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Gravimetric Method (gravimetric + method)
Selected AbstractsGravimetric method to find internal surface of macroporous silicon membranesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007A. A. Nechitailov Abstract A simple method to evaluate the internal surface area, porosity, pore diameter and pore density of macroporous silicon membranes has been proposed and tested. The porosity p is obtained from the mass loss under anodizing, and the surface area per unit volume Sv is determined from the mass of SiO2 formed on the pore surface as a result of thermal oxidation. The average pore diameter d and pore density N can be easily calculated from the obtained Sv and p. Experimental verification of d and N was performed by means of SEM and optical microscope images; Sv was checked by BET technique. Surface area and porosity on the resistivity of initial n-Si in the range , = 3,25 Ohm · cm have been studied for the samples with regular and self-organized macropore "lattices". The obtained values are within the limits p = 27,50%, Sv = 2800,6000 cm2/cm3, d = 1.9,6.5 ,m, N = 1.4,10 × 106 cm,2, and in a good agreement with the data of microscopic characterization. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Equilibrium moisture content and heat of desorption of saffronINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2010Hamid Reza Gazor Summary The equilibrium moisture contents of saffron (Crocus sativus L.) stigmas were determined experimentally using the standard gravimetric method at temperatures 30, 45 and 60 °C and water activity ranging from 11% to 83%. The sorption isotherm curves of saffron were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models GAB, modified Henderson, modified Chung-Pfost, modified Halsaey and modified Oswin were tested to fit the experimental isotherm data. Modified Oswin and modified Henderson models were found acceptable for predicting desorption moisture isotherms and fitting to the experimental data, respectively. The isosteric heats of desorption, determined from equilibrium data using the Clausius-Clapeyron equation, were found to be a function of moisture content. The net isosteric heat of desorption of saffron varied between 1.38 and 5.38 kJ mol,1 at moisture content varying between 2% and 20% (d.b). [source] Photografting of acrylic acid and methacrylic acid onto polyolefines initiated by formaldehyde in aqueous solutionsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Jianmei Han Abstract Formaldehyde aqueous solution can act as an effective photoinitiating system for water-borne photografting. The photografting of acrylic acid (AA) and methacrylic acid (MAA) onto high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene (PP) initiated by formaldehyde aqueous solutions has been reported. The effects of formaldehyde content and monomer concentration on grafting varied with the polymeric substrates and monomers used. For the grafting of AA onto HDPE, the extent of grafting increased with increasing formaldehyde content in the solution, monomer concentration had a little effect on grafting. Whereas for the grafting of MAA onto HDPE, the grafting performed in 8% formaldehyde aqueous solution lead to the highest extent of grafting, the extent of grafting increased with monomer concentration till 2.5 mol/L. MAA was easier to be grafted onto the polyolefins than AA. The easiness of grafting occurring on the polyolefins was in a decreasing order of LDPE > HDPE > PP. Qualitative and semi-quantitative Fourier transform infrared (FTIR) characterizations of the grafted samples were performed. For both grafted LDPE and PP samples, at the same irradiation time, the carbonyl index of the samples grafted with MAA was higher than that grafted with AA. The FTIR results are in accord with the results obtained by gravimetric method. The water absorbency of the grafted samples increased almost linearly with the extent of grafting. The PE films grafted with AA adsorbed more water than those grafted with MAA. This study had broadened the water-borne initiating system for photografting. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Li-Deficient, Off-Congruent MgO:LiNbO3 Crystals Prepared by Postgrown Li-Poor Vapor Transport Equilibration for Integrated OpticsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010De-Long Zhang Li-deficient, off-congruent Z -cut MgO:LiNbO3 (MgO:LN) crystals for integrated optics were prepared by carrying out postgrown Li-poor vapor transport equilibration (VTE) treatments on congruently grown MgO (5 mol% in melt):LiNbO3 plates at 1100°C for durations ranging from 40 to 395 h. Secondary ion mass spectrometry analysis, surface ordinary refractive index measurement, and neutron activation analysis were carried out on the VTE crystals to verify that the Mg and Nb ions did not diffuse out of the crystal during the VTE procedure and their distributions over the whole plate retain its homogeneity. The VTE duration dependence of the Li2O content reduction was determined using gravimetric method, and the crystalline phase was by powder X-ray diffraction. The results show that the Li2O content decreases with a prolonged VTE and the Li2O content reduction in the saturation regime is about 2.9 mol%. All of the VTE crystals still retain the LN phase, and Li-vacancy and NbLi are the major defects in the VTE crystal. OH absorption study reveals that the doped MgO concentration is below the photorefractive threshold for all VTE crystals. The optical absorption edge (OAE) of the VTE-treated MgO:LN was also measured as a function of the VTE duration. On the basis of the known Li2O content and measured OAE, the photon-energy fit reported previously, valid for the evaluation of Li2O content in a pure LN, is corrected for the Li-poor VTE-treated MgO:LNs. Finally, the applicability of the Li-deficient off-congruent MgO:LN crystals prepared by the Li-poor VTE method is demonstrated by characterizing the optical damage and Er diffusion properties of a single-mode Ti:MgO:Er:LiNbO3 strip waveguide fabricated on an Li-poor VTE-prepared MgO:LN crystal. [source] Citric acid production by Aspergillus niger ATCC 9142 from a treated ethanol fermentation co-product using solid-state fermentationLETTERS IN APPLIED MICROBIOLOGY, Issue 5 2009G. Xie Abstract Aims:, To investigate the ability of the citric acid-producing strain Aspergillus niger ATCC 9142 to utilize the ethanol fermentation co-product corn distillers dried grains with solubles for citric acid production following various treatments. Methods and Results:, The ability of A. niger ATCC 9142 to produce citric acid and biomass on the grains was examined using an enzyme assay and a gravimetric method, respectively. Fungal citric acid production after 240 h was higher on untreated grains than on autoclaved grains or acid-hydrolysed grains. Fungal biomass production was enhanced after autoclaving and acid-hydrolysis of the grains. Phosphate supplementation to the grains slightly stimulated citric acid production while methanol addition decreased its synthesis. Using the phosphate-supplemented grains, the optimal incubation temperature, initial moisture content of the grains and the length of fermentation time for ATCC 9142 citric acid production were determined to be 25°C, 82% and 240 h, respectively. Conclusions:,A. niger ATCC 9142 synthesized citric acid on corn distillers dried grains with solubles. The phosphate-treated grains increased citric acid production by the strain. Significance and Impact of the Study:, The ethanol fermentation co-product corn distillers dried grains with solubles could be useful commercially as a substrate for A. niger citric acid production. [source] Accuracy and precision of flowing afterglow mass spectrometry for the determination of the deuterium abundance in the headspace of aqueous liquids and exhaled breath waterRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2001Patrik, panel We have assessed the accuracy and precision of our flowing afterglow mass spectrometric method (FA-MS) for absolute measurements of deuterium abundance in water using standardised tap water/D2O mixtures within the D/H range from 155,ppm (local tap water) to 1104,ppm, prepared by the gravimetric method. The results of this study show that a precision and accuracy of 1% can be achieved for the deuterium abundance in water samples. This is quite adequate for the main application, which is the rapid, non-invasive measurement of total body water by deuterium analysis of breath water vapour using the D2O dilution method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Determination of the enantiomeric excess of an M3 antagonist drug substance by chemometric analysis of the IR spectra of different guest-host complexesCHIRALITY, Issue 5 2006Lili Zhou Abstract A novel approach for the potential on-line determination of the enantiomeric excess (ee) of an M3 antagonist drug substance combining attenuated total reflectance infrared (ATR-IR) spectroscopy, guest-host complexes, and chemometric data analysis is described. Chiral recognition through a formation of diastereomeric complexes was measured by ATR-IR. Small changes on the IR spectra reflect the interaction between the guest (M3) and host (chiral selector). These changes are measured as a function of M3 enantiomer excess. The standard error of prediction is 1.3 ee%. The prediction results based on the IR method were in good agreement with the gravimetric method. The robustness of the calibration model was evaluated by varying the concentration of the chiral selector, the pH of the solution, and the organic solvents. The stability of the calibration model was also demonstrated through measuring different sets of samples on different days. Chirality, 2006. © 2006 Wiley-Liss, Inc. [source] Measuring the surface area of aluminum hydroxide adjuvantJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2002Cliff T. Johnston Abstract The traditional method of determining surface area, nitrogen gas sorption, requires complete drying of the sample prior to analysis. This technique is not suitable for aluminum hydroxide adjuvant because it is composed of submicron, fibrous particles that agglomerate irreversibly upon complete removal of water. In this study, the surface area of a commercial aluminum hydroxide adjuvant was determined by a gravimetric/FTIR method that measures the water adsorption capacity. This technique does not require complete drying of the adjuvant. Five replicate determinations gave a mean surface area of 514 m2/g and a 95% confidence interval of 36 m2/g for a commercial aluminum hydroxide adjuvant. The X-ray diffraction pattern and the Scherrer equation were used to calculate the dimensions of the primary crystallites. The average calculated dimensions were 4.5,×,2.2,×,10 nm. Based on these dimensions, the mean calculated surface area of the commercial aluminum hydroxide adjuvant was 509 m2/g, and the 95% confidential interval was 30 m2/g. The close agreement between the two surface area values indicates that either method may be used to determine the surface area of aluminum hydroxide adjuvant. The high surface area, which was determined by two methods, is an important property of aluminum hydroxide adjuvants, and is the basis for the intrinsically high protein adsorption capacity. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1702,1706, 2002 [source] | |||||||||||||