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There are as many measurement values of the true column hold-up volume, V0, as techniques applied to evaluate this most important property in liquid chromatography (LC). The relative errors made on V0 measurements using conventional “non-retained” markers—such as acetone, uracil, or thiourea in reversed-phase liquid chromatography (RPLC), or benzene or acenaphthene in hydrophilic interaction chromatography (HILIC)—can be as large as ±30%. This situation is extremely confusing for LC users who wish to classify and predict the retention behavior of LC columns. In this work, along with advances in mass spectrometry (MS) instrumentation, the hold-up volume of any LC column—including, but not limited to, RPLC, HILIC, ion exchange chromatography (IEX), and mixed-mode columns—is accurately measured by injecting labeled deuterated acetonitrile (CD3CN) molecules and detecting them selectively by MS-single ion reaction (m/z = 45) using non-labeled and pure acetonitrile (CH3CN) as the eluent. This proposed harmonization of all conventional V0 measurement methods is illustrated and successfully applied to RPLC, HILIC, anion exchange (AEX), and RP-AEX mixed-mode chromatography, irrespective of the mobile phase composition selected. [ABSTRACT FROM AUTHOR]

An ultrahigh-pressure liquid chromatography-mass spectrometry (UHPLC-MS) research prototype instrument was built to improve the resolution power and the usability of conventional LC-MS hyphenated instruments for routine analyses in pharmaceutical applications. The improved characteristics of this UHPLC-MS system include: 1) the dramatic reduction of post-column sample dispersion; 2) the adoption of vacuum jacketed columns (VJC) for the reduction of undesirable radial temperature gradients across the column diameter; and 3) the presence of a column outlet end nut heater to refocus the distorted peaks prior to analyte ionization. The benefits of each of these added features are analyzed with a rigorous approach from a peak broadening perspective. A 2x improvement in peak capacities recorded with this prototype UHPLC-MS system compared to a standard system (Acquity UHPLC I-class/Xevo TQ-S) is illustrated for the gradient separation of seven small pharmaceutical compounds using a 2.1 mm x 100 mm column packed with sub-2-μm core-shell particles (1.6 μm Acquity UHPLC Cortecs C18 column). [ABSTRACT FROM AUTHOR]

The phenomenon of retention loss observed for reversed-phase liquid chromatography (LC) columns used with near 100% aqueous mobile phases when stopping and resuming the flow has often wrongly been attributed to phase collapse of the bonded alkyl chains onto the silica surface. However, this phenomenon is now explained as a process of pore dewetting with the expulsion of water from the hydrophobic pore network. The driving force for this process is the instability of the water liquid/vapor biphasic system when water is confined in hydrophobic mesopores with diameters <50 nm. Water is forced to leave the mesopore space in porous reversed-phase LC materials by the pressure difference between the vapor and liquid phases (also known as Laplace pressure). While the pore-dewetting phenomenon can occur with mobile phases containing <100% water, all experiments shown in this paper utilized a 100% aqueous mobile phase with flow rate interruptions as a worst-case scenario. We have accurately measured the effect on the kinetics of pore dewetting of various experimental variables, such as water pressure, temperature, the amount of dissolved gases in water, average pore size, the nature of the surface chemistry, and the surface coverage of the hydrophobic bonded groups. From these data, it is demonstrated why outlet column pressures kept above 50 bar, the use of degassed mobile phases, large mesopores (>20 nm), wide pore size distribution, the low surface coverage of the hydrophobic ligand (<2 µmol/m2), phenyl-bonded or charged surface alkyl-bonded stationary phases, and enhanced molecular disorder of the tip of the bonded phase would minimize (or eliminate) the retention loss phenomenon with fully aqueous mobile phases after flow rate interruptions. [ABSTRACT FROM AUTHOR]

The article demonstrates how a user-friendly vacuum-jacketed column (VJC) has been designed without the need of a large internal diameter vacuum chamber and low and high-vacuum pumps. It discusses the how to improve the coupling between the eluent preheater, chromatographic column and the electrospray ionization probe for mass spectrometry (MS) detection. It mentions the column efficiency under extreme viscous heating conditions.

Thermal effects occurring in ultrahigh-pressure liquid chromatography (UHPLC) and low-density supercritical fluid chromatography (SFC) have a negative impact on chromatographic performance, because peaks broaden and get distorted. A solution to this problem is to thermally insulate the chromatographic column. A strict adiabatic environment can be achieved by embedding the whole chromatographic column in a large vacuum chamber, itself connected to a turbomolecular pump that delivers a high vacuum. From a practical viewpoint, this prototype research apparatus is costly, its assembly is time-consuming, and it is complex. Consequently, it is not adapted to routine analyses in standard analytical laboratories. Therefore, a new approach, using vacuum-jacketed column technology, has been developed to cope with these practical limitations. The applications and advantages of this new technology relative to standard columns are presented and discussed for both UHPLC and SFC separations operated under extreme conditions. [ABSTRACT FROM AUTHOR]

The article highlights science behind packing high-efficiency columns and capillaries. Topics discussed include colloidal properties of particle suspensions; study of the relationship between the rheological behavior of packed beds and the final bed structure; and packing of highly efficient analytical and capillary columns with fully porous particles (FPPs) and superficially porous particles (SPPs).

Separating and quantifying both volatile and nonvolatile compounds in complex mixtures is a costly and time-consuming process presenting significant technical challenges. Fabrice Gritti from the Instrument, Core Research, Fundamental Group at Waters Corporation discusses his team's unique solution to this problem, combining high-vacuum technology and low-density fluid chromatography (LDFC) with carbon dioxide as a mobile phase for a rapid and complete baseline separation of both volatile and nonvolatile compounds on a single instrument, single column, and a single run without the associated loss of resolution. [ABSTRACT FROM AUTHOR]

An interview is presented with University of Tennessee Knoxville Distinguished Scientist Georges Guiochon. Topics discussed include how did he enter the field of analytical chemistry, his contributions to both the fundamental and practical aspects of gas chromatography and what inspired him to go to the U.S. to conduct a research program in preparative liquid chromatography.

This article reports on the physical phenomena that control column efficiency and on experimental protocols designed to accurately measure their contributions to band broadening of analytes during their passage from the injection to the detection device. The results of these protocols are analyzed, allowing for the accurate determination of the complete mass transfer mechanism in different separation modes and providing solutions and future directions to further improve the efficiency of liquid chromatography columns. [ABSTRACT FROM AUTHOR]

The article discusses physical phenomenon which control efficiency of liquid chromatography columns and accurately measure potential sources of band broadening of analytes during their passage from the injection to the detection device. It also discusses ways to determination the complete mass transfer mechanism in various separation modes and provides solutions and future directions for enhancing efficiency of liquid chromatography columns.

The article offers information on columns packed with Sub-3-um core-shell particles. It notes that pellicular particles are invented by Csaba Horváth to prepare columns offering efficient high performance liquid chromatography (HPLC) separations of high-molecular-weight compounds of biological origin. It says that pellicular particles met with stiff competition from packing materials made with fully porous particles.

The article offers information on the International Symposium on Capillary Chromatography (ISCC) and 16th GCxGC Symposium were held in Fort Worth, Texas from May 12-17, 2019 entitled "State-of-the-Art in Capillary Liquid Chromatography". It mentions that implementation of high particle slurry concentrations, high pressures, and sonication during the packing process to obtain efficient capillary columns.

The article focuses on a study conducted by researcher Fabrice Gritti and colleague to determine the evolution of the column efficiency in liquid chromatography, which appeared in a 2013 issue of the journal "Analytical Chemistry." The study compares the measurement of real eddy dispersion data with predictions of models of axial dispersion of Gunn and Giddings. The study concludes that the wall effects control the column plate height of high performance liquid chromatography columns.