The simultaneous determination of chromium and cobalt in water samples has been studied. Chemiluminescence registers based on the luminol-hydrogen peroxide reaction have obtained by a batch procedure. PLS algorithms have employed to model the time-response (formation and destruction of emitter). The influence of the presence of two metals and the non-linearity relationship between response and concentration have been evaluated in the signal. Different experimental designs and the selection of variables have been tested. The calibration set has been selected based on two criteria: unicomponent and/or bicomponent standard solutions and the slope calculated from linear univariate calibration. The response has been modelled providing high percentages of explained variance, robust models and low prediction errors. The proposed methodology has been validated using test standard solutions and a standard reference material of fresh water. Accurate results have proved the advantages of this method for the simultaneous determination of chromium and cobalt in water samples.