John W. Dolan

Getting started on the right foot is important for efficient method development.

How to avoid an expensive shot in the dark.

How can you reduce mobile phase expenses?

Different methods require different strategies.

In the fourth installment in a series on method development for liquid chromatography (LC), with an emphasis on devloping trouble-free methods quickly. John Dolan started out by considering some of the goals we might have and some method development strategies.

Faster isn't always better

Column temperature plays an important role in controlling peak spacing (selectivity) in reversed-phase liquid chromatography (LC) separations. Temperature has long been known to affect retention time, and more recently, its use in adjusting selectivity has gained popularity (see reference 1 for a review of temperature selectivity). In preparation of a paper for the most recent Pittsburgh Conference, I had an opportunity to reexamine some data that compare temperature selectivity with other variables used to control selectivity in LC separation. This month's instalment of "LC Troubleshooting" examines temperature selectivity and its relationship to pH selectivity.

Getting started on the right foot is important for efficient method development.

Mass overload is related to the mass of sample that can be injected before the stationary phase is sufficiently loaded to cause changes in the chromatography.

The topic of this month's instalment of "LC Troubleshooting" was prompted by a manuscript I recently reviewed and a question I received from a reader of this column. Both inputs related to the variability of retention times observed in liquid chromatography (LC) methods. Variable retention is a topic that has been touched on many times over the history of this column, sometimes just in passing and other times in depth. Yet, it seems to be a problem that keeps recurring, so I think it is worth considering again.

Different methods require different strategies.

I have to cede my seniority as an LCGC columnist to Ron Majors - he started several months before I did.

Is it more than meets the eye?

...it is important to acknowledge that environmental concerns can be more important than the economics of the reduction of solvent consumption.

Detector selection for a method should be made on a case-by-case basis.

Prompted by a recently reviewed manuscript and a question from a reader, John Dolan examines the variability of retention times observed in LC methods in this month's installment of "LC Troubleshooting."

As I write this instalment of "LC Troubleshooting", I have just completed teaching a series of liquid chromatography (LC) method development classes to pharmaceutical scientists in India. As a parting gift, my host gave me a copy of Thomas Friedman's The World is Flat?.1 One central theme of this book is that the technology and skills for the science and information technology sectors are available around the world and are no longer the exclusive domain of the US and Western Europe.

it has been more than 10 years since solvent recycling has been the main subject of an "LC troubleshooting" column, so this month, John Dolan revists this subject.

A reluctance to make any changes to a validated or compendial method is common, and often well founded.

John Dolan considers some techniques to improve detection limits, no matter what the application is.

Excess variability is not acceptable in a pharmaceutical method.

This month's instalment of "LC Troubleshooting" presents two examples of sample degradation inside the liquid chromatography (LC) column. Depending upon the type of samples you analyse, sample degradation might or might not be a problem that you encounter regularly. However, most of us run a sufficiently wide variety of sample types over our careers that we will probably run into some samples that do not behave as expected.

Chromatographers worldwide suffer from the same problems.

Sometimes it is easy to ignore the fittings and tubing that are used to connect various parts of the liquid chromatography (LC) system. After all, it's the pump, injector, column and detector that do all the work - right? Well, yes and no. It is possible to compromise an otherwise excellent separation by the improper use of fittings, but with reasonable care, you should not have problems with most applications. This month's instalment of "LC Troubleshooting" takes a look at the important components that are used to connect various parts of the LC system and how to use them wisely.

Excess variability is not acceptable in a pharmaceutical method.

What do you do when the sample changes inside the column?

This month's instalment of "LC Troubleshooting" focuses on two column-related problems reported by readers. The first deals with a column that takes several injections to "settle down" for each batch of samples. The second relates to short column life as a result of early fouling of the column. Although both of these problems are not encountered with most liquid chromatography (LC) methods, they both appear often enough that we all should be aware of them. It is only a matter of time before you meet one of these problem types with one of your methods.

This month's "LC Troubleshooting" takes a look at the important components that are used to connect various parts of the LC system and how to use them wisely.

Because each sample is unique, you will need to check for carryover under the conditions of each method.

John Dolan addresses two column-related problems reported by readers - the first deals with a column that takes several injections to "settle down" for each batch of samples while the second problem relates to short column life due to early fouling of the column.