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The polyatomic background at the major isotope of Cr was evaluated as a function of collision cell gas flow rate using three different mobile phases. The stability of Cr-VI was evaluated as a function of solution pH by fortifying samples with enriched Cr-53(VI). The Cr-53(VI) recovery was >= 95% at pH 7.8, but by pH 6.2 a significant amount of the enriched spike was recovered as Cr-53(III)-EDTA. The instability of Cr-III at pHs above 7.8 required that Cr-III be chelated prior to speciation. The concentration of EDTA was optimized by evaluating Cr-III recoveries in six finished drinking waters, a U.S. Geological Survey reference water, and a challenge water fortified with competing matrix cations. If the Cr-III was allowed to precipitate (characteristic of shipping a sample without field preservation), acceptable recoveries of Cr-III required the sample to be heated to 70 degrees C in 10 mM EDTA to quantitatively produce the Cr-III-EDTA complex. The overall preservation/speciation approach was evaluated using an enriched Cr-53(IV) and natural Cr-III in seven drinking water matrixes over a 46 day period. A linear least squares analysis was performed on each water, and the corresponding P-values were estimated. The method detection limits for Cr-III-EDTA and Cr-VI were 0.06 and 0.1 mu g/L, respectively.