Dialysis bag

In a dialysis experiment, a dialysis bag containing the dissolved humic materials is placed in a solution of a pollutant (preferably radiolabeled). The dialysis tubing is chosen so the pollutant is free to diffuse through the bag while the humic materials are retained inside the bag. The solution is shaken at constant temperature until it comes to an equilibrium point. At equilibrium, the pollutant inside the dialysis bag consists of two fractions that truly dissolved and the bound to the humic materials. The concentration of pollutant on the outside of the dialysis bag consists only of the free, truly dissolved fraction. Any increase of the pollutant concentration on the inside of the dialysis bag is due to binding by dissolved humic materials. A series of dialysis experiments, therefore, can measure the bound fraction concentration as a function of the free concentration. 

Figure 3 presents some measurements of the extent of binding of DDT to dissolved organic carbon in secondary sewage effluent. The data is somewhat noisy, partially due to the fact that a portion of the DOC was able to pass through the dialysis bag. Nonetheless, the experiments showed that the DDT was bound to the sewage effluent DOC. 

The DNA band is cut from the gel and placed in a dialysis bag containing a small volume of buffer. The bag is placed in an electrophoretic tank and, when the current is switched on, the DNA passes out of the gel. The polarity of the current is reversed for a few moments to cause any DNA actually on the dialysis membrane to move back into the buffer within the bag. The DNA in the buffer is then precipitated with ethanol. 

Meadows et al. (1998) conducted a 28 d exposure of brown trout (Salmo trutta), standard SPMDs and hexane fllled dialysis bags (Sodergren, 1987) to spring water (total organic carbon < 1 mg L ) contaminated with PCBs. Trout were not fed during the exposure, and temperature and flow conditions remained constant throughout the exposure. A good correlation (r = 0.89) was found between the uptake rate constants ( u,fs) for whole body trout and the uptake rate constants... 

Figure 7.6 Principle components analysis (PCA) of PCB congener concentrations in technical Aroclor mixtures, contaminated water, caged brown trout, SPMDs, and hexane filled dialysis bags. The plot shows that 77% of the variance of samples within the 95% confidence ellipse is explained by PCI and PC2 and that caged fish and SPMDs are clustered together (PCA plot courtesy of Kathy Echols, USGS-CERC, Columbia, MO, USA).

Echols, K.R. Meadows, J. Schwartz, T. Borsuk, P. Carline, R. Tillitt, D. 1996, Comparison of SPMDs, Caged Fish, and Hexane Filled Dialysis Bags for Sampling PCBs in Groundwater from a Spring at Sherman s Dale, PA. Presented at the 4th Annual SPMD International Workshop Kansas City, MO. June 11-13, 1996. 

In a dialysis procedure, enzyme should be preincubated with a concentration of inhibitor sufficient to reduce activity by at least 90%. A solution containing the inhibited enzyme is then placed inside a small bag fashioned from dialysis membrane with a molecular weight cutoff value substantially lower than the mass of the enzyme. The sealed dialysis bag is then placed in a beaker containing a large volume of buffer, and is left... 

At the end of the dialysis procedure, the bag is blotted dry and enzyme solution is removed prior to assessment of activity. It may be necessary to include cofactor in the assay mixture if it is possible that a dissociable cofactor was lost from the enzyme during dialysis. As the volume containing enzyme inside the dialysis bag changes to some degree during the dialysis procedure, it is usually necessary to correct measured enzyme activity to reflect this change in volume, and a correction based on protein concentration is often done in this regard. It is normal for activity thus measured to be expressed as a fraction of that in a parallel (dialyzed) control experiment. 

A (rapidly) reversible inhibitor will permit rapid and complete recovery of enzyme activity by dialysis. However, irreversible inhibitors are not removed by this procedure. Recovery from tight-binding inhibition is usually slow it is not uncommon for several dialysis bags containing enzyme to be prepared and for activity in each to be determined at various time points following the commencement of dialysis. The off-rate of these inhibitors is generally more rapid at higher temperatures. 

Micelle solutions of PlPAAm-Ci8H35 was prepared by direct dissolution of the polymer in cold water (4°C) due to its good water solubility [23]. Each solution of PIPAAm-PSt, PlPAAm-PBMA, and PIPAAm-PLA was prepared by dissolving each copolymer in DMF, A-ethylacetamide, and DMAc, respectively. The solutions were put into a dialysis bag (MWCO = 13,000) and dialyzed against distilled water at 10°C, 20°C, and 4°C, respectively, for 24 hours. The micelles were purified with ultrafiltration membrane of 200,000 molecular weight cut off at 4°C. The aqueous solution was lyophilized to leave a white powder of micelles. 

Root powdering and demineralization. Sixty-five frozen and pulp-free tooth roots were ground in a Waring blender and powdered under liquid nitrogen in a freezer mill (Spex, Edison NJ, USA). The sieved powder (< 450 pm) was demineralized in dialysis bags in 0.5 M EDTA, pH 7.4, at 4°C with regular replacement of the solution. Demineralization was continued until no further calcium release could be detected by atomic absorption spectrometry. 

Leave enough space in the dialysis bag so that the volume can double during... 

At least two different techniques are available to compress an emulsion at a given osmotic pressure H. One technique consists of introducing the emulsion into a semipermeable dialysis bag and to immerse it into a large reservoir filled with a stressing polymer solution. This latter sets the osmotic pressure H. The permeability of the dialysis membrane is such that only solvent molecules from the continuous phase and surfactant are exchanged across the membrane until the osmotic pressure in the emulsion becomes equal to that of the reservoir. The dialysis bag is then removed and the droplet volume fraction at equilibrium is measured. 

An emulsion that is, for instance, stable over many years at low droplet volume fraction may become unstable and coalesce when compressed above a critical osmotic pressure 11. As an example, when an oil-in-water emulsion stabilized with sodium dodecyl sulfate (SDS) is introduced in a dialysis bag and is stressed by the osmotic pressure imposed by an external polymer solution, coarsening occurs through the growth of a few randomly distributed large droplets [8]. A microscopic image of such a growth is shown in Fig. 5.1. 

Preheat 2 L of distilled water to 75 °C in an oven, then add 20 g unhydrolyzed crystals of Fe(N03)3 9H2O with rapid stirring. Return to the oven and leave there for 10-12 min. During this time the solution changes from gold to dark reddish brown indicating the formation of Fe hydroxy-polymers. No precipitate should form. Cool rapidly by plunging into ice water, transfer to a dialysis bag and dialyse for at least... 

Ryan et al. (2001) studied the effects of hydroxyapatite addition to soils impacted by Pb from smelter operations. Dialysis experiment were conducted where the soil and hydroxyapatite solids were placed in separate dialysis bags suspended in 0.01 M NaN03. Chloropyromor-phite formed on the dialysis membrane containing the soil. The dissolution of solid-phase soil Pb was the rate-limiting step for pyromorphite formation. EXAFS showed that after the 240 day incubation the hydroxyapatite treatment caused a change in the average, local molecular bonding environment of soil Pb. 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

Color Plate 31 Colloids and Dialysis (Demonstration 27-1) (a) Colloidal Fe(III) (left) and ordinary aqueous Fe(III) (right). (J ) Dialysis bags containing colloidal Fe(III) (left) and a solution of Cu(ll) (right) immediately after placement in flasks of water, (c) After 24 h of dialysis, the Cutll) has diffused out and is dispersed uniformly between the bag and the flask, but the colloidal Fe(III) remains inside the bag. 

Large molecules remain trapped inside a dialysis bag, whereas small molecules diffuse through the membrane in both directions. 

The removal of eluent from the sample can be also achieved by dialysis. When dialyzing the concentrated GuHCl solution in a dialysis bag, it is important to leave some space in the bag, since there is a significant increase in volume with the decrease of GuHCl concentration. 

Elution of the RNA from the gel pieces can be accomplished by diffusion ( cmsh-and-soak method ) or by electroelution (for example, electroelution into dialysis bags) [14]. Afterwards the RNA is precipitated and dissolved in selection buffer. 

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