Determination Of Thiocyanate Research Articles

Kinetic Determination of Thiocyanate on the Basis of Its Catalytic Effect on the Oxidation of Methylene Blue with Potassium Bromate

This study reports a sensitive kinetic spectrophotometric method for the determination of trace amounts of thiocyanate. In acidic solution, Methylene Blue (MB) is oxidized by bromate to form a colorless compound. The reaction is accelerated by trace amounts of thiocyanate and can be followed by measuring the absorbance at 664 nm. The absorbance of the reaction decreased with an increase in the reaction time. Under the optimum experimental conditions (0.56 M of sulfuric acid, 3.9 x 10(-5) M of MB, 3.0 x 10(-3) M of bromate, 180 s, 25 degrees C), thiocyanate can be determined in the range 5.0 - 180 ng/ml. The relative standard deviations (n = 8) are 2.81 and 1.43% for 10.0 and 150 ng/ml thiocyanate, respectively. The detection limit of this method is (3sigma) 3.8 ng/ml. This method was successfully applied to the determination of thiocyanate in real samples.

A Selective Membrane Electrode for Thiocyanate Ion Based on a Bis‐taurine‐salicylic Binuclear Copper(II) Complex as Ionophore

AbstractThe response characteristics of a new potentiometric membrane electrode with unique selectivity towards thiocyanate ion were reported. The electrode was prepared by incorporating bis‐taurine‐salicylic binuclear copper(II) complex into a plasticized PVC‐membrane. The resulting electrode exhibits anti‐Hofmeister selectivity sequence: SCN−>I−>ClO4−>Sal−>NO3−>NO2−>Br−>Cl−>SO3−>SO42− and a near‐Nernstian potential linear range for thiocyanate from 1.0Å×10−1 to 1.0Å×10−6 mol·L‐1 with a detection limit of 8.0Å×10−7 mol·L−1 and a slope of −56.5 mV/pc in phosphate buffer solution of pH 5.0 at 20°C. The UV/Vis spectra, IR spectroscopy and AC impedance studies showed that the excellent selectivity to thiocyanate was related to the unique interaction between the central metal and the analyte and a steric effect associated with the structure of the carrier. The electrode was successfully applied to the determination of thiocyanate in waste water and human urine samples.

Novel Membrane Potentiometric Thiocyanate Sensor Based on Tribenzyltin(IV) Dithiocarbamate

AbstractA novel PVC membrane ion‐selective electrode based on tribenzyltin(IV) dithiocarbamate [Sn(IV)–TBDTB] as neutral carrier was developed for thiocyanate (SCN−) determination. The electrode exhibits a near‐Nernstian response for SCN− with a slope of 62.8±2.0 mV per decade over a wide concentration range 1.0×10−1–2.0×10−6 mol L−1 and a detection limit of 1.0×10−6 mol L−1 in MES–NaOH buffer, pH 6.0, at 25 °C. The electrode prepared with 1.5 wt.% Sn(IV)–TBDTB, 32.5 wt.% PVC and 66.0 wt.% 2‐nitrophenyloctyl ether (o‐NPOE) shows optimal response characteristics. Anti‐Hofmeister selectivity sequence for a series of anions shown by the electrode was as follows: SCN−>Sal−>I−>ClO$\rm{ {_{4}^{-}}}$>phCOO−>CH3COO−>Br−>Cl−>NO$\rm{ {_{3}^{-}}}$>NO$\rm{ {_{2}^{-}}}$>Citrate>SO42−. The useful pH range for the electrode was found to be 3–7 with a response time 30–40 s. The electrode has been used for direct determination of thiocyanate in wastewater with satisfactory results.

Rhodium(II) Phthalocyanine as a Selective Carrier in Thiocyanate‐Selective Membrane Electrode

An anion‐selective electrode based on rhodium(II) phthalocyanine (RhPc) as a neutral carrier is reported. The prepared electrode displays an anti‐Hofmeister behavior with a high selectivity for thiocyanate. The potentiometric response characteristics and selectivities of the membrane electrodes with various ratios of cationic additive to ion‐carrier indicate that the observed potentiometric response is based on the formation of a 1:1 complex between RhPc and thiocyanate as an axial ligand. The membrane electrodes containing ∼60 mol percent of cationic additive (relative to ionophore) exhibit a near‐Nernstian response in a concentration range of thiocyanate between 1×10−6 M to 1×10−1 M, a detection limit of 7.9×10−7 M, and a slope of −56.3 mV/decade in pH 6.0 using 0.1 M phosphate buffer solution. In comparison to the previously reported CoPc‐based membrane electrode, the prepared electrode showed better selectivity for thiocyanate over the relatively more hard anions, such as SO4 2−, H2PO4 −, HCO3 −, NO3 −, F−, Cl−, C2O4 2− and OAc−. This preference in response is assisted by the softness property of Rh2+ in the center of RhPc. The prepared electrode revealed a fast response time, sub‐micromolar detection limit, and a long‐time stability of more than 2 months (with less than 3% decrease in the slope of the potentiometric response). Application of the electrode with the optimum composition for determination of thiocyanate in pharmaceutical preparations (erythromycin thiocyanate) and human urine samples is reported. The electrode is also applied as an indicator electrode in potentiometric titration of milimolar solutions of thiocyanate and silver nitrate.

Determination of Iodide and Thiocyanate in Seawater by Liquid Chromatography with Poly(ethylene glycol) Stationary Phase

Novel, simple, rapid, highly sensitive, and direct determination of iodide and thiocyanate ions in seawater has been performed by liquid chromatography (LC) with UV detection at 220 nm. The separation was achieved on a C30 column of conventional size (150 mm × 4.6 mm i.d.) modified with poly(ethylene glycol); an aqueous solution of 300 mM sodium sulfate and 50 mM sodium chloride was used as mobile phase. Detection limits (S/N=3) obtained by injecting a 20-μL sample were 0.5 and 6 ng mL−1 for iodide and thiocyanate, respectively. The method was successfully used for rapid and direct determination of iodide and thiocyanate in seawater samples, collected from the coasts of Japan, without any extra pretreatment.

Highly selective thiocyanate membrane electrode based on butane-2,3-dione bis(salicylhydrazonato)zinc(II) complex

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on butane -2,3-dione bis(salicylhydrazonato) zinc(II) [Zn (BDSH)] complex as carrier for thiocyanate-selective electrode is reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The sensor responds to thiocyanate in linear range from 1.0 × 10 −6 to 1.0 × 10 −1 M with a slope −56.5 ± 1.1 mV decade −1, over a wide pH range of 3.5–8.5. The limit of detection of the electrode was 7.0 × 10 −7 M SCN −. Selectivity coefficients determined with fixed interference method (FIM) indicate a good discriminating ability towards SCN − ion in comparison to other anions. The proposed sensor has a fast response time of about 5–15 s and can be used for at least 3 months without any considerable divergence in potential. It was applied as indicator electrode in titration of thiocyanate with Ag + and in potentiometric determination of thiocyanate in saliva and urine samples.

Determination of Thiocyanate in Waste Water

The present work proposes a new, simple, selective, and sensitive method for the on‐site spectrophotometric determination of SCN− ions in the industrial and municipal waste water. The method is based on color reaction of SCN− ions with V(V) and chelating agent: N‐hydroxy‐N,N′‐diphenylbenzamidine (HODPBA), and subsequent extraction of the deep green colored complex into chloroform. The value of apparent molar absorptivity (at enrichment factor of 5) is 7.00 × 103 L mol−1 cm−1 at λmax = 610 nm. The calibration curve is linear up to 5.0 µg mL−1 SCN− with slope, intercept, and correlation coefficient of 0.120, 0, and +0.99, respectively. The detection limit (an absorbance identical to blank absorbance +thrice of std. dev.) of the method is 66 ng mL−1 SCN− of the aqueous solution. Most of the ions associated did not interfere in the determination of SCN−. Only phenol interfered in the determination of SCN−, and could be removed by the prior extraction with chloroform solution. The method has been used for analysis of SCN− in industrial and municipal waste water samples. E‐mail: dg7j@hrz.tu‐darmstadt.de.

Simultaneous determination of nitrite, nitrate, thiocyanate and uric acid in human saliva by capillary zone electrophoresis and its application to the study of daily variations

Simultaneous determination of nitrite, nitrate, thiocyanate and uric acid in human saliva by capillary zone electrophoresis and its application to the study of daily variations

Amperometric Sensor Used for Determination of Thiocyanate with a Silver Nanoparticles Modified Electrode

A novel electrode modified with silver nanoparticles was fabricated. It is found that the reducibility of silver nanoparticles is higher than for bulk silver by comparing a silver nanoparticles modified electrode with a silver micro-disk electrode. When SCN- was added, a new oxidation peak occurred and the anodic peak current of silver nanoparticles decreased. The new anodic peak current is proportional to the thiocyanate concentration in the range of 5.0×10-7∼4.0×10-4 mol/L in pH 6.0 NaH2PO4-Na2HPO4 buffer solutions (PBS). The detection limit (S/N=3) is 4×10-8 mol/L. This method has been applied to the determination of saliva (smoker and non-smoker).

Amperometric Sensor Used for Determination of Thiocyanate with a Silver Nanoparticles Modified Electrode

A novel electrode modified with silver nanoparticles was fabricated. It is found that the reducibility of silver nanoparticles is higher than for bulk silver by comparing a silver nanoparticles modified electrode with a silver micro-disk electrode. When SCN- was added, a new oxidation peak occurred and the anodic peak current of silver nanoparticles decreased. The new anodic peak current is proportional to the thiocyanate concentration in the range of 5.0×10-7~4.0×10-4 mol/L in pH 6.0 NaH2PO4-Na2HPO4 buffer solutions (PBS). The detection limit (S/N=3) is 4×10-8 mol/L. This method has been applied to the determination of saliva (smoker and non-smoker).

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

AbstractThe 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.

English

The cyanide overload of 40 cassava (gari) processing workers, 25 frequent consumers of cassava foods and 20 cigarette smokers (all Nigerians) were assessed using a new simple kit method for determination of thiocyanate (cyanide metabolite) in urine. The mean thiocyanate measured in the urine of three groups of cassava processing workers were 9.48±2.8, 8.70±2.23, and 7.46±2.57 ppm. The mean thiocyanate measured in the urine of frequent cassava consumers and cigarette smokers were 3.57±0.6 and 13.99±13.81 ppm, respectively. The urine samples of 15% of the processing workers measured ³10 ppm SCN (172µmol/L), while two urine samples from the smokers measured 30, and 44 ppm SCN. The cyanide contents of some cassava based foods commonly consumed among Nigerians were determined and ranged from 0.68± 0.31 to 0.88±0.21 for total cyanide and 0.14±0.03 to 0.52±01 mgCN - 100g -1 DM for free cyanide. The toxicological implications of these findings are discussed. Keywords: Cyanide overload, thiocyanate, simple kit method, cassava foods. African Journal of Biotechnology Vol.3(7) 2004: 358-361

Simultaneous determination of nitrite, nitrate, thiocyanate and uric acid in human saliva by capillary zone electrophoresis and its application to the study of daily variations

Simultaneous determination of nitrite (NO 2 −), nitrate (NO 3 −), thiocyanate (SCN −) and uric acid in human saliva was performed by capillary zone electrophoresis using a coated capillary with reversed electroosmotic flow (EOF), using a 100 mM sodium phosphate buffer at pH 6.5 as a running buffer. Saliva samples were deproteinized with acetonitrile and filtered through a membrane filter. The important advantages of the reported method are: simple operation, short analysis time, minimal sample pre-treatment and sample dilution. In order to evaluate the daily variations of the anionic components, the concentrations were determined in the human saliva of four healthy volunteers upon waking and at 2 h intervals during a day.

Determination of Thiocyanate within Physiological Fluids and Environmental Samples: Current Practice and Future Trends

As the toxicological and physiological importance of thiocyanate has become more and more evident during the past 20 years, there has been an increasing interest in this anion. Thiocyanate is a detoxication product of cyanide and its content in human saliva is considered as a biomarker for identification of nonsmokers and smokers. Chronically elevated levels of thiocyanate in body fluids are known to be toxic and its relation to local goiter, vertigo, or unconciousness has been pointed out. On the other hand, thiocyanate-containing waste discharged into rivers is harmful to aquatic life due to its degradation to cyanide in the presence of oxidants. Therefore, precise knowledge of the thiocyanate content in biological fluids and environmental samples is mandatory. An overview of the existing analytical methodologies for thiocyanate is presented and their advantages and limitations are highlighted. This review is intended not only to provide a comparison of the different methods employed, but also to make it possible for the interested reader to quickly find developments and relevant work that have transpired over the past 10 years.

Polished Silver Solid Amalgam Electrode: Further Characterization and Applications in Voltammetric Measurements

Polished silver solid amalgam electrode (p‐AgSAE) appears to be a good alternative to hanging mercury drop electrode (HMDE). The present work focuses on analysis of the electrode material and of the working electrode surface. It has been demonstrated that this electrode can be successfully used in inorganic electrochemical measurements for determination of metal cations, nitrates, and thiocyanates, etc.

Novel selective thiocyanate PVC membrane electrode based on new Schiff base complex of 2.2-[(1,3-dimethyl-1,3-propanediylidene)dinitrilo]bis-benzenethiolato cadmium(ii)

An ion selective electrode for thiocyanate based on a complex as ionophore is described. The influence of membrane composition, pH and interference anions were investigated. The sensor responds to thiocyanate in the linear range from 1 × 10−6–1 × 10−1 M with a slope −58.9 ± 0.5 mV decade−1. The limit of detection is 5 × 10−7 M SCN−. Selectivity coefficients determined with the fixed interference method (FIM) indicate a good discriminating ability towards SCN− ion in comparison to other anions. The proposed sensor has a fast response time of about 5–20 s and can be used for at least 2 months without any considerable divergence in potential. It was applied as indicator electrode in the titration of thiocyanate with Ag+ and in the potentiometric determination of thiocyanate in saliva and urine samples.

Kinetic-Spectrophotometric Determination of Trace Quantities of Thiocyanate Based on Its Landolt Effect on the Reaction of Bromate with Hydrochloric Acid1

A new method for the rapid and sensitive determination of trace quantities of thiocyanate based on its Landolt effect on the bromate-hydrochloric acid reaction was developed. The induction period of the reaction is proportional to the SCN– concentration. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. We were able to determine thiocyanate in the range 2 × 10–7–4 × 10–5 M by this method. The relative standard deviation for 10 determinations of 1.5 × 10–6 M thiocyanate ion is 0.19% and the detection limit of the method was 7.00 × 10–8 M. The method was applied to the determination of thiocyanate in human blood serum and of saliva samples with satisfactory results.

Study of a bis-furaldehyde Schiff base copper(II) complex as carrier for preparation of highly selective thiocyanate electrodes.

A new highly selective thiocyanate electrode based on N,N'-bis-(furaldehyde)-1,2-phenylenediamine-dipicolyl copper(II) complex [Cu(II)-BFPD] as neutral carrier is described. The electrode has an anti-Hofmeister selectivity sequence: SCN->I->Sal->ClO4->Br->NO2->Cl->NO3->SO4(2-)>SO3(2-)>H2PO4- and a near-Nernstian potential linear range for thiocyanate from 1.0x10(-1) to 5.0x10(-6) mol L(-1) with a detection limit 2.0x10(-6) mol L(-1) and a slope of 57.5 mV decade(-1) in pH 5.0 of phosphate buffer solution at 20 degrees C. The response mechanism is discussed on the basis of results from A.C. impedance measurement and UV spectroscopy. The anti-Hofmeister behavior of the electrode results from a direct interaction between the central metal and the analyte ion and a steric effect associated with the structure of the carrier. The electrode has the advantages of simplicity, fast response, fair stability and reproducibility, and low detection limit. The selectivity of electrodes based on [Cu(II)-BFPD] exceeds that of classical anion-sensitive membrane electrodes based on ion exchangers such as lipophilic quaternary ammonium or phosphonium salts. Application of the electrode for determination of thiocyanate in waste water samples from a laboratory and a gas factory, and in human urine samples, is reported. The results obtained were fair agreement with the results obtained by HPLC.

Bis(2-mercaptobenzoxazolato)mercury(II) and bis(2-pyridinethiolato)mercury(II) complexes as carriers for thiocyanate selective electrodes

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on bis(2-mercaptobenzoxazolato)mercury(II) [Hg(MBO) 2] and bis(2-pyridinethiolato)mercury(II) [Hg(PT) 2] complexes as new carriers for thiocyanate-selective electrodes are reported. The electrodes were prepared by coating the membrane solution containing PVC, plasticizer, carriers and additives on the surface of graphite electrodes. Influence of the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses towards thiocyanate over a wide concentration range of 1×10 −6 to 0.1 M, with slopes of 60.6±0.8 and 57.5±1.2 mV per decade of thiocyanate concentration for Hg(MBO) 2 and Hg(PT) 2 carriers, respectively, over a wide pH range of 3–11. The limit of detection for both electrodes was ∼6×10 −7 M. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show fairly good discrimination of thiocyanate over several inorganic and organic anions. The electrodes were successfully applied to direct determination of thiocyanate in saliva and as indicator electrodes in precipitation titrations.

Creation and characteristics of phosphatidylcholine stationary phases for the chromatographic separation of inorganic anions

New stationary phases for chromatographic separation of anions, obtained by loading liposomes made from dimyristolyphosphatidylcholine (DMPC) onto reversed-phase packed columns (C 18 and C 30) are reported. Mono- and divalent anions were used as model analyte ions and retention data for these species were obtained using the DMPC stationary phases and used to elucidate the separation mechanisms involved in this chromatographic system. The DMPC stationary phases can separate anions by either a solvation-dependent mechanism or an electrostatic ion-exchange mechanism, depending upon the relative magnitudes of the negative electrostatic potential ( Ψ (−)) of the phosphate moiety (P −) and the positive electrostatic potential ( Ψ (+)) of the quaternary ammonium groups (N +) on the headgroup of DMPC. If Ψ (+)> Ψ (−), such as in case where Ψ (−) has been reduced either by binding of eluent cations (e.g., H + or divalent cations) onto the P − group of DMPC or by steric screening when a C 30 reversed-phase material was used to support the DMPC, then the overall electrostatic surface potential (and hence also the effective anion-exchange capacity) was generally large and the anions were separated on the basis of an electrostatic mechanism. However, if Ψ (+) was similar to Ψ (−), such as in the case of using a C 18 reversed-phase support and monovalent cations as eluent cations, then the overall electrostatic surface potential and the effective anion-exchange capacity were very small and the analyte anions were separated on the basis of a solvation-dependent mechanism. The DMPC stationary phases were found to be suitable for the direct determination of iodide and thiocyanate in highly saline water samples, such as seawater samples.