Liquid Chromatography (LC/HPLC)

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.

The fundamental aim of any computerized system validation should be to define its intended use and then test it to demonstrate that it complies with specification.

The gradient linearity and step tests are two of the most useful performance tests that can be made for a liquid chromatography (LC) system. These check the linearity of gradient generation and the accuracy of mobile phase proportioning. These tests, and examples of problems detected as a result of these tests, have been the subject of at least seven "LC Troubleshooting" columns over the last 18 years.1–7 We strongly recommend that every LC system undergo these tests at least on an annual basis, and preferably semiannually. When a new and different example of a problem detected by these tests is discovered, it is hard to bypass the opportunity to share it with our readers. So this month, you get yet another example of how an LC system can fail.

If cyclohexane is mixed with even low amounts of other solvents, the melting pressure increases remarkably.

The market for high performance liquid chromatography (HPLC) continues to be one of the most dynamic markets of the analytical instruments industry. A few years ago, the HPLC market began showing signs of maturity with little product innovation and slower growth rates. Although innovations in mass spectrometry (MS) helped to fuel growth, HPLC was an afterthought and considered to be a mere inlet to MS. However, the recent development of fast liquid chromatography (LC) systems is energizing the HPLC market.

The popular HPLC 2006 Symposium was held in June in San Francisco, California. It is the premier annual meeting in liquid phase separations technology.

In this article, we present data acquired on a 24-column microparallel LC system using a HPLC technique adapted from a routinely used method for measuring lactic acid.

Carryover is the appearance of an analyte in a run when a clank containing no analyte is injected. In this month's "LC Troubleshooting," John Dolan shows us how to measure it, and some ways to reduce carryover.

After having collected some industry accepted practices for implementing new LC technology, the duo discuss FDA guidance available on the subject with respect to LC, and using some recently introduced LC technology.

In this installment of "Column Watch," Ron Majors traces the developments in modern column design in analytical and preparative configurations and speculates on future directions.

The authors work to develop a universal high performance liquid chromatography method that is capable of simultaneously retaining and separating both cations and anions within a single chromatographic analysis for the purpose of quantification in pharmaceutical products.

Midazolam is a central nervous system depressant that is commonly used as a sedative before surgical or other medical procedures.

In the second of a two-part series, Marlin K.L. Bicking continues to explain his work concerning integration errors in peaks with approximately equal sizes (small peak ratios).

In this month's installment of "LC Troubleshooting," John Dolan takes a look at solvent strength and sees how we can use it to make predictable changes in the peak movement for reversed-phase LC separations.

Globally, 2005 sales of pharmaceuticals have been estimated at approximately $550 billion. A significant fraction of this amount was due to the top pharmaceutical companies in the world. The top five companies alone were responsible for total revenues of $168 billion, or 30% of the entire market.

This is the second installment of a two-part series on the practical aspects of configuring and operating a nano liquid chromatography-mass spectrometry (LC-MS) system.

John Dolan delves deeper into dwell volume, a subject that was touched upon in a recent installment of "LC Troubleshooting."

Testing helps you identify the soft spots in the method, select the best conditions for operation and develop troubleshooting strategies to correct problems when they do occur.

This article looks at current practices in bioanalytical chemistry by examining and critically assessing the various parameters that can be altered to achieve high-speed results with high resolution in LC–MS applications. The decision to opt for gradient or isocratic elution is also discussed.

When a problem is not solved quickly, it is a good idea to go back to basics and determine if the equipment is functioning properly or not.

This month's installment of "Column Watch" is the conclusion of a two part series in which Ron Majors examines the trends in columns and sample preparation at Pittcon 2006.

John Dolan ponders te question of whether or not you will be prepared when that method eventually fails.

In part I of a two-part series, the author introduces several methods to reduce error in your chromatographic analyses.