Holmium(III)-selective fluorimetric optode based on N,N-bis(salicylidene)-naphthylene-1,8-diamine as a neutral fluorogenic ionophore

• A selective fluorimetric optode for determination of trace amounts of Ho3+ was prepared.
• N,N-bis(salicylidene)-naphthylene-1,8-diamine (L) was used as a fluoroionophore.
• The response of the sensor is based on the strong fluorescence quenching of L by Ho3+ ions.

For the first time a highly sensitive and selective fluorimetric optode for determination of trace amounts of Ho3+ ions was prepared. The sensing system was prepared by incorporating of N,N-bis(salicylidene)-naphthylene-1,8-diamine (L) as a neutral Ho3+-selective fluoroionophore, in a plasticized PVC membrane containing sodium tetraphenyl borate as a lipophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Ho3+ ions. At pH 5.4, the proposed sensor displays a calibration curve over a wide concentration range of 1.0 × 10−10–1.0 × 10−3 M, with a relatively fast response time of less than 1 min. In addition to high stability, high reproducibility and a relatively long working lifetime, the sensor shows a good selectivity towards Ho3+ ion with respect to common coexisting cations. The fluorescence optode was applied to determination of holmium ion contents of water samples.

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