A simple synthesis of α, β-unsaturated aldehydes by 1,3-carbonyl transposition through one carbon homologation

α,β-Unsaturated aldehydes are conveniently prepared from ketones through their β-diethoxymethyl derivatives by sodium borohydride reduction followed by acid-catalysed rearrangement of the resulting diacetal carbinols.     

Pulsed reagent introduction through a membrane reactor for flow-injection systems

A method of intermittent reagent introduction, functionally equivalent to stop-go pumping, is described. A pneumatically pressurized reagent reservoir is used to deliver liquid through a high-speed on/off valve to the outer channel of an annular tube assembly. Except for this single entry point, the outer channel is otherwise sealed. The inner flow channel bearing the principal flow stream contains a short microporous membrane tube. When the reagent delivery valve is activated, reagent flows radially inward through the membrane into the principal flow stream.     

Mass spectrometry of metal compounds. Evidence of C?O cleavage in and effect of temperature on the mass spectra of chloropentacarbonylmanganese

The mass spectrum of Mn(CO)₅Cl has been studied at 70 eV and at varying inlet temperatures of 20–250°C. Like the heavier metal carbonyl derivatives, Mn(CO)₅Cl exhibits peaks due to carbido fragments. The spectrum run at 100°C shows the characteristic pattern of Mn₂(CO)₁₀ which originates from the formation and recombination of the Mn(CO)₅ radical. The spectral pattern changes further at an elevated temperature (250°C) showing the formation of Mn₂(CO)₈Cl₂. The effect of pyrolysis has been discussed.     

Determination of mycophenolic acid in human plasma by high-performance liquid chromatography

The development, validation and evaluation of high-performance liquid chromatography (HPLC) method for quantifying mycophenolic acid in human plasma is described. The method involved protein precipitation using acetonitrile, after addition of terazosin as an internal standard. Separation was achieved with a reversed-phase C18 column (250 mm x 4.6 mm) employing UV detection at 215 nm. The mobile phase consisted of 0.02 M potassium dihydrogenphosphate solution adjusted to pH 6.9 with 2 M potassium hydroxide solution-acetonitrile (80:20 (v/v)) at a flow rate of 1.5 ml/min. The total run time was 21.0 min. The assay was linear from 0.2 to 25 microg/ml with goodness of fit (r2) greater than 0.99 observed with three precision and accuracy batches during validation. The observed mean recoveries were 89.3 and 98.0% for drug and internal standard, respectively. The applicability of this method to pharmacokinetic studies was established after successful application during a 34-subject bioavailability study. The method was found to be precise, accurate and specific during the study.     

Portable flow-injection analyzer with liquid-core waveguide based fluorescence, luminescence, and long path length absorbance detector

We describe a multifunctional flow analysis instrument that is portable ( cm, 2.3 kg) for facile field deployment. Using a 50 cm long Teflon^® AF tubing as final reaction and optical measurement conduit, we combine a liquid-core waveguide (LCW) based fluorescence detector that is transversely illuminated by an addressable light emitting diode array, a chemiluminescence (CL) detector and an absorbance detector with a solid-state broadband (400-700 nm) source. Several illustrative experiments have been carried out to test the performance of the instrument in different detection modes. A S/N=3 limit of detection (LOD) of 0.25 μg l⁻¹ for chromium(VI) was established using the diphenylcarbazide chemistry, and an LOD of 5 μg l⁻¹ was similarly established for Al(III), using Pyrocatechol Violet (PCV) as the chelating chromogenic dye, in both cases using long path absorption detection. The LOD for aqueous hydrogen peroxide was 16 nM using a fluorescence method based on the formation of thiochrome from thiamine and 4 nM by a luminol chemiluminescence method. With a Nafion membrane diffusion scrubber (DS), the LOD was 8.0 pptv for gaseous hydrogen peroxide by the fluorescence method.     

Continuous on-line feedback based flow titrations. Complexometric titrations of calcium and magnesium

The methodology of continuous feedback-based flow titrations and the principle of compensating errors [Anal. Chem. 72 (2000) 4713; Anal. Chim. Acta 435 (2001) 289] were applied to the determination of calcium and magnesium ions with EDTA. The flow of the titrant, EDTA, varied linearly in response to a controller output voltage while the total flow (F_T, the sum of the metal ion sample flow and the titrant flow) was held constant. The sample was pre-doped with a metal ion indicator; the status of the indicator color in the mixed stream was monitored by an optical detector and was used for governing the controller output as well as for interpreting the results of the titrations. The titrant flow initially ramped upward linearly. As a change in the color corresponding to the equivalence point was sensed by the detector, the controller output (instantaneous value V_H) reversed its ramp direction, thus decreasing the titrant flow linearly at the same ramp rate. When the predefined absorbance corresponding to the equivalence point was sensed again, the controller voltage (instantaneous value V_L) was ramped in reverse once more, going upward. Because of the lag time between a change in the controller output and its effect being sensed by the detector, the controller voltage corresponding to the actual equivalence point was the average of V_H and V_L. Continuous sensor-governed operation of the controller resulted in a triangular waveform. The mean of this waveform during any cycle gives the equivalence point controller voltage V_E. This principle allowed true titrations with good reproducibility (0.2-0.7% R.S.D.) and throughput (33-42 s per titration).     

Simultaneous flow-injection measurement of hydroxide, chloride, hypochlorite and chlorate in Chlor-alkali cell effluents

A flow injection method is reported for the simultaneous determination of hydroxide, chloride, hypochlorite, and chlorate ions that exist in Chlor-alkali cell effluents in concentrations ranging from sub-millimolar to several molar. The hydroxide concentration is determined by the heat of neutralization of the injected sample into an acidic carrier stream and the chloride concentration is calculated from the measured conductance data. For the measurement of hypochlorite and chlorate, colorimetric iodometry is used. Iodide is oxidized to iodine by OCl(-) and ClO(3)(-) in acid solutions. While room temperature is sufficient for the reaction between OCl(-) and I(-), the reaction between ClO(3)(-) and I(-) requires an elevated temperature. The different reaction requirements are utilized to differentiate between NaOCl and NaClO(3), respectively.     

Wet effluent parallel plate diffusion denuder coupled capillary ion chromatograph for the determination of atmospheric trace gases

We describe an inexpensive, compact parallel plate diffusion denuder coupled capillary IC system for the determination of soluble ionogenic atmospheric trace gases. The active sampling area (0.6x10 cm) of the denuder is formed in a novel manner by thermally bonding silica gel particles to the surface of Plexiglas plates. The effluent liquid from the parallel plate diffusion denuder is collected and preconcentrated on a capillary preconcentrator column before analysis using a capillary ion chromatograph. Using SO(2) as the test gas, collection efficiency is essentially quantitative at air sampling rates up to 500 ml min(-1). The system provides a limit of detection (LOD) of 1.6 parts per trillion for SO(2) for a 10 min sampling period.     

Redox chemistry of [Fe2(CN)10]4−. Part 5. Reaction with thiourea

The reaction of the dimeric iron(III) complex [Fe2(CN)10]4– with a large excess of thiourea, tu, takes place in a series of stages, the first two of which have been examined in detail. The first stage is a one equivalent outer sphere electron transfer to form [Fe2– (CN)10]5– and the radical cation tu+· which dimerises to form the disulfide tu22+. There is kinetic evidence for the formation of a significant proportion of a precursor complex [Fe2(CN)10]4–·tu at high concentrations of tu. The second stage involves cleavage of the mixed valence dimer to yield [Fe(CN)5tu]2– and [Fe(CN)5H2O]3–. On standing, substitution of H2O by tu and oxidation by air occurs slowly, and finally all of the original iron is observed as [Fe(CN)5tu]2–.