SIMULTANEOUS QUANTITATIVE ANALYSIS OF PESTICIDES INCLUDING PHENOXYACIDS IN SURFACE

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Simultaneous Quantitative Analysis of Pesticides Including Phenoxy-Acids in Surface Water using UPLC-MS/MS with direct injection


G.Bondoux1*,, A. Paccou,1


1 Waters European Headquarters, Guyancourt, France


* Corresponding author email: [email protected]


Summary


Progresses in LC/MS/MS techniques make possible the determination of pesticides at ppt level using direct injection. Using fast polarity switching, it is possible to determine in a single injection substances that would traditionally require separate extraction methods and separate analysis. This has been applied to a simultaneous determination of 32 pesticides including phenoxy-acids in surface water. Analytical performances of the method have been evaluated, together with the economic aspect.



Introduction


LC/MS/MS is widely used for the determination of pesticides and other contaminants in environmental water samples. In Europe, most laboratories are targeting LOQs for pesticides in the 10 ppt range (10 times less than the regulatory maximum concentration for drinking water in Europe). This is traditionally achieved by pre-concentrating a large volume of sample (50 ml up to 1 l) on a solid phase extraction cartridges, eventual cleaning, elution with a strong solvent, evaporation and reconstitution in the mobile phase. This approach has obvious advantages in term of flexibility, cleaning of the sample, and allows reaching the needed detection limits even on an entry level LC/MS/MS instrument. There are also multiple drawbacks, in term of cost (consumable and labour time) and handling of solvents. When working on a large panel of molecules, it is difficult, if not impossible, to get good recoveries on both acid herbicides and other pesticides in a single extraction. This is why most laboratories run a specific method for acidic herbicides. Using separate methods also avoids any compromise for the MS detection conditions, as mobile phases can be optimised for both kinds of compounds. Moving to on-line automated solid phase extraction does not always help: the difficulties to achieve good recoveries for compounds belonging to very different families remain the same, and some surface water might be problematic for on-line SPE.

The evolution of HPLC to Ultra Performance LC (UPLC) and new generation of tandem-quadrupole mass spectrometer bring additional possibilities. The analysis of most pesticides is now possible at low ppt level by direct injection, overriding thus the difficulties previously listed.


Instrument and method


The LC-MS/MS method was developed for the quantitative analysis of 32 pesticides including phenoxy-acids. The chromatographic separation is done using a Waters ACQUITY UPLC system. The MS detector is a Waters Xevo TQ-S tandem quadruple, operated in ESI mode, with fast polarity switching. For each analyte, the most intense MRM transition was quantified and reported. A secondary transition was monitored for identity confirmation. This method allows the analysis of more than 4 samples per hour. Surface water samples were filtrated and spiked with the internal standard (deuterated compounds) before injection.

 

Results and discussion

SIMULTANEOUS QUANTITATIVE ANALYSIS OF PESTICIDES INCLUDING PHENOXYACIDS IN SURFACE This method revealed an excellent linearity across the studied range (5-500 ppt) and an excellent repeatability with RSDs typically lower than 2% over 10 injections at mid concentration. Limits of detection range from 5 ppt for the less sensitive compound (MCPB), to below 0,02 ppt for the most sensitive compound (Carbendazim). Despite the very minimum sample preparation, the UPLC column lifetime was several thousand injections.



Conclusions


This methods brings a significant gain in time (acidic and basic compounds in a single injection), and in cost (sample preparation is limited to filtration). Possible developments on this method is the inclusion of other molecules, including PPCP (Pharmaceutical and Personal Care Products




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Tags: analysis of, the analysis, simultaneous, including, surface, analysis, phenoxyacids, quantitative, pesticides