Analyser resolving power

In 1995, Moore and Jorgenson used the optically gated CZE system to obtain extremely rapid separations with HPLC coupled to CZE. The rapid CZE analysis made possible more frequent sampling of the HPLC column, thus increasing the comprehensive resolving power. Complete two-dimensional analyses were performed in less than 10 min, with the CZE analyses requiring only 2.5s. A peak... 

The main function of the mass analyser is to separate (resolve) the ions formed in the ionisation source on the basis of their mass to charge ratios (m/z). The resolving power of a mass spectrometer is a measure of its ability to separate two ions of any defined mass difference. More precisely, the resolution (R) of a mass analyser is defined as its ability to separate the ion envelopes of two peaks of equal intensity, i.e. the ratio of the mass of a peak (M ) to the difference in mass between this peak and an adjacent higher mass peak (Af2), i.e. ... 

The information amount of process analyses (under which term all time-dependent studies from chemical process control up to dynamic and kinetic studies are summarized) increases by the factor of time resolving power... 

Compared with that of common analyses which determine an average composition of the sample, the information amount of spatially resolved analyses increases by the factor of geometrical resolving power RA that may be in the concrete case... 

LC/MS analyses requiring high resolving power to separate all compounds present in a sample may be optimized as well to increase throughput. Optimizing in the LC dimension utilizes smaller particles as well more radical approaches may involve a change in workflow toward extremely high column efficiencies and peak capacities in contrast to the present common work flow of many individual runs with modified selectivities. 

Recent advances in electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), thermospray, and particle beam LC-MS have advanced the analyst toward the universal HPLC detector, but price and complexity are still the primary stumbling blocks. Thus, HPLC-MS remains expensive and the technology has only recently been described. Early commercial LC-MS uses particle beam and thermospray sources, but ESI and APCI interfaces now dominate. Liquid chromatography MS can represent a fast and reliable method for structural analyses of nonvolatile compounds such as phenolic compounds (36,37), especially for low-molecular-weight plant phenolics (38), but the limited resolving power of LC hinders the widespread use of its application for phenolics as compared to GC-MS. 

The utility of UPLC has been demonstrated for both qualitative and quantitative analyses. In 2005, Castro-Perez et al. (2005) compared the performance of a HPLC with that of a UPLC and showed that improved chromatographic resolution and peak capacity attained with UPLC lead to reduction in ion suppression and increased MS sensitivity. Comparison of the mass spectrum obtained using HPLC with that from UPLC (Fig. 1.15) revealed that the higher resolving power of the UPLC-MS system resulted in a much cleaner mass spectrum than that obtained using the HPLC-MS system. The sensitivity improvement directly resulted in a higher ion count in the UPLC mass spectrum (855 vs. 176). 

Last but not least, there is the characteristic of a mass analyser concerning the resolution or its resolving power. Resolution or resolving power is the ability of a mass analyser to yield distinct signals for two ions with a small m/z difference (Figure 2.1). The exact definition of these terms is one of the more confusing subjects of mass spectrometry terminology that continues to be debated. We will use here the definitions proposed by Marshall [1], This will be described in more details in Chapter 6. 

Low resolution or high resolution is usually used to describe analysers with a resolving power that is less or greater than about 10000 (FWHM), respectively. However, there is no exact definition of the boundary between these two terms. 

The resolving power of an analyser was defined earlier. We have seen at the beginning of... 

High resolving power also allows an increase in the selectivity of detection in analyses aimed at screening known target compounds. 

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