Liquid Chromatography (LC/HPLC)

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.

Ronald E. Majors presided over "HPLC: Optimization and Chemistry," an oral session held Tuesday afternoon that focused on the optimization of analytical- and preparative-scale LC separations.

Life sciences applications are a major driving force for the HPLC and the LC-MS market. Liquid chromatography is commonly used in biotechnology.

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.

Separation and retention of both polar and nonpolar compounds by the same stationary phase can be a useful approach for analyses of complex samples with a broad range of chemical properties. Typical stationary phases are designed for retention of either polar or nonpolar compounds so that multiple steps are required when designing a separation strategy. Hydride silica–based stationary phases are new materials with properties that allow for the simultaneous retention of both polar and nonpolar compounds over a range of aqueous–organic mobile phase compositions. Adjustment of the aqueous–organic ratio will determine whether polar or nonpolar compounds have greater retention.

Part 2 of the column explores using the right balance for the right job in the right way.

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.

It would help to have a restricted set of chromatographic systems (CS) that together serve as potential starting points in method development.

Check valves are the number one problem area for most LC pumps.

Purification of synthetic, natural and biological compounds in any quantity usually requires the use of preparative HPLC.

A more practical parameter for system suitability would be to use the peak width for a reference peak...

LCGC North America and its companion publication, LCGC Europe, are targeted for chromatographers in the United States and Europe, respectively. Sometimes I wonder whether or not the same types of problems are encountered by workers in liquid chromatography (LC) on both sides of the Atlantic. As I write this installment of "LC Troubleshooting," I have just completed three weeks of teaching LC short courses in Europe. I can assure you that the content of the questions I get in these classes is the same, no matter where they are taught. This column is based upon questions gleaned from the most recent courses - you can see that there are no national borders for LC problems.

The minimum peak size for reportable results for a liquid chromatographic (LC) method depends upon the application and the signal-to-noise ratio (S/N).

Higher productivity and faster analyses are two of the driving forces for continued improvement in high performance liquid chromatography (HPLC) column technology.

No column lasts forever, but in this month's installment of "LC Troubleshooting," John Dolan offers some tricks to help extend a column's life.

Once the visual problems have been eliminated as problem sources, you are left with problems related to system performance.

Because of progress in liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) instrumentation, data processing and reporting, the measurement of compounds' accurate masses is becoming routine practice in screening analysis based on target databases. As such databases of monoisotopic masses can be easily updated with recent data from the literature; rapid characterization of new compounds and metabolites is possible without the need for primary reference standards. This approach has already been established in comprehensive toxicological urine screening and in analysis of drugs-of-abuse in seized street drug samples. Currently, a mass accuracy within 5 ppm can be routinely achieved, and confirmation via a numerical isotopic pattern match (SigmaFit) is provided by a new generation LC/TOF-MS instrument.