Determination of molecular weights and Mark–Houwink constants for soluble electronically conducting polymers

Intrinsic viscosities and gel permeation chromatography data were used to evaluate the Mark–Houwink constants of the soluble electronically conducting polymer, poly(3-hexylthiophene) (P3HT):K and a are 2.28 × 10^-3 cm³/g and 0.96, respectively, in tetrahydrofuran (THF) at 25°C. Mark–Houwink constants were used to calibrate gel permeation chromatography (GPC) columns for P3HT. Number-average molecular weights of P3HT determined with modified calibration curves agreed well with those determined by an absolute method, embulliometry. Molecular weights estimated using unmodified polystyrene calibration procedures were significantly larger than true values.     

Effect of the copolymer composition on the K and a constants of the Mark–Houwink equation: Styrene–methyl methacrylate random copolymers

This article reports a study of the effect of composition in styrene–methyl methacrylate random copolymers on K and a constants in the Mark–Houwink equation. Copolymers with a variety of compositions and chain lengths were prepared through a controlled free‐radical copolymerization, with benzyl diethyldithiocarbamate and tetraethyl thiuram disulfide as iniferters. The synthesized products were analyzed with several techniques, including Fourier transform infrared, ¹H NMR, gel permeation chromatography, and viscometry. By relating the determined constants K and a of various copolymers to their composition, we found that the constant varied nonlinearly with the composition. The constant a decreased with increasing poly(methyl methacrylate) (PMMA) content in the copolymer molecule up to 60 wt %. After that, the constant increased with the PMMA content, reaching the value of the PMMA homopolymer. However, the constant K initially increased with the PMMA content up to a critical composition (60 wt %) and subsequently decreased with further increasing PMMA content. These results suggest that the molecular weight of a polystyrene–PMMA random copolymer of known composition cannot be approximated with a simple linear equation comprising the K and a values of each relevant homopolymers. The aforementioned trends are qualitatively discussed in relation to some possible sequential distribution in the copolymer molecules and the resulting conformation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 562–571, 2002; DOI 10.1002/polb.10119     

A simple and rapid method for the determination of particle size in emulsions from ultrasound data

Oil droplet size in emulsions can be determined from ultrasound velocity and attenuation spectra. We show that explicit solutions of the acoustic scattering matrix may be used to rapidly calculate a mean particle size for a limited but useful range of particle sizes. Our technique is well suited to in-line measurement. Both modelling and experiment indicate that the main scattering mechanism is thermal scattering. Calculations using the explicit solutions have been compared with experimental results from sunflower oil-in-water emulsions.     

A rapid method for the determination of organic nitrogen and phosphorus based on a single perchloric acid digestion

Results of nitrogen determinations obtained by perchloric acid digestion of organic matter under reflux were found to be equivalent to those obtained by the conventional sulfuric acid Kjeldahl method. A rapid determination of nitrogen and phosphorus was thus possible after a single perchloric acid digestion. Nitrogen was determined by nesslerization and phosphorus by a conventional molybdenum blue technique. The method devised was found satisfactory for a great variety of natural products and pure organic compounds, including materials containing all kinds of tertiary nitrogen.     

Remarks on the determination of kinetic constants from thermogravimetric data

The methods for determining kinetic constants may have significant effects on the estimation results. The two-variable linear correlation method leads to values of the kinetic constants for which the difference between the calculated and measured values is comparable to or greater than the measurement precision. The non-linear method for calculating kinetic constants by searching for the minimum of the error function \(S1 = \sum\limits_{i = 1}^N {(m_{it} - m_i )^2 /N}\) , wherem _i andm _i are the measured and calculated values, respectively, andN is the number of experimental data, gives very precise results. A simple calculating technique is necessary for the fitting of the minimum point and the confidence region limit at the significance level. An appropriate calculation was made for metal oxidation according to the parabolic law.     

A new method for determination of intrinsic viscosity

The Huggins and Kraemer equations generally used to determine intrinsic viscosity frequently do not yield identical results, and their constants often do not add up to 1/2 as is mathematically required. To overcome these difficulties an equation has been deduced which through linear plots gives unambiguous intrinsic viscosities, constants which meet the 1/2 condition, as well as two other flow constants. Extensive tests of the equation with precise data on solutions of poly(methyl methacrylates) and polystyrenes in benzene and toluene confirm the validity of the new equation in every respect. It is further shown that the four constants involved are interrelated, and that it is possible to express the values of three of these in terms of the fourth.     

On the determination of molecular weight distributions from sedimentation–diffusion equilibrium data at a single rotor speed

The problem of inferring molecular weight distributions from concentration gradient data taken at sedimentation-diffusion equilibrium for a single rotor speed is ill posed: significantly different distributions correspond to concentration gradients which differ so slightly that they cannot be distinguished by the experiment. It is this intrinsic property of the problem which accounts for the lack of success of the several schemes proposed for its solution. Integral equation theory is applied to show explicitly just what can be inferred with bounded error. Several methods for recovering this information are discussed and applied to example problems.     

A computational method for approximate evaluation of ionization constants from potentiometric data

A general equation is given for the evaluation of proton dissociation constants from potentiometric data. The method is applicable to monobasic acids, and also polybasic acids, where the successive dissociation steps may or may not overlap. A computer program was employed for the calculations. The method was tested by evaluation of the constants for 22 acids, from monobasic to octobasic, with satisfactory agreement with literature data.     

Derivative spectrophotometric method for determination of acidity constants of single step acid-base equilibria

A general derivative spectrophotometric method for determination of acidity constants is developed. The method appears suitable in cases when classical spectrophotometry cannot be employed due to little differences in the absorption spectra of conjugated acid-base pairs. Based on theoretical considerations, seven variants of the method have been established and their validity was checked, determining acidity constants of lorazepam and flurazepam as model compounds.     

Temperature variation effects on the determination of acidity constants through the internal standard–capillary electrophoresis method

The internal standard (IS) CE (IS‐CE) method is an interesting alternative to other methods for the determination of acidity constants of compounds. Although some of the advantages of this method have been already reported, the method has not been tested yet as regards to temperature effects. This has been the aim of this work, where it is demonstrated that the method can be applied successfully for the determination of pK_as at different temperatures, if the acidity constant of the IS at the desired temperature is known. The fact of obtaining the acidity constants at different temperatures allows the calculation of some thermodynamic quantities, such as the molar standard enthalpy and the molar standard entropy in a fast way. It is also demonstrated that if the IS and the test compound have similar standard enthalpy increment, the IS compensates uncontrolled possible temperature fluctuations (e.g., due to Joule heat) inside the capillary obtaining reliable acidity constant values at the desired temperature.     

Error analysis of the rapid lifetime determination method for single exponential decays with a non-zero baseline

The precision of Ashworth's baseline rapid lifetime determination method (BRLD) for treating an exponential decay on a constant baseline has been evaluated as a function of fitting region, noise level, and baseline contribution. Results have been compared with the weighted non-linear least squares method (WNLS). For the lifetime using the optimum fitting regions, the precision of the BRLD ranges from slightly better than, to about a factor of two worse than, WNLS depending on noise level and baseline contribution. For the preexponential factor, the BRLD is very close in performance to WNLS. Error surfaces for different conditions and possible applications are described.     

A rapid spectrophotometric method for determination of piperazine

A spectrophotometric method has been developed for the determination of piperazine and its salts (citrate, phosphate, and tartrate) without prior separation, based on the interaction of piperazine or any of its salts with phenothiazine and N-bromosuccinimide in aqueous methanol. The products exhibit absorption maxima at 448, 595 and 645 nm. Measurements are made at 595 nm. Beer's law is obeyed in the concentration range 0.5-5 mug/ml for piperazine salts and 0.5-3 mug/ml for piperazine hexahydrate. The method is rapid, simple and successful for analysis of some pharmaceutical preparations.     

A rapid iodometric method for the determination of copper and zinc

A method has been described for the iodometric simultaneous determination of zinc and copper. Copper is determined in the presence of sufficient KCNS and a small amount of KI. This is followed by the titration of the iodine equivalent to the zinc, which is liberated by the addition of potassium ferricyanide solution.Interference is eliminated completely by keeping the solution neutral or just acid with phosphoric acid.Within the range under investgation, results are obtained which are accurate to ± 0.7%.     

A simple and rapid chemical method for the determination of cephalosporins

A simple and rapid chemical assay for cephalosporins is described. It is a simple modification of the colorimetric determination of penicillins in which the narrow spectrum beta-lactamase (penicillinase) is replaced by a broad spectrum beta-lactamase (cephalosporinase) produced by Enterobacter cloacae. The method can be used for assay of fermentation broths as well as for pure cephalosporins.     

A sensitive and rapid method for determination of pyrophosphatase activity

A new, rapid and sensitive method of measuring the rate and amount of PPi hydrolysis is described. The method is based on registration of small pH changes, caused by decrease of hydrogen-ion concentration during the pyrophosphatase reaction. With this detected value of hydrogen-ion concentration change and the buffering capacity of each reaction mixture determined by titration, the rate and amount of PPi hydrolysis can be calculated. The results obtained by pH method are in good agreement with values determined by direct phosphate analysis. The described method can be applied to the continuous determination of pyrophosphatase activity in chromatophores, mitochondria, crude extracts or purified enzymes.     

A modified micro-dumas method for rapid determination of nitrogen

Summary The Pregl-Dumas method for the estimation of nitrogen has been modified to make it suitable for the rapid performance of a number of analyses in series. The usual combustion tube for carbon and hydrogen determination is used, and the tube filling and procedure are modified.

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Zusammenfassung Die Stickstoffbestimmung nach Pregl-Dumas wurde abgeändert, um die schnelle Durchführung von Serienanalysen zu ermöglichen. Das für Kohlenstoffbestimmungen übliche Verbrennungsrohr wird benutzt. Die Substanz wird in einem Schiffchen eingeführt, auf das eine Rolle aus oxydiertem Kupferdrahtnetz folgt.

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Résumé Modification de la méthode dePregl-Dumas pour permettre le dosage rapide de l'azote en série. Emploi du tube habituellement utilisé pour le microdosage du carbone et de l'hydrogène avec modification du remplissage et de la technique.