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Automated In-Line Pigment Removal for Multi-Residue Pesticide Analysis in Spinach by LC-MS/MS

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Matrix coextractives can lead to ionization suppression or enhancement, which can make it difficult to obtain accurate quantitative data for multiresidue pesticide analysis by LC-MS/MS. 

In this poster video, we’re going to show a new workflow using in-line sample preparation or ILSP for the removal of pigments that has been developed for the analysis of 63 pesticides in spinach.

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Hi, my name is Sharon Lupo. I work at Restek in the product development group and I will be presenting my poster “Automated In-Line Pigment Removal for the Analysis of Multiresidue Pesticides in Spinach by LC-MS/MS.”

Matrix coextractives can lead to ionization suppression or enhancement; this can make it difficult to obtain accurate quantitative data for multiresidue pesticide analysis by LC-MS/MS. A new workflow using in-line sample preparation, or ILSP, for the removal of pigments has been developed for the analysis of 63 pesticides in spinach.

Pigment removal is performed in-line using a dual-directional ILSP cartridge. A 6-port, high-pressure switching valve and auxiliary pump enable the capture and removal of interfering pigments from the sample during analysis. The analytical separation is performed on a Raptor ARC-18 column with a total cycle time of 9 minutes. Analysis and cleanup begins with the ILSP cartridge in the load position where it is in-line with the autosampler, analytical column, and mass spec. After trapping the pigments in the ILSP cartridge, the switching valve rotates to the wash position, bypassing the cartridge as the gradient program continues through the analytical column to the mass spec. Pigments are flushed to waste using the auxiliary pump before returning to the load position for equilibration in preparation for the next injection.

Performance of the new ILSP workflow was compared to a typical QuEChERS extraction using AOAC salts and dispersive solid phase extraction sorbents for cleanup. A comparison of the two procedures revealed that the extraction and cleanup steps of the ILSP workflow required only 20% of the time needed by the QuEChERS method to prepare 14 samples. Recovery and precision of the procedure was evaluated by spiking 63 representative pesticides into spinach.  Eighty-six percent of pesticides at the Low QC level, and 100% of pesticides at the High QC level met acceptance criteria for the ILSP workflow. The effectiveness of ILSP as an extract cleanup technique was benchmarked against multiple dSPE formulations containing varying concentrations of graphitized carbon black. Of the 63 pesticides tested, the ILSP technique in green shows the most pesticides with insignificant matrix effects, less than 20%, and the least with severe matrix effects, greater than 50%.

Since it is well known that the strong retentive properties of GCB can have an affinity for structurally planar pesticides as well as pigments, six planar pesticides were included in this experiment. Upon closer examination, all six exhibited severe matrix effects for the dSPE containing higher amounts of GCB, represented in yellow, orange, and grey, with declining matrix effects as the concentration of GCB decreases. ILSP utilizes an alternate mechanism for pigment removal; thus, planar pesticides are unaffected.

These samples were also evaluated for the presence of pigment ions by monitoring with MS in full scan. The sample extract cleaned using dSPE contains significantly more pigments than the ILSP sample. From this data, it becomes apparent that in order to prevent pesticide loss with the current QuEChERS workflow, insufficient removal of pigments must occur. Allowing pigments to remain in the sample can potentially compromise the LC analytical column and risk contaminating the MS interface, requiring more frequent instrument maintenance. 

In summary, the ILSP workflow takes significantly less time to perform and is more amenable to automation than a conventional QuEChERS extraction. ILSP enables the removal of pigments without the loss of planar pesticides while providing acceptable recovery and precision.

Thank you for watching my poster. If you would like more information, please see the link below.


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