Determination of SCN– in Urine and Saliva of Smokers and Non-Smokers by SCN–-Selective Polymeric Membrane Containing a Nickel(II)-Azamacrocycle Complex Coated on a Graphite Electrode

Abstract

The conventional anion-selective electrodes based on quaternary ammonium or phosphonium salts always display the so-called Hofmeister selectivity pattern. 1 Since the 1980's, research interest in anti-Hofmeister anion selective membrane electrodes has increased more and more. Recently, electrodes based on derivatives of vitamin B12 and transitional metal complexes of porphyrins, and phthalocyanines have been reported. [2][3][4][5][6] These electrodes demonstrated potentiometric anion selectivity sequences apparently deviating from the Hofmeister sequences. Such deviations result from the unique interaction of the central metals with an anion rather than from the hydration free energy and the relative solubility of the individual anions in the solvent mediator.Due to the vital importance of selective SCN -determination, especially in food, biological and water samples, there are several reports on the preparation of SCN -selective membrane electrodes based on a variety of ion carriers.5,7-13 However, most of these SCN -sensors have one, two or, in some cases, all of the following problems: a) high detection limit, b) narrow working concentration range and/or c) serious interfering effect of such anions as ClO4 -, I -and IO4 -.In this work we report a coated graphite membrane electrode based on Ni(II)-2,2′,4,9,9′,11-hexamethyltetraazacyclotetradecanediene perchlorate (NiL) for potentiometric monitoring of ultra trace amounts of SCN -. Experimental ReagentsReagent grade dibutyl phthalate (DBP), benzyl acetate (BA), acetophenone (AP), hexadecyltrimethylammonium bromide (HTAB), tetrahydrofuran (THF), and high relative molecular weight (PVC) were purchased from Aldrich and used as received. Nickel(II)-2,2′,4,9,9′,11-hexamethyltetraazacyclotetradecanediene perchlorate (NiL) was synthesized and purified as described elsewhere.14 Potassium salts of all anions used (all from Merck) were of the highest purity available; they were used without any further purification except for vacuum drying The construction, performance characteristics, and application of a novel polymeric membrane coated on a graphite electrode with unique selectivity towards SCN -are reported. The electrode was prepared by incorporating Ni(II)-2,2,4,9,9,11-hexamethyltetraazacyclotetradecanediene perchlorate into a plasticized poly(vinyl chloride) membrane. The influences of membrane composition, pH and foreign ions were investigated. The electrode displays a near Nernstian slope (-57.8 mV decade -1 ) over a wide concentration range of 1 × 10 -7 -1 × 10 -1 M of SCN -ion. The electrode has a detection limit of 4.8 × 10 -8 M (2.8 ng/cm 3 ) SCN -and shows response times of about 15 s and 120 s for low to high and high to low concentration sequences, respectively. The proposed sensor shows high selectivity towards SCN -over several common organic and inorganic anions. The electrode revealed a great enhancement in selectivity coefficients and detection limit for SCN -, in comparison with the previously reported electrodes. It was successfully applied to the d...

Novel Imidazole PVC-Based Sensor Based on a Thiopyrilium Compound

“…Table 1 Besides the critical role of the nature of the ion carrier in preparing membrane-selective sensors, some other important features of the PVC membrane, such as the amount of ionophore, the nature of solvent mediator, the plasticizer/PVC ratio, and, especially, the nature of the additives used, are known to significantly influence the sensitivity and selectivity of ion-selective electrodes. [9][10][11][12][13][14][15] As is obvious from Table 1 (No. 5,9 -11), among four different plasticizer used, DBP was a more effective solvent mediator in preparing the imidazole sensor.…”

“…formed. [9][10][11][12][13][14][15] The tube was then pulled out from the mixture and kept at room temperature for 1 h. The tube was then filled with an internal solution (1.0 × 10 -3 imidazole). The electrode was finally conditioned for about 12 h by soaking in a 1.0 × 10 -2 M of imidazole solution.…”

“…We have recently reported a number of sensors for various anions and cations such as Cu 2+ , 9 Ni 2+ , 10 Pb 2+ , 11 Ce 3+ , 12 SO4 2-, 13 SCN -, 14 and I -. 15 In this work we wish to introduce for the first time a novel membrane sensor for selective and sensitive monitoring of imidazole in different samples by using (TTP) as an excellent charged ionophore (Fig.…”

Thiocyanate Ion-selective PVC Membrane Electrode Based on N,N′-Ethylene-bis(4-methylsalicylidineiminato)nickel(II)

“…34 Table 4 lists the linear range, detection limit, slope, response time and selectivity coefficients of some of other thiocyanateselective electrodes against the proposed thiocyanate-selective electrode for comparative purposes. 25,[35][36][37][38] As can be seen from the table, the selectivity coefficients obtained for the proposed electrode are superior to those reported for other SCN --selective electrodes listed in Table 4.…”

Influence of Introduced Substituents on the Anion-selectivity of [14]Tetraazaannulene Complexes

“…In fact, ISEs based on Ni(II) and Zn(II) complexes of [14]tetraazaannulenes have been reported as I -, SCN -, and ClO4 --selective electrodes. [28][29][30] These facts encouraged us to investigate the anion-selectivities of other [14]tetraazaannulene nickel complexes as ISE ionophores. In this study, we have focused on the design of [14]tetraazaannulene nickel complexes with two aromatic rings incorporated into the azaannulene framework for anion sensing.…”