Experimental design ionization

Method development is important. LC-MS performance, probably more than any other technique involving organic mass spectrometry, is dependent upon a range of experimental parameters, the relationship between which is often complex. While it is possible (but not always so) that conditions may be chosen fairly readily to allow the analysis of simple mixtures to be carried out successfully, the widely variable ionization efficiency of compounds with differing structures often makes obtaining optimum performance for the study of all components of a complex mixture difficult. In such cases, the use of experimental design should be seriously considered. 

Rudaz, S., Cherkaoui, S., Gauvrit, J. Y., Lanteri, P., and Veuthey, J. L. (2001). Experimental designs to investigate capillary electrophoresis-electrospray ionization-mass spectrometry enantioseparation with the partial-filling technique. Electrophoresis 22, 3316—3326. 

The studies of calcium metabolism in normal children are underway with 15-20 children to be studied in the near future The data generated from these studies will be used as the basis for studies of diseases of calcium metabolism in children We anticipate being able to study a number of children with FOP and possibly contribute to innovative therapies for these children by monitoring changes in calcium kinetics Improvements in the thermal ionization source for the quadrupole mass spectrometer are underway a substantial improvement in sesitivity is expected from this effort The model used for data analysis is under continuing investigation in order to improve its predictive and experimental design capabilities ... 

In contrast, in tighter epithelia such as Caco-2 and in artificial membranes such as HDM, the permeability of the ionized forms of the drugs and the paracellular permeability are lower or insignificant, respectively. These findings will have implications in the experimental design and data interpretation of pH-dependent drug transport experiments in cell culture models as well as in artificial membrane models, such as HDM and PAMPA. 

Dron, J., Garcia, R., and Millan, E., Optimization of headspace solid-phase microextraction by means of an experimental design for the determination of methyl tert-butyl ether in water by gas chromatography-flame ionization detection, J. Chromatogr. A, 963, 259-264, 2002. 

Experimental design of time-resolved mass spectrometry (TRMS) systems can greatly affect temporal resolution in the analysis of dynamic samples (see also Section 4.2). The two popular MS approaches - laser desorption/ionization (LDI)-MS and electrospray ionization (ESI)-MS - are suitable for studies of enzymatic reactions [8]. 

This non-structural approach provides an effective complement to experimental design based on pK values. Solvation spheres and effects of pH on columns will inherently be taken into account, as is the ionization of unknown species. The key to this step is the small pH range extrapolation over a large range of pH values has little hope of being successful. 

To implement an experimental design in chemical ecology, suitable for metabolomic analyses, the two major analytical methods currently used are mass spectrometry (MS) and nuclear magnetic resonance (NMR), the choice of which first depends on the conditions of metabolite extraction and will then depend on the conditions used for separation ionization, and also on the solubility of the chemical constituents. The bases and principles of these widely used methods in chemical ecology are presented in Chapter 8. The technological progress in this domain is considerable [ZHA 12]. 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

There are several other methods which have been used in the experimental determination of electron impact ionization cross sections. Nottingham and Bell76,77 developed a method specifically for the purpose of accurately determining the absolute electron impact ionization cross section of mercury. A semicircular electron velocity analyzer included in their design ensured that very high energy resolution was possible since only electrons of the required velocity emerged from the analyzer into the ionization chamber. Other aspects of the experiment are similar to the condenser plate method. 

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