HPLC

Dissolution testing is a mandatory test for the physical evaluation of solid dosage forms such as capsules, tablets, ointments, and creams. The most basic form of testing measures the rate of dissolution or solubility of a drug tablet. Dissolution testing also can be used in ADME and bioavailability studies, release rates of a drug substance under different conditions, as well as provide information as to the efficacy of in-vivo performance.

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.

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.

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.

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.

This month's installment of "Column Watch" is the first of a two-part series in which Ron Majors examines the trends and highlights in columns and consumables at Pittcon 2006.

Check valves can be replaced with new ones, but often a simple cleaning procedure is sufficient to restore normal operation.

Capillary gas chromatography (GC) is a well-established separation technique. Rick Parmely reviews some of the capillary column basics by investigating a standard test mixture and observing some of the chromatographic effects that can affect peak response, peak shape and column bleed. He provides guidelines for obtaining the best performance from a capillary column. He discusses peak tailing, column overload, ghost peaks and column bleed and speculates on "when to give up." He concludes with a set of fundamental steps to be used in achieving better GC analyses.

John Dolan explores how an on-line discussion group can be a great source for free consultation from experts in the field.

The first of a two-part series addresses HPLC pumps, sample introduction systems, and columns for nanoLC-MS.

This article assesses the extent to which some familiar HPLC detectors can provide reliable quantitative analytical measurements when no suitable primary reference standard exists. The advantages and limitations of two candidate detector schemes are discussed ? evaporative light-scattering detection (ELSD) and chemiluminescent nitrogen detection (CLND). It was found that when the ERETIC (Electronic REference To access In-vivo Concentrations) method in proton NMR was used as a "gold standard" reference procedure the ability of CLND to provide reliable single calibrant quantification is superior to ELSD. Furthermore, ELSD showed bias towards underestimation of chromatographically-resolved impurities, resulting in an overestimation of analyte purity.