Helping Analysts Idenfify Pesticides in Complex Extracts

Since the 1940s, pesticides have helped farmers improve crop yields and alleviate food shortages. However, those benefits are tempered by the risks of using inherently dangerous chemicals in and around the food chain. Most pesticides can be toxic, some may cause cancer, and many are known or suspected endocrine disruptors, a class of chemicals that can interfere with normal hormonal processes in humans and animals. In many countries, public concern about potential health risks has led to closer monitoring and tighter regulation of pesticide levels not just in food products but also in water, soil and even the air.

The growth of international trade in food has expanded the list of compounds that many nations monitor and there are currently over 700 pesticides on regulatory watch lists around the world. The sheer number of compounds makes it difficult for analysts to detect the presence of prohibited pesticides and measure the allowable levels of legal pesticides. Their work is made more difficult by the fact that extracts of food or environmental samples are often very "dirty," containing co-extracted compounds that interfere with trace pesticide analysis.

Accelerating the screening process

Many labs first analyze samples using a gas chromatograph (GC) with element-selective detectors, tentatively identifying pesticides by their retention times and detector response. However, most labs look for only 100 to 200 compounds and any pesticides that are not on a lab's target list are usually missed.

Following screening, samples containing pesticides that exceed regulated levels are further analyzed for confirmation on a GC equipped with a mass selective detector (MSD). Until Agilent Technologies introduced retention time locking (RTL), retention times would vary from instrument to instrument or column to column, even when using the same method. Agilent's innovation made pesticide identification easier and more accurate, but the resulting data still required a lot of tedious review by a skilled chemist.

To help analysts overcome these problems, Agilent has developed a comprehensive screening tool that speeds, simplifies and automates the identification of pesticides and other compounds. Based on the Agilent 6890N GC/MSD system, Agilent's deconvolution reporting software (DRS) improves both the accuracy and speed of pesticide analysis. The DRS takes full advantage of retention time locking and Agilent's RTL mass spectral pesticide library. The library contains locked retention times for more than 560 compounds, including pesticides and suspected endocrine disruptors. Analysts can also add compounds to the library.

Combining results in one report

Available as an add-on to the Agilent MSD Productivity ChemStation software, the DRS uses three synergistic approaches to peak detection and combines them into one easy-to-read report. Three software packages perform complementary analyses of the data:

Deconvolution provides better matches from the mass spectral library and positive identification of pesticides that would otherwise be missed.

• The Agilent GC/MSD ChemStation software with RTL and the RTL mass spectral pesticide library, which identify and quantitate pesticides on the basis of their locked retention time and four target ions.
   
• The Automated Mass-spectral Deconvolution and Identification Software (AMDIS_32) from the US National Institute of Science and Technology (NIST), which searches the Agilent RTL pesticide library using the full set of deconvoluted spectra. The locked retention times are used as a qualifier for identification.
   
• The NIST 2002 Mass Spectral Search Program, which searches NIST's entire 147,000-compound mass spectral library (NIST02) using the full deconvoluted spectra.

By combining the results from these approaches, the system can screen for all 567 compounds in the RTL pesticide library and quantify target compounds in a single GC/MS run. What's more, the deconvolution process can find pesticides that are being masked by interferences in the mass spectra.

With the ability to handle more samples in less time—and with greater certainty—pesticide analysts will be better equipped to keep pace with new-generation pesticides and the increasingly tough regulations that protect people, animals and the food supply.

For more information

To learn more about Agilent solutions for pesticide analysis, please see the Pesticide Screening section of our website and download our pesticide solutions brochure. For additional information about these and other Agilent life sciences products and resources, please visit the Life Sciences/Chemical Analysis main page.