Evaluation of the dialysing yield of membranes with different composition. Application to the analysis of chloride in fruit juices by flow injection

In this paper, several home-made dialysing membranes with a high yield (around 56%) have been obtained allowing the easy and rapid analysis of minor components in food samples. Commercially available and home-made membranes with different chemical composition were tested by using a flow injection manifold. Polyetherimide-composed membranes (PEI) were selected because they showed a high dialysing yield and analytical signal, low blank signal and absence of membrane clogging. The influence of polymer concentration as well as the coagulation temperature on the membrane performance is discussed. A PEI membrane with 18% polymer concentration and around 40 °C as coagulation temperature was found to be the most suitable manufactured membrane to achieve the proposed aims. The photometric determination of chloride ion was used for membrane characterisation. To test the membrane, an on-line dialysis flow injection procedure was used in the analysis of chloride in fruit juices and derivatives with an easy-going pre-treatment. A good correlation between the flow injection manifold (linear range: 20–250 mg/l, RSD 1.1%, average recovery 102.2% and sampling frequency 25 h−1) and the reference method is obtained. The use of this membrane in on-line dialysis prior to the photometric determination of minor components in fruit derivatives is a simple and low-cost alternative to usual approaches.