Paraquat (methyl viologen) and diquat are
non-selective contact herbicideswidely used in
agriculture to control broadleaf and grassy
weeds (use of paraquat is restricted in the
United States).The highly charged dual quater-
nary amines (Figure 1) are readily soluble in
water.They also are highly toxic, and ingestion
of either compound can have serious effects.
The charged compounds are difficult to retain by
standard reversed phaseHPLC, so ion pairing
reversed phasemethods, such as US EPA
Method 549, and specialty columns have been
developed specifically for this analysis. One
widely used approach is to couple an ion
exchange columnwith a post-column reactor
that creates a fluorescing complex. Detection is
very sensitive, but the columns are costly, often
exceeding $1000US, as are the post-column
derivatization system and fluorescence detector.
The system can be beyond the budget of smaller
laboratories. Further, anymethod involving ion
pairing agents has inherent problems, due to
the complex chemistry andmethodology and to
variation amongmanufacturers’ HPLC columns.
Figure1
Chemical structuresof paraquat anddiquat.
Now, Restek chemists have developed a simple,
effective, reliable analysis for paraquat and
diquat, based on a newHPLC column, Ultra
Quat, and a uniquemobile phase.The analysis
can be performed on a conventional HPLC sys-
temwith a conventional UV detector. In place of
techniques that rely on the hydrophobicity of the
column and the strength of themobile phase,
this separationmakes use of a different analyti-
cal property—chaotropism: an ability to disrupt
the structure of water and thereby alter the
interactions among analyte, mobile phase, and
stationary phase. In this case, the objective is to
SimplifyParaquat/DiquatAnalysisand
ImproveSensitivity
Using anUltraQuat HPLCColumn, a SimpleMobile Phase,
and aNew Sample Extraction Process
by VernonBartlett, HPLCManager, KatiaMay, Ph.D., Senior R&DChemist, BruceAlbright, HPLCChemist,
LydiaNolan, Innovations Chemist, andRebeccaWittrig, Ph.D., HPLCProductMarketingManager
•Consistent retention and peak symmetry, without costly ion exchange columns.
•Eliminate complicatedmobile phases, improve sensitivity by 30%.
•Simplify sample preparation and improve detection limits.
!
new
★
paraquatdichloride [CAS#1910-42-5]
diquatdibromide
[CAS#85-00-7]
Figure2
Consistent resolution, retention times, andpeak symmetry for paraquat anddiquat
reference standards, usinganUltraQuat column.
Turning Visions into Reality
THE
RESTEK
ADVANTAGE
2004
vol.3
800-356-1688
814-353-1300
Improved Paraquat/Diquat
Analysis by HPLC . . . . . . . . . . . . . . .
1-2
Fast Analysis of Phthalateswith
anRtx
®
-5Sil MSColumn . . . . . . . . . . . . .
3
NewGCColumn for Pesticides
or PAHs . . . . . . . . . . . . . . . . . . . . . . . .
4-5
RapidAnalysis of Residual Solvents . . . .
6-7
ImprovingDetailedHydrocarbon
Analysis . . . . . . . . . . . . . . . . . . . . . . .
8-9
Restek on theRoad . . . . . . . . . . . . . . . . . . .
9
Faster GC/MSAnalysis of Volatile
Organics inWater . . . . . . . . . . . . . .
10-11
NewRestek ReferenceBooks . . . . . . . . . . . . . . .
11
New Environmental ReferenceMaterials . . . . . . .
12
ChangeGC/MSColumns inMinutes,Without
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Instrument Innovations . . . . . . . . . . . . . . . . . . . .
14
Peak Performers . . . . . . . . . . . . . . . . . . . . . . . . .
15
Replacement Lamps for HPLCDetectors . . . . . . .
16
in this issue
Column:
UltraQuat
Cat.#:
9181565
Dimensions: 150 x 4.6mm
Particle size: 5µm
Conditions:
Mobile phase: UltraQuat Reagent Solution:
acetonitrile, 95:5 (v/v)
Flow:
1.0mL/min.
Temp.:
27°C
Det.:
UV@ 257nm (paraquat)
UV@ 308nm (diquat)
Sample:
Inj.:
20µL
Conc.:
20ppm each component
(above); 20µg/mL, 40µg/mL,
and 100µg/mL each
component (left)
Solvent:
water
min.
1
2
LC_0321
Peak List:
Peak time (min.)
1. diquat
7.5
2. paraquat
8.8
promote the solubility of the two highly polar
analytes in a secondary substrate (the station-
ary phase). In other words, we bend the famil-
iar chemical rule of “like dissolves like”.
The packing for the newUltraQuat column is
based on a type B silica, to ensure proper
selectivity and analyte retention, and tomini-
All responses at
257&308nm.
308nm
257nm
1
2
