Mass sensitivity,optimization

Fig. 2.6.5 Hardware for high field NMR remote probe in (c) contains a relatively large saddle-detection. Photographs (a) and (b) show la- coil and is used for (flow) imaging. The detec-boratory-built remote detection probes with tor probe in (d) contains a microsolenoid coil both rf coils built into the same body (c), (d) for optimized mass sensitivity, which is parti-and (e) are detector-only remote probes that cularly useful for microfluidic NMR applica-can be inserted from the top or bottom into the tions. The same probe is shown in (e) with a NMR imaging assembly, so that the well mounted holder for a microfluidic chip that is...

The highest element sensitivity (see also Figure 6.12) is observed for the heavy radionuclide elements Th and U. In general, a similar dependence is found for RSCs from masses under optimized experimental conditions in LA-ICP-MS and ICP-MS using the ICP-QMS Elan 6000. 

Steuer et al. compared supercritical fluid chromatography with capillary zone electrophoresis (CZE) and high-performance liquid chromatography (HPLC) for its application in pharmaceutical analysis [24]. Efficiency, performance, sensitivity, optimization, sample preparation, ease of method development, technical capabilities, and orthogonality of the information were the parameters studied. They concluded that SFC is ideal for moderately polar compounds, such as excipients, for which mass detection is required. 

The importance of the extra column dispersion now becomes apparent, as equation (26) shows that the minimum detectable mass Increases linearly with the extra column dispersion. It Is also becomes obvious that it is of little use designing a detector for increased sensitivity (Xp) if this is achieved (as is often the case) at the expense of increased extra column dispersion (oe). Conversely, if the chromatographic system is designed to have very low extra column dispersion, a proportional reduction in the minimum detectable mass will be achieved even if the actual detector concentration sensitivity remains the same. It follows, that in the design of an optimized column for a particular analysis, the extra column dispersion will determine both the radius of the column and the mass sensitivity that will be available. 

The research for chemosensors began as a branch of analytical chemistry and is now an approved and independent field of activities at the interface between research and application. A chemosensor can be considered as a small unit for the acquisition of analytical data. It has been optimized for one distinct application includes a sensitive layer, whose physico-chemical properties are affected by the interaction with the substance to be detected. These effects are translated into electronic signals by microelectronic devices and can be processed by data acquisition systems [11]. In most cases, mass-sensitive or optical transducers are used, and some of them are listed in Table 10.1. 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a modern and more sensitive variation of MS detection of bismuth. Bismuthine is generated in a hydride generator and swept by argon directly into the ICP unit. The ions are then introduced into the mass spectrometer. Optimization of the mass spectrometer, reagent, and gas flow parameters leads to a detection limit of 20ngL (IfQand 1993). Phillips etal. (2001) examined the safety aspects of colloidal bismuth subcitrate (CBS) quadruple therapy for Helicobacter pylori. These authors used ICP-MS to determine blood Bi levels in 34 patients receiving CBS quadruple therapy, with whole blood Bi levels being deter-... 

It is seen from equation (20) that the minimum detectable mass, or mass sensitivity of a chromatographic system, where the column has been designed to have the optimum radius for the detector employed, is directly proportional to the extra column dispersion and the detector concentration sensitivity. It follows that detector dispersion is as important as detector sensitivity in its influence on the overall chromatographic mass sensitivity where the chromatographic system has been optimized with respect to the radius of the column. The effect of extra column dispersion and in particular, detector dispersion on the overall mass sensitivity of the chromatogaphic system is not generally appreciated or completely understood. As the total extra column dispersion is the integral of a variety of sources, the distribution and nature of the various sources of dispersion will now be considered in some detail. 

This step encompasses procedures that are usually performed within the scope of an optimization. In doing so, mostly the interactions between the sample and the stationary phase are changed. The intention is a change of the retention factor k (mostly enhancement), but ideally also of the separation factor Ct. Otherwise, at constant interaction strength ( chemistry constant and therefore k and a as well), one attempts to enhance the plate number or in the case of a miniaturization to prevent dilution or to enhance the relative mass sensitivity. Using a trial-and-error procedure, one needs 1-2 weeks. Using a systematic procedure, aided perhaps by an optimization program, the time can be reduced measurably see Part 4 for chapters on computer-aided optimization. 

Momabal et al. [76] proposed this new approach which combines separation power of CRYSTAF and TREF and provides very fast analysis in comparison to long analysis times of other crystallization based techniques. CEF can be performed in a typical column based TREF instrument and can easily adapt viscometry, light scattering, composition or other molar mass sensitive detectors. In another paper, Momabal et al. [77] demonstrated that dynamic crystallization analysis can be optimized by knowing the crystallization range of the sample and adapt the experimental conditions accordingly. CRYSTAF and dynamic crystallization... 

A common process task involves heating a slurry by pumping it through a well-stirred tank. It is useful to know the temperature profile of the slurry in the agitated vessel. This information can be used to optimize the heat transfer process by performing simple sensitivity studies with the formulas presented below. Defining the inlet temperature of the slurry as T, and the temperature of the outer surface of the steam coil as U then by a macroscopic mass and energy balance for the system, a simplified calculation method is developed. 

D. Eigeys, Y. Zhang and R. Aebersold, Optimization of solid phase microexti action-capillaiy zone electi ophoresis-mass specti ometi y for liigh sensitivity protein identification , Electrophoresis 19 2338-2347 (1998). 

---