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Analysis of Acidic Pesticides Entailing Conjugates and/or Esters in their Residue Definitions (Updated Version)

This document deals with the analysis of pesticides requiring a hydrolysis step to cover the full residue definition. A general overview on residue definitions entailing conjugates, esters or common moieties. 

The main focus lays in the analysis of pesticides with carboxylic groups, as well as their esters and conjugates following hyrolysis. Various hydrolysis possibilities (chemica,l enzymatic) to break up conjugated and ester-bound residues are given.
Four different QuEChERS-integrated chemical hydrolysis procedures are presented to hydrolyze resistant esters:

For “simple” commodities (like most fruits and vegetables) the hydrolysis conditions remain as described in CEN-QuEChERS (0.25 mmol/mL* / 40°C / 30 min).
For cereals and pulses harsher conditions are needed. The base amount is doubled but the temperature is kept at 40°C to avoid clumping, therefore the reaction time is extended (0.5 mmol/mL* / 40°C / 120 min).
For “complex” commodities of plant origin, such as citrus fruits, the harshest conditions are employed (0.5 mmol* /mL / 60°C / 60 min).
For commodities of animal origin the the cfollowing conditions are used 0.25 mmol/mL* / 60°C / 60 min).

*the base-strengths are calculated on the basis of 20 mL volume after addition of acetonitrile.

To give a hint on the extend of conjugation within real samples and the impact of hydrolysis on the release of acidic pesticides, a compilation of results from the analysis of incurred 2,4-D, Fluazifop and Haloxyfop, with and without applying hydrolysis, is presented.

Glucosidw-conjugated acidic pesticides are analyzed either directly (as such) or following hydrolysis by enzymatic or purely chemical means.

Link to Analysis of Pesticides Entailing Conjugates and/or Esters in their Residue Definitions

Link to List of Analytical Observations Reports

 

Last modified 07-05-2021, 20:10:21

Published 05-03-2020, 14:28:14

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