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Analysis of Regulated Pesticides in
Drinking Water Using Accela and EQuan
Jonathan R. Beck and Charles Yang; Thermo Fisher Scientific, San Jose, CA
Key Words
• TSQ Quantum
™
• Accela
™
LC System
• EQuan
™
• LC-MS/MS
• Pesticide
Analysis
• Water Analysis
Application
Note: 391
Introduction
Pesticides are used throughout the world to control pests
that are harmful to crops, animals, or people. Because
of the danger of pesticides to human health and the
environment, regulatory agencies control their use and set
pesticide residue tolerance levels. The limits of detection
(LODs) for many of these substances are at the parts-
per-trillion (ppt) level. In order to achieve this level
of detection, offline sample pre-concentration is often
performed. However, these sample preparation procedures
can be time consuming, adding as much as one to two
days to the total analysis time. Therefore, a method for
online sample pre-concentration that bypasses the offline
sample pre-concentration provides a significant time
savings over conventional methods.
We describe a method for online sample cleanup and
analysis using the EQuan system. This method couples
a Fast-HPLC system with two Hypersil
™
GOLD LC
columns (Thermo Scientific, Bellefonte, PA)–one for pre-
concentration of the sample, the second for the analytical
separation–and an LC-MS/MS instrument. Large volumes
of drinking water samples (1 mL) can be directly injected
onto the loading column for LC-MS/MS analysis, thus
eliminating the need for offline sample pre-concentration
and saving overall analysis time. Using this configuration,
run times of six minutes are achieved for the analysis of
a mixture of pesticides. For separation prior to analysis
using an LC-MS/MS instrument, Fast-HPLC allows for
significantly shorter run times than conventional HPLC.
Goal
To demonstrate the use of Fast-HPLC and a large volume
injection to analyze sub-ppb concentrations of regulated
pesticides in drinking water samples.
Experimental Conditions
Sample Preparation
Bottled drinking water was spiked with a mixture of
the following pesticides: carbofuran, carbaryl, diuron,
daimuron, bensulfuron-methyl, tricyclazole, azoxystrobin,
halosulfuron-methyl, flazasulfuron, thiodicarb, and
siduron. Concentrations were prepared at the following
levels: 0.5, 1, 5, 10, 50, 100, 500, and 1000 pg/mL (ppt).
No other sample treatment was performed prior to
injection. The mass transitions and collision energies
for each compound are listed in Table 1.
HPLC
Fast-HPLC analysis was performed using the Accela
High Speed LC System (Thermo Scientific, San Jose, CA).
A 1 mL water sample was injected directly onto a
20 mm
×
2.1 mm ID, 12 µm Hypersil GOLD loading
column in a high aqueous mobile phase at a flow rate
of 1 mL/min (see Figure 1a). After approximately one
minute, a 6-port valve on the mass spectrometer was
switched via the instrument control software. This enabled
the loading column to be back flushed onto the analytical
column (Hypersil GOLD 50
×
2.1 mm ID, 1.9 µm), where
the compounds were separated prior to introduction
into the mass spectrometer (Figure 1b). After all of the
compounds were eluted from the analytical column at a
14
151
269.21
Daimuron
24
182
435.11
Halosulfuron-methyl
15
372
404.16
Azoxystrobin
20
137
233.19
Siduron
24
182
408.08
Flazasulfuron
22
149
411.13
Bensulfuron-methyl
20
72
233.05
Diuron
10
145
202.14
Carbaryl
14
165
222.10
Carbofuran
14
88
355.06
Thiodicarb
10
106
190.09
Tricyclazole
Collision Energy (eV)
Product Mass
(m/z)
Precursor Mass
(m/z)
Analyte
Table 1: List of mass transitions and collision energies for each compound
analyzed.
Figure 1a: 6-port valve position
one (load position), for loading the
sample onto the loading column.
Figure 1b: 6-port valve position
two (inject position), for eluting the
compounds trapped on the loading
column onto the analytical column.