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: Gerard_c_bondoux@waters.com
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 tandemquadrupole 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
This method revealed an excellent
linearity across the studied range (5500 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