Abstract: Online dilution with argon was applied to direct determination of total arsenic in salt saturated water by inductively coupled plasma mass spectrometry to overcome matrix effect of high salt containing sample. The interference of ⁴⁰Ar³⁵Cl⁺ to arsenic was reduced by using collision cell technique. Sensitivity of arsenic was raised by adding methanol solution. As shown by the results, the linearity range of arsenic was within 10.0 μg·L^-1, with detection limit (3s) of 0.092 μg·L^-1. Values of recovery obtained by standard addition method were in the range of 90.2%-111%, and RSDs (n=6) were in the range of 1.7%-4.2%.