Surfactant effect on determination of Cu2+ and Cd2+ ions by ion-selective electrodes providing evidence for the discrepancy between the point of zero charge and the isoelectric point of CdS

The influence of the presence of some surface-active agents in the medium on determination of Cu2+ and Cd2+ ions via Orion ion-selective electrodes was investigated. Sodium dodecyl sulfate (SDS), cetyltrimethyl ammonium bromide (CTAB) and polyoxyethylene(10)isooctylphenyl ether (TX100) were used as anionic, cationic and non-ionic surface-active agents, respectively. SDS had minor effects on the potentiometric response of the ion selective electrode to Cu2+ ions while CTAB were observed to affect the determination of Cu2+ ions more remarkably. Both CTAB and TX100 caused to small decrements on the concentration readouts for Cd2+ ions but relatively large decrements were observed in the presence of SDS.The results of this study provided evidence for the discrepancy between the isoelectric point and the point of zero charge values of CdS, and showed that the isoelectric point of CdS has a value close to 5.5.