Among pesticide analytical applications, GC-MS and LC-MS serve as the most powerful tools commonly used to monitor pesticide residues in food. However, both GC–MS and LC–MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sam...
Among pesticide analytical applications, GC-MS and LC-MS serve as the most powerful tools commonly used to monitor pesticide residues in food. However, both GC–MS and LC–MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sample preparation, instrumentation, and operating conditions. Three QuEChERS versions (the original unbuffered method and two inter-laboratory validated versions: AOAC Official method, which uses acetate buffering, and EN 15662, which uses citrate buffering) were compared in terms of matrix effect. LC–MS/MS and GC–TOF/MS using these three methods were tested for the analysis of pesticides in apple–blueberry sauce, peas, and limes spiked with 32 representative pesticides. None of the QuEChERS versions gave significantly different matrix effects from each other with the instrument and conditions we used and the GC–TOF/MS total ion chromatograms of the matrix blank extracts for each commodity from the different methods were very similar within each sample type for all three methods.
The most common in pesticide residue applications is matrix-matched calibration, among the approaches that reduce matrix effects, because it is relatively inexpensive and simple. The quality of matrix-matched results depends on the consistency of matrix effects among diverse sample. The variability of matrix effects was measured for 38 representative pesticides in 20 samples each (including different cultivars) of rice, orange, apple, and spinach extracted using the QuEChERS method for analysis by LC–MS/MS and GC–TOF/MS. Using LC–MS/MS, only oranges gave >20% matrix effects for a few pesticides. GC–TOF/MS exhibited larger matrix effects, but as in LC–MS/MS, the differences were reasonably consistent among the 20 samples tested. Main conclusions of this study are that for the conditions utilized: (1) matrix-matching was not needed for most pesticides in the simpler food matrices; and (2) for the more complex orange matrix, acceptably accurate quantitative results were achieved by using matrix-matching even with a different sample of the same type.
The Allium genus is known as a complex matrix containing large amount of matrix interferences in pesticide residue analysis. To develop a sample preparation method to reduce matrix effect in Allium genus, the four methods for the sample processing were compared at different temperatures and grinding conditions: grinding at room temperature and waiting for 120 min, grinding at room temperature and waiting for 15 min, grinding after quick freezing with liquid nitrogen, and grinding with dry ice after slow freezing at -20℃. Onion and garlic were purified using QuEChERS sample preparation with citrate buffer after grinding and the extract is analyzed in LC-MS/MS and GC-MS/MS. The results demonstrated that matrix effect in onion and garlic decreased effectively by freezing the sample before grinding, and increased as the waiting time increase at room temperature after grinding. Grinding with dry ice after slow freezing provided a more effective removal of matrix co-extractives than that of rapid quick freezing with liquid nitrogen, which is also contributed to lower matrix effects. GC-MS/MS analysis also showed that the best method is grinding with dry ice after slow freezing and the use of internal standard decreased matrix effect significantly. These findings suggest that grinding with dry ice after slow freezing could be employed in other Allium genus to detect pesticides.
To investigate the factors at instrumental analysis that affect matrix effect in pesticide residue analysis, four kinds of experiments were conducted. Firstly, the impact of the injection volume on matrix effect in LC-MS/MS was studied using onion and garlic extracts at various injection volumes (1, 2, 5 and 10 µL). Secondly, the effect of sample dilution on matrix effect in LC-MS/MS was investigated using garlic and grapefruit extracts at various dilutions (0, 2, 5, 10 and 100 times dilution). Thirdly, the effect of pesticide mixtures on calibration was tested in LC-MS/MS. Lastly, applicability of cucumber raw extract as natural analyte protectant in GC-MS/MS was investigated using onion and garlic extracts. The increase in matrix effect by changing injection volume is negligible in onion. However, in garlic, the increase of injection volume increased matrix effect significantly, and a linear or logarithmic function of relation between matrix effects and injection volumes was observed. In terms of dilution, matrix effect of 95% and 97% of pesticides in grapefruit and garlic were decreased by ≤20% after 10 times dilutions. Relation between matrix effects and dilution factors of 1-10 in pesticides gave logarithmic function. Mixing of more than three pesticides with same retention times decreased peak signals of pesticides, especially at high concentration and large injection volume. In GC-MS/MS analysis, the use of cucumber raw extract as calibration solution decreased matrix effect remarkably. The use of analyte protectant chemicals with cucumber raw extract further decreased matrix effect. These results could be used to predict and reduce matrix effect in pesticide residue analysis.
Recently, zirconia-based sorbents were evaluated for the analysis of pesticide residues in high-fat food. The aim of this study was to evaluate the performance of different sorbents for the cleanup step in multiresidue pesticide analysis in low-fat food using QuEChERS sample preparation. The matrices were partitioned using acetonitrile with citrate buffer prior to cleanup step. The supernatant was purified using PSA and zirconia-based sorbents (Z-Sep and Z-Sep plus). The different sorbents were compared for 323 pesticides and metabolites in terms of recovery rates, relative standard deviations and matrix effects using LC–MS/MS and GC-MS/MS. Satisfactory recoveries with 70-120% were obtained from the 83-85% of pesticides in PSA, 82-84% in Z-Sep and 68-70% in Z-Sep plus. The recovery of base-labile pesticides was improved by use of zirconia with <5.2 of pH values. The best results in terms of matrix effects in LC-MS/MS were obtained with Z-Sep plus, while matrix effects for PSA and Z-Sep were similar. In case of matrix effect in GC-MS/MS, Z-Sep plus also gave the best result. PSA and Z-Sep gave similar matrix effects with ≤20% for all pesticides except 3 pesticides in grape. The study suggests that Z-Sep could be used in QuEChERS sample preparation as sorbent for analysis of low-fat food.
Among pesticide analytical applications, GC-MS and LC-MS serve as the most powerful tools commonly used to monitor pesticide residues in food. However, both GC–MS and LC–MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sample preparation, instrumentation, and operating conditions. Three QuEChERS versions (the original unbuffered method and two inter-laboratory validated versions: AOAC Official method, which uses acetate buffering, and EN 15662, which uses citrate buffering) were compared in terms of matrix effect. LC–MS/MS and GC–TOF/MS using these three methods were tested for the analysis of pesticides in apple–blueberry sauce, peas, and limes spiked with 32 representative pesticides. None of the QuEChERS versions gave significantly different matrix effects from each other with the instrument and conditions we used and the GC–TOF/MS total ion chromatograms of the matrix blank extracts for each commodity from the different methods were very similar within each sample type for all three methods.
The most common in pesticide residue applications is matrix-matched calibration, among the approaches that reduce matrix effects, because it is relatively inexpensive and simple. The quality of matrix-matched results depends on the consistency of matrix effects among diverse sample. The variability of matrix effects was measured for 38 representative pesticides in 20 samples each (including different cultivars) of rice, orange, apple, and spinach extracted using the QuEChERS method for analysis by LC–MS/MS and GC–TOF/MS. Using LC–MS/MS, only oranges gave >20% matrix effects for a few pesticides. GC–TOF/MS exhibited larger matrix effects, but as in LC–MS/MS, the differences were reasonably consistent among the 20 samples tested. Main conclusions of this study are that for the conditions utilized: (1) matrix-matching was not needed for most pesticides in the simpler food matrices; and (2) for the more complex orange matrix, acceptably accurate quantitative results were achieved by using matrix-matching even with a different sample of the same type.
The Allium genus is known as a complex matrix containing large amount of matrix interferences in pesticide residue analysis. To develop a sample preparation method to reduce matrix effect in Allium genus, the four methods for the sample processing were compared at different temperatures and grinding conditions: grinding at room temperature and waiting for 120 min, grinding at room temperature and waiting for 15 min, grinding after quick freezing with liquid nitrogen, and grinding with dry ice after slow freezing at -20℃. Onion and garlic were purified using QuEChERS sample preparation with citrate buffer after grinding and the extract is analyzed in LC-MS/MS and GC-MS/MS. The results demonstrated that matrix effect in onion and garlic decreased effectively by freezing the sample before grinding, and increased as the waiting time increase at room temperature after grinding. Grinding with dry ice after slow freezing provided a more effective removal of matrix co-extractives than that of rapid quick freezing with liquid nitrogen, which is also contributed to lower matrix effects. GC-MS/MS analysis also showed that the best method is grinding with dry ice after slow freezing and the use of internal standard decreased matrix effect significantly. These findings suggest that grinding with dry ice after slow freezing could be employed in other Allium genus to detect pesticides.
To investigate the factors at instrumental analysis that affect matrix effect in pesticide residue analysis, four kinds of experiments were conducted. Firstly, the impact of the injection volume on matrix effect in LC-MS/MS was studied using onion and garlic extracts at various injection volumes (1, 2, 5 and 10 µL). Secondly, the effect of sample dilution on matrix effect in LC-MS/MS was investigated using garlic and grapefruit extracts at various dilutions (0, 2, 5, 10 and 100 times dilution). Thirdly, the effect of pesticide mixtures on calibration was tested in LC-MS/MS. Lastly, applicability of cucumber raw extract as natural analyte protectant in GC-MS/MS was investigated using onion and garlic extracts. The increase in matrix effect by changing injection volume is negligible in onion. However, in garlic, the increase of injection volume increased matrix effect significantly, and a linear or logarithmic function of relation between matrix effects and injection volumes was observed. In terms of dilution, matrix effect of 95% and 97% of pesticides in grapefruit and garlic were decreased by ≤20% after 10 times dilutions. Relation between matrix effects and dilution factors of 1-10 in pesticides gave logarithmic function. Mixing of more than three pesticides with same retention times decreased peak signals of pesticides, especially at high concentration and large injection volume. In GC-MS/MS analysis, the use of cucumber raw extract as calibration solution decreased matrix effect remarkably. The use of analyte protectant chemicals with cucumber raw extract further decreased matrix effect. These results could be used to predict and reduce matrix effect in pesticide residue analysis.
Recently, zirconia-based sorbents were evaluated for the analysis of pesticide residues in high-fat food. The aim of this study was to evaluate the performance of different sorbents for the cleanup step in multiresidue pesticide analysis in low-fat food using QuEChERS sample preparation. The matrices were partitioned using acetonitrile with citrate buffer prior to cleanup step. The supernatant was purified using PSA and zirconia-based sorbents (Z-Sep and Z-Sep plus). The different sorbents were compared for 323 pesticides and metabolites in terms of recovery rates, relative standard deviations and matrix effects using LC–MS/MS and GC-MS/MS. Satisfactory recoveries with 70-120% were obtained from the 83-85% of pesticides in PSA, 82-84% in Z-Sep and 68-70% in Z-Sep plus. The recovery of base-labile pesticides was improved by use of zirconia with <5.2 of pH values. The best results in terms of matrix effects in LC-MS/MS were obtained with Z-Sep plus, while matrix effects for PSA and Z-Sep were similar. In case of matrix effect in GC-MS/MS, Z-Sep plus also gave the best result. PSA and Z-Sep gave similar matrix effects with ≤20% for all pesticides except 3 pesticides in grape. The study suggests that Z-Sep could be used in QuEChERS sample preparation as sorbent for analysis of low-fat food.
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