Crystallinity determination procedure

As an example of crystallinity determination by FTIR, the procedure used in Reference 38 for polyethylene is summarized here. The infrared spectrum of a solution-crystallized sample of polyethylene in the region of its CH2 rocking (and... 

Small amounts of moisture (up to about 0.5%) in crystalline sugars can be determined chemically by titration with Kad Fisher reagent. A volumetric Kad Fisher titration procedure for moisture in molasses is accepted by AO AC. Automatic Kad Fisher titrators are available, and as acceptance of pyddine-free reagents increases, their use may increase. 

Analysis. Many analytical procedures calling for determination of molecular stmcture are aided by crystallization or requite that the unknown compound be crystalline. Methodologies coupling crystalliza tion and analytical procedures will not be covered here (see X-RAY TECHNOLOGY)... 

Rossiter (1986) demonstrated the procedure for the production process of crystalline common salt from brine. It was found that the optimal median size is determined by the entrainment limit in the crystallizer. The crystallizer had to be operated at maximum allowable temperature and the slurry density measured for quality constraints. It was also suggested that cost discontinuities should be imposed based on temperatures of the available heat sources, possible materials of construction and other intrinsic properties of the system. 

Experiments at present are concentrated on sd-metals and Pt-group metals. The sp-metals, on which theories of the double layer have been based, are somewhat disregarded. In some cases the most recent results date back more than 10 years. It would be welcome if double-layer studies could be repeated for some sp-metals, with samples prepared using actual surface procedures. For instance, in the case of Pb, the existing data manifest a discrepancy between the crystalline system and the crystal face sequence of other cases (e.g., Sn and Zn) the determination of EgaQ is still doubtful. For most of sp-metals, there are no recent data on the electron work function. 

A relative crystallinity or "crystallinity index" has been used as an approximate method [55,56]. The simplest procedure involves determination of the intensity at a single scattering angle (26), in reference to the value for the amorphous halo at the same angular reflection. This method, for example, was useful to follow the variation of crystallinity of an iPP during isothermal melting [57]. 

Hydrolysis of xylan produces principally D-xylose.71 By hydrolysis of straw xylan in 3% nitric acid, Heuser and Jayme72 obtained crystalline D-xylose in 85% yield. Using a similar procedure, Hampton, Haworth and Hirst70 obtained a yield of 93% crystalline D-xylose from esparto xylan. A practically identical yield was indicated by reducing sugar determination made on the hydrolysis products of corn seedling xylan.68... 

The period under review has seen a small, but apparently real, decrease in the annual number of publications in the field of the vibrational spectroscopy of transition metal carbonyls. Perhaps more important, and not unrelated, has been the change in perspective of the subject over the last few years. Although it continues to be widely used, the emphasis has moved from the simple method of v(CO) vibrational analysis first proposed by Cotton and Kraihanzel2 which itself is derived from an earlier model4 to more accurate analyses. One of the attractions of the Cotton-Kraihanzel model is its economy of parameters, making it appropriate if under-determination is to be avoided. Two developments have changed this situation. Firstly, the widespread availability of Raman facilities has made observable frequencies which previously were either only indirectly or uncertainly available. Not unfrequently, however, these additional Raman data have been obtained from studies on crystalline samples, a procedure which, in view of the additional spectral features which can occur with crystalline solids (vide infra), must be regarded as questionable. The second source of new information has been studies on isotopically-labelled species. 

Recent developments and prospects of these methods have been discussed in a chapter by Schneider et al. (2001). It was underlined that these methods are widely applied for the characterization of crystalline materials (phase identification, quantitative analysis, determination of structure imperfections, crystal structure determination and analysis of 3D microstructural properties). Phase identification was traditionally based on a comparison of observed data with interplanar spacings and relative intensities (d and T) listed for crystalline materials. More recent search-match procedures, based on digitized patterns, and Powder Diffraction File (International Centre for Diffraction Data, USA.) containing powder data for hundreds of thousands substances may result in a fast efficient qualitative analysis. The determination of the amounts of different phases present in a multi-component sample (quantitative analysis) is based on the so-called Rietveld method. Procedures for pattern indexing, structure solution and refinement of structure model are based on the same method. 

D) We have found fhaf fhe mefhod of Wakelin et al. (1959), as used by Nara et al. (1978) fo calculafe fhe % relative crystallinity, is a reliable and reproducible procedure to determine the degree of gelatinization of sfarch by XRD powder diffracfomefry. This procedure, however, is nof sfraighfforward and needs suifable reference samples for 100% crysfalline and 100% amorphous material, and appropriate computer software to analyze data. 

All these results are encouraging for investigators planning to use X-ray diffraction in mixed solvents at subzero temperatures and the rest of the present article will be devoted to a discussion of methods and preliminary results in this field. The methodology for cryoprotection of protein crystals, its physical-chemical basis, and the specific problems raised by the crystalline state, as well as the devices used to collect data at subzero temperatures, will be described. Limitations and perspectives of the procedure will be discussed critically. First attempts to determine the structure of productive enzyme-substrate intermediates through stop-action pictures will be described, as well as investigations showing that X-ray diffraction at selected normal and subzero temperatures can reveal protein structural dynamics. 

Quantitative determination of the major and minor minerals In geological materials Is commonly attempted by x-ray diffraction (XRD) techniques. Mineralogists use a variety of sophisticated and often tedious procedures to obtain semlquantltatlve estimates of the minerals In a solid sample. The mineralogist knows that XRD Intensities depend on the quantity of each mineral component In the sample even through expressions for conversion of signal Intensity to quantitative analysis often are unknown or difficult to determine. Serious difficulties caused by variables such as particle size, crystallinity, and orientation make quantification of many sample types Impractical. Because of a lack of suitable standards, these difficulties are particularly manifest for clay minerals. Nevertheless, XRD remains the most generally used method for quan-... 

The value of the modulus and the shape of the modulus curve allow deductions concerning not only the state of aggregation but also the structure of polymers. Thus, by means of torsion-oscillation measurements, one can determine the proportions of amorphous and crystalline regions, crosslinking and chemical non-uniformity, and can distinguish random copolymers from block copolymers. This procedure is also very suitable for the investigation of plasticized or filled polymers, as well as for the characterization of mixtures of different polymers (polymer blends). 

The checkers also prepared racemic 1-[N-benzyloxycarbonyl-(1 )-1-amino-2-hydroxyethyl]-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane using the identical procedure (50% over 2 steps from racemic Cbz-serine purchased from Aldrich Chemical Company, Inc.). The enantiomeric ratio of the crystalline (S)-3 enantiomer (Note 20) was > 99.5 0.5 as determined by comparison with racemic 3 by courtesy of Mr. Eric Hortense (GlaxoSmithKline, Stevenage). Chiral HPLC (25 cm Chlracel OD-H, Column No ODHOCE-IF029, mobile phase ethanol/heptane 1 4 v/v, UV detector at 215 nm, flow rate... 

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