ADV01-05_1-298

• 18 •

800-356-1688 •

www.restek.com

2005 vol. 1

Chlorinated phenoxyacid acid herbicides used to

control broadleaf weeds are very persistent

contaminants in the environment, particularly in

drinking water. 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. To make these compounds

suitable for GC analysis they must be deriva-

tized to methyl esters. The most common deriva-

tization reagent is diazomethane. US

Environmental Protection Agency Method 515.4

describes a derivatization procedure using dia-

zomethane and an analysis of the methylated

esters using GC with an electron capture detec-

tor (ECD). The target list of Method 515.4 phe-

noxyacid herbicides consists of carboxylic acids

and phenols.

When monitoring these methylated 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 retained materials. The primary

column chosen for this analysis is a 30m,

0.32mm ID, 0.25µm Rtx

-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 to 340ºC. Figure 2 shows an analysis

of methylated chlorophenoxyacid herbicides on a

30m, 0.32mm ID, 0.25µm Rtx

-440 column.

Resolution is good, and the column exhibits very

low bleed at 340ºC. In combination, the two

columns resolve all target compounds, and the

reverse in elution order helps ensure correct iden-

tifications. Both columns provide fast analyses.

To design a chlorophenoxyacid herbicide refer-

ence material suitable for GC/ECD, detection

limits should be determined for each compound

in the mix. Because the ECD is highly sensitive,

and exhibits a narrow range of linear detection,

concentrations of the target compounds must be

determined carefully. Additionally, chlorinated

phenoxyacid herbicides are photosensitive and

heat-labile, so the materials must be packaged

in amber ampuls and kept away from heat.

Restek now offers a complete set of reference

materials for Method 515.4: a chlorinated acids

calibration mix, a methylated chlorinated acids

calibration mix, a surrogate standard (2,4-

dichlorophenylacetic acid), and an internal stan-

dard (4,4'-dibromooctafluorobiphenyl). Note that

the acids mix will degrade readily in the pres-

ence of alkaline compounds or strong oxidizers,

and working solutions must be prepared in acid-

ified glassware. The surrogate standard and

internal standard are per recommendations in

the EPA method. We selected the solvents for

the surrogate standard and internal standard

carefully, to ensure compatibility with the cali-

bration mixes, and we prepare both standards

at high concentrations, for more economical

analysis.

If you are analyzing chlorophenoxyacid herbi-

cides, and want 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

reference materials.

GC/ECD Analysis of Chlorophenoxyacid

Herbicides

Using Columns with Complementing Selectivity and New Reference Mixes

by John Lidgett, Analytical Reference Materials Technical Specialist

•Optimized analysis on two stationary phases.

•Complete set of reference mixes for US EPA Method 515.4.

•Acids / methyl esters calibration mixes are at concentrations designed for GC/ECD.

Figure 1

Chlorophenoyxacid methyl esters are well separated on an Rtx®-CLPesticides2 column.

Figure 2

Good resolution of chlorophenoyxacid methyl esters on an Rtx®-440 column.

In combination, an Rtx®-CLPesticides2 column and an Rtx®-440 column resolve all target compounds

and provide fast results.

Compound

Conc. (µg/mL)

1. dalapon methyl ester

100

2. 3,5-dichlorobenzoic acid

methyl ester

3. dicamba methyl ester

4. dichloroprop methyl ester

100

5. 2,4-D methyl ester

100

6. pentachloroanisole

7. 2,4,5-TP (Silvex) methyl ester 25

8. 2,4,5-T methyl ester

9. chloramben methyl ester

10. 2,4-DB methyl ester

100

11. dinoseb methyl ester

100

12. bentazon methyl deriv.

100

13. DCPA methyl ester (Dacthal

) 100

14. picloram methyl ester

15. quinclorac methyl ester

16. acifluorfen methyl ester

Column:

Rtx-CLPesticides2

30m, 0.32mm ID, 0.25µm (cat.# 11324)

Sample:

10-100µg/mL each methyl ester in MTBE (cat.# 32444)

Inj.:

1.0µL splitless (hold 0.45 min.), 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 1 min.) to 210°C @ 20°C/min. (hold 1 min.) to 300°C @ 5°C/min.

Det.:

ECD @ 320°C

GC_EV00755

Compound

Conc. (µg/mL)

1. dalapon m.e.

100

2. 3,5-dichlorobenzoic acid m.e. 50

3. dicamba m.e.

4. dichlorprop m.e.

100

5. 2,4-D m.e.

100

6. pentachloroanisole

7. 2,4,5-TP (Silvex) m.e.

8. chloramben m.e.

9. 2,4,5-T m.e.

10. 2,4-DB m.e.

100

11. dinoseb m.e.

100

12. bentazon (methyl deriv.)

100

13. picloram m.e.

14. DCPA m.e. (Dacthal

)

100

15. quinclorac m.e.

16. acifluorfen m.e.

GC_EV00756

Column:

Rtx

-440 30m, 0.32mm ID, 0.25µm (cat.# 12924)