Pre-enrichment

In order to avoid Ne-losses, the liquid nitrogen (j), which is fed to the low-pressure column as reflux, is withdrawn a few trays below the top of the pressure column. For such processes the Ne-yield is significantly over 90%, provided that none of the process air bypasses the pressure column in some way. 

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The electromagnetic separation plant built during World War 11 at Oak Ridge, involved two types of calutrons, alpha and beta. The larger alpha calutrons were used for the enrichment of natural uranium, and the beta calutrons were used for the final separation of U from the pre-enriched alpha product. For the electromagnetic separation process, UO was converted into UCl [10026-10-5] with CCl. The UCl was fed into the calutron for separation. The calutron technique has been used to separate pure samples of and stable isotopes of many other elements. The Y-12 calutron... 

Chemical exchange between hydrogen and steam (catalyzed by nickel—chromia, platinum, or supported nickel catalysts) has served as a pre-enrichment step in an electrolytic separation plant (10,70). If the exchange could be operated as a dual-temperature process, it very likely... 

Step 1. Automated, accelerated bacterial pre-enrichment, enrichment, and selective enrichment. 

Inoculate a flask containing 50 mL 2YT-Cm25 medium with an aliquot (—50pL) of the DMSO culture of the pre-enriched library. Shake the culture flask at 37 °C. 

Hydride and cold-vapour techniques represent a special combination of chemical separation and pre-enrichment with AAS determination, resulting in higher powers of detection for elements with volatile hydrides, eg, As, Bi, Se, Sb, Hg. Recent literature on vapour generation has been reviewed by Hill et al. (1991). Some examples of the use of hydride generation for the analysis of plant material are given by Muse et al. (1989), Leuka et al. (1990) and Ainsworth and Cooke (1990). Hydride generation can also be used with ICP-EAS (see below) and applications have been reviewed (Nakahara, 1991). 

The choice between an increase in calcine production rate and an improvement in product quality represents a classic operating trade-off in any production facility. Oxygen enrichment provides the capability to improve one or the other or a partial improvement of both. At a given enrichment level, greater productivity could be achieved if the calcine quality is maintained at the pre-enrichment level. Conversely, significant improvement in calcine quality can be achieved at the expense of a smaller increase in productivity. The choice must be made based upon the needs and relative economics of a given company. 

Is there zero metallicity gas (or stars for that matter) in galaxies Pre-enrichment by an initial stellar Population III also provides a solution to the G-dwarf problem and to the origin of metals seen in Lya forest clouds. What is the composition of the huge gas reservoirs in the outer parts of spirals and irregulars ... 

Initial conditions- One can assume that all the initial gas out of which the galaxy will form is already present when the star formation process starts or that the gas is slowly accumulated in time. Then one can assume that the initial chemical composition of this gas is primordial (no metals) or that some pre-enrichment has already taken place (e.g. Population III stars). As we will see in the following, different assumptions are required for different galaxies. 

Slow formation of the solar vicinity by gas infall -Variable IMF -Pre-enriched gas... 

If the number of target organisms in a sample is too low to be detected directly with one of these tests or if their growth is suppressed by competitive (non-target) microorganisms, it is necessary to carry out a pre-enrichment culture of the target organisms in a selective broth. This will never be a quantitative test, but more a presence/absence test. 

The presence/absence procedure was based on the ISO method for the detection of Salmonella (ISO 6579) which is summarised as follows (1) pre-enrichment in Buffered Peptone water (incubation time (18 2) h at (37 1)°C) and (2) selective enrichment in broth of own choice (incubation time and temperature according to own procedure). The detailed procedure is described elsewhere [37]. Each laboratory determined the presence or absence of Salmonella in 50 capsules. Four of these individually identified capsules were negative control capsules. The numbers of these capsules were unknown to the laboratories at the time of analysis. For the presence/absence procedure, all capsules showing typical colonies on the isolation agar were subjected to a confirmation for Salmonella. At least two colonies per capsule were used for this confirmation. All colonies (>1000 colonies) tested by the laboratories gave a positive Salmonella identification. The type of confirmation test used is described elsewhere [37]. 

To control the extent of water contamination with substances of environmental concern it is necessary to develop rapid and sensitive analytical methods. Modem gas chromatography (GC) and Hquid chromatography, especially in combination with mass spectrometry (MS), capillary electrophoresis (CE), and capillary electrochromatography are the most suitable techniques for the analysis of both an individual component and a complex mixture. However, as a mle, the concentration of solutes to be analyzed in water samples is too low, in the range of nanograms to micrograms per liter, to inject a probe directly into a chromatographic analytical column and, therefore, pre-enrichment of water samples is required. 

Breakthrough volume depends on the retention power of the SPE adsorbing material and determines the volume of the water sample, which can be percolated through the pre-column until the analyte arrives at the pre-column outlet. Thereby, the breakthrough volume determines the extent of analyte enrichment. Obviously, to achieve a high extent of pre-enrichment, the retention of the analyte should be a maximum at the sample loading step (but it should be a minimum at its elution step). 

A genosensor for bacterial detection should possess the following criteria sensitive (able to detect the bacterium in a small sample), specific (able to distinguish the target from non-target strains), precise, rapid and able to perform direct measurement without pre-enrichment. In addition, it would be desirable if the genosensor is portable or handheld, affordable and can be performed even by untrained personnel. 

Concentration by membrane filtration. Inoculation on a pre-enriched medium. Enrichment, subculturing on isolating agar. Identification. 

The HybriScan /) Beer kit detects all beer spoiling bacteria of the genera Lactobacillus, Pediococcus, Pectinatus mAMegasphaera. The sensitivity is 1-lOCFU/L after 24-30h pre-enrichment in NBB broth, or isolates can directly be used. 

Incineration PFC State-of-the-art technique for waste treatment Pre-enrichment is favorable (NF, UF, sorption), off line technique... 

In the first step, a pre-enrichment of about 4000 ppm of Kr and 400 ppm of Xe in liquid oxygen is achieved in the sump of an additional column (4), (Fig. 3.1). This column is integrated into the air separation unit... 

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