Samples hygroscopic

Use approximately 0 5 ml. of glycerol, and cork the flask A securely when weighing the glycerol by difference, owing to the very hygroscopic nature of the latter. Heat on the water-bath for 60 minutes instead of 30 minutes. Excellent results are obtained by this method if a freshly opened sample of anhydrous glycerol is available a sample which has been exposed to the air for even a short period will absorb sufficient water to give inaccurate results. 

The first binary mixture quantitatively studied was the water-thiazole system, thiazole being a very hygroscopic compound (104), Determining the purity of thiazole sample obtained by distillation, Metzger and Distel-dorf (287) observed the existence of a stable azeotropic mixture, the characteristics of which are the following ... 

Liquid cycloahphatic amines and diamines have exacting purity and color standards. Almost all are sold to specification, not performance standards. Use as isocyanate precursors requites low water content criteria for these hygroscopic fluids, hence nitrogen blanketing is often specified for product sampling as well as storage and transport. 

Equilibrium moisture content of a hygroscopic material may be determined in a number of ways, the only requirement being a source of constant-temperature and constant-humidity air. Determination may be made under static or dynamic conditions, although the latter case is preferred. A simple static procedure is to place a number of samples in ordinaiy laboratoiy desiccators containing sulfuric acid solutions of known concentrations which produce atmospheres of known relative humidity. The sample in each desiccator is weighed periodically until a constant weight is obtained. Moisture content at this final weight represents the equilibrium moisture content for the particular conditions. 

Sodium ethoxide [141-52-6] M 68.1. Hygroscopic powder which should be stored under N2in a cool place. Likely impurity is EtOH which can be removed by warming at 60-80" under high vacuum. Hydrolysed by H2O to yield NaOH and EtOH. Other impurities, if kept in air for long periods are NaOH and Na2C03 In this case the powder cannot be used if these impurities affect the reactivity and a fresh sample should be acquired [IR J Org Chem 21 156 1956]. 

Of course, a primary concern for any physical property measurement, including gas solubility, is the purity of the sample. Since impurities in ILs have been shown to affect pure component properties such as viscosity [10], one would anticipate that impurities might affect gas solubilities as well, at least to some extent. Since ILs are hygroscopic, a common impurity is water. There might also be residual impurities, such as chloride, present from the synthesis procedure. Surprisingly though, we found that even as much as 1400 ppm residual chloride in l-n-octyl-3-methylimi-dazolium hexafluorophosphate and tetrafluoroborate ([OMIM][PFg] and [OMIM] [BF4]) did not appear to have any detectable effect on water vapor solubility [1]. 

Nitronium tetrafluoroborate is very hygroscopic. It is stable as long as it is anhydrous, but it is decomposed by moisture, and all transfers should be in a dry box. Its purity can be checked by conventional elemental analysis. However, because of the hygroscopic nature of the salt, the submitters have found it convenient to use neutron activation analysis (B, F, N, O) of samples... 

Harris, Hygroscopicity of Ammonium Nitrate Samples , PATR 4052 (Apr 1970) 35) A.F. 

Desiccator Hygroscopic samples Samples which are more hygroscopic than the desiccant... 

All samples should normally be allowed to reach ambient temperature before analysis. Care should be taken to avoid hygroscopic samples taking up water, both when stored in a deep freeze or refrigerator and when warming back to room temperature. 

In recent years, with growing concern about the relative bioavailabilities of different samples of the same drug substance, polymorphism has become of prime interest. Miyazaki and co-workers (23) have reported the existence of two crystalline forms of CTC-HCl. The X-ray powder diffraction patterns, IR spectra, dissolution behaviors, and hygroscopicities that they reported were distinctly different and there were discrepancies in the bioavailabilities. 

The next layer of water, held between -30 and —1500 kPa, is available to plants and is therefore called plant available water. The water present between -1500 and -3200 kPa is held in capillaries so tightly that it is not available to plants but can be lost by evaporation. The layer closest to the soil solid is held at more than -3200 kPa and is called hygroscopic water. A soil sample, heated in an oven for 24 hours at 105°C, and then left exposed to the air will adsorb water until a layer of hygroscopic water has been formed, illustrating the strong attraction of soil surfaces for water. 

Martins and Banks (1991) modified pine and wood samples with phenyl or butyl isocyanate and investigated the water vapour sorption properties of the modified wood. Modification resulted in a reduction in EMC at a given RH up to about 35 % WPG with butyl isocyanate, although reaction with phenyl isocyanate above 25 % WPG resulted in an increase in sorption due to cell wall damage caused by the reaction. The butyl derivative was more effective at reducing hygroscopicity over all the WPGs studied. 

Optics Issues relative to hygroscopic optics and the need to pay attention to mirror mounts relative to vibration and/or thermal effects have already been addressed. Zinc selenide is an important alternative material, especially when antireflection (AR) coated. If potassium bromide absolutely has to be used for its lower transmission range (down to 400 cm ) then a protective coating such as Parylene must be used. Most process analyzers use protective windows between the spectrometer and the sample interface. If used, back reflections from the window surfaces into the interferometer must be avoided because these will cause photometric errors. Such reflection can be eliminated by wedging or tilting the optical windows, relative to the beam path. 

Borer et al. developed a NIR method to determine moisture in a highly hygroscopic product. Because the sample absorbed water very rapidly (0.02%/min), use of the Karl Fischer method as reference was very complicated. This led them to the choice of NIR spectroscopy, where the sample can be kept inside a sealed vial instead. Analyses were completed within a few seconds and the samples not exposed to ambient air at any time, which prevented moisture absorption and the ensuing determination errors. 

The dynamic mechanical thermal analysis also indicated molecular mixing of the two components. The Tg of the thermoplastic was lower than the composite, as determined from the inflection point of the E curve seen in Figures 13 1. The PEOX glass transition temperature appeared at 62°C, while that for PVP showed up at ll5°C. The discrepancy in the Tg of PVP had already been addressed. The Tg extrapolated from the DMTA thermogram was reported since no artifacts were to be introduced. The samples exemplified for all DMTA thermograms were processed in a normalized fashion. Any thermal or hygroscopic Influences were eliminated. Some water may be trapped in the neat thermoplastics but this was minimized since they are hot pressed at 150°C and stored under calcium... 

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