The changing breadth of chemicals demands new technologies and tweaks
People started applying pesticides to protect foods long ago. “Pesticides have been used since the Sumerians, 2,500 years ago,” says Phil Taylor, global marketing manager for food, environmental, and forensics at SCIEX (Framingham, MA). “We’ve been relying on pesticides since then to preserve crops and food.” Over time, the amount of pesticides used increased, and so did the diversity of products. “New pesticides are being created regularly,” says Taylor. "The challenge is how to keep on top of the analysis," and the uses of a pesticide allowed by regulatory groups. What’s more, some fake pesticides end up on the market, which means that something unexpected could end up in foods. Those applying pesticides and producing foods that have been treated with pesticides must follow specific rules.
“Pesticide use is strictly regulated,” says Katerina Mastovska, associate scientific director for global R&D and innovation leader at Covance Food Solutions (Princeton, NJ).
“Pesticide residue testing is needed to ensure compliance with the established maximum residue limits or tolerances and to make sure that foods do not contain unapproved substances.” She adds, “In addition to pesticide regulations, there are other regulatory requirements that have increased the need for pesticide testing, such as the Food Safety Modernization Act in the United States.”
Beyond the diversity of chemicals involved, analysts face other components. For example, Mastovska says, “We have to deal with more complex matrix types, such as dietary supplement ingredients and finished products, which require high detection selectivity.” From the application standpoint, farmers need help keeping up with the regulations. For that, they can turn to people like Mary Ann Rose, director of the pesticide safety education program at The Ohio State University in Columbus. “Our mission is to educate Ohio’s pesticide applicators,” she says, “who—depending on what they spray—may be required to hold a pesticide license and fulfill continuing education requirements.”
Rose and her colleagues work toward many objectives, including keeping applicators updated on laws and regulations in addition to developing safety guidelines. “We focus on the safety of the applicators as well as the customers down the road,” Rose says.
Safety from service labs
To keep the world’s food supply safe, testing for pesticides goes on at food companies and private labs. Anresco Laboratories (San Francisco, CA), for example, analyzes pesticides on many foods, including fruits, produce, spices, and processed foods. It runs multi-residue analysis (MRA) with methods such as QuEChERS, which stands for quick, easy, cheap, effective, rugged, safe.
Image courtesy of Anresco Laboratories.When asked if there are recent challenges that increase the need for pesticide testing in foods, Vu Lam, co-director in charge of chromatography at Anresco Laboratories, says, “Absolutely. Testing food is a tough business, to be honest with you.” He adds, “The reason is that every single product is slightly different from another, and one single method won’t cover everything.”
Lam also points out the diversity of pesticides. “You don’t know which one people used,” he says, “and they could have even used something that has been abandoned for five or ten years.” Consequently, labs usually screen foods for hundreds of pesticides, to cover as many as possible. “But it’s not always possible to find something at the lower levels,” he explains, “because of the limitations of the instrument or different matrices,” which are affected by the sample matrix. “So even with the QuEChERS method,” Lam continues, “you might modify it a bit from one sample to another.”
The problems go beyond diversity, sensitivity, and sample variation, because cost also plays a part. “Maybe you could spend a million dollars for an instrument that is capable of detecting pesticides at an extremely low detection level, so it can scan for more analytes at lower levels,” Lam says. “However, that will be expensive, and nobody wants to pay for that.” In general, spending more on the testing turns up more pesticides and at lower levels. Still, some samples need different approaches. “If there’s a problem with a method,” Lam says, “we tweak it a little—maybe use a different method of extraction to get a little better result.”
The idea of spending more on food testing, though, goes against a trend that Lam is seeing. “Most companies are scaling down for testing on pesticides,” he says.
“They only test at a much smaller scale, and that kind of defeats the purpose.”
To keep up with the changing chemicals, Covance Food Solutions launched an expanded multi-residue method for over 500 pesticides, Mastovska explains. This method employs liquid chromatography (LC), gas chromatography (GC), and mass spectrometry in two forms: LC-MS/MS and GC-MS/MS. “In the LC-MS/MS,” Mastovska says, “we developed an online dilution system for improved peak shape of normally difficult, early eluting analytes, and we implemented a triggered multiple reaction monitoring function, which allows acquisition of additional MS/MS data for increased confidence in analyte identification.”
Making the most of mass spectrometry
The selectivity and sensitivity of MS makes it a great tool for analyzing foods. “Pesticides have a wide range of chemical structures and polarities, so you need an analytical method that can detect compounds of all types,”
says Robert “Chip” Cody, product manager at JEOL (Peabody, MA). “To detect pesticides at trace levels in the presence of complex matrices like foods and beverages, you need high specificity and low detection limits.”
In most cases, a sample goes through LC or GC before being analyzed with MS. “For trace analysis, you need the additional specificity of a high-resolution or tandem mass spectrometer,” Cody explains. Using a cleanup method first, like QuEChERS, also helps.
JEOL developed a platform that provides targeted and untargeted analysis. “By combining comprehensive two-dimensional gas chromatography (GCxGC) with highly sensitive high-resolution mass spectrometry and a variety of ionization methods, JEOL’s AccuTOF-GCx system provides a powerful platform for targeted and untargeted analysis,” Cody says. This platform also allows various forms of ionization: electron ionization (EI), field ionization (FI), or photoionization (PI).
Aim a DART
For fast analysis, a scientist can use an ambient ionization system, like Direct Analysis in Real Time (DART) as offered on JEOL’s AccuTOF-DART system. “With this tool,” says John Dane, MS applications chemist at JEOL, “in many cases you can just walk up with your raw material, place it in the sample gap, and analyze the residues on the surfaces.”
Image courtesy of JEOLAs an example, Dane mentions that the surface of an orange usually has fungicides on it. “You can take an orange and—instead of doing an extraction for LC-MS or GCMS— place it in front of the DART instrument and see the fungicide signal directly off of the surface.” He adds, “You don’t necessarily need the sample prep up front.” In a minute or two, a scientist completes the analysis, but in some cases it might be followed up with confirmation steps, depending on the analysis being done.
When asked why DART is gaining ground as a choice for testing foods for pesticides, Dane says, “It’s the time-saving aspect more than anything else.” For example, he mentions, a customs agency might run into hundreds of samples, with each taking as long as an hour or two if it requires QuEChERS followed by chromatography and MS. “With DART, often with minimal sample preparation, they could just walk up and have the data within seconds,” Dane says. For a first look, Dane and his colleagues use DART.
“When we get a sample,” he says, “we almost always use DART as a starting point to test it quickly.” He adds, “Depending on the outcome of the analysis, we may add a sample preparation step—like a quick solvent extraction or perhaps even QuEChERS—to improve the analysis results, but the key is that the time-consuming chromatography step is not required for the DART analyses.”
Dirty samples create interference that some MS systems handle better than others. SCIEX’s X500R QTOF (quadrupole time of flight) system, says Taylor, “smashes through that.” He adds, “The X500R is different from ordinary QTOF, because it scans everything, and it’s really applicable to pesticides.”
Part of the difference comes from SWATH, which is SCIEX’s data acquisition technology that provides a wider mass range and more selectivity. “When you take the resulting data and cross-reference it with libraries, you’ll find pesticides that you’ve never seen before and that are not even on your list,” Taylor notes. “This combats the challenge of people using fake pesticides and unregulated pesticides.”
That can make a big difference in keeping foods safe. “If you have an apple and test it for only regulated pesticides, you’ll see them,” Taylor explains, “but if someone used something else, we could see it with SWATH in our QTOF, as well as any residues.” Like untargeted analysis, this platform works even when you don’t know what to expect.
Pushing beyond borders
People in some parts of the world worry about pesticides more than others, but making the technology more affordable could expand where it gets used. “Different countries have different priorities on where they spend their money, and pesticide testing may not be a big priority,” Taylor explains, “but ignoring it can be very harmful to people and livestock.”
Even where testing is done, the technology and the regulations keep changing. For instance, the U.S. Environmental Protection Agency reevaluates the safety of every pesticide on its list every 15 years. That means that acceptable levels can change, which might require more sensitive analysis.
So, the next time you bite into an apple, think about all the work that went into ensuring it “keeps the doctor away” instead of poisoning you. It takes a wide range of tools, regulations, and scientific expertise to keep our food supply safe.