Correction for Total Organic Carbon, Nitrate, and Chemical Oxygen Demand When Using the MF-millipore Filter Cheng P. Hwang*, Thomas H. Lackie, and Randolph R. Munch Civil Engineering Department, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OW0
The use of MF-millipore filters for particle size fractionation requires the determination of a blank correction of filters in order to obtain a representative and reliable result. An investigation was conducted to ascertain blank corrections of total organic carbon (TOC), chemical oxygen demand (COD), and nitrate (N03) when using 3.0-, 0.45-, and 0.025-pm MF-millipore filters. Experimental results indicated that the distilled water filtrate from the filter sizes investigated contained significant amounts of TOC, COD, and N o s , with the filtrate from the 0.025-pm filter being the most affected. The Millipore catalogue of 1976 ( I ) indicated that “MFmillipore filters are autoclavable, and are composed of pure, biologically inert mixtures of cellulose acetate and cellulose nitrate. This filter type is not attacked by dilute acids and alkalies, aliphatic and aromatic hydrocarbons, and non-polar liquids. It is recommended for all analytical, ultracleaning, and sterilizing applications below 75” C, except those involving ketones, esters, ether alcohols, nitroparaffins, or strong acids and alkalies”. Furthermore, from “Hackh’s Chemical Dictionary” (2) and the “Handbook of Chemistry and Physics” ( S ) , cellulose acetate and cellulose nitrate are insoluble in water. The results reported herein indicate that, at least in the case of the 0.025-pm filters, significant amounts of total organic carbon, nitrate, and chemical oxygen demand are washed from the filter itself when filtering distilled water.
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Experimental Three types of the MF-millipore filters were used for this investigation: 3.0 pm (Catalog No. SSWPO4700, lot no. C7Ml6754F), 0.45 pni (Catalog No. HAWG04700, lot no. 31093 4), and 0.025 pm (Catalog No. VSWPO4700, lot no. 33833 4): the diameter of all filters is 47 mm. The solution filtered was distilled mater. Apparatus used included a vacuum pump (20-in. Hg), a Pyrex funnel and base with coarse-frit glass filter support, anodized aluminum spring clamp, neoprene stopper, and a 1-L filtering flask with side arm for use in vacuum filtration
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(I). The total organic carbon (TOC) was measured by the combustion-infrared method ( 4 ) using a Beckman total organic carbon analyzer (Model 915). The experimental results were introduced into a “TOC computer program” that calculated the actual values obtained from equations for the standard calibration curves of the TOC analyzer. The chemical oxygen demand (COD) was measured by the dichromate method, which is based on the fact that most organic compounds are oxidized to carbon dioxide and water by the action of a strong oxidizing agent under acid conditions ( 4 ) .The nitrate (NO l ) was measured by the autoanalyzer method 3369W ( 5 ) . This method uses hydrazine sulfate containing a copper catalyst to reduce nitrate to nitrite, which is then measured colorimetrically.
Results a n d Discussion Distilled water (100 mL) was filtered through MF-millipore filters of 3.0-, 0.45, and 0.025-pm size separately and successively. The concentrations of TOC, COD, and NO3 in the filtrates are tabulated in Table I. The 3.0- and 0.45-pm filtrates had only moderate amounts of TOC, COD, and NO,?, 0013-936X/79/0913-0871$01.00/0
@ 1979 American Chemical Society
Volume 13, Number 7, July 1979
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