Page 45 - Volume 1, Issue 2, July 2008

Glassware sorption of glyphosate and AMPA

97

of the bottles. The first water washing

yielded about 80% of the missing gly-

phosate and AMPA from the methan-

olic solution. A second water washing

with half the volume was needed for

an almost complete recovery.

All the above results clearly demon-

strate the reduced apparent recovery of

glyphosate and AMPA from methano-

lic solutions prepared by mixing metha-

nol with an aqueous solution of the two

compounds, thus containing a low per-

centage of water (from 0.25 to 4%). In oth-

er tests, using solutions of the two com-

pounds in pure methanol, it was shown

that the presence of water is not neces-

sary for the recovery reduction to occur.

In these tests, a low concentration solu-

tion of glyphosate and AMPA in metha-

nol was prepared by directly dissolving

small quantities of the two compounds

in pure methanol with repeated stirring

and light heating in a polypropylene bot-

tle. When this solution was transferred to

glass bottles and analyzed as in the previ-

ous tests, a significant reduction of appar-

ent recovery (to levels about 50%) was ob-

served. Adding water to methanol at up to

5% had little effect on the apparent recov-

ery, while at 10% or more had an improv-

ing effect on it and resulted in a complete

recovery at water percentages of 50% in

the methanol.

Other researchers have used meth-

anol as a leaf wash for removing unab-

sorbed

14

C-labeled glyphosate, in studies

of herbicide penetration into leaves and,

as shown later, recovery is much better

with water (7).

In analytical work with glyphosate and

AMPA, therefore, methanol is not a good

solvent to be used either in the prepara-

tion of spiking stock solutions for calibra-

tion purposes or as an extractant for res-

idue determination in various matrices.

Strong adsorprion on surfaces of glass

containers and to a less extent to plastic

containers should be expectedwithmeth-

anolic solutions regardless if they contain

water (up to 50%). This certainly leads to

low apparent recoveries for both com-

pounds and may lead to erratic results if

measures are not taken. This adsorption

and reduced recovery problem associat-

ed with the use of methanol is expected

to become even more important in cases

where the determination of the two com-

pounds is at trace concentrations.

Literature Cited

Burns, D.T., Danzer, K., and Townshend A.

1.

2002. Use of the terms “recovery” and “appar-

ent recovery” in analytical procedures (IUPAC

Recommendations 2002).

Pure Applied Chem-

istry

, 74: 2201-2205.

California EPA. 1997. Chemical profile, p. 2, in

2.

Public Health Goal for Glyphosate in Drinking

Water.

Pesticide and Environmental Toxicol-

ogy Section, Office of Environmental Health

Hazard Assessment, California Environmen-

tal Protection Agency, pp. 14.

Nedelkoska, T.V. and Low, G.K-C. 2004. High-

3.

performance liquid chromatographic deter-

mination of glyphosate in water and plant

material after pre-column derivatisation with

9-fluorenylmethyl chloroformate.

Analytica

Chimica Acta

, 511: 145-153.

Patsias, J., Papadopoulou, A. and Papado-

4.

Figure 3.

Chromatograms of the first water wash of two 20-

ml glass bottles after removal of the solutions they contained.

The methanolic solution consisted of 500 ng/ml glyphosate,

500 ng/ml of AMPA and 1% water in methanol while the

aqueous solution consisted of the same concentrations of gly-

phosate and AMPA in pure water. Bottles had been filled with

5 ml of the respective solution and stood at room temperature

for about 16 hrs, before the solutions were removed and the

bottles were washed with 5 ml of deionized water.