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

A document dealing with the analysis of pesticides requiring the conduction of a hydrolysis step to cover the full residue definition is introduced. A short general overview on conjugates is given but the focus is on pesticides with carboxylic groups and the possibilities to break up conjugated and ester-bound residues. Both alkaline hydrolysis and enzymatic hydrolysis (with porcine liver esterase) are discussed.
Three different QuEChERS-integrated hydrolysis procedures are applied 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, such as citrus fruits, the harshest conditions are employed (0.5 mmol* /mL / 60°C / 60 min).

*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.

 

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

Link to List of Analytical Observations Reports

 

Last modified 05-03-2020, 14:29:28

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