HPLC

Many HPLC analyses could be performed at lower expenditure. This could involve a combination of reducing the analysis time, reducing the resolution between critical peaks, and lowering the consumption of mobile phase. Successfully optimizing the method in such instances - as well as in situations where it is necessary to transfer the method to another laboratory that lacks the same selection of columns - can save the analyst time and money.

This article investigates the different methods that can be used to compare the performance of liquid chromatography (LC) columns to assess the advantage of using them at high pressures and/or high temperatures. The main focus is on the kinetic plot method. This method, which is based on two simple equations, allows the user to transform the more common Van Deemter curve into a curve describing the ultimate separation speed as a function of the required plate number, or the required peak capacity or the required resolution.

John Dolan has discovered that check-value problems have jumped to the top of the list with LC users. He takes a look at them in this month's installment of "LC Troubleshooting."

Guest columnsist and LCGC Emerging Leader award recipient Gert Desmet considers the different methods that can be used to compare the performance of LC columns.

Advion Biosciences Inc. (Ithaca, New York), a developer of microfluidic sampling technology for mass spectrometry (MS) has bought almost all assets of its production supplier, Washburn Manufacturing Technologies Inc. (Trumansburg, New York) for an undisclosed amount.

In this instalment of "Column Watch", columnist Ron Majors examines the role of pressure in high performance liquid chromatography (HPLC) from two viewpoints: the impact of the ultrahigh pressures encountered in ultrahigh-pressure liquid chromatography (UHPLC) on chromatographic parameters and increases in column pressure encountered in normal daily use. The latter is of more practical consequence to HPLC users because increased back pressure usually implies that something has gone wrong with the column. Pressure increases as a result of physical and chemical contamination are explored and practical approaches to solve these problems are suggested.

Ion-pair chromatography can be your best friend or your worst enemy.

For this month's discussion, John Dolan shares some of the key resources that he recommends using when you have one of those "How do I?" questions.

To obtain a better understanding of the challenges faced during method development and validation, the authors - in cooperation with LCGC - conducted a survey earlier this year. This column summarizes the results.

This article demystifies the qualification procedures and proposes a well designed, easy and simple set of experiments upon which to establish internal standard operating proceduresfor the complete qualification of HPLC instruments.

A simple and inexpensive sample preparation method followed by reversed-phase high performance liquid chromatography (RP-HPLC) was developed to quantify oxytetracycline (OTC), chlortetracycline (CTC), and tetracycline (TC) residues in prawns. The total analytical time, including sample preparation, was 15 min for each sample and no organic solvents were used in the sample preparation or chromatography stages.

To characterize complex samples such as natural products or peptide digests, a single chromatographic dimension cannot completely separate and identify every single compound. For such cases, comprehensive two-dimensional liquid chromatography (LC x LC) is under rapid development.

In the last decade, research on the detection of all groups of doping agents has been investigated by LC-MS, and routine LC-MS screening applications are now available for almost all classes of doping agents.

This month's installment of "Column Watch" is the second part of a two-part series in which columnist Ron Majors examines the trends and highlights in columns and consumables at Pittcon 2008.

After taking a course on learning that stated most people only remember three main points from an eight-hour training class, John Dolan decided to use three points to form the core of a preventive maintenance program for your LC system.

If the problem source cannot be found or if found, cannot be corrected, an adjustment in flow-rate is justified.

This month's installment of "Column Watch" is the first of a two-part series in which columnist Ron Majors examines the trends and highlights in columns and consumables at Pittcon 2008.

A very efficient way to start an isocratic method development project is to make the first run as a scouting gradient run.

This article explores the progress that atmospheric pressure photoionization (APPI) has made in its relatively short history for LC–MS analysis. Specifically, the authors examine the combination of APPI and electrospray ionization (ESI).

After teaching a training class in China, John Dolan was reminded of how chromatographers worldwide encounter the same types of problems, such as method transfer. This month's column is dedicated to method transfer problems.

This study evaluates the use of HPLC to estimate the log P (the octanol–water partition coefficient) of two compounds, apocynin and diapocynin. The paper will discuss the effects of an unexpected reversal of retention that occurred when these compounds were chromatographed with various amounts of methanol–water mobile phases.

Trade extra resolution for speed.

The use of dual polarization interferometry (DPI) to measure the behaviour of alkyl-modified surfaces under different solvent regimes is described. The empirically observed and modelled behaviour of grafted long alkyl chain adlayers on a silica surface were in good agreement. The empirical data was also compared with data using analogous systems and these also matched well. This approach has the potential to gain much greater insight into the behaviour of reversed-phase (RP) columns and could help to design column surfaces that are resistant to phase collapse.

In 2001, the second glossary of common and not-so-common terms and "buzz words" for reference to HPLC columns and column technology was published. It is time for an update since new terms have arisen or, in some cases, their original meanings have expanded or changed.

Reversed-phase liquid chromatography (LC) is a simple and easy-to-use technique that will give satisfactory separations for the samples that most of us encounter. Here, John Dolan examines the pros and cons of this technique.

This article describes the method development and performance characteristics of the validated LFI assay and evaluates stability in human plasma.

High performance liquid chromatography (HPLC) enhances throughput in countless processes, including environmental analysis, dissolution testing, separation of biomolecules, and total drug analysis. To take advantage of the benefits of HPLC technology, samples and solvents must be cleared of particulate contaminants. Doing so protects instrument components and minimizes maintenance costs. This article outlines HPLC technology, explains the importance of sample preparation, and reviews the factors that must be considered when preparing HPLC samples by membrane filtration. The data from experiments to test these factors show that the physicochemical characteristics of membrane filters can affect HPLC results.

This month's "LC Troubleshooting" installment examines the possible reasons your retention times could have changed. If the root cause can be identified and corrected, no adjustment in flow rate will be necessary.

This article describes the factors that affect the selection of columns for two-dimensional (2D) LCxLC separations.