On-line sample treatment

The development of analytical strategies for the regulatory control of dmg residues in food-producing animals has also been reviewed (128). Because of the complexity of biological matrices such as eggs (qv), milk, meat, and dmg feeds, weU-designed off-line or on-line sample treatment procedures are essential. 

UAT Brinkman. On-line sample treatment for or via column liquid chromatography. J Chromatogr A 665 217-231,1994. 

Open-vessel microwave-assisted on-line sample treatment... 

In many cases, however, the costs arising from sample preparation will become decisive, which favors x-ray spectrometric methods, provided the earlier mentioned limitations are not encountered. Future progress will certainly depend on the avail-abilty of on-line sample treatment using, for example, flow injection and eventually on-line sample dissolution as is possible in some cases with microwave-assisted heating. Also the realization of separations in miniaturized systems and with minute amounts of reagents is very promising. In each instance the question of which method should be selected will have to be discussed for each type of analytical task to be solved. 

Brinkman, U. A. Th. and Vreuls, R. J. J. 1996. Solid-phase extraction for on-line sample treatment in capillary gas chromatography, LC-GC, 14 581-585. 

Goosens EC, de Jong D, de Jong GJ, and Brinkman UATh (1998) On-line sample treatment - capillary GC. Chromatograph ia 47 313-345. 

Installing additional accessories in front of the ion source can render analytes amenable to ionization and subsequent mass spectrometric analysis. On-line sample treatment is especially important when analyzing liquid-phase, complex, and/or concentrated samples. For example a thermal vaporizer was used to enable analysis of liquid samples by a process mass spectrometer designed for gas analysis [196], This system has been successfully implemented in the monitoring of an esterification reaction [197]. The obtained data were in a good agreement with those recorded by in-line mid-infrared spectrometry. The setup incorporated a magnetic sector analyzer with two detectors an electron multiplier detector... 

As will be highlighted in Chapter 7, microscale separations carried out on microfluidic chips can be coupled with MS. Some of them are very fast. For example, separations of pharmaceuticals and peptides could be accomplished within 2 s while the mass spectra were obtained by TOF operated at 100 Hz (Figure 6.7) [43], This result suggests that it may be possible to incorporate liquid-phase separations as a fast on-line sample treatment step while monitoring dynamic samples (e.g., reaction mixtures) by MS. 

There are still numerous problems to solve in order to warrant wide-spread use of TRMS. For example, many fast reactions are conducted in solvents that are incompatible with the ionization techniques used in MS. Reaction mixtures cannot always be directly pumped to the mass spectrometer using conventional ion sources and interfaces. Systems for solvent exchange need to be developed and made available. However, there always exists the risk that on-line sample treatment may influence sample composition and relative concentrations of reactants (e.g., in the case of chemical equilibria). Moreover, it is hard to verify the presence of such possible artifacts. There exist only few model dynamic systems that may be used as reference in the validation of newly developed TRMS methods. 

The Cobas Fara 11 provides on-line sample pre-dilution or pre-treatment, enabling total automation of assays such as serum, proteins and urine chemistries. Pre-diluted samples can also he pre-incubated before transfer to the analyser. These on-line features minimize labour and errors while ensuring result integrity. 

Wang, J. and E.H. Hansen. 2003. On-line sample-pre-treatment schemes for trace-level determinations of metals by coupling floe injection or sequential injection with ICP-MS. Trends Anal. Chem. 22 836-845. 

New detection systems will be developed for increased sensitivity which will place increased demands on prechromatographic sample treatment. Although many of the proposed liquid chromatographic/mass spectrometric interfaces have shown promise using model compounds (B3, B4, Bll, B22, C2, C6, H17, K4, S3, S29, S30), their routine use for on-line characterization is not yet practical. Similar problems have been encountered with liquid chromatographic/infrared detection (K3S, K36, T3). Detection systems such as electrochemical or radioactivity detectors will find increased use for the selective analysis or spectral characterization of eluting compounds (K24, Ml, Y3, Y4). 

An integrated module for on-line sample pre-analytical treatment and/or clean-up could be also included in the device. With this respect, field-flow fractionation (FFF) techniques, which can separate analytes based on their morphological characteristics (size, shape and superficial properties) can be exploited to develop pre-analytical modules for cells or macromolecules (e.g., proteins, protein complexes or adducts) fractionation, thus providing a selectively enriched fraction for the analysis. 

Economou, A. 2005. Sequential-injection analysis (SIA) A useful tool for on-line sample handling and pre-treatment. TrAC 24 416—425. 

Cheol-Su, K., Chang-Kyu, K.,Jong-In, L., and Kun-Jai, L. (2000). Rapid determination of Pu isotopes and atom ratios in small amounts of environmental samples by an on-line sample pre- treatment system and isotope dilution high resolution inductively coupled plasma mass spectrometry.J. Anal. At. Spectrom. 15,247-256. 

Other O2 Measurement Techniques The oxygen concentration in the emission gases of combustion processes is often measured based on the strong paramagnetic character of oxygen. A sampling line with appropriate sample treatments is required with this method. 

A. Earjam, J. J. Vreuls, W. J. G. M. Cuppen, U. A. Th Brinkman and G. J. de Jong, Duect introduction of large-volume urine samples into an on-line immunoaffinity sample pre-treatment-capillary gas chr omatogr aphy system . Awn/. Chem. 63 2481-2487 (1991). 

Fig. 5.3. Young s moduli Efle, as determined by flexural tests on small samples after thermal treatment are plotted against the densities of those samples. The dots are situated along a single line since the annealed samples are denser and more rigid than the quenched samples prepared from the same polymer...

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