This paper describes a rapid method to determine arsenite assay and arsenate impurity in Arsenic Trioxide Injection using a single conductivity detector. The arsenite assay was determined in a non-suppressed conductivity detection mode and arsenate impurity was quantified in a suppressed conductivity detection mode. Dual-conductivity detections were enabled by valve switching and time programming. The method was validated with respect to specificity, linearity, precision, accuracy, stability, and limit of quantification. The limit of detection and quantification for arsenite were 0.855 mg/L and 2.593 mg/L, and 0.044 mg/L and 0.133 mg/L for arsenate, respectively.