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A 12-Minute Purge and Trap GC/MS Analysis for Volatiles

Using an Rtx-VMS Column

The volatiles section in the CLP OLM 04.1 method in the US EPA’s Statement of Work (SOW) is derived principally from EPA drinking water method 524.2, and is followed for analysis of low- to medium-concentration samples of groundwaters or drinking waters collected from Superfund sites. To follow this method, the analyst must use a gas chromatograph/mass spectrometer system for analysis, in combination with a purge and trap system for concentrating and introducing the analytes from a 25mL sample. The method places a high demand on the chromatographic system, stipulating a set of response and recoverability criteria which must be met. System suitability is determined in part by the purging efficiency and inertness of the P&T apparatus, the inertness of the transfer pathway, the trapping and release characteristics of the trap, the selectivity and efficiency of the capillary GC column, and the sensitivity and scan rate capabilities of the MS. Further, sample throughput commonly is a concern in laboratories conducting these analyses.

One important decision toward ensuring system suitability is to select the proper capillary column. A 30m x 0.25mm ID x 1.4µm Rtx-VMS column is an excellent choice for this application, as it is for many other purge and trap analyses for volatiles. The unique selectivity of the Rtx-VMS column allows baseline resolution of most of the target analytes in less than 12 minutes. Another stipulation of the method, 90% resolution of the gaseous components, is particularly challenging, but is easily attained by the Rtx-VMS column, as shown in Figure 1.

Good resolution and peak shape for volatiles, by CLP OLM 04.1 or other purge and trap GC methods, are difficult to achieve, particularly for the gases. An Rtx-VMS column meets or exceeds these demands, with a rapid analysis time that allows excellent sample throughput, and with good reproducibility. We highly recommend this column for these analyses.

Figure 1: Achieve good resolution and peak shape in purge and trap GC/MS analyses of volatiles by using an Rtx-VMS column.

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GC_EV00812
ColumnRtx -VMS, 30 m, 0.25 mm ID, 1.40 µm (cat.# 19915)
Standard/Sample
CLP 04.1 VOA CAL2000 MegaMix, 2000μg/mL in methanol (cat.# 30456)
502.2 Calibration Mix #1 (gases), 2000μg/mL in methanol (cat.# 30042)
VOA Calibration Mix #1 (ketones), 5000μg/mL in methanol/water (90:10) (cat.# 30006)
VOA Internal Standard Mix, 2500μg/mL in methanol (cat.# 30011)
VOA Surrogate Spike Mix, 2500ug/mL in methanol (cat.# 30004)
Diluent:25mL water
Conc.: 20 ppb each analyte, ketones 100 ppb each
Injectionpurge and trap split (split ratio 35:1)
Liner:1mm Split (cat.# 20793)
Inj. Temp.:200 °C
Purge and Trap
Instrument:OI 4660 Eclipse Purge and Trap
Trap Type:#10 (Tenax/silica gel/carbon molecular sieve)
Purge: 11 min, flow 40 mL/min
Desorb Preheat Temp.:185 °C
Desorb: 0.5 min @ 190 °C, flow 35 mL/min
Bake: 8 min @ 210 °C
Interface Connection:injection port
Transfer Line Temp.:150 °C
Oven
Oven Temp.:40 °C (hold 4 min) to 90 °C at 16 °C/min to 220 °C at 32 °C/min (hold 5 min)
Carrier GasHe, constant flow
Linear Velocity:34 cm/sec @ 40 °C
DetectorMS
Mode:Scan
Transfer Line Temp.:150 °C
Ionization Mode:EI
Scan Range:35-300 amu
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EVAR3255-UNV