Resolution selectivity

The combination of bandwidth and lines of resolution selected for each machine-train must effect separation of the unique frequency components that represent a machine s operating dynamics. Resolution can be improved by reducing Fmax> increasing the lines of resolution, or a combination of both. 

In the AOAC procedure, the beer was treated with dilute HCl and sulfamic acid, and the added acid was then neutralized by addition of dilute alkali. Volatile nitrosamines were collected by atmospheric pressure distillation. The distillate was made alkaline and extracted with DCM. The extract was dried and concentrated to 1.0 ml and an aliquot was analyzed by GC-TEA. We used these concentrates, without further cleanup, for evaluating the GCMS high resolution selected ion monitoring procedure. 

Figures of merit (capacity, efficiency, speed, resolution, selectivity, LOD, LOQ, etc.)... 

Kinetic Resolution Selectively to Afford Diastereomers and Enantiomers I 691... 

Moritz, T. Olsen, J.E. Comparison Between High-Resolution Selected Ion Monitoring, Selected Reaction Monitoring, and Four-Sector Tandem Mass Spectrometry in Quantitative Analysis of Gib-berellins in Milligram Amounts of Plant Tissue. Anal. Chem. 1995, 67, 1711-1716. 

Continued advances in source/interface designs for the coupling of LC and MS/MS have increased ion formation and transfer into the mass spectrometer. Improved optics (focusing lenses, etc.) have increased ion transmission through the MS and to the detector. These improvements have resulted in a significant increase in sensitivity, and as a result, quantification at the parts per trillion concentration level is routine today and was not possible a decade ago. Advances in source/interface design to increase the abundance of ion formation, transfer, and transmission through the MS may lead to even more sensitive instruments. In addition, the use of smaller particle sizes in LC (e.g., UPLC) also increases resolution, selectivity, and sensitivity. 

Oxidoreductases such as dehydrogenases are also used for kinetic resolution. Selectivity of oxidoreductases is relatively high compared with that of hydrolytic enzymes. However, these enzymes have a drawback that the number of available and useful enzymes or microorganisms is still limited, and finding of new types of oxidoreductases that exhibit wide substrate specificities with high selectivities is awaiting. 

Further evidence for the characterization of compounds can be obtained by comparing the retention times of unknown compounds with those of the reference standards under different chromatographic conditions. This is not practical with multicomponent an yses where the chromatographic operating conditions have already been optimized for resolution, selectivity, and time of analysis. 

Figure 2-4. Relationship between resolution, selectivity, and column length.

Manual optimization of the gradient or the use of Drylab, Chromsword, ACD to determine the desired resolution/selectivity... 

CE has been widely used for the analysis of metal ions generally with indirect UV detection. A recent volume of J. Chromatography (201 has covered developments and applications. Typically a small amine such as imidazole or benzylamine is added to the buffer to provide the background UV absorbance signal. Low-pH buffers are normally employed to suppress EOF flow and enhance resolution. Selectivity of metal ion separations can be modified (21 ( by the addition of small oiganic acids such as lactic or formic acid. 

Gas chromatography is an extremely useful technique for quantification. It can afford the desired resolution, selectivity, and ease of quantification. The chief limitation, however, is that the sample must be volatile or must be made volatile by derivatization. This technique is very practical for organic volatile impurities (OVI). 

Selection of buffering ion does not directly affect resolution. Select a buffer in which the purified product should be collected and which is compatible with protein stability and activity. 

Two magnetic sector instruments have also been operated in tandem, with a collision ceil placed between the two instruments. These instruments permit high resolution selection of both parent and product ions. However, these mstruments are now rarely used as they are expensive and cumbersome to operate. Double focusing mass spectrometers can also be used as tandem mass spectrometers by a technique known as linked scanning. A product ion scan by linked scanning involves low resolution for MSI and high resolution for MS2,... 

Finlay EM, Gaskeli SJ. Determination of testosterone in plasma from men by gas chromatography/mass spectrometry, with high-resolution selected-ion monitoring and metastable peak monitoring. Clin Chem 1981 27 1165-70. 

SY Chang, TA Moore, LL Devaud, LCE Taylor, EB Hollingsworth. Analysis of rat brain dialysate by gas chromatography-high-resolution selected-ion monitoring mass spectrometry. J Chromatogr 562 111—118, 1991. 

G Wells, C Huston. High-resolution selected ion monitoring in a quadrupole ion trap mass spectrometer. Anal Chem 67 3650, 1995. 

This concept has been extended to the kinetic resolution (selective reaction of protons that are enantiotopic by external comparison) [30,130] and to selective reaction at proton pairs that are diastereotopic (double asymmetric induction) [131]. 

The Merck process group was able to use the Buchwald-Hartwig amination as a means to resolve rac-4,12-dibromo[2.2]paracyclophane 41.86 They report that (5)-[2.2]Phanephos was able to perform a catalytic, asymmetric amination of rac-4,12-dibromo[2.2]paracyclophane 41. This kinetic resolution selectively aminated (42), de-... 

Similar GC-MS methods have been developed for quantification of GAs [136] and ABA [Moritz, unpublished data] in small amounts of plant tissues without recourse to extensive sample purification. For analysis of GAs, high resolution selected ion monitoring (HR-SIM), SRM and four sector MS-MS were compared. The best selectivity was found with four-sector MS-MS, but the sensitivity was too low for the analysis of extracts from mg amounts of tissue. HR-SIM and SRM had similarly low limits of detection, but SRM provided the best balance of sensitivity and selectivity. This method has been used successfully for investigating GA levels in the apical zone of Salix pentandra [140]. However, analysis of GAs without extensive purification has to be performed with great care, as highly abundant GAs with similar retention times and mass spectra to the GAs of interest may interfere with the analysis. For example, GC-MS-SRM of a plant extract from Arabidopsis thaliana, without prior HPLC separation of some of the GAs of interest, resulted in inaccurate data being obtained [Moritz, unpublished data]. 

Furthermore, in some cases, these detectors may be used in conjunction with a higher chromatographic resolution/selectivity to minimize matrix interference. Comprehensive two-dimensional gas chromatography (GCxGC) has been under development for more than ten years [10(and references contained therein)] as an enhanced resolution technique. The technique involves continuously transferring or modulating short time periods from a primary column, the first dimension, to a second column of different polarity or selectivity, which serves as the second dimension. The modulation period is typically less than the peak widths observed on the... 

The utility of Equation 1.21 is that it permits one to independently assess the two factors that affect resolution, selectivity, and efficiency. The selectivity is reflected in the mobility of the analyte(s), while the efficiency of the separation process is indicated by N. 

The initial field data of the prediction model is the U U NCEP data. Two layer nested area is chosen as the forecast area. The horizontal network points of the first area is 75 x 75, the grid point distance is 81 kilometers the horizontal network points of the second area is 31 31, the grid point distance is 27 kilometers. The center point of the forecast area is located in 32°N and 118°E. The model vertical resolution selection is the inhomogeneous 31 layers (two layers in the surface layer), the iron tower and the radar observation point are both located in the second forecast area, its horizontal coordinate point is 22 its vertical coordinate point is 16. The initial time is at 00 00 GMT, 25 May 2002, the forecast time is 48 hours. For the stabilization of the calculation, the split-time-step method is adopt to cope with the acoustic item (u, V, w) in the forecast equation, which uses several short time step to replace the long time step for predicting the velocity field and the pressure field. The forecast areas are illustrated in Figure 3. 

In commercial streak cameras the deflection speed can be selected between 1 cm/50 ps to 1 cm/10 ns. With a spatial resolution of 0.1 nm, a time resolution of 1 ps is achieved. A femtosecond streak camera has been developed [761] that has a time resolution selectable between 200 fs to 8 ps over a spectral range 200-850 nm. Figure 6.64 illustrates this impressive resolution by showing the streak camera screen picture of two femtosecond pulses which are separated by 4 ps. Recent designs even reach a resolution of 200 fs. The spatial separation depends on the sweep voltage ramp. More details can be found in [760, 761, 763, 764]. 

A decrease in retention times is usually observed when either the micelle concentration or the concentration of organic solvent is increased. However, different components in a mixture respond in different ways to changes in concentration of surfactant and/or organic modifier, resulting in changes in resolution. Selection of pH in the mobile phase is also often extremely important for the resolution of complex mixtures, owing to the side acid-base reactions of many solutes. Other variables to be considered are temperature and ionic strength. 

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