There is no specification in either method for using a smaller pore 0.2 µm filter for standards. Labs should treat their standards and samples in the same manner. Sect. 4.3 of Method 300.0 (and Sect. 4.4 of Method 300.1) states: “Samples that contain particles larger than 0.45 µm and reagent solutions that contain particles larger than 0.2 µm require filtration to prevent damage to instrument columns and flow systems”. “Reagent solutions” refer to the mobile phase solutions, not standards. The 0.2 µm filter is typically used for microbial preservation in the field, not for removal of particulates in general laboratory operations. Unless they can provide more detail behind this request, It is not recommend that the lab makes any changes to the process, the methods make no provision for any other filtration options.
An instrument manufacturer is recommending that we use a 0.20 micron filter to filter samples for methods EPA 300.1 and 300.0. Would this be acceptable as the method states a 0.45 micron filter for samples and a 0.2 micron filter for standards?
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