Drawback miniaturization

Nanospray is a miniaturized version of electrospray. In the original setup of Wilm and Mann (8) it is utilized as an off-line technique using disposable, finely drawn (1 -gm tip), metallized glass capillaries to infuse samples at 10-30 nL/min flow rates. This allows more than 50 min analysis time with just a 1-pT sample. Due to the formation of much smaller droplets and the more effective ionization, there is often no need for LC separation, since the separation is accomplished in m/z or by MS/MS. However, limited reproducibility with respect to quantification and a more complex sample preparation can be seen as drawbacks. An on-line version for hyphenation with capillary and nano-LC as well as CE (slightly modified) is now commercially available. 

One drawback of capillary electrophoresis is the state of the capillary wall. Often, constituents of the buffer or analyte are absorbed on the sin-face, causing not only an irreproducible shift of EOF, but even the possibility of questionable binding isotherms. A lot of effort has gone into overcoming this problem. Capillaries with coated inner walls are now commercially available and capillary electrophoresis on chips of different materials is also under development now. Not only do these chips represent a miniaturized form of capillary electrophoresis, but this technique also enables the incorporation of such sample preparation steps as preconcentration and even PCR and immobilization of immunoreagents. It is not difficult to anticipate a very exciting development in this field, one with a high commercial impact. 

Methods have been proposed to miniaturize, speed up and automate the shake-flask approach. The main difficulties in this challenge are the number of time-consuming steps which cannot be totally eliminated and the persistence of well known drawbacks. For example, the mutual saturation and decantation of organic and aqueous phases, or the crucial separation of the two phases after shaking which multiplies the manipulations. Automation of the process is also difficult due to several compound-dependent parameters which have to be rigorously controlled, such as the volume ratio between organic solvent and aqueous phase according to the estimated log P, or the sample concentration. 

The obvious advantage of the symmetrical arrangement is that the processes at all internal interfaces can be well defined and that most nonidealities at the mem-brane/solution interface tend to cancel out. Because the volume of the internal reference compartment is typically a few milliliters, the electrode does not suffer from exposure to electrically neutral compounds that would penetrate the membrane and change the composition of this solution. This type of potentiometric ion sensor has been used in the majority of basic studies of ion-selective electrodes. Most commercial ion-selective electrodes are also of this type. The drawbacks of this arrangement are also related to the presence of the internal solution and to its volume. Mainly for this reason, it is not conveniently possible to miniaturize it and to integrate it into a multisensor package. 

The miniplant concept was proposed first by Ponton at the University of Edinburgh (UK) in 1993 [1,58-60], The potential benefits of distributed processing, as outlined above and reported elsewhere [2, 4], were identified, in particular focusing on an increase in process safety. However, the critical evaluation of the miniplant concept also revealed a number of potential drawbacks. For instance, the specific production costs of a small production units not only depend on reactor miniaturization, but are also determined by control instruments and other peripheral equipment. 

As a corollary to this, more direct sample preparation procedures have been the pursuit of many scientists, who believe that miniaturization of analytical techniques can be a key solution to many of the unwanted drawbacks of LLE and SPE. Currently, several miniaturized extraction systems have been investigated, which are based primarily on utilizing downsized liquid, solid, or membrane extraction phases. 

Recent developments in sensor technology allow to create different integrated and miniaturized sensor arrays. Using microsystemtechnology fluidics can be added creating whole micro-analytical devices on chip. However, there are drawbacks involving inappropriate sensor function in media and production. Using sophisticated sensor construction and microfluidics such drawbacks can be overcome. In this chapter different sensor systems and whole micro-analytical devices are presented with emphasis on their applications. 

Biosensors are being increasingly used as detectors in FIA systems [284,285, 322, 379, 476]. The drawbacks of biosensors as direct in situ sensors, namely their low dynamic range, their lack of ability to survive sterilization, their limited lifetime, etc. are no longer valid ex situ because the analyzer interfaces the biosensor which can be changed at any time and FIA can provide samples in optimal dilution. The need for chemicals and reagents can be drastically reduced when employing biosensors, specifically when the entire system is miniaturized [48]. 

An innovative way to perform a sample cleanup that is fast, accurate, and easy, is the use of solid-phase extraction (SPE) columns. In many ways these devices resemble miniature HPLC columns upon which a preseparation is done. Using these minicolumns for sample clean-up eliminates many of the drawbacks associated with traditional liquid-liquid extraction, such as (1) the use of large amounts of expensive organic solvent, (2) low recovery due to solvent emulsion formation, and (3) large requirements for labor, time, glassware, and bench space. 

The drawback of this approach turned out to be samples of submicrolitre level, which necessitated the development of a dedicated small measuring device with a very low dead volume. A portable lightweight apparatus, consisting in a miniaturized flow-through biosensor connected to a microdialysis probe at one side, and to a semi-vacuum pulse-free pump at the other was then built. A portable potentiostat equipped for data collection and storage was used to handle data. 

The previously mentioned drawback of biosensing devices, i.e., the possibility to measure just one metabolite at a time, is nowadays partially overcome through the recent advances in miniaturization and the development of arrays of sensors. Each of the sensors constituting the array can consist in a different biosensor, allowing multi-analyte determinations. In some cases, if the array is located in a flow cell, it can be coupled to microdialysis sampling. Examples have been presented by several authors, even if the proposed... 

Abstract Many companies are making significant efforts in the development of prototypes of DAFC (mainly DMFC) for replace batteries (battery charge and auxiliary power units) in portable devices. Some of the most relevant prototypes are summarized however, most of these devices are not ready to be commercialized due to the high cost and low power reached. Furthermore, for the massive application of the DAFC technologies is necessary solve some of the drawbacks (as miniaturization, products balance, cost reduction, etc.). The cost of the prototypes is analyzed as well as the degradation of the components that affects the durability of the devices. 

Last but not least, fundamental issues for the deployment of direct alcohol fuel cells—applicaticsi niches, costs, and durability—are introduced in Chap. 9. The major drawbacks for commercialization, such as miniaturization, product balance, cost reduction, and Ufetime extension, are addressed. 

Over the past decade, the drawbacks of conventional flow cytometers coupled with the increased need for miniaturization and sophisticated analysis have motivated the development of the micromachined flow cytometer. It has many potential benefits including disposability, smaller size, lower consumption of sample. 

---