Determination of chemical composition

The strict regulations of the pharmaceutical industry have a significant effect on the quality control of final products, demanding the use of reliable and fast analytical methods. The capacity that the technique has for the simultaneous determination of several APIs with no need of, or with minimum, sample preparation has considerably increased its application in pharmaceutical analytical control. The main limitation of NIR is the relatively low sensitivity that limits the determination of APIs in preparations when their concentration is less than 0.1%. Nevertheless, instrumental improvements allow the determination below this limit depending on the nature of the analyte and the matrix, with comparable errors to the ones obtained with other instrumental techniques. The reference list presents an ample variety of analytical methodologies, types of samples, nature of analyte and calibration models. A detailed treatment of each one is beyond the scope of 

Paracetamol Tablet Drug determination of grinded tablets in reflectance mode. Standard error of calibration (0.48%m/m) and prediction (0.71 %m/m) 32 

Dexketoprofen Gel Non-destructive drug quantitation method of a hydrogel in transflectance mode 35 

Acetylsalicylic acid Tablet Non-destructive quantitation method in three different formulations. Reflectance and transmittance modes compared 146 

Otilonium bromide Powder and tablet Non-destructive quantitation method for QC of three production steps (blend, cores and coated tablets). Validated method following ICH guidelines. Relative errors lower than 1 % 147 

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Trathnigg, B., Determination of chemical composition of polymers by SEC with coupled density and RI detection. I. Polethylene glycol and polypropylene glycol, /. Liq. Chromatogr., 13, 1731, 1990. 

In HRTEM, very thin samples can be treated as weak-phase objects (WPOs) whereby the image intensity can be correlated with the projected electrostatic potential of crystals, leading to atomic structural information. Furthermore, the detection of electron-stimulated XRE in the electron microscope (energy dispersive X-ray spectroscopy, or EDX, discussed in the following sections) permits simultaneous determination of chemical compositions of catalysts to the sub-nanometer level. Both the surface and bulk structures of catalysts can be investigated. 

Radioisotopes are widely used in die measurement of process variables, including the level of liquids and solids in tanks, silos, and other vessels, the density and specific gravity of fluids and solids, the thickness of sheets and coatings, the moisture content of soils and other solids, the mass flow of materials in pipelines or on belts, and the determination of chemical composition of raw materials, in-process materials, and end-products. Representative examples of these applications are given in Table 6. 

Illustrative applications include the determination of stereochemical structure, and conformational preferences. 9 Another application is the determination of chemical composition and chemical sequence distributions in copolymers. A final example is the study of relaxation processes and molecular motions in general, including the determination of transition temperatures from changes in resonance line widths. 

In the field of chemical measurements, the question as to which are the national measurement standards is far from being completely answered. There is no doubt, however, that primary reference materials, e.g. high-purity substances which are ultimately necessary as reference points, will play a role as national (or even better international) measurement standards. But these alone will not be sufficient. As the task of chemical analysis is usually the determination of chemical composition, national reference points closer to this task, namely standard reference mixtures, are also required, and if the preparation of these is not feasible, e.g. due to instability problems, devices and procedures furnishing well-known compositions with small uncertainties must also be included as national measurement standards. All these kinds of national references or standards are currently in use or under development. 

On-line SEC-NMR has successfully applied to the determination of chemical composition distribution in ethylene-propylene-diene terpolymers (EPDM) by the use of H-NMR at 750 MHz [24], EPDM containing 2-ethylidene-5-norbornene (ENB), as a diene... 

The Physical Methods of Chemistiy is a multivolume series that includes Components of Scientific Instruments (Vol. I), Electrochemical Methods (Vol. II), Determination of Chemical Composition and Molecular Structure (Vol. Ill), Microscopy (Vol. IV), Determination of Structural Features of Crystalline and Amphorous Solids (Vol. V), Determination of Thermodynamic Properties (Vol. VI), Determination of Elastic and Mechanical Properties (Vol. VII), Determination of Electronic and Optical Properties (Vol. VIII), Investigations of Surfaces and Interfaces (Vol. IX), and Supplement and Cumulative Index (Vol. X). 

When one of the constituents, A or B of a copolymer A-B, has an ultraviolet (UV) absorption and the other does not, a UV detector-refractive index (RI) combined detector system can be used for the determination of chemical composition or heterogeneity of the copolymer. A point-to-point composition, with respect to retention volume, is calculated from two chromatograms and a variation of composition is plotted as a function of molecular weight. The response factors of... 

High-efficiency filtration is the most common method of collecting particulate mailer for the determination of chemical composition. Chemical analysis of filter. samples provides information on the composition of the aerosol averaged over all particle sizes and over the time interval of sampling. For a constant gas-sampling rate, the mass concentration of species i averaged over particle size and time is related to the size compo.sition probability density function as follows ... 

We come now to one of the principal difficulties in the field of aerosol measurements, namely, the determination of chemical composition. The difficulties stem from a number of factors. Aerosols formed under uncontrolled circumstances such as many industrial emissions or the ambient aerosol are often multicomponent. Compo.sitlons differ significantly from particle to particle an individual particle may be a highly concentrated solution droplet containing insoluble matter such as chains of soot particles. The size composition probability density function (Chapter I) can be used to characterize the chemicals and size properties of such systems (but not their morphology). 

Mori S. (1988), Determination of chemical composition and molecular weight distributions of high-conversion styrene-methyl methacrylate copolymers by liquid adsorption and size exclusion chromatography. Anal. Chem., 60,1125-1128. 

In Table 8.3, analytical data published by Turner [173], Timell [172], Bhatia and Gupta [23], and McGovern [109] are given. These data differ significantly from the data of Whitford [191] and others cited by Harris [58]. The procedures for determination of chemical composition have been standardized and are described in numerous publications, including those of Turner [173], Wise, and Jahn [195]. 

Philipsen, H. J. A. Determination of chemical composition distribution of synthetic polymers, J. ChromatogrA 2004, 1037, 329-350. 

Exact mass measurement can aid in determining chemical composition. Every isotope (except carbon-12 which is assigned exactly 12.000 00 Da) has a unique, noninteger mass. Exact mass measurement thus allows determination of chemical composition. With sufficient resolution it is possible to distinguish between carbon monoxide (CO, 27.995 Da) and nitrogen (N2, 28.006 Da) by exact mass measurement. 

Several techniques are available that allow the size distribution of an aerosol to be determined in real time, but the determination of chemical composition, which has traditionally been done by impaction methods, is slow and yields only an average composition of the ensemble of particles in a given size range. It is essential, therefore, that new techniques be developed to allow the characterization of both the physical properties and chemical composition of aerosols, and that these operate on a time-scale that allows changes in the aerosol composition to be determined in real time. 

Winefordner, J. D. Epstein, M. S. Physical Methods of Chemistry Vol. IIIA, Determination of Chemical Composition and Molecular Structure Wiley New York, 1987,... 

The liquid inclusions analysis in the primary evaporites enables determination of chemical composition of primary solutions/brines from which the sulphates crystallized, as well as... 

K. Ikegaya, M. Iwamoto, J. Uozumi, R. K. Cho. Determination of chemical composition of Japanese green tea by near-infrared spectroscopy. M. Iwamoto, S. Kawano, eds, 2nd International NIRS Conference. Tsukuba, Japan Korin Publishing Co., 1990. 

J.L. DeBouver, B.G. Cottyn, L.O. Fiems, C.V. Boucque. Determination of chemical composition of beef by NIRS. In Bridging the Gap Between Data Analysis ondNIR Applications, K.I. Hildrum, T. Isaksson, T. Naes, A. Tandberg, eds. Ellis Horwood, 1992, p. 339-344. 

One of the main purposes of measuring NIR data is the determination of chemical composition or physical properties in a quantitative way. The principle of the measurement procedure for quantitative analysis is based on recording the NIR spectra of reference samples (the number depending on the number of components or parameters to be determined) of known composition. The levels of the constituents or the physical parameters are determined by independent, conventional analytical or physical methods. Then the set of reference spectra and the independently determined values of the parameters under investigation are used by a selected statistical method to build a calibration. This enables unknown samples to be evaluated with regard to the individual parameters of interest. The accuracy of the NIR technique depends upon the validity of the calibration data set, which must incorporate the entire range of concentrations that will be determined by the instrument. This set must contain samples with varying ratios of each component. NIR calibrations do not typically extrapolate or interpolate well across concentrations. Typical calibration sets include more than... 

Determination of Chemical Composition Distribution by Dual Detection Based on detection with independent concentration detectors, this approach provides information on the chemical composition of copolymers or polymer blends and the variation with the molar mass [26]. An independent detector signal is required for each comonomer in the macromolecule. Many results have been published for chemically heterogeneous samples using two detectors. Obviously, there is a practical limit (four signals have been reported so far), as there are not many detectors to choose from. In addition, the approach is limited by the contribution of each detector to band broadening. 

Teramachi S, Kato Y (1971) Study of the distribution of chemical composition in low-conversion copolymer by cross-lractionation. Macromolecules 4 54—56 Teramachi S, Hasegawa A, Hasegawa S, Ishibe T (1981) Determination of chemical composition distribution in a high-conversion copolymer of styrene and methyl acrylate by cross fractionation. Polym J 4 319-323... 

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