Extraction modification

The ionic and hydrophilic nature of the amino acids precludes their isolation from biological fluids by solvent/solvent extraction. Modification of the amino group, for example the formation of an N-acetyl group, makes solvent extraction accessible. 

During selection of the extraction methods to include in this chapter we considered the popularity of the method, maturity, simplicity of application in laboratory routine, cost, and prospects for development by further modification. New promising extraction modifications can be found in numerous current review papers. We... 

Derivatization and Extraction. Modifications of the procedures of Ebeler et al. (49) were used for all aldehyde analyses. Briefly, 3.0 mL of wine were mixed with 60 pL of internal standard (10 mg 2,4,5-trimethylthiazole/mL in 10% aqueous ethanol) and 1 mL of 0.03 M aqueous cysteamine (pH 8.5) the pH was adjusted with HCl or NaOH (pH s from 2-10 were evaluated as discussed below). Following reaction at room temperature for 1 hour, the pH was re-adjusted to 8.5 and the solution was extracted two times with 1.5 mL of chloroform the chloroform layer was removed each time and then combined to give a total of 3.0 mL of extract. Samples were injected onto a gas chromatograph fitted with either a mass spectrometer or nitrogen phosphorous detector. Peak area ratios of the internal standard to the analyte were used for all quantitative calculations. 

In the extraction modification of the method, add to the acidified sample solution (see above) 5 ml of 25% ammonium chloride solution, 5 ml of the SnCb solution, and 0.01 M HCl to 20 ml. Extract the solution with two portions of amyl acetate (containing 1% of resorcinol). Dilute the combined extracts with the solvent to the mark in a standard flask of suitable capacity, and measure the absorbance at 400 nm against the solvent. 

It has been shown that the complex formed at pH 5-6 is anionic, and is extractable by CHCI3 in the presence of organic bases. In extractive modifications of the method, nitron... 

It should be noted that sterility is very important when performing the nuclear extraction and first few steps of the TF protocol. Make sure that the water that is being used is RNase-free, DNase-free, and sterile. All centrifuge tubes must be sterile or previously autoclaved. All pipeting and transferring of materials should take place under a sterile hood. The derived nuclear extract is very sensitive to post extraction modifications and should therefore be handled very carefully. Once a sample is extracted and the protein concentration is taken, the sample should be used immediately or else aliquoted and frozen at -80 °C. Also, in order to assure consistency of results between trials, it is beneficial to use aliquots from the same original batch. 

Modification A without extraction Modification B with extraction... 

The nickel-diacetyl complex can be measured photometrically in the aqueous solution directly (modification A) or following extraction with chloroform and re-extraction (modification B). 

The sodium fusion and extraction, if performed strictly in accordance with the above directions, should be safe operations. In crowded laboratories, however, additional safety may be obtained by employing the follow ing modification. Suspend the hard-glass test-tube by the rim through a hole in a piece of stout copper sheet (Fig. 69). Place 1 -2 pellets of sodium in the tube, and heat gently until the sodium melts. Then drop the organic compound, in small quantities at a time, down — =. the tube, allowing the reaction to subside after each addition before the next is made. (If the compound is liquid, allow two or three small drops to fall at intervals from a fine dropping-tube directly on to the molten sodium.) Then heat the complete mixture as before until no further reaction occurs. 

The following is a modification of the process described and gives quite satisfactory results. Wash the crude mixture of benzonitrile and dibromopentane with sodium carbonate solution until the latter remains alkaline, and then with water. Distil it under reduced pressure and collect the fraction boiling up to 120°/18 mm. Dissolve this in twice its volume of light petroleum, b.p. 40-60°, which has previously been shaken with small volumes of concentrated sulphuric acid until the acid remains colourless. Shake the solution with 6 per cent, of its volume of concentrated sulphuric acid, allow to settle, and run ofi the sulphuric acid layer repeat the extraction until the acid is colourless or almost colourless. Wash successively with water, sodium carbonate solution and water, dry over anhydrous calcium chloride or calcium sulphate, and distil off the solvent. Distil the residue under diminished pressure and collect the 1 6-dibromopentane at 98- 100°/13 mm. 

A successful modification to the technique involves delayed pulsed-field extraction which allows discrimination between zero and near-zero kinetic energy electrons. About 1 ps after the laser pulse has produced photoelectrons, a small voltage pulse is applied. This has the effect of amplifying the differences in fhe velocities of fhe phofoelecfrons and allows easy discrimination befween fhem as a resulf of fhe differenf times of arrival af fhe defector. In fhis way only fhe elections which originally had zero kinetic energy following ionization can be counted to give fhe ZEKE-PE specfmm. 

Unique adsorption selectivities are employed in the separation of Cg aromatic isomers, a classical problem that caimot be easily solved by distillation, crystallisation, or solvent extraction (10). Although -xylene [106-42-3] can be separated by crystallisation, its recovery is limited because of the formation of eutectic with / -xylene [108-58-3]. However, either -xylene, / -xylene, (9-xylene [95-47-6] or ethylbensene [100-41-4] can be extracted selectively by suitable modification of seoUtic adsorbents. 

A modification of the conventional soy protein isolate process has been investigated on a small pilot-plant scale. It is based on the absorption of water from the aqueous protein after extraction at pH 8.5 using temperature-sensitive polyisopyropylacrylamide gels, followed by spray drying to give a 96% protein isolate (111). 

Farm animals produce recombinant proteins less expensively than bacteria or cells in culture because the farm animals produce large volumes of milk containing up to 5 g/L of recombinant protein. In addition, modifications to the proteins that can be performed only by mammalian cells are made by the cells of the mammary gland. Therefore, numerous pharmaceuticals that previously could only be made by cells in culture or extracted from human tissue or blood are being produced by lactating farm animals. 

Pentanedione is widely used in extraction processes for the separation and purification of metals because of its abiUty to form covalent metal chelates. It is also used as an intermediate in the production of heterocycHc substances and dyes, as a fuel additive (324), and in metal plating and resin modification. 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

Modifications and improvements to the basic process have been made to reduce the quantity of waste products (21,22) in the wet chemical process, to recover HF, and to economically process low Ta, high Nb containing raw materials (23). Several alternative extraction media have been reported in the hterature. Most, except for tributylphosphate (TBP) (24) and tri- -octylphosphine oxide (TOPO) (25), have never been used in industry. 

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