INTERLABORATORY COMPARISON OF EXTRACTION EFFICIENCY OF PESTICIDES FROM SURFACE AND LABORATORY WATER USING SOLID-PHASE EXTRACTION DISKS

Authors: SENSEMAN, SCOTT - TEXAS A & M UNIV.; MUELLER, THOMAS - UNIV. OF TN.; REILEY, MELISSA - CLEMSON UNIV.; Wauchope, Robert - Don; Clegg, Chris; YOUNG, RODDY - UNIV. OF VA.; Southwick Jr, Lloyd; MOYE, ANSON - UNIV. OF FL.; DUMAS, JOSE - UNIV. PUERTO RICO; MERSIE, WONDI - VA STATE UNIV.

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2003
Publication Date: 5/20/2003
Citation: SENSEMAN, S., MUELLER, T., REILEY, M., WAUCHOPE, R.D., CLEGG, C.M., YOUNG, R., SOUTHWICK JR, L.M., MOYE, A., DUMAS, J., MERSIE, W. INTERLABORATORY COMPARISON OF EXTRACTION EFFICIENCY OF PESTICIDES FROM SURFACE AND LABORATORY WATER USING SOLID-PHASE EXTRACTION DISKS. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 51:3748-3752. 2003.

Interpretive Summary: The Hatch Act Southern Region Technical Committee S-271, 'Pesticides in the Agricultural Environment' is a cooperative research project which brings together a group of Southeastern pesticide analytical chemists and environmental scientists to discuss methodology, keep each other up to date on pesticide issues, and develop interlaboratory projects to develop analytical techniques applicable to a wide variety of pesticides. This paper is one of three resulting from the preparation of standard very-low-concentration water solutions of 4 pesticides (atrazine, bromacil, chlorpyrifos and metolachor) and sharing them with all the laboratories to determine how reproducible our analytical methods are. We all used the 'solid phase extraction' (SPE) method, a widely-used method but one that has received little interlaboratory study. Results were complex. For all 4 pesticides there was good reproducibility of results within laboratories but measurable differences in results between laboratories and between analytical procedures. Generally atrazine and metolachor results were a success--they gave similar results between laboratories. Chlorpyrifos and bromacil were failures: extracted residues appear to be too unstable and/or volatile and results depended on laboratory technique and sample history in unpredictable ways. Clearly the SPE method needs to be validated for any given pesticide using the specific practices of the laboratory that plans to use it.

Technical Abstract: A continuation of an earlier interlaboratory comparison was conducted (1) to assess solid phase extraction (SPE) using Empore disks to extract atrazine, bromacil, metolachlor, and chlorpyrifos from various water sources accompanied by different sample shipping and quantitative techniques and (2) to compare quantitative results of individual laboratories with results of one common laboratory. Three replicates of a composite surface water (SW) sample were fortified with the analytes along with three replicates of deionized water (DW). A nonfortified DW sample and a nonfortified SW sample were also extracted. All samples were extracted using Empore C18 disks. After extraction, part of the samples were eluted and analyzed in house. Duplicate samples were evaporated in a 2 mL vial, shipped dry to a central laboratory (SDC), redissolved, and analyzed. Overall, samples analyzed in house had higher recoveries than SDC samples. Laboratory x analysis type and laboratory x water source interactions were significant for all four compounds. Seven laboratories participated in this interlaboratory comparison program. No differences in atrazine recoveries were observed from in house samples analyzed by laboratories A, B, D, and G compared with the recovery of SDC samples. In house atrazine recoveries from laboratories C and F were higher when compared with recovery from SDC samples. However, laboratory E had lower recoveries from in house samples compared with SCC samples. For each laboratory, lower recoveries were observed for chlorpyrifos from the SDC samples compared with samples analyzed in house. Bromacil recovery was <65% at two of the seven laboratories In the study. Bromacil recoveries for the remaining laboratories were >75%. Three laboratories showed no differences in metolachlor recovery; two laboratories had higher recoveries for samples analyzed in house, and two other laboratories showed higher metolachlor recovery for SDC samples. Laboratory G had a higher recovery in SW for all four compounds compared with DW. Other laboratories that had significant differences in pesticide recovery between the two water sources showed higher recovery in DW than in the SW regardless of the compound. In comparison to earlier work, recovery of these compounds using SPE disks as a temporary storage matrix may be more effective than shipping dried samples in a vial. Problems with analytes such as chlorpyrifos are unavoidable, and it should not be assumed that an extraction procedure using SPE disks will be adequate for all compounds and transferrable across all chromatographic conditions.