Abstract: The present invention provides a low pressure anion exchange chromatography—turbidimetric method for simultaneous online analysis of trace S2? and Cl? in water samples using an apparatus comprising a low pressure pump, a sample valve, a sample loop, a low pressure anion chromatographic column, a reactor, an optical flow cell, an optical detector, a computer system, a mixer, a sample flow path, a propelling solution flow path, and a color developer solution flow path, the method comprising: (a) mapping a baseline; (b) mapping spectrogram of S2? and Cl? in test samples; (c) mapping standard working curves; and (d) calculating the concentrations of S2? and Cl? in the test samples based on the peak heights of S2? and Cl? in the spectrogram and the regression equations of standard working curves.