• 2 •
800-356-1688 •
2004vol. 3
mize residual silanols andmetal ions on the
packing particles, which could interact with the
analytes and cause tailing and unwanted (and
sometimes unpredictable) retention.
The reagent solutionwe use in themobile
phase, UltraQuat Reagent Solution (cat.#
32441), alters the chemical nature of the ana-
lytes as perceived by the column andmobile
phase. It reduces the ability of water to solvate
the analytes and hydrogen bondwith them, forc-
ing the charged complexes into the stationary
phase and improving retention.
Unlike ion pairing techniques, our new approach
requires onlywater, UltraQuat Reagent Solution,
and acetonitrile (which cannot form hydrogen
bonds) to accomplish the separation. For highest
sensitivity, wemonitor for paraquat at 257nm
and for diquat at 308nm. Using the new column,
mobile phase, and conditions, the detection limit
for either herbicide is 6ppb in the final sample
extract—a detectable amount of 0.12
nanograms on column. Data are summarized in
Table 1. Using the solid phase extraction proce-
dure inTable 2, which concentrates samples 200-
fold (1L to 5mL), the detection limit is 0.03ppb—
a significant improvement over currentmethod-
ology. Analyte concentrations can be increased
bymodifying the solid phase extraction proce-
dure or by increasing the injection volume, to
improve quantification and detection limits.
Figure 2 overlays chromatograms of paraquat
and diquat reference standards at a range of
concentrations (20µg/mL–100µg/mL); resolu-
tion, retention times, and peak symmetry are
highly consistent. Concentrations up to
100µg/mL are consistent with linear detector
responses.
Note that glassware used to prepare and ana-
lyze samples and referencematerials for this
analysismust be deactivated (e.g., with
dimethyldichlorosilane—DMDCS, cat.# 31840).
EPAMethod 549.2 requires retesting of all sam-
ples if the response for the reference standards
changes bymore than 20% over the time of the
analysis.We found all reference standards
showed degradation after only 1 hour in
untreated glassware, with the lowest concentra-
tions being themost affected. 30% losses in
responsewere not uncommon; a diquat refer-
ence standard of 6ppb inwater became unde-
tectable.
When you perform the challenging
paraquat/diquat analysis, our newUltraQuat
column, UltraQuat Reagent Solution and
Paraquat/Diquat CalibrationMix, and extraction
procedurewill give you the edge you need to
obtain themost accurate and consistent infor-
mation.
UltraQuatHPLCColumn
Physical Characteristics:
particle size: 5µm, spherical
pH range: 2.5 to 7.5
temperature limit: 80°C
Sample Injection
Limit of
Limit of
Volume Volume Detection Quantification
(mL)
(µL)
(ppb)
(ppb)
1
20
6
20
100
20
0.06
0.2
250
20
0.024
0.08
1000
20
0.006
0.02
1
100
1.2
4
100
100
0.012
0.04
250
100
0.0048
0.016
1000
100
0.0012
0.004
1
200
0.6
2
100
200
0.006
0.02
250
200
0.0024
0.008
1000
200
0.0006
0.002
Table1
Approximatedetection/quantification
limits for paraquat anddiquat, usingan
UltraQuat column.
On column limit of detection (LOD): 0.12ng
On column limit of quantification (LOQ): 1.2ng
InSummary
Highly polar paraquat and diquat can’t be
separated on a reversed phaseHPLC column
without adding ion pairmodifier to themobile
phase, but the ion pair reagent in current
methodology does not provide optimum
resolution and does not permit detection
below 0.7µg/mL.We have developed a column
and amobile phasemodifier for rapid, com-
plete resolution of paraquat and diquat, with
detection to concentrations as low as
0.5µg/mL—an improvement of 30%.
SampleExtraction
SPETubes:
RestekWCX, weak cation exchanger, 3mL/500mg, cat.# 26062.
Samples:
1 liter deionizedwater containing 50µg each of diquat and paraquat.
Samples spikedwith 20µL 549.2 CalibrationMix, cat.# 32437, dilutedwithHPLC gradewater.
Conditioning: 3mL acetonitrile, then 3mL deionizedwater, applied sequentially.
Do not allow adsorbent bed to dry before applying sample.
Extraction:
Pass 1 liter water samples through SPE tubes at a rate of 5-10mL/min.
Arrange 5mL collection vessels under extraction tubes.
Place 1mL acidic elution solution* in each tube, draw into bed, allow to stand for up to 1min.
Pass solution at a slow (drop-wise) rate through SPE tubes into collection vessels.
Repeat with 2 x 2mL acidic elution solution.
Correct final volume in collection vessels to 5mLwith acidic elution solution.
Analysis:
Neutralize eluateswith approximately 20µL concentrated ammonium hydroxide, then analyze by
HPLC. Adjust amount of ammonium hydroxide used to assure each sample is neutral (test with pH
indicating paper).
*1mL 85%H
3
PO
4
diluted to 1 liter with deionizedHPLC gradewater (0.1%).
Results
Analyte Recovery (%) RSD (%)
diquat
99.0
0.89 (n=5)
paraquat
96.3
1.59 (n=5)
Table2
Solidphaseextractionof diquat andparaquat fromaqueous samples.
5µmColumn, 4.6mm ID
cat.#
price
150mm
9181565
$356
4.0mm ID
Length
cat.#
price
10mm
918150210
$129
20mm
918150220
$129
UltraQuatGuardCartridges
UltraQuatReagentSolution
Each
10-pk.
Inwater, 20mL/ampul
32441
$50
32541
$450
Extracted samples stored and analyzed in Silcote
™
CL7 deactivated
autosampler vials (cat.# 24671). Polypropylene vials and inserts
(e.g., cat.# 24651) alsomay be used.
diquat dibromide
paraquat dichloride
Paraquat&DiquatCalibrationMix
Each
1,000µg/mL each inwater, 1mL/ampul
32437
$25
w/data pack
32437-500
$35
Dimethyldichlorosilane (DMDCS)
Each
5-pk.
Neat, 20mL/ampul
31840
$20
31840-510
$90
WCXSolidPhaseExtractionTubes
3mL/500mg, 50-pk., cat.# 26062,
$130
Limited-time introductoryprice—
ordernow!
