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Environmental

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

using an Rtx®-VMS Column
By Jason Thomas, Environmental Innovations Chemist

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.

  1. dichlorodifluoromethane
  2. chloromethane
  3. vinyl chloride
  4. bromomethane
  5. chloroethane
  6. trichlorofluoromethane
  7. 1,1-dichloroethene
  8. carbon disulfide
  9. 1,1,2-trichloro-
    1,2,2-trifluoroethane
  10. methylene chloride
  11. acetone
  12. trans-1,2-dichloroethene
  13. methyl acetate
  14. methyl-tert-butyl-ether
  15. 1,1-dichloroethane
  16. cis-1,2-dichoroethane
  17. cyclohexane
  18. bromochloromethane (IS)
  1. chloroform
  2. carbon tetrachloride
  3. 1,1,1-trichloroethane
  4. 2-butanone
  5. benzene
  6. 1,2-dichloroethane-d4 (SS)
  7. 1,2-dichloroethane
  8. methylcyclohexane
  9. trichloroethene
  10. 1,4-difluorobenzene (IS)
  11. 1,2-dichloropropane
  12. bromodichloromethane
  13. cis-1,3-dichloropropene
  14. toluene d-8 (SS)
  15. toluene
  16. tetrachloroethane
  17. 4-methyl-2-pentanone
  18. trans-1,3-dichloropropane
  19. 1,1,2-trichloroethane
  1. dibromochloromethane
  2. 1,2-dibromoethane
  3. 2-hexanone
  4. chlorobenzene d-5 (IS)
  5. chlorobenzene
  6. ethylbenzene
  7. m-xylene
  8. p-xylene
  9. o-xylene
  10. styrene
  11. bromoform
  12. isopropylbenzene
  13. 4-bromofluorobenzene (SS)
  14. 1,1,2,2-tetrachloroethane
  15. 1,3-dichlorobenzene
  16. 1,4-dichlorobenzene
  17. 1,2-dichlorobenzene
  18. 1,2-dibromo-3-chloropropane
  19. 1,2,4-trichlorobenzene

Sample:

CLP 04.1 VOA MegaMix® (cat.# 30456) 2000µg/mL in methanol

502.2 Calibration Mix (gases) (cat.# 30042) 2000µg/mL in methanol

VOA Calibration Mix (ketones) (cat.# 30006) 5000µg/mL in methanol/water (90:10)

VOA Internal Standard Mix (cat.# 30011) 2500µg/mL in methanol

VOA Surrogate Spike Mix (cat.# 30004) 2500µg/mL in methanol

Purge and Trap

Model:

OI 4660 Eclipse

Trap:

#10 (Tenax®/silica gel/carbon molecular sieve)

Sample temp.:

ambient

Purge:

11 min. @ 40mL/min.

Desorb preheat:

185°C

Desorb:

0.3 min. @ 190°C

Desorb flow rate:

35.0mL/min.

Bake:

8 min. @ 210°C

Interface:

split injector

Transfer line temp.:

150°C

Chromatography

Inj:

split, split ratio 35:1, 1mm ID Siltek® treated split inlet liner (cat.# 20972-214.1)

Inj. temp.:

200°C

Carrier gas:

helium, constant flow

Linear velocity:

34cm/sec. @ 40°C

Oven temp.:

40°C (hold 4 min.) to 90°C @ 16°C/min., to 220°C @ 32°C/min. (hold 5 min.)

Det.:

MS

Transfer line temp.:

150°C

Scan range:

35-300 amu

Ionization:

EI

Mode:

scan

Tenax® Enka Research Institute Aruhem

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