Determination of trace thiocyanate by linear sweep polarography

In a thiocyanate solution containing iron (II), nitrite and ascorbic acid, a linear-sweep polarographic wave appears at ?0.42 V (vs. SCE). In anodic sweeps, the derivative peak current is directly proportional to the concentration of thiocyanate over the range 2×10^?8?1×10^?6 M; the detection limit is 1×10^?8 M. The procedure is used for the determination of trace thiocyanate (10^?3?10^?4 M) in saliva. The mechanism of the electrode process is discussed; the polarographic wave is ascribed to catalytic reduction of dissolved oxygen in the presence of an adsorbed ternary Fe/SCN/NO complex.     

Spectrophotometric determination of micro amounts of thiosulfate by liberation of thiocyanate from mercury(II) thiocyanate

The proposed determination of thiosulfate is based on the liberation of thiocyanate by the reaction of thiosulfate with mercury(II) thiocyanate and spectrophotometric determination of the thiocyanate with iron(III). The reaction of thiosulfate with mercury(II) thiocyanate is elucidated with reference to a system containing phosphate buffer; the phosphate is shown to participate directly in the reaction, and a balanced chemical equation is given. Optimum conditions are described for the stoichiometric formation of 3 mol of thiocyanate from 1 mol of thiosulfate. The method can be applied to the determination of thiosulfate in the range 3 × 10^?6–1.4 × 10^?4 M (1.7–78.5 μg thiosulfate in 5 ml).     

Spectrophotometric determination of chloride in non-polar media by the mercury(II) thiocyanate reaction

A simple, rapid and accurate method for the spectrophotometric determination of chloride in non-polar media is described. The method is based on the well-known reaction of mercury(II) thiocyanate with chloride to release thiocyanate, which then reacts with iron(III). The optimum concentrations of reagents for the determination of chloride in 2,2,4-trimethylpentane (iso-octane) and cyclohexane are reported. The molar absorptivity of the complex at 505 nm is 5120 ± 200 dm³ mol^?1 cm^?1 for iso-octane and 5340 ± 340 dm³ mol^?1 cm^?1 for cyclohexane. Beer's Law is obeyed in the range 2 × 10^?7–2 × 10^?5 mol dm^?3 (0.01–1 mg l^?1) chloride.     

A Novel Optical Sensor for Determination of Thiocyanate

Abstract

A novel optical sensor (optode) is described for the determination of thiocyanate using methyltrioctylammonium chloride immobilized on triacetylcellulose membrane. The response to thiocyanate is the result of adsorption of [Co(SCN)₄]^2? on sensing membrane, which caused the colorless membrane to change to blue. This optode can readily be regenerated by using 0.02 mol/l sodium oxalate solution. The linear range of the method was 3.44×10^?5 to 8.61×10^?4 mol/l of thiocyanate with a limit of detection 1.51×10^?5 mol/l. The relative standard deviation for eight replicate measurements of 8.61×10^?5 and 4.30×10^?4 mol/l of thiocyanate was 3.45 and 1.23%, respectively. The sensor was successfully applied for the determination of thiocyanate in saliva of smokers, nonsmokers and various water samples.     

A reaction-rate method for the determination of thiocyanate,based on its inhibitory effect on the iodate-hypophosphite reaction

An automatic spectrophotometric reaction-rate method is described for the determination of thiocyanate in aqueous solutions, based on its inhibitory effect on the iodate-hypophosphite reaction. The time required for the reaction to proceed between two pre-determined levels is measured automatically and related directly to the thiocyanate concentration. The recommended reaction-rate method is fast, simple, sensitive, accurate (to 2%) and precise (1.7%, relative standard deviation). The useful analytical range of concentrations of thiocyanate is 4 × 10^?5 to 5 × 10^?4M. Maximum tolerable amounts of interfering ions are also presented.     

Flow-injection determination of some sulphur anions via the catalyzed iodine-azide reaction

Investigations of the catalysis by sulphide, thiosulphate and thiourea of the iodineazide reaction under flow-injection conditions showed that the reaction was complete within 15 s, 30 s and 2 min, respectively. Determination of 0–1.0×10^?3 M sulphide, 0–8.0×10^?4 M thiosulphate and 0–1.0×10^?3 M thiourea is possible under optimized flow conditions. Catalysis by thiocyanate did not occur under these conditions so that thiosulphate could be determined in the presence of thiocyanate.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

[Cu(L)](NO3)2 (L=4,7‐Bis(3‐aminopropyl)‐1‐thia‐4,7‐diazacyclononane) as a Suitable Ionophore for Construction of Thiocyanate‐Selective Electrodes and Their Use in Determination of Urinary and Salivary Thiocyanate Concentration

The construction, performance characteristics, and application of polymeric membrane (PME) and coated graphite (CGE) thiocyanate‐selective electrodes are reported. The electrodes were prepared by incorporating the complex [Cu(L)](NO₃)₂ (L=4,7‐bis(3‐aminopropyl)‐1‐thia‐4,7‐diazacyclononane) into a plasiticized poly(vinyl chloride) membrane. The influence of membrane composition, pH of test solution, and foreign ions were investigated. The electrodes reveal Nernstian behavior over a wide SCN^? ion concentration range (1.0×10^?6–1.0×10^?1 M for PME and 5.0×10^?7–1.0×10^?2 M for CGE) and show fast dynamic response times of 15 s and lower. The proposed sensors show high selectivity towards thiocyanate over several common organic and inorganic anions. They were successfully applied to the direct determination of thiocyanate in urine and saliva of smokers and nonsmokers, and as an indicator electrode in titration of Ag⁺ ions with thiocyanate.     

Potentiometric response of graphite electrodes coated with modified polymer films

Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10^?1–1 × 10^?5 M sodium thiocyanate.     

Nucleophilic Substitution in Dipolar Aprotic Solvents: Hexamethylphosphoric triamide

The rate of the reaction between ethyl tosylate and chloride as well as bromide ion has been measured in hexamethylphosphoric triamide in the presence of several counterions. Rate constants for the free ions at 25.0° are 14.4 mole^?1 for chloride and 2.0 mole^?1min^?1 for bromide, both independent of the cation used. The equilibrium constants for ion pair dissociation of lithium-, ammonium- and tetra-n-butylammonium chloride are 3.97 × 10^?2, 1.52 × 10^?3 and 6.36 × 10^?3 mole, and for the corresponding bromides 3.30 × 10^?2, 9.65 × 10^?3, and 9.62 × 10^?3 mole.     

Poly (Vinyl Chloride) Matrix Membrane Electrodes Responsive to Thiocyanate,Perchlorate and Periodate

Abstract

Three types of PVC matrix membrane ion-selective electrodes (ISEs) are described. These are based on membranes containing nitron thiocyanate with 2-nitro-phenyl phenyl ether, 2-nitrophenyl phenyl ether alone and tetraphenylarsonium thiocyanate with 2-nitrophenyl octyl ether. Each type is conditioned and stored in 0.1M sodium thiocyanate. The first two electrodes have been evaluated for thiocyanate and perchlorate response and the best linear long range (linear range down to 2.5×10^?5M) response was obtained for perchlorate. The third electrode is suitable as a periodate ISE with linear calibration range down to 2×10^?4M. The plasticized (2-nitrophenyl phenyl ether) PVC electrode for thiocyanate and perchlorate had a much longer pH interference free range (1.5–12.5) than either of the other electrodes.     

A nafion/crown ether film electrode and its application in the anodic stripping voltammetric determination of traces of silver

Glassy carbon electrodes are modified by coating with dicyclohexyl-18-crown-6 in Nafion-117. The electrode is used for a very sensitive anodic stripping voltammetric determination of silver. High sensitivity is obtained owing to the release of crown molecules from the silver-crown complex during the deposition. The detection limit is 2×10^?12 M after electrodeposition for 30 min. The recommended supporting electrolyte is 4×10^?3–7×10^?3 M potassium chloride in 0.01 M nitric acid with a deposition potential of ?0.30 V vs. SCE and a linear potential scan. Three typical calibration graphs were linear over the range 2×10^?11–1×10^?8 M for deposition times of 30, 20 and 8 min, respectively. The silver content of reagent-grade ammonium nitrate was found to be 0.48×10^?4% with a relative standard deviation of 3.7% (n=7) for parallel determinations.     

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λ_max of [Fe(CN)₅PhNHNH₂]^3?, complex) under the optimum reaction conditions at: 2.5 × 10^?3 M [Fe(CN)₆]^4?, 1.0 × 10^?3 M [PhNHNH₂], 8.0 × 10^?7 M [Ag⁺], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO₃) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10^?8 M with a detection limit of 2 × 10^?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (K_CI), catalyst–substrate (K_s) and Michaelis–Menten constant (K_m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.     

Highly Selective and Sensitive Triiodide PVC‐Based Membrane Electrode Based on a New Charge Transfer Complex of 2‐(((2‐(((E)‐1‐(2‐Hydroxyphenyl) Methylidine) Amino) Phenyl) Imino) Methyl) Phenol for Nano‐Level Monitoring of Triiodide

Abstract

A highly selective and sensitive triiodide sensor based on a 2‐(((2‐(((E)‐1‐(2‐hydroxy phenyl) methylidine) amino) phenyl) imino) methyl) phenol with iodine (CTC) as membrane carrier was developed. The electrode revealed a Nernstian behavior over a very wide triiodide‐ion concentration range (5.0×10^?8–1.0×10^?2 M), and relatively low detection limit (3.0×10^?8 M). The potentiometric response is independent of the pH of solution in the pH range of 3.0–10.0. The electrodes manifest advantages of low resistance, very fast response (<12 s), and most importantly, good selectivities relative to a wide variety of inorganic and organic anions, including iodide, bromide, chloride, fluoride, sulfite, sulfate, cyanide, thiocyanate, and acetate. In fact, the selectivity behavior of the proposed triiodide ion‐selective electrode shows great improvements compared to the previously reported electrodes for the triiodide ion. The proposed membrane sensor can be used for at least 6 months without any significant divergences in the potential. The electrode was successfully applied as an indicator electrode in the titration of triiodide with thiosulfate ion.     

The effects of some electrolytes on flocculation with a cationic polyacrylamide

The effects of sodium chloride, sodium sulfate, and alum (aluminum sulfate) on the performance of a cationic polyacrylamide flocculant in a papermaking suspension consisting of bleached (hardwood: softwood, 50∶50) kraft wood-pulp fibres and anatase (TiO₂) were investigated. Sodium chloride and sodium sulfate, 1×10^?5 to 1×10^?2 M, in the presence of polymer, caused negligible changes in the electrophoretic mobility of the TiO₂ and in the first-pass retention of TiO₂ (heteroflocculation of TiO₂ and fibres). Alum at concentrations from 1×10^?5 to 1×10^?4 M at pH 4.0 and 4.5 increased retention with polymer; higher alum concentrations resulted in lower retentions. At pH 4.0 the electrophoretic mobility of the TiO₂ was positive over the entire range of alum concentrations investigated (1×10^?5?3.2×10^?3 M) whereas at pH 4.5 the mobility was negative at 1×10^?5 M alum and charge reversal was observed at about 4×10^?5 M alum. The intrinsic viscosity of the cationic polyacrylamide was decreased by the addition of alum, sodium chloride or sodium sulfate. The effect of alum on the polymer conformation appeared to be that of the non-specific interaction of sulfate ions with a cationic polyelectrolyte. Retention results are discussed in terms of the colloidal stability of TiO₂, the adsorption of polyacrylamide on TiO₂ and the conformation of adsorbed polymer.     

Highly Selective and Sensitive Triiodide PVC‐Membrane Electrode Based on a New Charge‐Transfer Complex of Bis(2,4‐Dimethoxybenzaldehyde)butane‐2,3‐Dihydrazone with Iodine

In this work, a highly selective membrane triiodide sensor based on a new charge‐transfer complex of bis(2,4‐dimethoxybenzaldehyde)butane‐2,3‐dihydrazone with iodine (Iodide Charge Transfer complex: ICT) as membrane carrier is introduced. The influences of five different solvent mediators on sensitivity and selectivity of the proposed sensor were considered. The best performance was obtained with the membrane composition containing 30% poly (vinyl chloride), 63% DBP, 5% ICT and 2% HTAB. The electrode shows a Nernstian behavior over a very wide triiodide ion concentration range (1.0 × 10^?7‐1.0 × 10^?2 M), and a detection limit value of 8.0 × 10^?8 M. The effect of pH on the potentiometric response of the sensor was also studied, and it was found that the response of the electrode is independent of the pH of the solution in the pH range of 4.0–10. The proposed sensor has a very fast response time (< 12 s), and good selectivities relative to a wide variety of common inorganic and organic anions, including iodide, acetate, bromide, chloride, fluoride, nitrite, nitrate, sulfite, sulfate, cyanide and thiocyanate. In fact the selectivity behavior of the proposed triiodide ion‐selective electrode shows great improvements compared to the previously reported electrodes for triiodide ion. The proposed membrane sensor can be used for at least 6 months without any divergence in the potentials. The electrode was successfully applied as an indicator electrode in the titration of triiodide with thiosulfate ion.     

Thiocyanate-Selective PVC Membrane Electrode Based on Copper and Nickel Complexes of Para-tolualdehydesemicarbazone as Carrier

Abstract

Copper(Cu) and nickel(Ni) complexes of para-tolualdehydesemicarbazone (pTSC) were used as carrier for an thiocyanate ion–selective electrode. The Ni(II)pTSC demonstrated higher selectivity for thiocyanate ions with better performance than Cu(II)pTSC as carrier. The electrode shows a Nernstian slope of 58.8 ± 0.3 mV decade^?1 with improved linear range of 1 × 10^?2 to 1 × 10^?7 M and a low detection limit of 1.25 × 10^?7 M in the pH range of 3–10, giving a relatively fast response and reversibility within 10 s. The selectivity coefficient was calculated using matched potential method. The electrode worked well for nearly 3 months. The response mechanism is discussed by UV-visible spectroscopic technique. The electrodes were used in potentiometric titration of thiocyanate with silver nitrate. Further, the electrode was successfully applied to determine the thiocyanate content in physiological fluids.     

Thiocyanate-selective membrane electrode based on cobalt(III) Schiff base as a charge carrier

A highly selective polyvinylchloride (PVC) membrane electrode based on Schiff base complex i.e. [Cobalt (Salpen) (PBu₃)] ClO4 · H2O (Salpen = bis(salycilaldehyde)propylene diamine) is reported as new carrier for thiocyanate selective electrode by incorporating the membrane ingredients on the surface of graphite electrodes. The proposed electrode possesses a very wide Nernestian linear range to thiocyanate from 1.0 × 10^?6 to 1.0 × 10^?1 M with slope of ?59.05 ± 0.91 mV per decade of thiocyanate concentration, very low detection limit (8.0 × 10^?7 M) and good thiocyanate selectivity over the wide variety of other anions. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (2.8–9.8) are advantages of the reported electrode. The sensor has a response time of <5 s and can be used for at least 14 weeks without any considerable change in respective potential response. The proposed electrode was used for the determination of thiocyanate in saliva, wastewater and human urine with satisfactory results and good agreement with colorimetric as reference method.     

Extraction-spectrophotometric determination of tungsten with thiocyanate and some amidines

The procedure is based on reduction of W(VI) to W(V) by tin(II) chloride in 6 M hydrochloric acid, and extraction of the resultant thiocyanate complexes with a benzene solution of amidine. The complex coagulates and is dissolved in the benzene by addition of 1-pentanol. The maximum molar absorptivities of the complexes with 8 amidines in benzene/1-pentanol (9:1, v/v) are in the range 12 100–18 400 mol^?1 cm^?1. The simplest compound, N,N-diphenylbenzamidine gives the best sensitivity; the linear range covers 5–90 μg W in 10 ml of final solution; the detection limit is 2 ng W ml^?1. The method is applied to alloy steels.     

Novel Bromide PVC‐Based Membrane Sensor Based on Iron(III)‐Salen

A novel bromide PVC‐based membrane sensor, based on iron(III)‐salen (IS) as an electroactive material, is successfully developed. The sensor possesses the advantages of low detection limit (6.0×10^?6), wide working concentration range (7.0×10^?6–1.0×10^?1 M), Nernstian behavior (slope of 59.0±0.5 mV per decade), low response time (<15 s), wide working pH range (3–9), and specially, high bromide selectivity over a wide variety of organic and inorganic anions, specially iodide, chloride, and hydroxide ions. The electrode was used in the direct potentiometric determination of hyoscine butylbromide, and as an indicator electrode in potentiometric titration of bromide ions with silver ions.