, the sample syringe dilution feature was used to generate a calibration curve from a single stock solution for a subset of EPA method 8260B compounds (1). This study not only validates the capability to perform accurate and precise dilutions, but also removes the risk of errors that can occur from manually preparing multiple standards. Lastly, it shows that a considerable amount of labor time can be saved when using this feature.

Experimental/ Instrument Conditions

The Atomx, equipped with a #9 adsorbent trap, an Agilent 7890A GC, and 5975C inert XL MSD were used for this analysis. Column: Restek Rtx-624 20 m × 18 mm ID × 1 µm, Constant flow 1.2 mL/min; Oven: 35 °C for 4 min, 16 °C to 85 °C for 0 min, 30 °C/min to 210 °C for 3 min, 14.29 min runtime. MS: 35–300 m/z.

Figure 1: Static experimental results and TIC of 50 ppb GRO calibration standard.

Calibration and Minimum Detection Limits

A 100 ppb working calibration standard containing the target and surrogate compounds (PVOC/GRO mix) was prepared in 500 mL of deionized water. After transferring the standard to six VOA vials, a calibration range of 2–100 ppb was achieved using the following dilution volumes: 1:1= 5 mL, 1:2= 2.5 mL, 1:5= 1 mL, 1:10= 500 µL, 1:25= 200 µL, and 1:50= 100 µL.

All dilutions were automatically brought to a 5 mL final volume with deioninzed water using the instrument supplied water reservoir. MDLs were generated at 1 ppb using the 1:100 dilution. A 125 ppm internal standard (IS) was prepared in methanol and injected in 1 µL volumes using the internal standard addition feature, providing a constant 25 ppb final concentration.

Agilent Chemstation software was used to process the calibration data. The relative response factors (RRF) of all the analytes were evaluated for %RSD. %RSD met EPA method 8260B performance criteria.

Conclusions

Teledyne Tekmar's Atomx continues to improve efficiency and throughput. By automating the calibration process using the sample dilution feature in conjunction with the automated internal standard addition feature, the calibration curve met the performance criteria. Using the Atomx, only one stock standard solution needs to be made, rather than an entire series. Switching to an automated calibration allows for the same performance, but with the benefit of less prep time. This automated calibration, as well as the other enhancement tools, aid the user in both productivity and cost savings.

Reference

(1) USEPA Method 8260B Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS) Revision 2, December 1996.

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