Gillham and O'Hannesin (1990) compared
tion of organic solutes by twenty of the sampling
sorption of low ppm levels of six monoaromatic
tubings that are commercially available and to
hydrocarbons (benzene, toluene, ethylbenzene,
look for leaching of contaminants from these ma-
and m-, o-, and p-xylene) by seven materials used
terials. The tubings we selected are given in Table
in sampling groundwater wells. The materials in-
1, where they are categorized by their flexibility.
cluded stainless steel (SS) tubing, RPVC pipe,
Thirteen tubings were very flexible and thus non-
FPVC tubing, PTFE tubing, polyvinylidene fluo-
rigid (i.e., easy to collapse with only finger pres-
ride (PVDF) rectangular wire, epoxy-impregnated
sure), and seven tubings were slightly flexible
fiberglass (FG) tubing, and flexible PE tubing.
(coilable) but rigid (i.e, a person could stand on the
They found that flexible tubings, PE and FPVC,
tubing without collapsing the tubing). Table 1 also
showed the highest rates of uptake, with signifi-
gives the abbreviations for the polymers tested,
cant losses (10% or more) of all six compounds
and the tubings' dimensions and cost. Cost of the
within the first five minutes. They found the more
tubings used in this study ranged from (LDPE)
rigid polymeric products were much less sorptive,
to 0 (fluoroelastomer) per 100 ft.
and SS did not sorb any of the analytes. They
ranked the materials from most sorptive to least
Materials and methods
sorptive as follows: FPVC > PE > PTFE > PVDF > FG
> RPVC > SS. For the rigid polymeric products,
Initial sorption study
they found that sorption agreed well with their
The test solution for this study consisted of
diffusion model (described previously by Rey-
mg/L concentrations of eight organic com-
nolds and Gillham [1985]).
pounds: nitrobenzene (NB), trans1,2-dichloro-
Studies by our laboratory (Parker et al. 1990,
ethylene (TDCE), m-nitrotoluene (MNT), trichlo-
Parker and Ranney 1994) have also shown that
roethylene (TCE), chlorobenzene (CLB), o-dichlo-
RPVC well casings were less sorptive of a suite of
robenzene (ODCB), p-dichlorobenzene (PDCB),
organic solutes than PTFE well casings and that
and tetrachloroethylene (PCE). The test solution
SS well casings did not sorb any of the analytes
was prepared by using a microliter syringe to add
tested. These studies also showed that the relative
a volume of neat organic solvent directly to well
rate of sorption by PTFE and RPVC was not affect-
water (taken from a deep water well in Hartland,
ed by concentration, i.e., ppb vs. ppm levels.
Vermont) contained in a 2-L glass bottle. Mercuric
chloride was added to the solution (40 mg/L) to
Summary of sorption studies
prevent any losses due to biological activity. After
From these studies, it appears that rigid tub-
adding all of the analytes, the bottle was filled to
ings are much less sorptive of organic solutes than
capacity with well water to eliminate any head-
flexible tubings. Two of the most sorptive tubings
space, capped with a glass stopper, tightly
were FPVC and silicone rubber. PTFE was among
wrapped with parafilm, and stirred for two days
the least sorptive polymeric tubings tested,
using a magnetic stirring device. Prior to pouring
although SS products have been shown to be non-
the solution into the tubings, we examined the so-
sorptive of organic solutes.
lution using a magnifying glass to make certain
that there were not any undissolved droplets of
organic solvents in the mixed test solution. The
RESEARCH STUDY
initial concentrations of the organic solutes varied
from 10 to 16 mg/L (Table A1).
Purpose of study
The twenty tubings were cut into different
The previous studies show that flexible tubing
lengths so that they would all have the same inter-
materials can affect analyte concentrations by
nal surface area, 40 cm2 (Table 1). This was neces-
sorbing organic contaminants and by leaching or-
ganic constituents. This is especially true for
sary because three types of tubing (PTFE, ethylene
FPVC. The fluoropolymers were among the least
tetrafluoroethylene [ETFE], and polyamide) had
sorptive tubings tested but were still highly sorp-
different internal diameters than the other tubings
tive of some organic solutes. A comprehensive
(Table 1). The tubing surface-area-to-solution-vol-
comparison of the many tubings that are commer-
ume ratios and the solution-volume-to-material-
cially available, especially for the various types of
volume ratios differed for these three materials
fluoropolymers that are now available, does not
and for one material (FEP-lined PE), which had a
exist.
different wall thickness (Table 1).
The purpose of this study was to compare sorp-
The cut tubing sections were rinsed with sev-
4
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