Simple and specific microdetermination of organoiodine via oxygen flask combustion

A rapid, simple, and reliable procedure for specific microdetermination of organoiodine is described. This procedure consists of oxygen flask combustion followed by an argentimetric titration with an iodide ion-selective electrode as indicator. Some advantages of this procedure over mercurimetric titration currently used in an AOAC method are detailed.     

Starting SCF calculations by superposition of atomic densities

We describe the procedure to start an SCF calculation of the general type from a sum of atomic electron densities, as implemented in GAMESS-UK. Although the procedure is well known for closed-shell calculations and was already suggested when the Direct SCF procedure was proposed, the general procedure is less obvious. For instance, there is no need to converge the corresponding closed-shell Hartree-Fock calculation when dealing with an open-shell species. We describe the various choices and illustrate them with test calculations, showing that the procedure is easier, and on average better, than starting from a converged minimal basis calculation and much better than using a bare nucleus Hamiltonian.     

Correct measurement of birefringence in a nonuniform medium

The birefringence of an object is usually obtained from its retardation. For an object of variable refractive index and optic axis orientation, a matrix procedure should be used for relating the retardation to the birefringence. There are many cases in the literature where this correct procedure has not been used. The correct procedure is illustrated for the case of a polymer spherulite.     

An optimization of the procedure for the calculation of Hosoya's index

An optimized procedure for the calculation of Hosoya's topological index is presented. The procedure has been implemented in PASCAL. The described procedure could be simply modified for calculations of different modifications of Hosoya's index and Merrifield-Simmon's index. As an example, four useful modifications of Hosoya's index are defined.     

Estimation of limits of detection and determination in X-ray fluorescence analysis by the dependence of the relative standard deviation on analyte concentration

An experimental dependence of the relative standard deviation on analyte concentration of hyperbolic type, characterizing the precision of quantitative chemical analysis, was used to estimate the limits of detection and determination in the X-ray fluorescence analysis. A method is proposed for the determination of their values using the approximation of the experimental dependence of the relative standard deviation on the analyte concentration by a power function. The choice of the values of the relative standard deviation, being criteria for the estimation of these limits, is substantiated. A concept of the limits of detection and determination of an analytical procedure is formulated, according to which the limit of detection of an analytical procedure is an objective value depending only on the precision of determinations, and the limit of determination of an analytical procedure is a subjective value depending not only on the precision of determinations but also on the requirements to their limiting (admissible) accuracy. The limits of detection and determinations of an analytical procedure found by this approach completely characterize the possibilities of an analytical procedure in determining low concentrations of analytes. The proposed approach can be used for the estimation of the limits of detection and determination of analytical procedures and in other methods of chemical analysis with the hyperbolic dependence of the relative standard deviation on the analyte concentration.     

Preparative isolation of angiotensin-converting enzyme from human lung.

Angiotensin-converting enzyme from human lung was purified to apparent homogeneity using a five-step purification procedure consisting of ammonium sulfate precipitation, ion-exchange chromatography on DEAE Sephadex A-50, gel permeation on Sephadex G-200, chromatofocusing on a polybuffer exchange (PBE 94) column and high-performance liquid chromatographic gel permeation on a Bio-Sil TSK-250 column. This procedure gave an approximately 700-fold purification with a 20% yield compared to a 550-fold purification and a 1% yield with an affinity chromatography-based procedure. The 20-fold greater yield of the five-step procedure offers a major advantage for preparative use in the structural characterization of angiotensin-converting enzyme.     

A procedure of determining potential energy surfaces of triatomic molecules from inversion of spectroscopic data

In this paper,we have suggested an iterative procedure of optimization of the linearparameters in an analytic potential energy function for a triatomic molecule,by combining both variational and second order perturbation methods.The most important feature of this procedure is that the objective function is an analytical expression which can be optimized easily.The application to the water molecule is presented.     

Determination of the quaternary ammonium ion components of Aliquat 336 by electrospray mass spectrometry

A procedure is described for the identification and determination of the quaternary ammonium ion components of the commercial solvent extraction reagent Aliquat 336 using Electro Spray Mass Spectrometry (ESMS). The procedure is extremely rapid when compared with an existing procedure based on gas chromatography and produces comparable results in terms of accuracy and precision.     

Analysis of ethoxylated alcohol surfactants in water by HPLC

Summary An HPLC procedure for the determination of linear alcohol polyethoxylates in surface water, waste water, and detergents is described. After extraction of the alcohol ethoxylates into an organic phase the alcohol ethoxylates are derivatized with phenyl isocyanate to apply an UV detection. A reversed-phase HPLC procedure is used to separate different ethoxylate species by their different alkyl chain length. A normal phase procedure is employed to separate alcohol polyethoxylates by their different number of ethoxylate groups in the molecule.     

Comparison study of RNAA and ICP-MS for the determination of ultra-traces of Th and U in geological and cosmochemical samples

In order to determine thorium and uranium traces in geochemical and cosmochemical samples, we developed an ICP-MS procedure, in which an anion-exchange step was introduced after sample digestion to separate major matrix elements, leading to decrease the dilution factor and increase the sensitivity for Th and U. The ICP-MS procedure was compared to the RNAA procedure which we recently developed for the same purpose. Both ICP-MS and RNAA procedures developed were found to yield similar detection limits (sub ppb) for Th and U.     

Determination of Arsenic as the Oxidate by Ion Chromatography

Abstract

An ion chromatographic procedure is described for the analysis of arsenic as the oxo anion. The procedure involves oxidations of the arsenic to arsenate in an aqueous solution and injection onto an anion separator column, Comparison is made with a standard wet chemical procedure, and data is presented on reproducibility. In addition, there is a brief discussion of the applicability of this method to the determination of other oxo anions.     

Quantitative analysis of morphine in dried blood spots by using morphine-d3 pre-impregnated dried blood spot cards

Two different internal standard dried blood spot (DBS) pre-impregnation procedures (prior to blood spotting) were investigated. In the first procedure DBS pre-impregnation is performed by immersing the DBS card fully into an internal standard solution. In the second procedure pre-impregnation is performed by pipetting a certain volume of an internal standard solution onto the DBS card. Morphine-d3 was used as the model compound for all experiments. The pre-impregnation procedure by immersing was further investigated with respect to homogeneity of impregnation, influence of different blood spotting techniques and the influence of spotting different blood volumes on the internal standard distribution, calibration and stability of pre-impregnated cards. Finally, the immersing procedure was used for the analysis of morphine in dried blood spots and the results were compared to the conventional procedure in which the internal standard morphine-d3 was added to the extraction solvent. The new pre-impregnated cards couple simplicity of operation and convenient use in the field to results equivalent to the conventional procedure.     

Diastereoselective Synthesis of Chiral Pyrrolidine and Piperidine Ring Systems

A diastereoselective method for the synthesis of chiral pyrrolidine and piperidine ring containing compounds was described. The protocol of bromination followed by aminocyclization furnishes an easily handled while highly efficient procedure for the intramolecular amidation of an isolated double bond. High diastereomeric excess was observed in this synthetic procedure.     

Fractionation of polyvinyl acetate and the use of a new method of GPC data processing

Experimental results are given for the characterization of polyvinylacetate fractions and calculation of their Mark-Houwink constants in THF at 25°. Use is made of GPC and viscometry; the results are processed according to the procedure established by Ambler but an alternative procedure for the selection of the Mark-Houwink a value has been tried. The Mark-Houwink constants obtained by this procedure and through fractionation are substantially in agreement.     

Convenient,multicomponent, one-pot synthesis of highly substituted pyridines under solvent-free conditions

Highly substituted pyridine derivatives have been accessed through an efficient, one-pot, multicomponent reaction of aldehydes, malononitrile, and ammonium acetate in the presence of triethylamine as a catalyst under solvent-free conditions. This procedure affords the desired products in high purity and has advantages such as short reaction time, excellent yields, and simple workup procedure. This procedure affords the desired products in moderate to high yields and has such advantages as short reaction time and simple workup procedure.     

Photometric determination of mercaptans in light petroleum products

A procedure for the photometric determination of mercaptan sulfur in light petroleum products was developed. This procedure is based on the formation of colored analytical species in an aqueous extract to an alkaline solution of sodium nitroprusside. The determination level was 3 mg/L at a sample volume of 1 mL.     

Development and validation of a near infrared method for the analytical control of a pharmaceutical preparation in three steps of the manufacturing process

A near infrared diffuse reflectance spectroscopy (NIRS) procedure for the quantitative control analysis of the active compound (otilonium bromide) in a pharmaceutical preparation in three steps of the production process (blended product, cores and coated tablets) and a methodology for its validation are proposed. The analytical procedure is composed by two consecutive steps. First, the sample is identified by comparing its spectrum with a second derivative spectral library. If the sample is positively identified, the active compound is quantified by using a previously established partial least squares (PLS) calibration model. The procedure was validated by studying repeatability, intermediate precision, accuracy and linearity. To this end, an adaptation of ICH (International Conference on Harmonisation) validation methodology to an NIR multivariate calibration procedure is proposed. The relative standard error of prediction (RSEP) was ≤ 1% and the suitability of the procedure for control analysis was confirmed by the results obtained analysing new production samples produced over a three-month period.     

Development and validation of a near infrared method for the analytical control of a pharmaceutical preparation in three steps of the manufacturing process

A near infrared diffuse reflectance spectroscopy (NIRS) procedure for the quantitative control analysis of the active compound (otilonium bromide) in a pharmaceutical preparation in three steps of the production process (blended product, cores and coated tablets) and a methodology for its validation are proposed. The analytical procedure is composed by two consecutive steps. First, the sample is identified by comparing its spectrum with a second derivative spectral library. If the sample is positively identified, the active compound is quantified by using a previously established partial least squares (PLS) calibration model. The procedure was validated by studying repeatability, intermediate precision, accuracy and linearity. To this end, an adaptation of ICH (International Conference on Harmonisation) validation methodology to an NIR multivariate calibration procedure is proposed. The relative standard error of prediction (RSEP) was < or = 1% and the suitability of the procedure for control analysis was confirmed by the results obtained analysing new production samples produced over a three-month period.     

Quantitative analysis of the Maksikold multicomponent anticatarrhal preparation by pH-gradient high-performance liquid chromatography

A procedure was developed for the rapid analysis of a new multicomponent anticatarrhal medication Maksikold by high-performance liquid chromatography (HPLC). The possibility of the simultaneous determination of all active substances in the preparation, including ascorbic acid, is an advantage of the proposed procedure. For the efficient resolution of the peaks of analytes and interfering additives, a mobile phase with the pH varied in the course of an experimental run was used. The procedure was used to analyze pilot samples of the preparation. The results obtained exhibit a high precision.     

Determination of Chloroacetic Acids in Drinking Water by Reaction Gas Chromatography

A procedure was developed for determining chloroacetic acids in drinking water. The procedure is based on solid-phase extraction followed by the conversion of chloroacetic acids to trifluoroacetic esters and their separation and determination by gas–liquid chromatography with an electron capture detector. Esterification conditions were optimized. The procedure was used for analyzing samples of drinking water.