AL
Sensitivity is also useful because it allows for greater dilutions of extracts while still able to meet the required action-limit detection levels. The complexity of the cannabis matrix often causes peak shape problems that can interfere with the detection of a compound. In these situations, diluting the extract can greatly improve the peak shape, but it is important that the instrumental sensitivity is sufficient to still allow for the MRL to be achieved with the dilution. The effect of dilu- tion can be seen in Figure 1. In this figure, a plant extract was spiked to a concentration of 4.5 ppb with Spinosyn D, an isomer in Spi- nosad. This concentration corresponds to a plant concentration of 0.1 ppm, which is half the action level of 0.2 ppm (9.1 ppb in the ex- tract); the action level for this compound is 9.1 ppb. The peak from an undiluted extract, a 4× dilution and a 10× dilution, are shown. These data are for Spinosyn D and the corre- sponding Oregon action level for the extract is 9.1 ppb. Clearly, it is not possible to measure the peak area in the undiluted sample. It is possible, however, to measure an accurate peak area at both 4× and 10× dilution. The data also indicate that the LC-MS/MS has sufficient sensitivity to analyze much lower concentrations than is required by the state’s action limits.
Figure 2 shows the data for myclobutanil, one of the most common chemicals found in cannabis samples due to its effectiveness as a fungicide. The data show the results for a flower extract that has been spiked to a con- centration of 0.45 ppb (0.01 ppm in the plant). For this compound, the Oregon action level is 0.2 ppm, which is 20 times higher than the spiked level. These data show the excellent sensitivity and linearity achieved using LC-MS/ MS, even at concentrations well below the ac- tion limits. The three peaks in the top pane of the figure are three replicate injections of a flower extract spiked to a concentration of 0.45 ppb. This demonstrates the outstanding precision that is achievable in matrix us- ing LC-MS/MS. The data from Figures 1 and 2 are typical of the performance for most compounds on the Oregon list, and show suit- ability of LC-MS/MS for this analysis.
Possibly the most important criterion for analysis in a production laboratory is the
AMERICAN LABORATORY 11
ruggedness of the method. Figure 3 shows the peak areas for the quantitation transition for 12 compounds from a 20-ppb QC check sample analyzed as a calibration check during the analysis of sample extracts. These are raw peak areas, and not peak ratios, using an inter- nal standard. The data show the area for these compounds over a three-month period rep- resenting approximately 9000 injections, and demonstrate the ruggedness and stability that
can be expected for LC-MS/MS over extended periods of time in actual production. During this time, solvent was replaced daily, guard columns were replaced weekly, the ion source orifice was rinsed every two weeks, and the analytical column was replaced monthly. None of these maintenance procedures removed the instrument from service and did not affect laboratory productivity. The data show that the response drift was well below the 20% QC
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www.anton-paar.com/svm JUNE/JULY 2017
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