Water/Wastewater

Determination of Routinely Monitored Herbicides in Drinking Water Samples Using Automated Solid Phase Extraction Prior to Liquid Chromatography/Tandem Mass Spectrometry

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Most countries have regulations or monitoring programs to research and track the level of herbicide contaminants in drinking water. Many populations obtain drinking water from ground water supplies, and it is these supplies that are at potential contamination risk from leaching contaminants, such as herbicides.1   The US EPA has implemented an exposure research program aimed at conducting drinking water research on methods as part of the Microbiological and Chemical Exposure Assessment. This research is aimed at evaluating the chemical pollutants and their role and levels in which there is an unacceptable risk to either humans or wildlife, as well as evaluating the methodologies currently being used to determine levels of chemical pollutants.2 

 

 LC/MS/MS Analysis:

• System:  Waters Micromass Quattro Mass Spectrometer

Column:  Agilent Zorbax SB-C8, 3.0-mm X 100mm, dp= 5 um  

• Pre-Column:  Upchurch pre-column filter, 0.5µm frit

• HPLC System:  Waters Alliance Model 2690 

• Injection Volume: 50 µL

Results:

Calibration standards were injected before and after water sample spikes. A 7-point calibration curve was used with levels ranging from 200 ppb to 0.6 ppb, with Alachlor OXA linearity results at 0.9996 (Figure 2).  An example calibration standard chromatogram and mass spectra is shown in Figure 3. An example water sample spike chromatogram and mass spectra is shown in Figure 4. Blank injections were performed as part of the injection sequence, with herbicide compound levels lower than what could be quantitated.  

Recoveries were calculated for the full suite of 12 compounds.  Average recoveries from the triplicate water samples were reported, as well as %RSD values (Table 2).

Herbicide Compound Name

Mean Recovery (n=3)

% RSD (n=3)

Acetochlor

111

5.8

Acetochlor OXA

112

9.6

Acetochlor ESA

132

7.7

Alachlor

111

5.9

Alachlor OXA

108

10.7

Alachlor ESA

135

9.6

Dimethenamid

101

4.6

Dimethenamid OXA

102

8.2

Dimethenamid ESA

96

5.8

Metolachlor

98

5.9

Metolachlor OXA

99

11.7

Metolachlor ESA

111

9.4

 

Conclusion: 

Recovery determination of a suite containing 12 chloroacetanilide and chloroacetanilide metabolites can utilize simple automation to concentrate the SPE step for determination of levels within regulatory limits for drinking water samples.  Automated solid phase extraction provides excellent recoveries for these herbicide compounds and compound metabolites. In addition, automation of the extraction procedure provided less technician intervention, creating a more efficient laboratory workflow, resulting in more reproducible performance. 

The use of the SmartPrep Extractor to concentrate and cleanup water samples produced LC/MS/MS results that passed the requirements for mean recovery of water samples being 50-150% of the true spiked value of each of the 12 herbicide compounds, as well as passing the requirements for meeting the <20% RSD criteria for the precision criteria of the same water samples. Resulting recoveries ranged from 96 – 135%, with reproducibility ranging from 5.8% to 11.7%.  Method detection levels were at 0.6 ppb.  Blank injections resulted in no quantifiable herbicide compounds to report.

 

References:

1. Tatarkova, V., Hiller, E., and Halko, R. (2014): Retention Characteristics of Acetochlor in Soils Collected from Different Depths in Relation to Soil Properties, Soil & Water Res., 9, (2): 58–65.

2. US EPA Drinking Water Methods Developed by EPA’s Exposure Research Program (http://www.epa.gov/nerlcwww/ordmeth.htm), last visited on October 10, 2014.

3. Tomlin C.D.S. (2001): The E-pesticide Manual. Version 2.0. 12th Ed. British Crop Protection Council, [CD-ROM]. 

4. Official Journal of the European Communities (1998):  Council Directive 98/83/EC, L 330/32.

5. US EPA Method 535, Measurement of Chloroacetanilide and Other Acetamide Herbicide Degradates in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS), Version 1.1, April 2005, J.A. Shoemaker and M.V. Bassett, National Exposure Research Laboratory.

6. Water-Technology website:  (http://www.water-technology.net/contractors/wastewater/-nsf-international-global-testing/pressnsf-develops-water-treatment-device-standard.html).

7. NSF website:  (http://www.nsf.org/newsroom/emerging-contaminants-in-driking-water-cause-consumer-health-concerns/), , last visited on October 10, 2014. 

8. Environmental Protection Agency, 40 CFT Part 141, EPA-HW-OW-2012-0155; FRL-9917-87-OW, Announcement of Preliminary Regulatory Determinations for Contaminants on the Third Drinking Water Contaminant Candidate List.

9. Environmental Protection Agency, Reregistration Eligibility Decision (RED), EPA 738-R-98-020, December 1998.


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