01 May 2008
By:Ronald E. Majors
In this instalment of "Column Watch", columnist Ron Majors examines the role of pressure in high performance liquid chromatography (HPLC) from two viewpoints: the impact of the ultrahigh pressures encountered in ultrahigh-pressure liquid chromatography (UHPLC) on chromatographic parameters and increases in column pressure encountered in normal daily use. The latter is of more practical consequence to HPLC users because increased back pressure usually implies that something has gone wrong with the column. Pressure increases as a result of physical and chemical contamination are explored and practical approaches to solve these problems are suggested.
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01 July 2007
By:Mark Sinnott, Simon Jones, Allen Vickers
Modern gas chromatography (GC) capillary columns are rugged and forgiving but some care should be taken when handling and using these high-efficiency columns. In this instalment of "Column Watch", the authors discuss the issues surrounding avoiding column breakage, stationary phase damage and column contamination. Prolonging the life of a column by keeping an oxygen-free system, providing a cleaner sample and not exceeding the upper temperature limit of the stationary phase are highlighted in this practical discussion.
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01 January 2007
By:Ronald E. Majors
In any field there are often "misconceptions" or "myths" that are perpetuated and passed on to the next generation. These myths are often driven by a lack of understanding by practitioners of the real issues. In this instalment of "Column Watch", the 10 most popular myths around high performance liquid chromatography (HPLC) column technology will be demystified by discussing the issues at hand. Among some of the popular myths that will be dispelled are that "All C18 (L1) columns are the same", "You can't reverse an HPLC column", "High temperature always leads to better separations" and "The higher the carbon load the better the reversed-phase column".
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01 June 2006
By:Ronald E. Majors
Higher productivity and faster analyses are two of the driving forces for continued improvement in high performance liquid chromatography (HPLC) column technology. Reduction in the average particle size of HPLC porous column packings below 2 ?m has resulted in sub-1.0 min separations in the gradient and isocratic modes. In this instalment of "Column Watch", Ron Majors traces the development of particle technology from the beginning of HPLC to the present, discusses why small particles are desirable, and probes some of the difficulties to be encountered, including extracolumn band broadening, pressure restrictions, and instrumental considerations. Finally, he shows a wide variety of fast- and ultrafast applications examples from commercial products in the sub-2 ?m range. Speculation on future directions in HPLC in particle technology concludes the column.
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01 March 2006
By:Rick Parmely
Capillary gas chromatography (GC) is a well-established separation technique. Rick Parmely reviews some of the capillary column basics by investigating a standard test mixture and observing some of the chromatographic effects that can affect peak response, peak shape and column bleed. He provides guidelines for obtaining the best performance from a capillary column. He discusses peak tailing, column overload, ghost peaks and column bleed and speculates on "when to give up." He concludes with a set of fundamental steps to be used in achieving better GC analyses.
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01 January 2006
By:Matthew Przybyciel
Guest columnist Matt Przybyciel reviews the structure, behaviour and applications of both alkyl- and phenyl-fluorinated phases in HPLC. The author presents some guidelines on potential areas of application for alkyl and phenyl-fluorinated phases, in which conventional C8, C18 and phenyl phases might have insufficient selectivity or too strong retention.
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01 June 2005
In the last part of this series, the authors provide a technical review of the means for method adjustment and the pertinent regulations concerning the required validation of adjusted methods.
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01 May 2005
This month’s column provides an overview of green chemistry issues relating to preparative chiral SFC chromatography in support of preclinical development in the pharmaceutical industry.
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01 April 2005
In the first part of this series, the authors look at method modification from a scientific and regulatory standpoint with regard to changing a column and the operating parameters.
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