Dwight R. Stoll

The offerings of commercially available columns for reversed-phase liquid chromatography (LC) continue to expand. Are these columns similar or different compared to what is already available?

The challenges we face in troubleshooting problems with liquid chromatography (LC) separations are highly diverse. This month we take a closer look at topics that have garnered more attention recently.

How many new columns truly offer new selectivity?

In reversed-phase separations, retention generally increases as the fraction of water in the eluent increases. When we encounter situations where retention is too low for an analyte of interest, we tend to use eluents with higher and higher levels of water. But how much water is too much?

When can we use completely aqueous eluents with reversed-phase stationary phases, and what happens if we make a mistake?

The challenges we face in troubleshooting problems with liquid chromatography (LC) separations are highly diverse. This month we take a closer look at topics that have garnered more attention recently.

Is an ultraviolet (UV) detector signal good for anything if the analyst is using a mass spectrometer?

Several new materials and columns have been introduced in recent years for size-exclusion separations of proteins. How do I know which one to choose, and which separation conditions will be the best for my protein separation?

Is a mixer needed between the injector and column in high performance liquid chromatography (HPLC)?

What happens when we inject a sample into the mobile-phase stream? Many LC practitioners are surprised to learn just how serious the effect of the injected sample solvent can be.

Many LC users are unclear what happens when we combine two (or more) flow streams in LC systems, and when mixers are needed to blend the fluids. This discussion explains why mixers are needed, and when and how you might consider using something other than the default mixer setting.

What types of mixers are needed with different types of liquid chromatography (LC) pumps? Are different mixers needed for different applications?

Much of the conventional wisdom regarding size-phase separations of proteins has been negated thanks to development of superior chemistries and advances in research. In this article, details that the authors have found to be especially beneficial in achieving effective SEC separations are examined.

Several new materials and columns have been introduced in recent years for size-exclusion separations of proteins. How do I know which one to choose, and which separation conditions will be the best for my protein separation?

Several new materials and columns have been introduced in recent years for reversed-phase separations of proteins. How do I know which one to choose, and which separation conditions will be best for my protein separation?

We examine instances where contaminants are problematic in LC–MS, as well as successful methods to decrease their influence.

Several new materials and columns have been introduced in recent years for reversed-phase separations of proteins. How do I know which one to choose, and which separation conditions will be best for my protein separation?

For reversed-phase separations of proteins, you must consider pore size,column temperature, and stationary-phase chemistry. Here are some guidelines.

Is that peak “pure”? How do I know if there might be something hiding under there?

Is that peak “pure”? How do I know if there might be something hiding under there?

Here, we see how 2D-LC can solve coelution problems that are difficult or impossible to address using peak purity tools or curve resolution methods.

A bad connection between an LC column and the rest of the system can ruin a good separation. New technologies may improve the quality of these connections and the likelihood of establishing a good connection in the first place. Understanding the issues will help you choose the best option for you.

With so many choices for fittings to use in making connections in my liquid chromatography (LC) system, how do I know which ones are the right ones for my application?

In part II of this series, we explore how curve resolution methods advance purity assessments and illustrate one of the most popular techniques, which adds a powerful tool to the chromatographer’s arsenal.

Is that peak “pure”? How do I know if there might be something hiding under there?

When preparing buffers for hydrophilic interaction chromatography (HILIC) separations, is the buffer concentration considered relative to the aqueous portion of the eluent only, or to the aqueous-organic mixture?

Certain details related to mobile-phase preparation that can be assumed in reversed-phase LC separations can be much more consequential in HILIC.

Is that peak “pure”? How do I know if there might be something hiding under there?

Is that peak “pure”? How do I know if there might be something hiding under there? In part I of this series, we explore some of the concepts behind peak purity assessments, describe some tools that are used in commercially available software for these assessments,

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