LCGC North America-06-01-2016

In this column, we introduce the basics of today’s approaches for doing intact protein dissociation with mass spectrometry (MS), or top-down sequencing (that is, rather than the more conventional peptide-based “bottom-up” sequencing where future improvements might occur, advantages and limitations of using top-down sequencing, possible applications, and why it has become such an important and pursued research area for many.

Different techniques of LC mobile phase mixing can give different results… and have different problems.

In recent years industry has been moving to columns with smaller and smaller inner diameters-moving from 4.6 and 3.0 mm i.d. columns to 2.1 mm, 1.0 mm, and even smaller. While small inner diameter columns have some clear advantages, they also bring challenges. Reduction of extracolumn volumes must be given greater consideration by both customers and manufacturers. Additionally, experimental evidence suggests that the very narrow confinement of chromatographic particles can result in packed bed structures that promote increased dispersion and reduced efficiency. This article focuses on the sources of band broadening within high performance liquid chromatography (HPLC) columns with particular emphasis on eddy dispersion. The physical mechanisms of dispersion are discussed and a review of the current literature as it pertains to small inner diameter columns is presented.

How to optimize the key variables in GC analysis – sample introduction

A universal generic HPLC or UHPLC method with a primary modern column that works well for most drug analyses in a few minutes would be an attractive idea for many laboratories. With advances in column technologies, this ideal scenario is becoming more realistic, as demonstrated in the proposed 2-min generic method shown here. In addition, rationales for the selection of column and operating conditions are discussed, together with ways to extend this generic method as a starting point for stability-indicating applications by simple adjustments of gradient time and range.

UHPLC instruments from different manufacturers and instruments with different configurations can produce significant variations in chromatographic separation. The variety in instrument configuration increases the complexity of the method development process, which now requires a more thorough evaluation of the effect of instrument variations on the method. The studies presented here determined the typical inter-instrument variations in dwell volume, extra-column dispersion, and mixing efficiency as measured by mobile phase compositional accuracy. Additionally, the dwell volume and extra-column dispersion were independently and systematically varied to evaluate the resulting impact on resolution for a small molecule test mixture during gradient elution. To account for these inter-instrument variations, dwell volume and wash-out volume method translation and adjustment techniques were evaluated.

This is part one of a series of tutorials that explain, in the simplest manne, how statistics can be useful, even to chromatographers who normally find statistics difficult, with a minimal understanding of its features. Part I explains how to collect and examine your data.

Leading separation scientists discuss their approaches to improving the analysis of large molecules.

Click the title above to open the LCGC North America June 2016 regular issue, Vol 34 No 6, in an interactive PDF format.