Filter Papers for EPA Method 353.2

Janet experienced some trouble while running Nitrate (NO₃) by automated Colorimetry using EPA Method 353.2. There seemed to be an interference from the filter paper that resulted in a false positive. She noticed that the false positive was not seen when analyzing for NO₂. The filter paper used in Janet's analysis was Whatman filter paper 541 - Hardened Ashless. She wondered if there might be a more appropriate filter paper.

	RE: Filter Papers for EPA Method 353.2 Dear Janet,      Unfortunately, Method 353.2 does not specify the type of filter paper to use. I suggest a syringe filter paper that is certified for low ionic background levels. Since it is used for Ion Chromatography applications, it will not contribute nitrate contamination. This filter paper should be used for aqueous samples only. It comes in a polypropylene housing with Luer fittings. These filters are available from Aldrich as follows: • 0.2um pore size (13mm) diamerer, catalog# Z26,032-0 • 0.2um pore size (25mm) diamerer, catalog# Z26,034-7 • 0.45um pore size (13mm) diamerer, catalog# Z26,033-9 • 0.45um pore size (25mm) diamerer, catalog# Z26,035-5      The 13mm size comes in packages of 100 and are priced at about $170/pkg and the 25mm size comes in packages of 50 and is priced at around $120/pkg. Please contact me if you have any other questions.     Paul R. Gaines, Ph.D. Serving you in chemistry