The results obtained from the application of molecular absorption spectrophotometry using Azomethine H to establish breakthrough curves for the boron purification process are presented in order to determine the breakthrough point, or maximum acceptable effluent concentration, which is regulated by environmental legislation. The breakthrough capacity of the ion-exchange process and the degree of column utilisation were also calculated. The results were highly satisfactory at the level of experimental work in the laboratory; however, although the method of the Azomethine H stands out for its simplicity and sensitivity, it is slow as a method for control of the exchange process and of regeneration in a pilot plant or an industrial plant. For the purpose of obtaining an in-line method, pH and specific conductivity of the aliquot of the effluent were determined. A sample for this was taken during the test of elution in the fixed bed of resin. The combined representation and the comparison of the values of boron concentration, pH and specific conductivity of the effluent showed that the pH cannot be adapted for a quick determination of the breakthrough point; however, the conductivity can. A conductivity sensor can be designed to quickly detect the moment that the breakthrough point is reached.