Cryogenic Sample Processing with Liquid Nitrogen for Effective and Efficient Monitoring of Pesticide Residues in Foods and Feeds

Automated micro-solid-phase extraction clean-up and gas chromatography-tandem mass spectrometry analysis of pesticides in foods extracted with ethyl acetate

Generic extraction methods for the multi-compound pesticide analysis of food have found their solid place in laboratories. Ethyl acetate and acetonitrile extraction methods have been developed as fast and easy to handle standard multi-compound methods, both feature benefits and limitations. The direct injection to gas chromatography can be impaired by a high burden of coextracted matrix, resulting in deterioration of the chromatographic system and matrix effects, requiring frequent maintenance. Therefore, common clean-up methods, such as dispersive solid-phase extraction, freeze-out of fats, or gel permeation chromatography, have been applied in clean-up. Automated clean-up using micro-solid-phase extraction (µSPE) is a recent development with several demonstrated advantages when employed in the analysis of pesticides and other contaminants in foods extracted with acetonitrile, but it has not yet been evaluated in this application using ethyl acetate for extraction. In this study, an automated procedure using µSPE cartridges was developed and established on an x,y,z robotic sampler for the raw extract clean-up and preparation of diluted samples for injection on a GC-MS/MS system. Validation experiments for 212 pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons in lettuce, avocado, raspberry, paprika, egg, and liver extracts were performed using µSPE with MgSO4, PSA, C18, and CarbonX. The performance in routine operation is briefly discussed.

Quality Control of Pesticide Residue Measurements and Evaluation of Their Results

Pesticide residues are monitored in many countries around the world. The main aims of the programs are to provide data for dietary exposure assessment of consumers to pesticide residues and for verifying the compliance of the residue concentrations in food with the national or international maximum residue limits. Accurate residue data are required to reach valid conclusions in both cases. The validity of the analytical results can be achieved by the implementation of suitable quality control protocols during sampling and determination of pesticide residues. To enable the evaluation of the reliability of the results, it is not sufficient to test and report the recovery, linearity of calibration, the limit of detection/quantification, and MS detection conditions. The analysts should also pay attention to and possibly report the selection of the portion of sample material extracted and the residue components according to the purpose of the work, quality of calibration, accuracy of standard solutions, and reproducibility of the entire laboratory phase of the determination of pesticide residues. The sources of errors potentially affecting the measured residue values and the methods for controlling them are considered in this article.

Chromatographic analysis of dithiocarbamate residues and their metabolites in foods employed in dietary exposure studies-a review

Dithiocarbamates (DTCs) belong to a group of compounds used as fungicides in food production and can be divided into three major groups. Since DTCs easily oxidise and hydrolyse in alkaline and acidic medium respectively, precautions have to be implemented during preparation/homogenisation and extraction of samples. As such, test samples are commonly prepared individually by cutting into small pieces just before the digestion of DTCs with a hot acid to give carbon disulphide (CS₂) and the results are expressed as CS₂ without any differentiation of individual DTCs. However, individual DTCs have different toxicological potencies whilst their metabolites are more toxic than the parent compound. Apart from the hot digestion method, chromatographic separation of three major groups of DTCs has been developed by a number of different researchers. This review provides a comprehensive examination of sample preparation, extraction, clean-up and chromatographic methods for the determination of individual DTCs and their more toxic metabolites in foodstuffs. Moreover, this review also studies on how dietary exposure of DTCs can be efficiently and effectively estimated using different methods of analysis.

The QuEChERSER Mega-Method

Introduced in 2003, the “quick, easy, cheap, effective, rugged, and safe” (QuEChERS) sample preparation approach has been widely adopted in many applications, particularly in chemical residue analysis of foods. Prior to QuEChERS, sample preparation generally entailed several time-consuming, labor-intensive, and reagent-excessive steps, but the commercialization at the time of powerful, cost-effective, benchtop gas chromatography–mass spectrometry (GC–MS) and liquid chromatography–tandem MS (LC–MS/MS) instruments enabled the implementation of the QuEChERS procedure. Despite analytical technologies continuing to improve over the last two decades, many laboratories are still using QuEChERS protocols developed for outdated instrumentation. Recently, QuEChERS has been updated into QuEChERSER (with “efficient and robust” being added to the portmanteau) to better take advantage of the features provided by modern sample preparation and analytical techniques. Most notably, QuEChERSER is a “mega-method” that covers a broader scope of polar and nonpolar analytes in diverse sample types. In this article, the new QuEChERSER approach and its advantages over QuEChERS are explained.

Sources of Random Variation of Pesticide Residue Analytical Results

BACKGROUND

Pesticide residues are analyzed in thousands of samples yearly by national authorities and private laboratories. Intensive research is ongoing to develop new methods or improve existing ones concentrating on extraction, cleanup, and detection techniques. Little attention has been paid to the contribution of prior steps in the determination process to overall laboratory sampling errors, though several publications demonstrate their practical importance. Consequently, the repeatability and reproducibility of the results are often reported based on the recovery tests alone. A few previous publications are cited in this paper which illustrate the magnitude of random errors derived from subsampling, comminution of analytical samples, and selection of small test portions.

OBJECTIVES

We aim to call attention to the importance of considering all steps of laboratory sampling and analysis processes in calculating the combined uncertainty of results and realistic performance assessments of methods including their long-term intermediate precision.

METHOD

Validation of laboratory sampling of large fruits is used to illustrate the recommended procedures, determination of their random error, and long-term method performance.

RESULTS

The results indicate that subsampling, comminution, and selection of test portions can be major contributors to the combined uncertainty of results.

CONCLUSIONS

All these steps should be considered in estimation of random variation (uncertainty) of measured residues.

HIGHLIGHTS

Random error of laboratory sampling for pesticide residues. Mass reduction of large crop units. Internal quality control of laboratory operations.

Determination of multi-pesticide residues in vegetable products using a "reduced-scale" Quechers method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry

The aim of the present research was the development of an analytical method for the determination of multi-pesticide residues (88 target analytes) in four vegetable products (tomatoes, cucumbers, sweet red peppers and iceberg lettuce) using a "reduced-scale" QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and flow-modulated comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry. In particular, the suitability of flow modulation [with relatively high second-dimension gas flow conditions (8 mL min^-1)] for trace analyte determination was evaluated. The samples were prepared according to the QuEChERS procedure as reported by the official European Union method, namely EN 15662:2018, based on the use of 3 g of vegetable product. Matrix-matched calibration processes were carried out for all the samples. The figures-of-merit determined were recovery, linearity, precision, limits of detection (LoDs), and limits of quantification (LoQs). Specifically, recoveries were in the 53-160% range, regression coefficients were between 0.9156 and 0.9999, the LoDs were in the 0.1-6.3 μg kg^-1 range, the LoQs were in the 3.0-21.0 μg kg^-1 range, and coefficients of variation were between 1 and 28% (at the 50 μg kg^-1 level).

The Role of Suspension Array Technology in Rapid Detection of Foodborne Pollutants: Applications and Future Challenges

Food safety is an important livelihood issue, which has always been focused attention by countries and governments all over the world. As food supply chains are becoming global, food quality control is essential for consumer protection as well as for the food industry. In recent years, a great part of food analysis is carried out using new techniques for rapid detection. As the first biochip technology that has been approved by the Food and Drug Administration (FDA), there is an increasing interest in suspension array technology (SAT) for food and environmental analysis with advantages of rapidity, high accuracy, sensitivity, and throughput. Therefore, it is important for researchers to understand the development and application of this technology in food industry. Herein, we summarized the principle and composition of SAT and its application in food safety monitoring. The utility of SAT in detection of foodborne microorganisms, residues of agricultural and veterinary drugs, genetically modified food and allergens in recent years is elaborated, and the further development direction of SAT is envisaged.

Assessment of Test Portion Sizes after Sample Comminution with Liquid Nitrogen in an Improved High-Throughput Method for Analysis of Pesticide Residues in Fruits and Vegetables

In this study, sample processing of bulk commodities using an efficient one-step comminution procedure with liquid nitrogen (LN₂) was devised and assessed in the analysis of pesticide residues in fruits and vegetables. LN₂ was added to the fresh samples from a tank by opening a valve, and the standard food chopper was kept in a laboratory hood to reduce safety risks. Test portions of four replicates each of 0.25, 0.5, 1, 2, 5, 10, and 15 g were taken from eight fruits and vegetables (tomato, squash, broccoli, apple, grape, peach, green bean, and cucumber) individually comminuted with LN₂. For comparison without comminution, similar test portions of a reconstituted freeze-dried certified reference material of pesticides in cucumber were also analyzed by the same method. More than 100 pesticides were monitored by both ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and instrument top sample preparation (ITSP) + fast low-pressure gas chromatography-tandem mass spectrometry (LPGC-MS/MS). A new version of QuEChERS-based sample preparation was followed, in which 5 mL of 4:1 (v/v) acetonitrile/water per gram of sample is used for extraction and 200 μL of initial extract is quickly evaporated, reconstituted in water, and ultracentrifuged for UHPLC-MS/MS analysis. For ITSP+LPGC-MS/MS, another portion of the initial extract undergoes salt-out partitioning with 4:1 (w/w) anhydrous MgSO₄/NaCl and the upper layer extract is transferred to an autosampler vial for automated cleanup and analysis in parallel. Quality control spikes were made during the comminution, extraction, cleanup, and analysis steps to isolate and estimate the individual and overall measurement uncertainties of the approach. The recommended test portion size is 2 g for routine monitoring by this approach, but results demonstrated that subsamples as low as 0.5 g typically gave overall biases and relative standard deviations of <10% for nearly all pesticides, commodities, and methods, which is 3-5% lower than previously evaluated sample processing and analytical methods. This approach can be used to improve data quality, laboratory efficiency, and sample throughput in routine monitoring programs for regulatory, risk assessment, and other purposes.