Food & Beverage Analysis
Five Key Practices for Pesticide Analysis in Challenging Food Matrices by GC/MS
Anastasia A. Andrianova and Limian Zhao, Agilent Technologies, Inc
Global food demand is rising, and so is the use of pesticides, with over a thousand different chemicals on the market [1]. However, pesticide residues can pose risks to the global food supply chain, the environment, and the consumer when proper agricultural practices are not followed.
Concerns about trace level pollutants in food are driving the demand for more rapid and reliable ways to identify and quantify chemical residues. One measure of food safety is the maximum residue limit (MRL), which is the highest level of pesticide residue allowed to remain in or on the treated food commodity. In this article we highlight fi ve key ways to ensure successful pesticide analysis using gas chromatography / triple quadrupole mass spectrometry.
Global food demand is rising, and so is the use of pesticides, with over a thousand different chemicals on the market [1]. However, pesticide residues can pose risks to the global food supply chain, the environment, and the consumer when proper agricultural practices are not followed.
Concerns about trace level pollutants in food are driving the demand for more rapid and reliable ways to identify and quantify chemical residues. One measure of food safety is the maximum residue limit (MRL), which is the highest level of pesticide residue allowed to remain in or on the treated food commodity. For example, in the US, MRLs are known as tolerances [2].
MRLs may vary over a broad concentration range depending on the type of pesticide and the food product treated. For example, the US Environmental Protection Agency (EPA) has established tolerances for 68 pesticides in spinach that vary from 10 parts per billion (ppb) for fl udioxonil to 60,000 ppb for boscalid [3].
This range of limits presents a challenge for gas chromatography/mass spectrometry (GC/MS) analysis, requiring both high sensitivity and the ability to calibrate over a wide dynamic range. Five key components can ensure successful pesticide analysis:
• Effective sample extraction and matrix cleanup • Evaluation of the matrix in full scan data acquisition mode • Midcolumn backfl ushing
• A leak-free triple quadrupole GC/MS system (GC/TQ) • Proper inlet and liner selection
Here, we describe how these fi ve components enabled the GC/MS/MS analysis of over 200 pesticides in three challenging matrices: a high chlorophyll fresh matrix spinach, a complex dry matrix cayenne pepper, and an oily dry matrix walnut. Two separate GC/TQ models (Figures 1A and 1B) were used and confi gured to achieve the best performance over a wide calibration range. GC/MS/MS is extremely selective, sensitive, linear, and robust technic used for quantitating pesticides in various matrices. It is often used in combination with liquid chromatography/mass spectrometry (LC/MS/MS) for a comprehensive analysis of both nonpolar and polar pesticides and residual contaminants in food.
downtime; it should meet the required sensitivity, which can be at sub-ppb levels; and it must enable calibration performance over a wide dynamic range that encompasses the MRLs for the compounds monitored.
Robust pesticide analysis that supports a high-throughput workfl ow entails a series of requirements. It must provide extended maintenance-free operation with minimal downtime; it should meet the required sensitivity, which can be at sub-ppb levels; and it must enable calibration performance over a wide dynamic range that encompasses the MRLs for the compounds monitored.
Our process enabled accurate quantifi cation of pesticides in these matrices at their MRLs, achieving matrix-matched calibrations with R2 >0.99 over dynamic ranges as wide as 0.1 to 5,000 ppb with high method sensitivity. In addition, these strategies minimise instrument downtime, which is confi ned to liner and septum replacement about every 100 injections. Across 1,000 injections of the three complex matrix extracts (spinach, cayenne pepper, and walnut), there was no need to perform TQ MS tuning, source cleaning, or GC column trimming. The details on system performance during the longevity study can be found in this publication:
https://www.agilent.com/cs/library/ applications/an-gc-ms-ms-analysis-of-203-pesticides-in-10-minutes-in-spinach-5994- 4967en-agilent.pdf
Sample Preparation
Effective sample extraction and matrix cleanup allow for minimal matrix background and interferences while maintaining high pesticide recoveries. Analysing crude QuEChERS extracts, especially of complex pigmented and oily matrices, can signifi cantly increase the need for liner replacement, inlet cleaning, GC column trimming, and MS source
cleaning. Such maintenance procedures decrease throughput of the analysis. Performing an effi cient matrix cleanup following QuEChERS extraction reduces in-source matrix loading and interferences with targets, while improving signal-to-noise ratio, accuracy, and reproducibility for target pesticides.
The sample preparation workfl ow, shown in Figure 2 included two major steps:
sample extraction by traditional QuEChERS extraction and an appropriate pass-through cleanup \with Captiva EMR with Carbon S. The new sample cleanup protocol is a simplified procedure that demonstrates an improvement on both sample matrix removal and targets overall recovery and reproducibility.
Sample extraction by traditional QuEChERS extraction and an appropriate pass-through cleanup with Captiva EMR with Carbon S. These EMR with Carbon S cartridges can be adopted directly after QuEChERS extraction using the simplifi ed pass-through procedure and demonstrates the improvement on both sample matrix removal and targets overall recovery and reproducibility. The Captiva EMR with Carbon S cartridges selection is based on the plant origin sample matrix complexity and pigmented level according to the selection guide from previous study. (
https://www.agilent.com/cs/library/applications/ an-captiva-emr-gpf-5994-4764en-agilent.pdf) Figure 2 shows the entire fl ow chart for sample preparation.
Figure 1. The Agilent 8890/7000E and 8890/7010 GC/QT system (A) and system configuration (B)
Figure 1. The Agilent 8890/7000E and 8890/7010 GC/QT system (A) and system confi guration (B)
Our process enabled accurate quantification of pesticides in these matrices at their MRLs, achieving matrix-matched calibrations with R2 >0.99 over dynamic ranges as wide as 0.1 to 5,000 ppb with high method sensitivity. In addition, these strategies minimise instrument downtime, which is confined to liner and septum replacement about every 100 injections. Across 1,000 injections of the three complex matrix extracts (spinach, cayenne pepper, and walnut), there was no need to perform TQ MS tuning, source cleaning, or GC column trimming. The details on system performance during the longevity study can be found in this publication:
Figure 2. Sample preparation flowchart including traditional QuEChERS extraction, followed with Captiva EMR pass-through cleanup.
Figure 2. Sample preparation fl owchart including traditional QuEChERS extraction, followed with Captiva EMR pass-through cleanup.
As shown in Figure 3, the abundance of TIC signal in full scan data acquisition mode was noticeably reduced for spinach, walnut, and cayenne pepper extracts after cleanup compared to crude extracts before cleanup.
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