The goal of this research was to develop a U.S. Environmental Protection Agency method for the determination sub-ppb concentrations of the perchlorate anion (ClO₄ ^-) in drinking waters and in waters high in total dissolved solids. To date, ion chromatography using a KOH mobile phase, electrolytic conductivity suppression (Dionex Corporation, Sunnyvale, CA) and electrospray ionization mass spectrometric detection (ThermoFinnigan, San Jose, CA) has been explored with the following salient features: low-level linear calibration from 0.01 - 1.0 ppb with an R² ≥0.999; method detection limits (MDLs) in deionized and high ionic waters (up to 1000 ppm common anions sulfate, chloride and carbonate) from 0.03 - 0.11 ppb with no significant difference between MDLs when using mass 99 or mass 101 as quantitation ions at =0.01; precision of replicate injections at 1 ppb was less than 5% relative standard deviation on masses 99 and 101 on a daily basis; accuracy as determined by analysis of a certified reference material was ±5% of certified value in deionized water; and, ruggedness as determined by the reproducibility of area counts of 1.0 ppb check standards analyzed periodically over a day of continuous analysis of high ionic matrices revealed some deterioration of signal intensity (~15% drop). Simple measures were implemented to preserve signal intensity over time and in high ionic matrices. Includes 2 references.