Membrane disk adsorption

Membrane disk adsorption devices are used in the same way as SPE columns, and are listed in the same tables. Matrix solid phase dispersion is a workup method in which... 

Membranes offer a format for interaction of an analyte with a stationary phase alternative to the familiar column. For certain kinds of separations, particularly preparative separations involving strong adsorption, the membrane format is extremely useful. A 5 x 4 mm hollow-fiber membrane layered with the protein bovine serum albumin was used for the chiral separation of the amino acid tryptophan, with a separation factor of up to 6.6.62 Diethey-laminoethyl-derivatized membrane disks were used for high-speed ion exchange separations of oligonucleotides.63 Sulfonated membranes were used for peptide separations, and reversed-phase separations of peptides, steroids, and aromatic hydrocarbons were accomplished on C18-derivatized membranes. 

The possibility of making such MIP membrane disks has been well demonstrated yet we do not know of real-life analytical applications. This may be related to the low selective capacity of the MIPs, the slow adsorption kinetics, and the known bleeding of MIPs which may be disturbing in environmental ultratrace analysis. A further problem is that the matrix of the large sample volume (typically aqueous) may not be compatible with the MIP separation. 

Yamini, Y. Alizadeh, N. Shamsipur, M. Sohd phase extraction and determination of ultra trace amounts of mercury(II) using octadecyl silica membrane disks modified by hexathia-18-crown-6-tetraone and cold vapour atomic adsorption. Anal. Chim. Acta 1997, 335, 69. 

A platinum disk electrode was electrolytically platinized in a platinum chloride solution to increase the surface area and enhance the adsorption power. The platinized platinum electrode was then immersed in a solution containing 10 mg ml l ADH. 0.75 mM and 6.2 mM NAD. After sufficient adsorption of these molecules on the electrode surface, the electrode was transferred into a solution containing 0.1 M pyrrole and 1 M KC1. Electrochemical polymerization of pyrrole was conducted at +0.7 V vs. Ag/AgCl. The electrolysis was stopped at a total charge of 1 C cm 2. An enzyme-entrapped polypyrrole membrane was deposited on the electrode surface. 

Porous MIP membranes are much closer to our topic. These are similar to SPE disks which are commercially available and commonly used in analytical laboratories. Such disks allow the collection of low concentration analytes from large volumes of sample. This type of problem is often encountered in environmental analysis. The disks have high flow permeability and show fast adsorption kinetics so that large sample volumes can be extracted with them in a short time. One may consider these disks as extremely short and wide chromatographic or SPE columns. The purpose may be mainly the concentration of the analyte(s) but separation may also be achieved between substances differing rather much in their distribution coefficients. 

Wankat and Koo (110) have shown that the efficient mass transfer achievable with small ( 10 micron diameter) monodisperse packing can provide excellent resolution on very short columns, even when adsorption isotherms are nonlinear. For high-throughput processes, the most efficient columns resemble squat disks or pancakes (109). The ultimate "column" geometry may well be a membrane or consolidated packing with mobile phase flow through monodisperse pores. 

The strong chemical interaction of a lipid thiol monolayer developed on a gold disk electrode yields a structure resembling a biological membrane. The blocking ability of various substances was tested for the cyclic voltametry redox reaction of [Fe(CN)g]3-ions, upon adsorption on the thiol monolayer. This was applied to measure the threshold concentrations for detection of various odor substances. The order of response shown in series 30 was the same as the one followed by the human olfactory sense, pointing to... 

Sample centrifugation onto PVDF membranes represents an alternative method to TCA precipitation and is particularly suited for very dilute protein samples. The following protocol is suitable for the adsorption of proteins onto PVDF disks prior to sequencing using the ProSpin sample preparation cartridge (Applied Biosystems). 

The problem of distorted flow and voids between the membranes in the stack does not exist in cartridges that accommodate only a single thicker disk of porous material. In addition, Belenkii s theory of critical distance in adsorption chromatography leads to a conclusion that even a very short layer of a separation medium such as the disk can be sufficient for an efficient separation of large molecules [85], These provisions led to development of rigid disks for rapid chromatography of biopolymers by Tennikova and Svec in the late 1980s [86]. 

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