I am planning on doing a titration with EDTA to find % Zn quantitatively. So far, the brass has been dissolved in concentrated nitric, boiled off, etc. Sn was filtered out, then Cu and Pb were found by electrodeposition (well PbO2, but you see what I mean). Now for the Zn, I have 'heard' there is a method of using EDTA to find an approximate end point, and subsequent concentration etc., except that I cannot seem to find the method. Also, since there may still be trace elements in solution (namely, Cu, Sn and Pb), I was wondering if anyone knew of a good masking agent I could use.. I have heard thiosulfate perhaps, but not sure if that's the actual case. Also, if you have a reference that would be preferred but not necessary. Any help is MUCH appreciated!