Liquid Chromatography

Q: I am running an isocratic method with a 250 x 4.6 mm, 10 µm particle column at 1 mL/min with a 20% acetonitrile (ACN)/buffer mobile phase. I dissolve my sample in ACN and inject. Normally my compound of interest comes out at 7.7 min. I switched...

This technical article looks at the best way to clean the frits used in the HPLC system. In this example, the reader had been sonicating them in nitric acid, but wasn’t sure if that was the best way to approach the problem.

A reader complained about retention times that changed in an overnight HPLC run and wondered how to diagnose the problem source. The question left too many possibilities, and because there was no complaint about changing resolution, I’ll assume that...

Recently, a reader sent a question about how to get started with a method that required separation of enantiomers by reversed-phase HPLC. Unfortunately, the problem is a non-starter in this context. Enantiomers cannot be separated by reversed-phase...

A reader recently sent in this e-mail: “I am trying to find information that I can put in an SOP regarding how long a mobile phase can be used before it must be discarded. I’ve heard 1-2 weeks from some sources, whereas others say a month, and some...

This technical article addresses why formic acid would be specified as an additive for the mobile phase in an HPLC method. Formic or trifluoroacetic acid at 0.1% concentrations are common, especially for LC-MS work. There are a number of reasons for...

PEEK (poly-ether-ether-ketone) tubing and fittings have become a standard part of most HPLC systems today. The flexibility and ease of cutting the tubing, coupled with the convenience of finger-tightened fittings make a combination that is hard to...

This article considers the dilemma that occurs with any discussion regarding method alteration in that it can be open to interpretation.

This technical article discusses the possible effect caused from interactions between changes from different variables.

The separation power of HPLC combined with the very high sensitivity and selectivity of MS detection is widely used to develop analytical methods that are required to achieve ultra-low detection and quantification limits. Examples of such demanding...

The sample solvent, also called dissolution solvent or injection solvent, is the solvent used to prepare the solution in which the compound to be analysed by HPLC is dissolved. The choice of the sample solvent is fundamental for a successful...

It is matter of fact that the samples most chromatographers have to face are rather complex for sample number and compound variety. In these situations, gradient elution is largely preferred for the separation of analytes with different retention...

Mostly in HILIC conditions, by increasing column temperature a decrease in the retention time is observed.

This article discusses the pH of the mobile phase that should be selected in order to enhance the hydrophilicity of the analytes.

In this technical article the effect of the salt content in HILIC mobile phases and the preparation is discussed.