Containment loss centrifuges

General Considerations. With liquids and solutions the most serious losses are due to (a) transference from spherical flasks and difficulties of drainage, (b) retention by filter-papers, (c) absorption by large corks. As containers for small quantities of liquids it is therefore often convenient to use pear-shaped flasks A and conical test-tubes or centrifuge-tubes B (Fig. 29). (In this and subsequent figures, approximate dimensions are given to indicate a convenient size.)... 

A general method of eliminating the adsorption of trace materials on solid residues, or container walls, is difficult to predict and each situation must be evaluated on the basis of its own unique conditions. It should be emphasized that, assuming there are only small quantities of contaminating materials present that could adsorb a proportion of the sample, significant losses would only arise when the solutes of interest are present in the sample at the ppm level. Such problems of adsorption are reduced considerably if the contaminating solid material is removed by centrifugation. 

Pre-concentration by vacuum centrifugation is a common technique used in many versions of current in-gel digestion methods and pHPLC. Throughout the process, the sample is exposed to many surfaces, which may contain a minimal number of active sites where losses can occur. The amount of sample loss may be negligible for concentrated samples, but loses at lower peptide concentrations, such as the femtomole (fm=10 M) level (see Table 3.1), increase markedly. ... 

To summarize, chiral heterogeneous catalysts were prepared from rhodium-diphosphine complexes and aluminum-containing mesoporous materials. The bonding occurred via an ionic interaction of the cationic complex with the host. These catalysts were suitable for asymmetric hydrogenation of functionalized olefins. The catalysts can be recycled easily by filtration or centrifugation with no significant loss of activity or enantioselectivity. 

After shaking, the vials were centrifuged to remove the fines from the supernatant and an aliquot of the supernatant was counted against a standard of the particular formulated liquid phase. All experiments were performed in triplicate, at constant activity and Hg-carrier concentration (20 pg Hg/ ml) with controls (liquid phase without sorbent) to check for possible adsorption losses on the container. The experiments were carried out in nitrate and chloride media at pH 1-10. 

Adsorption (or desorption) is the process by which a net accumulation (or loss) of a substance occurs at an interface between two phases. In a typical experiment, two phases are mixed intimately to provoke a chemical reaction leading to adsorption or desorption, and then a physical separation is made, with one of the separates being a single phase and the other, a mixture of the two reacted phases. For example, a solid-phase adsorbent and an aqueous solution could be mixed, and then separated by centrifugation into an aqueous phase (supernatant solution) and a slurry that contains both the solid adsorbent and some aqueous solution. If is the moles of substance i in the reacted mixture and m is the molality of substance i in the separated aqueous phase, then the relative surface excess, np, of substance i, as compared to another substance j, is defined by1... 

Methyl derivatives were used by Martin and Driscoll [509] they were prepared by treatment with dimethyl sulphate and applied to the analysis of barbiturates in serum, as follows. A 2-ml volume of a saturated solution of sodium dihydrophosphate and 10 ml of diethyl ether were introduced into a test-tube containing 2 ml of serum. The test-tube was closed and shaken vigorously for 30 sec, centrifuged for 1 min, then 7 ml of the extract were transferred into another test-tube and the ether was removed in a stream of air in a water-bath. The residue was dissolved in 2 ml of methanol with 10% of water (v/v), saturated with potassium carbonate, and 0.1 ml of dimethyl sulphate were added and the mixture was heated in a water-bath at 60°C for 4 min. At this temperature methanol was removed in a stream of air (3 min) and the residue was extracted into 1.5 ml of -heptane with the addition of 1 ml of 1 M acetate buffer (pH 6). A 1 -ml volume of the n-heptane extract was transferred into a small test-tube, evaporated carefully in order that losses of the derivatives might be avoided, and dissolved in 100 (A of acetone (containing an internal standard if necessary) 5 jul were analysed on a column packed with 5% of SE-30 at 175°C. 

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