the polyurethane tubing had a number of peaks,
desirable if it did not affect sample quality during
but we were unable to identify any of the com-
the relatively short contact time typical of most
pounds that leached. The best match was for the
sampling situations. It is possible that the biases
largest peak, which was tentatively identified as 2-
we observed in this study may either increase
ethyl hexanoic acid, with a 78% match. Hexanoic
or decrease under dynamic conditions. With re-
acid (caproic acid) is used in the manufacture of
spect to sorption of organic solutes, we expect that
rubber chemicals and resins. The sample solution
losses due to sorption would be reduced, or possi-
exposed to the PVC tubing had one major peak;
bly eliminated, with time as equilibrium is
hexacosane (a 26-carbon alkane) was a 90% match.
approached. The unanswered question is how
However, we are at a loss to explain its presence
much time is required for equilibration to occur.
unless it was used as a lubricant. The sample solu-
Leaching of constituents, however, may increase
tion exposed to the polyester-lined PVC tubing
or decrease with exposure. Several leaching stud-
had a number of peaks but no good matches.
ies (Packham 1971a,b; Gross et al. 1974, Boettner et
Based on these findings, the following tubing
al. 1981) have shown that much of the leaching
materials appear to be least desirable for sampling
that occurs from RPVC pipe decreases with time
organics, since each of them appeared to leach
and is considered a surface phenomenon. It is pos-
several contaminants: polyurethane, polyamide,
sible that leaching of contaminants from other
FPVC, polyester-lined PVC, and silicone-modified
polymers may also be a surface phenomenon. If
TPE. In addition, PP, plasticized PP (formulation
this is the case, we would expect that leaching
1), P(VDF-HFP), and the fluoroelastomer tubings
would be minimized under dynamic conditions.
each appeared to leach one contaminant and thus
On the other hand, if higher flow rates increase
may be less desirable than those tubings that did
leaching as Junk et al. (1974) observed with FPVC,
not leach any contaminants (i.e., the PE and rigid
then it may be leaching rather than sorption that
fluoropolymer tubings).
dictates which types of tubing are acceptable for
sampling groundwater. Only a series of studies
conducted under dynamic conditions with a suite
CONCLUSIONS
of organic contaminants will determine whether
Based on the results from these studies, the rig-
the biases we observed in this study disappear
id fluoropolymers appear to be the best materials
under dynamic conditions. We are currently con-
for sampling groundwater because they were the
ducting studies to address these issues.
least sorptive of organic solutes and do not appear
to leach any contaminants. Among the fluoropoly-
LITERATURE CITED
mers, FEP, FEP-lined PE, and PVDF were the least
sorptive materials tested. If one also considers
Aller, L., T.W. Bennett, G. Hackett, R.J. Petty, J.H.
cost, PVDF is the least expensive of these three
Lehr, H. Sedoris, D.M. Nielsen and J.E. Denne
materials: its price was approximately 5060% of
(1989) Handbook of Suggested Practices for the Design
the FEP and FEP-lined PE tubings. In fact, PVDF
and Installation of Ground Water Monitoring Wells.
was the least expensive of all the rigid fluoro-
Dublin, Ohio: National Water Well Association.
polymers tested.
Backhus, D.A., J.N. Ryan, D.M. Groher, J.K. Mac-
In some instances, a more flexible tubing may
Farlane and P.M. Gschwend (1993) Sampling col-
be required--for example, in the head of a peristal-
loids and colloid-associated contaminants in
tic pump. Among the flexible tubings, the two flu-
ground water. Ground Water, 31(3): 466479.
orinated tubings (the fluoroelastomer and P[VDF-
Barcelona, M.J., J.P. Gibb and R.A. Miller (1984) A
HFP]) were much less sorptive of organic solutes
guide to the selection of materials for monitoring
than the other flexible tubings. In addition, these
well construction and ground water sampling.
two tubings and the two plasticized polypropy-
U.S. Environmental Protection Agency, Report
lenes appeared to leach the fewest constituents.
Number EPA-600/2-84-024, U.S. Government
However, if we also consider cost, we see that the
Printing Office, Washington, D.C.
fluoroelastomer was the most expensive of all the
Barcelona, M.J., J.A. Helfrich and E.E. Garske
(1985) Sampling tubing effects on ground water
tubings tested, while the price of the P(VDF-HFP)
samples. Analytical Chemistry, 57: 46064.
tubing was less than 25% of the cost of the fluo-
roelastomer tubing.
Boettner, E.A., G.L. Ball, Z. Hollingsworth and R.
Aquino (1981) Organic and organotin compounds
Because all the fluoropolymer tubings tend to
leached for PVC and CPVC pipe. U.S. Environ-
be expensive, a less expensive material would be
11
Previous Page
