Liquid chromatographic–electrospray mass spectrometric determination of cyclosporin A in human plasma

A rapid, sensitive and selective liquid chromatography–mass spectrometry (LC–MS) assay has been developed for determination of cyclosporin A (CyA) in human plasma; cyclosporin B (CyB) was used as internal standard (IS). The method utilized a combination of a column-switching valve and a reversed-phase symmetry column. The mobile phase was a 25:75 (v/v) mixture of 10% aqueous glacial acetic acid and acetonitrile. Running time per single run was less than 10 min. Sample preparation included C₈ SPE of human plasma spiked with the analyte and internal standard, evaporation of the eluate to dryness at 50°C under N₂ gas, and finally reconstitution in the mobile phase. Detection of cyclosporin A and the IS was performed in selected ion-monitoring mode at m/z 601.3 and 594.4 Da for CyA and IS, respectively. Quantitation was achieved by use of the regression equation of relative peak area of cyclosporin to IS against concentration of cyclosporin. The method was validated according to FDA guideline requirements. The linearity of the assay in the range 5.0–400.0 ng mL^–1 was verified as characterized by the least-squares regression line Y=(0.00268±1.9×10^–4)X+(0.00078±1.8×10^–3), correlation coefficient, r=0.9986±1.1×10^–3 (n=48). Intra and inter-day quality-control measurements in the range 5.0–350.0 ng mL^–1 revealed almost 100% accuracy and 9% CV for precision. The mean absolute recovery of CyA was found to be 84.01±9.9% and the respective relative recovery was 100.3±9.19. The limit of quantitation (LOQ) achieved was 5 ng mL^–1. Eventually, stability testing of the analyte and IS in plasma or stock solution revealed that both chemicals were very stable when stored for long or short periods of time at room temperature or –20°C.     

Detection of ethanol in human body fluids by headspace solid-phase micro extraction (SPME)/capillary gas chromatography

Summary Ethanol has been found extractable from human whole blood and urine samples by headspace solid-phase micro extraction (SPME) with a Carbowax/divinylbenzene-coated fiber. After heating a vial containing the body fluid sample with ethanol, and isobutanol as internal standard (IS) at 70°C in the presence of (NH₄)₂SO₄, a Carbowax/divinylbenzene-coated SPME fiber was exposed in the headspace of the vial to allow adsorption of the compounds. The fiber needle was then injected into a middle-bore capillary gas chromatography (GC) port. The headspace SPME-GC gave intense peaks for both compounds; a small amount of background noises appeared, but did not interfere with the detection of the compounds. Recoveries of ethanol and IS were 0.049 and 0.026% for whole blood, respectively, and 0.054 and 0.085% for urine, respectively. The calibration curves for ethanol showed excellent linearity in the range of 80–5000 mg L^–1 for whole blood and 40–5000 mg L^–1 for urine; the detection limits for both samples were 20 and 10 mg L^–1, respectively. The data on actual determination of ethanol after the drinking of beer are also presented for two subjects.     

The behaviour of plutonium in aqueous basic media

Behaviour of Pu(IV) and Pu(VI) in basic media has been investigated by studying their stabilities and quantitative determination by spectrophotometry. Beer's law was found to be obeyed in the range of 1·10^–3 to 5·10^–3 M Pu(IV) at 485 nm peak with a molar absorption coefficient of 95M^–1· cm^–1 in sodium carbonate medium. In case of Pu(VI), in the same medium Beer's law was obeyed in the concentration range of 2·10^–3 to 1·10^–2M at 550 nm with a molar absorption coefficient of 50M^–1·cm^–1. Distribution ratios of Pu(IV) and Pu(VI) for their sorption on Al₂O₃ and Amberlyst A-26 (MP) resin from bicarbonate and carbonate media have been determined. High distribution ratios obtained indicate the feasibility of decreasing the plutonium content of basic carbonate streams in reprocessing. 10% breakthrough capacities for Pu(IV) and Pu(VI) with these exchangers during column operations have also been determined.     

On the characteristics and mechanism of the radiation-induced chain reaction between sulfur dioxide and molecular oxygen in acid solutions

Characteristics of the -induced chain reaction between sulfur dioxide and molecular oxygen in perchloric and sulfuric acid media in the presence of Ce(III) ions have been studied. The concentration effects of dissolved oxygen (0.2·10^–3–9.4·10^–3 mol/dm³, sulfur dioxide (0.3·10^–1–2.0·10^–1 mol/dm³ and Ce(III) (0.2·10^–3–4.8·10^–3 mol/dm³) and dose rate (0.26·10¹⁹–1.0·10¹⁹ eV/dm³·s) on the radiation — chemical yield of oxygen consumption G(–O₂) and accumulation of sulfate G(HSO ₄ ^– ), have been investigated. The reaction proceeds with G(–O₂) reaching 10²–10³ molecule/100eV in a catalytic regime. The reaction rate in perchloric acid medium is 3–4 times lower than that in the sulfuric acid medium and depends on the SO₂, O₂ and Ce(III) concentrations, the reaction order varying from 1.0 to 0 and/or in the reverse direction. The mechanism of the process involves chain propagation with 3 stages and 3 intermediates: SO₃H, HSO₅ and Ce(IV). The catalytic effect is caused by the interaction of HSO₄ with Ce(IV) ions followed by their reduction when interacting with SO₂, yielding SO₃H radicals. Chain termination may be due to one or two of the three intermediates or due to all three particles, the kinetics depending on this. Kinetic equations describing the experimental data have been obtained.     

Rapid determination of telmisartan in pharmaceuticals and serum by the parallel catalytic hydrogen wave method

The polarographic characteristics of telmisartan have been investigated in 0.8 mol L^–1 NH₃.H₂O–NH₄Cl (pH 8.9)–0.01 mol L^–1 H₂O₂ as supporting electrolyte. The results demonstrate that the polarographic reduction wave at ca. –1.30 V in the absence of H₂O₂ is a catalytic hydrogen wave, and the reduction wave enhanced by H₂O₂ is a so-called parallel catalytic hydrogen wave. The analytical sensitivity of the parallel catalytic hydrogen wave is ca. 60 times higher than that of the corresponding catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave a novel method has been developed for determination of telmisartan by linear sweep polarography. The calibration curve is linear in the range 2.0×10^–8–2.0×10^–6 mol L^–1 and the detection limit is 1.0×10^–8 mol L^–1. The precision is excellent with relative standard deviations of 2.6% at a concentration of 1.0×10^–7 mol L^–1 telmisartan. The proposed method has been applied to the direct determination of the telmisartan in capsule forms and biological samples. The proposed method has been proved to be advantageous over existing CZE and MEKC methods in simplicity, rapidity, and reproducibility.     

Preparation,characterization and electrical conductivity of new heterobimetallic chalcogenates and their 1,10-phenanthroline adducts

New mixed metal chalcogenate coordination polymers, MPb(SCN)₂(SeCN)₂ [M = Co^II, Ni^II or Hg^II], Ag₂-Pb(SCN)₂(SeCN)₂, and the complex heterobimetallic salts, [M(phen)₃][Pb(SCN)₂(SeCN)₂][M = Co^II or Ni^II; phen = 1,10-phenanthroline] that have been prepared and characterized by elemental analyses, i.r. and u.v.–vis. spectra, and by powder XRD patterns. Their solid state electrical conductivities have been investigated, show _rt in the 10^–10–10^–6 S cm^–1 range, and semiconduct at 313–383 K with band gaps in the 0.28–0.91 eV range. [Co(phen)₃][Pb(SCN)₂(SeCN)₂], exhibits a remarkable increase, i.e. 10⁴ order of magnitude, in conductivity at higher temperature, which reflects a disordered metallic system where charge carriers have difficulty in crossing the non-conducting barrier at low temperature.     

Polarographic behaviour of 2-benzilidenimino-benzohydroxamic acid (2-BIBH) and 2-BIBH-Mo(VI) system

The polarographic behaviour of 2-benzilideniminobenzohydroxamic acid (2-BIBH) solutions and of 2-BIBH solutions in the presence of Mo(VI) have been studied by using differential pulse polarography and cyclic voltammetry. The polarographic characteristics of the resulting waves have been studied and possible mechanisms of the processes involved have been proposed. A linear relationship has been observed betweenI _p and Mo(VI) concentration in the range 2×10^–6 to 1.6×10^–5 M when using 3×10^–4 M 2-BIBH. Standard deviations of 5.6×10^–8 and 1.2×10^–8 M were found for 3×10^–6 and 8 × 10^–6 M Mo(VI), respectively.     

Tin(IV) complexes ofSchiff bases derived from salicylaldehyde and aminoalcohols

11 and 12 molar reactions of tin(IV) chloride with theSchiff bases, HO–C₆H₄CHNROH [where R=–(CH₂)₂–, –CH₂–, –CH(CH₃)–, –(CH₂)₃–, and –CH(C₂H₅)CH₂–] have been studied in different stoichiometric ratios and derivatives of the type SnCl₄(SBH₂) and SnCl₄(SBH₂)₂ (whereSBH₂ represents theSchiff base molecule) have been isolated. These have been characterised by elemental analysis, conductivity measurements and I.R. spectral studies.     

Solvent Extraction Separation of Th(IV) and U(VI) with PC-88A

Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO₃ acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10^–2M and 2.·10^–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR₄·4HR and UO₂R₂·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%.     

Transport study of V(V), Zn(II) and Be(II) using supported liquid membranes

V(V), Zn(II) and Be(II) have been studied to test oxine and tri-n-butylphosphate (TBP) as carriers for transport through supported liquid membranes in polypropylene film. All the three types of ions can be passed through such membranes using oxine in case of V(V) and TBP in case of Zn(II) and Be(II). Maximum flux of metal ions has been observed from 0.01M H₂SO₄ for V(V) (3.22·10^–6 mol·m^–2·s^–1) and 2M HCl containing 3M CaCl₂ for Zn(II) solution (1.4·10^–6 mol·m^–2·s^–1). Low flux was observed in case of Be(II) since the membrane was affected by sulphocyanide group and did not remain hydrophobic. Mechanism of transport for these metal ions have been proposed separately. Distribution coefficient data for V(V) have also been evaluated to determine theoretical values of the permeability coefficient, and compared with experimental values.     

Characterization of europium(III) carbonate complexes in simulated groundwater by solvent extraction

The complex formation of Eu(III) by bicarbonate/carbonate ions has been studied at 0.1 M ionic strength and 25°C using synergistic solvent extraction system of 1-nitroso-2-naphthol and 1,10-phenanthroline in chloroform. Concentrations of bicarbonate (5·10^–3 to 1·10^–1 M) and carbonate (5·10^–4 to 1·10^–2 M) ions in the aqueous phase have been varied in the pH range of 8.0 to 9.1 to simulate ground and natural water compositions. Under these conditions, the following species have been identified: Eu(HCO₃)²⁺, Eu(HCO₃)₂ ⁺, Eu(CO₃)⁺ and Eu(CO₃)₂ ^–. Their conditional formation constants (log ) have been calculated as 4.77, 6.74, 6.92 and 10.42, respectively. These values suggest that the carbonate complexes of Eu(III) are highly stable.     

Formation and decomposition of thin rhodium oxide films

Interaction of O₂ with Rh (poly) and Rh (100) has been studied by Auger Electron Spectroscopy and thermal desorption method at O₂ pressures of 10^–5–10³ Pa and at 400–1600 K. At P(O₂)<10^–5 Pa chemisorption of O₂ occurs, at P(O₂)=10^–5–10^–1 Pa surface oxides are formed, at P(O₂)>1.0 Pa a bulk Rh₂O₃ oxide starts to grow. The growth of rhodium oxide film proceeds via the Cabrera-Mott mechanism. Its decomposition occurs via a mechanism including electron transfer across the oxide film, O₂ desorption from the surface layer and rearrangement of the oxide layer.     

A Potentiometric and Spectroscopic Investigation of Copper(II)– and Zinc(II)–Orotate Complex Equilibria Under Physiological Conditions

A quantitative study of zinc(II) and copper(II) complex formation with orotic acid has been performed under physiological conditions (37°C; 0.15 mol-dm^–3 NaCl) using the glass electrode potentiometric technique. Several species have been identified within the pH range 2–10 for the metal-to-ligand concentration ratios investigated. Three mononuclear complexes, ML, ML₂, and ML₂H_–1, have been characterized with both metals. In addition, the polynuclear species M₃L₂H_–2 has been found with copper(II). Formation constants for all these species have been calculated with the help of the SUPERQUAD computer program. UV absorption and IR spectroscopic measurements combined with speciation calculations have been used to confirm corresponding structures.     

Die kinetische polarographische Stufe des Urans in Gegenwart von Chlorat-Ionen

An increase of the 2nd polarographic uranium(VI) wave has been observed in the presence of chlorate ions in HClO₄–NaClO₄, or HClO₄–NaClO₄–NaCl supporting electrolyte, resp. The polarographic measurements at different temperatures and at various perchloric acid concentrations show that this increase is due to a kinetic U(III)-U(IV) current. The activation parameters of the U(III)-U(IV) oxidation reaction with ClO₃ ^– have been calculated usingKautecky's method.The approximately 5fold increase of the 2nd polarographic wave allows the determination of small amounts of uranium (10^–5–10^–6 mole/l).

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Mit 2 Abbildungen     

Tetrakisisopropoxy tantalum(V)O,O′-alkylene dithiophosphate complexes

Summary Tetrakisisopropoxytantalum(V) alkylene dithiophosphato complexes, (G=–CMe₂CMe₂–, –CHMeCHMe–, –CH₂CMe₂CH₂– and –CH₂CEt₂CH₂–) have been prepared from equimolar ratios of tantalum(V) isopropoxide and alkylene dithiophosphoric acids in benzene. These moisture-sensitive compounds, which are soluble in common organic solvents and are monomeric, have been characterized by elemental analysis, molecular weight determinations and by their i.r. and n.m.r. spectra. An octahedral geometry is suggested in which the ligand is bidentate.     

Influence of molar ratios of precursor,catalyst, solvent and water on monolithicity and physical properties of TMOS silica aerogels

In continuation to our earlier work on aerogels, the experimental results on the monolithicity and physical properties of silica aerogels as a function of the molar ratios of tetramethoxysilane (TMOS) precursor, catalyst (NH₄OH), methanol (MeOH) solvent and water, are reported. The molar ratios of NH₄OH/TMOS, MeOH/TMOS and H₂O/TMOS were varied from 7.1 × 10^–6 to 9.6 × 10^–1, 1 to 90 and 1 to 18 respectively. It has been found that larger molar ratios of NH₄OH/TMOS (10^–2), MeOH/TMOS (13 to 60) and H₂O/TMOS (>10) resulted in transparent but cracked aerogels, and very low molar ratios of these combinations gave monolithic but less transparent or opaque aerogels. The best quality silica aerogels, in terms of monolithicity, transparency and low density, have been obtained with TMOS:MeOH:H₂O:NH₄OH in the molar ratio of 1:12:4:3.7 × 10^–3 respectively. The aerogels have been characterized by density, optical transmission, surface area and porosity measurements. The results have been discussed by taking into account the hydrolysis and condensation reactions, and syneresis effects.     

Preconcentration of neptunium by supported liquid membranes for luminescent analysis of environmental samples

The possibilities of liquid membrane preconcentration of neptunium from environmental samples of different nature have been studied. The use the solid-supported liquid membrane containing a trioctylmethylammonium nitrate carrier allows to achieve preconcentration factors of 10²–5×10². The teflon solid support does not interact with the luminescent matrix (CaF₂, PbMoO₄) during calcination at 900 °C, so it makes practical to measure the neptunium content by luminescence without reextraction to aqueous solution. As a result, the detection limit of neptunium is lowed down to 10^–13 g ml^–1 and 5×10^–13 g g^–1 for pure solutions and soils, respectively.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.     

Gas-phase combination reactions of SF4 and SF5 with F in plasmas of SF6

Reactions of both SF₄ and SF₅ with F have been studied at 295 K in a gas-flow reactor sampled by a mass spectrometer. The rate coefficient for the combination reaction of F with SF₄ to produce SF₅ was found to increase from (0.9 to 3.0)×10^–12 cm³ s^–1 when the helium bath gas number density was increased from (2 to 26)×10¹⁶ cm^–3. The values obtained here are three orders of magnitude higher than a recent estimate of the high-pressure value based on the modelling of photochemical studies. The experimental results have been compared with RRKM and master equation calculations in which a simplified Gorin model has been used to determine the structure of the transition state. These calculations show that reasonable agreement can be obtained between the experimental data and the calculation if a small (2 KJ/mol) activation energy is assumed. The rate coefficient for the reaction between SF₅ and F to produce SF₆ was found to be independent of helium bath gas number density within the range given above. The value obtained for the rate coefficient was 9×10^–12 cm³ s^–1 with an uncertainty of a factor of 2. This value is close to that of 1×10^–11 cm³ s^–1 computed from the simplified Gorin model and to the value of 1.7×10^–11 cm³ s^–1 deduced from modelling of photochemical experiments.     

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.