Stationary phases metal oxide-based

Nawrocki, J. et al. Part II. Chromatography using ultrastable metal oxide-based stationary phases for HPLC. J. Chromatogr. A. 2004,1028, 31-62. 

J. Nawrocki, C. Dunlap, A. McCormick, and E W. Carr, Part I. Chromatography using ultra-stable metal oxide-based stationary phases for HPLC, /. Chromatogr. 

A few applications have employed conventional packed columns, although recent developments in new thermally stable stationary-phase materials have generated a renewed interest and the temperature stability of the different stationary-phase materials has been reviewed by Claessens and van Straten [43]. The new materials have included stable metal oxide materials, based on zirconia (Figures 18-4 and 18-5) and titania [44, 45] and hybrid phases combining silica and methylene or ethyl bridges [46]. These have been applied in a number of applications to pharmaceutical compounds (Table 18-1). 

Recent developments in chip-based GC have been significant, especially in terms of speed, rapid heating, stationary phases and sensitive and selective detection. For detection, the development of both a mini FID - and a mini FPD - have been reported. Metal oxide semiconductor detectors and a plasma emission detector have also been used for on-chip GC. 

NPLC stationary phases include metal oxides and moderately or strongly polar chemically bonded phases. Unmodified silica gel and silica-based bonded phases are most frequently used nowadays. Considerable effort in the development of new HPLC column packing materials in the past years has resulted in significant improvement of the column efficiency, reproducibility, and increased stability at elevated temperatures and at higher pH, enabling better compatibility with HPLC/mass spectrometry techniques and rapid analyses. Even though the new column technologies were primarily focused on RPLC separations, normal-phase HPLC also benefits from the improved properties of the support materials with uniform small particles and well-defined pore size. 

A more recent development that has yet to be widely accepted in the trace quantitation community is that of HPLC analysis at higher temperatures using stationary phases based on metal oxides (mainly zirconia and some titania). The many experimental adjustments that must be made to achieve the potential advantages (faster separations, partial or complete elimination of the need for organic solvents in the mobile phase etc.) are described in a recent review (McNeff 2007). However, no account of interfacing this novel HPLC approach to mass spectrometry appears to have been published as yet. 

With the advance of three-way catalysis for pollution control, used mainly in automobile catalytic conversion but also for the purification of gas exhausts from stationary sources, a need has arisen to develop a basic understanding of the reactions associated with the reduction of nitrogen oxides on transition metal catalytic surfaces [1,2]. That conversion is typically carried out by using rhodium-based catalysts [3], which makes the process quite expensive. Consequently, extensive effort has been placed on trying to minimize the amount of the metal needed and/or to replace it with an alternatively cheaper and more durable active phase. However, there is still ample room for improvement in this direction. By building a molecular-level picture of theprocesses involved,... 

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