effect of leaching from filters on laboratory analyses - Environmental ...

EFFECT OF LEACHING FROM FILTERS ON LABORATORY ANALYSES OF 

COLLECTIVE ORGANIC CONSTITUENTS 

ABSTRACT 

Eakalak Khan,* Sindhuja Subramania-Pillai** 

*Department <strong>of</strong> Civil Engineering 

North Dakota State University 

Fargo, North Dakota 58105 

**North Dakota State Water Commission, Bismarck, North Dakota 

Membrane and glass fiber <strong>filters</strong> are widely used in laboratory water and wastewater analyses. 

During sample filtration, some <strong>filters</strong> release organic compounds, which may interfere with 

organic analyses. This research investigated the interferences due to organic <strong>leaching</strong> in the 

determinations <strong>of</strong> dissolved organic carbon, biodegradable dissolved organic carbon, soluble 

biochemical oxygen demand, and soluble chemical oxygen demand and the appropriate cleaning 

method for the <strong>filters</strong>. Nineteen <strong>filters</strong> studied included 16 membrane <strong>filters</strong> and 3 glass fiber 

<strong>filters</strong>. A wide variation was observed on the amount and characteristics <strong>of</strong> organics <strong>leaching</strong> 

<strong>from</strong> the <strong>filters</strong>. Some <strong>filters</strong> showed no organic <strong>leaching</strong> while some others had very high 

organic <strong>leaching</strong>. Soaking the <strong>filters</strong> in deionized distilled water (DDW) resulted in more 

leachable organics <strong>from</strong> the <strong>filters</strong> compared with filtering DDW through them. Certain <strong>filters</strong> 

should be avoided for use in the above analyses and soaking in DDW is a more suitable cleaning 

method than discarding initial filtration volumes for most <strong>filters</strong>. 

KEYWORDS 

Leaching, organics, <strong>filters</strong>, interference, laboratory analyses. 

INTRODUCTION 

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Filtration is used to process water samples in a variety <strong>of</strong> science and engineering fields 

(Horowitz et al., 1996). In the field <strong>of</strong> water quality, it is mainly employed to distinguish 

between suspended and dissolved constituents (Otsuki and Fuwa, 1977; Danielson, 1982; Aiken 

and Leenheer, 1993; Burgess et al., 1996). Filtration is carried out mainly using either membrane 

<strong>filters</strong> or glass fiber <strong>filters</strong>. The <strong>filters</strong> used should neither introduce any artifacts to the analysis 

nor affect the analytical procedure. Some problems associated the use <strong>of</strong> <strong>filters</strong> are as follows: 

<strong>leaching</strong> <strong>of</strong> organic carbon and ultraviolet (UV) absorbing components, absorption <strong>of</strong> dissolved 

and colloidal matter, and clogging <strong>of</strong> membrane surface because <strong>of</strong> the build up <strong>of</strong> the particulate 

matter (Karanfil et al., 2003). 

The operational definition <strong>of</strong> dissolved constituents in water is the portion that passes through a 

0.45 μm pore size filter (APHA et al., 1998; U.S. Environmental Protection Agency, 1999). Only 

membrane <strong>filters</strong> are available with a uniform absolute pore size (Retention efficiency <strong>of</strong> 100% 

for rated pore size) <strong>of</strong> 0.45 μm. The smallest nominal pore size (Retention efficiency 60 to 98% 

Copyright © 

2006 Water Environment Foundation. All Rights Reserved 

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for rated pore size) <strong>of</strong> glass fiber <strong>filters</strong> is larger than 0.45 μm. As a result, they are not 

appropriate for use in dissolved constituent measurements. However, membrane <strong>filters</strong> because 

<strong>of</strong> their organic composition suffer <strong>from</strong> organic <strong>leaching</strong>. In order to avoid the possible organic 

contamination <strong>from</strong> membrane <strong>filters</strong>, some researchers (Dubruiel et al., 1997; Khan et al., 1998) 

used glass fiber <strong>filters</strong> for dissolved organic carbon determination while some other researchers 

used the membrane <strong>filters</strong> after decontaminating them. Rinsing the <strong>filters</strong> with dilute nitric acid, 

dilute hydrochloric acid followed by distilled water, or deionized distilled water (DDW) have 

been reported as the decontamination methods (Buffle et al., 1992; Baeyens et al., 1998; Karanfil 

et al., 2003). 

Hwang et al. (1979) examined the concentrations <strong>of</strong> total organic carbon (TOC), chemical 

oxygen demand (COD) and nitrate in the filtrates <strong>of</strong> a Millipore mixed cellulose acetate and 

cellulose nitrate membrane filter. Moderate to significant amounts <strong>of</strong> TOC, COD, and nitrate 

were released <strong>from</strong> the filter. Norrman (1993) used pre-packed and membrane <strong>filters</strong> for 

dissolved organic carbon (DOC) determination. The filtrates <strong>from</strong> the membrane <strong>filters</strong> showed 

severe contamination <strong>of</strong> DOC. Kaplan et al. (1993) reported that polyvinylidene difluoride and 

mixed cellulose ester <strong>filters</strong> used for sterilizing incubation water leached significant amounts <strong>of</strong> 

DOC and assimilable organic carbon (AOC) and that polysulfone and nylon <strong>filters</strong> released DOC 

even after copious washing with deionized water. Their study also indicated that AOC 

concentrations were significantly higher with membrane filtration than with glass fiber filtration. 

Shaw et al. (2000) found that as much as 2 mg/L <strong>of</strong> biodegradable dissolved organic carbon 

(BDOC) is released <strong>from</strong> a 0.22 μm pore size cellulose acetate membrane filter. Details 

regarding the amount <strong>of</strong> sample filtered were not provided by the authors. Khan et al. (1998) 

studied the organics released <strong>from</strong> the same type <strong>of</strong> filter. The <strong>filters</strong> released about 0.40 to 0.50 

mg <strong>of</strong> TOC. The organics leached <strong>from</strong> the <strong>filters</strong> were about 50% to 85% biodegradable. The 

biodegradability <strong>of</strong> the organic <strong>leaching</strong> <strong>from</strong> other types <strong>of</strong> <strong>filters</strong> has not been reported. 

Karanfil et al. (2003) tested seventeen different <strong>filters</strong> for their interferences in DOC and 

ultraviolet absorbance at 254 nm (UV254) measurements. For all seventeen <strong>filters</strong> tested, UV254 

<strong>of</strong> the first 100 mL extract was less than 0.0045 cm -1 . For UV scans between 200 and 800 nm <strong>of</strong> 

the 100 mL filtrate, there were no light absorbing impurities detected. Hydrophilic 

polyethersulfone <strong>filters</strong> followed by hydrophilic polypropylene <strong>filters</strong> exhibited the least organic 

<strong>leaching</strong> and thus interference with DOC analysis. To minimize the interferences, the <strong>filters</strong> 

should be rinsed with a minimum <strong>of</strong> 30 mL distilled and deionized water per cm 2 <strong>of</strong> filter surface 

area or at least 500 mL on a 47-mm diameter filter to make the filtrate free <strong>of</strong> DOC and UV 

absorbing components. 

Filtration through a filter is an essential step for determining DOC, soluble COD (SCOD), 

soluble biochemical oxygen demand (SBOD) and BDOC <strong>of</strong> a water sample. The interference 

due to filter <strong>leaching</strong> on DOC measurement was thoroughly investigated (Karanfil et al., 2003) 

while its <strong>effect</strong>s on SCOD and BDOC measurements were studied only for one type <strong>of</strong> filter 

(Hwang et al., 1979; Khan et al., 1998; Shaw et al., 2000). The interference <strong>from</strong> the <strong>filters</strong> on 

SBOD measurement has not been studied. 

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This paper presents a detailed investigation on the interferences contributed by filter <strong>leaching</strong> on 

DOC, SCOD, SBOD, and BDOC measurements for commonly used <strong>filters</strong>. The interference on 

DOC measurement was investigated to confirm the results <strong>from</strong> a previous study (Karanfil et al., 

2003) and to select the <strong>filters</strong>, that have substantial organic <strong>leaching</strong>, for SBOD and BDOC tests. 

The variations in organic <strong>leaching</strong> generated by different filter manufactures and pore sizes were 

examined. In addition, the <strong>effect</strong> <strong>of</strong> filter soaking in DDW on the leachable organics was studied 

and compared with a common filter cleaning practice by discarding initial volumes <strong>of</strong> the filtrate 

to determine an appropriate method for minimizing the interference caused by organic <strong>leaching</strong>. 

METHODOLOGY 

Filters 

Nineteen different <strong>filters</strong> made <strong>of</strong> 11 different materials were studied (Table 1). The selection <strong>of</strong> 

filter materials was based on a survey by Karanfil et al. (2002), which was conducted among 

drinking water practitioners and researchers to determine current practices for measuring DOC 

and UV absorbance in water samples. The <strong>filters</strong> tested in this study covered all filter materials 

reported in Karanfil et al. (2002) except for glass fiber <strong>filters</strong> with binders. Glass fiber <strong>filters</strong> 

with binders were not studied as Standard Methods (APHA et al., 1998) explicitly recommends 

using glass fiber <strong>filters</strong> without binders for UV absorbance measurements. This study included 

hydrophilic nylon <strong>filters</strong> <strong>of</strong> 0.45 µm pore size manufactured by four different manufacturers in 

order to determine the differences in the organics <strong>leaching</strong> <strong>from</strong> the <strong>filters</strong> <strong>of</strong> the same pore size 

and filter material but produced by different manufacturers. Filters made <strong>of</strong> the same material, 

manufactured by the same manufacturer but <strong>of</strong> different pore sizes were included to determine 

the differences in organics <strong>leaching</strong> caused by pore size. They were hydrophilic polyethersulfone 

<strong>of</strong> pore sizes 0.20 µm, 0.45 µm and 0.80 µm, cellulose acetate filter <strong>of</strong> pore sizes 0.20 µm and 

0.45 µm and glass fiber <strong>filters</strong> <strong>of</strong> pore sizes 0.70 µm and 1.5 µm. 

Water Samples 

Laboratory grade DDW was used as water samples. It was prepared using electrically heated 

stills (Barnstead/Thermolyne, Model A1013–B, Dubuque, Iowa) and the E-pure 

(Barnstead/Thermolyne, Model D4631, Dubuque, Iowa) water purification system, which 

consisted <strong>of</strong> the following three cartridges in sequence: macropure, ultrapure, and organic free. 

Only DDW, that had higher than 17 MΩ resistivity, was collected and stored for use in high 

density polyethylene carboys (Nalgene Co., Rochester, New York). The DDW was always 

checked for its organic carbon concentration before using it and always had less than 0.1 mg 

TOC/L. 

Experimental Setup and Procedure 

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The experimental setup and procedure was divided in to two parts: filtration test and soak test. 

Two different types <strong>of</strong> tests were conducted on the <strong>filters</strong> in order to determine the behavior <strong>of</strong> 

the <strong>filters</strong> with respect to <strong>leaching</strong> <strong>of</strong> organics, when subjected to different test conditions. 

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Table 1 - Filters Used in the Study 

Filter Type Filter Material 

Gelman 

Versapor 

Gelman GN-6 

Gelman FP- 

Vericel 

Gelman HT- 

Tuffryn 

Gelman 

Nylaflo 

Millipore 

Nylon 

Osmonic 

Magna Nylon 

Whatman 


Gelman Supor 

200 

Gelman Supor 

450 

Gelman Supor 

800 

Whatman 

(WCN) 

Hydrophilic acrylic 

polymer 

Hydrophilic mixed 

cellulose ester 

Hydrophilic 

polyvinylidene 

fluoride 

Hydrophilic 

polysulfone 

Pore Size 

(µm) 

0.45 

0.45 

0.45 

0.45 

Application Manufacturer Information 

Prefiltration <strong>of</strong> difficult to filter solutions and 

serum 

Microbiological analysis <strong>of</strong> potable, waste, process 

and natural waters 

HPLC sample preparation, mobile phase 

filtration/degassing and solvent filtration 

Sterlization <strong>of</strong> culture media and other aqueous 

solutions 

Hydrophilic nylon 0.45 Aqueous and solvent based applications 

Hydrophilic nylon 0.45 

Hydrophilic nylon 0.45 

Used in clarifying aqueous or organic solutions 

prior to HPLC analysis 

Aqueous filtration without wetting and organic 

solvent filtrations such as HPLC, for 

microbiological work 

Hydrophilic nylon 0.45 Biotechnology and chromatography applications 

Hydrophilic 

polyethersulfone 

Hydrophilic 


Hydrophilic 


0.20 

0.45 

0.80 

Cellulose nitrate 0.45 

Biological, pharmaceutical and sterlizing filtration 

requirements 


requirements 


requirements 

Routine applications involving particles and cells 

<strong>from</strong> 0.1 to 5.0mm 

Pall corporation, 

Ann Arbor, MI, USA. 









Millipore corporation, 

Bedford, MA, USA. 

Osmonics Inc., 

Minnetonka, MN, USA. 

Whatman International 

Ltd., Maidstone, UK. 









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Table 1 - Filters Used in the Study (Continued) 

Filter Type Filter Material 

Whatman 

Nucleopore 

Gelman GH 

Polypro 

Polycarbonate 0.40 

Hydrophilic 

propylene 

Pore Size 

(µm) 

0.45 

Advantec Cellulose acetate 0.45 

Advantec Cellulose acetate 0.20 

Whatman 

GF/F 

Application Manufacturer Information 

Medical, industrial filtration, fluid analysis, water 

testing, chemical assay, solvent filtration and 

bacteria monitoring 

Filtration <strong>of</strong> aqueous solutions and aggressive 

solvents 

Tissue culture media, protein, enzyme, biological 

media sterilization, 

Tissue culture media, protein, enzyme, biological 

media sterilization, 

Glass fiber 0.70 Filtration <strong>of</strong> dilute aqueous solutions 

Gelman A/E Glass fiber 1.00 

Whatman 934- 

AH 

For dissolved and suspended solids testing in 

sanitary water analysis procedures 

Glass fiber 1.50 Suspended solids in water analysis 





Advantec MFS Inc., 

Pleasonton, CA, USA. 

Advantec MFS Inc., 

Pleasonton, CA, USA. 







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Filtration Test. The filtration test apparatus consisted <strong>of</strong> 300 mL capacity glass funnel, stainless 

steel support screen for the filter, glass base for the stainless steel support, silicone stopper, 

polytetrafluoroethylene support screen gaskets, aluminum clamp, and graduated Erlenmeyer 

flask with a side arm to attach to vacuum. The vacuum (25 in mmHg) was applied by using 

lubricated reciprocating laboratory pumps (Model No. 0522-V4B-G18ODX, Gast Manufacturing 

Corporation, Benton Harbor, Michigan). 

The filtration test for DOC measurement was carried out in 50 mL increments. The filtrates were 

collected in separate vials for each 50 mL increment and then analyzed for TOC. Filtration was 

continued up to a cumulative volume <strong>of</strong> 300 mL for all <strong>filters</strong> studied except for Gelman FP- 

Vericel and Gelman HT-Tuffryn. For these two <strong>filters</strong>, the filtration was carried out up to a 

cumulative volume <strong>of</strong> 1000 mL because both were found to be highly contaminated in a previous 

study (Karanfil et al., 2003). For each type <strong>of</strong> filter, in order to determine the average DOC 

<strong>leaching</strong> <strong>from</strong> the <strong>filters</strong>, 3 to 4 <strong>filters</strong> were tested. For each type <strong>of</strong> filter, a clean setup was used. 

The setup was tested for any organic contamination by passing 50 mL <strong>of</strong> DDW through it twice 

without the filter and testing the passing water for TOC. 

For COD determination, according to Standard Methods (APHA et al., 1998), the maximum 

volumes <strong>of</strong> sample are 10 mL and 50 mL for the closed and open reflux methods, respectively. 

Since the objective <strong>of</strong> this study was to determine the organic <strong>leaching</strong> <strong>from</strong> the <strong>filters</strong>, and to 

find its interference in the organic parameter determination, COD was determined for the first 50 

mL filtrate only. The sample for COD was withdrawn <strong>from</strong> the 50 mL filtrate before it was 

analyzed for DOC. 

SBOD and BDOC measurements were studied for the <strong>filters</strong> whose 100 mL filtrate had DOC ≥ 

0.3 mg/L. This cut<strong>of</strong>f initial DOC was chosen to be high enough for the method detection limit 

(MDL) <strong>of</strong> the BDOC procedure (or DOC difference before and after incubation), which is 0.10 

to 0.15 mg/L (Khan et al., 1999). 

Biochemical oxygen demand (BOD) analysis can be carried out in 60 mL or 300 mL BOD 

bottles. For BDOC measurement, there is no standard method. BDOC is the measure <strong>of</strong> DOC 

depletion in the sample after inoculation with microorganisms. Assuming that the DOC 

measurement requires 40 mL, the volume <strong>of</strong> sample required for BDOC is at least 80 mL. As a 

result, for BDOC measurement, 100 mL is probably a minimum volume that would be filtered. 

In this study, 300 mL BOD bottles were used for simultaneous SBOD and BDOC 

determinations, and the minimum volume required was 340 mL: 40 mL for initial DOC 

measurement (for BDOC determination) and 300 mL for incubation. 

The BDOC and SBOD measurements for each filter type were conducted in four replicates. To 

obtain sample for two replicate analyses, eight 100 mL filtrates <strong>from</strong> 8 different <strong>filters</strong> were 

combined. Then, the mixture was transferred to a 1 L pyrex bottle. After that, 800 µL <strong>of</strong> BOD 

nutrient salt solution was added to the sample. The sample was then aerated for 20 to 30 minutes 

using Kimble glass diffusers to attain dissolved oxygen (DO) saturation in the sample for BOD 

measurement. Then, the sample was transferred into two 40 mL vials for initial DOC 

measurement and two BOD bottles, which contained 0.25 mL <strong>of</strong> washed mixed liquor suspended 

solids (MLSS) as a seed. 

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The MLSS was obtained <strong>from</strong> an activated sludge municipal wastewater treatment plant. The 

sample for two more replicates was obtained following the same procedure. 

BDOC was based on 5 days <strong>of</strong> incubation. For FP-Vericel, HT-Tuffryn, Millipore Nylon, and 

GH Polypro <strong>filters</strong>, DOC concentration remaining after 5 days <strong>of</strong> incubation was high. In order 

to check whether the BDOC at 5 days (BDOC5) was a major portion <strong>of</strong> total biodegradable 

leached organics, the incubation was continued for these <strong>filters</strong> until 28 days and BDOC was 

determined (BDOC28). When the filtrate <strong>from</strong> the FP Vericel filter was tested for BOD without 

any dilution, the final DO after 5 days <strong>of</strong> incubation was below 1 mg/L. The criteria for BOD 

measurement are the depletion <strong>of</strong> DO ≥ 2 mg/L and the final DO ≥ 1 mg/L. This filtrate was later 

diluted at a 1:2 ratio (1 portion <strong>of</strong> the sample and 2 portions <strong>of</strong> DDW) for the BOD and BDOC 

tests. 

Soak Test. Wide-mouthed, 500 mL Erlenmeyer flasks were used. The <strong>filters</strong> were individually 

placed inside the flasks with 100 mL DDW. The <strong>filters</strong> were allowed to be in the DDW for 24 

hours, and then, 40 mL <strong>of</strong> the water were taken for DOC analysis. Then, the remaining water 

was drained and refilled with a new batch <strong>of</strong> 100 mL DDW and the DOC analysis <strong>of</strong> samples 

was performed after 24 hours. This was continued until there was no <strong>leaching</strong> observed <strong>from</strong> the 

<strong>filters</strong> (when the DOC was less than 0.10 mg/L). The soak test on <strong>filters</strong> would provide a 

reasonable estimation <strong>of</strong> the maximum <strong>leaching</strong> <strong>from</strong> the <strong>filters</strong>. Results <strong>from</strong> the soak test could 

be used to determine how much organics leach during the filtration test compared with the 

maximum <strong>leaching</strong> and to provide information on the possibility <strong>of</strong> using a different filter 

cleaning method. The soak test samples were analyzed only for DOC as DOC is the most 

accurate and precise parameter among the four parameters measured in the filtration test. 

Moreover, the soak test does not represent the way the filter is used for measuring SCOD, 

SBOD, and BDOC, so there is no necessity to get the information on the other parameters for the 

soak test samples. DOC is a good enough parameter to serve the purpose <strong>of</strong> the soak test. 

Glassware Cleaning 

All the glassware used for this study except the filtration funnel and filtration base was cleaned 

by the following procedure. First, all the glassware was washed with hot water and a laboratory 

grade cleaning solution (7X, ICN Biomedicals Inc., Aurora, Ohio). Then, it was rinsed pr<strong>of</strong>usely 

with DDW, soaked in 10% nitric acid overnight and again rinsed pr<strong>of</strong>usely with DDW, 

respectively. The 10% nitric acid used for the soaking was prepared <strong>from</strong> a 70% reagent grade 

solution (Mallinckrodt Baker, Inc., Phillipsburg, New Jersey). Lastly, the cleaned glassware was 

baked at 550°C in a muffle furnace for 30 minutes. The cleaning <strong>of</strong> the filtration funnel and 

filtration base included all cleaning steps but baking. 

Analyses and Measurements 

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DOC was determined according to Standard Methods (APHA et al., 1998) using a TOC analyzer 

(Phoenix 8000, Emerson Process Management: Tekmar-Dohrmann Division, Mason, Ohio, 

USA). The COD for the samples were analyzed by using the closed reflux colorimetric method 

(APHA et al., 1998) using a spectrophotometer (Hach, DR/4000V, Loveland, Colarado, USA) 

and the Hach digestion vials (Hach, Loveland, Colarado, USA) with a concentration range <strong>of</strong> 0 

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to 40 ppm. BOD and BDOC <strong>of</strong> the samples were measured simultaneously following the 

procedure by Khan et al. (1999). The only modifications to the procedure were the usage <strong>of</strong> 0.25 

mL MLSS instead <strong>of</strong> 2 mL and elimination <strong>of</strong> the initial filtration step using a 0.7 µm pore size 

glass fiber filter. Only 0.25 mL <strong>of</strong> MLSS was used as inoculum, as it resulted in the DO 

depletion <strong>of</strong> < 1 mg/L in the blank (Criterion for depletion <strong>of</strong> DO in the blank, APHA et al., 

1998). The initial filtration step was eliminated because the samples for SBOD and BDOC 

analyses were likely to be particulate free as they were the filtrates <strong>from</strong> different <strong>filters</strong> and 

DDW was used to generate them. DO was measured using a meter (Orion model 850A Plus, 

Thermo Orion, Beverly, Massachusetts, USA). 

Statistical Analyses 

The data were analyzed using the Tukey-Kramer multiple comparisons, t-test, and paired t-test. 

The statistical analyses were performed using the Micros<strong>of</strong>t Excel XP and Statistical Analysis 

S<strong>of</strong>tware (SAS® 1999 version 8, Cary North Carolina, USA). 

RESULTS AND DISCUSSION 

Filtration Test 

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DOC Results. The DOC <strong>leaching</strong> <strong>of</strong> all <strong>filters</strong> until a cumulative filtration volume <strong>of</strong> 300 mL is 

shown in Figure 1. It is evident that in all <strong>filters</strong> except for Gelman FP-Vericel and Gelman HT- 

Tuffryn the DOC <strong>leaching</strong> ceased within the first few initial incremental volumes. Gelman FP- 

Vericel had the highest organic <strong>leaching</strong> continuing until a cumulative filtration volume <strong>of</strong> 1000 

mL (data not shown) followed by Gelman HT-Tuffryn, which had DOC <strong>leaching</strong> until a 

cumulative filtration volume <strong>of</strong> 500 mL (data not shown). The DOC values <strong>of</strong> the filtrates 

reported in this study compares well with those reported by Karanfil et al. (2003) for all <strong>filters</strong> 

except for Gelman GH Polypro. The reason for observing the difference for this filter is not 

clear. It might be because <strong>of</strong> the lot or batch variation <strong>of</strong> the <strong>filters</strong> tested. 

Statistical analysis <strong>of</strong> the mass <strong>of</strong> carbon <strong>leaching</strong> <strong>from</strong> hydrophilic nylon <strong>filters</strong> using the 

Tukey-Kramer procedure indicated significant difference among the manufacturers (p = 0.05 

criterion, data not shown). The difference among the manufacturers could be because <strong>of</strong> the 

differences in the manufacturing processes and/or the additives. For the polyethersulfone <strong>filters</strong> 

<strong>of</strong> different pore sizes, there was no significant difference in the mass <strong>of</strong> carbon <strong>leaching</strong> <strong>from</strong> 

Supor 450 filter (0.45 µm pore size) when compared with those <strong>from</strong> Supor 200 (0.20 µm pore 

size) and Supor 800 (0.80 µm pore size), but there was a difference between those <strong>from</strong> Supor 

200 and Supor 800 (Tukey-Kramer procedure, p = 0.05 criterion, data not shown). This suggests 

that when the difference in pore size between the <strong>filters</strong> compared is large, the difference in 

organics <strong>leaching</strong> <strong>from</strong> them becomes significant. This observation was confirmed by no 

significant difference in mass <strong>of</strong> carbon <strong>leaching</strong> between the cellulose acetate <strong>filters</strong> <strong>of</strong> two 

different pore sizes (0.20 µm and 0.45 µm) and a significant difference in mass <strong>of</strong> carbon 

<strong>leaching</strong> between the Whatman GF/F and 934-AH glass fiber <strong>filters</strong> (pore sizes <strong>of</strong> 0.70 µm and 

1.50 µm) based on two tailed t-test at p = 0.05. 

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Figure 1 - DOC Results <strong>from</strong> Filtration Test on all 19 Filters 

DOC (mg/L) 

20 

15 

10 

5 

0 

Versapor 

GN-6 

FP Vericel 

HT Tuffryn 

Nylaflo 

Millipore nylon 

Magna nylon 

Whatman nylon 

Supor 200 

Supor 450 

Supor 800 

WCN 

Polycarbonate 

GH Polypro 

Cellu.ace. (0.45) 

Cellu. ace. (0.20) 

GF/F 

A/E 

934-AH 

Filter type 

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50 mL 

100 mL 

150 mL 

200 mL 

250 mL 

300 mL 

For all three filter materials tested for the <strong>effect</strong> <strong>of</strong> pore size, organic <strong>leaching</strong> tended to increase 

with decreasing pore size. The higher organic <strong>leaching</strong> <strong>from</strong> <strong>filters</strong> <strong>of</strong> smaller pore size can be 

because <strong>of</strong> one or more <strong>of</strong> the following reasons. The <strong>filters</strong> with smaller pore sizes had more 

amounts <strong>of</strong> membrane materials that were tightly packed than the <strong>filters</strong> with larger pore sizes. 

There were more membrane surface areas available for contact with DDW in the smaller pore 

sized <strong>filters</strong> than the larger pore sized <strong>filters</strong>. In addition, the contact time <strong>of</strong> DDW filtered on the 

filter was higher for the smaller pore sized <strong>filters</strong> compared to that <strong>of</strong> the larger pore sized <strong>filters</strong>. 

As a result, more <strong>leaching</strong> <strong>from</strong> the smaller pore sized <strong>filters</strong> was observed. 

SCOD Results. The COD <strong>of</strong> the first 50 mL filtrate <strong>from</strong> all 19 <strong>filters</strong> is shown in Figure 2. The 

error bars represent standard deviation. FP-Vericel filter, which had the highest DOC 

contamination, also showed highest COD in its filtrate. Average COD <strong>of</strong> the filtrates <strong>from</strong> four 

different FP-Vericel was 48 ± 3 mg/L. FP-Vericel filter was followed by HT-Tuffryn in the 

amount <strong>of</strong> DOC contamination and so was COD. The average COD <strong>of</strong> the filtrates <strong>from</strong> HT- 

Tuffryn filter was 35 ± 4 mg/L. The COD <strong>of</strong> the filtrates <strong>from</strong> the other <strong>filters</strong> were less than 8 

mg/L which should not be concerned as Standard Methods (APHA et al., 1998) states that COD 

values less than 25 mg/L would be qualitative than quantitative. 

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Figure 2 - COD Concentration <strong>of</strong> the First 50 mL Filtrate 

<strong>from</strong> all 19 Filters 

COD (mg/L) 

60 

50 

40 

30 

20 

10 

0 

Gelman Versapor 

Gelman GN-6 

Gelman FP-Vericel 

Gelman HT-Tuffryn 

Gelman Nylaflo 

Millipore Nylon 

Osmonic Magna Nylon 

Whatman Nylon 

Gelman Supor 200 



Whatman (WCN) 

Corning 

Gelman GH Polypro 

Cellulose Acetate (0.45 ) 

Cellulose Acetate (0.2 ) 

Whatman GF/F 

Whatman A/E 

Whatman 934-AH 

Filter type 

SBOD Results. The results <strong>of</strong> SBOD analysis are shown in Table 2. Only the types <strong>of</strong> <strong>filters</strong>, 

that met the DOC criterion specified above in the Experimental Setup and Procedure subsection, 

are presented except 0.20 µm pore size cellulose acetate filter. The filtrate <strong>from</strong> 0.20 µm pore 

size cellulose acetate filter was not included for BOD and BDOC analyses, since the mass <strong>of</strong> 

carbon <strong>leaching</strong> <strong>from</strong> it was not statistically different <strong>from</strong> that <strong>from</strong> 0.45 µm pore size cellulose 

acetate filter. Moreover, for SBOD and BDOC determinations, the pore size <strong>of</strong> the filter required 

is only 0.45 µm (the cut-<strong>of</strong>f for soluble or dissolved fraction). The filtrates <strong>from</strong> Gelman FP- 

Vericel, Gelman HT-Tuffryn and Gelman GH Polypro had BOD concentration greater than the 

MDL <strong>of</strong> 2 mg/L while for the filtrates <strong>from</strong> the other <strong>filters</strong>, their BOD concentrations were 

below 2 mg/L. The BOD concentrations <strong>of</strong> the filtrates <strong>from</strong> Gelman FP-Vericel and HT-Tuffryn 

were high and proper cleaning <strong>of</strong> these <strong>filters</strong> should be carried out before using them for SBOD 

determination. The BOD concentration <strong>of</strong> the sample is determined using the following equation: 

BOD = [(DOi – DOf)sample - (DOi – DOf)blank]F 

WEFTEC®.06 

where DOi is the initial dissolved oxygen concentration, DOf is the final dissolved oxygen 

concentration, blank refers to DDW with just the seed, and F is the dilution factor. 

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Table 2 - SBOD and BDOC Results 

Filter Type 

Average 

BOD 

(mg/L) 

Average 

Initial 

DOC 

(mg/L) 

Average 

BDOC5 

(mg/L) 

Average 

Percent 

Biodegradable 

Average 

BDOC28 

(mg/L) 

Average 

Percent 

Biodegradable 

Significant 

Difference 

between 

BDOC5 and 

BDOC28 

95 Percent 

Confidence 

Interval <strong>of</strong> 

Total BDOC 

(mg/L) 

Gelman GN-6 0.59 ± 0.29 0.36 ± 0.06 0.23 ± 0.04 63 ± 7 - - - 0.28 – 0.29 

Gelman FP- 

Vericel 

14.48 ± 0.53 7.14 ± 0.03 4.59 ± 0.06 64 ± 1 6.20 ± 0.04 87 ± 1 Yes 6.14 – 6.26 

Gelman HT- 

Tuffryn 

5.11 ± 0.49 2.51 ± 0.07 1.86 ± 0.16 74 ± 8 2.00 ± 0.17 80 ± 9 No 1.72 – 2.27 

Millipore Nylon 0.91 ± 0.69 0.60 ± 0.03 0.34 ± 0.10 56 ± 15 0.57 ± 0.03 95 ± 2 Yes 0.52 – 0.62 

Osmonics Magna 


0.68 ± 0.27 0.35 ± 0.03 0.00 ± 0.00 0 - - - 0.00 – 0.00 

Whatman Nylon 0.81 ± 0.38 0.81 ± 0.02 0.65 ± 0.05 80 ± 4 - - - 0.57– 0.72 

Whatman (WCN) 1.40 ± 0.16 0.40 ± 0.02 0.18 ± 0.02 42 ± 11 - - - 0.10 – 0.24 

Gelman GH 

Polypro 

2.97 ± 0.32 1.49 ± 0.08 0.84 ± 0.11 56 ± 5 0.95 ± 0.10 64 ± 3 No 0.80 – 1.11 

Cellulose Acetate 

(0.45 µm) 

0.13 ± 0.10 0.30 ± 0.00 0.20 ± 0.01 66 ± 3 - - - 0.18 – 0.21 

Whatman A/E 0.94 ± 0.22 0.49 ± 0.05 0.43 ± 0.03 88 ± 9 - - - 0.39 – 0.47 

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With interference <strong>from</strong> the <strong>filters</strong>, the DOf <strong>of</strong> the sample will be less because <strong>of</strong> the additional BOD 

exerted by the organic <strong>leaching</strong> <strong>from</strong> the <strong>filters</strong> and this will result in SBOD overestimation. For 

samples <strong>of</strong> which the SBOD determination requires dilution, the interference <strong>from</strong> the <strong>filters</strong> will be 

amplified by the dilution factor if the dilution <strong>of</strong> the sample is performed before filtration. If the 

dilution is performed after filtration, depending on the dilution factor, the interference <strong>from</strong> the 

<strong>filters</strong> in the SBOD determination either remains unchanged (because <strong>of</strong> the inclusion <strong>of</strong> the dilution 

factor) or becomes too low to be detected. 

BDOC Results. The BDOC results <strong>of</strong> the <strong>filters</strong> tested are shown in Table 2. BDOC5 <strong>of</strong> the 

filtrates <strong>from</strong> Gelman GN-6, Whatman (WCN) and cellulose acetate (0.45 µm) <strong>filters</strong> were close 

to the MDL <strong>of</strong> the BDOC procedure <strong>of</strong> 0.15 mg/L. These results indicate that the interference in 

BDOC measurement <strong>from</strong> these <strong>filters</strong> is minimal when compared with the other <strong>filters</strong>. 

The filtrates <strong>from</strong> Gelman FP-Vericel filter, which had the highest organics <strong>leaching</strong>, had the 

highest BDOC concentration among the <strong>filters</strong> tested. There was a significant difference (t-test, p 

= 0.05 criterion, n = 4) in the BDOC concentration obtained after 5 and 28 days <strong>of</strong> incubation 

suggesting that when sufficient amount <strong>of</strong> incubation is provided all <strong>of</strong> the organics <strong>leaching</strong> 

<strong>from</strong> it will be biodegradable (p = 7.77×10 -9 ). The BDOC <strong>of</strong> the filtrates <strong>from</strong> Gelman HT- 

Tuffryn filter was also high. The continuation <strong>of</strong> incubation until 28 days for this filter did not 

show BDOC concentration significantly different <strong>from</strong> that obtained after 5 days <strong>of</strong> incubation 

(t-test, p = 0.05 criterion, n = 4) indicating that the <strong>leaching</strong> <strong>from</strong> this filter has both 

biodegradable and non-biodegradable organics (p = 0.28). Similar results were obtained for the 

filtrates <strong>from</strong> Gelman GH Polypro. There was no significant difference (p = 0.18) between the 

BDOC concentrations obtained after 5 and 28 days <strong>of</strong> incubation. 

The BDOC <strong>of</strong> the filtrates <strong>from</strong> the three hydrophilic nylon <strong>filters</strong> tested were different as seen in 

Table 2. Most <strong>of</strong> the organics <strong>leaching</strong> <strong>from</strong> Whatman nylon <strong>filters</strong> were biodegradable after 5 

days <strong>of</strong> incubation and about 50% <strong>of</strong> the organics <strong>leaching</strong> <strong>from</strong> Millipore nylon were 

biodegradable after 5 days. The incubation when continued until 28 days for the filtrates <strong>from</strong> 

Millipore nylon <strong>filters</strong> indicated that there was no significant difference between the initial DOC 

<strong>of</strong> the leached organics and BDOC28 (t-test, p = 0.19). All <strong>of</strong> the <strong>leaching</strong> organics <strong>from</strong> them 

were biodegradable if sufficient time was allowed. For the other hydrophilic nylon filter, namely 

Osmonics nylon, the <strong>leaching</strong> organics were not susceptible to biodegradation. 

Although the membrane material <strong>of</strong> Osmonics magna nylon filter is same as that <strong>of</strong> the Whatman 

and Millipore nylon <strong>filters</strong>, the biodegradability <strong>of</strong> the leached organics was completely 

different. No BDOC exertion in the filtrates <strong>from</strong> Osmonics magna nylon <strong>filters</strong> could be 

because either the organics <strong>leaching</strong> <strong>from</strong> them are in fact biorefractory/nonbiodegradable or the 

leachate contains some toxic compounds that affect the microbial activity on the DOC. There 

will be no interference when using Osmonics magna nylon filter for BDOC measurement if the 

reason for no BDOC is because they are not biodegradable. On the other hand, if toxicity is the 

reason for having no biodegradability, the usage <strong>of</strong> this filter will impose an error in the BDOC 

measurement. The interference <strong>from</strong> the <strong>filters</strong> during BDOC measurement varies for different 

types <strong>of</strong> <strong>filters</strong>. However, the exact magnitude <strong>of</strong> interference in BDOC measurement <strong>from</strong> the 

<strong>filters</strong> cannot be determined <strong>from</strong> this study alone as there are several factors, such as volume <strong>of</strong> 

sample filtered, type and volume <strong>of</strong> inoculum, and incubation time, that can affect the BDOC 

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esult. 

Soak Test 

WEFTEC®.06 

The DOC data <strong>of</strong> the samples <strong>of</strong> all 19 <strong>filters</strong> <strong>from</strong> the soak test are shown in Table 3. In 18 <strong>of</strong> 

the 19 <strong>filters</strong>, the soak test samples showed that DOC stopped <strong>leaching</strong> (DOC ≤ 0.10 mg/L) 

within four days. Gelman FP-Vericel filter, exhibited the <strong>leaching</strong> until 10 days (data not 

shown). For most <strong>of</strong> the <strong>filters</strong>, the DOC <strong>leaching</strong> was found only in the samples obtained after 

soaking the <strong>filters</strong> for one day in DDW. The DOC data <strong>of</strong> the soak test samples had less 

variability when compared with the DOC data <strong>of</strong> the filtration test samples. 

The comparison <strong>of</strong> mass <strong>of</strong> carbon <strong>leaching</strong> <strong>from</strong> different <strong>filters</strong> when subjected to filtration and 

soak tests is shown in Table 4. Significant difference between the mass <strong>of</strong> carbon <strong>from</strong> the 

filtration and soak tests was determined statistically using t-test at p = 0.05. The difference in the 

mass for <strong>filters</strong>, which had DOC concentration less than 0.1 mg/L in either the filtration test or 

soak test, was not determined. From the table, it is observed that in all <strong>filters</strong> except for 

Whatman GF/F filter, the mass <strong>of</strong> carbon <strong>leaching</strong> <strong>from</strong> the <strong>filters</strong> when subjected to the soak 

test was statistically either not different <strong>from</strong> or greater than the mass <strong>leaching</strong> <strong>from</strong> the filtration 

test indicating that soaking the <strong>filters</strong> would result in removing most <strong>of</strong> the leachable organics 

<strong>from</strong> the <strong>filters</strong>. The possible reason for the different results <strong>from</strong> the two tests could be because 

<strong>of</strong> the presence <strong>of</strong> less soluble organics in the <strong>filters</strong>. The less soluble organics were less 

susceptible to <strong>leaching</strong> during the filtration test because <strong>of</strong> less contact time with DDW. 

Guidelines for the Use and Cleaning <strong>of</strong> Filters 

Table 5 summarizes the interference caused by organic <strong>leaching</strong> <strong>from</strong> <strong>filters</strong> on organic analyses 

and the recommended filter cleaning method. The interference with DOC analysis was found in 

14 out <strong>of</strong> the 19 <strong>filters</strong> tested. The interference in SCOD analysis was observed only in 2 <strong>filters</strong>. 

The interference in SBOD analysis was found in 3 out <strong>of</strong> the 10 <strong>filters</strong> tested. Although the BOD 

<strong>of</strong> the filtrates <strong>from</strong> other <strong>filters</strong> was less than the MDL <strong>of</strong> 2 mg/L, the interference will be 

amplified by the dilution factor if the sample is filtered through the filter after dilution. This 

amplification <strong>of</strong> the interference by the dilution factor is applicable to all the organic parameters 

studied. The BDOC <strong>of</strong> the filtrates was greater than the MDL <strong>of</strong> 0.15 mg/L in 9 out <strong>of</strong> the 10 

<strong>filters</strong> tested. For the other filter (Osmonics Magna Nylon), the organics leached were not 

biodegradable at all. However, it cannot be concluded that there is no interference <strong>from</strong> this filter 

since the exact reason for no biodegradability in the leached organics is not known. Thus, 

interference <strong>from</strong> this filter in BDOC analysis is reported as inconclusive in Table 5. 

Table 5 reveals that in most <strong>filters</strong> which showed interference in organic analysis, the suggested 

cleaning method is to soak the <strong>filters</strong> in DDW. In <strong>filters</strong>, which either had no organic <strong>leaching</strong> or 

had no statistical difference in the total mass <strong>of</strong> carbon <strong>leaching</strong> when subjected to filtration and 

soak tests, the suggested cleaning method is discarding initial filtration volumes, as it consumes 

less time than the cleaning by soaking. It is clear <strong>from</strong> Table 5 that the soak time and the 

filtration volume to be discarded differ <strong>from</strong> filter to filter. 

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Table 3 - Soak Test Results 

Filter Type 

Average DOC <strong>of</strong> Soak Samples (mg/L) 

Day 1 Day 2 Day 3 Day 4 

Average Total 

Mass <strong>from</strong> 

Soak Test 

(µg) 

95 Percent Confidence 

Interval Estimate <strong>of</strong> the 

Total Mass <strong>of</strong> Carbon 

(µg) 

Gelman Versapor 0.70 ± 0.02 0.04 ± 0.04 - - 70 ± 2 67 – 74 

Gelman GN-6 1.32 ± 0.16 0.06 ± 0.04 - - 132 ± 12 106 – 158 

Gelman FP-Vericel 21.8 ± 1.40 3.47 ± 0.55 1.49 ± 0.12 1.07 ± 0.05 3076 ± 124 1 2878 – 3274 1 

Gelman HT-Tuffryn 5.24 ± 0.34 0.63 ± 0.02 0.35 ± 0.00 0.06 ± 0.02 623 ± 33 569 – 676 

Gelman Nylaflo 0.09 ± 0.00 - - - 9 ± 0.4 9 – 11 

Millipore Nylon 0.84 ± 0.03 0.04 ± 0.04 - - 84 ± 3 79 – 89 

Osmonic Magna Nylon 0.40 ± 0.07 0.01 ± 0.01 - - 40 ± 7 29 – 51 

Whatman Nylon 0.91 ± 0.03 0.08 ± 0.02 - - 91 ± 3 86 – 96 

Gelman Supor 200 0.29 ± 0.02 0.23 ± 0.04 0.01 ± 0.02 - 52 ± 6 43 – 61 

Gelman Supor 450 0.12 ± 0.05 0.13 ± 0.02 0.09 ± 0.00 - 24 ± 3 19 – 30 

Gelman Supor 800 0.23 ± 0.01 0.03 ± 0.02 - - 23 ± 1 21 – 26 

Whatman (WCN) 0.66 ± 0.08 0.14 ± 0.02 0.05 ± 0.01 - 80 ± 9 66 – 95 

Whatman Nucleopore 0.05 ± 0.01 - - - 5 ± 0.8 4 – 6 

Gelman GH Polypro 1.46 ± 0.15 0.11 ± 0.02 0.04 ± 0.03 - 157 ± 16 131 – 183 

Cellulose acetate (0.20 µm) 0.57 ± 0.03 0.04 ± 0.00 - - 57 ± 3 52 – 62 

Cellulose acetate (0.45 µm) 0.28 ± 0.04 0.07 ± 0.03 - - 28 ± 4 22 – 34 

Whatman GF/F 0.11 ± 0.02 0.03 ± 0.01 - - 11 ± 2 8.0 – 14 

Gelman A/E 0.82 ± 0.11 0.08 ± 0.01 - - 82 ± 12 64 – 100 

Whatman 934-AH 0.07 ± 0.00 - - - 7 ± 0 6 – 9 

1 Based on 10 days <strong>of</strong> soaking (data not shown). 

WEFTEC®.06

Table 4 - Comparison <strong>of</strong> Mass <strong>of</strong> Carbon <strong>from</strong> Filtration and Soak Tests 

Filter Type 

Mass <strong>of</strong> 

Carbon <strong>from</strong> 

Filtration Test 

(µg) 

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Mass <strong>of</strong> 

Carbon <strong>from</strong> 

Soak Test 

(µg) 

Gelman Versapor 18.5 ± 2.6 70± 2 26 

Percent 

Mass <strong>from</strong> 

Filtration 

Test 

Significant 

Difference 

between Soak and 

Filtration Tests 

Yes (p = 8.79E- 

08) 

Gelman GN-6 94 ± 21 132 ± 12 71 Yes (p = 0.278) 

Gelman FP-Vericel 1063 ± 32 3076 ± 124 35 Yes (p = 7.3E-08) 

Gelman HT-Tuffryn 390 ± 44 623 ± 33 63 Yes (p = 0.0002) 

Gelman Nylaflo 3 ± 3 1 9 ± 0 1 - - 

Millipore Nylon 81 ± 6 84 ± 3 96 No (p = 0.38) 

Osmonic Magna Nylon 32 ± 5 40 ± 7 80 No (p = 0.09) 

Whatman Nylon 80 ± 8 91 ± 3 88 Yes (p = 0.04) 

Gelman Supor 200 17 ± 9 52 ± 6 33 

Yes (p = 2.03E- 

05) 

Gelman Supor 450 7 ± 4 1 24± 3 29 - 

Gelman Supor 800 5 ± 1 1 23 ± 1 22 - 

Whatman (WCN) 30 ± 7 80 ± 9 38 Yes (p = 0.0001) 

Whatman Nucleopore 4 ± 1 1 5 ± 1 1 - - 

Gelman GH Polypro 87 ± 30 157 ± 16 55 Yes (p = 0.024) 

Cellulose acetate (0.20 µm) 39 ± 5 57 ± 3 68 Yes (p = 0.002) 

Cellulose acetate (0.45 µm) 32 ± 7 28 ± 4 114 No (p = 0.28) 

Whatman GF/F 21 ± 5 11 ± 2 190 Yes 2 (p = 0.024) 

Whatman A/E 56 ± 16 82 ± 12 68 Yes (p = 0.035) 

Whatman 934-AH 2 ± 2 1 7± 1 1 - - 

1 

Values below the DOC cut-<strong>of</strong>f <strong>of</strong> 0.1 mg/L and therefore not included in comparison. 

2 

Only filter which showed statistically higher carbon mass in filtration test than soak test. 

Gelman FP-Vericel and Gelman HT-Tuffryn <strong>filters</strong> should be avoided for dissolved organic 

analyses because <strong>of</strong> their high organic contamination and cleaning difficulty. The 0.45 µm pore 

sized, Gelman Versapor, Gelman GN-6, Millipore Nylon, Whatman Nylon, Osmonics Magna 

Nylon, Gelman Supor 450, Whatman Cellulose Nitrate, Gelman GH Polypro, and Cellulose 

acetate <strong>filters</strong> can be used for dissolved organics analyses after appropriate cleaning. Gelman 

Nylaflo, does not introduce any artifacts to organic analyses, and thus can be used for organic 

analyses without any pretreatment. However, because <strong>of</strong> the possible variation among <strong>filters</strong> 

<strong>from</strong> lot to lot, they should be tested for contamination before use. Although some <strong>of</strong> the other 

<strong>filters</strong>, which are not listed above, had minimal or no organic <strong>leaching</strong>, they were not <strong>of</strong> 0.45 µm 

pore size, and thus their use in dissolved organic analyses should be avoided. It should also be 

noted that the interference estimated in this study is based on DDW, but in real water samples 

the interference <strong>from</strong> the <strong>filters</strong> might be or might not be the same. This is because the 

characteristics <strong>of</strong> the real water sample such as the chemical composition, pH, and particle size 

distribution may not be the same as those <strong>of</strong> DDW. These characteristics could affect the 

interaction between the sample and the filter material resulting in different degrees <strong>of</strong> 

interference. 

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Table 5 - Summary <strong>of</strong> Interference Caused by Organic Leaching From Filters on Analyses and Suggested Cleaning Method 

Filter Type 

Interference in the Analysis <strong>of</strong> 

DOC COD BOD BDOC 

Suggested Cleaning Method 

Gelman Versapor Yes N 1 N 1 Soak in 100 mL DDW for 24 hours 

Gelman GN-6 Yes Yes Soak in 100 mL DDW for 24 hours 

Gelman FP-Vericel Yes Yes Yes Yes Soak in 100 mL DDW for 10 days 

Gelman HT-Tuffryn Yes Yes Yes Yes Soak in 100 mL DDW for 72 hours 

Gelman Nylaflo N 1 N 1 Requires no pretreatment, however filter at least 100 mL <strong>of</strong> 

DDW before use for analysis 

Millipore Nylon Yes Yes Filter at least 150 mL <strong>of</strong> DDW before use for analysis 

Osmonic Magna Nylon Yes I 2 Filter at least 100 mL <strong>of</strong> DDW before use for analysis 

Whatman Nylon Yes Yes Soak in 100 mL DDW for 24 hours 

Gelman Supor 200 Yes N 1 N 1 Soak in 100 mL DDW for 48 hours 

Gelman Supor 450 N 1 N 1 Requires no pretreatment, however filter at least 100 mL <strong>of</strong> 

Gelman Supor 800 N 1 N 1 


Requires no pretreatment, however filter at least 100 mL <strong>of</strong> 


Whatman (WCN) Yes Yes Soak in 100 mL DDW for 48 hours 

Whatman Nucleopore N 1 N 1 Requires no pretreatment, however filter at least 100 mL <strong>of</strong> 


Gelman GH Polypro Yes Yes Yes Soak in 100 mL DDW for 48 hours 

Cellulose acetate (0.20 µm) Yes Yes Soak in 100 mL DDW for 24 hours 

Cellulose acetate (0.45 µm) Yes Yes Filter at least 150 mL <strong>of</strong> DDW before use for analysis 

Whatman GF/F Yes N 1 N 1 Filter at least 150 mL <strong>of</strong> DDW before use for analysis 

Gelman A/E Yes Yes Soak in 100 mL DDW for 24 hours 

Whatman 934-AH N 1 N 1 

1 N-Not tested. 

2 I-Inconclusive. 

Requires no pretreatment, however filter at least 100 mL <strong>of</strong> 


WEFTEC®.06

CONCLUSIONS 

This research determined the interference caused by the organics <strong>leaching</strong> <strong>from</strong> 19 commonly 

used <strong>filters</strong> in the analyses <strong>of</strong> organic matter and compared the amount <strong>of</strong> organic <strong>leaching</strong> <strong>from</strong> 

the <strong>filters</strong> when subjected to two different conditions namely soak and filtration tests. Five <strong>filters</strong> 

had negligible or no organic <strong>leaching</strong> (DOC < 0.1 mg/L) while two <strong>filters</strong>, Gelman FP-Vericel 

and Gelman HT-Tuffryn, had very high organic <strong>leaching</strong> (DOC > 5 mg/L) and should not be 

used without proper cleaning. Different amounts <strong>of</strong> organic <strong>leaching</strong> were observed in the <strong>filters</strong> 

made <strong>of</strong> the same material but <strong>from</strong> different manufacturers and in the <strong>filters</strong> made <strong>of</strong> the same 

material, manufactured by the same manufacturer but <strong>of</strong> substantially different pore sizes. The 

SCOD concentrations <strong>of</strong> the filtrates <strong>from</strong> 17 <strong>filters</strong> were much lower than the quantitative level 

<strong>of</strong> concern established by Standard Methods (APHA et al., 1998). Only Gelman FP-Vericel and 

Gelman HT-Tuffryn <strong>filters</strong> interfered with the COD test. These two <strong>filters</strong> also leached BOD 

contributing substances above the detection limit along with Gelman GH Polypro. Due to higher 

sensitivity <strong>of</strong> the parameter, several more <strong>filters</strong> interfered with the BDOC test compared to the 

SBOD test. The soak test showed higher organic <strong>leaching</strong> than the corresponding filtration test 

for most <strong>of</strong> the <strong>filters</strong>. The guidelines for the application and cleaning <strong>of</strong> <strong>filters</strong>, which are useful 

for water quality laboratory practitioners and researchers, were generated based on the results <strong>of</strong> 

this study. 

REFERENCES 

WEFTEC®.06 

American Public Health Association; American Water Works Association; and Water 

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