Improved nitrate sensing using ion selective electrodes based on urea–calixarene ionophores

Abstract

Urea-calix[4]arenes 1 and 2 were synthesised and incorporated into ISE membranes for assessment as sensors for inorganic anions in water. 1 revealed a strong response to all anions following the Hofmeister selectivity order. For ISEs of 2, the response to a portion of the anion series was suppressed, increasing the margin of selectivity of nitrate over chloride, a common interferant of nitrate in fresh and marine water samples. The performance of ISEs containing 2 was compared to commercially available alkylammonium nitrate ion-exchange salts used for nitrate sensing. Our ISEs performed favourably in terms of sensitivity, linear range and LOD with an improved selectivity coefficient over chloride of log K NO 3 À Cl À pot of À3.4, an order of magnitude better than commercially available nitrate ISEs. The pre-conditioning of ISEs in nonprimary chloride salt was essential for obtaining these results.

Calixarene-based anionic receptors

“…Urea-calix [4]arenes 104a and 104b were synthesised and incorporated into ion-selective electrode (ISE) membranes for assessment as sensors for inorganic anions in water [93]. Table 10 contains the selec- Table 10.…”

Synthesis and Anion‐Binding Properties of Novel Redox‐Active Calixarene Receptors

“…Urea fragments have already been introduced into the para positions of the calixarene skeleton mostly by direct linkage to elaborate supramolecular capsular materials [4][5][6][7][8][9] and anionic or ditopic receptors. [10][11][12][13][14][15][16][17][18][19][20][21][22] The incorporation of metallocene fragments, usually cobaltocene or ferrocene, into such systems has been pursued essentially to act as sensors or to activate molecular level processes. Moon and Kaifer reported a redox-controlled dissociation of a self-assembled dimer, [23] whereas Beer et al took advantage of the receptor's electrochemical activity as a signal of a recognition event.…”

Nitrate Ion Selective Electrode Based on Ion Imprinted Poly(N-methylpyrrole)

“…Nitrate is well known for being a weak coordinator requiring a complexation site of a specific size, shape and charge. Many approaches have been tried to prepare nitrate ionophores [4][5][6]. Most ionophores for nitrate are employed in conventional membrane ion selective electrodes.…”