Heptane, solvent matrix

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. 

Alternatively, coacervation or solvent extraction is often used to produce microspheres (Fig. 3). The protein and polymer emulsion is stirred with a nonsolvent for the polymer such as silicone oil, resulting in the formation of embryonic microspheres (for a review, see Lewis, 1990). The nonsolvent extracts the methylene chloride or ethyl acetate firom the polymer phase, causing precipitation of the polymer and entrapment of the protein in the polymer matrix. To remove the nonsolvent, a volatile second nonsolvent (e.g., heptane) is added, and the microspheres are allowed to harden in the nonsolvent. After repeated extraction with the volatile nonsolvent, the final microspheres are then dried. While this method offers the advantage of avoiding contact between the protein phase and an aqueous phase as in the solvent evaporation method, the additional solvents utilized in this process are often difBcult to completely remove and are a safety and toxicity concern. 

To explore the difficulties in practical implementation of the above concepts, mixed matrix membranes, with 20% molecular sieves (by volume), were prepared by solution deposition on top of a porous ceramic support. The ceramic supports used were Anodise membrane filters which had 200 A pores that open into 2000 A pores and offer negligible resistance to gas flow. Initially the molecular sieve media, zeolites (4A crystals) or carbon molecular sieves, was dispersed in the solvent, dichloromethane, to remove entrapped air. After two hours, Matrimid was added to the mixture, and the solution was stirred for four hours. The solutions used varied in polymer content from 1-5 wt %. The solution was then deposited on top of the ceramic support, and the solvent was evaporated in a controlled manner. The membranes were then dried overnight at 90°C under vacuum. This was followed by a reactive intercalation post treatment technique 15) to eliminate defects. This technique involves imbibing a reactive monomer (e.g. diamine) from an inert solvent (e.g. heptane) into any micro defects. Next, a second reactive monomer (e.g. acid chloride) was introduced to reactively close defects by forming a low permeability polymer. The membranes were dried again to remove the inert solvent. Individual membrane thickness was determined by weight gain and varied from 5 to 25 Jim. 

We now turn from binary polymer solvent systems to ternary polymer matrix solvent systems. Dielectric relaxation studies using polyisoprenes as probe chains in polybutadiene -heptane solutions were examined by Urakawa,... 

A new method is described for the quantitative determination of some sulphur-containing antioxidants in PE. The polymer matrix is dissolved in hot n-heptane/ isopropyl alcohol, 97/3 v/v at 160 deg.C under elevated pressure (0.33 MPa) and precipitated by cooling. The solution is injected directly into a normal-phase silica gel column flushed with the same solvent as used for the dissolution of the polymer. This method gives high recovery of the antioxidants, good repeatability of the analysis and a low detection limit of 0.011 mg 4,4 -thiobis(3-methyl-6-tert-butylphenol) (Santonox R) /I g PE 0.074 mg ditetradecyl-beta,beta -thiodipropionate (Chimox 14) / 1... 

Polysaccharides, the most abundant biopolymers in nature, have also been used in chromatography as CS. Although intrinsically chiral, the materials used for this purpose are polysaccharide derivatives. Among them, esters and carbamates of cellulose and carbamates of amylose, in particular the 3,5-dunethylphenylcarbamates of either of them, are the most popular. When the CSPs are constituted by a silica gel matrix onto which the CS is simply coated, the composition of the mobile phase is limited to those solvents that do not solubilize the polysaccharide derivative. Mixtures of a hydrocarbon, hexane, or heptane, with an alcohol, usually 2-propanol, methanol, or ethanol, are common mobile phases. Although aqueous mobile phases can be used together with acetonitrile or methanol, these conditions tend to provide lower enantioselectivity values. ... 

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