Duration: 10/01/2003 to 09/30/2008

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Isolation of crop management chemicals from water presents many different problems. Large volumes of water must be extracted to obtain the sensitivity necessary for governmental regulations. Often large volumes of water have to be refrigerated and transported to analytical laboratories. Depending on the methods of shipment this can be expensive as well as difficult to obtain without interferences and breakage. Possible chemical degradation of the sample prior to analysis and the EPA suggestion that analysis be accomplished within 24 hours can also impose complications.

In addition to these technical difficulties, the analysis of some crop management chemicals in the past has typically consumed large volumes of solvents, which then become large volumes of hazardous wastes that laboratories must dispose of properly. The need for the analysis of crop management chemicals is not likely to end in the near future even though the amount of organically grown produce is increasing at a rate of approximately 20% each year in the United States (NRC report). The National Research Council report (Berenbaum et al., 2000) suggested that there is no indication that chemical pesticides will be abandoned in the near future. The committee associated with the report concluded that chemical pesticides will continue to play a significant role in US agriculture for at least another decade because of two major factors:

Effective and affordable alternatives to crop management chemicals are not universally available

Environmental compatibility and safety of newer crop management chemicals is increasing.

Reluctance of some countries and people to accept the use of genetically modified foods will also result in a continued reliance on the use of crop management chemicals for controlling plant diseases, weed species and insects in the foreseeable future.

Due to the continuing use of crop management chemicals in US agriculture there needs to be a continued improvement in the methodology used for the extraction and analysis of these chemicals. Work associated with a previous Multi-State Regional project has indicated that solid phase extraction (SPE) techniques can be used for the extraction of pesticides at one site with shipment of disks to a second analytical laboratory with minimal losses (Mueller et al., 2000). This technique has been tested with a variety of pesticides. These SPE procedures seem to be generally applicable, although some pesticides such as bifenthrin, chlorpyrifos and chlorothalonil, gave low recoveries from water (Mersie et al., 2002).

SPE extraction disks have been available for many years and they have several advantages in that they are particularly effective when extractions from large volumes of water with a corresponding increase in sensitivity are needed. There are several different types of disks currently available for different compounds. The use of these disks can eliminate the need for large amounts of organic solvents during the extraction procedure. Several problems have been associated with the use of these disks especially in field situations. These problems include the need for glassware for an extraction manifold which can be easily broken, realignment of the disk at a cooperating laboratory after the disk has been transported from the extraction site to the site of analysis even when laboratories have the same type of manifold, and the need to pre-filter turbid surface water samples prior to disk extraction.

New approaches to the use of solid phase extraction may eliminate problems noted in earlier research (Mueller et al., 2000, Senseman et al., 2003). Companies are continually introducing new products to be used in the extraction of various crop management chemicals from water which could alleviate some of the problems known in extraction procedures. It is necessary to investigate these new products and develop procedures which can be utilized throughout the world to obtain reliable accurate results. Testing of these materials across a multidisciplinary interlaboratory group and transporting these materials across state and regional borders provides the basis for the widespread utilization of these procedures for various applications while proving the validity and robustness of the procedures. Research concerning the applicability, robustness, and validity of a new analytical procedure is necessary before a procedure can be widely adapted for use in the analysis of crop management chemicals. The research proposed in this project will have a significant impact on the development of better and more environmentally friendly procedures while developing methods that can be used in remote field situations, where laboratory and analytical equipment for analysis may be unavailable.

The added advantage of this research is that it will be applicable to many important environmental chemicals. These chemicals may include pesticides as well as mycotoxins, plant growth regulators, and animal and secondary plant products which are associated with agricultural operations. The research is also applicable to various industrial chemicals associated with water resources.

The proposed research is appropriate to two of the goals outlined for the Southern Region Priority areas for Multi-State Research activities. These goals are: Goal 4. Greater Harmony between Agriculture and the Environment and Goal 5. Enhanced Economic Opportunity and Quality of Life for American. The improvement in analytical techniques for the analysis of crop management chemicals is important to air, soil and water resource conservation and enhancement, natural resource and ecosystem management, environmental policies and regulations, risk management and assessment in agricultural systems, and agriculture-related social and consumer concerns which are associated with these Goals. To accomplish these goals we have to be able to provide valid and sensitive analytical techniques for the presence of crop management chemicals upon which the general public and our stakeholders can rely. The development of new and improved methodology for the detection, extraction and analysis of crop protection chemicals as well as other chemicals associated with agricultural operations must be conducted by a multidisciplinary interlaboratory group. The reasons for this are often illustrated when one laboratory is unable to reproduce methods published by a second laboratory. The use of an interlaboratory group in method development allows for the identification of problems in the early stages of method development. The time involved in the development of new EPA and FDA methods illustrates how slow this process can be. Their methods must be extensively tested in multiple laboratories prior to their approval. The group assembled to conduct this research has different research emphasis areas such as crop, soil and plant sciences, pesticide research, watershed research, biochemistry, and water quality and environmental toxicology. This mix provides a good basis of individuals with knowledge to identify potential problem chemicals which can be incorporated into the research. The soil and water resources associated with member sites also provide different climatic and geological sites for testing of procedures. For example, research in a previous multistate project showed that Puerto Rico had problems related to high humidity when compared to Texas and methods were amended to obtain a final method that was amenable to both sites. This type of collaborative development is expected in the proposed research. The consequences of not conducting this research will be that the adaption of more environmentally friendly extraction and analysis methods will be slowed.

Related, Current and Previous Work

As agricultural research has become more related to biotechnology fewer individuals are conducting research in or being trained in the analysis and extraction of crop management chemicals. The general public however continues to ask for the analysis of more water samples for these chemicals. The public is also requesting that lower levels of sensitivity be obtained while using more environmentally friendly extraction procedures.

In the previous Multi-State Research project, work was conducted to determine if solid phase extraction disks could be used to extract pesticides from water samples at one site, then be shipped to another site for analysis. Results indicated that shipping disks eliminated problems associated with the shipment of water samples, and possible pesticide degradation. Shipping the disks containing pesticides instead of water did not affect the recovery of atrazine, chlorpyrifos, and metolachlor, however, recovery results were variable with bromacil (Mueller, et al., 2000).

Several problems were noted during the conduct of this research such as the difficulty of realigning disks in extraction manifolds at a second site even when using exactly the same type manifold and the usage of the glassware associated with the manifold was not deemed suitable for field situations. Due to the variability of analytical conditions used in different laboratories associated with the study, research was conducted to examine variability of samples when all samples were analyzed at one site compared to the variability of samples analyzed in-house. Based on this study a majority of the variability observed in the previous study is accounted for by the variation in analytical conditions at the various sites (Senseman, et al., 2003).

Additional pesticides were tested using the procedure with the shipment of disks to a second site for comparison to analysis conducted in house. These chemicals included chlorothalonil, alachlor, metalaxyl, bifenthrin, fenamiphos, acetochlor, cyanazine, disulfoton, ametryne, and metribuzin. Results indicated that some compounds such as bifenthrin were not well suited to the methodology (Mersie, et al. 2002). Investigation of variations in the methods and the use of other solid phase extraction matrices is needed to determine possible alternatives to improve the recovery of these previously identified problem chemicals.

Presently, new SPE matrices are being developed which might result in better extraction procedures and ones which are more amenable to moving the extraction procedure into field situations. For example, J. T. Baker has designed a solid phase extraction disk enclosed in a plastic housing that attaches to the most commonly used manifolds. This setup would eliminate the problem of realignment of disks at the cooperating laboratory and would eliminate the need for fragile glassware associated with previous systems in field extraction situations. These Speedisk. extraction disks can also be purchased with a prefilter associated with the setup making the extraction process a one step filtration process. These types of SPE disks could possibly be utilized in field situations with turbid, dirty water samples. Testing across an interlaboratory group could determine the feasibility of using these SPE disks in field situations for extraction with shipping to distant sites for analysis.

The use of other disk matrices instead of octyldecyl silica may also be a solution for the analysis of compounds which are not amenable to the previously tested methodology. Recent research has also shown that different solid-phase extraction matrices can be layered to improve the recovery of certain crop protection chemicals (Ferrer, et al., 1999).

Another possible SPE method uses a fiber technique (solid phase microextraction) that has been commercially available since 1994 and has been advertised as being effective with small samples (< 50 mL) (general review, Lord and Pawliszyn, 2000). Utilization of these fibers would eliminate filtration and therefore the problems associated with turbidity and suspended material in samples could possibly be eliminated. The possibility of utilizing these fibers may be limited by high levels of organic matter in samples. The use of the commercially available fibers (Supelco) has been reported for the extraction of various crop management chemicals in various laboratories (Aguilar et al, 1999; Beltran et al, 1998, 2000; Dugay et al., 1998; Lord and Pawliszyn, 2000; Tomkins and Ilgner, 2002). The broad applicability of these fibers and their limitations have not been widely researched. The detection limits of these fibers and applicability to pesticide detection at low levels in water samples need to be further investigated. Extraction using these fibers followed by transportation to another site has not been reported. Previous research has shown that the fibers were able to detect organophosphorus pesticides between 2 and 8 ug/L using a 10 mL sample volume (Tomkins and Ilgner, 2002). Multi-fibers (C18 bonded silica) have been shown to have high absorption rates and high extraction efficiencies, enabling the positive identification of unknown compounds at sub-part-per-billion levels in full scan mode with a benchtop quadrupole GC/MS (Xia and Leidy, 2001). The adsorption rate was highest when fibers were prewet with acetone and magnetic stirring of water samples was used during extraction.

Currently there are less than five individual CRIS projects relating to the development of analytical methods for crop management chemicals in water or in looking for ways to improve the methodology associated with the extraction and analysis of these chemicals from water. Of these projects, several are associated with members of the previous Multi-State Research project or are members of the currently proposed project. This project is the only project proposing to investigate methods for the extraction of samples in remote field sites with shipment of samples to a separate site for analysis. This could be especially important when working in areas with minimal resources available for the analysis of chemical residues. Improved methodology is needed, and the ability to conduct interlaboratory studies before the release of new methods is a vital component in developing methodology which can be recommended for use.

Objectives

1. Compare and evaluate various solid phase extraction techniques using disk, fiber and cartridge devices for sampling water for a wide range of crop management chemicals
   
2. Investigate the storage stability and transportability of crop management chemicals extracted utilizing various SPE matrices for application to field extraction procedures
   
3. Investigate the problems associated with the usefulness of successful SPE matrices for investigations involving turbid water samples
   
4. Investigate the feasibility of using developed procedures for field extractions for crop protection chemicals
   
5. 
   

Methods

(Year 1, Objectives 1 and 2) - AR, MS, PR, SC, TN, TX, VA , Kentucky State University, USDA-ARS, Virginia State University Compare the use of Speedisk. C18XF (contains a prefilter)and fiber SPE's with previously investigated Empore. disks for the extraction and transport of pesticides from distilled water for the extraction of four pesticides (atrazine, metolachlor, chlorothalonil and chlorpyrifos). This group of crop management chemicals includes two herbicides, one insecticide, and one fungicide. These chemicals were selected because they have Sw's (water solubilities) ranging from 0.4 to 530 mg/L and Koc's (soil organic carbon sorption coefficient) ranging from 100 to 6070. To conduct this investigation standards for addition to samples will be made up at one site and shipped to all other sites for spiking of samples. At each site three non-fortified distilled water samples and three fortified distilled water samples will be extracted and analyzed utilizing each of the SPE matrices on site. In addition three non-fortified distilled water samples and three fortified distilled water samples utilizing each matrix will be extracted and then shipped to a corresponding site (See listing at the end of this section). Extraction procedures are outlined in Appendix 1-3. Samples extracted utilizing the Speedisk. C18XF will not be filtered prior to extraction. These tests will indicate the variability of recovery percentages associated with the different types of C18 matrices. In shipment of samples, Hobo dataloggers (Onset Computer Corporation) will be included to determine the variability of temperatures that extraction matrices are exposed to during shipment from one site to another. The correlation between temperature and recovery percentages at the sites following shipment will be determined. The objective in shipping matrices without dry ice or blue ice containers is to reduce costs associated with shipping and minimize equipment and supplies needed in field situations where minimal resources may be available. Field extraction apparatus will be constructed at the various sites based on work previously published with minor modification for the utilization of Speedisk. (See Figure for field extraction setup in Appendix 4. The use of Speedisk will eliminate the need to pre-filter water samples and will reduce the breakable glassware associated with the extraction apparatus (Mattice, et al. 2002). (Year 2, Objective 3 and 4) - AR, MS, PR, SC, TN, TX, VA , Kentucky State University, USDA-ARS, Virginia State University Compare the use of Speedisk. C18XF (contains a prefilter) and fiber SPE's with previously investigated Empore. disks for the extraction and transport of pesticides from local surface water samples for the extraction of four pesticides (atrazine, metolachlor, chlorothalonil and chlorpyrifos). To conduct this investigation, standards for addition to samples will be made up at one site and shipped to all other sites for spiking of samples. At each site three non-fortified local water samples and three fortified local water samples will be extracted and analyzed utilizing each of the SPE matrices on site. In addition three non-fortified local water samples and fortified spiked local water samples utilizing each matrix will be extracted and then shipped to a corresponding site (See last paragraph of this section). Extraction procedures are outlined in Appendix 1-3. Samples extracted utilizing the Speedisk. C18XF will not be filtered prior to extraction. These tests will indicate the variability of recovery percentages associated with the turbidity of various water samples and also the possibility of utilizing the Speedisk. C18XF with turbid samples from various sites without prefiltration. These tests will also give an indication of the variability and recovery percentages associated with not prefiltering samples using the Speedisk. C18XF. Hobo's will be included with all shipment of samples to determine the variability of temperatures that extraction filters are exposed to during shipment from one site to another. The correlation between temperature and recovery percentages at the sites following shipment will be determined. The objective in shipping matrices without dry ice or blue ice containers is to reduce costs associated with shipping and minimize equipment and supplies needed in field situations where minimal resources may be available. Local water will be characterized based on the determination of pH, total solids, total dissolved solids, and total suspended solids (American Public Health Association, 1998). Initial testing of the field extraction apparatus will be conducted utilizing distilled water and the addition of the standard pesticide mix. At each site three non-fortified distilled water samples and three fortified distilled water samples will be extracted and analyzed back in the laboratory associated with the site. In addition three non-fortified distilled water samples and three fortified distilled water samples will be extracted and then shipped to a corresponding site. (Year 3, Objectives 1 and 2) - AR, MS, PR, SC, TN, TX, VA , Kentucky State University, USDA-ARS, Virginia State University Compare the use of Oasis cartridge (Waters Corporation), Speedisk. C18XF, Empore disk and fiber SPE's for the extraction and transport of pesticides from distilled water for additional crop management chemicals especially newer crop protection compounds as agreed upon by committee members. Degration products of important agrochemicals will also be investigated. Selection of chemicals will be based on chemicals that are being found to be problems in the various sites and which are being more commonly used. Decisions concerning the chemicals tested will be determined during the previous years annual meeting and between the corresponding sites. Based on information from the Hobo temperature data and recovery percentages alterations may be made in the shipment conditions of samples (possible addition of frozen blue ice and styrofoam containers). The field extraction apparatus will be tested in a field situation at each site with samples being analyzed at the site with an identical group of samples being sent to the corresponding laboratory for analysis. (Year 4, Objectives 2, 3, and 4) - AR, MS, PR, SC, TN, TX, VA , Kentucky State University, USDA-ARS, Virginia State University Compare the use of Oasis cartridge, Speedisk. C18XF, Empore disk and fiber SPE's for the extraction and transport of pesticides from a local surface water for the extraction of chemicals utilized in studies the previous year. Additional tests utilizing possible stacking of disks (Ferrer, et al., 1999) may be conducted depending on previous results and the occurence of compounds and degradation products which are identified to have lower recoveries. Local water will be characterized based on the determination of pH, total solids, total dissolved solids, and total suspended solids (American Public Health Association, 1998). Field extractions will be conducted with the local water samples and the same crop management chemicals and compared to the samples conducted completely in the laboratory after the collection of the samples. A identical set of samples will be sent to corresponding laboratory for determination of transportability. (Year 5, Objective 4) - AR, MS, PR, SC, TN, TX, VA , Kentucky State University, USDA-ARS, Virginia State University Compare the use of cartridge, Speedisk. C18XF, and fiber SPE's for the extraction and transport of pesticides from water samples fortified and extracted at a field site followed by transport and analysis at a local analytical laboratory. A corresponding set of samples will be shipped to a corresponding laboratory (See last paragraph of this section). Changes may be made in specific chemicals based on chemicals that are being found to be problems in the various sites and the addition of new crop protection chemicals for which analytical methodology is limited. In laboratories the storage stability of Oasis cartridges, Speedisk, and Empore disk will be conducted by placing 3 replicates of each material at each of three conditions (0 C, ambient tempberature and 45 C) for 7 d. These temperatures have been noted in previous shipments. Additional testing will be conducted using new SPE technology as it becomes available. One such possibility is the multi-fiber which has been developed and tested in one of the previous cooperators laboratories but that is not yet commercially available. Another possiblity is use of a stir bar extractor. Laboratories involved in this project will be paired with another laboratory to test the feasibility of shipping samples after extraction instead of all of the extraction and analysis being completed in one site. This will be beneficial in determining the feasibility of trasnsporting samples from sites without analytical resources but which may have significant contaminant problems where analysis needs to be conducted. Interested individuals may be added to this project at any time and this may result in some alterations in pairings over the course of the project. Decisions concerning pairing of laboratories will be determined at the annnual meeting each year.

Measurement of Progress and Results

Outputs

• Comparisons of various solid phase extractive techniques and materials across multiple laboratories.
• Evaluation of storage stability and transportability of various solid phase matrices for the analysis of crop managment chemicals from water.
• Development of extraction methodology for analysis of crop management chemicals from water which is adaptable to field situations where analytical equipment is unavailable.
• Assessment of problems with surface water samples when using solid phase extraction methods for crop managment chemicals.

Outcomes or Projected Impacts

• Initial outcome is the development of a valid method which can be used for the extraction of crop management chemicals from water. These procedures can be used in laboratories throughout the world.
• Development of extraction methodology for crop management chemicals which can be utilized in field sites where analytical methodology is not available. This will allow samples to be extracted in any site and then shipped to distant location for analysis.
• Development of methods which are workable at various locations and can provide consistent results across these laboratories.

Milestones

(1):rst Year - Compare the use of Speedisk. C18XF (contains a prefilter) with previously investigated Empore. disks for the extraction and transport of pesticides from distilled water for the extraction of four pesticides (atrazine, metolachlor, chlorothalonil and chlorpyrifos). Begin development of field extraction apparatus at various sites.

(2):cond Year - Compare the use of Speedisk. C18XF (contains a prefilter) with previously investigated Empore. disks for the extraction and transport of pesticides from turbid water samples for the extraction of four pesticides (atrazine, metolachlor, chlorothalonil and chlorpyrifos) to determine the effect of sample turbidity. Begin initial testing of the field extraction apparatus at various sites. Submit for publication the results of the evaluation of the comparison of various C18 matrices (Journal of AOAC).

(3):ird Year - Compare the use of cartridge, Speedisk. C18XF, Empore disk and fiber SPE's for the extraction and transport of pesticides from distilled water for additional crop management chemicals especially newer chemicals and chemicals that are problems in various areas. This will determine the feasibility of the methodology for a wide range of chemicals. Make changes in field extraction apparatus technology as needed for obtaining reproducible results across the various laboratories. Submit for publication results of the effects of turbid water on extraction methodology for the initial compounds utilizing the various C18 matrices (Journal of AOAC).

(4):urth Year - Compare the use of cartridge, Speedisk. C18XF, Empore disk and fiber SPE's for the extraction and transport of pesticides from turbid local water for the extraction of chemicals tested during the previous year and determine feasibility of stacking disks to improve analysis of problem chemicals. Submit for publication the results of the extraction methodology for various newer crop protection chemicals and problem chemicals (Journal Agricultural and Food Chemistry).

(5):fth Year - Compare the use of cartridge, Speedisk. C18XF, and fiber SPE's for the extraction and transport of pesticides from water samples fortified and extracted at a field site followed by transport and analysis at a local analytical laboratory and compared to analysis done at a distant analytical laboratory. Submit for publication results of effects of turbid water on extraction of newer crop protection and problem chemicals as well as the use of extracting disks for improvement of recoveries (Journal of AOAC).

(6): Sixth Year - Submit for publication data from the various laboratories utilizing field extraction units and publish results with suggestions for best extraction at field sites and the shipment of these samples to distant analytical laboratories (Journal Agriculture and Food Chemistry).

Projected Participation

View Appendix E: Participation

Outreach Plan

The results of this project will be published in refereed publications in a timely manner following the completion of various components of the research. The research will also be presented by various professional association meetings as deemed appropriate by the members of the project. The research is most applicable to fellow researchers in the area of crop management chemical residue analysis and these are deemed to be the most appropriate avenues for reaching those individuals.

Organization/Governance

1. Officers.

All voting members of the project are eligible for office regardless of sponsoring agency affiliation. Each office must be held by a separate individual. Voting members are identified in Appendix E (one vote/entity).

The Chair in consultation with the Administrative Advisor, notifies the project members of the time and place of meetings, prepares the agenda, and presides at meetings concerning the project. Term of office is one year.

The Vice-Chairman records minutes and performs other duties as assigned by the project members or the Administrative Advisor, and is responsible for the preparation and submission of the Minutes and Annual Report of the Multi-State Research Project. Term of office is one year.

The Host Member arranges facilities for the annual meeting. The host member is a resident of the site for the meeting and makes local arrangements for lodging. Term of office is one year.


2. Executive Committee.

The Executive Committee consists of the Chairman, Vice Chairman, Past Chairman and Host Member, and will conduct the business of the Committee between meetings, consult as needed with the Administrative Advisor and perform other duties as assigned by the Committee. At each annual meeting The Executive Committee will nominate two voting members of the Multi-State Research Project to serve as the new Vice Chairman and Host Member. Alternative nominations shall be accepted from other voting members of the Committee and an election will be conducted to determine these officers. At the close of the yearly meeting the Vice Chairman will become the Chairman, the Chairman will become Past Chairman and the new officers will begin their term.

Literature Cited

Aguilar, C., A. Penalver, E. Pocurull, J. Ferre, F. Borrull, and R. M. Marce. 1999. Optimization of solid-phase microextraction conditions using response surface methodology to determine organochlorine pesticides in water by gas chromatography and electron-capture detection. J. Chrom. 844:425-432.

American Public Health Association. 1998. Standard Methods for the Examination of Water and Wastewater. L. S. Clesceri, A. E. Greenber, and A. D. Eaton, eds. American Public Health Association:Washington.

Beltran, J., F. J. Lopez, O. Cepria, and F. Hernandez. 1998. Solid-phase microextraction for quantitative analysis of organophosphorus pesticides in environmental water samples. J. Chrom. 808:257-263.

Beltran, J., F. J. Lopez and F. Hernandez. 2000. Solid-phase microextraction in pesticide residue analysis. J. Chrom. 885:389-404.

Berenbaum, M., M. Brusseau, J. Dipeitro, R. M. Goodman, F. Gould, J. Gunsolus, B. Hammock, R. Hartung, P. Marrone, B. Maxwell, K. Raffa, J. Ryals, J. Seiber, D. Shaner, and D. Zilberman. 2000. The Future Role of Pesticides in US Agriculture. National Academy Press:Washington

Dugay, J., C. Miege, and M. -C. Hennion. 1998. Effect of the various parameters governing solid-phase microextraction for the trace determination of pesticides in water. J. Chrom. 795:27-42.

Ferrer, I., D. Barcelo, and E. M. Thurman. 1999. Double-disk solid-phase extraction: simultaneous cleanup and trace enrichment of herbicides and metabolites from environmental samples. Anal. Chem. 71:1009-1015.

Lord, H., and J. Pawliszyn. 2000. Evolution of solid-phase microextraction technology. J. Chrom. 885:153-193.

Mattice, J. D., S. A. Senseman, J. T. Walker, and E. E. Gbur, Jr. 2002. Portable system for extracting water samples for organic analysis. Bull. Environ. Contam. Toxicol. 68:161-167.

Mersie, W., T. C. Mueller, S. A. Sensman, R. D. Wauchope, C. Clegg, R. W. Young, L. M. Southwick, M. B. Riley, H. A. Moye, J. A. Dumas, J. D. Mattice, and R. B. Leidy. 2002. Interlaboratory comparison of pesticide recovery from water using solid-phase extraction disks and gas chromatography. J. AOAC 85:1324-1330.

Mueller, T. C., S. A. Sensman, R. D. Wauchope, C. Clegg, R. W. Young, L. M. Southwick, M. B. Riley, H. A. Moye, J. A. Dumas, W. Mersie, J. D. Mattice, and R. B. Leidy. 2000. Recovery of atrazine, bromacil, chlorpyrifos, and metolachlor from water samples after concentration on solid-phase extraction disks: Interlaboratory study. J. AOAC 83:1327-1333.

Senseman, S. A., T. C. Mueller, T. C., R. D. Wauchope, C. Clegg, R. W. Young, L. M. Southwick, M. B. Riley, H. A. Moye, J. A. Dumas, W. Mersie, J. D. Mattice, and R. B. Leidy. 2003. An interlaboratory comparison of extraction efficiency of pesticides from surface and laboratory water using solid-phase extraction disks. J. AOAC (submitted for review).

Tomkins, B. A. and R. H. Ilgner. 2002. Determination of atrazine and four organophosphorus pesticides in ground water using solid phase microextraction (SPME) followed by gas chromatography with selected-ion monitoring. J. Chromatography A 972:183-194.

Xin-Rui, X. and R. B. Leidy. 2001. Preparation and characterization of porous silica coated multi-fibers for solid-phase microextraction. Anal. Chem. 73:2041-2047.

Attachments

Land Grant Participating States/Institutions

AR, GA, KY, MS, OK, PR, SC, TN, VA

Non Land Grant Participating States/Institutions

USDA, ARS