Preparation of high-efficiency HILIC capillary columns utilizing slurry packing at 2100 bar

Complex mixture analysis requires high-efficiency chromatography columns. Although reversed phase liquid chromatography (RPLC) is the dominant approach for such mixtures, hydrophilic interaction liquid chromatography (HILIC) is an important complement to RPLC by enabling the separation of polar compounds. Chromatography theory predicts that small particles and long columns will yield high efficiency; however, little work has been done to prepare HILIC columns longer than 25 cm packed with sub-2 μm particles. In this work, we tested the slurry packing of 75 cm long HILIC columns with 1.7 μm bridged-ethyl-hybrid amide HILIC particles at 2,100 bar (30,000 PSI). Acetonitrile, methanol, acetone, and water were tested as slurry solvents, with acetonitrile providing the best columns. Slurry concentrations of 50-200 mg/mL were assessed, and while 50-150 mg/mL provided comparable results, the 150 mg/mL columns provided the shortest packing times (9 min). Columns prepared using 150 mg/mL slurries in acetonitrile yielded a reduced minimum plate height (hmin) of 3.3 and an efficiency of 120,000 theoretical plates for acenaphthene, an unretained solute. Para-toluenesulfonic acid produced the lowest hmin of 1.9 and the highest efficiency of 210,000 theoretical plates. These results identify conditions for producing high-efficiency HILIC columns with potential applications to complex mixture analysis.

Open tubular liquid chromatography: Recent advances and future trends

Nano-liquid chromatography (nanoLC) is gaining significant attention as a primary analytical technique across various scientific domains. Unlike conventional high-performance LC, nanoLC utilizes columns with inner diameters (i.ds.) usually ranging from 10 to 150 μm and operates at mobile phase flow rates between 10 and 1000 nl/min, offering improved chromatographic performance and detectability. Currently, most exploration of nanoLC has focused on particle-packed columns. Although open tubular LC (OTLC) can provide superior performance, optimized OTLC columns require very narrow i.ds. (< 10 μm) and demand challenging instrumentation. At the moment, these challenges have limited the success of OTLC. Nevertheless, remarkable progress has been made in developing and utilizing OTLC systems featuring narrow columns (< 2 μm). Additionally, significant efforts have been made to explore larger columns (10-75 μm i.d), demonstrating practical applicability in many situations. Due to their perceived advantages, interest in OTLC has resurged in the last two decades. This review provides an updated outlook on the latest developments in OTLC, focusing on instrumental challenges, achievements, and advancements in column technology. Moreover, it outlines selected applications that illustrate the potential of OTLC for performing targeted and untargeted studies.

Chromatographic separation of peptides and proteins for characterization of proteomes

Characterization of proteomes aims to comprehensively characterize proteins in cells or tissues via two main strategies: (1) bottom-up strategy based on the separation and identification of enzymatic peptides; (2) top-down strategy based on the separation and identification of intact proteins. However, it is challenged by the high complexity of proteomes. Consequently, the improvements in peptide and protein separation technologies for simplifying the sample should be critical. In this feature article, separation columns for peptide and protein separation were introduced, and peptide separation technologies for bottom-up proteomic analysis as well as protein separation technologies for top-down proteomic analysis were summarized. The achievement, recent development, limitation and future trends are discussed. Besides, the outlook on challenges and future directions of chromatographic separation in the field of proteomics was also presented.

Nano liquid chromatography, an updated review

Low flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for mass spectrometry have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow liquid chromatography , the types of columns employed, and strategies for multi-dimensionality of separations, which is key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend towards biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy to use platform.

Liquid Chromatographic Separation Using a 2 μm i.d. Open Tubular Column at Elevated Temperature

We have experimentally demonstrated the extraordinarily high resolving power of liquid chromatography (LC) using a narrow open tubular (OT) column. In this work, we show that we can further increase its efficiency, peak capacity, and separation speed by elevating the operation (or column) temperature; all of these three numbers can be improved without mutual compromises. We use a mixture of five amino acids as a sample and show that we can increase the efficiency by 34%-260% and the separation speeds by 7%-10% by raising the operation temperature from 30 to 70 °C. When we use a 2 μm i.d. × 80 cm in length OT column coated with OTMS at a temperature of 70 °C, we can frequently obtain peak capacities of 700-800 within 20-30 min for separating cytochrome C digests. By increasing the column length to 160 cm, we can obtain a peak capacity of 2720 within 143 min for separating a complex peptide sample. This peak capacity is the highest peak capacity to date for one-dimensional LC separations. Importantly, heating the column is easy to implement and does not cost much, and many commercial LC systems already have compartments to control column temperatures. Running LC using a narrow OT column at an elevated temperature should broaden the applications of OT-LC in chemical and biochemical analyses.

An overview of open tubular liquid chromatography with a focus on the coupling with mass spectrometry for the analysis of small molecules

Open tubular liquid chromatography (OT-LC) can provide superior chromatographic performance and more favorable mass spectrometry (MS) detection conditions. These features could provide enhanced sensitivity when coupled with electrospray ionization sources (ESI-) and lead to unprecedented detection capabilities if interfaced with a highly structural informative electron ionization (EI) source. In the past, the exploitation of OT columns in liquid chromatography evolved slowly. However, the recent instrumental developments in capillary/nanoLC-MS created new opportunities in developing and applying OT-LC-MS. Currently, the analytical advantages of OT-LC-MS are mainly exploited in the fields of proteomics and biosciences analysis. Nevertheless, under the right conditions, OT-LC-MS can also offer superior chromatographic performance and enhanced sensitivity in analyzing small molecules. This review will provide an overview of the latest developments in OT-LC-MS, focusing on the wide variety of employed separation mechanisms, innovative stationary phases, emerging column fabrication technologies, and new OT formats. In the same way, the OT-LC's opportunities and shortcomings coupled to both ESI and EI will be discussed, highlighting the complementary character of those two ionization modes to expand the LC's detection boundaries in the performance of targeted and untargeted studies.

Visual and real-time imaging focusing for highly sensitive laser-induced fluorescence detection at yoctomole levels in nanocapillaries

We developed a highly sensitive laser-induced fluorescence detection system, involving visual and real-time imaging focusing instead of the use of fluorescent reagents, for the detection of analytes in nanocapillaries.

High-Temperature Liquid Chromatography and the Hyphenation with Mass Spectrometry Using High-Pressure Electrospray Ionization

Increasing the operating temperature of the liquid chromatography (LC) column has the same effect as reducing the diameter of the packing particles on minimizing the contribution of C-term in the van Deemter equation, flattening the curve of plate height vs. linear velocity in the high-speed region, thus allowing a fast LC analysis without the loss of plate count. While the use of smaller particles requires a higher pumping pressure, operating the column at higher temperature reduces the pressure due to lower liquid viscosity. At present, the adoption of high-temperature LC lags behind the ultra-high-pressure LC. Nevertheless, the availability of thermally stable columns has steadily improved and new innovations in this area have continued to emerge. This paper gives a brief review and updates on the recent advances in high-temperature liquid chromatography (HTLC). Recent efforts of hyphenating the capillary HTLC with mass spectrometry via a super-atmospheric pressure electrospray ionization is also reported.

Recent advancements in open-tubular liquid chromatography and capillary electrochromatography during 2014-2018

This review critically discusses the developments on open-tubular liquid chromatography (OT-LC) and open-tubular capillary electrochromatography (OT-CEC) during 2014-2018. An appropriate Scopus search revealed 5 reviews, 4 theoretical papers on open-tubular format chromatography, 29 OT-LC articles, 68 OT-CEC articles and 4 OT-LC/OT-CEC articles, indicating a sustained interest in these areas. The open-tubular format typically uses a capillary column with inner walls that are coated with an ample layer or coating of solid stationary phase material. The ratio between the capillary internal diameter and coating thickness (CID/CT) is ideally ≤ 100 for appropriate chromatographic retention. We, therefore, approximated the CID/CT ratios and found that 22 OT-LC papers have CID/CT ratios ≤100. The other 7 OT-LC papers have CID/CT ratio >100 but have clearly demonstrated chromatographic retention. These 29 papers utilised reversed phase or ion exchange mechanisms using known or innovative solid stationary phase materials (e.g. metal organic frameworks), stationary pseudophases from ionic surfactants or porous supports. On the other hand, we found that 68 OT-CEC papers, 7 OT-LC papers and 4 OT-LC & OT-CEC papers have CID/CT ratios >100. Notably, 44 papers (42 OT-CEC and 2 OT-LC & OT-CEC) did not report the retention factor and/or effective electrophoretic mobility of analytes. Considering all covered papers, the most popular activity was on the development of new chromatographic materials as coatings. However, we encourage OT-CEC researchers to not only characterise changes in the electroosmotic flow but also verify the interaction of the analytes with the coating. In addition, the articles reported were largely driven by stationary phase or support development and not by practical applications.

Experimentally Validating Open Tubular Liquid Chromatography for a Peak Capacity of 2000 in 3 h

The advancements in life science research mandate effective tools capable of analyzing large numbers of samples with low quantities and high complexities. As an essential analytical tool for this research, liquid chromatography (LC) encounters an ever-increasing demand for enhanced resolving power, accelerated analysis speed, and reduced limit of detection. Although theoretical studies have indicated that open tubular (OT) columns can produce superior resolving power under comparable elution pressures and analysis times, ultrahigh-resolution and ultrahigh-speed open tubular liquid chromatography (OTLC) separations have never been reported. Here we present experimental results to demonstrate the predicted potential of this technique. We use a 2 μm i.d. × 75 cm long OT column coated with trimethoxy(octadecyl)silane for separating pepsin/trypsin digested E. coli lysates and routinely produce exceptionally high peak capacities (e.g., 1900-2000 in 3-5 h). We reduce the column length to 2.7 cm and exhibit the capability of OTLC for ultrafast separations. Under an elution pressure of 227.5 bar, we complete the separation of six amino acids in ∼800 ms and resolve these compounds within ∼400 ms. In addition, we show that OTLC has low attomole limits of detection (LOD) and each separation requires samples of only a few picoliters. Importantly, no ultrahigh elution pressures are required. With the ultrahigh resolution, ultrahigh speed, low LOD, and low sample volume requirement, OTLC can potentially be a powerful tool for biotech research, especially single cell analysis.

Recent advances in open tubular capillary liquid chromatography

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007–2018.

Nano liquid chromatography columns

Nano liquid chromatography (nanoLC), with columns having an inner diameter (ID) of ≤100 μm, can provide enhanced sensitivity and enable analysis of limited samples.