Implementing electrokinetics

The traditional methods described above require the use of heavy machinery, which may be difficult to access in a built-up environment. Since time is of essence in arresting the spread of contaminants to minimize the cleanup cost, novel methods that can overcome these difficulties are needed. The creation of an electrokinetic barrier is one such method that can address these concerns. In this method, an electrical field generated within/outside the contaminated zone causes the formation of a counter-gradient that can control the flow of water and contaminants. The relative ease of implementing electrokinetic barriers has generated a lot of interest in this technique as a viable alternative to traditional methods. The principles governing the creation of electrokinetic barriers are described in the next section. 

T vo types of remediation activities are possible under CERCLA removal and remedial actions. Remedial actions are longer-term permanent solutions to hazardous waste contamination. Removal actions are short-term cleanup actions that address immediate threats at a site. They are conducted in response to an emergency situation (e.g. to avert an explosion, to clean up a hazardous waste spill, or to stabilize a site until a permanent solution can be found). Electrokinetic remediation technologies are likely to be part of a CERCLA remedial action. There are nine general criteria that must be addressed by those wishing to implement electrokinetic technologies as part of CERCLA remedial actions ... 

Before implementing electrokinetics, it is necessary to find if the site conditions match the requirements necessary for the successful performance of the technology. This can be done by a number of field and laboratory screening tests ... 

The early phase of development can be characterized by a transfer of concepts from conventional CE to the planar format, such as capillary gel electrophoresis, micellar electrokinetic chromatography, sample stacking and pre- and postcolumn sample derivatization. Emphasis was laid on the demonstration of the specific advantages mainly from the separation science point of view. With only very few exceptions, detection has received much less attention yet. LIF detection with confocal imaging has been used in most of the early work owing to its high sensitivity and its relatively easy implementation. If not explicitly mentioned otherwise, all experiments described in the following sections were carried out with LIF detection [28,29]. 

Another possible solution to this problem has been implemented by Attiya et al. [97]. The device contained a large sample introduction channel with a volume flow resistance >105-fold lower than that in the analysis microchannels. This approach enabled interfacing the large sample introduction channel with an external pump (up to 1-mL/min flow rate) for pressure-driven sample delivery without perturbing the solutions and electrokinetic manipulations within the... 

Hansen HK, Rojo A, Ottosen LM. (2007). Electrokinetic remediation of copper mine fadings—Implementation of bipolar electrodes. Electrochimica Acta 52(10) 3355-3359. 

The cost of electrokinetic remediation, like any other remediation technology, is highly site specific. There have been relatively few full-scale installations of electrokinetic processes when compared with conventional remediation processes. There have been more applications of electrokinetics in Europe than in the USA. Since 1987, more than 75 electrokinetic projects have been implemented in Europe (Holland Environment, pers. comm.), while in the USA, very few full-scale appUca-tions have been successfully completed. 

Short-term effectiveness addresses the period of time needed to achieve lasting protection of human health and the environment as well as any adverse impact that may be posed during the construction and implementation period before the cleanup goals are achieved. Electrokinetics is expected to present minimal short-term risks to workers and the nearby community, including noise and exposure to airborne contaminants. 

Electrokinetic implementation for full-scale site remediation requires consideration of many practical parameters not typically encountered in laboratory settings. 

FAS can be implemented on microchips in a very similar manner as capillary electrophoresis. However, the requirement of low ionic strength sample buffer for FAS puts limitation on its use as general preconcentration technique. Variations of the technique, such as transient isotacho-phoresis and micellar electrokinetic sweeping, have been more successfully used. Jung et al. reported (Mi-chip transient isotachophoresis... 

Li and Harrison carried out the first cell assay in microchannels [2]. This seminal work made use of electrokinetically driven flow (electroosmosis and electrophoresis) to transport bacteria, yeast, and mammalian cells in channels and to implement low-volume chemical lysis (cell death). This theme of microfluidics-based cell transport, sorting, and lysis has continued to be a popular application, as well as related work in using microfluidics to culture cells and to pattern them into structures. The utility of these methods is acknowledged (and that they are featured in several good reviews [1] and other entries in the encyclopedia) but focuses here on describing microfluidics-based cell assays that fit the definition described above - application of a stimulus and measurement of a response. 

Targeted cells are then deflected or sorted from the sample stream for subsequent analysis. This cell sorting is commonly achieved by the active control of either the fluid flow or the par-ticle/cell motion itself. The switch of flow is implemented by either electrokinetic or hydrodynamic means or by a combination of the two. In addition to this, cell motion can be control by optical forces. 

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