Expert Insight: How to optimize sample preparation for rapid analysis of contaminants in foods by LC-MS/MS

Choose the right mobile phase chemistries to speed up analysis while maintaining good peak resolution in challenging matrices

11 Nov 2019

Joe Konschnik, Restek
Joe Konschnik, Business Development Manager, Food & Agriculture Market, Restek

Understanding the pros and cons of different approaches for detecting and quantifying pesticides and toxins in different foods is essential when optimizing your LC workflows, especially for challenging matrices.

In this expert webinar, Joe Konschnik, the business development manager for the Food and Agriculture Market at Restek, presents insights into the recent advances in chromatography technology. Konschnik also discusses how to apply these technologies to food commodity testing workflows to overcome common challenges, simplify sample preparation, speed up analysis, and minimize the reporting of false negatives and positives in your results.

Read on for highlights from the Q&A session or register to watch the full webinar on demand>>


Q: When you combine 10 ampules of pesticide mixes together for your experiment, how stable are the 200+ pesticides after they’ve been mixed?

JK: We've conducted studies at Restek that demonstrate not only what happens when we mix them together but what happens when we crack open ampules and store them in the refrigerator. The data showing how long these are stable for was recently presented at the AOAC 2019 Conference in Denver, Colorado. We found that within one day of combining 10 mixes together, whether we stored them on an auto-sampler with at 4℃ or if we recapped them and stored them in the refrigerator, several compounds were lost per day. 

There was a gradual increase in the number of pesticides that degraded in our working mixes. Therefore, it's wise for each laboratory to conduct similar studies with the compounds they're working with and determine the best quality assurance practices specific to their operational needs, making sure they're aware of which compounds break down and how long their mixes are usable. A general rule of thumb, based on our study, is to mix your working mixes together on a daily basis and to not let them sit around too long.

Q: Why didn't you use an SPE cleanup for your work on mycotoxins?

JK: What we're hearing from the community is that many SPE approaches are expensive and take up a lot of time. Laboratories are looking for ways to speed up sample preparation and get them loaded onto the instruments. We wanted to test a dilute and shoot application, both matrix-matched and stable isotope dilution, to show that there are faster ways of achieving the same result and that columns can handle the extra material being loaded onto them. The purpose of the study was to bypass any cleanup and carry out a simple extraction and a dilute and shoot to show that it can be done. Consequently, some of the results weren't acceptable for some of the mycotoxins, but we believed we got good data and it displayed what could be accomplished.

Q: A few of your myosin recoveries in cornmeal using matrix-matched calibration were not consistent. What do you think caused such variation?

JK: One thing we've learned from the community is that, when measuring mycotoxins in grains, fungi tend to distribute unevenly in grain matrices. We're talking about very large quantities of grains here - sometimes it's a ship tanker or perhaps it's a barrel or even just a bucket. You can take two or three samples out of that bucket after mixing it and you won’t get an even distribution of the mycotoxins because the fungi exist in pockets and excrete their mycotoxins close to where they reside. Perhaps we could have done a better job of homogenizing our samples and achieved more consistent results.  

Q: Will you carry out more work on pesticides and mycotoxins based on these studies?

JK:  No matter where I look it seems people are working on these. I think for pesticides, I would like to see some more studies done with different matrices. We're getting a lot of requests to look for pesticides in things like fish tissues and other types of extracted oils. I'd also like to see how our products perform on those as well. I'd like to see how other mycotoxins behave too, in addition to the aflatoxins and ochratoxins. Perhaps it would also be good to work on some more lifetime studies with the Raptor Biphenyl SPP Column to see how well it holds up with hundreds of injections in a grain matrix, because those matrices are really tough on the columns.

Q: How do food matrices differ from other matrices if you're analyzing pesticides?

JK: When we're analyzing pesticides, some of the challenges we see are that different pesticides are used for different commodities, which present different challenges because they have different matrix characteristics. For example, if you're looking at the orange peel versus the fruit on the inside, the fruit has high water content, but the peel has low water content and high oil content. We saw this borne out when we tried to analyze the whole orange. When the fruit and the peel were separated and treated differently, we saw that we could overcome the ability of the oils and the skin to pull some of the pesticides out and not allow them to be transferred to the solvent. With the high-water portion of the fruit, extraction happened much more readily because of the characteristics of the fruit. The same thing can be observed with avocado. The high-fat content of avocados means we require more sorbent in our dispersive cleanup. If there’s not enough, you see low recoveries for some pesticides. 

Some of the challenges from different types of commodities present themselves when we see different pesticides being used in different countries and the commodities are then shipped all over the world. One of the challenges is to decide which pesticides to test for which commodities. More and more commercial labs are scanning for larger lists of compounds between 450 and 600, which is another huge challenge when testing for pesticides.

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