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Environmental Article

Fast, Accurate Semivolatiles Analysis!

Using New Rxi®-5Sil MS GC Columns

By Robert Freeman, Environmental Innovations Chemist
  • Ultra-low bleed columns save you time and money with faster baseline stabilization.
  • Highly inert for more accurate low-level analysis of active compounds.
  • Guaranteed column-to-column reproducibility.

Semivolatiles methods, such as EPA Method 8270, place stringent demands on gas chromatography (GC) systems—particularly on the analytical column. These test methods monitor for a broad range of environmental contaminants that are analyzed as a complex mixture of acidic and base/neutral analytes. The complexity of the samples, coupled with the increasing need for lower detection limits, has tightened analytical requirements for column bleed, efficiency, and inertness.

5% diphenyl/95% dimethyl polysiloxane (“5” phase) columns typically are used for this GC/MS analysis. Manufacturers have made significant advances to the standard “5” phase by incorporating phenyl rings into the backbone of the polymer (Figure 1). This stiffens the siloxane backbone, which then reduces thermal breakdown and column bleed. Conventional “5” phase selectivity is maintained by adjusting the content of this additional phenyl group. The silarylene polymer not only exhibits improved thermal stability and reduced bleed, but also shows increased peak efficiencies for polycyclic (polynuclear) aromatic hydrocarbons (PAHs), including benzofluoranthene isomers (Figure 2). Restek has applied its Rxi® deactivation technology (1) to our existing silarylene phase resulting in the Rxi®-5Sil MS column, a low bleed column with excellent inertness for active analytes. Here we evaluate the performance of two popular dimensions of Rxi®-5Sil MS columns for semivolatiles analysis in terms of bleed, efficiency, and activity.

Figure 1: Silarylene stationary phase chemistry: aromatic rings lower bleed and increase efficiencies.
silarylene

Figure 2: Excellent resolution of benzo(b)fluoranthene and benzo(k)fluoranthene on the Rxi®-5Sil MS column.

gc_ev00945b

For conditions see Figure 4.

GC_EV00945B

Low column bleed reduces the amount of noise contributed by the column, and thereby increases the signal-to-noise ratio of the analytical system. Low bleed Rxi®-5Sil MS columns are ideal for GC/MS applications requiring high sensitivity. For semivolatile analysis, bleed interferes with the ability to quantify low levels of late eluting compounds, most notably the PAHs. Here we evaluated bleed levels using 10ng on-column and found the Rxi®-5Sil MS columns to be exceptionally low bleed (Figures 3 and 4). Increased sensitivity and subsequently lower detection limits are a direct result of improved signal-to-noise ratios. Decreased bleed also results in less bleed ion interference with the mass spectral data, making more accurate peak identifications possible.

The separation of several difficult PAHs is critical in semivolatiles analysis. The 30m x 0.25mm x 0.25df column (Figure 3) and the 20m x 0.18mm x 0.18df column (Figure 4) both show high efficiency for PAHs. The narrow bore 0.18mm ID column has slightly better resolution of the difficult to resolve isomeric pair, benzo(b)fluoranthene & benzo(k)fluoranthene. Two other polycyclic (polynuclear) aromatic hydrocarbons also are resolved better using the 0.18mm ID column, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene.

Figure 3: Separate difficult PAHs easily using a 30m x 0.25mm ID x 0.25µm
Rxi®-5Sil MS column.
  1. 1,4-dioxane
  2. n-nitrosodimethylamine
  3. pyridine
    c.   toluene
  4. 2-fluorophenol (SS)
  5. phenol-d6 (SS)
  6. phenol
  7. aniline
  8. bis(2-chloroethyl) ether
  9. 2-chlorophenol
  10. 1,3-dichlorobenzene
  11. 1,4-dichlorobenzene-d4 (IS)
  12. 1,4-dichlorobenzene
  13. benzyl alcohol
  14. 1,2-dichlorobenzene
  15. 2-methylphenol
  16. bis(2-chloroisopropyl) ether
  17. 4-methylphenol/3-methyl
    phenol
  18. n-nitroso-di-n-propylamine
  19. hexachloroethane
  20. nitrobenzene-d5 (SS)
  21. nitrobenzene
  22. isophorone
  23. 2-nitrophenol
  24. 2,4-dimethylphenol
  25. benzoic acid
  26. bis(2-chloroethoxy)methane
  27. 2,4-dichlorophenol
  28. 1,2,4-trichlorobenzene
  29. naphthalene-d8 (IS)
  30. naphthalene
  31. 4-chloroaniline
  1. hexachlorobutadiene
  2. 4-chloro-3-methylphenol
  3. 2-methylnaphthalene
  4. 1-methylnaphthalene
  5. hexachlorocyclopentadiene
  6. 2,4,6-trichlorophenol
  7. 2,4,5-trichlorophenol
  8. 2-fluorobiphenyl (SS)
  9. 2-chloronaphthalene
  10. 2-nitroaniline
  11. 1,4-dinitrobenzene
  12. dimethyl phthalate
  13. 1,3-dinitrobenzene
  14. 2,6-dinitrotoluene
  15. 1,2-dinitrobenzene
  16. acenaphthylene
  17. 3-nitroaniline
  18. acenaphthene-d10 (IS)
  19. acenaphthene
  20. 2,4-dinitrophenol
  21. 4-nitrophenol
  22. 2,4-dinitrotoluene
  23. dibenzofuran
  24. 2,3,5,6-tetrachlorophenol
  25. 2,3,4,6-tetrachlorophenol
  26. diethyl phthalate
  27. 4-chlorophenyl phenyl ether
  28. fluorene
  29. 4-nitroanaline
  30. 4,6-dinitro-2-methylphenol
  31. n-nitrosodiphenylamine (diphenylamine)
  32. 1,2-diphenylhydrazine (as azobenzene)
  33. 2,4,6-tribromophenol (SS)
  34. 4-bromophenyl phenyl ether
  35. hexachlorobenzene
  1. pentachlorophenol
  2. phenanthrene-d10 (IS)
  3. phenanthrene
  4. anthracene
  5. carbazole
  6. di-n-butyl phthalate
  7. fluoranthene
  8. benzidine
  9. pyrene-d10 (SS)
  10. pyrene
  11. p-terphenyl-d14 (SS)
  12. 3,3'-dimethylbenzidine
  13. butyl benzyl phthalate
  14. bis(2-ethylhexyl) adipate
  15. 3,3'-dichlorobenzidine
  16. benzo(a)anthracene
  17. bis(2-ethylhexyl) phthalate
  18. chrysene-d12 (IS)
  19. chrysene
  20. di-n-octyl phthalate
  21. benzo(b)fluoranthene
  22. benzo(k)fluoranthene
  23. benzo(a)pyrene
  24. perylene-d12 (IS)
  25. dibenzo(a,h)anthracene
  26. indeno(1,2,3-cd)pyrene
  27. benzo(ghi)perylene

c = contaminant

gc_ev00943

Column: Rxi®-5Sil MS, 30m, 0.25mm ID, 0.25µm (cat.# 13623)
Sample: US EPA Method 8270D Mix, 1µL of 10µg/mL (IS 40µg/mL)
8270 MegaMix® (cat.# 31850)
Benzoic Acid (cat.# 31879)
8270 Benzidines Mix (cat.# 31852)
Acid Surrogate Mix (4/89 SOW) (cat.# 31025)
Revised B/N Surrogate Mix (cat.# 31887)
1,4-Dioxane (cat.# 31853)
SV Internal Standard Mix (cat.# 31206)

1.0µL (10ng on-column concentration),
4mm Drilled Uniliner® (hole on bottom) inlet liner (cat.# 20756),
pulsed splitless: pulse 25psi @ 0.2min., 60mL/min. @ 0.15 min.

Inj. temp.: 250°C
Carrier gas: helium, constant flow
Flow rate: 1.2mL/min.
Oven temp.: 40°C (hold 1.0 min.) to 280°C @ 25°C/min. to 320°C @ 5°C/min. (hold 1min.)
Det: MS
Transfer line temp.: 280°C
Scan range:

35-550amu
Ionization: EI
Mode: scan

GC_EV00943

Figure 4: Semivolatile compounds resolved on a 20m x 0.18mm ID x 0.18µm
Rxi®-5Sil MS column.
  1. 1,4-dioxane
  2. n-nitrosodimethylamine
  3. pyridine
    c.   toluene
  4. 2-fluorophenol (SS)
  5. phenol-d6 (SS)
  6. phenol
  7. aniline
  8. bis(2-chloroethyl) ether
  9. 2-chlorophenol
  10. 1,3-dichlorobenzene
  11. 1,4-dichlorobenzene-d4 (IS)
  12. 1,4-dichlorobenzene
  13. benzyl alcohol
  14. 1,2-dichlorobenzene
  15. 2-methylphenol
  16. bis(2-chloroisopropyl) ether
  17. 4-methylphenol/3-methyl
    phenol
  18. n-nitroso-di-n-propylamine
  19. hexachloroethane
  20. nitrobenzene-d5 (SS)
  21. nitrobenzene
  22. isophorone
  23. 2-nitrophenol
  24. 2,4-dimethylphenol
  25. benzoic acid
  26. bis(2-chloroethoxy)methane
  27. 2,4-dichlorophenol
  28. 1,2,4-trichlorobenzene
  29. naphthalene-d8 (IS)
  30. naphthalene
  31. 4-chloroaniline
  1. hexachlorobutadiene
  2. 4-chloro-3-methylphenol
  3. 2-methylnaphthalene
  4. 1-methylnaphthalene
  5. hexachlorocyclopentadiene
  6. 2,4,6-trichlorophenol
  7. 2,4,5-trichlorophenol
  8. 2-fluorobiphenyl (SS)
  9. 2-chloronaphthalene
  10. 2-nitroaniline
  11. 1,4-dinitrobenzene
  12. dimethyl phthalate
  13. 1,3-dinitrobenzene
  14. 2,6-dinitrotoluene
  15. 1,2-dinitrobenzene
  16. acenaphthylene
  17. 3-nitroaniline
  18. acenaphthene-d10 (IS)
  19. acenaphthene
  20. 2,4-dinitrophenol
  21. 4-nitrophenol
  22. 2,4-dinitrotoluene
  23. dibenzofuran
  24. 2,3,5,6-tetrachlorophenol
  25. 2,3,4,6-tetrachlorophenol
  26. diethyl phthalate
  27. 4-chlorophenyl phenyl ether
  28. fluorene
  29. 4-nitroanaline
  30. 4,6-dinitro-2-methylphenol
  31. n-nitrosodiphenylamine (diphenylamine)
  32. 1,2-diphenylhydrazine (as azobenzene)
  33. 2,4,6-tribromophenol (SS)
  34. 4-bromophenyl phenyl ether
  35. hexachlorobenzene
  1. pentachlorophenol
  2. phenanthrene-d10 (IS)
  3. phenanthrene
  4. anthracene
  5. carbazole
  6. di-n-butyl phthalate
  7. fluoranthene
  8. benzidine
  9. pyrene-d10 (SS)
  10. pyrene
  11. p-terphenyl-d14 (SS)
  12. 3,3'-dimethylbenzidine
  13. butyl benzyl phthalate
  14. bis(2-ethylhexyl) adipate
  15. 3,3'-dichlorobenzidine
  16. benzo(a)anthracene
  17. bis(2-ethylhexyl) phthalate
  18. chrysene-d12 (IS)
  19. chrysene
  20. di-n-octyl phthalate
  21. benzo(b)fluoranthene
  22. benzo(k)fluoranthene
  23. benzo(a)pyrene
  24. perylene-d12 (IS)
  25. dibenzo(a,h)anthracene
  26. indeno(1,2,3-cd)pyrene
  27. benzo(ghi)perylene

c = contaminant

gc_ev00945


Column: Rxi®-5Sil MS, 20m, 0.18mm ID, 0.18µm (cat.# 43602)
Sample: US EPA Method 8270D Mix, 1µL of 10µg/mL (IS 40µg/mL)
8270 MegaMix® (cat.# 31850)
Benzoic Acid (cat.# 31879)
8270 Benzidines Mix (cat.# 31852)
Acid Surrogate Mix (4/89 SOW) (cat.# 31025)
Revised B/N Surrogate Mix (cat.# 31887)
1,4-Dioxane (cat.# 31853)
SV Internal Standard Mix (cat.# 31206)
Inj.: 1.0µL (10ng on-column concentration),
4mm Drilled Uniliner® (hole on bottom) inlet liner (cat.# 20756),
pulsed splitless: pulse 20psi @ 0.2min., 60mL/min. @ 0.15 min.
Inj. temp.: 250°C
Carrier gas: helium, constant flow
Flow rate: 1.0mL/min.
Oven temp.: 50°C (hold 0.5 min.) to 260°C @ 20°C/min. to 280°C @ 5°C/min. to 330°C @ 20°C/min. (hold 1.0min.)
Det: MS
Transfer line temp.: 280°C
Scan range: 35-550amu
Ionization: EI
Mode: scan
GC_EV00945

Finally, since the analysis of semivolatiles covers such a diverse range of compounds it is critical that the column perform well for both basic and acid compounds at low levels. Surface activity in a column is revealed by peak shape and response for active analytes such as 2,4-dinitrophenol (acidic) and pyridine (basic). Most manufacturers struggle with adequate response and good peak shapes for both types of analytes. By using the unique Rxi® deactivation process Restek has developed a silarylene phase that shows unsurpassed inertness and excellent response for both of these active analytes. Figures 5 and 6 illustrate the response of 2,4-dinitrophenol and pyridine at 10ng on-column, respectively. Analytically, 2,4-dinitrophenol is considered the most problematic compound in the Method 8270D target list. The Rxi®-5Sil MS column passed method requirements even in the single ng on-column range (Figure 7).

Figure 5: Excellent peak shape for 2,4-dinitrophenol at 10ng on-column.

GC_EV00943D

For conditions see Figure 3.

GC_EV00943D

Figure 6: Excellent response for pyridine at 10ng on-column.

gc_ev00943a

For conditions see Figure 3.

GC_EV00943A

Figure 7: Low-level response for 2,4-dinitrophenol exceeds method requirements (1ng on-column, 20m x 0.18mm ID x 0.18df Rxi®-5Sil MS column).

gc_ev00950

Column:

Rxi®-5Sil MS, 20m, 0.18mm ID, 0.18µm (cat.# 43602)

Sample: US EPA Method 8270D Mix, 1µL of 1µg/mL (IS 40µg/mL)
8270 MegaMix® (cat.# 31850)
Benzoic Acid (cat.# 31879)
8270 Benzidines Mix (cat.# 31852)
Acid Surrogate Mix (4/89 SOW) (cat.# 31025)
Revised B/N Surrogate Mix (cat.# 31887)
1,4-Dioxane (cat.# 31853)
SV Internal Standard Mix (cat.# 31206)
Inj:

1.0µL (1ng on-column concentration),
4mm Drilled Uniliner® (hole on bottom) inlet liner (cat.# 20756),
pulsed splitless: pulse 20psi @ 0.2min., 60mL/min. @ 0.15 min.
Inj. temp.: 250°C
Carrier gas: helium, constant flow
Flow rate:

1.0mL/min.
Oven temp.: 50°C (hold 0.5min.) to 260°C @ 20°C/min. to 280°C @ 5°C/min. to 330°C @ 20°C/min. (hold 1.0min.)
Det: MS
Transfer line temp.: 280°C
Scan range:

35-550amu
Ionization:

EI
Mode: scan

GC_EV00950

The Rxi®-5Sil MS columns most commonly used for semivolatiles analysis are the 30m x 0.25mm ID columns with either 0.25µm or 0.5µm film thicknesses. These dimensions generally offer the best balance of sample capacity, analysis time, and column lifetime. However, if sample throughput is paramount, shorter narrow bore columns such as the 20m x 0.18mm ID with either 0.18µm or 0.36µm film thicknesses are preferred. Due to increased peak efficiencies, temperature programs can be accelerated without compromising key separations. Regardless of which dimension you choose, the new Rxi®-5Sil MS columns are ideal for analyzing semivolatile compounds.

REFERENCES

  1. New Rxi® Fused
    Silica Columns: Revolutionary Thinking