Determination of Vitamins E and D3 in Some Preparations by High-Performance Liquid Chromatography with Indirect Spectrophotometric Detection

The behavior of vitamins E and D₃ was studied under the conditions of reversed-phase high-performance liquid chromatography with the use of unmodified and modified mobile phases. Acetonitrile modified with chlorophyll (a + b) (Chl) and tetraphenylporfyrin (H₂TPP) was selected for the indirect spectrophotometric detection of vitamins. It was demonstrated that detection limits are 2.3 g (8.33 × 10^–6 M H₂TPP, = 404 nm) and 3.5 ng (8.6 × 10^–6 M Chl, = 430 nm) for vitamin E and 0.12 g (3.0 × 10^–7 M H₂TPP, = 420 nm) for vitamin D₃. Pharmaceutical preparations containing vitamins E and D₃ were analyzed.     

Differential pulse-polarographic determination of adenine, adenosine and mono-, di- and tri-phosphate of adenosine

Summary The application of differential pulse polarography for the quantitative trace determination of adenine, adenosine, adenosine-3-monophosphate, adenosine-5-monophosphate, adenosine-5-diphosphate and adenosine-5-triphosphate has been investigated. Optimum conditions were found (pulse amplitude 100 mV, scan rate 2 mV · s^–1, drop time 2s). The effect of pH was studied, and the optimum pH was determined to give the highest sensitivity. The detection limit for adenine, adenosine and A-5-MP is ca. 2.2 ×10^–6M, 1.5×10^–6M and 2.99×10^–6M, respectively; for the other adenosine nucleotides it is 4.45×10^–6M. The validity of this method is supported by the constancy of the i _DPP/C values.

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Bestimmung von Adenin, Adenosin sowie Adenosinmono-, -di- und -triphosphat durch Differential-Puls-Polarographie

Zusammenfassung Die Anwendbarkeit der Differential-Puls-Polarographie zur quantitativen Spurenbestimmung von Adenin, Adenosin, Adenosin-3-monophosphat, Adenosin-5-monophosphat, Adenosin-5-diphosphat und Adenosin-5-triphosphat wurde geprüft und optimale Bedingungen ausgearbeitet (Pulsamplitude 100mV, Abtastgeschwindigkeit 2 mV/s, Tropfzeit 2s). Der Einfluß des pH-Wertes wurde untersucht und der optimale pH für maximale Empfindlichkeit bestimmt. Die Nachweisgrenzen für Adenin, Adenosin und A-5-MP betragen etwa 2,2 · 10^–6M, 1,5 · 10^–6M bzw. 2,99 · 10^–6M, für die übrigen Adenosinnucleotide 4,45 · 10^–6M. Die Brauchbarkeit der Methode ergibt sich aus der Konstanz der i _DPP/C-Werte.

     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Isotope exchange reaction between NaCl-36 and triphenyltin chloride in dioxane-water (8020% w/w) and ethanol-water (9010% w/w) mixed solvents has been studied at 25, 35 and 50 °C. The exchange reaction was found to proceed via a bimolecular S_N2, limiting mechanism with reaction rates depending on the solvent used. Inhibition of the exchange in ethanol-water is probably due to solvation of chloride ion through hydrogen bond formation. The rate laws for the exchange reactions are: R_e=3.24×10⁹ e^–65550/RT [Rh₃SnCl] [NaCl] in dioxanewater and R_e=6.61×10⁸ e^–69600/RT [Ph₃SnCl] [NaCl] in ethanol-water, where is the degree of dissociation of NaCl and R_e is the rate of exchange in mol l^–1 s^–1. The activation parameters H^*, S^* and G^* are reported.     

Solvent extraction and spectrophotometric including graphite furnace atomic absorption determination of molybdenum in the environment

A selective and sensitive method for the extraction and microgram determination of molybdenum (VI) with hydroxamic acid as yellow molybdenum-hydroxamate complex from acidic medium is described. The molybdenum-PCPPSAHA complex has _max 388 nm, molar absorptivity 5.0 × 10³l mol^–1 cm^–1. The system obeys Beer's law in the range of 1–28 g/ml of molybdenum(VI). Sandell's sensitivity is 0.0192 g cm² and stoichiometry of the complex is 12, molybdenum: PCPPSAHA while mixed complex molybdenum-PCPPSAHA-morin has _max 400 nm and molar absorptivity 5.9 × 10³lmo1^–1 cm^–1 and stoichiometry of the complex is 121.The molybdenum is determined by graphite furnace atomic absorption spectrophotometry after directly pipetted the extract into the furnace which increases the sensitivity 20 fold.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Extractive spectrophotometric determination of dioxouranium(VI) with the sodium salt of hexamethyleneiminecarbodithioate

The optimum conditions for the extractive spectrophotometric determination of dioxouranium(VI) with hexamethyleneiminecarbodithioate(HMICdt) have been established. Dioxouranium(VI) reacts with this ligand at pH 4.5 to form a yellowish-orange uncharged 12 metal-ligand complex which can be extracted by chloroform. The calibration graph was linear in the range of 1–20 g ml^–1 of dioxouranium(VI) at 335 nm. The molar absorptivity of the extracted species is 5.952×10³ l mol^–1 cm^–1 with Sandell's sensitivity of 0.04 g cm^–2. The average of 10 determinations of dioxouranium was 49.75 g for the samples containing 50 g of U(VI) and the variation from the mean at 95% confidence limit was 49.75±0.5955.     

Untersuchung der Ionengleichgewichte in Tetrahydrofuranlösungen des 2-Naphthonitril-Natriums

With the aid of conductometric measurements the ion equilibria inTHF solutions of 2-naphthonitrile sodium were studied. It was established that in the concentration interval of 10^–4–10^–5 mol/l the equilibrium ion pairs—free ions is predominant . The ion pairs are contact (average interion distance about 4.1 Å). In the temperature interval of 25 to 40° the heat of dissociation –H=3.1 kcal/mol, whereas between –40 and –70°–H is 1.26 kcal/mol. At higher concentrations (10^–2–10^–3 mol/l) triple ion formation is observed.     

Effect of Sodium Thiosulfate on the Kinetics of Electron–Ion Processes in Powdered Silver Chloride

The results of a microwave photoconductivity study on the effect of pretreatment of a silver chloride powder with sodium thiosulfate (STS) aqueous solutions on the kinetics of electron–ion processes in silver chloride are reported. At an UV light fluence of <10¹⁴ photon/cm^–2 per pulse, photoresponse decay after the end of the pulse consisted of two exponential components over the entire concentration range 10^–8–10^–2 mol STS/mol AgCl examined. The amplitude of the components and the ratio between the slow ^s and fast ^f components depended on the sodium thiosulfate concentration, which was due to the formation of an additional number of new electron traps in AgCl. An analysis of the kinetics in terms of models taking into account various types of decay of an excess electron made it possible to obtain data on the depth of both old traps (0.45 eV) and new STS-created traps (0.45–0.63 eV) in AgCl.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H₂C=N and HC=NH radicals, respectively (the molar absorption coefficients are k ₂₇₀ 2.7 × 10²l mol^–1cm^–1and k ₂₉₀ 1.5 × 10²l mol^–1cm^–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with 300 nm, can belong to the cyanide ions (CN^–) and H₂C=N⁺cations (the molar absorption coefficients of the ions are k _ion= (0.4–1.0) × 10²l mol^–1cm^–1). In the photobleaching of -irradiated HCN ( = 236–280 nm), H₂C=N⁺radicals were additionally formed by the photoinduced reaction of electron transfer from the CN^–anion to the H₂C=N⁺cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.     

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.     

Chemiluminescent determination of vanadium in steel

Summary A chemiluminescent method for the determination of vanadium in steel with cinchomeronic hydrazide as analytical reagent is proposed. The optimum conditions are pH 11.75 (phosphate buffer), 1.0×10^–3 mol/l cinchomeronic hydrazide, 6.6×10^–3 mol/l hydrogen peroxide and 2.8×10^–3 mol/l V(IV). The maximum chemiluminescent emission is obtained at 420 nm. A linear relationship exists in the range of 0.04–1.00 g/ml of V(IV) with a 3.6% variation coefficient at 0.50 g/ml of V(IV) level for ten replicates. Cobalt(II), copper(II) and chromium(VI) show strong interference and a chloroform extraction procedure with -benzo-inoxime is recommended to avoid these interferences. This method has been applied to determine vanadium in a certified steel with excellent results.Presented at Euroanalysis VII     

A new route to the asymmetric Schiff base ligands. The ligand exchange in [Mo(CN)<Subscript>3</Subscript>O(salhy)]<Superscript>2−</Superscript> ion. Kinetics and mechanism

The kinetics of the ligand exchange in (PPh₄)₂[Mo(CN)₃O(salhy)]. 6H₂O (Hsalhy = salicylaldehyde hydrazone) by a solvent molecule and by 2,2-bipyridine (bpy) have been studied in EtOH. For the ligand exchange by a solvent molecule the pseudo-first order rate constant equals k _obs = 3.2 (±0.2) × 10^–3 s^–1 (t=25 °C), H =67 (± 7) kJ mol^–1, S =–75 (±23) J mol^–1 K^–1, while for the exchange by a bpy molecule k _obs=3.5 (±0.2) × 10^–3 s^–1 (t=25 °C), H =56 (±7) KJ mol^–1, S = –104 (±8) J mol^–1 K^–1. It was found, that all reactions proceed via the same mechanism which involves the chelate ring opening cis to the Mo=O bond. The mechanism of the reaction was proposed and was proved by the synthesis of (PPh₄)₂[Mo(CN)₃O(N-pic)]. 2.5H₂O (N-pic denotes that the nitrogen of picolinic acid is trans to Mo=O) by ligand exchange in EtOH, while in aqueous solution the O-pic analogue is formed exclusively.     

Novel Coated-Wire Membrane Sensor Based on Bis(Acetylacetonato) Cadmium(II) for the Determination of Chromate Ions

A new electrode based on a complex of chromate ions with bis(acetylacetonato) cadmium(II) as a carrier was developed for detection of chromate in aqueous solution. The electrode exhibited linear response with Nernstian slopes of –28.8±0.5mVper decade for chromate within the concentration range of 2.5×10^–6–0.1M. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plots was almost 1.0×10^–6M. The electrodes exhibited good selectivities for chromate. The response time of the electrode was <25s over the entire concentration range. The electrode can be used in the pH range 8.0–12.0 for chromate. It was used as an indicator electrode in titration with Pb(NO₃)₂ and for the determination of chromate ion in wastewater samples.     

Enzyme sensor for L-lactate using differential pulse amperometric detection

An enzyme sensor using differential pulse (DP) amperometric detection has been developed based on the measurement of the reduction current of the oxidized form of -nicotinamide adenine dinucleotide (NAD⁺) consumed by an enzyme reaction. This biosensor has the definite advantage to prevent interference caused by electrooxidative species such as ascorbate and uric acid and exhibits higher sensitivity and selectivity in comparison to the classical DC amperometric detector. The linear detection range of this biosensor was 5.0×10^–5 — 5.0×10^–4 mol/l and the relative standard deviation (R.S.D.) at 2.5×10^–4 mol/l was 5.0%.     

All-Solid-State PVC Membrane Ag+-Selective Electrodes Based on Diaza-18-Crown-6 Compounds

Two diaza-crown ether compounds were synthesized and evaluated as Ag⁺-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75±10mV per decade) over the concentration range of 1×10^–1 to 7×10^–6M of Ag⁺ ion and a detection limit of 3×10^–6M, at a wide range of pH (pH 4–7). The response time of the electrode was fast (less than 10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag⁺ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag⁺-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag⁺ ion in solution.     

Gas Chromatographic Determination of Diacetylmorphine with Mass Spectrometric Detection

The possibility of determining diacetylmorphine traces in various matrices by gas chromatography with mass spectrometric detection is demonstrated. Diacetylmorphine can be reliably determined by gas chromatography–mass spectrometry in the range 0.02–7.5 g/mL. A procedure is developed for the quantitative determination of diacetylmorphine and its concomitants, including acetylated opioid derivatives, in forensic samples. The detection limit for diacetylmorphine without preconcentration is 0.01 g/mL. The detection limit in the selective-ion monitoring mode with preconcentration is 1 × 10^–4 g/mL.     

Di-μ-hydroxo bridge-cleavage reactions between [Co(nta)(μ-OH)]2 2− and different monodentate ligands

The cleavage of the di--hydroxo bridges of [Co(nta)(-OH)]₂ ^2– by dimethylaminopyridine (dmap) and pyridine (py) has been investigated. [Co(nta)(-OH)]₂ ^2– equilibrates rapidly in aqueous basic solutions with a mono--hydroxo bridged Co^III species [pK _OH = 3.26(2)] and both these species react with the incoming ligand to form different ion associated species which react in the subsequent rate-determining steps (k ₁ and k ₂) to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co--OH-Co(nta)(L)]^2–. Values for k ₂, the preferred mono--hydroxo bridged substitution pathway for these reactions, vary between 6.8(2) × 10^–4 s^–1 (py) and 8.5(4) × 10^–2 s^–1 (dmap).     

Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study

Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm^–3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB²⁺ chelate. At 25 °C, the rates and activation parameters for the reactions Ni_II + AEB NiAEB²⁺ and Ni^II + AEBH⁺ NiAEB²⁺ + H⁺ are k _f ^L(dm^–3 mol^–1 s^–1) = (2.17 ± 0.24) × 10³, H (kJ mol^–1) = 40.0 ± 0.8, S (JK^–1 mol^–1) = – 47 ± 3 and k _inff ^pHL (dm³ mol^–1 s^–1) = 33 ± 10, H (kJ mol^–1) = 42.0 ±2.7, S (JK^–1 mol^–1) = – 72 ± 9. The dissociation of NiAEB²⁺ was acid catalysed and k _obs for this process increased linearly with [H⁺] in the 0.01–0.15 mol dm^–3 (10–30 °C) range with k _H(dm³ mol^–1s^–1) (25 °C) = 329 ± 6, H (kJ mol^–1) = 40 ± 2 and S (JK^–1 mol^–1) = – 61 ± 8. The results also indicated that the formation of NiAEB²⁺ involves a chelation-controlled, rate-limiting process. Analysis of the S ° data for the acid ionisation of AEBH _inf2 ^p2+ and the formation of NiAEB²⁺ showed that the bulky AEBH⁺ ion has a solvent structure breaking effect as compared to AEB [s _aqS ° (AEBH⁺) – s _aq ° (AEB) = 69 JK^–1 mol^–1], while AEBH _inf2 ^p2+ is a solvent ordering ion relative to NiAEB²⁺ [s _aq° (NiAEB²⁺) – ovS _aq ° (AEBH _inf2 ^p2+ ) = 11 JK^–1 mol^–1].Author to whom all correspondence should be directed.