REPORTS--"Filtration of Water-Sediment Samples for the Determination of Organic Compounds" by Mark W. Sandstrom
In Reply Refer To: August 27, 1991
Mail Stop 412
OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM 91.09
Subject: REPORTS--"Filtration of Water-Sediment Samples for
the Determination of Organic Compounds"
by Mark W. Sandstrom
The attached report documents procedures used by the U.S.
Geological Survey for processing water-sediment samples from
surface and ground water for determination of anthro-pogenic
organic compounds. More general procedures for processing
surface-water samples for determination of nutrients, inorganic
constituents, and dissolved organic carbon are described in Open-
File Report 90-140, "Methods for Collection and Processing of
Surface-Water and Bed-Material Samples for Physical and Chemical
Analyses," J.R. Ward and C.A. Harr, editors. This report by
Sandstrom complements that publication.
David A. Rickert
Chief, Office of Water Quality
Attachment
This memorandum supplements Office of Water Quality Technical
Memorandum 91.02.
Key Words: Organic compounds
Distribution: A, B, S, FO, PO
FILTRATION OF WATER-SEDIMENT SAMPLES FOR THE
DETERMINATION OF ORGANIC COMPOUNDS
By Mark W. Sandstrom
Purpose and Scope
The purpose of this report is to describe the procedures used
by the U.S. Geological Survey for processing water-sediment
[Footnote: Used throughout this report, the term refers to water
and/or a mixture of water and suspended sediment (Ward and Harr,
1990)] samples from surface and ground water for determination of
manmade organic compounds. More general procedures for processing
surface water samples for determination of nutrients, inorganic
constituents, and dissolved organic carbon are described in Ward
and Harr (1990). Detailed discussion of field methods and
equipment for measuring fluvial sediment is given in Edwards and
Glysson (1988). This document represents part of a forthcoming
manual on the methods used for collection and processing surface
water, suspended sediment, bottom sediments, and ground water for
the determination of manmade organic compounds (Sandstrom, in
preparation).
Principles and Concepts
Water-sediment samples collected for the analysis of organic
compounds are filtered to separate solid and aqueous phases, to
provide a more detailed understanding of the environmental fate of
organic compounds, and to reduce analytical processing errors.
Manmade organic compounds in surface waters interact with sediment
particles (particulate organic matter, lipids of organisms)
through sorptive processes (Smith and others, 1988). Because of
these sorptive interactions between organic compounds and organic
matter attached to sediment particles, a description of the fate
and transport of manmade organic compounds needs to consider the
organic content of both the dissolved phase and the sediment-
particle sorbed phases. This requires separate analyses of the
dissolved and sediment-particle associated phases for organic
compounds. In addition, problems can arise during extraction of
the organic compounds from water-sediment mixtures. In liquid-
liquid extraction methods, formation of emulsions during
separation of the water and organic solvent phases can cause low
recoveries of organic compounds. Also, extraction efficiency can
be lower in samples with high concentrations of suspended
particles because of inefficient interaction of the particles with
the organic solvent. In solid-phase extraction methods, which
utilize bonded silica sorbents packed into an extraction column,
sediment particles must be removed to prevent blockage of the
column.
Constituents passing through a filter are operationally
defined as "dissolved". Separation of dissolved and particulate
material by filtration requires precise definition of the filter
medium and filtration procedure since some solid phase material,
for example colloids, may not be removed by filtration.
Traditionally, the 0.45-micrometer (um) pore-sized membrane filter
has been used to distinguish between dissolved and suspended
material because this size filter was the smallest that could be
reliably manufactured at the time (Ward and Harr, 1990). Membrane
filters commonly used for analysis of nutrients and inorganic
constituents in water are made of cellulose or polycarbonate
polymers. These materials are not suitable for analysis of
organic compounds, mainly because they are not compatible with the
organic solvents used to preclean sampling equipment and supplies.
Instead, depth-filters made of glass fibers are used for
analysis of organic compounds because they can be precleaned with
organic solvents or by baking at 450 degrees C. Depth-filters
also have a higher loading capacity than membrane filters. Hence
they are more suitable for organic sample preparation methods that
frequently require larger sample volumes (1-5 liters) than
inorganic or nutrient analyses. The 0.7-um nominal pore-size
glass fiber filter is the smallest size available, and is used to
operationally define the dissolved and sediment-particle phases of
organic compounds.
Membrane filters made of silver with a 0.45-um pore-size are
used to process water-sediment samples for the determination of
dissolved organic carbon (Ward and Harr, 1990). Although
resistant to organic solvents, these membrane filters become
blocked too quickly for filtering the relatively large sample
volumes (1-5 L) required for analysis of most organic compounds.
Although plastic membrane filters generally should not be
used to process water-sediment samples for organic compound
determination, they have been approved for use in at least one
specific method. Water-sediment samples analyzed for
organonitrogen herbicides by solid-phase extraction and gas
chromatography mass spectrometry (GC/MS) with selected ion
monitoring (SIM) are filtered using nylon membrane filters
contained in polypropylene holders.
EQUIPMENT
Equipment needed for isolation of dissolved and suspended-
sediment phases of manmade organic compounds by filtration
includes glass fiber filters, positive displacement pumps, and in-
line filtration units. All components need to be made of
materials that will not contaminate or sorb analytes, and are
suitable for use with organic solvents.
Glass-Fiber Filters
1--Application
Glass-fiber filters, binder-free and 0.7-um nominal pore
size, are used to process water-sediment samples. Field
application is mostly for filtration of water-sediment samples to
isolate dissolved and suspended phases, allowing separate
determinations of organic compounds in each phase. For
hydrophobic organic compounds that partition to sediment organic
matter, filtration is mainly used to concentrate suspended
sediment on the filter in order to improve extraction efficiency
and lower analytical detection limits. This is especially useful
for water-sediment samples with low concen-trations of suspended
material where large volumes (4-40 L) of water-sediment can be
filtered to provide a much larger mass of suspended sediment than
if a typical 1-L sample were extracted. For hydrophilic organic
compounds (miscible with water), filtration is used to remove
suspended material trapped on the filter because it often contains
analytical interferences that are coextracted with the analytes.
Filtration also is used as a method of sample preservation for
organic compounds because it removes microorganisms from the
sample (Ogawa and others, 1981).
2--Description
Glass-fiber filters are made of borosilicate glass and
combine the properties of a depth filter and a microporous medium.
The glass fiber mesh retains sediment particles by entrapment
within the mesh. In addition, the fiber mesh forms an approximate
pore size distribution across the filter surface, providing some
of the characteristics of a microporous membrane. Particle
retention efficiency is determined by the fineness and length of
the constituent microfibers and depth of the fiber mat. Because
of the random nature of the glass fiber mesh, the size of the
particles retained is less precise than for membrane filters.
Particle retention efficiency is expressed in terms of the
smallest particle size at which a retention level of 95-98 percent
is attained. For this reason, the glass fiber filters are
described by a nominal particle retention rating (in um).
The glass filter surface is basically inert, and is resistant
to organic solvents used in precleaning or extraction of organic
compounds from sediment particles trapped by the filter. Filters
without binders must be used for organic analysis because acrylic
resin binders can leach and contaminate samples.
Binder-free glass fiber filters are available in a variety of
standard disc sizes ranging from 13 to 293 mm in diameter. The
smallest nominal pore size of glass fiber filters currently
available is 0.7 um. The filters are precleaned by baking in a
muffle furnace at 450 degrees C for at least 2 hours.
Precleaned glass-fiber filters are available through the
National Water-Quality Laboratory (NWQL).
Disposable Membrane Filters
1--Application
Nylon membrane filters contained in disposable polypropylene
housing units, commonly 25 mm in diameter and 0.45-um pore size,
are used to process water-sediment samples for determination of
organonitrogen herbicides by a solid-phase extraction method (NWQL
Schedule 1379). This method requires that suspended particles be
removed from the water-sediment sample to prevent blockage of the
solid-phase cartridge. While membrane filters are generally not
suitable for organic samples, disposable nylon membrane filters
are suitable in this particular case. This is because the method
uses gas chromatography with mass spectrometry (GC/MS) and
selected ion monitoring (SIM) for determination of the herbicides,
and potential interferences from the plastic components of the
filter units are not detected. Also, the sample volume (100 mL)
is small enough that blocking of the membrane filter is not a
problem. Finally, the organic compounds determined by this method
have a low tendency to partition into particulate organic matter,
and so the particulate material trapped on the filter can be
discarded.
2--Description
The membrane filters tested for use in the determination of
organonitrogen herbicides in water-sediment samples by solid-phase
extraction are made of a thin film of nylon 25 mm in diameter, and
have a pore size of 0.45 5m. The membrane is contained in a
disposable housing made of polypropylene, with female luer lock
inlet and male luer lock outlet connections. The filter units are
pre-rinsed prior to use with about 10 mL of sample. Filter units
tested for this procedure are available through the NWQL.
Positive Displacement Pump Filtration System
1--Application
Pumping filtration systems force water through a filter by
positive pressure from a pump placed between the unfiltered sample
and filter unit. They can filter both large and small volumes of
water that have moderate to high concentrations of suspended
sediment. Pumping filtration systems used to process water-
sediment samples for determination of organic compounds need to be
constructed of materials compatible with organic solvents used in
cleaning procedures. These include stainless steel, aluminum,
fluorinated polymers such as Teflon-TFE (poly-tetrafluoroethylene),
glass and non-porous ceramics (hard fused microcrystalline
alumina). Other materials proven to be sufficiently resistant to
attack by solvents used in cleaning, so as not to introduce
contaminants or cause absorptive losses, can be used. Plastics,
rubber, oils and other lubricants need to be avoided to prevent
sample contamination and/or sorbtive losses.
2--Description
Positive displacement pumping systems (fig. 1) consist of an
in-line filter holder, a valveless, piston-type metering pump, and
Teflon-FEP tubing. The filter units are available in standard
diameters ranging from 13 to 293 mm, and the size selected is
determined by the sample volume and suspended sediment
concentration. The filter units are available with stainless
steel, aluminum, or Teflon components, depending on the diameter
of the filter unit.
The valveless, piston-type metering pump consists of a pump
head with a reciprocating piston driven by a 12-volt direct
current (DC), variable speed motor. The pump head and all wetted
parts are constructed of ceramic or Kynar-PVDF (polyvinylidine
fluoride) components, which are resistant to organic solvents.
Although these pumps can tolerate suspended solids in the pumped
fluid, high levels of suspended solids can cause excessive demand
on the pump motor. The ceramic shaft of these pumps will break if
the motor amperage exceeds 4 amps. To avoid this, either a 4-amp
DC breaker should be used in-line with the pump, or a 115- to 12-
volt converter with 4-amp maximum output should be used. A pump
commonly used by the U.S. Geological Survey is capable of pumping
approximately 0-500 mL per minute.
The pump and filter unit are connected by 1/4-in diameter
meter convoluted Teflon-FEP tubing. The convoluted tubing does
not crimp when bent, unlike straight Teflon tubing.
The filter holder most widely used for filtration of surface
waters by the U.S. Geological Survey consists of two machined
aluminum or stainless steel plates, 142-mm diameter, that are held
together by three locking bolts or a locking ring. The plates
have Teflon, Teflon-coated silicone, or Viton o-rings set in
grooves to seal the filter, and a stainless steel support screen
on the lower plate for the filter. A valve is located in the
upper plate to exhaust trapped air. Threaded holes 3/8-in
diameter at the center of each plate are used to attach tubing
fittings for inlet and outlet Teflon tubing.
For small sample volumes or samples with relatively low
suspended sediment concentrations, 47-mm diameter flow-through
filter units can be used. These filter units consist of two
Teflon plates held together by a threaded locking ring. The
bottom plate contains a Teflon support screen for the filter, and
threaded holes 1/4-in diameter at the center of each plate are
used to attach fittings for inlet and outlet Teflon tubing.
Teflon tape wrapped around the threads of the upper Teflon plate
prevents leaking during filtration.
Other in-line filter units, including 13- and 25-mm stainless
steel filter units, or the disposable nylon membrane filter unit
used in the organonitrogen SPE method can be connected to the
pumping system using appropriate tubing to luer-lock-syringe
reducing fittings (fig. 2).
3--Care and Maintenance
The filter assemblies need to be thoroughly cleaned prior to
use with a nonphosphate laboratory detergent. The unit should be
disassembled and immersed in a sink or container and gently
scrubbed with a soft brush. The components are then rinsed with
tap water to remove all traces of detergent, followed by a rinse
with high purity methanol. [Footnote: CAUTION: when rinsing with
methanol, use a fume-hood or well-ventilated area and take
necessary safety precautions to prevent skin and eye contact.]
The positive displacement pump and attached Teflon tubing are
cleaned by pumping laboratory detergent through the tubing
followed by rinses with tap water and methanol. For samples
containing relatively high concentrations of hydrophobic organic
compounds such as polychlorinated biphenyls, the methanol rinse
may not be sufficient to remove all traces of contaminants. In
that case, additional rinsing with dichloromethane or hexane after
the methanol rinse might be required. NOTE: These solvents are
not soluble in water, so they must be used for rinsing only after
the equipment is dry (the methanol rinse speeds the drying
procedure). After cleaning, the filtration system should be
reassembled and all openings covered with aluminum foil for
storage between uses.
PROCEDURES
At the field site a relatively clean workspace for sample
filtration is required. It is important to select a location that
can be protected from potential contamination from exhaust fumes,
dust, etc. Appropriate areas include a bench set up in a van or a
building conveniently located near the sampling site. All
sampling equipment must be cleaned according to recommended
procedures before each use.
Sampling methods and devices that are capable of collecting
water samples that accurately represent the water-quality
characteristics of the water body at a given time or location
should be used. Detailed descriptions of sampling methods used by
the U.S. Geological Survey for obtaining depth- and width-
integrated samples from streams are given in Edwards and Glysson
(1988). The US-series samplers described in these documents must
be used with Teflon nozzles and glass or Teflon sample containers
when sampling for organic constituents. For the filtration of
depth- and width-integrated samples for the determination of
manmade organic compounds, a 19- or 38-L stainless steel milk can
is a suitable container for holding the composite sample prior to
filtration. Recommended procedures for obtaining representative
ground water samples are described by Barcelona and others (1985),
and Hardy and others (1989). The in-line filter unit can be
connected to the outlet line of a down-hole ground water sample
pump in this case, provided appropriate consideration is given to
pump material suitability for sampling organic compounds.
General Filtration Procedures for Organic Compounds
Cover the bench or table with a sheet of aluminum foil to
make a clean workspace. Place the sample to be filtered, filter
unit, pump system, filters, forceps, and sample bottles (fig. 1)
on the clean workspace, and remove the protective aluminum foil
wrapping from the pre-cleaned equipment. Wear disposable
laboratory gloves to avoid contamination of the clean filter unit.
Remove the upper plate of the filter unit and place a precleaned
glass fiber filter onto the lower plate of the filter unit, using
stainless steel forceps to manipulate the filter. Avoid touching
the filter with fingers. Wet the filter unit with a few drops of
organic-free water contained in a Teflon squeeze bottle to help
keep the filter in place as the unit is reassembled. Replace the
upper plate of the filter unit, gently tightening the hold-down
clamps. Add 10 to 20 mL of organic-free water through the upper
filter plate inlet opening to completely wet the filter, and
firmly tighten the clamps. If the filter is dry when the unit is
tightened, it may tear. Connect the pump tubing to the inlet of
the filter unit.
Remove the protective cover from the inlet line of the filter
unit and place it into the composite sample. Place a container
under the outlet of the filter unit and turn on the pump to rinse
about 125 mL (use an 8 oz plastic bottle to measure) through the
lines to remove any distilled water-methanol that remains from
cleaning procedures. Turn off pump, and then begin sample
filtration by placing an appropriate sample container under the
outlet of the filter unit, and collecting sufficient sample
required for each organic compound determination. Do not
completely fill bottles; leave at least 2-3 cm headspace to allow
addition of matrix spike standards (if required) and to prevent
sample loss by expansion or from spilling when the bottles are
opened at the laboratory.
If the filter becomes clogged before the required volume of
sample has been collected, replace it with a new filter, and
continue the filtration. NOTE: These filter units do not have
upper screens so the filters cannot be backflushed. Allow the
first 125 mL (collected in a waste container such as an 8 oz
plastic bottle) to rinse the filter unit to remove any sediment
particles that may have moved below the filter during the
replacement procedure. This volume of sample rinsed through the
filter must be measured and recorded if the sediment collected on
the filter is to be analyzed for organic contaminants.
If the concentration of manmade organic compounds in the
suspended sediment phase is to be determined, the volume of water
filtered needs to be accurately determined (+/- 1 mL). When
filtration is completed or the filter becomes blocked, remove as
much water as possible from the inside of the filtration unit by
pumping air through the lines or using a syringe to apply pressure
to the inlet of the filter unit. This is needed to prevent
spilling of a water-sediment slurry when the filter unit is
disassembled and the top plate is removed. When all water from
the filter unit has passed through the filter, release the clamps
and remove the top plate of the filter unit. Using stainless
steel forceps, carefully fold the filter in quarters and transfer
to a clean glass sediment jar.
Specific Filtration Procedures for Organonitrogen Herbicides
Cover the bench or table with a sheet of aluminum foil to
make a clean workspace. Assemble the sample to be filtered,
disposable filter unit, pump system and sample bottles (fig. 2) on
the clean workspace, and remove any protective aluminum foil
wrapping on openings of the clean equipment. Wear disposable
laboratory gloves to avoid contamination of the pump tubing.
Place inlet line from the pump into the sample to be filtered.
The disposable filter units do not have air vents so air needs to
be removed from the lines prior to attaching the filter unit.
Turn on pump and pump a few mL of sample to remove air from the
pump and tubing. With the pump on, connect the tubing from the
pump to the inlet of the filter unit, and begin collecting
filtrate in a glass sample container. The filters are precleaned
with methanol-water so a filter rinse is not required. Do not
completely fill the sample container; leave a 2- to 3-cm
headspace. If the filter becomes blocked before sufficient
samples has been filtered, the filter unit can be replaced and
filtration continued until at least 100 mL has been collected.
When completed, discard filter units and rinse pump and tubing
with detergent, followed by tap water and high purity methanol.
REFERENCES
Barcelona, M.J., Gibb, J.P., Helfrich, J.A., and Garske, E.E.,
1985, Practical guide for ground water sampling: Champaign,
Illinois State Water Survey, 94 p.
Clescern, L.S., Greenberg, A.E., and Trussell, R.R., eds., 1989,
Standard methods for the examination of water and wastewater (17th
ed.): Washington, APHA, AWWA, WPCF.
Edwards, T.K., and Glysson, G.D., 1988, Field methods for
measurement of fluvial sediment: U.S. Geological Survey Open-File
Report 86-531, 118 p.
Eichelberger, J.W., Behymer, T.D., and Budde, W.L., 1988, Method
525. Determination of organic compounds in drinking water by
liquid-solid extraction and capillary GC/MS, in Methods for the
determination of organic compounds in drinking water: U.S.
Environmental Monitoring and Support Laboratory, Cincinnati, p.
325-356.
Hardy, M.A., Leahy, P.P., and Alley, W.M., 1989, Well installation
and documentation, and ground-water sampling protocols for the
pilot national water-quality assessment program: U.S. Geological
Survey Open-File Report 89-396, 36 p.
Liska, I., Krupcik, J., and Leclercq, P.A., 1989, The use of solid
sorbents for direct accumulation of organic compounds from water
matrices--A review of solid-phase extraction techniques: Journal
High Resolution Chromatography, v. 12, p. 577-590.
Ogawa, I., Junk, G.A., and Scev, H.J., 1981, Degradation of
aromatic compounds in groundwater, and methods of sample
preservation: Talanta, v. 28, p. 725-729.
Sandstrom, M.W., in preparation, Methods for the collection and
processing of ground-water, surface-water, and bed-material
samples for the determination of manmade organic compounds: U.S.
Geological Survey Open-File Report.
Smith, J.A., Witkowski, P.J., and Fusillo, T.V., 1988, Manmade
organic compounds in the surface waters of the United States-A
review of current understanding: U.S. Geological Survey Circular
1007, 92 p.
Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection and
process-ng of surface-water and bed-material samples for physical
and chemical analyses: U.S. Geological Survey Open-File Report
90-140, 71 p.
Appendix 1- DESCRIPTION OF APPARATUS SPECIFIED IN THIS METHOD
General procedure for filtration of water-sediment samples for
determination of organic compounds (figure 1):
1) Unfiltered sample container, stainless steel milk can with
lid, 19 L (5 gal), No. SS-20 from Coshocton Valley Manufacturing
Corporation, or equivalent. Clean glass bottles with Teflon-TFE-
lined lids are also suitable.
2) Ceramic-piston valveless metering pump, 12-V direct current
motor, with flow rates from 0-500 mL/ min. The Model QB-1 CSC
from Fluid Metering, Inc. has been shown to be suitable for this
purpose. The Teflon-TFE diaphram pump head No. N-07090-42 for
Masterflex pump drives available from Cole-Parmer Instrument
Company is also satisfactory.
3) In-line filter unit, 142-mm dia . The aluminum filter unit,
No. 0860, available from Geotech Environmental Equipment Inc., has
been shown to be suitable for this purpose.
4) Convoluted Teflon-FEP tubing, 1/4-in outside diameter, Cole-
Parmer Instrument Company No. L-06486-02 or equivalent.
5) Union, 1/4-in tube, Swagelock fitting No. SS-400-6 or
equivalent.
6) Tube fitting, 1/4-in dia. tube to 1/4-in dia. pipe thread,
Swagelock fitting No. SS-400-1-4 or equivalent.
7) Glass-microfiber filters, 142-mm dia., 0.7 micron nominal pore
size, Whatman GF/F grade, No. 1825C142 or equivalent. Note:
filters require heating at 450 degrees C in a muffle furnace for
at least 2 hours before use.
8) Filtered sample bottle, amber borosilicate glass, 1 L, with
Teflon-TFE-lined cap. Precleaned sample bottles are available
from the NWQL.
9) Tube fitting, 1/4-in dia. tube to 3/8-in dia. pipe thread,
Swagelock fitting No. SS-400-1-6 or equivalent.
Procedure for filtration of water-sediment samples for
determination of organonitrogen herbicides by solid-phase
extraction in NWQL Schedule 1379 (figure 2):
1) Unfiltered sample container, stainless steel milk can with
lid, 19 L (5 gal), No. SS-20 from Coshocton Valley Manufacturing
Corporation, or equivalent. Clean glass bottles, with Teflon-TFE-
lined lids are also suitable.
2) Ceramic-piston valveless metering pump, 12-V direct current
motor, with flow rates from 0-260 mL/min. The Model RHB1 CKC from
Fluid Metering, Inc. has been shown to be suitable for this
purpose. The Teflon-TFE diaphram pump head No. N-07090-42 for
Masterflex pump drives available from Cole-Parmer Instrument
Company is also satisfactory.
3) Teflon-PFA tubing, 1/8-in outside diameter, Cole-Parmer
Instrument Company No. CL-06375-01, or equivalent.
4) Union, 1/8-in tube, Swagelock fitting No. SS-200-6 or
equivalent.
5) Tube fitting, 1/8-in dia. tube to 1/4-in dia. pipe thread,
Swagelock fitting No. SS-200-1-4 or equivalent.
6) Tefzel male luer to 1/4-28 thread connector, Upchurch
Scientific No. P-625, or equivalent.
7) Tefzel union, 1/4-28 thread, Upchurch Scientific No. P-631, or
equivalent.
8) Tefzel nut, 1/8-in tubing to 1/4-28 thread, Upchurch
Scientific No. P-315, or equivalent.
9) Teflon variable-bore connector, Omnifit to tube up to 11-mm
outside diameter, Omnifit No. 1108, or equivalent.
10) Teflon male luer to Omnifit connector, Omnifit No. 1201, or
equivalent.
11) Filtered sample container, amber borosilicate glass, 125 mL,
with Teflon-TFE lined cap. Precleaned sample bottles are
available from the NWQL.