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Figure 1
The Rtx®-200 column provides unique
separation of the VOCs listed in
US EPA Method 8260.
• 4 •
Xylenes are aromatic hydrocarbons that naturally
occur in petroleum and coal tar; they also can be
commercially derived from these substrates. The US
Environmental Protection Agency (EPA) does not
require separation of the three xylene isomers(m-,
p-, o-xylene), but rather requests their calculation
as totals or sums.1 Some states, such as New York,
have action limits based on m- and p-xylene sepa-
rately. However, the isomers of m- and p-xylene are
difficult to resolve using gas chromatography (GC)
and most capillary columns.
Separating m- and
p-Xylene Isomers
Using an Rtx®-200 GC Column
by Christopher English, Environmental Innovations Chemist
The common way to perform a GC separation of
m- and p-xylene is by using a polyethylene glycol
(PEG) stationary phase, such as the Restek
Stabilwax® column. Chromatographically, baseline
separation is possible with this column; however,
the highly polar phase does not separate many of
the other volatile organic compounds (VOCs).
The more ideal column choice for this separation is
the Rtx®-200 column. The Crossbond® trifluoro-
propylmethyl polysiloxane (TFP) stationary phase
features exceptionally low bleed at operating tem-
peratures up to 360°C.
The Rtx®-200 column provides unique separation
of VOCs listed in US EPA Methods 524 and 8260
(Figure 1), and is the best column to separate
xylene isomers for specific state requirements
(Figure 2). The only limitation of this column is the
resolution of the gases.
Trifluoropropyl stationary phases, like that of the
Rtx®-200 column, have a unique selectivity because
of the electrophilic nature of the fluorine-contain-
ing polymer. This creates interactions with electron-
rich molecules like ketones and halogenated com-
pounds. The unique selectivity results in different
elution orders and resolves compounds that phenyl,
cyano, and methyl phases cannot. The Rtx ®-200
column can be used to confirm tentatively identified
compounds and resolve multiple coelutions, mak-
ing it ideal for requirements such as those dictated
by New York State.
1. Toxicologicological Profile for Total Xylenes. Prepared by
Clements Associates, Inc., under Contract No. 205-88-0608.
Prepared for Agency of Toxic Substances and Disease Registry,
US Public Health Services, Atlanta, GA. December 1990.
Reference not available from Restek.
57
58
59
60
61
62
63,64
67
68
57. 1,3-dichloropropane
58. ethyl methacrylate
59. bromoform
60. 1,1,1,2-tetrachloroethane
61. ethylbenzene
62. 4-methyl-2-penanone
63. chlorobenzene
64. chlorobenzene-D5
65. m-xylene
66. 2-picoline (250ppb)
67. p-xylene
68. n-butyl acetate
69. o-xylene
Conditions for Figures 1 & 2
60m, 0.25 mm ID, 1.0µm Rtx ®-200 (cat.# 15056)
10ppb each component in 5mL of RO water;
Concentrator: Tekmar LSC-3100 Purge and Trap;
Trap: Vocarb® 3000 (type K); Purge: 11 min. @
40mL/min. @ ambient temperature;
Dry purge: 1 min. @ 40mL/min.; Desorb preheat:
245°C; Desorb: 250°C for 2 min., flow 10mL/min.;
Bake: 260°C for 8 min.; Interface: transfer line
0.53mm ID Silcosteel® MXT® tubing; Oven program:
40°C (hold 10 min.) to 100°C @ 6°C/min. (hold 1
min.) to 210°C @ 30°C/min. (hold 7 min.); Carrier
gas:helium @ ~1.3mL/min. constant flow (adjust
dichlorodifluoromethane to a retention time of 4.1
min. @ 40°C); Detector: Agilent 5973 MS, scan
range 35 to 300 AMU
65,66
m-
xylenep-
xylene
Ions 91 and 106
(peaks 65, 67, 69, Figure 1)
Ion 91
Ion 106
o-
xylene
Figure 2
An extracted ion chromatogram shows the Rtx®-200 column separates m/p-xylene isomers.
Innovations at Work
Separate m/p-xylene isomers!
✔ Rtx®-200 Columns (Crossbond® trifluoropropylmethyl polysiloxane) Stable to 360°C
For the complete Rtx®-200 column offering, refer to Restek’sAnnual Chromatography Products Guide (lit. cat.# 59960).
Rtx®-200 (Fused Silica Tubing)
ID df (µm) temp. limits 15-Meter 30-Meter 60-Meter 105-Meter
0.25mm 1.00 -20 to 290/310°C 15050 15053 15056 15059
MXT®-200 (MXT® Tubing)
ID df (µm) temp. limits 15-Meter 30-Meter
0.25mm 1.00 -20 to 310°C 75050 75053
for moreinfo
Request Applications Note #59190.
69
22 20 min.
GC_EV00381
GC_EV00380
✔ Unique separation of VOCs
satisfy state requirements
✔ Low bleed at high operating
temperatures (stable to 360°C)
An extensive selection of analytical reference materials for US EPA
Method 8260B is available from Restek. Please see page 16 of this
newsletter or visit our web site at for ordering
information.
22.00 21.80 22.40 22.20 22.80 22.60 23.00 min.