Solvent traces

Therefore it is possible to determine absorption spectra directly on the TLC plate by comparison with a substance-free portion of the layer. The wavelengths usually correspond to the spectra of the same substances in solution. However, adsorbents (silanols, amino and polyamide groups) and solvent traces (pH differences) can cause either bathochromic (ketones, aldehydes [60, 61], dyestuffs [62]) or hypsochromic (phenols, aniline derivatives [63]) shifts (Fig. 23). 

Trace Solvent Removal. Several papers were written by Nadeau (4) and by Gilbert (5) and co-workers on gas chromatographic methods for determining solvent traces remaining in flexible packaging films after printing or adhesive lamination. With proper equipment and techniques,... 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

The base was being prepared by distilling a mixture of hydroxylamine hydrochloride and sodium hydroxide in methanol under reduced pressure, and a violent explosion occurred towards the end of distillation [1], probably owing to an increase in pressure above 53 mbar. It explodes when heated under atmospheric pressure [2], Traces of hydroxylamine remaining after reaction with acetonitrile to form acetamide oxime caused an explosion during evaporation of solvent. Traces can be removed by treatment with diacetyl monoxime and ammoniacal nickel sulfate, forming nickel dimethylglyoxime [3], An account of an extremely violent explosion towards the end of vacuum distillation had been published previously [4], Anhydrous hydroxylamine is usually stored at 10°C to prevent internal oxidation-reduction reactions which occur at ambient temperature [5], See other REDOX REACTIONS... 

Yudin and Sharpless reported on the utilization of much cheaper, readily available inorganic Re catalysts [Re207, ReOsfOH), ReOs (0.5-1 mol%)] in combination with bis(trimethylsilyl) peroxide as oxidant and 0.5-1 mol% of pyridine (equation 52) . In this oxidation process high epoxide yields (78-96%) were obtained using CH2CI2 or THF as solvent. Traces of water or other protic species have been found to be essential for rapid turnover and accelerate the reaction. 

IR spectroscopy becomes even more easy to use for identification of various fulleranes if deuterium is used instead of hydrogen. Experiments with deuterisation of C60 proved that it occurs in the same way as with hydrogen (Tarasov et al. 2001 Shulga et al. 2003). However, using deuterium allows to identify peaks due to C-D bonds of fulleranes clearly distinctly from any contamination hydrocarbons which are typically found in almost any fullerene sample due to presence of solvent traces etc. 

As mentioned above, a possible drawback of recrystallization is the potential presence of solvent traces in the ionic liquid. This might result in the formation of yellowish compounds, as was reported by Appetecchi et al. [123]. 

The C4 acetylenes, which have higher solubilities in NMP than 1,3-butadiene, are removed by the solvent in the bottoms and returned to the rectifier. A crude butadiene (BD) stream, from the overhead of the second extractive distillation column, is fed into the BD purification train. Both extractive distillation columns have a number of trays above the solvent addition point to allow for the removal of solvent traces from the overheads. 

The extractor is operated under atmospheric condition, 30°C to 50°C and 1 to 3 bar pressure. Column 2 is divided in 2 sections. The bottom product from the extractor is fed into the column (from above) between sections 1 and 2, and additional solvent is fed in above section 1. Section 3 is used to strip the aromatics from the solvent. Some of the vapors produced in the bottom are used to heat the ED and some are fed into a small lateral column where the pure aromatic product is separated from the solvent. The overhead vapor of the lateral column are condensed. The reflux washes down the solvent traces in the vapors. 

Description The progressive Morphylane extractive distillation is a single-column extractive distillation configuration. The aromatics are removed from the vaporized feed material by the solvent in packing (2) until a residual content of 0.5-1% is reached. However, some of the nonaromatics are also dissolved. These are stripped off by aromatics vapors in packing (3). The solvent traces which go to the column head with the nonaromatics proportionate to the vapor pressure of the solvent are washed back with the nonaromatics reflux. 

Solvent traces are removed from the aromatics vapors in packing (4), again by reflux. It is, however, packing (5), where the aromatics are stripped off from the solvent that is of crucial importance. Extractive distillation can only be effective if the aromatics content is drastically reduced to 0.1%. Intensive aromatics stripping is crucial for the aromatics yield. 

Recently it has been found (2 ) that tetrahydrofurane (THF) retained by poly(vinyl chloride) (PVC) in amounts of 2 to 6 may influence the photodegradation of polymers. Free radicals which are formed during the photolysis of THF in PVC matrix are capable of abstracting hydrogen and forming macroradicals. If the effects of solvent traces are ignored a false interpretation of observed phenomena may result. 

Mass spectrometry does not directly monitor the drying bed but monitors the offgases for solvent traces. It has good specificity for individual solvent entities and can sense to very low levels. 

The film thickness to be chosen depends on the band absorptivity (see Table 3). Thin films are more easily obtained by evaporation from a solution in solvents such as carbon tetrachloride, tetrachloroethylene, xylene, decalin, etc. directly on the NaCl or KBr disks. Slight heating under vacuum should allow removal of solvent traces. Films cast from... 

Polymeric thin films in this thickness range can easily be prepared from solution by spin coating or doctor blading techniques. Drying the films at elevated temperatures under high vacuum or under inert atmosphere is necessary to remove residual solvent traces, which cause softening of the material and contribute to fast relaxation of the oriented chromophores to an isotropic state. 

Conventional extraction was carried out with 200mL of hexane on lOg of crushed cranberry seeds. The extraction was allowed to proceed for 24h in the dark at the boiling point of hexane. The extract, thus obtained was concentrated by rotary evaporation and the residue was left under continuous vacuum for 24h to remove solvent traces. The weight of this residue was considered to be 100% recovery. The experiments were performed in triplicate. 

First, the solvents should be relatively free of trace impurities while dissolving the compounds of interest effectively. The solvent trace impurities, while not detectable in the bulk, can produce spurious peaks after the concentration of the volume of extracted sample. Whenever an extensive solvent clean-up is either impossible or impractical, appropriate sample blanks should frequently be run. With today s capabilities of high-resolution GC and spectral identification, occasional solvent impurities are tolerated as convenient markers . A good sample solubility is required to minimize possible losses due to sample adsorption on the glassware or, simply, its unnoticed precipitation. 

The vapors rising from the extractive distillation section consisting of non-aromatic components still contain small quantities of solvent. These solvent traces are separated in the raffinate section located above the extractive distillation section. The purified non-aromatics are withdrawn as overhead product. 

The influence of air moisture is due to competition between water molecules and adsorbate. Activated carbon is generally useful at room temperature until a relative humidity of about 70 - 80 % for pollutant concentrations ranging from 1 to 1,000 mg m . However, the most important parameter is the ratio of molecule and water concentration. That is to say, a high humidity will inhibit the removal of solvent traces. In contrast, a high humidity will have no effect on high solvent concentration removal. 

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