Hydrodynamic method

In this chapter, we describe some of the more widely used and successful kinetic techniques involving controlled hydrodynamics. We briefly discuss the nature of mass transport associated with each method, and assess the attributes and drawbacks. While the application of hydrodynamic methods to liquid liquid interfaces has largely involved the study of spontaneous processes, several of these methods can be used to investigate electrochemical processes at polarized ITIES we consider these applications when appropriate. We aim to provide an historical overview of the field, but since some of the older techniques have been reviewed extensively [2,3,13], we emphasize the most recent developments and applications. 

The washing of capillaries with dilute alkaline solution is advisable before analysis. The alkaline solution can be followed by deionized water and buffer. Capillaries can be washed between runs too. Samples can be introduced into the capillary by hydrodynamic and electro-kinetic methods. The hydrodynamic method applies a pressure difference (5-10 sec) between the two ends of the capillary. The pressure difference can be achieved by overpressure, vacuum or by creating a height difference between the levels of the buffer and sample reservoirs. In the case of electrokinetic injection, the injection end of the capillary is dipped into the sample for a few seconds and a voltage of some thousand volts is applied. 

The ability of varying the rate of the mass transport by agitating the solution (or the working electrode) constitutes the basis of hydrodynamic methods (hydrodynamics = liquids in motion), which are a further support to the study of electrode kinetics. Nevertheless we wish to cite them here simply to cover a drawback of cyclic voltammetry. In fact, cyclic voltammetry is unable to discriminate between oxidation and reduction processes, and vice-versa. 

In all hydrodynamic methods we have the effect of both the hydrodynamic and thermodynamic interactions and these do not contribute additively but are coupled. This explains why the theoretical treatment of [77] and of the concentration dependence of has been so difficult. So far a satisfactory result could be achieved only for flexible linear chains [3, 73]. Fortunately, the thermodynamic interaction alone can be measured by static scattering techniques (or osmotic pressure measurement) when the scattering intensity is extrapolated to zero scattering angle (forward scattering). Statistical thermodynamics demonstrate that this forward scattering is given by the osmotic compressibility dc/dn as [74,75]... 

Note 1 An infinite number of molar-mass averages can in principle be defined, but only a few types of averages are directly accessible experimentally. The most important averages are defined by simple moments of the distribution functions and are obtained by methods applied to systems in thermodynamic equilibrium, such as osmometry, light scattering and sedimentation equilibrium. Hydrodynamic methods, as a rule, yield more complex molar-mass averages. 

Professor Ubbelohde s suggestions are certainly worthwhile. But there are many directions that we are trying to pursue more detailed studies of the conformation of the polymers, introduction of new functional groups, macro molecular characterization by hydrodynamic methods, and so on. If I were a professor at Imperial College, I could assign all these problems, and those you suggest, to members of the staff but I am constrained by a smaller research group. 

CA 73, 89708q(1970) (Hydrodynamic Method for detg the relative efficiency of expls consisted of explns carried out in a chamber provided with a brass plate in the bottom and filled with water. The extent of deformation... 

The major advantage of protein adsorption studies on high surface area materials is that changes of some extensive properties which accompany the process of adsorption are large enough to be directly measured heat of adsorption through microcalorimetry 141), uptake or release of small ions by a combination of electrokinetic methods and titration 142), thickness of adsorbed layer or an increase of the volume fraction of solid phase by a hydrodynamic method like viscometry 143). Chromatographiclike analysis can also be applied to protein adsorption 144). 

Nuclease behaves like a typical globular protein in aqueous solution when examined by classic hydrodynamic methods (40) or by measurements of rotational relaxation times for the dimethylaminonaphth-alene sulfonyl derivative (48)- Its intrinsic viscosity, approximately 0.025 dl/g is also consistent with such a conformation. Measurements of its optical rotatory properties, either by estimation of the Moffitt parameter b , or the mean residue rotation at 233 nin, indicate that approximately 15-18% of the polypeptide backbone is in the -helical conformation (47, 48). A similar value is calculated from circular dichroism measurements (48). These estimations agree very closely with the amount of helix actually observed in the electron density map of nuclease, which is discussed in Chapter 7 by Cotton and Hazen, this volume, and Arnone et al. (49). One can state with some assurance, therefore, that the structure of the average molecule of nuclease in neutral, aqueous solution is at least grossly similar to that in the crystalline state. As will be discussed below, this similarity extends to the unique sensitivity to tryptic digestion of a region of the sequence in the presence of ligands (47, 48), which can easily be seen in the solid state as a rather anomalous protrusion from the body of the molecule (19, 49). 

Concerning the experimental side of polymer adsorption studies the quantity A was only measurable at the early stage of the study, but in 19SS the thickness of the adsorbed layer became accessible to measurement by a hydrodynamic method and in 1961 the quantity p was first determined by infrared spectroscopy. Ellipsometry came up in 1963, which enabled both the adsorbance and the thickness of the adsorbed layer to be measured simultaneously. 

Actually, information regarding the internal structure of the swollen particle is not necessary since the change in particle volume is equal to the volume of water absorbed, and the expanded particle settles slower, as its average density decreases, according to Equation 2 in either case. As with other hydrodynamic methods, sedimentation does not offer easy access to information regarding particle morphology. 

In addition, maximum expansion occurred at pH = 12.5 in the PCS experiments compared with approximately 10.5 observed in the sedimentation and viscometry experiments. Since PCS is carried out at much lower particle concentrations, interactions between the charged particles at the higher concentrations are probably involved. Similar comparisons with non-expanding carboxylic latex particles were carried out in an effort to separate interparticle charge effects from true particle expansion in interpreting apparent particle sizes determined by hydrodynamic methods. 

Be familiar with methods for protein molecular weight determination and the limitations of such methods gel filtration, gel electrophoresis, and hydrodynamic methods. 

Figure 22 also demonstrates that the hydrodynamic thickness due to segments in loops alone is considerably less than that due to all segments. Indeed, previous calculations (Cohen Stuart et al., 1984c Anderson and Kim, 1987 Scheutjens et al, 1986) indicate that hydrodynamic methods probe the outer region of the adsorbed layer where tails dominate. 

Samples are injected into the capillary tube at the opposite end from the detector using one of two methods, i.e. hydrodynamic or electrokinetic. These are illustrated in figure 4.47. The end of the tube is dipped into the sample solution. and a very small volume (I to SOnl) introduced into the capillary either using gravity, positive pressure or a vacuum (hydrodynamic method) or... 

Byron, O. (1996) Size determination of proteins - A. Hydrodynamic methods, in Proteins Labfax (Price, N.C., Ed.). BIOS Scientific Publishers, Cambridge. 

Studying molecular properties of rigid-chain polymers by hydrodynamic methods, specific difficulties sometimes arise. Thus, many polymers with aromatic chains that are of great practical importance are molecularly soluble only in very aggressive media such as concentrated sulfuric acid. Hence, experiments in these systems require specific instruments ... 

Most of hydrodynamic methods have focused on increasing the particle back transport from the membrane-liquid interface by increasing the shear rate and the flow instability in the boundary layer. These techniques include secondary flows, spacers and inserts, pulsed flow, high shear rate devices, vibrations, and two-phase flow. The physical methods that are currently been tested to enhance filtration performance of membranes include the application of electric fields and ultrasound. 

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