Precipitation procedures

These are the most widely used ones. The structure and physicochemical properties of the LDHs depend on several factors, such as the precise precipitation process followed, the natiue of the reagents, their total and relative concentrations, precipitation pH, temperature, stirring speed, ageing time after precipitation, the presence of impurities, and the washing and drying conditions [97]. Important differences are also observed depending on the use of variable or constant pH (coprecipitation). 

Titration of a solution containing salts of the metal cations to be precipitated with a basic solution, usually an alkaline metal hydroxide or carbonate [98, 99] is one of the simplest methods to prepare LDHs. A sequential precipitation of the metal hydroxides (forming particles with the less soluble hydroxide in the nuclei and an external shell formed by the hydroxide of the divalent cation), could be expected, but it is generally found that a true mixed hydroxide is formed it seems that precipitation of M(OH)j induces the simultaneous precipitation of MCOH).  

The method consists of the addition of a solution of the metal cations to a basic alkaline metal solution (usually NaOH or KOH). The crystallinity of the particles formed is rather low and they need to be submitted to hydro-thermal or other ageing treatment to increase it [100]. 

This is the most widely used method. It consists of the slow addition of the metal cations solution to a reactor containing water or a solution of the anion to be inserted between the brucite-like layers. A second (basic) solution is simultaneously added to keep pH at a constant value, leading to simultaneous precipitation of the hydroxides. 

Coprecipitation takes place by condensation of hexaquo complexes in solution, forming brucite-like layers where both cations are homogeneously distributed, and with the anions (and water molecules) hosted between the layers. Observation of recently precipitated particles and powder X-ray diffraction (PXRD) studies show that formation of the layers and of the interlayer domains is immediate, without previous delamination of the brucite-like layers [54]. 

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Isolation. Isolation procedures rely primarily on solubiHty, adsorption, and ionic characteristics of the P-lactam antibiotic to separate it from the large number of other components present in the fermentation mixture. The penicillins ate monobasic catboxyHc acids which lend themselves to solvent extraction techniques (154). Pencillin V, because of its improved acid stabiHty over other penicillins, can be precipitated dkecdy from broth filtrates by addition of dilute sulfuric acid (154,156). The separation process for cephalosporin C is more complex because the amphoteric nature of cephalosporin C precludes dkect extraction into organic solvents. This antibiotic is isolated through the use of a combination of ion-exchange and precipitation procedures (157). The use of neutral, macroporous resins such as XAD-2 or XAD-4, allows for a more rapid elimination of impurities in the initial steps of the isolation (158). The isolation procedure for cephamycin C also involves a series of ion exchange treatments (103). 

Under nitrogen, anhydrous DMF (10 mL) was added to a mixture of 83 (0.240 g, 0.5 mmol), 84 (0.063 g, 0.5 mmol), and Et3N (1 mL). Pd(PPh3)4 (0.027 g, 0.025 mmol) and Cul (0.005 g, 0.025 mmol) were then added and the reaction mixture was stirred at 100°C for 48 h. After being cooled to room temperature, die reaction mixture was poured into MeOH and filtered. The solid was washed with MeOH and dried under vacuum. The repetition of the precipitation procedure gave polymer 85 as orange powder in 96% yield (0.212 g). GPC (polystyrene standards) Mn — 15.100. 

Crompton [81] has reported in detail fractional precipitation procedures for various polymers, such as polyolefins, acrylic polymers, PS, PVC, PUR, rubbers, polyarylamide, and various copolymers. Metcalf and Tomlinson [624] have reported fractional precipitation of antioxidants from PE. Separation of low-MW species from the polymer by repeated fractional precipitation [625] is unsatisfactory for routine use because of the time and manipulative skills required. 

Applications APCI-MS is often more widely applicable than ESI-MS to the analysis of classes of compounds with a low molecular weight, such as basic drugs and their metabolites, antibiotics, steroids, oestrogens, benzodiazepines, pesticides, surfactants, and most other organic compounds amenable to El. LC-APCI-MS has been used to analyse PET extracts obtained by a disso-lution/precipitation procedure [147]. Other applications of hyphenated APCI mass spectrometric techniques are described elsewhere LC-APCI-MS (Section 7.33.2) and packed column SFC-APCI-MS (Section 73.2.2) for polar nonvolatile organics. 

Native factor VIII is traditionally purified from blood donations first screened for evidence of the presence of viruses such as hepatitis B and HIV. A variety of fractionation procedures (initially mainly precipitation procedures) have been used to produce a factor VIII product. The final product is filter-sterilized and filled into its finished product containers. The product is then freeze-dried and the containers are subsequently sealed under vacuum, or are flushed with an inert gas (e.g. N2) before sealing. No preservative is added. The freeze-dried product is then stored below 8 °C until shortly before its use. 

By careful control of these parameters aluminium may be separated, and few interferences are observed if the precipitation is carried out from an ammoniacal-cyanide-EDTA solution. When large amounts of Ca or Mg are present the homogeneous precipitation procedure (Table 5.18) is usefully employed at pH = 5. The precipitate is readily filtered and may be weighed after drying at 150°C as the anhydrous compound. 

Typical protein precipitation procedures use one volume of plasma plus three to six volumes of acetonitrile or methanol (or a mixture) with the internal standard at an appropriate concentration for the assay. Poison et al.102 reported that protein precipitation using acetonitrile eliminates at least 95% of the proteins after filtration or centrifugation, the supernatant can often be directly injected into the HPLC/MS/MS system. Usually this step is performed using 96-well plates that are ideal for semi-automation of sample preparation. Briem et al.103 reported on a robotic sample preparation system for plasma based on a protein precipitation step and a robotic liquid handling system that increased throughput by a factor of four compared to a manual system. 

Thereafter, analysis was done by faster techniques based on oxalate-permanganate titrations which involved a precipitation procedure followed by quick titration of pre-heated solutions containing oxalate ions. 

Xu, X. Zhou, Q. Korfmacher, W. A. Development of a low volume plasma sample precipitation procedure for liquid chromatography/tandem mass spectrometry assays used for drug discovery applications. Rapid Commun Mass Spectrom 2005, 19, 2131-2136. 

Drug/Lab test interactions Because false-positive readings were reported with the Ames N-Muitistix SG dipstick test for urinary protein when gabapentin was added to other antiepileptic drugs, the more specific sulfosalicylic acid precipitation procedure is recommended to determine the presence of urine protein. 

Reetz et al. 16) were the first to recover and recycle a dendritic catalyst through a precipitation procedure. The dimethylpalladium complex of the phosphine-functionalized DAB-dendr-[N(CH2PPh2)2]i6 dendrimer (la) is an active catalyst for the Heck reaction of bromobenzene and styrene to give trara-stilbene (89% trans-stilbene and 11% 1,1-diphenylethylene, at a conversion of 85—90%, Scheme 8). 

Aluminium and magnesium hydroxides are difficult to produce directly in any useable form from their natural ores. Filler grade calcium carbonate is widely produced from natural sources, but grinding costs appear to become prohibitive when ultra-fine particles are required and precipitation procedures then become competitive. Further details of precipitation procedures will be found under the specific filler types. 

TIMS) by Walczyk and von Blanckenburg.23 Precise iron isotope ratio measurements of iron from whole blood matrix by MC-ICP-MS (Neptune, Thermo Fisher Scientific) after microwave digestion and ashing decomposition, anion exchange and precipitation procedures are discussed by Stenberg et at.46... 

Soy isolate was prepared by the isoelectric precipitation procedure developed at the Food Protein Research and Development Center, Texas A M University System (23). A commercial soy isolate. Promine F (Central Soya Inc., Fort Wayne, IN), was also used in this study. 

Addition of appropriate amounts of salts, such as ammonium or sodium sulfate (2), or other chemicals, such as PEG, cause precipitation of IgG from serum. Caprylic acid can also be used to fractionate proteins from serum Although such IgG is usually contaminated with other proteins, the ease of these precipitation procedures coupled with the high yield of IgG produced has led to them being very widely used to produce enriched IgG preparations suitable for many immunochemical procedures, e.g., production of immunoaffinity columns, and as a starting point for further purification. The precipitated IgG is usually very stable and such preparations are ideally suited for long-term storage or distribution and exchange between laboratories. 

The methods available for protein purification range from simple precipitation procedures used since the nineteenth century to sophisticated chromatographic and affinity tech-niques that are constantly undergoing development and improvement. Methods can be classified in several alternative ways—perhaps one of the best is based on the properties of the proteins that are being exploited. Thus the methods can be divided into four distinct but interrelated groups depending on protein... 

These particulate, and also many apparently soluble, DPO enzyme preparations frequently exhibit the phenomenon of latency. This is manifested as atypically low DPO activity when the tissue is known to be rich in DPOs. When the enzyme is treated with a chaotropic agent such as SDS or 8 M urea, or is subjected to an acetone-precipitation procedure, a marked increase in DPO activity is revealed (Palmer, 1963 Walker and Hulme, 1965). This effect is thought to come about by the release of the membrane-bound enzyme and/or effects upon the tertiary structure of the enzyme and the active site. 

Significant concentrations of contaminant radium may be submicromolar. Therefore, radiochemical separations are commonly employed that make use of a carrier, a nonradioactive element with chemical properties similar to those of radium. For radium, barium is the element of choice, and radium is coprecipitated from solution with barium sulfate, BaSCH Correction for losses in the precipitation procedure may be made by adding a tracer consisting of an isotope of radium not expected in the sample and noting its recovery at the end of the analytical procedure. The isotope radium- 223 can be used for this purpose. 

A third co-precipitation procedure has also been devised for the study of transuranic oxidation states (Lovett, pers. comm.). In this procedure, water samples... 

Polyanion precipitation has been used for separating apo-B-containing lipoproteins from other lipoproteins. Gidez et al. (G4) have used a fractional precipitation procedure with dextran sulfate and Mn2+ to precipitate apoB-containing lipoproteins first, then HDL2. 

G4. Gidez, L. I, Miller, G. J., Burstein, M., and Eder, H. A., Analyses of plasma high density lipoprotein subclasses by a precipitation procedure Correlation with preparative and analytical ultracentrifugation. In Report of the High Density Lipoprotein Methodology Workshop (K. Lippel, ed.), pp. 328-340. U.S. Department of Health, Education and Welfare. NIH publication No. 79-1661, Bethesda, Md., 1979. 

In Figure 3.9, a SEM micrograph of a powder sample of a BaCe0 95Yb0 05O3 5 perovskite, which was synthesized following the previously described acetate precipitation procedure, is shown [51],... 

A similarly poor efficiency in extraction can also be seen in Fig. 11, where the extraction result for the product obtained by the radiation grafting of styrene onto polyethylene terephthalate)(PET) fibers13 is shown. In this case the unreacted PET can be extracted after most of PS homopolymer has been extracted by repeated solution-precipitation of the sample. It should be mentioned here that the solution procedure is also necessary to extract the unreacted PET. Such a solution-precipitation procedure is also necessary for nylon-styrene13 and poly(vinyl chloride)-acrylo-nitrile14 graft products so as to remove the homopolymers to a sufficient extent. 

Guyot and Benevise also recorded the chlorine content of the dissolved and reprecipitated polymer obtained from degraded resin samples. Although the degraded sample, as a whole, showed appreciable loss of chlorine, the reprecipitated samples had contents close to that of un-dehydrochlorinated polymer. According to the authors, this precipitation procedure left in solution small amounts of low molecular weight fragments which did not contain chlorine. 

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