Impact of instrument and column parameters on high-throughput liquid chromatography performance

A singular chromatographic column breakthrough: Achieving full polarity range separations with the epoxy propanol molecular cage bonded silica stationary phase

The epoxy propanol molecular cage bonded silica stationary phase, RCC3-GLD@silica, synthesized through the ring-opening reaction of secondary amine with epoxy propanol using RCC3-R as the scaffold unit, was successfully prepared as confirmed by infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption-desorption characterization. This stationary phase demonstrated excellent separation performance in both reversed-phase and hydrophilic chromatography modes, effectively separating a wide variety of compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, phenols, anilines, sulfonamides, nucleosides, amino acids, sugars, and acids. The development of RCC3-GLD@silica benefits from the synergistic effects of its hydrophobic and hydrophilic actions, as evidenced by the U-shaped characteristic of the retention factor for nucleoside compounds with changes in the aqueous content of the mobile phase, further confirming the simultaneous presence of reversed-phase and hydrophilic chromatography mechanisms. Not only did this stationary phase successfully separate 33 compounds in reversed-phase chromatography mode, but it also separated 54 compounds in hydrophilic interaction chromatography mode, showcasing its broad separation capability from weakly polar to strongly polar compounds on a single chromatographic column. This indicates a wide application prospect in the field of chromatographic analysis.

The use of predictive models to develop chromatography-based purification processes

Chromatography is the workhorse of biopharmaceutical downstream processing because it can selectively enrich a target product while removing impurities from complex feed streams. This is achieved by exploiting differences in molecular properties, such as size, charge and hydrophobicity (alone or in different combinations). Accordingly, many parameters must be tested during process development in order to maximize product purity and recovery, including resin and ligand types, conductivity, pH, gradient profiles, and the sequence of separation operations. The number of possible experimental conditions quickly becomes unmanageable. Although the range of suitable conditions can be narrowed based on experience, the time and cost of the work remain high even when using high-throughput laboratory automation. In contrast, chromatography modeling using inexpensive, parallelized computer hardware can provide expert knowledge, predicting conditions that achieve high purity and efficient recovery. The prediction of suitable conditions in silico reduces the number of empirical tests required and provides in-depth process understanding, which is recommended by regulatory authorities. In this article, we discuss the benefits and specific challenges of chromatography modeling. We describe the experimental characterization of chromatography devices and settings prior to modeling, such as the determination of column porosity. We also consider the challenges that must be overcome when models are set up and calibrated, including the cross-validation and verification of data-driven and hybrid (combined data-driven and mechanistic) models. This review will therefore support researchers intending to establish a chromatography modeling workflow in their laboratory.

Retention prediction of monoamine neurotransmitters in gradient liquid chromatography

Retention prediction of monoamine neurotransmitters has been compared for the generally applied linear solvent-strength model and quadratic polynomial three-parameter model. The design of experiments protocol has been applied to plan linear gradients within the experimental space with altered gradient time, mobile phase flowrate, and column temperature. Relative prediction errors increased at elevated temperature, which is more significant for the linear solvent-strength model when compared to the polynomial model. On the other hand, the predefined design of experiments space controls the retention time errors, as predictions for LC conditions that are outside of the plan are much less accurate and should be avoided. The final part of the work deals with the effect of extracolumn band dispersion on the peak capacity of linear gradients at various gradient times, mobile phase flowrates, and column temperature. The peak capacity determined for corrected experimental data were consistent with the published results dealing with the optimization of peak capacity in gradient elution. This article is protected by copyright. All rights reserved.

An approach to high throughput measurement of accurate retention data in liquid chromatography

Efforts to model and simulate various aspects of liquid chromatography (LC) separations (e.g., retention, selectivity, peak capacity, injection breakthrough) depend on experimental retention measurements to use as the basis for the models and simulations. Often these modeling and simulation efforts are limited by datasets that are too small because of the cost (time and money) associated with making the measurements. Other groups have demonstrated improvements in throughput of LC separations by focusing on "overhead" associated with the instrument itself - for example, between-analysis software processing time, and autosampler motions. In this paper we explore the possibility of using columns with small volumes (i.e., 5 mm x 2.1 mm i.d.) compared to conventional columns (e.g., 100 mm x 2.1 mm i.d.) that are typically used for retention measurements. We find that isocratic retention factors calculated for columns with these dimensions are different by about 20%; we attribute this difference - which we interpret as an error in measurements based on data from the 5 mm column - to extra-column volume associated with inlet and outlet frits. Since retention factor is a thermodynamic property of the mobile/stationary phase system under study, it should be independent of the dimensions of the column that is used for the measurement. We propose using ratios of retention factors (i.e., selectivities) to translate retention measurements between columns of different dimensions, so that measurements made using small columns can be used to make predictions for separations that involve conventional columns. We find that this approach reduces the difference in retention factors (5 mm compared to 100 mm columns) from an average of 18% to an average absolute difference of 1.7% (all errors less than 8%). This approach will significantly increase the rate at which high quality retention data can be collected to thousands of measurements per instrument per day, which in turn will likely have a profound impact on the quality of models and simulations that can be developed for many aspects of LC separations.

Review of HPLC-MS methods for the analysis of nicotine and its active metabolite cotinine in various biological matrices

In recent years, tobacco smoking is a risk factor for a series of diseases including cardiovascular diseases, cerebrovascular diseases, and cancers. Nicotine, the primary component of tobacco smoke, is mainly transformed to its active metabolite cotinine, which is often used as biomarker for tobacco exposure for its higher blood concentration and longer residence time than nicotine. Various analytical methods have been developed for the determination of nicotine and cotinine in biological matrices. This article reviewed the HPLC-MS based methods for nicotine and/or cotinine analysis in various biological matrices. The sample preparation, mass and chromatographic conditions and method validation results of these methods have been summarized and analyzed. Sample was mainly pretreated by protein precipitation and/or extraction. Separation was achieved using methanol and/or acetonitrile:water (with or without ammonium acetate) on C18 columns, and acetonitrile:water (with formic acid, ammonium acetate/formate) on HILIC columns. Nicotine-d3, nicotine-d4 and cotinine-d3 were commonly used internal standards. Other non-deuterated IS were also used such as ritonavir, N-ethylnorcotinine, and milrinone. For both nicotine and cotinine, the calibration range was 0.005-35000 ng/mL, the matrix effect was 75.96% - 126.8% and the recovery was 53% - 124.5%. The two analytes were stable at room temperature for 1-10 days, at -80 °C for up to 6 months, and after 3-6 freeze-thaw cycles. Comedications did not affect nicotine and cotinine analysis.

Mass spectrometry based high-throughput bioanalysis of low molecular weight compounds: are we ready to support personalized medicine?

Liquid chromatography coupled to mass spectrometry (LC-MS) is the gold standard in bioanalysis for the development of quantitative assays to support drug development or therapeutic drug monitoring. High-throughput and low-cost gene sequencing have enabled a paradigm shift from one treatment fits all to personalized medicine (PM). However, gene monitoring provides only partial information about the health state. The full picture requires the combination of gene monitoring with the screening of exogenous compounds, metabolites, lipids, and proteins. This critical review discusses how mass spectrometry–based technologies and approaches including separation sciences, ambient ionization, and ion mobility are/could be used to support high-throughput bioanalysis of endogenous end exogenous low molecular weight compounds. It includes also various biological sample types (from blood to expired air), and various sample preparation techniques.

Implications of dispersion in connecting capillaries for separation systems involving post-column flow splitting

It is common practice in liquid chromatography to split the flow of the effluent exiting the analytical column into two or more parts, either to enable parallel detection (e.g., coupling the separation to two destructive detectors such as light scattering and mass spectrometry (MS)), or to accommodate flow rate limitations of a detector (e.g., electrospray ionization mass spectrometry). In these instances the user must make choices about split ratio and dimensions of connecting tubing that is used between the split point and the detector, however these details are frequently not mentioned in the literature, and rarely justified. In our own work we often split the effluent following the second dimension (²D) column in two-dimensional liquid chromatography systems coupled to MS detection, and we have frequently observed post ²D column peak broadening that is larger than we would expect to result from dispersion in the MS ionization source itself. For the present paper we describe a series of experiments aimed at understanding the impact of the split ratio and post-split connecting tubing dimensions on dispersion of peaks exiting an analytical column. We start with the simple idea - based on the principle of conservation of mass - that analyte peaks entering the split point are split into two parts such that the analyte mass (and thus peak volume) entering and exiting the split point is conserved, and directly related to the ratio of flow rates entering and exiting the split point. Measurements of peak width and variance after the split point show that this simple view of the splitting process - along with estimates of additional dispersion in the post-split tubing - is sufficient to predict peak variances at the detector with accuracy that is sufficient to guide experimental work (median error of about 10% over a wide range of conditions). We feel it is most impactful to recognize that flow splitting impacts apparent post-column dispersion not because anything unexpected happens in the splitting process, but because the split dramatically reduces the volume of the analyte peak, which then is more susceptible to dispersion in connecting tubing that would not cause significant dispersion under conditions where splitting is not implemented. These results will provide practitioners with a solid basis on which rational decisions about split ratios and dimensions of post-split tubing can be made.

The theory and practice of ultrafast liquid chromatography: A tutorial

Modern high-throughput experimentation and challenging analytical problems of academic/industrial research have put the responsibility on separation scientists to develop new fast separation approaches. With the availability of high-pressure pumps, small particles with hydrolytically stable surface chemistries, reduced extra-column band broadening, and low volume detectors with fast signal processing, it is now feasible to do sub-minute to sub-second chromatography. Herein, the fundamental theoretical principles of ultrafast chromatography, along with practical solutions, are reviewed. Approaches for rapid separations in packed beds, narrow open tubular columns, and monoliths are demonstrated, along with the challenges that were faced. The instrumentation requirements (pumps, injection systems, detectors, column packing process) for using short columns ranging from 0.5 to 5 cm are examined, followed by real applications. One of the main problems in ultrafast chromatography is partial or complete peak overlap. As per Gidding's statistical overlap theory, peak overlap cannot be avoided for a completely random sample for a column with a given peak capacity. Signal processing techniques based on Fourier transform deconvolution of band broadening, power laws, derivatives, and iterative curve fitting are explained to help improve the chromatographic resolution. An example of ten peaks separated in under a second is shown and discussed. Other ultrafast separations in supercritical fluid chromatography or capillary electrophoresis are briefly mentioned to provide a complete understanding of this emerging field.

Strategies in developing high-throughput liquid chromatography protocols for method qualification of pharmacopeial monographs

Method qualification is a key step in the development of routine analytical monitoring of pharmaceutical products. However, when relying on published monographs that describe longer method times based on older high-performance liquid chromatography column and instrument technology, this can delay the overall analysis process for generated drug products. In this study, high-throughput ultrahigh pressure liquid chromatography techniques were implemented to decrease the amount of time needed to complete a 24-run sequence to identify linearity, recovery, and repeatability for both drug assay and impurity analysis in 16 min. Multiple experimental parameters were tested to identify a range of experimental settings that could be used for the sequence while still maintaining this fast analysis time. The full sequence was replicated on a different system and with different columns, further demonstrating its robustness.