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.