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Compilation of Analytical Observations Reports

The table below compiles various observations made during the analysis of pesticide residues.

Laboratories within the NRL/OL-Network are encouraged to submit their own analytical observations. The idea is to gradually build up a large collection of observations with the aim to conserve knowledge and to offer laboratories a useful and practical source of information. A link to the EURL-DataPool is planned. Details on the Method Finder List can be found here: Link.

Compound No. of Method Finder List/Version/Date of Update Link
Acidic Pesticides SRM-02/(V1)/20.05.2015 Link

Short Description: Two methods, the QuEChERS method (EN 15662) and the acidified-QuEChERS method (A-QuEChERS) were tested for the analysis of acidic pesticides. A-QuEChERS involved extraction with acetonitrile containing 1% formic acid and the use of partitioning salts composed of NaCl and MgSO4 only. Recovery experiments were conducted on cucumber, grapes and maize. No alkaline hydrolysis step was conducted and thus the focus was on free acids only. Most compounds showed satisfactory recovery figures by both methods. There were some pesticides, however, where average recoveries using QuEChERS were unsatisfactory (< 70%) using QuEChERS but satisfactory using A-QuEChERS.

Carbofuran SRM-23/(V1)/20.04.2016 Link
Short Description: The final method developed is as follows: (a) Extraction: Apply the citrate buffered QuEChERS (EN 15662). Weigh 10 g of frozen fruit or vegetable homogenate or 5 g of cereals; adjust water content to 10 mL where necessary, add 10 mL acetonitrile and internal standard (e.g. 100 µL of an appropriately concentrated solution of Carbofuran-D3 ). Shake 15 min using a mechanical shaker. Add a mixture of 4g MgSO4, 1g NaCl, 1 g trisodium citrate dihydrate and 0.5 g disodium hydrogen citrate sesquihydrate, shake 1 min and centrifuge. (b) Cleanup:  Cleanup via dispersive SPE is optional for fruits and vegetables. (c) Hydrolysis: Transfer 1 mL of raw extract into vial and add 10 µL 5N H2SO4. Nearly quantitative transformation of BF, CS and FT into CF is achieved by heating the vials for 3h at 80°C. (d) LC-MS/MS analysis:  For screening purposes CF, 3-OH-CF as well as BF, FT and CS may be analyzed by LC-MS/MS directly in QuEChERS raw extracts or cleaned-up extracts. In case of positive findings the hydrolysis step can be conducted as described above and LC-MS/MS analysis of CF repeated.
1mL final extract will represent approximately 1 g matrix.
For measurement conditions and recovery figures see EURL-SRM - Analytical Method Report (Analysis of Residues of Carbofuran (sum) using QuEChERS method).
Dicofol SRM-11/(V1)/23.04.2013 Link
Short Description: Dicofol is often extensively (often completely) degraded during sample preparation and GC-analysis. This often results in poor recoveries and poor analytical precision. The use of isotope-labeled dicofol (e.g. dicofol-D8) as internal standard (ILIS) is the most efficient and convenient way to eliminate most sources of errors. If added to the final extract the ISTD can match for any decomposition and signal fluctuations in GC. If added at the beginning of the procedure it will also match for any losses during extraction and cleanup. Even when using the IL-IS it is important that dicofol does not disappear completely. Keeping the pH low during extraction and the final extract is helpful. If d-SPe with PSA sorbent is performed re-acidification should be rapid. Also helpful  is the use of Analyte Protectants (APs) that help to reduce degradation-rates during GC.
Dithianon SRM-13/(V2.1)/09.05.2016; see also under Methods (SRM-12) Link
Short Description: Dithianon often shows low or variable recovery rates from various commodities and especially from those exhibiting high natural pH. Recoveries become acceptable when conducting QuEChERS under acidic conditions and skipping the cleanup with PSA. Stability in QuEChERS extracts is improved when pH is low.
Dodine SRM-15/(V1)/23.02.2015 Link
Short Description: Using QuEChERS and LC-MS/MS for measurement dodine often shows overestimated recovery rates when quantified using calibration solutions prepared in pure solvents. The effect is attributed to the tendency of dodine to interact with active surfaces, especially in absence of competitive matrix components, and can vary considerably from instrument to instrument. The effect  typically temporarily improves when cleaning the tubing within the injector. To effectively eliminate the effect calibration standards prepared from extracts of blank commodities should be used. Alternatively acidification of solvent-based calibration standards (e.g. with formic acid) will also help to minize these interactions.
Ethoxyquin  Plant Origin SRM-21/(V2)/30.03.2015 Link
Short Description: Ethoxyquin typically shows notoriously low recoveries in commodities with low antioxidative activity. The addition of the antioxidant ascorbic acid to the analytical portion of the sample prior to QuEChERS extraction helps to increase recoveries. To further minimize the losses during the analytical procedure it is further recommended to add ascorbic acid already prior to the cryogenic milling step (1g per 100 g sample).
 Animal Origin SRM-24/(V1)/17.05.2016 Link
Short Description: The use of EQ as animal feed additive can lead to residues in food of animal origin such as poultry meat and eggs as well as in farmed fish and shrimp. EQ converts into a multitude of transformation products including ethoxyquin dimer (EQDM), ethoxyquin quinone imine (EQI or QI) and dihydroethoxyquin (DHEQ). Some of these metabolites also exhibit antioxidant properties themselves. In recovery experiments on wild Atlantic salmon AA showed a strong protective effect on EQI and a weaker but well notable protection effect on EQ parent and the metabolite DHEQ. EQDM was more stable and not notably affected by the addition of AA. In contrast, the impact of AA on EQ extraction yields from farmed salmon was minimal. We assume that this is due to the high levels of other antioxidants added to fish feed and accumulating in farmed fish. Recoveries for QI could be improved from 11% when no AA was added prior or during extraction to 96% when AA was added to the frozen salmon prior to QuEChERS extraction. Analysis of farmed salmon showed only residues of EQ and EQDM. To be on the safe side, addition of AA prior to QuEChERS extraction or even during cryogenic milling is still recommended.
Organotins SRM-16/(V1)/22.04.2013 Link
Short Description: Using QuEChERS, organotin compounds tend to give low recoveries in various types of commodities with high pH commodities being affected the most. recovery improvements were achieved by lowering the pH during the extraction step. Various versions of the QuEChERS method entailing different acidification approaches were tested. All showed a positive impact on the recoveries of fenbutatin oxide, cyhexatin and fentin.
Prochloraz SRM-19/(V3)/30.07.2016  Link
Short Description: The current residue definition of Prochloraz requires the conduction of a hydrolysis step to transform a number of Prochloraz metabolites to 2,4,6-trichlorophenol. In a recent reasoned opinion EFSA proposes a new residue definition which includes the parent and two metabolites (BTS 44595 and BTS 44596) which can all be covered by multiresidue methods. Several experiments were conducted showing that the consideration of the above prochloraz metabolites within the current residue definition can be quite tricky from the analytical and calculative points of view and that certain aspects have to be considered in LC-MS/MS and GC-MS analysis.
Propamocarb  SRM-20/(V1)/24.10.2012 Link
Short Description: Propamocarb showed a very strong signal enhancement effect in LC-MS/MS analysis of cucumber and lettuce extracts. Matrix effects could be eliminated using a more polar stationary phase where propamocarb is more strongly retained and obviously better separated from those matrix components inducing signal enhancement.
Pymetrozine SRM/V1/18.04.2016 Link
Short Description: Pymetrozine shows pH-dependent recovery rates using the QuEChERS method. pH should optimally exceed 5 for the pymetrozine recovery rates to be well above 70%. pH can be increased by replacing the citrate salts with acetate salts. The following mixtures were found to work well for 10 g sample: 4 g MgSO4 +1 g NaCl + 0.5 g sodium acetate and 4 g MgSO4 +1 g Mg-Acetate.
 SRM-22/(V1)/30.03.2015 Link
Short Description: The degradation of Pyridate into pyridafol (CL 9673) during QuEChERS sample preparation was studied. It was shown that pyridate degrades at high pH levels, for example when perfoming d-SPE cleanup with PSA-sorbent. Furthermore, being slightly acidic in nature, pyridafol experiences losses during the dSPE step when PSA-sorbent is used.
Other Aspects
Analyte protectants  -/V1/22.04.2013 Link
Short Description: Analyte protectants (APs) are compounds that are added to extracts or standard solutions with the aim to protect the analytes from interactions with active sites within the GC-system. Typically APs are added at concentrations exceeding by far those of the analytes to be protected. Most effective as APs are compounds with multiple hydroxy groups with which they can mask active sites on the surface of the GC-system via hydrogen bonds.
BNPU (1,3-bis(4-nitrophenyl) urea)  -/V1/14.4.2016 Link
Short Description: BNPU (a component of nicarbazin) is often used as a volumetric correction Internal Standard (IS) for acidic pesticides. As IS-losses can lead to severe overestimation of pesticides levels, it is important that there is no IS losses along the procedure. Extensive BNPU-losses aredetected when conducting dSPE-cleanup of QuEChERS extracts with GCB (Graphitized Carbon Black). Thus, if nicarbazin (BNPU) is used as IS, dSPE with GCB sorbent should be avoided and vice versa. dSPE cleanup of QuEChERS extracts does not result in any notable losses but if QuOil extract are subjected to cleanup with PSA BNPU losses are dramatic. No notable losses of BNPU are noticed when 5% water is added to QuOil extracts prior to cleanup with PSA.  


Obsolete versions of the Analytical Observations can be found here: List of Obsolete Versions.



Published 01-02-2013, 12:21:33

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