AUTOMATED PH-ISFET MEASUREMENTS UNDER HYDROSTATIC-PRESSURE FOR MARINEMONITORING APPLICATION

Association of microsensors and flow measurement techniques could prov ide many advantages for the in-situ monitoring of marine environment. First, adaptability of such sensors to autonomous measurement and unde r pressure conditions has to be considered. This paper presents a labo ratory study devoted to seawater pH flow measurement using ISFETs. The measurement principle had to circumvent drift problems associated wit h these sensors. This was performed by measuring potential steps produ ced by a fast alternation of the sample and a standard buffer over the sensor.:ln addition, interference of seawater ionic matrix on ISFET r esponse was circumvented by the use of saline buffers. The precision o f the method is better than 0.01 pH and could be further increased. It s optimal accuracy will be limited to 0.01 pH, clue to uncertainties o n the pH of saline buffers. The ability of ISFETs to operate under pre ssure, up to 30 bars, over 43 h was demonstrated, without significant decrease in sensitivity. The method could also be suitable for long-te rm unmanned measurements. These first results incline to further exami nation of the potentialities of this technique for pH monitoring at de pth. (C) 1997 Elsevier Science B.V.