This is the final part of the blog series “Tips on the analysis of pesticides and mycotoxins in cannabis products: Matrix matters!” In Part I (here) and II (here), we covered various practical aspects related to matrix effects, spiking procedures, and recoveries. We gave real examples about how matrix type, matrix effects, and spiking strategies can affect the final quantitative data in different ways. We also provided several suggestions about how to assess and account for such effects in your analytical method. In part III, we want to highlight that reliable quantitative data is achievable even if your recoveries are not exhaustive. As we mentioned at the end of Part II, accuracy and recovery are terms with different meanings. However, sometimes these terms are used interchangeably, but this isn’t the best practice. Accuracy is defined as the proximity or closeness of a given measurement (typically a mean value) to the true value. On the other hand, recovery refers to the extraction efficiency of a given analytical method, and it is determined by comparing the amount of analyte extracted from a spiked sample vs. the total amount of analyte initially added. In some cases, the term recovery is used to refer to the % calculated using the equation (estimated concentration/spiked concentration (nominal value))*100 which may result in confusion of the terms in some cases
Reliable and robust methods need to consistently provide accurate and precise measurements of target analytes over the concentration range expected in real samples. This does not necessarily mean that the extraction method should provide 100% recoveries. To demonstrate this, we can look at the data in Table 1, which corresponds to daminozide recoveries and accuracy values obtained in three different matrices: brownies, dark chocolate, and gummies. After trying out various sample preparation conditions, we were not able to achieve recoveries higher than 30% in both brownies and gummies.

Table 1. Recovery, accuracy, and precision values obtained for daminozide in three different cannabis edibles.

a) Sample preparation for brownies: brownies samples were prepared as described in our technical article (here).

b) Sample preparation for dark chocolate: dark chocolate samples (0.5 g) were extracted by using isopropyl alcohol (0.5 mL) and acetonitrile acidified with acetic acid at 1% (2.5 mL); subsequently, 2 mL of the extract were passed through a Restek Resprep C18 cartridge (Restek Cat.#26030). 750 µL of organic extract was mixed with 250 µL of water. 2 µL of final extract was injected into the LC-MS/MS system.

c) Sample preparation for gummies: gummies chopped in pieces (1 g) were mixed with 5 mL of water and then vigorously vortexed until all gummy pieces were fully solubilized. 5 mL of acetonitrile acidified with 1% acetic acid was added to each sample, and this was followed by a 30 sec vortex agitation. Then, a pouch of European EN 15662 QuEChERS extraction salts (cat.# 25849) was added to each sample. Samples were vortexed for 30 sec and then centrifuged for 5 min. 750 µL of organic extract was mixed with 250 µL of water. 2 µL of final extract was injected into the LC-MS/MS system.

As we have emphasized in parts I and II, daminozide is a very polar pesticide, therefore exhaustively extracting it is not an easy task in every matrix, especially when performing multiresidue pesticide testing. However, accuracy and precision values estimated at two different concentration levels in the three edible types demonstrated that our methodologies are reliable and robust. This was enabled by the use of daminozide-d6, a deuterated analogue of this tricky pesticide, which not only corrects for matrix effects, but also accounts for the non-exhaustive recovery of daminozide in the different matrix types. In cases where achieving exhaustive recoveries is not feasible, it is crucial to employ an appropriate internal standard that shows consistent and reproducible recoveries with the target analyte, ideally an isotopically-labeled analogue.
I hope this blog series was able to provide useful tips and tricks to develop successful methods for the analysis of pesticides and mycotoxins in different cannabis matrices. If you have any questions or comments you can type them in the box below. Thanks for reading!