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14
CLPesticides column and the Rtx
®
-CLPesticides2 column is 330°C, making it
similar to the 5% phenyl Rtx
®
-5 column.
When using cyanopropyl-phase or phenyl-phase columns, laboratories typi-
cally must calibrate using 5-point curves, injecting mix A and mix B com-
poundsseparatelybecause the targetcompoundscoelute.Becausenocoelution
problems occur with the Rtx
®
-CLPesticides columns, the mixes can be com-
bined. This eliminates the need for at least 5 injections during calibration of
the instrument, andmay free aminimum of 2.5 hours a day to analyzemore
samples. (The CLP method, however, mandates the separate calibration se-
quence—it is the onlymethod to do so.) Restek provides the calibration stan-
dards as a singlemix for laboratorieswishing to use only one calibrationmix
in their calibration curves (see the product listings beginning on page 18 for
details).
Although Rtx
®
-CLPesticides columns are available in all three common ID
dimensions, we typically recommend using the 0.32mm ID size. This size
provides the best combination of capacity and peak width (Figure 4). If your
sample extractsareparticularly contaminated, youmay find that the0.53mm
ID columns allow for longer duration of calibration, because of the large ca-
pacity (Figure 5). Columns of 0.25mm ID provide better resolution, but can-
nothandlecontaminatedor largesamples (Figure6). Inmostcases, the0.32mm
ID is the size of choice for this analysis.
When configuring the column pair, use a 5m section of guard tubing to con-
nect the glass “Y” to the injection port. This allows enough of a retention gap
so that the sample is evenly split into the two columns. The best flow rates
and oven programs are listed on the chromatograms, but it is possible to get
a total run time as low as 16minutes using hydrogen as a carrier gas (Figure
7). Some laboratories may not be comfortable using hydrogen, though it af-
fordsa shorter run time. Inany event, bothheliumandhydrogenworkwell as
a carrier gaswhenusing Rtx
®
-CLPesticides columns for this analysis.
The separations of US EPA Method 508 pesticides (Figure 8) and US EPA
Method 8151 herbicides (Figure 9) also are shown because these analyses
typically are run on the same instrument as the chlorinated pesticides al-
ready shown. It is important to note that Rtx
®
-CLPesticides columns also ex-
hibit baseline separation for these compounds, except for a few that are not
commonlyobserved.TheRtx
®
-CLPesticidescolumnand theRtx
®
-CLPesticides2
column combination results in the resolution of all compounds, allowing the
use of one column pair and the same instrument flow rate formany different
analyses.
Summary
Although the analysis of chlorinated pesticides historically has been one of
themore difficult tests performed by environmental testing laboratories, us-
ingRestek’sRtx
®
-CLPesticides columns, coupledwith themethods presented
in this guide will make your analyses easier. Optimized sample preparation
and extract cleanup, the proper injection technique, suitable analytical col-
umns and standards, and accurate quantitation will improve your results
and increase your lab’s throughput.
When problems occur, using proper troubleshooting andmaintenance tech-
niques can quickly reestablish system integrity. When faced with difficulties
in your pesticide or PCB analysis, remember that the majority of problems
occur during the sample preparation and cleanup step, or at the injection
port of the GC. If you are still having difficulties with your analysis after fol-
lowing the steps in this guide, please contact Restek’s technical service at
800-356-1688, ext. 4, andwe will be happy to help you.
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Figures 6–9 are shown on
pages 16 and17. Product
listings beginonpage 18.
Rtx
®
-CLPesticidesand
Rtx
®
-CLPesticides2columns
baseline resolve all 22
chlorinatedpesticides (USEPA
Methods 8081, CLP, and608)
inunder 25minutes. See page
18 for ordering information.
