Precipitate, redissolution

PCI Positive chemical ionisation PRLC Precipitation-redissolution liquid... 

It has been reported by Celik and Somasundaran T381 that the interaction of divalent (and trivalent) cations with sulfonate surfactants causes surfactant precipitation followed by dissolution of the precipitate at higher concentrations. The precipitate redissolution phenomenon is not observed with monovalent ions. Indeed, some surfactant precipitation in the spinning drop tube was observed above concentrations corresponding to the first minimum of Figure 8 it is not known whether redissolution took place at higher concentrations resulting in the second tension minimum. 

Celik, M.S., Ananthapadmanabhan, K.P., and Somasundaran, P. "Precipitation/Redissolution Phenomena in Sulfonate/AlCl, Solutions," SPE paper 11796, 1983 SPE International Symposium on Oilfield and Geothermal Chemistry, Denver, June 1-3. 

The deprotected oligonucleotide synthetic product is precipitated twice in ethanol, and a 0.5 fig/fd solution in water is prepared (concentration is measured from a UV absorption spectrum). One microliter of the oligo-deoxynucleotide solution is mixed with 2 fd of 10X PL, 5 fd of [y-32P]ATP (or [y-35S]ATP), 1 fd of T4 polynucleotide kinase, and 11 fd water. After incubation at 37 ° (for 45 min with [y-32P]ATP or for 2 hr with [y-35S]ATP), the reaction is stopped by the addition of 150 [A of 5 M ammonium acetate, pH 5.5, and 130 fd water and 10 fd of the yeast tRNA solution are added to the mixture before precipitation with 1 ml ethanol. After chilling at —70° for at least 15 min, the precipitate is collected by centrifugation (12,000 g, 15 min), redissolved, and submitted to two additional cycles of precipitation-redissolution. Finally, the precipitate is redissolved in 20 fd of gel loading mix and the mixture analyzed on a 8% acrylamide-7 Af urea slab gel in IX electrophoresis buffer, until the bromphenol blue has reached the middle of the gel. 

The methods used to obtain chemical composition and functionality distributions for complex polymers are based on precipitation/redissolution, sorption and exclusion ef-... 

The copolymers of acrylamide and alkylacrylamide were prepared according to a micellar process in which sodium dodecyl sulfate was used to solubilize the water-insoluble monomer to enable copolymerization with the water-soluble monomer to occur (i). The mixture before the polymerization was clear and free of any emulsion particles or undispersed monomer. Potassium persulfate was used to initiate polymerization, which was taken to complete conversion at 50 °C for 24 h. The polymers were purified from the surfactant by acetone precipitation-redissolution and then dried in a vacuum oven at 25 °C. The amount of hydrophobe actually incorporated was taken to be equal to that used in the polymerization. 

An example of a separation where both sorption and precipitation-redissolution can be seen for the same sample is shown in Fig. 43 the separation of a SO,000-Da polystyrene sample by gradient elution (water/ tetrahydrofuran gradient, Cig column). The heavy, dashed curve and solid data points represent the solubility curve for this sample, showing the saturation-concentration (Cnn, x axis) plotted versus mobile-phase composition 0. The light curve and open dides are retention data, plotted as mobUo-phase composition at elation (4> versus sample mass (equivalent to... 

EG-LC polymer separations with the phase separation (precipitation - redissolution) retention mechanism. These authors can be considered founders of EG-LC of synthetic polymers. 

Petro and co-workers [31] used a moulded monolithic rod of macro porous PS-divinyl benzene copolymer as a separation medium for the HPLC of styrene oligomers and copolymers, e.g., styrene-2-naphthyl-methacrylate. On column precipitation redissolution chromatography is an alternative to size-exclusion chromatography (SEC). The solvent gradient used comprises a poor solvent (water, methanol, acetonitrile) and increasing amounts of a good solvent such as tetrahydrofuran. 

An additional technique that has been found useful in analysis of the composition of polymers and blends is liquid chromatography. Pasch and Rode used the critical point of adsorption of the least polar component of a blend to determine the liquid chromatographic conditions for separating blends of polymethacrylates into components (50). High pressure liquid chromatography (HPLC) in combination with mass spectroscopy was used to analyze the components of an epoxy resin (51). HPLC has also been used with a precipitation-redissolution technique to separate polymer molecular weights for several polymers as a shorter technique compared to SEC (52). Reverse-phase liquid chromatography with UV detection was useful in qualitative determination of brominated flame retardants in polymeric waste materials (53). 

One scheme for separating polymer mixtures by HPLC is based on a selective precipitation redissolution model [11]. It has been used with the evaporative light-scattering detector to monitor the separation of a three-polymer mixture (Fig. 20). Solvent programming was used. The author suggests that this technique can be used to determine chemical composition of copolymers, but no examples are shown. 

Morner isolated two water-soluble glycoproteins (called urinary mucoids) from urine by alcohol precipitation, redissolution, and precipitation with chloroform in the presence of acetic acid 4)- Interest in these substances was stimulated by the isolation of a purified urinary glycoprotein which proved to be a strong inhibitor of the hemagglutination by influenza virus and similar viruses 82, 83). Sialic acid (see below) is said to be removed from the glycoprotein by the virus. 

On the other hand, high-performance liquid chromatography (HPLC) is an important tool for the fast separation of complex polymers with regard to chemical composition. HPLC separations can be achieved via different mechanisms, including adsorption-desorption and precipitation-redissolution. In gradient HPLC, precipitation and adsorption processes are frequently combined. 

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