Liquid Chromatography (LC/HPLC)

I do not believe in classic linear separations anymore—further, I think separations science is wildly underdeveloped and under-appreciated.

Reducing the column inner diameter results in a reduction in chromatographic dilution and increased sensitivity, allowing for more efficient tandem mass spectrometry sampling (MS/MS) and a higher number of molecule identifications.

Dispersion of analyte peaks outside of chromatography columns can seriously erode the resolution provided by good columns. Here, we focus on the contribution of the sample injection step to the total level of extracolumn dispersion in an LC system.

The effects of water on retention and selectivity in gas–solid chromatography of various adsorbent PLOT columns is reviewed.

Our annual review of new liquid chromatography columns and accessories, introduced at Pittcon and other events over the past 12 months.

This instalment focuses on basic concepts in extracolumn dispersion (ECD) that occurs in high performance liquid chromatography (HPLC) systems, and the impact of this dispersion on the performance of columns of different dimensions and efficiencies.

Over the 17 years since the original Hydrophobic Subtraction Model for HPLC selectivity was published, those who curate the model have collected a huge amount of data as new HPLC stationary phases have been added. Analysis of this new data on almost 600 stationary phases has allowed us to update or adjust several of the stationary phase–analyte interaction terms within the model as well as adding one entirely new term to better describe the dipolar interactions with more modern stationary phases such as the pentafluoro phenyl-type phases.

The talks in this session highlight developments in liquid chromatography (LC), including a computer-assisted modeling approach to simplify 2D-LC method development, the use of aligned continuous gradient stationary phases, the development of alkaline-stable packing materials based on calcium carbonate, and more.

This Friday morning session honors the 2021 LCGC award winners: Paul Haddad of the University of Tasmania, and the foundation director of the Australian Centre for Research on Separation Science (ACROSS); and Erik L. Regalado, of the pharmaceutical company Merck & Co.

A UHPLC–MS/MS method is described for rapid quantification of five major bioactive alkaloids in rat urine. The results obtained help lay the foundation for the clinical application and safety evaluation of the bioactive ingredients of menispermi rhizoma, used in herbal medicines.

Ron Majors was the 2020 recipient of the Chromatography Forum of the Delaware Valley (CFDV) Award, which is given to those who have provided exceptional service for the Forum in addition to outstanding contributions within the field of chromatography. Readers of LCGC are well aware of his nearly 60 years of research and leadership in this area (1), but few outside the Delaware Valley region know of his decades of membership on the CFDV Executive Committee, including two terms as president. As part of this well-deserved honor, Ron gave a (remote) address to the organization in October 2020, detailing his many accomplishments in the field and summarizing the current state-of-the-art in high performance liquid chromatography (HPLC) column technology (2). However, it was his introduction describing the early days of HPLC that stood out to me, specifically a name I had not heard before: Elmar Piel. For this month’s blog post, I invited Ron to join me in writing a bit more about this scientist who may be unfamiliar to many chromatographers.

A method is described using a triple quadrupole LC–MS instrument with isotopic dilution to obtain the highest accuracy and confidence for analysis of per- and polyfluoroalkyl substances (PFAS) in water. Excellent method spike recoveries and robustness were found in wastewater.

Presenting a novel chromatographic modelling method to establish QbD-compliant comparative testing of eluent design spaces.

We investigate a phenomenon observed by many practitioners of reversed- phase LC: a dramatic loss in retention volume or time after the column flow is stopped and resumed when using highly aqueous mobile phases with certain columns.

LC users that are new to charged aerosol detection (CAD) will find behaviours that are different from ultraviolet (UV) detectors. This article discusses some of the most important of these behaviours and provides tips to shorten the path to usable data.

A deeper theoretical understanding the relationship between peak area and flow rate will help analysts diagnose problems when using UV absorbance detection.

Many users have questions about how long LC columns should be re-equilibrated following solvent gradient elution separations. Here we show satisfactory results with short re-equilibration periods, for both reversed-phase and HILIC separations.

In this installment, tips, tricks, and suggestions are provided for best practices in reversed-phase separations, in both 1D and 2D LC, with gradient elution for minimum variations in retention time.

Carefully diluting a sample with weak solvent can mitigate the impact of sample solvent on peak shape in both reversed-phase and HILIC separations, but we need to understand how the choice of sample diluent can affect analyte recovery.

Re-equilibrating a reversed-phase stationary phase following aqueous gradient elution can be achieved much faster than you think.

Liquid Chromatography and High-Resolution Mass Spectrometry In food analysis, HPLC and triple-quadrupole mass spectrometry are established techniques. Jon Wong of the Center for Food Safety and Applied Nutrition at the U.S. Food and Drug Administration discusses why his agency and others have been developing food analysis methods using UHPLC and HRMS.

Dwight Stoll, who will take the reins of “LC Troubleshooting” next month, spoke with John Dolan to get some insight on the current state of chromatography with John Dolan to get some insight on the current state of chromatography training, future troubleshooting problems, John’s toughest troubleshooting challenge, and the most common chromatographic mistakes.

Monitoring lipid oxidation during the shelf life of lipid-containing food emulsions, such as mayonnaise, is challenging. It is, however, essential for the development of improved, consumer-preferred products. Determining the nonvolatile lipid oxidation products (NONVOLLOPS), the precursor compounds for rancidity, is required to determine the effectiveness of product stabilization technologies. A method based on normal-phase liquid chromatography with atmospheric pressure photo ionization-mass spectrometry (LC–APPI-MS) was developed for this purpose. The inclusion of a size-exclusion chromatography (SEC) step was needed to remove interfering diacylglycerides and free fatty acids from the samples. The combined SEC and normal-phase LC–APPI-MS method allowed the identification of a wide range of oxidized species including hydroperoxides, oxo-2½ glycerides, epoxides, and other oxidized species. The method was found to be more suitable for the analysis of large sample sets. The relative levels of NONVOLLOPS from bo

Topics that stood out at HPLC 2017 include advances in large-molecule separations, multidimensional chromatography, HILIC, and chiral separations.

When developing or modifying an LC separation, a common strategy is to change selectivity by choosing a new column. Here’s guidance for making that selection.

This is an exciting time for 2D-LC, as the expanding community of users works to develop creative solutions involving 2D-LC to solve analytical challenges that are very difficult or impossible to solve by conventional means.

Leading separation scientists share their perspectives on current challenges in separation science and where the field is heading.

You have to be careful when adjusting gradient conditions.

UHPLC’s benefits include fast analysis, high-resolution separations, reduced solvent and sample usage, enhanced sensitivity and precision, and more.

A surfactant based diluent was used in sample preparation for reversed phase HPLC analysis of a drug product and its impurities in a phospholipid formulation. The use of the didodecyl trimethylammonium bromide (DDAB) enabled a consistent, quantitative extraction of the analytes of interest from the lipid matrix in a much more aqueous, weak solvent. Water was added as an anti-solvent to precipitate out the surfactant from the system to eliminate HPLC injection pressure spikes, enabling large volume injections and achieving a consistent, robust method for long term use. Method development and validation steps are described.