Mass sensitivity Table

SALI compares fiivorably with other major surface analytical techniques in terms of sensitivity and spatial resolution. Its major advantj e is the combination of analytical versatility, ease of quantification, and sensitivity. Table 1 compares the analytical characteristics of SALI to four major surfiice spectroscopic techniques.These techniques can also be categorized by the chemical information they provide. Both SALI and SIMS (static mode only) can provide molecular fingerprint information via mass spectra that give mass peaks corresponding to structural units of the molecule, while XPS provides only short-range chemical information. XPS and static SIMS are often used to complement each other since XPS chemical speciation information is semiquantitative however, SALI molecular information can potentially be quantified direedy without correlation with another surface spectroscopic technique. AES and Rutherford Backscattering (RBS) provide primarily elemental information, and therefore yield litde structural informadon. The common detection limit refers to the sensitivity for nearly all elements that these techniques enjoy. 

Another aspect of cost reduction would be solvent economy. The need to preferentially select inexpensive solvents and employ the minimum amount of solvent per analysis would be the third performance criteria. Finally, to conserve sample and to have the capability of determining trace contaminants, the fourth criterion would be that the combination of column and detector should provide the maximum possible mass sensitivity and, thus, the minimum amount of sample. The performance criteria are summarized in Table 1. Certain operating limits are inherent in any analytical instrument and these limits will vary with the purpose for which the instrument was designed. For example, the preparative chromatograph will have very different operating characteristics from those of the analytical chromatograph. 

The optimum mobile phase velocity will also be determined in the above calculations together with the minimum radius to achieve minimum solvent consumption and maximum mass sensitivity. The column specifications and operating conditions are summarized in Table 4. 

Flow limitations restrict application of the DFI interface for pSFC-MS coupling. pSFC-DFI-MS with electron-capture negative ionisation (ECNI) has been reported [421], The flow-rate of eluent associated with pSFC (either analytical scale - 4.6 mm i.d. - or microbore scale 1-2 mm, i.d.) renders this technique more compatible with other LC-MS interfaces, notably TSP and PB. There are few reports on workable pSFC-TSP-MS couplings that have solved real analytical problems. Two interfaces have been used for pSFC-EI-MS the moving-belt (MB) [422] and particle-beam (PB) interfaces [408]. pSFC-MB-MS suffers from mechanical complexity of the interface decomposition of thermally labile analytes problems with quantitative transfer of nonvolatile analytes and poor sensitivity (low ng range). The PB interface is mechanically simpler but requires complex optimisation and poor mass transfer to the ion source results in a limited sensitivity. Table 7.39 lists the main characteristics of pSFC-PB-MS. Jedrzejewski... 

GC detectors can be grouped into concentration-sensitive detectors and mass-sensitive detectors. The signal from a concentration-sensitive detector is related to the concentration of solute in the detector, which does not usually destroy the sample. Mass-sensitive detectors usually destroy the sample, and the signal is related to the rate at which solute molecules enter the detector. The response of a mass-sensitive detector is unaffected by make-up gas, while that of a concentration-sensitive detector will lower with make-up gas. A summary of some important characteristics of the GC detectors specifically used in drug residue analysis is presented in Table 23.1. 

Table 4.2 Mass sensitivities of five types of acoustic wave devices... 

As has been discussed, the combination of SEC and molar-mass-sensitive detectors is a powerful tool for the analysis of complex polymers. However, it is important to distinguish between claimed versus actual capabilities and between potential expectations and demonstrated performances. Tables 1 and 2, taken from a critical review of different techniques, summarize the informational content and additional details of SEC-light scattering and SEC-viscometry coupling... 

Table 1. SEC analysis using molar-mass-sensitive detectors ...

Table S.1 Typical Mass Sensitivities of Acoustic Wave Devices ...

Quadrupole mass filters are one of the most common and cost effective mass analyzers. Although they have limited mass resolution (Table 10.2) and are less sensitive than other mass analyzers, they are durable and suitable for high-throughput analyses. To perform a tandem mass analysis (MS/MS), a triple quadrupole MS is used in which three quadrupoles are placed in series to select, fragment, and analyze ions of interest. Quadrupole ion-trapping devices such as linear 2D ion traps are... 

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. 

Obviously a small wave velocity in the crystal improves the mass sensitivity of the sensor for a given mechanical resonance frequency/), whereas a large wave velocity increases the mass sensitivity if thickness of the crystal must not fall below a specific value. Table 1 illustrates these basic findings for AT-cut (exemplarily for a small Vq) and BT-cut quartz (exemplarily for a high Vq) for two cases a lOOnm rigid film (Sauerbrey case) and a semi-infinite hquid with a viscosity of 1 cP (Kanazawa case). 

Table 2 Mass-sensitive methods based on microcantilvers...

From eqn. (9), it follows that the mass sensitivity Cf of a quartz crystal microbalance can be calculated from the general properties of the quartz plate. Calibration was performed with various film materials using electromechanical microbalances and chemical microanalysis. As can be seen in Table 2, the experimentally found sensitivity values Cf exp are in very good agreement with calculated values. 

The increased mass sensitivity for concentration-sensitive detectors is the direct result of reduced dilution of the sample in small ID columns and is inversely proportional with the square of the reduction in column diameter. As a result of miniaturization in LC, a variety of new column formats were developed, which can be subdivided according to the ID. In Table 5.4-1, the ID, typical flow rate, and sample loading are listed for various HPLC techniques. 

Table 33. Comparative H mass sensitivities for various probe configurations discussed in the text (data for entries 1-6 courtesy of Broker Biospin)...

Table 2 Simulated example for molar mass sensitive detectors true and recuperated average molar masses from several MMDs.

Table 11. Transducer noise of the new polymer-coaled 155 MHz BAW in air in comparison with mass-sensitive an SAW-transducer of different operating frequencies from literature values. The integration limes of the frequency counters were in the range between 1.0 s and 2.0 s resonance frequency fo...

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