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LC-MS/MS Analysis of Herbicides in Drinking
Water at Femtogram Levels Using 20 mL EQuan
Direct Injection Techniques
Jonathan R. Beck, Charles Yang, Thermo Fisher Scientific, San Jose, CA, USA
Introduction
As concerns grow over the toxic effects of herbicides and
other chemicals in our environment, the need to accurately
monitor these substances in drinking water and foods
becomes even more critical. LC-MS/MS is routinely used
by the environmental and food industries to identify and
quantify pesticide and herbicide residues. However, this
method typically requires extensive offline sample
preconcentration methods, which can be expensive and
time-consuming, to meet the stringent requirements and
low limits of detection set forth by federal and international
regulatory authorities. An online preconcentration and
cleanup method has been developed that improves both
sensitivity and precision and yields unmatched throughput.
The Thermo Scientific EQuan
™
system for online
sample cleanup and analysis consists of a triple quadrupole
mass spectrometer with an electrospray ionization source
(ESI), two LC quaternary pumps, an autosampler, and two
LC columns having C18 selectivity – one for preconcentration
of the sample, the second for analytical separation. A
6-port valve switches between the columns and is controlled
by the instrument software. In addition to quantitative
information, qualitative full scan product ion spectra are
collected in the same analytical run and data file, using a
technique called Reverse Energy Ramp (RER). This full
scan spectrum provides additional confirmatory information
for the compounds being analyzed. The resulting product
ion spectra can be library searched for positive identification,
or ion ratios can be used to confirm the presence of a
particular compound, helping to eliminate “false positive”
samples. This method uses drinking water for direct injection
onto the loading column, with no sample preparation or
offline concentration. This application note provides a
comparison of the online sample preconcentration of 1 mL,
5 mL, and 20 mL injections of drinking water samples
spiked with herbicide compounds.
Goal
To compare different large volume injections using a loading
column and an analytical column with two HPLC pumps.
Experimental Conditions
Sample Preparation
Drinking water containing 0.1% formic acid was spiked
with a mixture of the following herbicides: ametryn, atraton,
atrazine, prometon, prometryn, propazine, secbumeton,
simetryn, simazine, terbuthylazine, and terbutryn (Ultra
Scientific, North Kingstown, RI). The concentrations of
the herbicides in the spiked water ranged from 0.1 pg/mL
to 10 pg/mL. Calibration standards were prepared at the
following concentrations: 0.1, 0.5, 1.0, 5.0, and 10.0 pg/mL.
HPLC
Spiked water samples and blank water samples (1 mL, 5 mL,
or 20 mL) were injected directly onto a loading column
(Thermo Scientific Hypersil GOLD
™
20 mm x 2.1 mm ID,
12 µm) using an HTC PAL autosampler (CTC Analytics,
Zwingen, Switzerland). After the sample was completely
transferred from the sample loop to the loading column, a
6-port valve was switched to enable the loading column to
be back flushed onto the analytical column (Hypersil GOLD
50 mm x 2.1 mm ID, 3 µm), where the compounds were
separated prior to introduction into the mass spectrometer.
After all of the compounds were eluted, the valve was
switched back to the starting position. The loading and
analytical columns were cleaned with a high organic phase
before being re-equilibrated to their starting conditions
(Figure 1a and 1b). Control and timing of the 6-port
valve was through the computer data system, LC
QUAN
™
(Thermo Fisher Scientific, San Jose, CA).
Key Words
• TSQ Quantum
Access
• EQuan System
• Herbicides
• QED
• Water Analysis
Application
Note: 437
Figure 1: a) 6-port valve in position 1 (load position), for loading the sample onto the loading column. b) 6-port valve in position 2 (inject position), for eluting the
compounds trapped on the loading column onto the analytical column.
a
b