Analyte infusion

Figure 5.19 Effect of HPLC injections on the APCI signal from the analyte infused post-column at a constant rate the isocratic mobile phase was 80 % acetonitrile and 20 % aqueous ammonium acetate (1 % w/v), and the analyte solution that was infused postcolumn was 1 p.g.mL in the mobile phase, (a) Infusion of parent compound with no injection on the HPLC (mobile phase only) (b) enhancement effect of injection of water on the signal from infused analyte (c) suppression effect of injection of extract of a blank plasma sample on the signal from the infused analyte (see Section 5.3.5a). The diagonal line is drawn to connect the injection times in the different chromatograms. Reproduced from Sangster (2004), Rapid Commun. Mass Spectrom. 18, 1361, with permission of John Wiley Sons, Ltd.

Figure 5.58 Reconstructed LC-MS-MS ion chromatograms for selected-reaction monitoring of methoxyfenozide using the m/z 367 to m/z 149 transition from the continual post-column infusion of a standard solution of analyte during the HPLC analysis of a...

Residuum oil supercritical extraction (ROSE) (petroleum deasphalting) Polymer and edible oils fractionation CO2 enhanced oil recovery Analytical SCF extraction and chromatography Infusion of materials into polymers (dyes, pharmaceuticals)... 

The MS/MS response for each analyte must first be optimized on the specific instrument to be used. This is usually done by infusing a solution of the analyte into the HPLC mobile phase without a column present. The composition of the mobile phase should match that expected at the time of analyte elution within 25%. The instrument is first operated in the LC/MS mode, and the settings for the electrospray interface are... 

In polymer science and technology, linear, branched and crosslinked structures are usually distinguished. For crosslinked polymers, insolubility and lack of fusibility are considered as characteristic properties. However, insoluble polymers are not necessarily covalently crosslinked because insolubility and infusibility may be also caused by extremely high molecular masses, strong inter-molecular interaction via secondary valency forces or by the lack of suitable solvents. For a long time, insolubility was the major obstacle for characterization of crosslinked polymers because it excluded analytical methods applicable to linear and branched macromolecules. In particular, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect metho ds only [ 1 ], or was expressed relatively by the fraction of crosslinking monomers used in the synthesis. 

Relative extraction efficiencies of polar polymeric neutral, cation, and anion exchange sorbents (HLB, MCX, and MAX) for 11 beta antagonists and 6 beta agonists in human whole blood were probed.109 Initial characterization of MCX and MAX for acidic and basic load conditions, respectively, showed that both the agonists and antagonists were well retained on MCX, while they were recovered from MAX in the wash with either methanol or 2% ammonia in methanol (see Table 1.6). Blood samples were treated with ethanol containing 10% zinc sulfate to precipitate proteins and the supernatants loaded in 2% aqueous ammonium hydroxide onto the sorbents. After a 30% methanol and 2% aqueous ammonia wash, the analytes were eluted with methanol (HLB), 2% ammonia in methanol (MCX), or 2% formic acid in methanol (MAX). The best recoveries were observed with MCX under aqueous conditions or blood supernatant (after protein precipitation) spiked sample load conditions (see Table 1.7). Ion suppression studies by post-column infusion showed no suppression for propranolol and terbutaline with MCX, while HLB and MAX exhibited suppression (see Figure 1.6). 

The multiple reaction monitoring (MRM) conditions for each analyte were optimized by infusing 0.1 jxglmL of analyte in mobile phase. The Ionspray needle was maintained at 4.0 kV and the turbo gas temperature was 650°C. Nebulizing gas, auxiliary gas, curtain gas, and collision gas flows were set at 35, 35,40, and 4, respectively. In the MRM mode, collision energies of 17,16, and 15 eV... 

Tandem mass spectrometric methods have demonstrated superb specificity because of their ability to isolate analytes selectively in the presence of endogenous interferences. Attempts to further increase sample throughput led to the idea of using LC/MS/MS without the LC. Traditional chromatographic separations were replaced with flow injection analysis (FLA) or nanoelectrospray infusion techniques. The MS-based columnless methods attracted a lot of attention because of their inherent fast cycle times and no need for LC method development. 

Mass Spectrometric Instrumentation Used in Infusion or Direct Analytical Methods for Chemical Identification and Structure Elucidation. 152... 

While the idea of limited sample preparation and direct infusion into the MS are promising, this technique has not yet caught on in many laboratories. Ion suppression continues to be a limitation of this technique. It is also a limitation in other fast sample preparation methods and fast analyses. Protein precipitation is a quick and dirty technique, and many components from the plasma matrix remain. With this direct infusion into the MS, these matrix components are also sprayed into the source with the analytes of interest and can cause ion suppression. Additionally, many samples can contain several analytes, often including internal standards. In many instances, these analytes cause self-suppression when infused together into the source. With a proper sample cleanup such as SPE, either off-line or on-line, this technique may prove to be more useful in the future. 

Inject conti l sample extract while infusing analyte into the column eluant at a flow rate of - 10 pL/min and follow path A. 

Fig. 13.7 Post-column infusion study of a ballistic gradient. The matrix effects can be seen at the early part of the chromatogram, but the later part of the chromatogram where the analytes should elute did not show matrix effects. Adapted from [99], with permission from John Wiley and Sons.

General CE problems (e.g., wall interactions of proteins) have been discussed elsewhere. All ACE techniques working with a ligand added to CE buffer (classical ACE, Hummel-Dreyer principle, vacancy peak analysis) imply the potential problem that any continuously infused matrix can increase background noise and, even worse, deteriorate the ionization of the analyte due to competition. 

The galenical information describes the formulation (purity, stability, etc.) of the compound and the analytical method. For intravenous formulations the compatibility with infusion solutions and infusion set material should also be known. 

The world of aroma compounds is becoming more and more complex. In the early days people used aromatic products like fruit juices or fruit juice concentrates which were relatively weak and still close to the related foodstulf. Later, with more knowledge of separation techniques, infusions, extracts, oleoresins and absolutes ranging from weak to strong impact were used to impart aroma. Essential oils such as spice oils already had a very strong impact. Modern analytical technologies allowed the evaluation of the chemical compositions of extracts and essential oils, so that isolates either as powerful mixtures or even as single compounds could be obtained. 

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