Dwight R. Stoll

In this installment of "LC Troubleshooting," Dwight Stoll discusses several essential principles related to when and why buffers are important, as well as practical factors, such as commonly used buffering agents, that are recommended for use with different types of detectors.

It has been more than five years since the last update in this column on the evolution of the Hydrophobic Subtraction Model (HSM) of reversed-phase selectivity and characteristics of new stationary phases recently characterized using the model. In this installment, Dwight Stoll discusses the continuing evolution of the model.

In this installment of “LC Troubleshooting,” we describe an artifact that can arise because of compound degradation during the transfer of fractions of the first dimension (1D) column effluent to the 2D separation.

In this installment of “LC Troubleshooting,” we discuss strategies that can be used to minimize the likelihood of compound degradation in the isolation process.

In this episode, podcast co-hosts Dr. Dwight Stoll and Dr. James Grinias discuss highlights and observations from HPLC 2024, which was held in Denver, Colorado in July.

In this month’s column, I highlight some of the primary considerations we face in method development and point to resources that can help users overcome uncertainty and develop highly effective 2D-LC methods.

In this installment, we apply the concepts developed in last month’s installment by demonstrating how they can be used to help troubleshoot problems in LC involving pressure and flow.

The analogy that electrons flowing in wires is like water flowing through a tube can be remarkably effective. In this installment, the basics of that analogy are discussed.

The concept of gradient delay volume (GDV) in liquid chromatography (LC) poses challenges for both beginners and experienced practitioners. The GDV, which affects the arrival time of mobile phase composition changes at the column inlet, can have a significant impact on method throughput, influencing the time required for mobile phase changes at both the beginning and end of the LC method. Different pump designs and column characteristics affect efficient use of the available analysis time, as well as overall throughput. Notably, achieving repeatable equilibration, rather than full equilibration of LC columns following mobile phase gradients, is often sufficient for many LC applications, which can also be leveraged to increase method throughput.

In this installment, I illustrate the impact of different gradient delay volumes when transferring a method between instruments and discuss some strategies that can be used to mitigate these challenges.

The gradient delay volume is arguably one of the most important, yet least appreciated, parameters that affect how gradient elution separations in LC work. This has implications both for method development and for method transfer during the lifecycle of a LC method. In this installment, I will review the concept of gradient delay volume, its physical connection to the LC instrument, and how it can impact method development and separation quality.

The 15th Multidimensional Chromatography Workshop is a free event involving keynote and contributed presentations, a poster session, and discussion groups on all multidimensional techniques, and will be held in-person on the campus of California State University, Los Angeles, from January 10 to 12, 2024.

There are three important habits and practices that can improve the effectiveness and efficiency of any troubleshooter.

Understanding how approaches to degassing have evolved is helpful for troubleshooting problems with pumps and detection.

Troubleshooting continues to evolve constantly, changing how we overcome issues such as chemical causes of peak tailing.

Mobile phase degassing has become very useful for troubleshooting problems with pumps and detection.

As chromatography technology evolves, our use of it should change also. This article outlines a number of protective and troubleshooting methods for LC and how these approaches have changed over time.

The author outlines multiple protective and troubleshooting methods for liquid chromatography and how these approaches have changed over time.

Understanding the relationship between a number of variables and analysis time, and their effects on other choices made during method development, is helpful for developing methods that are both effective and time-efficient.

We present two cases where understanding the specific interactions between particular analyte functional groups and LC instruments and columns is critical for successful separations.

How to design scouting gradients, how to use the resulting data to make decisions about next steps, and how to improve the separation once an elution mode has been chosen.

Several factors strongly influence separation speed, including the pressure available to drive the separation, column temperature, particle size, and column length. Developing efficient methods to improve speed while not sacrificing accuracy require an understanding of the abovementioned variables and analysis time.

Building up knowledge of how different factors affect resolving power from a theoretical point of view, as well as what changes are possible within practical constraints, is powerful when we are confronted with a separation that needs to be improved, or when an existing separation is not performing as expected.

What are the options available when adjusting selectivity (peak spacing or elution pattern) when dealing with relatively simple mixtures?

Scouting gradients can simplify LC method development. Here’s what you need to get started using them.

The variables that are most important for improving the separation of complex samples are quite different from those for simpler samples. Considering these differences can save time and resources.

A systematic approach to method improvement can save time and resources by using methods that are likely to be better, and more robust, than those developed using a trial-and-error approach.

When can analyte retention deviate from what is expected or normal? We explain three subtle causes.

Even relatively simple mixtures are not always easy to separate. What are the options for adjusting selectivity in reversed-phase LC separations?

In this latest instalment of our series on recurring challenges in liquid chromatography (LC), we turn our attention to peak widths that are wider than expected. Estimating the expected peak widths can help determine when a column and LC system are not working quite right, and to decide when troubleshooting should be initiated.