In response to tightening pesticide regulations in food produce, laboratories engaged in the business of food sample analysis in China are faced with increasing pressure to detect lower levels of contaminants, increase productivity or sample throughput and maintain the highest levels of data quality.
Triple quadrupole mass spectrometry combined with liquid chromatography (LC-TQ) is the method of choice for reliably quantifying trace components in complex samples like food, plasma, and environmental samples. They deliver exceptional sensitivity, precision, accuracy, linearity and dynamic range for multiple reaction monitoring (MRM) assays. The application of this for agricultural produce is illustrated with pesticide analysis in zucchini, using the QuEChERS sample preparation technique on the EVOQ™ Qube from Bruker.
With an increasing portfolio of trade partners and broad range of exports, China is a world leader in the global food trade. Few might realize that at the present time China is the worlds largest producer of honey, while over 80 percent of garlic sold worldwide is grown on Chinese farms. From smoked salmon to frozen pizzas, western food tables have sported Chinese produce for years while hungry western diners may be surprised to learn just how far their meals have travelled.
Agricultural exports from China have increased markedly over the past few years, both to its traditional neighbouring trading partners and on a global level. In fact between the years of 2005 to 2010, the value of Chinese food exports worldwide almost doubled to $41 billion. However, despite this it has been suggested that any further growth is jeopardised in part by the incompatibility between Chinese and western pesticide concentration regulations.
China is the world’s largest producer and consumer of pesticides, often with both concentrations and brands in direct conflict with western regulations. For example, in 2012, 14 shipments of Chinese tea were banned from entering the European Union after failing to meet the European Unions (EU’s) standards for pesticide residue tolerance. In addition, groups such as Greenpeace have independently reported the presence of illegal pesticides within imported Chinese tea, whereas in Vietnam, pesticides in imported fruit have been detected in excessively high concentration.
In response to this, and in part due to domestic health issues, China has made steps towards revising its pesticide regulations. Last year alone the Chinese Ministry of Agriculture moved to ban production of 22 hazardous pesticides, and it appears that China is gradually adapting to the changing trends in the global market. To support this change good methodology and instrumentation is required to analyze contaminants within food for both foreign and domestic consumption.
Pesticide Problems - Diazinon
Despite China’s progressive steps toward pesticide regulation many substances which are banned or highly regulated in western markets are still produced and used in substantial quantities. For example, atrazine and diazinon are strictly regulated globally but are still readily used as effective biological agents in China, particularly for non-seasonal growth (Figure 1).
Diazinon acts as an enzyme inhibitor for the acetyl cholinesterase substrate in insects preventing the hydrolysis of acetylcholine neurotransmitter. This results in abnormal accumulation of acetyl cholinesterase in the nervous system. However, at excessive concentrations, diazinon has been shown to be harmful to humans as well. The initial symptoms of acute exposure within humans include nausea, headaches and dizziness, which can progress to abdominal cramps, vomiting and diarrhoea. Long-term exposure has also been known to cause psychiatric symptoms such as depression and memory loss. Some countries, including the U.S. have made steps to phase out diazinon, a move that has not yet been followed by China.
Atrazine is one of the most widely used herbicides in the world; however, it is also one of the most controversial. Various sources report Atrazine as causing severe hormonal mutations within amphibians, whereas as an endocrine disruptor, it has been linked to hormonal disruption, birth defects and compromised nervous or endocrine systems within humans.
Gradually over the past decade, its use has been limited particularly throughout Europe. Some countries, namely Switzerland, have always heavily restricted the chemicals use. Italy and Germany introduced a complete ban about ten years ago. Atrazine has failed to be re-registered for use within the EU, technically making it an illegal substance, although a maximum concentration limit (MCL) for drinking water still exists, set at 0.1 μg/L.
The U.S. has a more liberal attitude towards atrazine with widespread agricultural use and a drinking water MCL of 3.0 μg/L, 300 times higher than Europe. Within food this concentration is reduced to 0.3 μg/L, a smaller but significant concentration. In 1998 China aligned its Atrazine MCL with that of the United States, potentially segregating European from North American exports.
This wide variety in regulations further complicates matters, particularly for large agricultural exporters such as China, which look to trade with both Europe and the Americas. To comply with the variety of international regulations, powerful and efficient pesticide detection and analysis tools are required.
Detecting Pesticides with LC-MS/MS
Crops grown in bulk for export are regularly sprayed with pesticides, which is often taken up from the water into the biomass. The variety and concentration of the species considered acceptable vary greatly depending on both the crop in question and, importantly, the targeted consumer. This creates the necessity for powerful multi-residue analysis techniques within the food production industry. A case study from Bruker shows how the EVOQ™ liquid chromatography with triple quadrupole mass spectrometry (LC-MS/MS) can be used to perform such an analysis.
A supermarket brought “pesticide-free” zucchini was spiked with 50 ppb ISTD d5-atrazine and 87 pesticides at 10, 30 and 100 ppb levels and analyzed with the EVOQ (Figure 2). Prior to analysis the sample underwent the industry standard QuEChERS preparation method. QuEChERS, an acronym for quick, easy, cheap, effective, rugged and safe is an encompassing method that can extract multiple classes of pesticides from a wide variety of samples.
Pesticide analysis in zucchini matrix using EVOQ showed good linearity with 75 percent of the 87 total pesticides having an R2 greater than 0.995. Responses of d5-atrazine in matrix samples give a RSD of 8.85 percent for 21 injections, demonstrating good instrument precision and robustness against QuEChERS extraction. The system also demonstrated good sensitivity and linearity for analysis of pesticides within the matrix samples.
MRM mode is the analytical tool of choice for multi-residue analysis in food samples due to its high sensitivity and selectivity for low level analysis in complex matrix like a QuEChERS matrix (Table 1). When this is used in tandem with the separative power of liquid chromatography, triple quadruple mass spectrometry offers one of the best solutions for pesticide analysis because of its sensitivity and robustness.
The Bruker EVOQ LC-MS/MS software in particular is designed with a compound-based scanning (CBS) system, which allows for easy MRM method set-up from a factory-supplied MRM library. Timed MRMs automatically calculate scan time for each compound based on its retention time, average peak width and defined peak points, significantly simplifying the method development. When used in collaboration with a library of hundreds of pesticides the system can quickly, effectively and accurately measure a broad range of pesticides at a variety of concentrations.
There was a time when China’s ability to supply agricultural produce in bulk at low cost was all that mattered to western importers. Today, with both foreign and domestic regulations becoming increasingly litigious, the impetus has moved towards produce that can be qualitatively proven to meet regulations and still retain a low cost of production. This changing global environment can be supported by high performance LC-MS/MS analytical tools, such as the EVOQ Qube.
Kefei Wang and Rohan Thakur are at Bruker Chemical & Applied Markets in Fremont, CA.
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