Page 44 - Volume 1, Issue 2, July 2008

Giannopolitis & Kati 96
creased with time for an equilibration
period of about 2-3 hours and in any
case it had reached the lowest level by
the next day (at room temperature).
Shaking the solution always increased
or accelerated the apparent recovery
reduction (results from a typical ex-
periment in Table 2) and this provides
further support for the adsorption ex-
planation.
When recovery of missing quantities 3.
of both compounds was attempted,
it was succeeded by a washing of the
container with water. In Figure 3, the
typical chromatogram obtained with
the first water wash of a glass bot-
tle that contained a methanolic solu-
tion (apparent recovery about 50%)
is shown against the same chromato-
gram from the reference glass bottle
that contained a similar aqueous so-
lution (apparent recovery 100%). So-
lutions from both bottles had been as
thoroughly as possible removed and
the bottles left to dry of methanol be-
fore an equal volume of deionized wa-
ter was added. The water was ana-
lyzed after a vigorous hand shaking
Table 1. Apparent recovery of glyphosate and AMPA from an aqueous and a methanolic solution
prepared and kept in two types of containers at three volume ratios.
Solution1 Container2 Volume ratio3 Recovery %
Glyphosate AMPA
Aqueous PP bottle 0.25 102 101
Glass test tube 1.00 103 102
0.50 103 102
0.25 102 101
Methanolic PP bottle 0.25 98 88
Glass test tube 1.00 66 64
0.50 58 56
0.25 55 41
1 The solutions contained 500 ng/ml of glyphosate and AMPA in pure water (aqueous) or in methanol + 1%
water (methanolic).
2 Results presented here are with a 250-ml, all-polypropylene, screw-cap, centrifuge bottle and a 20-ml,
glass, screw cap, test tube.
3 The ratio of the solution volume to the total container volume.
Table 2. Effect of shaking on glyphosate and AMPA apparent recovery from a methanolic solu-
tion.
Treatment
Recovery (%)
Glyphosate AMPA
No shaking 41 46
Hand shaking, 5 min 30 40
Ultra sonic, 5 min 31 40
Ultra sonic, 10 min 28 28
The methanolic solution (500 ng/ml each of glyphosate and AMPA and 1% water) was prepared in the 20-ml
screw-capped glass bottles (5 ml of solution/bottle) and kept at room temperature until analyzed the next
day. Shaking was done just before analysis. A similar solution in pure water was used as reference (100%
recovery).