Analytica Chimica Acta 481 (2003) 85–90 Novel monohydrogenphosphate sensor based on vanadyl salophen Mohammad Reza Ganjali a,∗ , Farhang Mizani a , Masoud Salavati-Niasari b a Department of Chemistry, Tehran University, P.O. Box 14155-6455, Tehran, Iran b Department of Chemistry, Kashan University, Kashan, Iran Received 13 August 2002; received in revised form 16 January 2003; accepted 16 January 2003 Abstract A novel PVC-based membrane sensor based on vanadyl salophen (VNSP) for determination of trace amounts of mono- hydrogenphosphate (MHP) ions is introduced. The electrode revealed Nernstian response towards monohydrogenphosphate over the wide concentration range from 1.0 × 10 -1 to 1.0 × 10 -6 M at the pH of 8.2. The effect of solvent mediator, cationic additives and amount of ion-carrier on the behavior of the sensor was investigated. The sensor shows a short response time (<20 s) in the whole concentration ranges. The selectivity of the electrode is very high, and it can be used for detection of trace amounts of monohydrogenphosphate in the presence of large amounts of other anions. The detection limit of the electrode was 5.0 × 10 -7 M (48 ng/ml) and it could be used for 14 weeks without any measurable changes in the slope. The potentiometric selectivity coefficients data revealed negligible interference from 16 common anions. It was successfully applied for the direct determination of monohydrogenphosphate in fertilizer samples and, as an indicator electrode, in potentiometric titration of HPO 4 2- ion with barium nitrate. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Monohydrogenphosphate; Vanadyl salophen; Potentiometry; Fertilizer 1. Introduction The increasing use of ion sensors in the field of clinical, environmental, agricultural, industrial and medicinal analysis is putting more and more pressure on analytical chemists to develop new sensors for the fast, accurate, reproducible and selective determina- tion of various species. Due to the vital importance of phosphate in many biological, environmental and industrial systems, and the urgent need for a phosphate-selective electrodes for potentiometric monitoring of HPO 4 2- or H 2 PO 4 - ∗ Corresponding author. Fax: +98-21-6495291. E-mail address: ganjali@khayam.ut.ac.ir (M.R. Ganjali). in different samples, only four ion-carriers have been used in the construction of phosphate-selective elec- trodes [1–4]. In 1988, various dialkyl and diaryltin derivatives were used as ionophore, in monohydro- genphosphate (MHP) membrane electrodes by Glazier and Arnold, but these electrodes displayed low stabil- ity and short lifetimes [1]. In 1997, Liu et al. used tribenzyltin oxide in construction of monohydrogen- phosphate membrane electrode with good selectiv- ity (except NO 3 - , Br - and I - ions) [2]. In 1997, Antonisse et al. used uranyl salophen with relatively good selectivity (except for F - ion) for H 2 PO 4 - has been obtained [3]. Fibbioli et al., in 2000, used a zwitterionic bis(guanidinium) ionophore in plasticized membrane electrode, but it displayed poor selectivity 0003-2670/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0003-2670(03)00075-8