Strategies for Analysis of Pyrethroid Insecticides in Complex Matrices

Transcription

1 Strategies for Analysis of Pyrethroid Insecticides in Complex Matrices Del A. Koch 1 and Kevin Clark 1 1E EAG/ABC Laboratories, 7200 E. ABC Lane, Columbia, MO rd Annual North American Chemical Residue Workshop TradeWinds Island Grand, St. Pete Beach, Florida July 17-20, /28/2016

2 Synthetic Pyrethroids Many synthetic pyrethroids are esters of naturallyoccurring chrysanthemic acid, with a variety of substituents Chrysanthemic acid 8/28/2016 Slide 2

3 Synthetic Pyrethroids Two Examples of Synthetic Pyrethroids: Cypermethrin Esfenvalerate 8/28/2016 Slide 3

4 Synthetic Pyrethroids Pyrethroids exhibit low mammalian activity and have a variety of uses: Agricultural insecticides External structure barriers, lawn insecticides, and internal home use Lice, flea, and tick control (permethrin) Adult mosquito control (permethrin for West Nile/Zika virus vector control and treatment of clothing and netting) 8/28/2016 Slide 4

5 Pyrethroids are notable for low water solubility 8/28/2016 Slide 5 Water Solubility Compound (µg/l) Bifenthrin Deltamethrin 0.20 Cyfluthrin 2.3 Cypermethrin 4.0 Lambda-Cyhalothrin 5.0 Permethrin 5.5 Esfenvalerate 6.0 Fenpropathrin 10.3 Diflubenzuron 140 Chlorpyrifos 2,000 Diazinon 40,000 Carbaryl 120,000 Oxamyl 280,000,000 Sources: (Pyrethroids) Laskowski, D.A., Res Environ Contam Toxicol 174:49-170, 2002 (Others) The Agrochemicals Handbook, Royal Society of Chemistry, 2nd Ed.

6 Pyrethroid Analytical Considerations Multi-analyte methods often are based upon gas chromatography with negative chemical ionization with mass spectral detection (NCI-GC- MS) as the determinative step Negative chemical ionization (using methane or ammonia as the ionization gas) is a softer technique which produces less molecular fragmentation than electron ionization (EI) Monitoring for specific, characteristic, ions for each compound provides for enhanced sensitivity/specificity GC provides separation of some stereoisomers, which can produce a characteristic fingerprint 8/28/2016 Slide 6

7 Pyrethroid Analytical Challenges Pyrethroids have a notable tendency to sorb onto vessel wall (and any other available) surfaces Can lead to low recoveries Laboratory cross-contamination, especially at what are becoming increasingly lower levels of interest, may occur Water samples containing particulates (and even dissolved organic carbon) require some discretion as far as the best method to apply 8/28/2016 Slide 7

8 Pyrethroid Analytical Challenges Strategies for handling sorption issues Low recoveries -- Use methodology which includes extraction/organic solvent rinsing on the sample container Laboratory cross-contamination Avoid the use of non-disposable glassware (such as separatory funnels) 8/28/2016 Slide 8

9 Pyrethroid Analytical Challenges Strategies for handling sorption issues, continued Water samples For total pyrethroids, extract the entire sample in the original container. For dissolved (and complexed with dissolved organic carbon) only, filter the sample rapidly prior to analysis. For free (non-complexed; i.e., bioavailable) only, considering using solid phase micro-extraction (SPME) as the determinative step (without further treatment that might allow wall losses) 8/28/2016 Slide 9

10 Pyrethroid Analytical Challenges Gas chromatographic analysis methods at trace levels are inherently challenged to maintain a consistent relationship between analyte concentration/detector response Sample co-extractive matrix effects in the injector inlet can result in differing responses from sample extracts and standards in solvent having the same concentrations for a given analyte Over time there may be a drift in the detector response, especially after injection of dirty sample extracts 8/28/2016 Slide 10

11 Pyrethroid Analytical Challenges One approach to reducing differential injector effects is to add analyte protectants (matrix modifiers) to standard and sample solutions Goal is for standard solvent composition to be closer to that of samples and also to reduce the tendency of the analytes to stick in the GC injection system Success has been achieved, for example, by adding 0.1% peanut oil to sample final extracts, as well as to the solvent standards 8/28/2016 Slide 11

12 Use of Stable Label Pyrethroid Analogues A reliable approach to normalizing injector effects and/or detector drift is the use of (as available) appropriate stable isotope analogues in conjunction with mass selective detection methods Stable isotope analogues behave almost identically to the corresponding native analyte. By adding a known amount of a stable isotope to both standards and sample extracts and quantifying using the ratios of native analyte/stable isotope response, biases due to injector and/or detector variability may be virtually eliminated 8/28/2016 Slide 12

13 Use of Stable Label Pyrethroid Analogues Choice of stable isotopes to be consistent with the existing NCI-GC-MS instrumental technique Some 13 C phenoxy stable isotopes were commercially available But for the 8 targeted compounds, only one of the primary quantification NCI-GC- MS fragment ions contained the phenoxy group Stable labels on the primary quantification fragment ions were therefore needed 8/28/2016 Slide 13

14 Use of Stable Label Pyrethroid Analogues Methyl groups on the acid side of the molecules were chosen for labelling: CH 3 CH 3 Cypermethrin CH 3 CH 3 Esfenvalerate 8/28/2016 Slide 14

15 Examples of NCI-GC-MS Target Ions CH 3 CH 3 Cypermethrin Target Ion = m/z 207, Qualifier = m/z 209 CH 3 CH 3 Esfenvalerate Target Ion = m/z 211, Qualifier = m/z 213 8/28/2016 Slide 15

16 Examples of NCI-GC-MS Target Ions CD 3 CD 3 Cypermethrin-D6 Target Ion = m/z 213, Qualifier = m/z 215 CD 3 CD 3 8/28/2016 Slide 16 Esfenvalerate-D6 Target Ion = m/z 217, Qualifier = m/z 219

17 Pyrethroid Example Mass Spectrum Cypermethrin mass scan: No response at m/z 213 Primary ion monitored for the D6 cypermethrin internal standard = =213 8/28/2016 Slide 17

18 D6 Pyrethroid Example Mass Spectrum D6 Cypermethrin mass scan: Primary ion monitored for the D6 cypermethrin internal standard = 213 8/28/2016 Slide 18

19 Biosolids Case Study Preliminary PWG monitoring studies showed that biosolid samples from publicly owned treatment works (POTWs) showed that POTW biosolids can contain pyrethroids (arising from various residential uses) and therefore a robust method was required for this complex matrix This matrix represents challenges, some of which (already discussed) are common to to analysis of pyrethroids in other matrices such as water and crops 8/28/2016 Slide 19

20 Biosolids Case Study Biosolid samples, continued Biosolids in particular can be of significantly variable composition Biosolids have some unique challenges in choosing/obtaining appropriate clean control materials for laboratory fortifications No organic store with certified pesticide-free materials available 8/28/2016 Slide 20

21 Biosolids Samples Representative Biosolids Sample 8/28/2016 Slide 21

22 Biosolids Case Study Example of difficulty in using samples with incurred background residues for recovery determinations: Compound A Background, ppb Fortified, ppb Total Measured, ppb Fortified ppb, corrected for True background Corrected recovery, % True value Measured low end 400 (+/- 20%) 180 (+/- 10%) Measured high end 600 (+/- 20%) 220 (+/- 10%) /28/2016 Slide 22

23 Biosolids Case Study Use of D6 isotope analogues to evaluate method performance in a representative or designated -- biosolids sample For analytes with a high background level for a given analyte, utilize the corresponding D6 analogue for fortification This will require using a different D6 pyrethroid (ideally one which has a similar GC retention time) as the method internal standard Empirically this has been demonstrated to be an acceptable workaround 8/28/2016 Slide 23

24 Biosolids Case Study Regarding the challenge of sample-to-sample variability -- the use of surrogates is a common practice in the Environmental Lab industry EPA Definition of Surrogate (Method 507): A pure analyte(s), which is extremely unlikely to be found in any sample, and which is added to a sample aliquot in known amount(s) before extraction and is measured with the same procedures used to measure other sample components. The purpose of a surrogate analyte is to monitor method performance with each sample {emphasis added}. 8/28/2016 Slide 24

25 Biosolids Case Study Esfenvalerate-D6 and fenpropathrin-d6 were used as surrogates for samples from a POTW monitoring study Very unlikely to be found in biosolids samples GC Retention time window for the multianalyte method is min Fenpropathrin-D6 elutes near the beginning of the range (18.4 min, just after bifenthrin) Esfenvalerate-D6 elutes near the end (24.5 and 24.7 min for the two measurable peaks, just before deltamethrin) 8/28/2016 Slide 25

26 Biosolids Case Study Esfenvalerate-D6 and fenpropathrin-d6 were used as surrogates to measure method recovery in every sample Thus these two D6 materials could not be used as instrumental internal standards to accurately and precisely quantify native esfenvalerate and fenpropathrin, respectively Experimentation indicated that deltamethrin- D6 and bifenthrin-d6 served adequately as replacement internal standards for the quantification of native esfenvalerate and fenpropathrin, respectively 8/28/2016 Slide 26

27 Biosolids Method Flow Chart Fortify w/ surrogate Add MeOH w/formic acid, homogenize sample Reconstitute in hexane, load on Silica SPE Wash SPE with hexane Elute SPE with 9:1 hexane:diethyl ether N-Evap to dryness Reconstitute in hexane, load on Florisil SPE (discard) 8/28/2016 Slide 27 Bring to volume, N-Evap aliquot to dryness Shake with 50:50 MeOH:Me 2 Cl 2 Decant Thru Na 2 SO 4 to dry N-Evap to dryness Elute with hexane then 85:15 hexane:diethyl ether Solids Second shake with 50:50 MeOH:Me 2 Cl 2 Decant Reconstitute in 0.1% peanut oil in cyclohexane internal standard (IS) Solution Dilute as necessary with 0.1% peanut oil in cyclohexane IS Quantify/confirm by NCI-GC/MS

28 Method Recoveries and Surrogate Results from POTW Biosolids Monitoring Compound Name Fort. Conc. (ng/g) n Average Recovery Std. Dev. Bifenthrin Cyfluthrin Cypermethrin Deltamethrin Esfenvalerate 200/ Fenpropathrin Lambda-Cyhalothrin Permethrin Surr-Esfenvalerate-D Surr-Fenpropathrin-D Surr-Esfenvalerate-D Surr-Fenpropathrin-D /28/2016 Slide 28

29 Method Recoveries from POTW Biosolids Monitoring Biosolids Data Recovery Std. Dev /28/2016 Slide 29

30 In Conclusion While there are significant challenges inherent to the analysis of pyrethroids as a class, through awareness of the difficulties and judicious use of the available analytical tools and strategies, the production of quality data is achievable The availability of the D6 standards has been a key component to the improvement of analytical methodology Used as instrumental internal standards, injector effects and detector drift are compensated for As surrogates, the D6 standards are superior to other possible analytes which less closely mimic analyte behavior and recoverability Contact dkoch@eag.com for additional D6 standard information 8/28/2016 Slide 30

31 Acknowledgements The assistance and responsiveness of Kalexsyn, Inc. in supplying the stable isotope internal standards and surrogates are gratefully acknowledged. The collaboration and support of the PWG member companies (AMVAC, BASF, Bayer, FMC, Syngenta, and Valent) were key factors in the successful development of the analytical methods, and are greatly appreciated. 8/28/2016 Slide 31