Vacuum concentration

The urea solution stream is then fed to the vacuum concentrator unit which operates at 17.3 kPa (130 mm Hg abs) and produces 88.7 wt % urea. It then goes to either two-stage evaporators if prills are made, or a single-stage unit for granule production. 

The aqueous extract is usually vacuum-concentrated although freeze concentration has been described.103... 

For precipitation of DNA and RNA, add 10% of the volume sodium acetate, pH 7 or 5.2, respectively. Add four parts of ice-cold 98% ethanol and mix well. Add 1 pi of linear acrylamide (3%). Incubate for 2 h at -20°C and centrifuge at 12,000 for 30 min in a tabletop centrifuge. Carefully remove the supernatant—the DNA or RNA should be visible against the light as one or several small shiny specks, usually attached to the tube, but they may be loose—and wash the pellet with 200 pi 80% ethanol. Remove the supernatant, and dry the DNA or RNA (3 min in a speed vacuum concentrator) until all visible liquid has gone, but avoid overdrying of the pellet because the DNA or RNA will then be difficult to redissolve. Dissolve the DNA in 100 pi dd H O. 

The analysis is carried out on a Micromass Quattro II tandem mass spectrometer, coupled to a Hewlett Packard HP 1100 HPLC system. All other laboratory equipment is standard equipment,with exception of a Centrivap vacuum concentrator (Lab-con ). 

NFDM, which retains casein micelles similar to those in fresh milk, is produced by pasteurization of sklmmllk, vacuum concentration and spray drying under processing conditions that result in either "low heat" or "high heat" product. Low heat NFDM is required for most applications that depend upon a highly soluble protein, as the case for most emulsification applications, since it is manufactured under mild temperature conditions to minimize whey protein denaturation and complexation with casein micelles. 

Partly demineralized whey is produced by subjecting whey to electrodialysis or ion exchange processing treatments to prederen-tlally remove polyvalent ions, vacuum concentrated and spray dryed. 

Production of lactose essentially involves concentrating whey or ultrafiltration permeate by vacuum concentration, crystallization of lactose from the concentrate, recovery of the crystals by centrifugation and drying of the crystals (Figure 2.15). The first-crop crystals are usually contaminated with riboflavin and are therefore yellowish a higher grade, and hence more... 

Among these amines, iso-propylamine was the most suitable for this process, because it was released from 7 during the C-C bond-forming reaction as a byproduct and was able to be reused for the CIDT without adding any additional amine. In fact, vacuum concentration of the C-C bond-forming reaction mixture left a catalytic amount of iso-propylamine in the residue, and the residual isopropylamine effectively catalyzed CIDT without the addition of further amine to afford threo-8 in 89% yield with >99% dr. The level of residual iso-propylamine was... 

These experiments point out the need to avoid vacuum concentration during the recovery of hydrophobic compounds such as the... 

Isophorone, 5-chlorouracil, and quinoline were probably lost by vaporization from the column effluent, F7. Each of these solutes is sufficiently water-soluble to not adsorb to Teflon, but each is volatile enough to be lost during the vacuum concentration of F7. Recall that only 20 of 15 mg of quinoline was recovered during lyophilization of a solution to half of its original volume (Table III). Isophorone and 5-chlorouracil were detected in F7, and at least part of the unrecovered fraction of each of these compounds must have been lost during the vacuum concentration of this effluent. (Eluates of the anion-exchange bed were not analyzed for 5-chlorouracil, which also could have been present on this bed see Table IX.) Quinoline was not detected in F7,... 

Compare the techniques of lyophilization and centrifugal vacuum concentration. Give advantages and disadvantages of each. 

The SpeedVac centrifugal vacuum concentrator Courtesy of Savant Instruments (savantec savec com)... 

Dry the gel pieces completely in a centrifugal vacuum concentrator. Caution should be exercised in handling the dried gel pieces, as they are easily lost from tubes or plates. 

Vacuum concentration of the acid using Mantius, Swenson and other concentrators was used to some extent, but presented operational difficulties. 

Estes el al. [722] described a method for the measurement of triethyl- and trimethyllead chloride in potable water, using fused silica capillary column gas chromatography with microwave excited helium plasma lead specific detection. Element specific detection verified the elution of lead species, a definite advantage to the packed column method. The method involved the initial extraction of trialkyllead ions from water into benzene, which was then vacuum reduced to further concentrate the compounds. Direct injection of the vacuum concentrated solutions into the gas chromatography-microwave excited helium plasma system gave delectability of triethyllead chloride at the 30mg L 1 level... 

The urea solution that leaves the stripper bottom is further purified in HP (17.5 bar) and LP (2.5 bar) decomposers. The urea solution is first concentrated to 88.7% in a vacuum concentrator and then to the required concentration for prilling or granulating110. 

The organic and acid phases are separated in a static separator located at the top of the process building. From the separator the acid phase discharges to the vacuum concentrator, while the organic phase passes to the washing section. 

Isolation of Volatiles from Tomato Condensate. Condensate from commerical tomato paste production using vacuum concentration was stored at 5°C in the dark and used within a few days. 

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