ADV01-05_1-298

Paraquat (methyl viologen) and diquat are

non-selective contact herbicides widely 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 phase HPLC, so ion pairing

reversed phase methods, 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 column with a post-column reactor

that creates a fluorescing complex. Detection is

very sensitive, but the columns are costly, often

exceeding $1000 US, as are the post-column

derivatization system and fluorescence detector.

The system can be beyond the budget of smaller

laboratories. Further, any method involving ion

pairing agents has inherent problems, due to

the complex chemistry and methodology and to

variation among manufacturers’ HPLC columns.

Figure 1

Chemical structures of paraquat and diquat.

Now, Restek chemists have developed a simple,

effective, reliable analysis for paraquat and

diquat, based on a new HPLC column, Ultra

Quat, and a unique mobile phase. The analysis

can be performed on a conventional HPLC sys-

tem with a conventional UV detector. In place of

techniques that rely on the hydrophobicity of the

column and the strength of the mobile phase,

this separation makes 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

Simplify Paraquat/Diquat Analysis and

Improve Sensitivity

Using an Ultra Quat HPLC Column, a Simple Mobile Phase,

and a New Sample Extraction Process

by Vernon Bartlett, HPLC Manager, Katia May, Ph.D., Senior R&D Chemist, Bruce Albright, HPLC Chemist,

Lydia Nolan, Innovations Chemist, and Rebecca Wittrig, Ph.D., HPLC Product Marketing Manager

•Consistent retention and peak symmetry, without costly ion exchange columns.

• Eliminate complicated mobile phases, improve sensitivity by 30%.

•Simplify sample preparation and improve detection limits.

new

★

paraquat dichloride [CAS# 1910-42-5]

diquat dibromide

[CAS # 85-00-7]

Figure 2

Consistent resolution, retention times, and peak symmetry for paraquat and diquat

reference standards, using an Ultra Quat column.

Turning Visions into Reality

THE

RESTEK

ADVANTAGE

2004

vol. 3

800-356-1688

814-353-1300

www.restek.com

Improved Paraquat/Diquat

Analysis by HPLC . . . . . . . . . . . . . . .

1-2

Fast Analysis of Phthalates with

an Rtx

-5Sil MS Column . . . . . . . . . . . . .

New GC Column for Pesticides

or PAHs . . . . . . . . . . . . . . . . . . . . . . . .

4-5

Rapid Analysis of Residual Solvents . . . .

6-7

Improving Detailed Hydrocarbon

Analysis . . . . . . . . . . . . . . . . . . . . . . .

8-9

Restek on the Road . . . . . . . . . . . . . . . . . . .

Faster GC/MS Analysis of Volatile

Organics in Water . . . . . . . . . . . . . .

10-11

New Restek Reference Books . . . . . . . . . . . . . . .

New Environmental Reference Materials . . . . . . .

Change GC/MS Columns in Minutes, Without

Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Instrument Innovations . . . . . . . . . . . . . . . . . . . .

Peak Performers . . . . . . . . . . . . . . . . . . . . . . . . .

Replacement Lamps for HPLC Detectors . . . . . . .

in this issue

Column:

Ultra Quat

Cat. #:

9181565

Dimensions: 150 x 4.6mm

Particle size: 5µm

Conditions:

Mobile phase: Ultra Quat Reagent Solution:

acetonitrile, 95:5 (v/v)

Flow:

1.0 mL/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.

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 new Ultra Quat column is

based on a type B silica, to ensure proper

selectivity and analyte retention, and to mini-

All responses at

257 & 308nm.

308nm

257nm