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Environmental Article

Low-Level GC/MS for Semivolatiles in Drinking Water

Excellent Responses at 10ng On Column, Using an Rxi®-5ms Column

By Robert Freeman, Environmental Innovations Chemist
  • Inert, ultra-low bleed column improves low level analyses.
  • Excellent peak shapes and responses for active analytes.
  • Drilled Uniliner® inlet liner minimizes sample breakdown in the injector.

Semivolatile organic chemical contaminants in drinking water are target compounds in many analytical methods, worldwide. US EPA Method 525.2, for example, is a general purpose solid-phase extraction/GC/MS procedure for identifying and quantifying a wide range of semivolatile compounds. Analytes, and introduced internal standards and surrogates, are extracted from a 1-liter water sample by passing the sample through a solid phase extraction disk containing a bonded C18 phase (e.g., Resprep™-C18, cat. #24004). Target compounds are trapped on the disk, then eluted in a small amount of solvent. The extract is concentrated by evaporating the solvent, and the sample components are separated, identified, and quantified by GC/MS.

As is true for many other semivolatiles methods, the extensive target compound list for Method 525.2 encompasses numerous classes of analytes. These diverse compounds present varying difficulties in the analysis, including differing modes of degradation. Coupled with the continual need for lower levels of detection, these challenges make extreme demands on the chromatography column, and the analysis requires an inert, thermally stable, low-bleed stationary phase. To meet these needs, we recommend a 30 meter, 0.25mm ID, 0.25µm Rxi®-5ms column. Enhanced surface deactivation provides Rxi®-5ms columns with exceptional inertness and ultra-low bleed, ensuring resolution and symmetric peaks for these difficult analytes.

Figure 1 shows the total ion chromatogram for semivolatiles commonly analyzed in drinking water, and listed in US EPA Method 525.2, at 10ng each on an Rxi®-5ms column. Resolution and peak shapes are exceptionally good.

To minimize analyte degradation in the injection port, and discrimination among analytes by molecular weight, we recommend installing a Drilled Uniliner® inlet liner in the injection port. This liner forms a Press-Tight® seal with the inlet end of the column, eliminating contact between the sample and the hot metal surfaces in the injection port and assuring near-complete sample transfer. The small hole in the wall of the liner allows the liner to be used with split/splitless injections. As an additional precaution to minimize analyte breakdown, we use a pulsed splitless injection (50psi / 0.3 min.; 1µL sample) to reduce the time the analytes spend in the injection port.

Exceptional inertness and ultra-low bleed enable an Rxi®-5ms column to perform exceptionally well in analyses of complex mixtures of semivolatile compounds. We recommend pairing an Rxi®-5ms column with our recently revised analytical reference mixes for semivolatile pollutants in water. Restek can provide all the materials needed for a semivolatiles analysis: extraction disks, analytical reference materials, and a column capable of excellent responses for all target analytes at low on-column concentrations.


Figure 1  Excellent resolution and symmetric peaks for commonly analyzed drinking water semivolatiles, at 10ng each on an Rxi®-5ms column.

  1. isophorone
  2. 2-nitro-m-xylene (SS)
  3. naphthalene
  4. dichlorvos (DDVP)
  5. hexachlorocyclopentadiene
  6. EPTC
  7. mevinphos
  8. butylate
  9. vernolate
  10. dimethyl phthalate
  11. pebulate
  12. etridiazole (Terrazole®)
  13. 2,6-dinitrotoluene
  14. acenaphthylene
  15. acenaphthene-d10 (IS)
  16. chlorneb
  17. tebuthiuron
  18. 2,4-dinitrotoluene
  19. molinate
  20. diethyl phthalate
  21. fluorene
  22. propachlor
  23. ethoprop (ethoprophos)
  24. cycloate
  25. chlorpropham
  26. trifluralin
  27. atraton
  28. hexachlorobenzene
  29. prometon
  30. simazine
  31. atrazine
  32. propazine
  1. pentachlorophenol
  2. terbufos
  3. pronamide (propyzamide)
  4. diazinon
  5. phenanthrene-d10 (IS)
  6. phenanthrene
  7. disulfoton
  8. methyl paraoxon
  9. anthracene
  10. terbacil
  11. chlorothalonil
  12. metribuzin
  13. simetryn
  14. ametryn
  15. alachlor
  16. prometryn
  17. terbutryn
  18. di-n-butyl phthalate
  19. bromacil
  20. cyanazine (Bladex)
  21. metalochlor
  22. chlorpyrifos (Dursban®)
  23. triademefon
  24. Dacthal® (DCPA)
  25. MGK-264 (isomer A)
  26. diphenamid
  27. MGK-264 (isomer B)
  28. merphos
  29. heptachlor epoxide
  30. fluoranthene
  31. stirofos
  32. disulfoton sulfone
  1. butachlor
  2. pyrene-d10 (SS)
  3. fenamiphos
  4. pyrene
  5. napropamide (Devrinol®)
  6. trans-nonachlor
  7. merphos oxide
  8. tricyclazole (Beam)
  9. carboxin
  10. chlorobenzilate
  11. butyl benzyl phthalate
  12. norflurazon
  13. bis(2-ethylhexyl) adipate
  14. hexazinone (Velpar®)
  15. triphenylphosphate (SS)
  16. benzo(a)anthracene
  17. chrysene-d12 (IS)
  18. chrysene
  19. bis(2-ethylhexyl) phthalate
  20. fenarimol
  21. cis-permethrin
  22. trans-permethrin
  23. di-n-octyl phthalate
  24. benzo(b)fluoranthene
  25. benzo(k)fluoranthene
  26. benzo(a)pyrene
  27. fluridone (Sonar®)
  28. perylene-d12 (SS)
  29. indeno(1,2,3-cd)pyrene
  30. dibenzo(a,h)anthracene
  31. benzo(ghi)perylene

Column:

Rxi®-5ms, 30m, 0.25mm ID, 0.25µm (cat.# 13423)

Sample:

US EPA Method 525.2 mix, 10µg/mL each analyte, 25µg/mL each internal standard and surrogate: Method 525.2 Semivolatile Mix (cat.# 31899), Organonitrogen Pesticide Mix #1 (cat.# 33012), Organonitrogen Pesticide Mix #2 (cat.# 33011), Organophosphate Pesticide Mix #1 (cat.# 33013), Nitrogen/Phosphorous Pesticide Mix #2 (cat.# 32423), Method 525.2 Internal Standard Mix (cat.# 31825), Method 525.2 Surrogate Standard Mix (cat.# 31826)

Instrument:

Agilent 6890

Inj.:

1.0µL, pulsed splitless injection: 50psi (0.3 min.), 80mL/min. (0.15 min.), gas saver 15mL/min. (1 min.), 4mm Drilled Uniliner® inlet liner, hole near bottom (cat#20771)

Inj. temp.:

250°C

Carrier gas:

helium, constant flow

Flow rate:

1.2mL/min.

Oven temp.:

90°C (1 min.) to 270°C @ 20°C/min., to 315°C @ 6°C/min.

Det.:

Agilent 5973 MSD

Interface line temp.:

280°C

Scan range:

35-550 amu

Solvent delay:

3.00 min.

Tune:

DFTPP

Ionization:

EI