Evaporation procedures

Concentration. Evaporation procedures depend on the concentration of the solution produced during neutralization and the water content required for the subsequent production of soHd product. Neutralizer solutions can contain as Httle as 2% and as much as 25% water feeds to drum granulators can contain 5% water, prill towers 0.3 to 0.5% water. 

North American Chemical Co. produces borax pentahydrate and decahydrate from Seades Lake brines in both Trona and West End, California (see Chemicals frombrines). The 88 km dry lake consists of two brine layers, the analyses of which are given in Table 11. Two distinct procedures are used for the processing of upper and lower lake brines. Borax is produced in Trona from upper lake brines by an evaporative procedure involving the crystallization of potash and several other salts prior to borax crystallization as the pentahydrate (104). A carbonation process is used in West End, California to derive borate values from lower lake brines (105). Raw lower stmcture brine is carbonated to produce sodium bicarbonate, which is calcined and recrystallized as sodium carbonate monohydrate. The borate-rich filtrate is neutralized with lake brine and refrigerated to crystallize borax. 

Lyophilization is a similar technique and is, in fact, evaporation at reduced temperature under vacuum. In some cases, an aqueous sample can be frozen and the vapor pressure of the ice is sufficient to produce a relatively rapid rate of evaporation. It can also be used effectively where the substances of interest have vapor pressures that are sufficiently high at room temperature, to cause substance loss under normal evaporation procedures. As the vapor pressure of a substance is exponentially related to the temperature, a relatively small reduction in temperature can reduce the vapor pressure of the sample components sufficiently to render any loss during evaporation relatively insignificant. This technique is gentler than evaporation and,... 

A solvent evaporation procedure particularly useful for entrapment of water-insoluble agents in the biodegradable polymers has... 

Poly(DL-lactide) was used as the excipient in microspheres of CCNU, a nitrosourea, prepared by a solvent evaporation procedure (96,97). PLA-CCNU microspheres 3.0 pm in diameter were injected i.v. and leukemia cell survival was determined by spleen colony assay. A 100-fold decrease in leukemia cell survival was observed with the microspheres in both spleen and liver compared to untreated controls. Promising results were also obtained with Lewis lung carcinoma in mice. These studies showed that 2- to 4-ym microspheres were preferentially targeted to the lungs. 

Extensive studies have been reported with cisplatin in the field of chemoembolization (59,98). Microspheres prepared by a solvent evaporation procedure were characterized in vitro and critical processing parameters in regard to drug release kinetics were identified. 

Several antiinflammatory compounds have been formulated in lactide/ glycolide polymers (107-111). Methylprednisolone microspheres based on an 85 15 DL-lactide/glycolide copolymer were developed for intra-articulate administration (111). The microspheres, prepared by a solvent evaporation procedure, are 5—20 jam in diameter and are designed to release low levels of the steroid over a extended period in the joint. Controlled experiments in rabbits with induced arthritis showed that the microspheres afforded an antiinflammatory response for up to 5 months following a single injection. 

Bissery, M. C., Puisieux, F., and Thies, C., A study of the parameters in the making of microspheres by the solvent evaporation procedure. Expo. Congr. Int. Technol. Pharm. 3rd. 

These facts suggest that variable recoveries of parathion from the evaporation procedure, as used routinely, should be expected. In general, however, the recovery data did not demonstrate a clear-cut distinction between acetone and benzene for the purpose at hand. A slow steady loss of parathion in proportion to the volume of either solvent evaporated (1) was not noted, which would indicate that the rate of evaporation is also important. The final decision as to solvent was determined by certain incidental properties of the parathion. 

For example, in Figure 3 it is demonstrated that tetrahydrofuran (THF) and formamlde can be mixed AO 60 to establish a cosolvent as designated. Recognition of this fact makes it possible to explore a number of casting solutions which, because they contain a volatile component, do not require the difficult evaporation procedures discussed above. In addition, it is possible to explore a number of non-classical or novel casting solutions as will be demonstrated below. 

In another context, the electrical properties of thin films obtained by different procedures, for example, thermal evaporation in vacuum, have been investigated in much detail. However, the films deposited by the LB technique have only recently been used in electrical applications. Thickness in LB films can be varied from only one monomolecular layer (ca. 25A = 25 10 10m), while this is not possible by evaporation procedures. 

The very slow diffusion rate in the solid state below 850°C. This kinetic limitation can be overcome in the case of thin films where intimate mixing of the cations at the atomic level has already been obtained during the evaporation procedure. Therefore, in this case crystallization of the correct phase can be obtained directly from the amorphous mixture, around 650°C for the optimized processes (14). 

Solvents used here for a general liquid-liquid extraction method were selected from Snyders solvent selectivity triangle. As extraction liquids have to be composed of mixtures of three solvents which may enter into maximum interaction with the analyte, three solvents had to be selected that represent a wide variety of selective interactions. In addition, the solvents should be sufficiently polar to ensure quantitative extraction. Besides selectivity and polarity requirements, the solvents should also meet a few other criteria, mainly for practical reasons they should not be miscible with water, have low boiling points (for relatively fast evaporation procedures) and have densities sufficiently different from the density of water, for pure solvents as well as for selected binary or ternary mixtures of solvents. 

If a negative response is observed in all three assays of step 1, then the liquid is concentrated by rotary evaporation at 40 °C in step 2. These conditions are gentle enough so that although most volatile solvents (acetone, methanol, etc.) are removed, the integrity of concentrated, thermally labile components is maintained. If the sample volume (or weight) can be reduced by a factor of at least 10 by the evaporation procedure, the concentrate is retested by using the plate incorporation and the pre-incubation assays. If a solid residue is produced, then it is dissolved in a minimum amount of DMSO prior to assay. 

The solution coating technique in most cases is preferred to the evaporative method because there is more uniform deposition of the phase and because there is less chance for damage of support particles. The evaporative procedure is more convenient for preparing high concentration packings (15-20%) of the viscous phases such as Carbowax, and for preparing packings with two or more stationary phases which are not soluble in a common solvent. 

During sampling cruises 3-5, 20 L of sample from the ultrafilter was preserved with chloroform, shipped back to an analytical laboratory, and vacuum-evaporated to 500 mL before being passed through a 500-mL column of XAD-8 resin (27). This revised procedure should have increased the recovery of DOM because of a 10-fold increase in the resin water ratio. In addition, hydrophilic organic solutes that did not adsorb on the XAD-8 resin were isolated by a vacuum-evaporation procedure whereby water is distilled from acetic acid and inorganic salts precipitate in the acetic acid (28). Recoveries of DOC by the two procedures are presented in Table IV. 

Using a syringe the phases were carefully separated and transferred to different vials. The ionic liquid phase was then submitted to an evaporation procedure (rotary evaporator, 50 °C, 10 mbar, 6 h). Shortly after connecting to vacuum bubble generation could be observed. 

Anhydro-D-glucose, Glucose and Sorbitol Transfer 30 mg of sample, accurately weighed, into a screw-cap vial, and add about 2 mL of pyridine. While flushing the vial with a stream of dry air or nitrogen, heat at 80° to 90° until the solution volume is reduced to 0.2 to 0.5 mL. Add a second portion of pyridine, and repeat the evaporation procedure. Continue as directed in the monograph for Polydextrose. Nickel Determine as directed under Nickel Limit Test, Appendix IIIB. 

Jn the evaporation procedure (by EN 73), in which the light components of oil arc removed, there is practically no the change of cell wall structure, moreover, the concentration of the surface hydrophilic groups somewhat increases. 

The activity of both the cultures relative to die sample subjected to the evaporation procedure (EN 73) are close, i.e. the destructive action of i. lepideus is only by 10% stronger, in comparison with the case of C puteana. 

The waste solutions are neutralized with calcium or sodium hydroxide in order to avoid explosion in the following evaporation procedure. Calcium hydroxide is inexpensive and suitable for use in the treatment of a large amount of waste, whereas sodium hydroxide is preferred for neutralizing the waste containing sulphate. 

In addition, more product can be loaded on a silica gel than on reversed phase materials. Furthermore the separated products are readily recovered by simple evaporation procedures, while the isolation of products from an RP separation process often require additional work-up steps. These steps include the removal of salts or other aqueous phase additives and extraction of the target product after evaporation of the organic phase (Section 4.3.3.5). 

One of the primary advantages of evaporative procedures is that they can often be combined with other process operations to reduce equipment requirements and/or time cycles. In addition, it is possible in some cases to complete the crystallization without the addition of a second solvent, thereby avoiding the costs of separation and recovery. Some of the process advantages that may be realized are as follows ... 

NanoStore technology uses 1536 well plates on a NanoCarrier to store compounds after the DMSO is evaporated (Benson et al., 2005). Compounds in a dry state avoid issues associated with DMSO storage. The evaporation procedure eliminates DMSO, thus, it can be used in assays that are sensitive to DMSO. 

Pre-concentration is concerned with the reduction of a larger sample into a smaller sample size. It is most commonly carried out by using solvent evaporation procedures after an extraction technique (see, for example, Chapters 7 and 8). The most common approaches for solvent evaporation are rotary evaporation, Kudema-Danish evaporative concentration, the automated evaporative concentration system (EVACS) or gas blow-down . In all cases, the evaporation method is slow, with a high risk of contamination from the solvent, glassware and blow-down gas. 

Solvent evaporation would be used when you are trying to perform ultra-trace analysis. It allows a sample extract to be further preconcentrated. An example would be analysis of pesticides in natural water. Initially, solid-phase extraction may have been performed to concentrate the pesticides from the water. However, to detect pesticides in natural waters will require additional pre-concentration via solvent-evaporation procedures. 

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