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Environmental Article

Analysis of Semivolatile Organics

Using the new Rxi™-5ms Capillary GC Column

by Robert Freeman, Environmental Innovations Chemist, and
Christopher M. English, Innovations Group Leader
  • Low column bleed, outstanding inertness, excellent column-to-column reproducibility.
  • Symmetric peaks and good response factors for acidic or basic analytes.
  • Resolve 94 analytes in less than 18 minutes.

Sub-nanogram Analysis of Semivolatile Organics

Analyzing basic or acidic semivolatile environmental pollutants at low nanogram-on-column concentrations puts demands on the entire analytical system. Using our new Rxi™-5ms column, we have developed an analytical procedure that assures good performance for both acids and bases.

Rxi™-5ms Column Offers Sensitivity for Acids and Bases

One of the most active basic compounds listed in semivolatiles methods is pyridine. This early-eluting compound can elicit poor performance in the injection port and on the column, and many currently available columns give a poor peak shape for pyridine. Columns with a slightly basic surface can perform well with pyridine, but will perform poorly with the acidic compounds, such as 2,4-dinitrophenol.

Figure 1 combines extracted ion chromatograms for the initial three US EPA Method 8270D target compounds, at 0.5ng per compound on-column. The extracted ion for 1,4-dioxane shows that injection port and oven conditions were optimized. The pyridine and N-nitrosodimethylamine peaks are symmetric, even at this low level of detection. An excessively tailing pyridine peak, or a pyridine peak smaller than that for 1,4-dioxane at the same concentration, would indicate on-column activity. With an Rxi™-5ms column, and the conditions listed for Figure 3, pyridine can be detected reliably at low concentrations.

Analytically, 2,4-dintrophenol is considered the most problematic compound in the Method 8270 target list. 2,4-Dinitrophenol and the other system performance check compounds (SPCC) - N-nitroso-di-n-propylamine, hexachlorocyclopentadiene, and 4-nitrophenol - must exhibit a minimum average response factor (RF) of 0.050. An optimized system generally will provide response factors greater than 0.1 for these compounds, but the lower the calibration curve for these compounds, the more difficult it is to achieve passing response factors. If any of these compounds fails to meet the Method 8270 response factor criterion, system maintenance must be performed to bring response factors to passing before samples can be analyzed. Figure 2 shows the inertness of the Rxi™-5ms column, which exhibits a response factor of 0.136 for 0.5ng on-column of 2,4-dinitrophenol.

The total ion chromatogram for our optimized analysis is shown in Figure 3. There are at least five scans across each target analyte, which assures good spectral integrity and good peak shape, and the last compound is eluted in less than 18 minutes.

The Result

The Rxi™-5ms column introduces a new generation of Restek columns that exhibit low bleed, outstanding inertness, and excellent column-to-column reproducibility.

An Rxi™-5ms column, used in an optimized system, provides excellent chromatography for Method 8270 semivolatile compounds, including difficult-to-analyze acidic or basic compounds, at low on-column concentrations. These new columns give the performance needed, at the sensitivity required, column after column.


Figure 1  An Rxi™-5ms column provides sharp, easily quantified peaks for active analytes (extracted ion chromatograms).

GC_EV00821b


Figure 2  Excellent response for 0.5ng 2,4-dintrophenol on an Rxi™-5ms column.

GC_EV00829


Figure 3  Separate 94 semivolatile compounds in less than 18 minutes, using an Rxi™-5ms column.
  1. 1,4-dioxane
  2. N-nitrosodimethylamine
  3. pyridine
  4. 2-fluorophenol
  5. phenol-d6
  6. phenol
  7. aniline
  8. bis(2-chloroethyl) ether
  9. 2-chlorophenol
  10. 1,3-dichlorobenzene
  11. 1,4-dichlorobenzene-d4
  12. 1,4-dichlorobenzene
  13. benzyl alcohol
  14. 1,2-dichlorobenzene
  15. 2-methylphenol
  16. bis(2-chloroisopropyl) ether
  17. a. 4-methylphenol
    b. 3-methylphenol
  18. N-nitroso-di-n-propylamine
  19. hexachloroethane
  20. nitrobenzene-d5
  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
  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
  9. 2-chloronaphthalene
  10. 2-nitroaniline
  11. 1,4-dinitrobenzene
  12. dimethyl phthalate
  13. 1,3-dinitrobenzene
  14. 2,6-dinitrotoluene
  15. acenaphthylene
  16. 1,2-dinitrobenzene
  17. 3-nitroaniline
  18. acenaphthene-d10
  19. acenaphthene
  20. 2,4-dinitrophenol
  21. 4-nitrophenol
  22. dibenzofuran
  23. 2,4-dinitrotoluene
  24. 2,3,4,6-tetrachlorophenol
  25. 2,3,5,6-tetrachlorophenol
  26. diethyl phthalate
  27. 4-chlorophenyl phenyl ether
  28. fluorene
  29. 4-nitroanaline
  30. 4,6-dinitro-2-methylphenol
  31. N-nitrosodiphenylamine
    (as diphenylamine)
  1. 1,2-diphenylhydrazine
    (as azobenzene)
  2. 2,4,6-tribromophenol
  3. 4-bromophenyl phenyl ether
  4. hexachlorobenzene
  5. pentachlorophenol
  6. phenanthrene-d10
  7. phenanthrene
  8. anthracene
  9. carbazole
  10. di-n-butyl phthalate
  11. fluoranthene
  12. benzidine
  13. pyrene-d10
  14. pyrene
  15. p-terphenyl-d14
  16. 3,3’-dimethylbenzidine
  17. butyl benzyl phthalate
  18. bis(2-ethylhexyl) adipate
  19. 3,3’-dichlorobenzidine
  20. benzo(a)anthracene
  21. chrysene-d12
  22. chrysene
  23. bis(2-ethylhexyl) phthalate
  24. di-n-octyl phthalate
  25. benzo(b)fluoranthene
  26. benzo(k)fluoranthene
  27. benzo(a)pyrene
  28. perylene-d12
  29. indeno(1,2,3-cd)pyrene
  30. dibenzo(a,h)anthracene
  31. benzo(ghi)perylene

GC_EV00823

Column:

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

Sample:

US EPA Method 8270D mix: 8270 MegaMix™ (cat.# 31850), Benzoic Acid Standard (cat.# 31879), Benzidine Standard (cat.# 31852), Acid Surrogate Mix (cat.# 31025), B/N Surrogate Standard Mix (cat.# 31887), 1,4-Dioxane (cat.# 31853)

Inj.:

1.0µL, 10ppm each analyte (10ng on column), splitless (hold 0.1 min.)
4mm Drilled Uniliner® inlet liner (hole at bottom) (cat.# 20756)

Instrument:

Agilent 6890

Inj. temp.:

250°C

Carrier gas:

helium, constant flow

Flow rate:

1.2mL/min.

Oven temp.:

50°C (hold 0.5 min.) to 265°C @ 25°C/min., to 330°C @ 6°C/min. (hold 2 min.)

Det.:

Agilent 5973 GC/MS

Transfer line temp.:

280°C

Scan range:

35-550 amu

Solvent delay:

2 min.

Tune:

DFTPP

Ionization:

EI