Acidic herbicides and o-phenylphenol (both with hydrolysis) in orange

It is essential to apply a hydrolysis step for this ring test. An analysis of the esters and the free acids only results in an underestimation of the spiked levels! The test samples MUST be analysed twice - with and without hydrolysis. 

The residue definitions of acidic herbicides according to regulation (EC) No. 396/2005 include the esters, salts and conjugates of the acidic herbicides. The conjugates can contribute significantly to the total amount of the respective herbicides determined in routine samples. An alkaline hydrolysis step is applied to quantify residues of the conjugates in routine samples.

The residue definition of 2-phenylphenol (sum of 2-phenylphenol and its conjugates, expressed as 2-phenylphenol) includes the conjugates as well. Please be prepared to analyse the conjugates of 2-phenylphenol as well.

P2428-RT is designed to cover all aspects of the analysis of acidic herbicides and 2-phenylphenol, including the hydrolysis step in accordance with the residue definition.

For that purpose the test material is spiked with selection of

  • conjugates of acidic herbicides and 2-phenylphenol,
  • commercially available esters of acidic herbicides, and
  • free acids of acidic herbicides.

In order to ensure that the results are unambiguously, either the conjugate or the ester or the free acid is spiked for each of the selected herbicide. In case of one of the herbicides, the conjugate, an ester and the free acid is spiked to simulate the residue situation in routine samples. Acidic herbicides within the scope of the test are summarised below (see parameters).

The participants are asked to report the results with and without hydrolysis. The results after alkaline hydrolysis (sum of conjugates, esters and free acids) are considered for evaluation of the trueness of results. 

The analytical data are assessed with respect to

  • the identification of the spiked acidic herbicides,
  • the comparability (z-score), and
  • the trueness (70 to 120% of the spiked level).


Analytical results without hydrolysis

2-phenylphenol, 4-CPA (free acid), 2,4-D (free acid), 2,4-DB (free acid), 2,4-dichlorprop (free acid), 2,4,5-T (free acid), 2,4,5-TP (free acid), clopyralid (free acid), dicamba (free acid), fenoxaprop (free acid), fluazifop (free acid), fluroxypyr (free acid), haloxyfop (free acid), MCPA (free acid), MCPB (free acid), triclopyr (free acid)

Analytical results with hydrolysis

2-phenylphenol (sum), 4-CPA (sum), 2,4-D (sum), 2,4-DB (sum), 2,4-dichlorprop (sum), 2,4,5-T (sum), 2,4,5-TP (sum), clopyralid (sum), dicamba (sum), fenoxaprop (sum), fluazifop (sum), fluroxypyr (sum), haloxyfop (sum), MCPA (sum), MCPB (sum), triclopyr (sum)

Expected time schedule

Please register before:
15 December 2023
Dispatch of samples:
19 February 2024
Deadline for reporting results:
13 March 2024

Costs of P2428-RT

Ring test and material Amount Price per unit
Acidic herbicides and o-phenylphenol (both with hydrolysis) in orange 850 €
Test material
Orange, homogenised, spiked with free acids, ester, and conjugates of acidic herbicides and conjugates of o-phenylphenol
100 g included
Analytical results without hydrolysis
Free acids and esters, o-phenylphenol.
Analytical results with hydrolysis
Sum of free acids, esters and conjugates.
Blank material
Orange, homogenised, unspiked
100 g 70 €

Note: PROOF-ACS reserves the right to cancel tests in case of less than ten participants.