Page 43 - Volume 1, Issue 2, July 2008

Glassware sorption of glyphosate and AMPA 95
ters have suspected a tendency of these
compounds to adsorb on glass surfaces
and have used polypropylene containers
during sample preparation and preserva-
tion (3, 4, 6). It is reasonable, therefore, to
assume that an increased sorption onto
the glass surfaces may account for the re-
duced apparent recovery associated with
the methanolic solutions. A first evidence
for this assumption was obtained by com-
paring the recovery reductions from
methanolic solutions prepared in the
same glass bottles as above and in poly-
propelene tubes (Figure 2). The apparent
recovery reduction was significantly high-
er in the glass bottles than in the propyl-
ene tubes.
Results from a series of supplementa-
ry tests further verified the apparent re-
covery reduction and provided additional
evidence that a stronger sorption of gly-
phosate and AMPA on glassware surfaces,
when they are in methanolic solutions, is
responsible for the reduced apparent re-
covery from such solutions:
When apparent recovery of the two 1.
compounds was examined with so-
lutions prepared and kept in oth-
er types of clear glass containers (e.g.
25-ml glass volumetric flasks, 20-ml
screw-capped glass tubes, 4-ml crimp-
capped glass bottles), it was in all cas-
es found to be significantly lower from
the methanolic solutions compared
to that from aqueous solutions of the
same concentration in the same type
of container. Differences in apparent
recovery reduction were observed
among the various types of glassware
suggesting that some may be more
adsorptive than others. Polypropelene
containers (a 250-ml polypropelene
centrifuge bottle was used in these
tests) do cause a recovery reduction
with the methanolic solutions but gen-
erally seem to be less adsorptive than
glass containers. Differences were also
observed within a type of glass con-
tainer depending on the ratio of the
solution volume to the total volume
of the container (results from a typical
experiment in Table 1). This indicates a
positive correlation of the apparent re-
covery reduction to the area of avail-
able glassware surfaces and provides
further support to the adsorption ex-
planation.
When apparent recovery of the two 2.
compounds was examined at vari-
ous time intervals after preparation of
the methanolic solution in a glass con-
tainer, it was realized that recovery de-
Figure 2. Apparent recovery of glyphosate and AMPA from
methanolic solutions prepared and kept for 24 h either in poly-
propelene tubes or in glass bottles. Similarly prepared pure
water solutions served as controls (100% recovery).