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3) Use a thin-film columnby reducing the concentration
of calibration standards.
Athin-filmRtx
fi
-5SilMS column can reduce the analysis time to
less than 22minutes for the compounds listed inEPAMethod
8270 (see compound list for Figure 2, p.3). TheRtx
fi
-5SilMS
column features a silarylene stationary phase that exhibits lower
bleed and optimized separation of semivolatile compounds.
Usually, a thinner film column has less sample capacity than a
thicker film column, which can lead to column overload. To pre-
vent column overload, the concentration of the calibration stan-
dards should be reduced by
1
/
5
, so that the on-column concentra-
tion ranges from 4ng to 32ng. Table I shows the response factors
and linearity of active and late-eluting semivolatile compounds.
Also, reducing the standard concentration by a factor of 5 off-sets
the increased extract volume, resulting in the same reporting lim-
its.
4) Optimize oven temperature programming.
Amulti-rampGC temperature program can optimize the separa-
tion of critical compound pairs. Increasing the initial hold time
helps resolve early-eluting compounds; then a fast ramp rate can
be used through non-critical areas, and a lower ramp rate used to
elute later compounds. Extracted ion chromatograms of the close-
ly eluting compounds show resolution between them (Figure 3).
5) CalibrationCurve
We used
1
/
5
the recommended concentration level ofMethod
82701 L injection of 4, 10, 16, 24, and 32ppm standard. The
internal standardswere also reduced to
1
/
5
the concentration and
are at 8ppm.As seen in Figure 2, the 16ng on-column injection
shows excellent signal-to-noise ratio, and low column bleed and
injection port discrimination.
Conclusion
Anumber of techniques can be used to increase sample through-
put for the analysis of semivolatile compounds. Increasing extract
volumewill reduce preparation time and injection port contamina-
tion. Using a drilled Uniliner
fi
injection port liner results in a
more inert sample pathway and eliminates injection port discrimi-
nation. In addition, the use of a thin-film column reduces analysis
time helping laboratories increase sample output.
Compound
Ret. time Int. Stnd.
m/z
4ppm 10ppm 16ppm 24ppm 32ppm Ave.
5-point
4-point
(min.) for quant.
RRF
RRF
RRF
RRF
RRF
RRF %RSD %RSD
(w/o 4ppm)
N-nitrosodimethylamine
3.79
1
74
0.724
0.736
0.775
0.742
0.748 0.745
3
2
pyridine
3.80
1
79
1.055
0.951
1.058
0.967
1.004 1.007
5
5
aniline
6.28
1
93
1.777
1.773
1.962
1.933
1.946 1.878
5
5
N-nitroso-di-n-propylamine
7.12
1
169
0.776
0.746
0.801
0.740
0.770 0.767
3
4
benzoic acid
7.84
2
122
0.148
0.193
0.201
0.203
0.228 0.195
15
7
2,4-dichlorophenol
7.94
2
162
0.215
0.248
0.240
0.249
0.259 0.242
7
3
hexachlorocyclopentadiene
9.14
3
237
0.283
0.310
0.323
0.333
0.357 0.321
9
6
3-nitroaniline
10.21
3
138
0.323
0.318
0.343
0.339
0.348 0.334
4
4
2,4-dinitrophneol
10.34
3
184
0.110
0.139
0.156
0.155
0.169 0.146
16
8
4-nitrophenol
10.41
3
109
0.162
0.168
0.185
0.187
0.202 0.181
9
7
azobenzene
11.07
3
77
1.387
1.446
1.436
1.369
1.414 1.410
2
2
nitrosodiphenylamine
11.04
4
169
0.718
0.698
0.723
0.771
0.738 0.729
4
4
pentachlorophenol
11.81
4
266
0.094
0.122
0.132
0.132
0.146 0.125
15
7
benzidine
13.72
5
184
0.213
0.178
0.188
0.206
0.269 0.211
17
19
benzo(b)fluoranthene
17.88
6
252
1.344
1.448
1.504
1.506
1.628 1.486
7
5
benzo(ghi)perylene
21.76
6
276
1.341
1.428
1.492
1.488
1.593 1.468
6
5
ISTD
1,4-dichlorobenzene-d14
6.62
1
152
naphthalene-d8
8.10
2
136
acenaphthene-d10
10.22
3
164
phenanthrene-d10
12.02
4
188
chrysene-d12
15.70
5
240
perylene-d12
18.73
6
264
Table I
Response factors and linearity of active and late-eluting semivolatile compounds.
