13 Minute Chlorophenoxyacid Herbicides Analysis

On New Rtx®-CLPesticides & Rtx®-CLPesticides2 Columns

Jason Thomas, Environmental Innovations Chemist

• Higher throughput compared to typical methods of 20 minutes or more.
• Use one column pair for multiple dual column ECD methods.
• Versatility and durability to harsh samples lead to longer life and less down time.

The analysis of chlorophenoxyacid herbicides is a very common assay performed routinely in most environmental laboratories today. Chlorophenoxyacid herbicides, as a group, are used to prevent the growth of broadleaf plants in agricultural fields. The most common, 2,4-D, was introduced around the end of World War II, and with simple additions or deletions of chlorine or methyl groups during production, a wide variety other herbicides can be produced. However, improper monitoring of manufacturing conditions can lead to undesirable impurities, such as 2,3,7,8-TCDD.

EPA Method 8151A, commonly used for chlorophenoxyacid herbicide analysis, involves the extraction of acidified aqueous samples with ethyl ether after a basic CH2Cl2 cleanup. The extracts are then concentrated to 10mL and derivatized to methyl ester form by either a diazomethane or PFBBr procedure. This methylation step is used to make the compounds more volatile, and hence, more amenable to gas chromatography (GC). GC analysis using an electron capture detector (ECD) is the analytical procedure of choice, although mass spectrometry is also used. ECD detection requires the use of second column confirmation for quantification of target analytes.

The Rtx®-CLPesticides and Rtx®-CLPesticides2 column pair is an excellent choice for chlorophenoxyacid herbicide analysis. Now, with an optimized film thickness for the 0.32mm ID version, this difficult analysis can be made in less than 13 minutes on both the primary and confirmation columns. Near baseline resolution is achieved for all analytes except for bentazon/picloram on the Rtx®-CLPesticides column; however, this pair is fully resolved on the Rtx®-CLPesticides2 column (Figure 1).

Figure 1: Excellent resolution of chlorophenoxyacid herbicides on the Rtx®-CLPesticides column pair.

dalapon methyl ester 3,5-dichlorobenzoic acid methyl ester (SS) 4-nitroanisole DCAA methyl ester (SS) dicamba methyl ester MCPP methyl ester MCPA methyl ester dichlorprop methyl ester 4,4?-DBOB (IS) 2,4-D methyl ester pentachloroanisole 2,4,5-TP methyl ester 2,4,5-T methyl ester chloramben methyl ester 2,4-DB methyl ester dinoseb methyl ester bentazon methyl ester DCPA picloram methyl ester acifluorfen methyl ester C. contaminant Column: Rtx®-CLPesticides2, 30m, 0.32mm ID, 0.25µm (cat.# RE11324) and Rtx®-CLPesticides, 30m, 0.32mm ID, 0.32µm (cat.# RE11141), with 5m x 0.32mm ID Rxi® deactivated guard tubing (cat.# RE10039), connected using Deactivated Universal "Y" Press-Tight® Connector (cat.# RE20405-261) Sample: 200ng/mL Herbicide Mix #1 (cat.# 32055) in hexane 1,000ng/mL Herbicide Mix #2 (cat.# 32057) in hexane 20,000ng/mL Herbicide Mix #3 (cat.# 32059) in hexane 200ng/mL Herbicide Mix #4 (cat.# 32062) in hexane 250ng/mL Herbicide Internal Standard (cat.# 32053) in hexane 400ng/mL Herbicide Surrogate (cat.# 32050) in hexane Inj.: 1.0µL splitless (hold 0.75 min.), 4mm Cyclo Double Gooseneck inlet liner (cat.# 20895) Inj. temp.: 250°C Carrier gas: helium, constant pressure Flow rate: 36cm/sec. @ 70°C Oven temp.: 70°C (hold 0.5 min.) to 190°C @ 25°C/min. (hold 1 min.) to 300°C @ 11°C/min. (hold 5 min.) Det.: ECD @ 325°C GC_EV00971-971A

In conclusion, the Rtx®-CLPesticides and Rtx®-CLPesticides2 column pair is an excellent choice for chlorophenoxyacid herbicide analysis due to the unique selectivity, low bleed, and durability of the columns. The Rtx®-CLPesticides column pair can also be used for other environmental ECD methods, including chlorinated pesticide analysis.