Analysis of Pesticides in Spaghetti Sauce by Direct Immersion SPME Using an Overcoated Fiber

Klaus Buckendahl, Advanced Analytical , Merck/Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany
Katherine Stenerson, Milliporesigma/supelco, Bellefonte, U.s.a.
Bob Shirey, Milliporesigma/supelco, Bellefonte, U.s.a.
Yong Chen, Milliporesigma/supelco, Bellefonte, U.s.a.
Tyler Young, Milliporesigma/supelco, Bellefonte, U.s.a.

Solid phase microextraction (SPME) is a solvent-less extraction method that is easily automated and does not require the use of solvents or sorbent materials.  SPME is often used for headspace extraction prior to GC analysis, especially if the sample matrix is extremely complex. However, many pesticides cannot be sampled in this manner due to their low vapor pressures. If direct immersion is used with complex matrices such as foods, standard SPME fibers can become prematurely fouled, leading to rapid loss in analyte response and contamination of the GC system. A recent advance in SPME fiber technology is the use of a polydimethylsiloxane (PDMS) overcoating on an adsorbent PDMS/divinylbenzene (PDMS/DVB) fiber. The overcoating serves as a barrier between the adsorbent DVB layer and macromolecules in the matrix, but allows smaller analytes to migrate through and be retained.   In this work, we utilized this new overcoated fiber in development of an SPME method for analysis of pesticide residues from a complex food matrix- spaghetti sauce. Performance of the fiber with regards to accuracy, reproducibility, durability, and method ruggedness were compared with a standard, non-overcoated fiber of the same chemistry. Overall, the overcoated fiber was found to produce better results with regards to accuracy and reproducibility in the analysis of spaghetti sauce samples spiked with pesticides from a variety of classes.  Data will also be presented showing a significant improvement in fiber durability and SPME method ruggedness using the overcoated fiber.  Finally, results obtained using the optimized SPME method with the overcoated PDMS/DVB fiber were compared to analysis of the same pesticides from spaghetti sauce using a standard QuEChERS method for extraction and cleanup. The SPME method was found to achieve higher sensitivity, and produced less background in comparison to the QuEChERS sample preparation method.