• 18 •
800-356-1688 •
2005vol. 1
Chlorinated phenoxyacid acid herbicides used to
control broadleaf weeds are very persistent
contaminants in the environment, particularly in
drinkingwater.These strongly polar compounds
readily contribute to hydrogen bonds, making
them poorly volatile and strongly adsorptive to
chromatographic stationary phases. As a conse-
quence, chlorophenoxyacid herbicides are diffi-
cult to analyze by GC.Tomake these compounds
suitable for GC analysis theymust be deriva-
tized tomethyl esters.Themost common deriva-
tization reagent is diazomethane. US
Environmental Protection AgencyMethod 515.4
describes a derivatization procedure using dia-
zomethane and an analysis of themethylated
esters usingGCwith an electron capture detec-
tor (ECD).The target list of Method 515.4 phe-
noxyacid herbicides consists of carboxylic acids
and phenols.
Whenmonitoring thesemethylated esters by
GC/ECD two columns are needed, to provide
identification and confirmation. Further, it is
important to select stationary phases that have
low bleed and high thermal stability, because
the columns should be heated between analyses
to drive off any retainedmaterials.The primary
column chosen for this analysis is a 30m,
0.32mm ID, 0.25µmRtx
®
-CLPesticides2 column.
The Rtx
®
-CLPesticides2 stationary phase is high-
ly selective for electronegative compounds and
so is very effective in analyses of chlorophe-
noxyacid herbicides (Figure 1).We selected our
new, intermediate-polarity Rtx
®
-440 column as
the confirmation column because it has unique
selectivity for chlorinated pesticides and is ther-
mally stable to340ºC. Figure2 showsananalysis
ofmethylated chlorophenoxyacidherbicidesona
30m, 0.32mm ID, 0.25µmRtx
®
-440 column.
Resolution isgood, and the columnexhibits very
lowbleedat 340ºC. In combination, the two
columns resolveall target compounds, and the
reverse inelutionorder helpsensure correct iden-
tifications. Both columnsprovide fast analyses.
To design a chlorophenoxyacid herbicide refer-
encematerial suitable for GC/ECD, detection
limits should be determined for each compound
in themix. Because the ECD is highly sensitive,
and exhibits a narrow range of linear detection,
concentrations of the target compoundsmust be
determined carefully. Additionally, chlorinated
phenoxyacid herbicides are photosensitive and
heat-labile, so thematerialsmust be packaged
in amber ampuls and kept away from heat.
Restek now offers a complete set of reference
materials forMethod 515.4: a chlorinated acids
calibrationmix, amethylated chlorinated acids
calibrationmix, a surrogate standard (2,4-
dichlorophenylacetic acid), and an internal stan-
dard (4,4'-dibromooctafluorobiphenyl). Note that
the acidsmixwill degrade readily in the pres-
ence of alkaline compounds or strong oxidizers,
andworking solutionsmust be prepared in acid-
ified glassware.The surrogate standard and
internal standard are per recommendations in
the EPAmethod.We selected the solvents for
the surrogate standard and internal standard
carefully, to ensure compatibilitywith the cali-
brationmixes, andwe prepare both standards
at high concentrations, formore economical
analysis.
If you are analyzing chlorophenoxyacid herbi-
cides, andwant fast analyses and reliable
results, we highly recommend the combination
of an Rtx
®
-CLPesticides2 column and an Rtx
®
-
440 column, together with our complete set of
referencematerials.
GC/ECDAnalysisofChlorophenoxyacid
Herbicides
Using Columnswith Complementing Selectivity andNewReferenceMixes
by John Lidgett, Analytical ReferenceMaterialsTechnical Specialist
•Optimized analysis on two stationary phases.
•Complete set of referencemixes for US EPAMethod 515.4.
•Acids /methyl esters calibrationmixes are at concentrations designed for GC/ECD.
Figure1
Chlorophenoyxacidmethyl esters arewell separatedonanRtx®-CLPesticides2 column.
Figure2
Good resolutionof chlorophenoyxacidmethyl estersonanRtx®-440 column.
In combination, anRtx®-CLPesticides2 columnandanRtx®-440 column resolveall target compounds
andprovide fast results.
Compound
Conc. (µg/mL)
1. dalaponmethyl ester
100
2. 3,5-dichlorobenzoic acid
methyl ester
50
3. dicambamethyl ester
50
4. dichloropropmethyl ester
100
5. 2,4-Dmethyl ester
100
6. pentachloroanisole
10
7. 2,4,5-TP (Silvex) methyl ester 25
8. 2,4,5-Tmethyl ester
25
9. chlorambenmethyl ester
50
10. 2,4-DBmethyl ester
100
11. dinosebmethyl ester
100
12. bentazonmethyl deriv.
100
13. DCPAmethyl ester (Dacthal
®
) 100
14. piclorammethyl ester
50
15. quincloracmethyl ester
50
16. acifluorfenmethyl ester
50
Column:
Rtx-CLPesticides2
®
30m, 0.32mm ID, 0.25µm (cat.# 11324)
Sample:
10-100µg/mL eachmethyl ester inMTBE (cat.# 32444)
Inj.:
1.0µL splitless (hold 0.45min.), 4mm Siltek
®
double gooseneck splitless liner (cat.# 20784)
Inj. temp.:
225°C
Carrier gas:
helium, constant pressure
Inlet pressure:
10.5psi set@ 70°C
Oven temp.:
70°C (hold 1min.) to 210°C@ 20°C/min. (hold 1min.) to 300°C@ 5°C/min.
Det.:
ECD@ 320°C
GC_EV00755
Compound
Conc. (µg/mL)
1. dalaponm.e.
100
2. 3,5-dichlorobenzoic acid m.e. 50
3. dicambam.e.
50
4. dichlorpropm.e.
100
5. 2,4-Dm.e.
100
6. pentachloroanisole
10
7. 2,4,5-TP (Silvex) m.e.
25
8. chlorambenm.e.
50
9. 2,4,5-Tm.e.
25
10. 2,4-DBm.e.
100
11. dinosebm.e.
100
12. bentazon (methyl deriv.)
100
13. picloramm.e.
50
14. DCPA m.e. (Dacthal
®
)
100
15. quincloracm.e.
50
16. acifluorfenm.e.
50
GC_EV00756
Column:
Rtx
®
-440 30m, 0.32mm ID, 0.25µm (cat.# 12924)
Sample:
10-100µg/mL eachmethyl ester inMTBE (cat.# 32444)
Inj.:
1.0µL splitless (hold 0.45min.), 4mm Siltek
®
double gooseneck splitless liner (cat.# 20784)
Inj. temp.:
225°C
Carrier gas:
helium, constant pressure
Inlet pressure:
10.5psi set@ 70°C
Oven temp.:
70°C (hold 1min.) to 210°C@ 20°C/min. (hold 1min.) to 300°C@ 5°C/min.
Det.:
ECD@ 320°C
quantity
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