Pesticides in Daphnia using GC
This worksheet is based on the article: Anal Bioanal Chem (2016) 408:1055–1066
“Measuring internal azole and pyrethroid pesticide concentrations in Daphnia magna using QuEChERS and GC-ECD—method development with a focus on matrix effects” by Andreas Kretschmann, Nina Cedergreen & Jan H. Christensen
- In one sentence, what is the purpose of this study?
- Why are they studying these pesticides and Daphnia?
- Why are they focused on matrix effects here? What are the possible matrix effects in this analysis?
- Figure 1 shows the work flow for each step of the QueCheRs extraction. What is the purpose of each step?
- A. Read the figure caption well for Fig. 2 so you know what the symbols mean. What does it mean that in the A. hexaconazole figure, the dark and open circles are about the same, while in the A. Propicanizole figure, the open circles are above the dark circles, while in the A. Expoxiconazole figure, the open circles are mainly below the dark circles? What matrix effects explain this result?
- Some of the graphs show signals that go steadily down over time. What matrix effects cause this type of response?
- Given data such as Fig. 2, why is a matrix matched calibration considered the best solution for calculating pesticide concentrations?
- A. The authors are performing a common sample clean-up procedure here called solid phase extraction (SPE). Briefly describe how SPE works and how it cleans up samples.
- The methods details two different sorbents they use one with C18, primary-secondary amines but without carbon black (sorbent A) and one with those ingredients and carbon black (sorbent B). How is the performance of the two sorbents expected to differ given the analytes they are studying?
- Looking at Table 1, which gives retention times for GC, comparing HEX, BIF, and ES, how can you explain their order of elution?
- The bottom of the table gives accuracy (% recovery) measurements. How is this experiment performed? What does it mean to have a greater than 100% recovery?
- What does the data about precision tell you in the table? Do you think these are good precision values or not?
- The instrument here is a GC with ECD detector. Why would they choose an ECD detector for these analytes?
- A. Figure 4 shows the data in the real samples. How do you interpret the points below the LOQ and DL lines?
- The PP concentrations appear to remain elevated even after exposure while the CYM drops over time. What are the environmental implications of these results?