Report No FR0371

K M Moore, S Gibby, S Jones and S Shurvell

Apr 1993



Monitoring pesticides in drinking and related waters is a difficult and expensive exercise. The availability of appropriate multiresidue (MR) methods of analysis will save costs and enable regulations to be met.


To develop MR analytical methods for a range of pesticides which may potentially find their way into drinking water sources and supplies.


The Water Supply (Water Quality) Regulations 1989 impose a duty on water undertakers to monitor regularly for pesticides in water supplies. Because in principle many pesticides could find their way into drinking water sources there is a need for MR analytical methods to minimise the cost of monitoring. These MR analytical methods must be of sufficient accuracy and sensitivity to monitor compliance with the prescribed values set by the Water Supply Regulations.


Development work was carried out on an acid herbicides MR analytical method. It was found that, although the pentafluorobenzyl derivatisation of the acid herbicides allowed greater sensitivity on gas chromatography - mass spectrometry (GC-MS), the reproducibility of the derivatisation was worse than the alternative method using methylation. Consequently, methylation was used for analysis. Conditions which quantitatively hydrolysed all of the esters of the acid herbicides under study could not be found. Consequently, a compromise had to be established in setting the conditions for the hydrolysis step. If a hydrolysis step is not included in the analytical method for acid herbicides, a small proportion of some esters in the sample would still be detected, since the acidic extraction conditions used for the analytical method lead to some hydrolysis. This is important since it means that analytical methods for acid herbicides using extraction under acidic conditions do not exclusively analyse the free acid form of the acid herbicides.

MR analytical methods capable of monitoring compliance with the Water Supply Regulations have been developed and tested for a selection of acid herbicides, uron and carbamate pesticides and neutral/basic pesticides. Since the MR methods all use mass spe ctrometric detection, they are more specific and therefore less prone to interference than many methods in use. The method for neutral/basic pesticides encountered a few problems which need to be resolved before it can be put into routine use.

The herbicides imazapyr and triclopyr had been identified as being of priority for analytical method development in the report on the review of MR analytical methods (FR0312). They were both tested using the acid herbicides MR analytical method. The method performed satisfactorily for triclopyr, but imazapyr was not detected. Some preliminary development work on an analytical method for both herbicides has shown that it should be possible to analyse them using a method based on diethyl ether extraction under acidic conditions, methylation and determination by gas chromatography with nitrogen/phosphorus detection.


Pentafluorobenzyl derivatisation of the acid herbicides potentially allows greater sensitivity on GC-MS than methylation. It should therefore be considered whether it is worthwhile trying to improve the reproducibility of pentafluorobenzyl derivatisation in order to achieve better limits of detection for the analysis of acid herbicides.

Further development work should be carried out on an effective hydrolysis step to convert the esters of acid herbicides into free acids. Current methods may be underestimating acid herbicide concentrations in water.

The reasons for the poor recovery of pesticides for some batches of quality control samples in the MR analytical method for neutral/basic pesticides should be investigated before the method is put into routine use. The reason for unrealistically high recoveries and poor precision for a few of the pesticides should also be investigated to widen the scope of the analytical method.

The analytical method development work for imazapyr and triclopyr should be completed.


Mass spectrometry-based MR analytical methods were developed for potentially important pesticides and a few transformation products in water. Three MR analytical methods were developed for acid herbicides, uron and carbamate pesticides and neutral/basic pesticides. These analytical methods were performance tested to determine their suitability for monitoring compliance with the Water Supply Regulations.

Some initial analytical development work was carried out for the herbicides imazapyr and triclopyr.

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