Membrane-based preconcentration

Figure 5.7 Layout and dimensions of a membrane-based preconcentration device, (a) Filter-CE unit, (b) concentrator-CE device, (c) dimension of microchannel, and (d) out look of concentrator-CE device [83].

A liquid emulsion membrane based on trioctylphosphine oxide extractant was applied for separation of uranium and thorium from Ce, Cu and Cd [2]. Highly selective U02 imprinted polymer (synthesized using uranium vinylbenzoate, divinylbenzene in styrene and 2,2 -azobisisobutyronitrile) was proposed for purification, preconcentration and determination of the uranyl ion [3]. Dibenzoylmethane was used as a colorimetric reagent. The detection limit of 160 ppt was achieved. 

In the last two decades, BOHLM techniques were intensively used in analytical chemistry for separation and preconcentration of metals, organic acids, organic, and pharmaceutical compounds. Some membrane-based... 

Li, Y., Membrane-based protein preconcentration microfluidic devices, M.S. Thesis, Brigham Young University, 2006. 

By adjusting the pore size, one can allow the passage of buffer ions and small molecules but exclude larger molecules of interest. With the formation of nanofilters or nanoporous membranes within the microfluidic systems, this strategy can be implemented easily. Membrane (filtration)-based preconcentration will not have any chemical bias (mainly dependent on the size of the molecule), but continuous membrane filtration could generate eventual clogging of the system, which is one of the main problems in this technique. 

Fontas, C, Palet, C., Salvado, V. Hidalgo, M. (2000). A hollow fiber supported liquid membrane based on Aliquat 336 as a carrier for rhodium(III) transport and preconcentration. Journal of Membrane Science, 178,1-2,131-139, ISSN 0376-7388 Frade, R. F. M., Rosatella, A. A., Marques, C. S., Branco, L. C., Kulkarni, R S., Mateus, N. M. M, Afonso, C. A. M. Duarte, C. M. M. (2009). Toxicological evaluation on human colon carcinoma cell line (CaCo-2) of ionic liquids based on imidazolium, guanidinium, ammonium, phosphonium, pyridinium and pyrrolidinium cations. Green Chemistry, 11,10,1660-1665, ISSN 1463-9262 Fraser K. J. MacFarlane D. R. (2009). Phosphonium-based ionic liquids An overview. 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

Thermex is a commercially available ex situ technology that is based on the use of membrane separation technology for preconcentrating plant radioactive wastewater and evaporation for drying the preconcentrates. The technology is designed to minimize the volume of waste that would require storage or disposal. 

C. Mendiguchia, C. Moreno and M. Garcia-Vargas, Determination of copper in seawater based on a liquid membrane preconcentration system. Anal. Chim. Acta, 460(1), 2002, 35-40. 

Yang et al. [47,48,53,54] developed a HWG sensing system for liquid and soil analyses based on an extractive polymer membrane coated onto the inside of the HWG. The polymer coating performs a solid-phase microextraction of the analyte from the headspace of the sample and preconcentrates the analyte prior to IR analysis. 

Blanchard and Hardy (1985, 1986) developed a method that allows for continuous monitoring or intermittent analysis of volatile organic priority pollutants in environmental media. The method is based on permeation of volatile organic compounds through a silicone polycarbonate membrane from wastewater sample matrix, into an inert gas stream and directed into a capillary GC/FID via a sampling loop (Blanchard and Hardy 1986). Advantages of this procedure are that it is simple, it does not require time-consuming preconcentration steps, and it can be used either in the field or in the laboratory. 

Zip-Tips (Billerica, Massachusetts) are automation-compatible pipette tips that contain a chromatography sorbent held in the tip with a membrane. These tips allow for microscale solid-phase extraction to purify and preconcentrate samples. Some examples of this approach are sample cleanup step with isoelectric point (pl)-based fractionation of peptides prior to matrix-assisted laser-desorption/short ionization (MALDl) spotting [29] or chip-based ESI analysis of colon adenocarcinoma (Caco-2) screening samples [30]. The preliminary results of induction-based fluidics in which nanoliter volumes... 

Extraction and stripping of copper(I) as a neocuproine complex in a surfactant medium was used to determine Cu in steel [4], Solid-phase extraction based on the preconcentration of the complex with neocuproine on a preconditioned membrane disc containing octadecyl-bonded silica followed by extraction of Cu and elution with isopentyl alcohol was applied to the determination of copper in distilled, tap and spring waters [5]. 

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