1.0
PP
PTFE
EFA
0.8
PTFE
Polyamide
P(VDFHFP)
FVDF
0.6
Fluoroelastomer
FEPlined PE
EP
0.4
Figure 2. Sorption of tetrachloroethyl-
0.2
ene by the 10 least sorptive tubings
studied (Parker and Ranney 1996).
(Values for PTFE, ETFE, and polyamide
were adjusted to comparable surface-area-
0
20
40
60
80
to-solution-volume ratios.)
Contact Time (h)
0
1.0
PP
PTFE
EFA
0.8
PTFE
Polyamide
P(VDFHFP)
FVDF
0.6
Fluoroelastomer
FEPlined PE
EP
0.4
Figure 3. Sorption of p-dichloroben-
zene by the 10 least sorptive tubings
0.2
studied (Parker and Ranney 1996).
(Values for PTFE, ETFE, and polyamide
were adjusted to comparable surface-
20
40
60
80
area-to-solution-volume ratios.)
Contact Time (h)
that the rigid fluoropolymers (Table 1) were the
two fluorinated tubings, a fluoroelastomer and a
least sorptive. As an example, Figure 2 shows
copolymer of PVDF and hexafluoropropylene
sorption of tetrachloroethylene (PCE) and Figure
[P(VDF-HFP)], were much less sorptive of organ-
3 shows sorption of p-dichlorobenzene (PDCB)
ic solutes than the other flexible tubings (Parker
by the ten least sorptive materials tested. Among
and Ranney 1996).
the rigid fluoropolymers, the fluorinated ethyl-
Only a few studies have examined losses of
ene (FEP), FEP-lined polyethylene (PE), and
organic solutes from solutions that were pumped
polyvinylidene fluoride (PVDF) tubings were the
through various types of tubings, i.e., under dy-
three least sorptive materials. However, even
namic conditions. Pearsall and Eckhardt (1987)
though these three tubings were the least sorp-
found that concentrations of two VOCs tested
tive, it should be noted that they were still highly
were 815% lower in samples pumped through
sorptive of the more hydrophobic analytes test-
silicone rubber tubing than in samples pumped
ed. For example, FEP-lined PE sorbed the least
through Teflon tubing (at flow rates of 0.71.0 L/
amount of PDCB, and yet loss of this analyte was
min). Ho (1983) reported that concentrations of
nearly 30% after only 1 hr!
organics were up to 15% lower in samples
In some instances a more flexible tubing may
pumped through silicone rubber tubing than in
be required, such as in the head of a peristaltic
the initial test solution (flow rates were 2.64.0
pump. Among the flexible tubings tested, the
L/min). Ho also reported that there were signifi-
3
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