180 / 413
• 6 •
2008 vol. 2
Acetamide herbicides are used in large quantities to suppress weed growth in corn and soybean fields. However, due to the polar
nature of ethanesulfonic acid (ESA) and oxanilic acid (OA) degradation products, contamination of drinking water sources is a con-
cern. EPA Method 535 is designed to monitor drinking water for ESA and OA breakdown products of these herbicides.
Chromatographic analysis is extremely important for this method because two analytes, alachlor ESA and acetochlor ESA, are
isomers that share the same mass spectral multiple reaction monitoring (MRM) transitions, and thus must be separated chromato-
graphically.
Resolution of all Method 535 analytes, including alachlor ESA and acetochlor ESA isomers, can easily be accomplished using Restek's
full line of Method 535 products, which includes reference standards, solid phase extraction (SPE) cartridges, and HPLC columns
that meet method guidelines. In the procedure shown here, 6mL CarboPrep™ 90 SPE cartridges were used for sample preparation,
both to help extend the lifetime of the analytical column as well as to prevent matrix enhancement or suppression. LC/MS/MS analy-
sis was performed on an Ultra C18 column coupled to an Applied Biosystems API 3200™ LC/MS/MS system equipped with a
TurboIonSpray® probe for the Turbo V™ source.
One Stop Shop for EPA Method 535
Reliably Analyze Acetamide Herbicide Degradates by LC/MS/MS
By Jason Thomas, Innovations Chemist, Julie Kowalski, Ph.D., Innovations Chemist, and Christopher Borton, Applied Biosystems
• Full package: reference standards, SPE cartridges, and HPLC columns.
• Chromatographic resolution of alachlor ESA and acetochlor ESA isomers.
• Meet method requirements, with superior sensitivity.
Figure 1
Easily resolve Method 535 herbicide degradates on an Ultra C18 HPLC column.
alachlor OA
acetachlor OA
1. alachlor ESA
3. acetachlor ESA
4. metalochlor ESA
2. metalochlor OA
dimethachlor ESA (SS)
butachlor ESA
Sample:
acetamide herbicides
Inj.:
25µL
Conc.:
50ng/mL
Sample diluent: 5mM ammonium acetate in water
Column:
Ultra C18
Cat.#:
9174312
Dimensions:
100mm x 2.1mm
Particle size:
3µm
Pore size:
100Å
Conditions:
Mobile phase:
A: 5mM ammonium acetate
B: methanol
Time:
%B
0.0
20%
4.0
30%
10.0
30%
15.0
50%
17.0
85%
18.0
85%
18.1
20%
28.0
20%
Flow:
250µL/min.
Temp.:
ambient
Excellent response at
low concentrations!
Fully resolve alachlor ESA
and acetochlor ESA isomers.
Det.:
API 3200™ LC/MS/MS system
Ion Source:
TurboIonSpray
®
probe for Turbo V™ source (negative)
Mode:
MRM
Curtain gas:
25
Collision gas:
medium/5
IonSpray voltage:
-4,500
Temperature:
500°C
Ion source gas 1:
50
Ion source gas 2:
50
Interface heater:
on
Dwell time:
50
Vertical probe position: 2
Analytes
RT (min) Quantifer MRM Qualifier MRM
dimethachlor ESA 7.9
300/80
300/121
alachlor OA
14.5
264/160
264/158
acetochlor OA 14.8
264/146
264/144
1. alachlor ESA
16.1
314/80
314/121
2. metolachlor OA
16.4
278/206
278/174
3. acetochlor ESA 16.4
314/80
314/121
4. metolachlor ESA 16.9
328/80
328/121
butachlor ESA
19.7
356/80
356/121
LC_EV0477
Environmental