Enhanced Analytics Initiative

Initially the main reason for miniaturising separations was to enhance analytical performance and the combination of integration of components and small size were seen as advantages. These chip devices are based mainly on chromatography though electrophoretic separations play an increasing part. As the years go by, these on-chip separation devices have become more and more important as analytical instrumentation tools. 

Enhanced hydrophobicity of hypercrosslinked polystyrene, combined with additional 7r-interactions with aromatic moieties, explains the unusually strong retention of phenol and its derivatives from aqueous solutions. This makes it possible to pre-concentrate traces of phenols and chloro- and nitrophenols from water samples directly on the top of the analytical HPLC column (with MN-200 disintegrated to 15 im particles) [199] and then analyze the mixture on the same column with an aqueous-acetonitrile RP eluent. This approach increases the sensitivity of the determination because the whole amount of analytes initially present in the sample appears in the column and arrives at the detector, contrary to the situation with the off-line solid phase extraction (SPE) pre-concentration approach. 

Patti, G.J., et al. (2010) Detection of carbohydrates and steroids by cation-enhanced nanostructure-initiator mass spectrometry (NIMS) for biofluid analysis and tissue imaging. Analytical Chemistry, 82,121-128. 

Noncatalytic Reactions Chemical kinetic methods are not as common for the quantitative analysis of analytes in noncatalytic reactions. Because they lack the enhancement of reaction rate obtained when using a catalyst, noncatalytic methods generally are not used for the determination of analytes at low concentrations. Noncatalytic methods for analyzing inorganic analytes are usually based on a com-plexation reaction. One example was outlined in Example 13.4, in which the concentration of aluminum in serum was determined by the initial rate of formation of its complex with 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone. ° The greatest number of noncatalytic methods, however, are for the quantitative analysis of organic analytes. For example, the insecticide methyl parathion has been determined by measuring its rate of hydrolysis in alkaline solutions. 

Fig. 11.6. Diagram depicting desorption ionization (MALDI, FAB or SIMS). The operating principles of the three techniques are similar. The initiating event is exposure of the analyte to a beam of photons, atoms or ions. In order to prevent damage to the fragile analyte molecules and enhance the conversion of the involatile molecules into gas-phase ions, a matrix is employed. For MALDI, the matrix compounds are UV absorbing compounds such as hydroxycinnamic acid. The most commonly used FAB matrix was glycerol and ammonium chloride was employed by some investigators in SIMS experiments (although at low ion beam fluxes molecular species could be effectively ionized for many analytes with minimal evidence of damage by the primary ion beam).

The theoretical considerations discussed briefly above have been further enlarged and the enhanced calculation of optimal gradient programmes was achieved involving three factors gradient slope, initial eluent composition and gradient curvature. In the case of an ACN organic modifier the retention of an analyte can be described by... 

Due to the complexity of the food samples, it is possible that the presence of some compounds in the matrix interferes with analyte determination even when working in LC-MS/MS, certain compounds present in the sample can affect the initial ionization of the analyte through what is often called ion suppression/ enhancement or matrix effects. 

Bio)chemical reactions may take place prior to or after the continuous separation module and are intended to enhance or facilitate mass transfer, detection or both. The earliest and simplest approach to integrated analytical steps in continuous-flow systems involves a combination of chemical reactions and continuous separations [4,5]. Such is the case with the formation of soluble organic chelates of metal ions in liquid-liquid extractions with the ligand initially dissolved in the organic stream [6], the formation and dissolution of precipitates [7], the formation of volatile reaction products in gas difiusion [8] and that of volatile hydrides in atomic absorption spectro-... 

To ensure overall extraction of a polar solute, the pressure or density must be increased or a modifier must be added to the extraction fluid after an initial low-pressure extraction. In this way, the analyte of interest can be collected separately from the oily interference. Polar solutes may be removed more easily from matrices with higher moisture content. It is believed that the analyte is solubilized in the entrained water and removed from the matrix with physical removal of water. Since polar analytes benefit from the presence of water in samples, water has been added as a mobile phase modifier to enhance extraction recoveries (152). 

For very small electric fields ( <105 Vm"1), the linear term in E is positive and so the applied electric field enhances the escape of oppositely charged ions from each other. With small electric fields, where only the linear and quadratic terms need be considered, the influence of the electric field on the escape probability is small. Other analytical and numerical techniques have been discussed [327—331], There is little reason to anticipate any correlation of the orientation of an ion-pair when initially formed with the external electric field. Presuming that the distribution of ion-pair orientations is random with respect to the electric field, the escape probability of an ion-pair depends on r0 and E alone [332]. Averaged over 0 < 90 < 27t, eqn. (151) gives... 

As stated by Manz, the pTAS was envisioned as a new concept for chemical sensing, needed since sensors at that time were not providing the best results in terms of selectivity and lifetime. Initially, the main reason for miniaturisation was to enhance the analytical performance of the device rather than to reduce its size. However, it was also recognised that a small scale presented the advantage of a smaller consumption of sample and reagents. Moreover, the total chemical analysis system scheme could provide an integration of several laboratory procedures such as sample preparation, filtration, preconcentration,... 

Cesium-ion concentrations in distilled water and synthetic ground-waters were measured after contact with the feldspars for various periods of time, over the temperature range 150°C to 200°C. It was found that for short reaction times (< 5 days), there was little reduction in the concentration of cesium ion, i.e. little sorption of Cs+ by the minerals. Removal of Cs+ from solution was enhanced by increased mineral surface area, reaction temperature and time. It was observed that in the extreme case for powdered labradorite, 98% of an initial 10 2 mol dm 3 solution of Cs+ was sorbed after 14 days at 200°C in distilled water. The morphology, composition and chemical structure of the mineral surfaces were investigated by several analytical methods, as described below. 

Initially, the main goal of miniaturization was to enhance the analytical performance of devices rather than to reduce their size. However, it was found that such tools had the advantage of reducing the consumption of sample and reagents, for example, the smaller consumption of carrier and mobile phases in separation systems (the first analytical system to be miniaturized was the gas chromatograph). Research in this area focused on the development of components such as micropumps, microvalves, and chemical sensors. 

---