Columns | Column: LC Troubleshooting

Paying attention to the details of mobile-phase preparation can have a big impact on the reproducibility of HILIC separations.

What are the most useful chromatography books on your bookshelf? What are the most useful web-based resources (such as websites, downloadable documents, videos) about separation science? What are the most useful tools supporting your work (such as calculators and simulators)? In this installment, Dwight Stoll compiles input from the separation science community (both individuals and vendors) to guide you to the resources that people find most useful.

What’s not in your standard operating procedure? Documenting details can prevent headaches associated with method transfers between laboratories.

In his final column before retirement, John Dolan reflects on the changes he has seen during his 34 years as the author of “LC Troubleshooting,” and shares his short list of best practices that still hold true today.

When developing or modifying an LC separation, a common strategy is to change selectivity by choosing a new column. Here’s guidance for making that selection.

You have to be careful when adjusting gradient conditions.

We consider some of the details associated with preparing a column for storage, with an eye toward choices that will pay dividends in future use.

How much of a change can you make to a USP method without revalidating the method?

Several variables can be used to change selectivity in a liquid chromatographic (LC) separation. Here we compare the variables in an effort to prioritize which experiments will be most effective.

We’ll see how to find the “sweet spot” in terms of retention for a liquid chromatographic separation as well as how much retention change is to be expected for a selected change in mobile-phase percent organic or column temperature.

When considering column efficiency, more is not always better. We look at some ways to quickly estimate the effects of changes in column length and particle diameter rather than trying the experiments in the laboratory.

Delivering samples to the analytical column in ‘clean’ mobile phase is important for robust methods and high quality results.

The mobile phase pH can be a powerful tool to control retention and selectivity, but it can also get you in trouble if not controlled properly.

A reader’s problem of a method that fails the repeatability of the system suitability test serves as an example of how to approach LC method troubleshooting.

What could be causing a peak to be eluted before the column dead time? In last month’s “LC Troubleshooting” (1) we looked at problems two readers had with ghost peaks in gradient runs. This month, we’ll continue looking at submitted questions and examine one submitted by another reader of this column.

Interfering peaks or high baseline background can compromise the results of gradient LC separations.

Fluorescence detection can be a strong alternative to ultraviolet or other detectors for some compounds.

Detectors based on ultraviolet absorbance are the most common detectors in use for liquid chromatography.

A reliable autosampler is one key requirement for unattended operation of a liquid chromatograph.

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

Understanding how liquid chromatographic pumps operate can help streamline solving pump problems.

Retention times drop from one injection to the next. A systematic approach to troubleshooting can help to quickly identify the problem source.

How suitable is the column plate number for system suitability testing?

The silica-based packing in reversed-phase columns is not inert. Here we consider what happens when the mobile phase pH is too high or too low.

Strongly retained sample compounds can cause various changes in the appearance of a chromatogram.

Particulate matter from the sample or the system can cause havoc in the chromatogram.

How to get started in the process of identifying the problem source for column-related problems.How to get started in the process of identifying the problem source for column-related problems.

Are your solvent costs too high? Here are some ideas about how to decrease the amount of mobile phase you use.

I recently returned from a tour of teaching liquid chromatography (LC) classes to users in Minnesota, the United Kingdom, Poland, and Malta. One thing that always impresses me on such trips is that no one group has a corner on the LC problem market. The same problems pop up in most laboratories, no matter where they are located, the role of the laboratory (for example, analytical, forensic, production, research), what industry is involved, or the brands of instrumentation used.

How to distinguish between LC column overload and detector overload.