An online xanthate monitoring system was constructed for the continuous determination of xanthate concentrations in laboratory flotation pulps. This system consists of an online filter which is immersed in the pulp in a flotation cell, a peristaltic pump to draw clear solution through the filter and pump it through a UV spectrometer set at 301 nm (where aqueous solutions of xanthate have an absorbance maximum), and a computer and screen to record and display the data as a function of time. Calibration of the system showed that a straight line was obtained up to 0.25 mM (about 40 ppm) sodium ethyl xanthate. The detection limit of this system is 0.001 mM xanthate. The spectrometer does not distinguish between different xanthates (e.g., ethyl and/or amyl) but gives a total value. A check on the online analyses by analysing a solution sample by HPLC showed the amount of each xanthate present, and that the sum of the concentrations of the two xanthates present was in good agreement with the online value. Hence the online unit gives a clear indication of the total xanthate present in solution at any given time, and this can be used as a guide as to whether or not further additions of xanthate are required or desired. Only a few other reagents are known to interfere. Laboratory flotation tests showed that the filter did not block in a 50 min flotation test with a pulp containing 30% w/v solids. Tests with a sulphide ore showed that the longer chain xanthates such as amyl were adsorbed on the sulphides more quickly than the shorter chain xanthates such as ethyl. (C) 2008 Published by Elsevier B.V.