Conventional Preconcentration Techniques

Conventional Preconcentration Techniques for Explosive Vapors (1973) (AD A026117)... 

The most important advantage of cloud point extraction is that only small amounts of nonionic or zwitterionic surfactants are required and consequently the procedure is less costly and more environmentally benign than other conventional extraction techniques such as liquid-liquid extraction and solid liquid extraction [107,108]. Moreover, CPE offers the possibility of combining extraction and preconcentration in one step. 

The preconcentration techniques that have to date been most used in microfluidic devices have been presented in the preceding pages. Most of the techniques were originally developed for conventional CE or liquid chromatography and have (more or less simply) been adapted to microchips. FASS, ITP, and lEF are examples of these types of techniques. A few new techniques have been developed for the preconcentration of samples on microfluidic devices. TGF and nanofluidic filtering are both examples of techniques that have been developed solely for microfluidic chips. High enrichment factors can be achieved with both techniques, on the order of 10,000 and 1,000,000, respectively. Table 50.1 summarizes the top performers in each device category with respect to preconcentration factor and time. 

Zone refining is a powerful tool for separation and concentration. Following preconcentration, conventional analytical techniques are used to identify and quantify the impurity. This has enabled certain observed abnormalities in properties to be correlated with the presence of impurities in ultratrace amounts that had earlier remained undetected. In another version, the distribution coefficient, k, of a metallic solute is determined by adding its radioisotope under the conditions of the zoning experiment. If the concentration of the nonradioactive form of the solute in the starting material is measurable by an available analytical technique but subsequently falls below the detection limit after refining, its final concentration can still be calculated from the value of k and the zone refining curves. 

To achieve high sensitivity when analyzing trace inorganic elements in a sample solution using an atomic absorption spectrometry (AAS) or Inductively coupled plasma (ICP) atomic-emission spectrometry (ICP-AES), conventional preconcentration methods such as evaporation, ion exchange, and solvent extraction techniques have... 

Several research groups have reported ways to preconcentrate samples in Lab-on-a-Chip devices. While most on-chip preconcentration approaches evolve from conventional capillary electrophoresis and chromatographic column techniques, these preconcentration techniques play an increasingly important role in chip-based system. The basic preconcentration strategies applied on microfluidic devices can be classified into three large categories electrokinetic preconcentration, chromatographic preconcentration and membrane preconcentration. 

The calibration of atomic spectrometers can be handled much easier than that of conventional IC detectors using the large dynamic range of ICP techniques. Those simple off-line calibrations had been used for ICP-AES and ICP-MS in on-line preconcentration applications. With its ability to decide between isotopes the ICP-MS is well suited for isotope dilution analysis (IDMS), a calibration tool which increases the accuracy, the results and saves time due to reduced calibration work. The use of IDMS in combination with on-line coupling methods allows a significant speedup of the usually to IDMS applied time consuming separation processes. 

The term solid-phase extraction was introduced by personnel of the J. T. Baker Company in 1982. The method consists of retention of the analytes from a liquid or gaseous sample to a solid stationary phase and subsequent removal of analytes using an appropriate eluent. The main purpose of SPE is isolation and preconcentration of compounds of interest or sample clean-up and simplification of the matrix. Application of this sample preparation technique also allows extract fractionation. As a result of significant reduction in the volume of organic solvents used, high recovery, and the possibility of process automation, SPE is a good alternative for conventional liquid-liquid extraction. According to their affinity for the compound of interest, stationary phases are classified as follows ... 

It is clear that the use of mPC-CE and lA-CE afford a powerful approach for preconcentration and on-line sample eleanup of antilyte mixtures prior to separation by CE. While these techniques continue to be refined, they overcome the current limitations of poor CLOD in conventional CE. Finally, the use of these devices as microreactors affords enhanced chemical derivatization or enzymatic reactions a lower analyte concentrations than is currently possible by conventional solution chemistries. 

A similar preconcentration process was developed by Lochmuller, Galbraith and Walter (41) for the analysis of water for trace metals. The membrane after equilibration with the water sample is in this case analyzed by proton induced X-ray emission. Claimed advantages of the latter technique are a wider range of applicability than neutron activation, easier applicability to rapid routine analysis than anodic stripping and greater sensitivity than conventional X-ray fluorescence spectroscopy. 

Determination LC-PDA recoveries 1 to 56% preconcentration cartridges prepacked with 0.5 g of silica and 10 mg of antifluorene antibodies and OSP-2 cartridges prepacked with 80 mg of silica and 2 mg of antifluorene antibodies other preconcentration precolumns prepacked with C18 silica higher selectivity of the antifluorene immunosorbent compared to conventional cleanup (immunosorbents more reliable technique than use of alumina for cleanup of complex environmental samples) methodology using immunosorbents can be automated LOD 0.9 to 37 /ig/l... 

---