Extractant loss from membranes

Three commercially available filtering media were evaluated for the collection of airborne particulates of the organoarsenical compounds. These were cellulose ester, Fluoropore, and Mitex membrane filters. The evaluation was based on the following requirements l) the collection medium must quantitatively collect the particulates 2) the collection medium must be capable of. retaining the compounds without loss or chemical change before analysis 3) the collected species must be extracted quantitatively from the collection medium for analysis and b) the method must be efficient at temperatures up to 50°C and a relative humidity of... 

The radical H02 formed reversibly from 02 in acidic solutions (p a = 4.7) is similar in reactivity to R02 radicals, formed by oxygen addition to alkyl and related radicals, or by H-atom loss from ROOH molecules. As radicals, they are more reactive than 02 ions and can extract active hydrogen, as in reaction [1.5] to give allyl radicals. The resulting hydroperoxide, like H202, is quite reactive, as is the allyl radical which, formally, has ca. 50% spin-density on two almost equivalent carbon atoms, as indicated. Reaction [1.5] is of major importance in certain membrane reactions, since it is one of the stages in the au-toxidation of unsaturated lipid groups (see Chapter 2). The total reaction comprises [1.5] followed by [1.6] which, in turn is followed by [1.5], These two steps constitute a chain reaction which may continue... 

PIMs have the potential to overcome many of these limitations mentioned above. The encapsulation of the extractant within the membrane polymer matrix significantly lessens reagent losses to the aqueous solutions in contact with the membrane. Although PIMs suffer from relatively slow mass transport through the membrane, due to their mechanical stability the membranes can be made into very thin films which can somewhat mitigate the diffusive resistance effects (Nghiem et al, 2006). 

Since hematin inhibits Taq polymerase, it is absolutely essential to eliminate red blood cell contamination. Selective lysis of red blood cells can be accomplished with a buffer mixture consisting of 155 mM ammonium chloride, 10 mM potassium bicarbonate, and 0.1 mM EDTA adjusted to pH 7.4. Alternatively, the cytoplasmic membrane of all cells can be dissolved with a buffer mixture containing the non-ionic detergent Triton-X 100, leaving behind nuclei of white blood cells from which DNA can be extracted. However, this technique will result in the loss of cytoplasmic DNA to the supernatant, and hence will not be able to extract mitochondrial DNA (B11). 

Methods for (bio)catalyst retention include (i) heterogenization on supports (ii) recovery through phase change, such as precipitation or extraction of the catalyst and (iii) membrane filtration of a homogeneous catalyst. All methods, in principle, enable repeated use of a chiral catalyst without much loss of activity or selectivity. In a recent review (Kragl, 2001), examples are given from laboratory and... 

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