Here’s some food for thought: After they have been washed and shelved at the local grocery, sweet bell peppers have, on average, 11 different pesticides residing on their skin. And that apple a day? A 2009 study showed more than 80 percent of apples in a single sample tested positive for up to nine pesticides.[1]

Every day, the average American is exposed up to 13 pesticide residues from food, beverages and drinking water.[2] Moreover, residual pesticides in imported vegetables and processing foods have become a public concern. While chemical levels are low in most cases, human exposure poses risk factors in the development of medical conditions ranging from learning disabilities to Alzheimer’s disease.

Health and environmental agencies in all industrialized nations are responsible for establishing Maximum Residue Limits (MRLs) of pesticides and ensuring that both domestic and imported food products comply with these rules. In 1996, the Environmental Protection Agency introduced the Food Quality Protection Act (FPQA), which mandated a single, health-based safety standard for all pesticide residues in foods.[3]

To keep pesticide data updated, FPQA requires periodic re-evaluation of pesticides and MRLs. Increased sensitivity and throughput for MRL analysis is an important goal to meet this need. Gas chromatography and liquid chromatography, when coupled with mass spectrometry (GC/MS and LC/MS, respectively), have become invaluable methods for evaluating pesticide MRLs.

GC/MS Analysis
GC/MS methods for pesticide residue analysis in foods are commonly used for regulatory monitoring because fast pesticide determination is frequently required. GC/MS can identify unknown pesticides from the combination of the retention time and mass spectrum for each compound it analyzes. The mass spectrum is compared with mass spectra from a list of registered pesticides, and a degree of similarity is calculated for each relevant spectrum in that list.

Confirmation of target compounds (pesticides) in samples with complex matrices such as food is often very difficult. Target compound peaks can be masked by co-eluting matrix background peaks of higher intensity. To identify that target compound peak in food, deconvolution software can be applied to GC/MS data.

In one study using a carrot, cabbage and orange peel as samples, researchers added more than 100 pesticides and analyzed them in 15 minutes using fast GC/MS. Data were processed by chromatogram deconvolution software to obtain mass chromatograms that were free of co-eluting compounds. When combined with fast GC/MS, the chromatogram deconvolution software significantly shortened the pesticide analysis time and showed accurate results for the three samples.

GC/MS with Selected Ion Monitoring
Full-scan GC/MS analysis is a commonly used data collection mode for screening pesticides because it provides qualitative and quantitative information. Selected ion monitoring (SIM) provides more sensitivity, but it neither gives information regarding non-target analytes, nor does it provide any confirmation information. Combining these two modes into one analysis method called FASST (fast automated scan/SIM technique) provides the best of both worlds.

Using the FASST technique to analyze pesticides, full-scan and SIM data are obtained in the same GC/MS run by alternating at high speed between scan and SIM mode data acquisition.

A quantitative analysis for more than 50 selected pesticides was conducted on carrot abstracts spiked with pesticide standards using FASST data acquisition and conventional calibration procedures. Screening and semi-quantitative analysis for more than 200 additional pesticides was accomplished from that data using specialized software.

Researchers added pesticides to the carrot extract sample corresponding to 0.01 ug/kg in the raw carrot. Although some high-intensity matrix peaks overlapped target chromatograms, all of the target pesticide compounds were detected easily.

LC/MS Analysis
In the past, the use of liquid chromatography in determining pesticide and herbicide residues was often limited to groups of compounds when no gas chromatographic conditions were available. The development of advanced LC/MS techniques has opened up greater opportunities for analyzing pesticides and MRLs in foods.

Today, the use of modern phenoxypropionic herbicides is allowed under strict conditions for weed control in the cultivation of medicinal plants and herbs. Highly effective, these herbicides have very low toxicity to mammals. Poisoning can only occur after exposure to very high levels of these compounds, which result from careless storage or negligent management.

However, the potential hormonal action of these chemicals has been under critical debate recently. Because they are suspected of hormonal action, an efficient control of the pollution levels of foods by herbicide residues is imperative. Residue for phenoxypropionic herbicides are routinely carried out using LC/MS.

Dual LC/MS
When analyzing for pesticides in crops, it is not uncommon for analysis of a given crop to be successful on one occasion and unsuccessful in another. This may be due to the interaction of various chemical compounds on fruits or vegetables that may lead to decomposition or interfere with measurement, leading to secondary analysis.

When chromatographic analysis is adversely influenced by interfering compounds, pretreatment (purification) has been traditionally used to remove the interfering chemicals. Typically, scientists try to separate the target pesticides from the interfering components by modifying the analytical conditions used for LC. In principle, scientists conduct this re-analysis when a problem occurs; however, it’s likely that the compounds will change during the re-analysis preparation.

Dual LC/MS systems overcome this problem by automatically conducting LC/MS under two sets of conditions that can always be expected to provide separation selectivity. The two sets of conditions can be selected freely depending on the research objective.

HPLC/MS Analysis
High performance liquid chromatography/mass spectrometry (HPLC/MS) provides very sensitive detection of mycotoxins in foods. Mycotoxins—produced by mushrooms, yeasts and molds—were originally discovered when scientists sought out disease triggers that did not stem from microorganisms, plant toxins or pesticide residues. It wasn’t until analytical research methods became more sensitive and a larger number of foods could be tested that scientists discovered these toxins could cause human disease.

Mycotoxins can attack peaches, apricots and cherries, and they are the main cause of rot in apples and other vegetables. In studies, about 40% of brown rot in apples can contain more than 80 mg/kg of a mycotoxin called patulin. That means only a small number of moldy apples are needed to cause patulin contamination in large volumes of apple juice (patulin concentrations of 50 ug/kg or higher). According to European Union standards established in 2003, 50 ug/kg is the highest allowable level of patulin in apple products.

There is a growing trend to use HPLC/MS for identifying and quantifying patulin and other mycotoxins in food. In fact, to attain a higher sensitivity and selectivity for determining patulin at the trace level, a specific HPLC method was developed using single quadrupole LC/MS for MS detection.

Patulin is not the only mycotoxin that can be detected with HPLC/MS. Other HPLC/MS methods exist for mycotoxins such as aflatoxins, ochrtoxin and fusaric toxins. Due to the high selectivity of MS detection, simultaneous determination of various toxins in a single analysis is also possible.

The use of such highly sensitive detection methods as GC/MS and LC/MS for mycotoxins, herbicides and pesticides will continue to form the basis for further research into health hazards and analyzing food contamination. ♦

References
1. www.foodnews.org/methodology.php.
2. Benbrook, C. 2008. Simplifying the pesticide risk equation: The organic option. State of Science Review.
3. www.epa.gov/pesticides/regulating/laws/fqpa/backgrnd.htm.