Photokinetic voltammetric method for the determination of thiocyanate

Thiocyanate traces have a strong inhibitory effect on the oxidation of Neutral Red by potassium bromate under UV irradiation in diluted phosphoric acid. Neutral Red exhibits a sensitive second derivative oscillopolarographic wave at -0.6 V(vs. SCE) in diluted phosphoric acid and sodium acetate solution. The oscillopolarographic behavior of Neutral Red was selected as indicator component for its photo-activated oxidation. The photochemical reaction rate equation was determined. A detection limit of 0.3 ng mL(-1) (3sigma/k) and a linear calibration curve from 2.0-48.0 ng mL(-1) thiocyanate were obtained. The method was applied to the determination of thiocyanate in urine, saliva and serum with satisfactory results.     

Equilibrium (NAD+/NADH) potential on poly(Neutral Red) modified electrode

The electrochemical regeneration of nicotinamide adenine dinucleotide (NAD⁺/NADH) has been one of the central subjects of bioelectrochemistry during past three decades. We report on the unique chemical electrocatalyst for NAD⁺/NADH regeneration based on electropolymerized Neutral Red. Using poly(Neutral Red) modified electrodes, the reversible polarographic waves of nicotinamide adenine dinucleotide reduction–oxidation and the equilibrium (NAD⁺/NADH) potential were observed. This was impossible using all known catalytic and mediator systems. The unique poly(Neutral Red) based electrocatalyst allowed us to determine the standard (NAD⁺/NADH) potential more precisely (E^′≅0.59 V SCE, pH 6.0).     

Catalytic determination of ultratrace amounts of ruthenium with oscillopolarographic detection

The oscillopolarographic behaviour of Methyl Red in sodium hydroxide medium has been studied, and the results show that the wave at -0.79 V is an irreversible two-electron adsorption wave. A very sensitive and selective catalytic reaction-oscillopolarographic method for the determination of Ru down to 3 ng/l. is described, based on the Ru(III)-catalysed redox reaction of Methyl Red and potassium periodate in hydrochloric acid medium. Potassium thiocyanate is used to quench the reaction and the oscillopolarography is then performed with sodium hydroxide as the supporting electrolyte. The influence of 41 foreign ions has been examined. Ruthenium in ore samples has been determined by the method, with satisfactory results.     

Catalytic determination of ultra trace amounts of tellurium by 2.5-order differential oscillopolarography

A highly sensitive and selective catalytic method with 2.5-order differential oscillopolarographic detection is described for the determination of tellurium, based on its activation effect on the slow Pd(II)-catalyzed reaction of sodium hypophosphite and methyl red in hydrochloric acid medium at 100?°C. Methyl red exhibited a sensitive 2.5-order differential polarographic wave at –0.35 V ¶(vs. SCE) in the supporting electrolyte of pH 5.0 acetate buffer solution and was chosen as the indicating component for the indirect determination of tellurium. A calibration curve of tellurium in the range of 0.02–2.0 ng mL^–1 was obtained by the fixed-time procedure. The detection limit was 0.007 ng mL^–1. Possible interferences by co-existing substances were examined. The new method has been used to analyze trace tellurium in organs of white mice with satisfactory results. RSD was 0.54% to 2.10%, recovery 98.4% to 95.7%. The mechanism is also discussed.     

Chromotropic acid-formaldehyde reaction in strongly acidic media. The role of dissolved oxygen and replacement of concentrated sulphuric acid

The procedure for formaldehyde analysis recommended by the National Institute for Occupational Safety and Health (NIOSH) is the Chromotropic acid spectrophotometric method, which is the one that uses concentrated sulphuric acid. In the present study the oxidation step associated with the aforementioned method for formaldehyde determination was investigated. Experimental evidence has been obtained indicating that when concentrated H₂SO₄ (18 mol l⁻¹) is used (as in the NIOSH procedure) that acid is the oxidizing agent. On the other hand, oxidation through dissolved oxygen takes place when concentrated H₂SO₄ is replaced by concentrated hydrochloric (12 mol l⁻¹) and phosphoric (14.7 mol l⁻¹) acids as well as by diluted H₂SO₄ (9.4 mol l⁻¹). Based on investigations concerning the oxidation step, a modified procedure was devised, in which the use of the potentially hazardous and corrosive concentrated H₂SO₄ was eliminated and advantageously replaced by a less harmful mixture of HCl and H₂O₂.     

Resonance Rayleigh scattering method for the determination of trace amounts of cadmium with iodide-basic triphenylmethane dye systems

In dilute phosphoric acid solution, cadmium (II) reacts with a large excess of I^– to form [CdI₄]^2– which reacts further with basic triphenylmethane dyes such as crystal violet (CV), ethyl violet (EV), methyl violet (MV), brilliant green (BG) or malachite green (MG) to form an ion-association complex. This results in a significant enhancement of resonance Rayleigh scattering (RRS) intensity and the appearance of new RRS spectra. The characteristics of RRS spectra of the ion-association complexes, the influencing factors and the optimum conditions of these reactions have been investigated. The intensity of RRS is directly proportional to the concentration of cadmium from ¶0 to 60 ng mL^–1 for EV and MV systems, 0 to 80 ng mL^–1 for CV system, and 0 to 100 ng mL^–1 for BG and MG systems. The methods exhibit high sensitivities and the detection limits for cadmium are between 0.35 and 2.00 ng mL^–1 depending on the different reaction systems. The new RRS method was applied to the direct determination of traces of cadmium in pure zinc and synthetic water samples.     

Spectrophotometric determination of vanadium(V) with methoxypromazine maleate and its application to vanadium steels and minerals

The reagent in 8-fold excess forms a violet species with vanadium(V) instantaneously in 1–3 M phosphoric acid. The absorption maximum is at 565 nm; the molar absorptivity is 1.65 × 10⁴ l mol^?1 cm^?1. Beer's law is obeyed over the range 0.1–6.5 mg l^?1 vanadium (V); the optimum range is 0.3–6.0 mg l^?1; the Sandell sensitivity is 3.1 ng cm^?2. The method is simple and selective. The method is applicable for the determination of vanadium in vanadium steels and minerals.     

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.     

Determination of undecenoic acid in dermatological preparations by liquid chromatography with direct UV detection

Separation on a ODS reversed-phase column with acetonitrile—0.1% phosphoric acid (65 + 35) as mobile phase provides a simple and rapid method for the determination of undecenoic acid in dermatological preparations. Common preservatives, bactericides and antiseptics do not interfere. Tolnaftate was employed as the internal standard throughout the assay. A linear relationship was established between the peak-area ratio of undecenoic acid to the internal standard and concentration of undecenoic acid over the range 0.01–0.1 ng ml^?1.     

Determination of Protamine and Insulin Using Short-End Injection Capillary Electrophoresis

A fast and inexpensive method for simultaneous determination of total protamine and insulin has been developed using capillary electrophoresis in the short-end injection setup with a bare-fused silica capillary. Optimized background electrolyte consists of 45 mM aqueous solution of phosphoric acid, pH 1.85. Separation is finished within 1 min; total analysis time including preconditioning is 4 min. The method exhibits excellent linearity within the concentration range 2.5–500 μg mL⁻¹ for both analytes. Limits of detection are 1.0 and 0.7 μg mL⁻¹ for protamine and insulin, respectively. Accuracy of the method has been successfully tested on a real sample of Neutral Protamine Hagedorn Insulin (NPH insulin) injection. The background electrolyte employed is inexpensive and experiments have shown that it does not need to be exchanged for at least 20 subsequent analyses.

     

Fast analysis of thiocyanate by ion-pair chromatography with direct conductivity detection on a monolithic column

Fast analysis of thiocyanate by ion-pair chromatography using a silica-based monolithic column and direct conductivity detection was carried out. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e using tetrabutylammonium hydroxide （TBA）-phthalic acid-acetonitrile as eluent. The effects of eluent concentration, eluent pH value, column temperature and flow rate on retention time of thiocyanate were investigated. The optimized chromatographic conditions for the determination of thiocyanate were as follows： 0.25 mmol/L TBA-0.18 mmol/L phthalate-7% acetonitrile （pH 5.5） as eluent, column temperature of 30 ℃, and flow rate of 6.0 mL/min. Retention time of thiocyanate was less than 1 min under the conditions. Common anions （Cl^-, NO3 , SO42 and I^- ） did not interfere with the determination of thiocyanate. Detection limit （S/N = 3） of thiocyanate was 0.96 mg/L. Calibration graph between peak area and the concentration of thiocyanate was linear in the range of 2.0- 100.0 mg/L. Relative standard deviation （RSD） of chromatographic peak area was 1.4% （n = 5）. This method has been applied to the determination of thiocyanate in ionic liquids. Recoveries of thiocyanate after spiking were 100.5%.     

Effect of oxidation-reduction on the extraction of uranium from wet phosphoric acid by DEHPA/TOPO

Uranium is recovered from wet phosphoric acid by DEHPA/TOPO in kerosene. Uranium is present in wet phosphoric acid in the tetravalent and hexavalent states but DEHPA/TOPO extracts uranium in the hexavalent state only. The ratio of U⁴⁺/U⁶⁺ depends on several factors such as the origin of the phosphate rock, the method of preparation of phosphoric acid and the presence of other impurities. Therefore it is important to oxidize the wet acid to convert all uranium to U⁶⁺ before extraction. Uranium is stripped from the solvent by a reverse process where a concentrated phosphoric acid is used under reducing conditions. This paper studies the oxidation of wet phosphoric acid from Homs plant/Syria by H₂O₂ oxidant and the effect of oxidation on extraction coefficientK. It also studies the reduction by iron and its effect on back extraction of uranium from the solvent to phosphoric acid.     

Gleichzeitige oscillopolarographische Bestimmung von Wismut und Blei in mineralischen Rohstoffen

Zusammenfassung Eine Methode zur oscillopolarographischen Bestimmung von Wismut und Blei in mineralischen Rohstoffen wurde ausgearbeitet. Die Abtrennung beider Elemente wurde in einem Arbeitsgang durch Chloroformextraktion der Diäthyldithiocarbamidate aus einer Lösung, die NatriumKaliumtartrat, Tiron, Schwarzenbachs Puffer und Kaliumcyanid enthielt, durchgeführt. Die extrahierten Elemente wurden durch Reextraktion mit 2 m Salzsäure (Pb) und 6 m Salzsäure (Bi) voneinander getrennt.Die oscillopolarographische Bestimmung von Wismut wurde in 3 m Salzsäure durchgeführt. Für Spurenkonzentrationen wurde eine Lösung von 1 m Perchlorsäure und 0,2 m Ammoniumchlorid verwendet.Blei wurde oscillopolarographisch in einer Lösung von 0,1 m Ammoniumthiocyanat, 0,25 m Hexamethylentetramin und 0,5 m Ammoniumperchlorat bestimmt. Die Methode eignet sich zur Bestimmung verhältnism äßig kleiner Mengen bis zu Spurenkonzentrationen von Wismut und Blei. Sie ist verhältnismäßig schnell, denn sie ermöglicht eine fast gleichzeitige Bestimmung beider Elemente aus einer Einwaage. Das Verfahren wurde mit Erfolg bei Erzen angewendet. Der Fehler liegt in einem Bereich von 3–5%.

---

Summary The simultaneous oscillopolarographic determination of bismuth and lead has been worked out: The separation of both elements together from interfering material is carried out by extraction with diethyldithiocarbamidate and chloroform from a medium of sodium potassium tartrate, tiron, Schwarzenbach buffer and potassium cyanide. The extracted elements are subsequently separated by re-extraction with 2 M hydrochloric acid (Pb) and 6 M hydrochloric acid (Bi). The oscillopolarographic determination of bismuth is performed in 3 M hydrochloric acid (in the case of trace concentrations a solution of 1 M perchloric acid and 0.2 M ammonium chloride is applied). For the oscillopolarographic determination of lead a solution of 0.1 M ammonium thiocyanate, 0.25 M hexamethylene-tetramine and 0.5 M ammonium perchlorate is employed. The method is suitable for the determination of low concentrations of lead and bismuth in the range of 10^–5–10^–6 M and is recommended especially for ores. The relative error is ±3–5%.

     

A simple and rapid HPLC‐UV method for the determination of retigabine in human plasma

A simple and rapid high‐performance liquid chromatographic method with ultraviolet detection was developed for the quantitative determination of retigabine, known also as ezogabine, in human plasma. The assay uses a simple solid‐phase extraction for sample preparation and direct injection of the extract into the chromatograph. Flupirtine is used as an internal standard. Chromatographic separation is achieved on a C₁₈ Chromolith column (Chromolith Performance, 100 × 4.6 mm i.d.), using as mobile phase water/acetonitrile/methanol (72:18:10 v/v/v) mixed with 0.1% of 85% phosphoric acid. Isocratic elution is conducted at a flow rate of 1.5 mL min⁻¹. The total duration of a chromatographic run is 7 min. Calibration curves are linear over the 25–2000 ng mL⁻¹ concentration range, with a limit of quantitation of 25 ng mL⁻¹. Other performance characteristics include high precision (intra‐ and inter‐day coefficients of variation ≤12.6%) and high accuracy (99.7%–108.7%). The method is suitable for the investigation of concentration–response relationships in patients receiving therapeutic doses of retigabine.     

Doping phosphoric acid in polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

Polybenzimidazole (PBI) membranes were doped in phosphoric acid solutions of different concentrations at room temperature. The doping chemistry was studied using the Scatchard method. The energy distribution of the acid complexation in polymer membranes is heterogeneous, that is, there are two different types of sites in PBI for the acid doping. The protonation constants of PBI by phosphoric acid are found to be 12.7 L mol^?1 (K¹) for acid complexing sites with higher affinity, and 0.19 L mol^?1 (K²) for the sites with lower affinity. The dissociation constants for the complexing acid onto these two types of PBI sites are found to be 5.4 × 10^?4 and 3.6 × 10^?2, respectively, that is, about 10 times smaller than that of aqueous phosphoric acid in the first case but 5 times higher in the second. The proton conducting mechanism is also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2989–2997, 2007     

Synthesis of N-octylmonoaza-15-crown-5 having a dodecylphosphoric acid functional group and the binding ability toward alkali metal cations

A new N-octylmonoaza-15-crown-5 having an alkylphosphoric acid functional group ( 3c ) was synthesized. It was revealed that 3c selectively transported sodium ion under neutral source phase/acidic receiving phase condition, and selectively transported lithium ion under basic source phase/acidic receiving phase condition. From an ir and ¹³C nmr spectral study of the lithium hydroxide and sodium thiocyanate complexes of 3c , it is suggested that 3c does not incorporate cations into the three dimensional cavity using the crown ring and the phosphoric acid site, but that the crown and the phosphoric acid sites act on the cations independently; only the crown ether site of 3c significantly coordinates to the cations under neutral source phase condition, and the phosphate anion is mainly employed under basic conditions.     

Simultaneous Determination of Three Flavonoids in Rat Plasma by RP-LC After Oral Administration of the Total Flavonoids of Scutellaria barbata

A liquid chromatographic method for the simultaneous determination of three flavonoids, scutellarin (SCU), isoscutellarein-8-O-glucuronide (ISO) and luteolin (LUT) in rat plasma was developed and validated. Following a single-step liquid–liquid extraction with ethyl acetate, the analytes and internal standard (IS) (rutin) were successfully separated on a Diamonsil C₁₈ column using a mobile phase composed of acetonitrile (A)–0.2% phosphoric acid aqueous solution (B) (0–5 min, 20% A–29% A; 5–25 min, 29% A, v/v) at a flow rate of 1.0 mL min^?1. The linear range was 0.044–2.20 μg mL^?1 for SCU, 0.042–2.08 μg mL^?1 for ISO, and 0.056–2.80 μg mL^?1 for LUT, with the correlation coefficients of 0.9995, 0.9989 and 0.9963, respectively. The limit of quantification of SCU, ISO and LUT were 44, 41.6 and 56 ng mL^?1, respectively. The accuracy of assay was between 88.4 and 103.0%. The inter-day and intra-day precisions (RSD) were less than 10.5%. The developed method was simple, rapid and applied successfully to study the pharmacokinetics of SCU, ISO and LUT after oral administration of the total flavonoids of Scutellaria barbata.     

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.     

Simultaneous analysis of ten low‐molecular‐mass organic acids in the tricarboxylic acid cycle and photorespiration pathway in Thalassiosira pseudonana at different growth stages

A method using high‐performance liquid chromatography coupled with tandem mass spectrometry was developed for the simultaneous determination of organic acids in microalgae. o‐Benzylhydroxylamine was used to derivatize the analytes, and stable isotope‐labeled compounds were used as internal standards for precise quantification. The proposed method was evaluated in terms of linearity, recovery, matrix effect, sensitivity, and precision. Linear calibration curves with correlation coefficients >0.99 were obtained over the concentration range of 0.4–40 ng/mL for glycolic acid, 0.1–10 ng/mL for malic acid and oxaloacetic acid, 0.02–2 ng/mL for succinic acid and glyoxylic acid, 4–400 ng/mL for fumaric acid, 20–2000 ng/mL for isocitric acid, 2–200 ng mL⁻¹ for citric acid, 100–10000 ng mL⁻¹ for cis‐aconitic acid, and 1–100 ng mL⁻¹ for α‐ketoglutaric acid. Analyte recoveries were between 80.2 and 115.1%, and the matrix effect was minimal. Low limits of detection (0.003–1 ng/mL) and limits of quantification (0.01–5 ng/mL) were obtained except cis‐aconitic acid. Variations in reproducibility for standard solution at three different concentrations levels were <9%. This is the first report of the simultaneous analysis of ten organic acids in microalgae, which promotes better understanding of their growth state and provides reference value for high‐yield microalgae cultures.     

Electrochemical and spectroscopic studies of metal cyclam complexes with thiocyanate. Evidence for mixed ligand complex formation

Complexes of Ni^II, Co^II and Cu^II containing the macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane (cyclam), and their ability to form mixed ligand complexes with thiocyanate have been studied. These complexes in a 1:2 mole ratio, exhibit new absorption peaks at 450, 538 and 512 nm respectively. Addition of thiocyanate to the nickel–cyclam complex (1:2:5 mole ratio) led to the formation of a purple complex, exhibiting three distinct new absorption peaks at 330, 455 and 662 nm. A purple complex (1:2:10 mole ratio) separated, having absorption peaks at 352, 503 and 693 nm in CHCl₃. The Co^II–cyclam complex with thiocyanate in the same mole ratio exhibits two absorption peaks at 437 and 519 nm without appearance of any precipitate. The Cu^II–cyclam complex with thiocyanate did not form a mixed ligand complex. Electrochemical studies also confirmed the complex formation of Ni^II–cyclam with the thiocyanate with the appearance of two new oxidation peaks close to 1.25 and 1.60 V versus Ag/AgCl in H₂O and CHCl₃. The Co^II–cyclam complex with thiocyanate exhibited an oxidation peak at 1.2 V versus Ag/AgCl, while no peak was observed for the Cu^II–cyclam complex with thiocyanate. Based on spectroscopic and electrochemical studies the geometry of the complex has been evaluated.