Liquid Chromatography Blog

Method Adjustment vs Change Part 4: Flow Rate and Particle Size

In prior instalments of this series on method adjustment, we’ve looked at the guidelines from the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP) for allowable adjustments in pH (Part 1), mobile phase (Part 2), and column...

Method Adjustment vs Change Part 3: Column Dimensions

In this series on method adjustment vs method change, we first took an overview of the concept (Part 1) then at specific guidelines for mobile-phase adjustment (Part 2). In this article, we’ll take a closer look at some of the potential...

Method Adjustment vs Change Part 2: Aqueous-to-Organic Ratio

In the previous article (Part 1), we took an overview of the concept of method adjustment vs method change in reversed-phase HPLC, in light of the guidelines of the European Pharmacopoeia (EP) and United States Pharmacopoeia (USP). We also looked...

Method Adjustment vs Change Part 1: Overview

We all know that no HPLC method is perfect and that it may need to be “tweaked” once in a while to make it operate properly. But in today’s highly regulated environment, there’s always a question about whether or not such adjustments are allowed....

PEEK Fitting Slippage

PEEK (poly-ether-ether-ketone) fittings and tubing are in widespread use for HPLC applications. The convenience of using your fingers instead of a wrench to tighten the fittings and the flexibility of the tubing make PEEK the material of choice...

Too Much Retention

As part of the HPLC Master Classes that I teach, I start each class by gathering questions or topics that the attendees would like to know more about. In a recent class in London, one of the topics was the causes of excessive retention – a method...

Temperature and Retention

Ever have an HPLC method that specifies “ambient” as the column temperature? That’s a good sign of potential problems in the future for the method. We’ll get back to the interpretation of “ambient” in a bit, but first, let’s take a look at the...

Back to Basics #10: Fundamental Resolution Equation – k

In the previous three instalments of this series ('#7: Fundamental Resolution Equation, Part 1', '#8: Fundamental Resolution Equation, N', '#9: Fundamental Resolution Equation – Alpha'), we’ve looked at the fundamental resolution equation

Back to Basics #9: Fundamental Resolution Equation – Alpha

In the previous two articles ('#7 Fundamental Resolution Equation, Part 1' and '#8 Fundamental Resolution Equation, N'), we’ve looked at the fundamental resolution equation

Back to Basics #8: Fundamental Resolution Equation, N

In the previous article we began our study of the fundamental resolution equation

Back to Basics #7: Fundamental Resolution Equation, Part 1

In our last Back-to-Basics discussion (#6 Resolution), we looked at the way we measure resolution, Rs, from a chromatogram using the following equation:

Solvent Nomograph

During method development in HPLC, one of the powerful variables that can be used to change selectivity is to switch from one solvent to another. For example, the B-solvent can be changed from acetonitrile (ACN) to methanol (MeOH) or...

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