Method and system for detecting pesticide residue in argicultural products using mass spectrometry imaging analysis

A method for detecting pesticide residues, comprising:

• (a). preparing two identical extracts obtained from a first sample to be analyzed, and turning one of the two extracts into a first sample solution with no additives, and the other extract to a second, spiked sample solution in which at least one first pesticide standard of a known concentration (X1) is added;
• (b). preparing another two identical extracts obtained from a second sample to be analyzed, and turning one of the two extracts into a first sample solution with no additives, and the other extract to a second, spiked sample solution in which at least one second pesticide standard of a known concentration (X2) is added;
• (c). introducing the first and second sample solutions of the first sample consecutively into a chromatographic and mass-spectrometric system to create a first mass chromatogram for the first sample solution and a second mass chromatogram for the second, spiked sample solution, wherein a peak of the first pesticide standard added in the second, spiked sample solution of the first sample is to be detected at a retention time as shown in the second mass chromatogram;
• d). running an image recognition algorithm to compare the first and second mass chromatograms of the first sample in order to determine whether a peak appears at the same retention time in the first mass chromatogram, and the peak in the first mass chromatogram has a shape substantially identical or similar to that of the peak of the first pesticide standard in the second mass chromatogram, and an intensity slightly smaller than that of the peak of the first pesticide standard;
• if no, it is determined that the first sample contains no pesticide residue of the same kind as the first pesticide standard;
• and
• if yes, executing an image analysis to calculate an increased integral area (A1), representative for the concentration (X1) of the first pesticide standard, by which the peak of the second, spiked sample solution in the second mass chromatogram exceeds the peak of the first sample solution in the first mass chromatogram at the same retention time, and then determining a concentration (Y1) of a pesticide residue in the first sample with the formula:
• Y1=(A2/A1)X
• where A2 is an integral area of the peak in the first mass chromatogram at the same retention time, A1 is the increased integral area, and X1 is the concentration of the first pesticide standard.
• (e). after the injection of the first and second sample solutions of the first sample into the chromatographic and mass-spectrometric system, introducing the first and second sample solutions of the second sample consecutively into the chromatographic and mass-spectrometric system to create a first mass chromatogram for the first sample solution and a second mass chromatogram for the second, spiked sample solution, wherein a peak of the second pesticide standard added in the second, spiked sample solution of the second sample is to be detected at a retention time as shown in the second mass chromatogram;
• f). running an image recognition algorithm to compare the first and second mass chromatograms of the second sample in order to determine whether a peak appears at the same retention time in the first mass chromatogram, and the peak in the first mass chromatogram has a shape substantially identical or similar to that of the peak of the second pesticide standard in the second mass chromatogram, and an intensity slightly smaller than that of the peak of the second pesticide standard;
• if no, it is determined that the second sample contains no pesticide residue of the same kind as the second pesticide standard;
• and
• if yes, executing an image analysis to calculate an increased integral area (A3), representative for the concentration (X2) of the second pesticide standard, by which the peak of the second, spiked sample solution in the second mass chromatogram exceeds the peak of the first sample solution in the first mass chromatogram at the same retention time, and then determining a concentration (Y2) of a pesticide residue in the second sample with the formula:
• Y2=(A4/A3)X2
• where A4 is an integral area of the peak in the first mass chromatogram at the same retention time, A3 is the increased integral area, and X2 is the concentration of the second pesticide standard.

A pesticide residue detection system, comprising:

• a chromatographic and mass-spectrometric system having an inlet for injection of a first sample solution and a second, spiked sample solution, which are prepared from two identical extracts of a sample with the first sample solution having no additives and the second, spiked sample solution having at least one pesticide standard of a known concentration (X) added;
• a computer coupled to the chromatographic and mass-spectrometric system and configured to create a first mass chromatogram for the first sample solution and a second mass chromatogram for the second, spiked sample solution, wherein a peak of the pesticide standard added in the second, spiked sample solution is to be detected at a retention time as shown in the second mass chromatogram;
• the computer further configured to carry out an image recognition algorithm to compare the first and second mass chromatograms in order to determine whether a peak appears at the same retention time in the first mass chromatogram, and the peak in the first mass chromatogram has a shape substantially identical or similar to that of the peak of the pesticide standard in the second mass chromatogram, and an intensity slightly smaller than that of the peak of the pesticide standard;
• if no, it is determined that the sample contains no pesticide residue of the same kind as the pesticide standard;
• and
• if yes, the computer further executes an image analysis to calculate an increased integral area (A1), representative for the concentration (X) of the pesticide standard, by which the peak of the second, spiked sample solution in the second mass chromatogram exceeds the peak of the first sample solution in the first mass chromatogram at the same retention time, and then determines a concentration (Y) of a pesticide residue in the sample with the formula:
• Y=(A2/A1)X
• where A2 is an integral area of the peak in the first mass chromatogram at the same retention time, A1 is the increased integral area, and X is the concentration of the pesticide standard.