The Power of Mobile Phase Strength
July 1st 2006After you have worked with liquid chromatography (LC) for several years, adjustment of the mobile phase to move peaks around comes almost as second nature. To the newcomer, however, such changes border on magic. One of the rules of thumb that I teach in my short courses is "nothing's magic". This is meant to remind us that chromatography is a very systematic process - study it carefully and you will minimize your surprises. In this month's instalment of "LC Troubleshooting," we'll look at solvent strength and see how we can use it to make predictable changes in the peak movement for reversed-phase LC separations. Hopefully, you will be able to make some practical use out of the principles presented here the next time you need to develop or adjust a method.
Fast and Ultrafast HPLC on sub-2 μm Porous Particles — Where Do We Go From Here?
June 1st 2006Higher 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.
The Thermal Conductivity Detector
June 1st 2006Thermal conductivity detectors have been in use since before the beginning of gas chromatography. Essential for fixed-gas detection - no substitute has the same ease of use and stability - thermal conductivity detectors are also employed when the auxiliary or combustion gases required by flame ionization or other detectors are unsafe or impractical. Although they cannot match the sensitivity of ionization detectors, thermal conductivity detectors are the third most used detector, surpassed only by flame ionization and bench-top mass-spectrometry detectors. This month's instalment of "GC Connections" takes a look at the operating principles and inner workings of the thermal conductivity detectors.