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.