Page 41 - Volume 1, Issue 2, July 2008

Hellenic Plant Protection Journal

1:

93-98, 2008

SHORT COMMUNICATION

Strong sorption of glyphosate and aminomethylphosphonic

acid frommethanolic solutions on glassware surfaces

C.N. Giannopolitis

1

and V. Kati

1

Summary

In HPLC analyses with direct injection of aqueous and methanolic solutions of gly-

phosate and its metabolite aminomethylphosphonic acid (AMPA), it was observed that apparent

recovery of the two analytes is significantly lower from the methanolic (containing or not water

up to 10%) than from the aqueous solutions. The reduced recovery is associated with a stronger

adsorption of glyphosate and AMPA on the glassware surfaces in the methanolic solutions. The

reduction correlates to the ratio of the solution volume against the total container volume and is

increased when shaking the solutions. Determination of the two compounds, therefore, requires

special attention if methanol is used for sample spiking or extraction.

Additional keywords:

AMPA, adsorption, recovery, quantitative determination, HPLC analysis

parent recoveries for both compounds

and this prompted an investigation for

the causes. The term “apparent recovery”

is used in these studies as more appropri-

ate to the term “recovery” (1).

Glyphosate is insoluble in methanol

and other organic solvents (2) and the

same is true for AMPA. Therefore, for the

purpose of this investigation, the two

compounds were first dissolved in water

and then transferred to methanol by add-

ing small volumes of the water solution to

it.

Aqueous stock solutions contain-

ing 50 or 100 μg/ml of each, glyphosate

and AMPA, were prepared using analyt-

ical reference standards (Monsanto, cer-

tified as 99.8 and 99.5% respectively) of

the two compounds and HPLC grade wa-

ter (Fisher Scientific). Working methano-

lic solutions were prepared by adding a

volume of 25, 50 or 100 μl of one of the

above aqueous stock solutions to meth-

anol (same grade and origin as water) to

obtain three concentration levels for gly-

Glyphosate [N-(phosphonomethyl) gly-

cine]

has been one of the most applied

herbicides in the world since it came on

the market in 1974 and its use is expand-

ing dramatically in recent years with the

incorporation of resistance genes into sev-

eral crops grown in large acreage. Moni-

toring for residues of glyphosate and its

major metabolite aminomethylphospho-

nic acid (AMPA) in soils, natural waters

and agricultural commodities is therefore

of increasing importance.

During a procedure of analytical per-

formance optimization and method val-

idation in this laboratory, a methanolic

solution of glyphosate and AMPA was re-

ceived as an external quality control ma-

terial (LEAP Scheme of FAPAS). Quantita-

tive determination of the analytes in this

material resulted in unexpected low ap-

1

Laboratories of Chemical Weed Management and

Weed Biology, respectively, Department of Weed

Science, Benaki Phytopathological Institute, 8

St. Delta str., GR-145 61 Kifissia (Athens), Greece.

Corresponding author:

C.Giannopolitis@bpi.gr