Supernatant phase, total solids

Complex Coacervation Procedures. Gelatin/alginate (G/A), gelatin/ polyphosphate (G/P), and gelatin/gum arabic (G/GA) complex coacervate and supernatant phases were used in this study. G/A complex coacervate and supernatant phases were formed at pH 4.2 with a 3.7 1 (w/w) mixture of gelatin (227 bloom) and sodium alginate (total solids 1.8 wt. percent). G/P complex coacervate and supernatant phases were formed at pH 4.4 with a 9 1 (w/w) mixture of gelatin (283 bloom) and polyphosphate (total solids ... 

Table I. Total Solids Content of Complex Coacervate and Supernatant Phases...

The reaction mixture is cooled in a water-ice bath, and a saturated aqueous ammonium chloride solution is added at such a rate as to maintain the temperature below 35°C. Ammonium chloride solution is added in portions until addition produces no further exothermic reaction (Note 3). The supernatant solution is decanted through glass wool onto 400 g of ice in a 4-L separatory funnel. The residual solids are washed with three portions of hexane, approximately 1000 nt total, and the washes are decanted into the separatory funnel. After the phases are separated, the aqueous phase is washed with an additional 500-mL portion of hexane. The combined organic extracts are washed with 500 nl of saturated ammonium chloride, and then with 500 nl. of brine. The organic layer is dried over anhydrous magnesium sulfate and filtered. Most of the solvent is removed by a rotary evaporator and the residual oil is distilled at reduced pressure using an ice water-cooled fraction cutting head. After a small forerun, approximately 390-392 g (94% of theory) is collected as a colorless oil, bp 116°C/1.6 nm (lit. 155°C/17 rim). ... 

On the basis of the experience accrued so far, the extraction efficiency can be affected by both the nature of the sample under test and the As species actually present in the sample. The lipid content of the sample and the presence of As species with hydrophobic residues play a key role in this context. As a consequence, it may be useful to remove or partition lipids with an organic solvent prior to the methanol-water extraction in order to increase the extraction efficiency. This approach is also viable to prevent emulsification of methanol and lipids, which could otherwise significantly reduce the extraction efficiency [26]. Thus, sample preparation prior to As speciation usually starts with the chloroform-methanol extraction, followed by centrifugation of the sample solution to remove solid particles. Subsequently, after the addition of methanol and water, the supernatant is separated in a funnel. The amount of As remaining in the organic phase is usually quantified as total As by wet digestion after solvent evaporation. Obviously, this entails the loss of all speciation information related to the lipid-soluble As species [2]. Speciation analysis is finally carried out on the methanol-water phase, usually after solvent evaporation (see Table 19.2). 

To minimize the loss of materials, selective extractions were conducted in the centrifuge tubes in which the solids were originally stored. The volumes of the extracting solutions were proportioned to the weight of solids in the tube. Between each successive extraction, separation was affected by centrifugation (Sorvall Model RC2-B) at 10,000 rpm for 30 minutes. The supernatant was removed with a pipet and analyzed for trace elements. The concentrations of these elements in the extracts were determined by flameless atomic absorption spectrophotometry as described for the dissolved trace element analyses (15). The total concentration of a solid phase-associated trace element is the sum of the four extraction concentrations and does not include the residual (14) or crystalline (11) solid fraction. 

After choosing the best solvent, determine the minimum concentration required of that solvent by titrating 1 vol of whole broth with increasing amounts of solvent. Titration should start with a low solvent concentration such as 10% (v/v) and proceed with small increases. Samples should be mixed for at least 60 min and then centrifuged or filtered to remove the solids. Product concentration in the supernatant is measured, and the total quantity of product in the liquid phase is determined by multiplying liquid volume and product concentration. A solvent concentration is selected that is slightly less than that required for maximum product extraction (Note 13). 

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