Question: If you had a lot food of samples to extract and not a lot of time or money to do it, how would you extract?
Our answer: Since we didn’t have a lot of time, room, or additional funding we used the QuEChERS technique.
David Steiniger, Senior MAD Scientists in the lab, worked with the procedure as written and adjusted it into something that we could use with the Ion Trap GC/MS system. It also worked ridiculously well with the Triple Quadrupole GC/MS. The quechers flowchart, in the attached file, that he came up with simplified the process to the point where even the MAD MANager could do it, that would be me.
Now that the samples are extracted the question is how would you analyze the samples? In the case of these four matrices, onion, lettuce, rice, and tea we chose an Ion Trap GC/MS. This technology were chosen because there was a limited number of matrices and we knew the list of pesticides that would be on each crop,that number was below 60.
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This group of methods covers the preparation of extracts, seen in the flow chart above, and the optimization of the analytical parameters of the splitless injection, separation, and detection. The determination of pesticides in fruits, vegetables, grains and herbs has been simplified by a new sample preparation method, QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe), published recently as AOAC Method 2007.01. The sample preparation is simplified by using a single step buffered acetonitrile (MeCN) extraction and liquid-liquid partitioning from water in the sample by salting out with sodium acetate and magnesium sulfate (MgSO4). QuEChERS can be used to prepare samples for analysis using the ITQ ion trap GC-MS/MS system.
The series of studies were performed to determine the linear ranges, quantitation limits and detection limits for a long list of pesticides that are commonly used on these crops. All of the samples were prepared in matrix using the QuEChERS sample preparation seen above. A splitless injection of the pesticides was made with detection in EI MS/MS. Since the extracts are prepared in MeCN, a solvent exchange was made to hexane/acetone (9:1) prior to conventional splitless injection. The final solvent exchange provides a final solvent that is more amenable to splitless injection. It seemed to make the consumables last longer and give one final clean-up step. It took about 30 minutes for an entire batch of samples. Once the calibration curve was constructed, multiple matrix spikes were analyzed at levels of 100, 200, or 300 ng/g (ppb) and low-level spikes of 5, 10, 15, 25, or 50 ng/g (ppb) were used to verify the precision and accuracy of the analytical method.