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Table 1 Absolute retention times for semivolatile tar-
get compounds, in seconds.
Compound TR (sec.)
1. N-nitrosodimethylamine 36.5
2. 2-fluorophenol 62.7
3. phenol-d6 90.9
4. phenol 91.3
5. 2-chlorophenol-d4 93.9
6. bis(2-chloroethyl) ether 94.2
7. 2-chlorophenol 94.5
8. 1,3-dichlorobenzene 99.6
9. 1,4-dichlorobenzene-d4 101.8
10. 1,4-dichlorobenzene 102.4
11. 1,2-dichlorobenzene-d4 107.0
12. 1,2-dichlorobenzene 107.6
13. benzyl alcohol 108.1
14. 2-methylphenol 112.9
15. bis(2-chloroisopropyl) ether 113.7
16. N-nitrosodipropylamine 118.8
17. 4-methylphenol 119.3
18. hexachloroethane 119.8
19. nitrobenzene-d5 123.1
20. nitrobenzene 123.9
21. isophorone 134.1
22. 2-nitrophenol 136.7
23. 2,4-dimethylphenol 140.7
24. bis(2-chloroethoxy) methane 145.0
25. 2,4-dichlorophenol 146.8
26. benzoic acid 148.0
27. 1,2,4-trichlorobenzene 149.8
28. naphthalene-d8 151.6
29. naphthalene 152.5
30. 4-chloroaniline 156.8
31. hexachlorobutadiene 159.1
32. 4-chloro-3-methyl phenol 180.3
33. 2-methylnaphthalene 183.4
34. hexachlorocyclopentadiene 190.9
35. 2,4,6-trichlorophenol 197.5
36. 2,4,5-trrichlorophenol 198.5
37. 2-fluorobiphenyl 201.7
38. 2-chloronaphthalene 205.1
39. 2-nitroaniline 212.1
40. dimethyl phthalate 222.9
41. acenaphthylene 223.5
42. 2,6-dinitrotoluene 224.8
43. acenaphthene-d10 230.3
44. 3-nitroaniline 231.6
45. acenaphthene 231.9
46. 2,4-dinitrophenol 236.6
47. dibenzofuran 240.3
48. 4-nitrophenol 242.2
49. 2,4-dinitrotoluene 243.0
50. fluorene 256.0
51. diethyl phthalate 256.7
52. 4-chlorophenyl phenyl ether 258.5
53. 4-nitroaniline 260.2
54. 4,6-dinitro-2-methylphenol 261.3
55. N-nitrosodiphenylamine 264.6
56. 2,4,6-tribromophenol 267.4
57. 4-bromophenyl phenyl ether 280.8
58. hexachlorobenzene 281.0
59. pentachlorophenol 291.5
60. phenanthrene-D10 299.0
61. phenanthrene 300.2
62. anthracene 302.6
63. carbazole 312.2
64. dibutyl phthalate 334.5
65. fluoranthene 355.7
66. pyrene 365.7
67. p-terphenyl-d14 377.5
68. butyl benzyl phthalate 404.4
69. benzo(a)anthracene 423.0
70. chrysene-d12 423.4
71. chrysene 424.6
72. 3,3'-dichlorobenzidine 425.4
73. bis(2-ethylhexyl) phthalate 434.3
74. di- n-octyl phthalate 463.6
75. benzo(b)fluoranthene 470.2
76. benzo(k)fluoranthene 471.4
77. benzo(a)pyrene 483.0
78. perylene-d12 485.1
79. indeno(1,2,3-cd)pyrene 524.4
80. dibenzo(a,h)anthracene 526.0
81. benzo(ghi)perylene 533.0
Nine-Minute Analysis of Semivolatile
Organic Compounds
Using an Rtx® -5Sil MS Capillary GC Column in Combination with TOFMS
by Frank Dorman, Ph.D., Director of Technical Development
•Monitor 81 analytes and internal standards in 9 minutes.
• Excellent resolution of critical target compounds.
•At least 20 scans for each peak.
•Use split injection, to minimize injection problems and extend reporting limits.
Analysts in many environmental laboratories
struggle to increase sample throughput. Fast GC
techniques have enabled analysis times to be
decreased, but methods employing mass spec-
trometric detection often can’t make use of
these techniques, due to scan-speed limitations
of commonly used instruments. While some
manufacturers have improved the scan rates of
their instruments, methods employing either
quadrupole or ion-trap mass filters are limited
by the residence time of an ion as it passes
through the detector. In most cases, the scan-
speed limitations of these devices preclude very
rapid analyses of a wide range of compounds,
such as the semivolatiles in environmental
matrices, even though current capillary column
and gas chromatograph technology would allow
fast separations.
In order to adequately characterize a chromato-
graphic peak as it elutes from the column, most
methods require, at a minimum, 6 to 7 data
points (scans) across the peak. Certainly, addi-
tional data points yield a better peak profile, and
thus improved precision, so it is always better to
have more than the 6 to 7 scan minimum. For a
typical semivolatiles analysis, this correlates to a
minimum scan rate of approximately 2
scans/second, with peak widths of 3 to 5 sec-
onds considered “typical.” It is important to note
that this rate must be maintained over the entire
expected mass range, or identifications, espe-
cially for unknown compounds, will be compro-
mised. As faster GC techniques are investigated,
peak widths are reduced and, as a result, the
detector struggles to collect data at a rate that
is fast enough to adequately characterize the
peak profile. Unfortunately, for most GC/MS sys-
tems, this dictates a total analysis time of about
15 minutes, or longer, given the characteristics
of most instruments used in this application.
In a recent collaboration, Restek and LECO
Corporation developed a much faster analysis of
common semivolatile organic compounds by tak-
ing advantage of both fast GC column technolo-
gy and the speed of acquisition of the time-of-
flight mass spectrometer (TOFMS). Using a 10
meter, 0.18µm ID, 0.18µm film Rtx®-5Sil MS fast
GC column (phase optimized for semivolatiles
analysis; low bleed) and TOFMS, the analysis
time for this separation was less than 10 min-
utes, and at least 20 scans were recorded for
each peak. Table 1 lists the retention times for
the semivolatile target compounds, in seconds,
and each compound had approximately a 1-sec-
ond peak width at the base.
Figure 1 is the total ion chromatogram of a mid-
level calibration standard of these compounds,
analyzed under the conditions listed with the fig-
ure. Another valuable benefit of TOFMS is that
there is a sensitivity improvement relative to
most scanning instruments, enabling the analyst
to use split injection. Split injection typically cre-
ates fewer maintenance issues than splitless
injection, due to the much shorter residence
time of the analytes in the injector, and pro-
duces narrower peaks, increasing resolution.
For this analysis, theTOFMS system offers sen-
sitivity sufficient to allow calibration beyond the
20 to 160ng/µL “normal” calibration range, to a
range of 0.2 to 160ng/µL, even at a 50:1 split
ratio, thus allowing laboratories to extend
reporting limits (sensitivity) to lower levels.
Finally, extracts of actual samples were ana-
lyzed using this method, and results were com-
pared to values obtained by a commercial envi-
ronmental laboratory using conventional
GC/MS. The results compared well, even for
samples with high levels of non-target contami-
nants. Detailed information about this work is
available on request, and will be presented at
the 2005 Pittsburgh Conference.1
If your laboratory is analyzing semivolatile
organic compounds by GC/MS, and you are
interested in significantly increasing sample
throughput by reducing analysis time to less
than 10 minutes, we urge you to request a copy
of the complete report of this work, and/or
attend our presentation at the Pittsburgh
Conference.
Pittcon® presentation
1. Improved Sensitivity and Analysis Time for Semivolatile
Organic Compounds, Using GC-TOFMS: Can this Analysis
Really be Performed in Less Than 10 Minutes? Frank L.
Dorman, Jack W. Cochran (LECO Corporation), Gary B.
Stidsen, Chris M. English, Michael S. Wittrig
PittCon 2005, Monday, Feb. 28. Oral Session 380, Room
S210C, presentation 380-3, 2:10 pm.
Acknowledgement
This investigation was conducted in collaboration with Jack
Cochran, Director of Separation Science, LECO Corporation,
Las Vegas, NV.