Our laboratory has a client requesting for both dissolved and total hexavalent chromium by EPA 7199. We normally report the results as dissolved hexavalent chromium since the method calls for filtration of the aqueous sample using a 0.45 μm filter.
Is the method intended for determination of dissolved Cr6+ only? Or, does the way Section 6.2 is written, i.e., “For the determination of dissolved Cr(VI)…”, imply that EPA 7199 is intended for both dissolved and total Cr6+? If the method is intended for both total and dissolved, how should analysis of total hexavalent chromium be carried out?
Although the method is not perfectly clear on this matter, Section 6.1 states that the sample should be filtered and pH-adjusted at the time of collection or as soon as possible. Section 6.2 then describes the procedure for filtering and preserving mentioned in 6.1 and clarifies that this is for dissolved hexavalent chromium. Therefore, only dissolved hexavalent chromium can be analyzed by this method.