The AOAC annual meeting is fast approaching. Beginning this Sunday, September 30th and running through next Wednesday, October 3rd, the 2012 AOAC meeting in Las Vegas, Nevada promises to be another exciting conference. The final program has been announced and Restek chemists will be participating in meeting events and giving several technical presentations. Visit us at Booth 209 or stop by one of the posters listed below to learn more about our latest innovations and applications.
Poster Session: “Analysis of Non-Foodborne Contaminants and Residues”
A New Capillary GC Column for Highly Efficient Separation of Polycyclic Aromatic Hydrocarbons, Including the EFSA PAH4
Poster Number: P-M-070
Julie Kowalski, Amanda Rigdon, Jack Cochran, Shawn Reese, and Roy Lautamo
Abstract: Polycyclic aromatic hydrocarbons (PAHs) are toxic (carcinogenic, mutagenic, teratogenic, etc.) compounds sometimes found in food and require monitoring by capillary gas chromatograph with mass spectrometry (MS), often at very low levels. Some of these PAHs are isobaric so MS will not be sufficient to quantify them in an unbiased fashion, which means they must be separated by GC prior to detection. Some are more toxic than others, including the PAH4 noted by EFSA, benz[a]anthracene, chrysene, benzo[b]fluoranthene, and benzo[a]pyrene. Possible GC coelutions that would lead to qualitative and quantitative bias include triphenylene and chrysene (m/z 228), benzo[b]- and benzo[k]fluoranthene (m/z 252), and benzo[e]- and benzo[a]pyrene (m/z 252). The triphenylene and chrysene coelution can be particularly difficult to resolve.
A new GC stationary phase has been developed that separates the PAH4, the PAH8, and many more PAHs that can be present in food samples. Chromatograms that detail these separations will be shown, and column ruggedness will be explored with QuEChERS oyster and smoked paprika spice extracts.
Feasibility of Dilute-and-Shoot LC-MS/MS, Solvent-Only Calibration and Multiple Food Types for Multiresidue Pesticide Analysis: Lazy Chemists and Old Instruments
Poster Number: P-M-068
Julie Kowalski, Sharon Lupo and Jack Cochran
Abstract: Increased selectivity and better sensitivity of LC-MS/MS have impacted how multiresidue methods are performed, sometimes by decreasing the need for rigorous sample preparation. However, this technique is susceptible to matrix effects causing poor data quality and quantification to be difficult. Often instrument manufactures tout the dilute-and-shoot technique which greatly decreases processing time as no sample cleanup is performed, but it also often requires the sensitivity of the newest instrumentation. Using a robust, but older LC-MS/MS with sensitivity limitations, we investigated two aspects of multiresidue methods, sample preparation and calibration strategies, to determine the best procedures considering both data quality and time/cost. A variety of food types and two sample preparation methods, dilute-and-shoot and QuEChERS methods were performed and experimentally determined matrix effects were compared. Calibration methods were evaluated by determining recovery values using both solvent-only calibration and matrix-matched calibration. This allows assessment of sample preparation/calibration method combinations. We determined that with the easiest commodities, the dilute-and-shoot method and solvent-only calibration gave acceptable recovery values. However, for other commodities either a matrix-matched curve or cleanup was needed to obtain good recovery values. The high carbohydrate and citrus commodities proved to be too difficult. In almost every case, matrix-matched calibration provided improvement.
The QuEChERS Sample Preparation Approach with Dispersive and Cartridge SPE Cleanup, GCxGC-TOFMS, and LC-MS/MS for the Analysis of Pesticides in Tobacco
Poster Number: P-M-067
Julie Kowalski, Michelle Misselwitz, Sharon Lupo, Jack Cochran
Abstract: The production of tobacco, a high-value crop for the United States, is increased by the use of pesticides that are specifically approved for use on tobacco by the Environmental Protection Agency (EPA). Even after the processing of tobacco, some pesticide residues remain on the product and under its pesticide registration program EPA is charged with assessing risks to smokers from exposure to these residues. Because tobacco is such a complex matrix, the challenges associated with determining pesticides at trace levels are substantial. This includes pesticide extraction from tobacco and the instrumental analysis step, which can be complicated by matrix interferences.
We used the Quick – Easy – Cheap – Effective – Rugged – Safe (QuEChERS) sample preparation approach to isolate pesticide residues from tobacco leaf, ranging from such small, polar pesticides, such as methamidophos, to relatively nonvolatile, nonpolar, large pesticides, like deltamethrin. We also explored two extract cleanup methods, dispersive solid phase extraction (dSPE) and cartridge SPE (cSPE), monitoring their efficiency at pesticide recovery and matrix reduction. Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-TOFMS) and liquid chromatography with tandem mass spectrometry (LC-MS/MS) were compared and contrasted for their ability to determine pesticide residues in the resulting extracts.
The Holy Grail: Comprehensive Polycyclic Aromatic Hydrocarbon Analysis by Serial Combination of HPLC Columns with Different Selectivities and UV and Fluorescence Detection
Poster Number: P-M-069
Julie Kowalski, Sharon Lupo, Ty Kahler, Jack Cochran
Abstract: Polycyclic aromatic hydrocarbon analyses are performed regularly throughout the world for both food safety and environmental testing. Many organizations test for PAH residues in food products, but the analyte lists vary from organization and country. For example, domestically, the EPA, FDA, AOAC, and NOAA all test for PAHs, but do not share the same target compound lists. Internationally, the EU and individual countries test for different PAH compounds. Chromatographic methods are typically tailored to specific target compounds and are not transferable when target compounds change. A further complication is the need to separate interfering compounds that are not considered target compounds, but that do occur in samples, like triphenylene, perylene, and benzo[e]pyrene.
In this work, we developed a chromatographic solution that allows the separation of 29 PAH compounds including interfering compounds. This was accomplished by combining two HPLC columns in series: a PAH-specific phase and an aromatic bond selective phase. Separate column selectivities were tested and then combined based on a predicted ratio of the column lengths that would results in no coelutions. Temperature was also determined to play a critical role in the elution order and resolution of the PAHs tested. Time programmed fluorescence detection was optimized to yield the best sensitivity possible, ppb range, with closely eluting compounds.