Perspectives on recent advances in the speed of high-performance liquid chromatography

Optimization of hydrolysis conditions of alginate based on high performance liquid chromatography

Alginate is the most abundant polysaccharide compound in brown algae, which is widely used in various fields. At present, the determination of the content of alginate is mostly carried out using sulfuric acid and trifluoroacetic acid hydrolysis followed by the determination of the content, but the results are not satisfactory, and there are problems such as low hydrolysis degree and low recovery rate. Therefore, in this study, based on the optimization of high performance liquid chromatographic conditions for pre-column derivatization of 1-phenyl-3-methyl-5-pyrazolone (PMP), the hydrolysis effects of sulfuric acid, trifluoroacetic acid (TFA), oxalic acid, and formic acid were compared and the hydrolysis conditions were optimized. The results showed that formic acid was the best hydrolyzing acid. The optimal hydrolysis conditions were 95 % formic acid at 110 °C for 10 h. The hydrolysis effect was stable, with high recovery and low destruction of monosaccharides, which made it possible to introduce formic acid into the subsequent polysaccharide hydrolysis. The pre-column derivatization high performance liquid chromatography method established in this study was accurate and reliable, and the hydrolysis acid with better effect was screened, which provided a theoretical basis for the subsequent determination of alginate content.

A review of analytical parameters in 'rapid' liquid chromatographic methods for bioanalysis: Can we do better?

Rapid bioanalysis is beneficial to many applications. However, how 'rapid' a method is, or could be, is often an unanswered question. In this statistical review, the authors have assessed multiple pre-analytical (i.e. sample preparation), and analytical method parameters specifically for liquid chromatography to assist researchers in developing and validating 'rapid' bioanalytical methods. We restricted the search to urine and plasma matrices only. Data were extracted from over 2,000 recent studies and evaluated to assess how these parameters affected the 'on-instrument' analysis time. In addition to methods using ultra-violet (UV) detection, there were a large number of mass spectrometric (MS) methods, allowing additional review of the differences between high- and low-resolution MS on analysis time. We observed that most (N = 922, 70 %) methods used 5 or 10 cm columns, and that whilst uptake of ultra-high performance (U)HPLC columns was good, the use of sub-5 cm columns and/or flow rates in excess of 1 mL/min was incredibly rare (N = 25, 3 %). The detector of choice for quantitative (U)HPLC-MS remains the triple quadrupole, although a number of groups report the use of high-resolution MS for such methods.

On-Chip Comparison of the Performance of First- and Second-Generation Micropillar Array Columns

Because of its dimensions, the recently introduced micropillar array columns are most suited for high-efficiency liquid chromatography separations in proteomics. Unlike the packed bed columns and capillary-based column formats, the micropillar array concept still has significant room to progress in terms of the reduction of its characteristic size (i.e., pillar diameter and interpillar distance) to open the road to even higher-efficiency separations and their applications. We report here on the on-chip comparison between first-generation (Gen 1) and second-generation (Gen 2) micropillar array columns wherein the pillar and interpillar size have been halved. Because of the on-chip measurements, the observed plate heights H represent the fundamental band broadening, devoid of any extra-column band-broadening effects. The observed reduction of H with a factor of 2 around the uopt-velocity and with a factor of 4 in the C-term dominated regime of the van Deemter-curve is in full agreement with the theoretically expected gain. This shows the pillar and interpillar size reduction could be effectuated without affecting the theoretical separation potential of the micropillar arrays. Compared to Gen 1, Gen 2 offers a 4-fold reduction of the required analysis time around the optimal velocity and about a 16-fold reduction in the C-term-dominated range.

Self-Generation of Distinguishable Fluorescent Probes via a One-Pot Process for Multiple MicroRNA Detection by Liquid Chromatography

To address the challenge of signal production and separation for multiple microRNA (miRNA) detection, in this work, a "one-pot" process to self-generate distinguishable fluorescent probes was developed. Based on a long and short probe amplification strategy, the generated G-quadruplex fluorescent dye-free probes can be separated and detected by a high-performance liquid chromatography-fluorescence platform. The free hairpin probes enriched in guanine with different lengths and base sequences were designed and could be opened by the target miRNAs (miRNA-10b, miRNA-21, and miRNA-210). Cleaved G-quadruplex probes with fluorescent signal could be generated in a one-pot process after a duplex-specific nuclease-based cleavage, and the detection of multiple miRNAs could be realized in one run. No solid nanomaterials were applied in the assay, which avoided the blocking of the column. Moreover, without modification of expensive fluorescein, the experimental cost was greatly reduced. The one-pot reaction process also eliminated tedious preparation steps and suggested feasibility of automation. The limits of detection of miRNA-10b, miRNA-21, and miRNA-210 were 2.19, 2.20, and 2.75 fM, respectively. Notably, this method was successfully applied to multiplex detection of miRNAs in serum samples from breast cancer patients within 30 min.

Simultaneous Extraction and Determination of Characteristic Steroidal Saponins and Homoisoflavonoids in Zhejiang Ophiopogon japonicus

Zhejiang Ophiopogonjaponicus (ZOJ) is a specific variety of Ophiopogon japonicus with characteristic steroidal saponins and homoisoflavonoids, which are also main pharmacodynamic constituents with clinical effects, including curing inflammation and cardiovascular diseases. However, few analysis methods were applied to simultaneously and quantitatively determine two kinds of its constituents, and hazardous organic solvents are mostly used for extraction. In this study, a new validated simultaneous extraction and determination method for four characteristic steroidal saponins and homoisoflavonoids in ZOJ was established by ionic liquid–ultrasonic extraction (IL-UAE) combined with HPLC-DAD-ELSD analysis, which can be used for the quality control of ZOJ. Chromatographic separation was performed with a DAD wavelength at 296 nm, and the ELSD parameters of the drift tube temperature (DTT), atomizer temperature (AT), and nitrogen gas pressure (NGP) were set at 20% heating power, 70 °C, and 25 psi, respectively. The optimal IL-UAE conditions were 1 mol/L [Bmim]CF₃SO₃ aqueous solution, a liquid–material ratio of 40 mL/g, and an ultrasonic time of 60 min. The proposed method is reliable, reproducible, and accurate, which were verified with real sample assays. Consequently, this work will be helpful for the quality control of ZOJ. It can also present a promising reference for the simultaneous extraction and determination of different kinds of constituents in other medicinal plants.

Emerging Applications of Metabolomics to Assess the Efficacy of Traditional Chinese Medicines for Treating Type 2 Diabetes Mellitus

Diabetes is a common and complex disease that can exacerbate the complications related to cardiovascular disease, and this is especially true for type 2 diabetes mellitus (T2DM). In addition to the standard pharmacological therapies, T2DM has also been treated with nonconventional regimens such as traditional Chinese medicine (TCM), e.g., herbal medicines and TCM prescriptions, although the mechanisms underlying the therapeutic benefits remain unclear. In this regard, many studies have used metabolomics technology to elucidate the basis for the efficacy of TCM for T2DM. Metabolomics has recently attracted much attention with regard to drug discovery and pharmacologically relevant natural products. In this review, we summarize the application of metabolomics to the assessment of TCM efficacy for treating T2DM. Increasing evidence suggests that the metabolic profile of an individual patient may reflect a specific type of T2DM syndrome, which may provide a new perspective for disease diagnosis. In addition, TCM has proved effective for countering the metabolic disorders related to T2DM, and this may constitute the basis for TCM efficacy. Therefore, further determining how TCM contributes to the reversal of metabolic disorders, such as using network pharmacology or by assessing the contribution of host–gut microbiota interactions, will also provide researchers with new potential targets for pharmacologic-based therapies.

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a "one-pot" strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.

Versatile quantitative biopsy: an approach for cost-effective detection of hydrogen peroxide in tissue specimens

In the presence of H₂O₂, the amylose released by the micelles is converted into glucose by glucoamylase and detected by a PGM.

A Plug-and-Play High-Pressure ESI Source with an Emitter at Ground Potential and Its Application to High-Temperature Capillary LC-MS

A new high-pressure ESI source that can be readily used for commercial API mass spectrometers in a plug-and-play manner without any modification on the ion sampling interface is introduced. The emitter can be operated at ground potential, and the positive mode electrospray is generated by applying a negative high potential to the counter electrode. A shielding electrode effectively shields the opposing electric field and improves the ion transmission. This feature facilitates the direct connection of the ESI emitter to the electrically grounded components. The application of the present ion source to the high-temperature (>100 °C) capillary liquid chromatography for high-speed separation of peptide and proteins is demonstrated using a monolithic polymeric column.

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.

A pH-stable, crosslinked stationary phase based on the thiol-yne reaction

Stationary phases that can withstand extremes of pH and temperature are needed to allow a single column to accommodate a wider set of solutes and separation criteria. We used a simple multi-step process using the thiol-yne reaction following the modification of the silica surface with a thiol-containing silane. The monomers 1,4-diethynylbenzene (DEB) and 1,6-hexanedithiol were used to create a crosslinked thiol-yne (CTY) stationary phase along the surface of the thiol functionalized silica. In the Tanaka test characterization, the CTY phase showed a low phase ratio, methylene selectivity typical of a reversed phase, and extremely high shape selectivity compared to commercial reversed phases. The hydrophobic subtraction model characterization showed a high positive steric resistance, a low hydrogen bond acidity, and a high cation-exchange capacity compared to most reversed phases. At pH 0.5 with an 85% aqueous mobile phase the phase showed no significant change over 114 h. With a 50% aqueous mobile phase the phase took four more days than a sterically protected C18 phase for the k' to decline 25%. At pH 12.6, 50% aqueous mobile phase, a sterically protected C18 phase showed a 20% decrease in k' and more than a 60% decrease in theoretical plates per meter in three hours. The CTY phase actually showed modest increases in k' and theoretical plates per meter after three hours.

On the Enantioselective HPLC Separation Ability of Sub-2 µm Columns: Chiralpak® IG-U and ID-U

Silica with a particle size of 3-5 µm has been widely used as selector backbone material in 10-25 cm HPLC chiral columns. Yet, with the availability of 1.6 µm particles, shorter, high-efficiency columns practical for minute chiral separations are possible to fabricate. Herein, we investigate the use of two recently commercialized sub-2 µm columns with different substituents. Thus, Chiralpak® IG-U and ID-U were used in HPLC for the fast enantioseparation of a set of drugs. Chiralpak® IG-U [amylose tris (3-chloro-5-methylphenylcarbamate)] has two substituents on the phenyl ring, namely, a withdrawing chlorine group in the third position and a donating group in the fifth position. Chiralpak® ID-U [amylose tris (3-chlorophenylcarbamate)] has only one substituent on the phenyl ring, namely a withdrawing chlorine group. Their applications in three liquid chromatography modes, namely, normal phase, polar organic mode, and reversed phase, were demonstrated. Both columns have similar column parameters (50 mm length, 3 mm internal diameter, and 1.6 µm particle size) with the chiral stationary phase as the only variable. Improved chromatographic enantioresolution was obtained with Chiralpak® ID-U. Amino acids partially separated were reported for the first time under an amylose-based sub-2-micron column.

Detailed efficiency analysis of columns with a different packing quality and confirmation via total pore blocking

We report on a systematic study involving columns with a clearly different efficiency (4 distinct quality groups) obtained by packing the columns that were C₁₈ bonded and endcapped with a different carbon loading. Using B-term analysis (via peak parking) and theoretical models to estimate the magnitude of the C_m- and C_s-term contributions, it could be concluded that the difference in efficiency among the groups was entirely due to a difference in eddy dispersion. As such, the columns provided an ideal testing ground to verify how well the total pore blocking (TPB)-method can be used to probe differences in packing heterogeneity. In agreement with earlier literature observations, it turns out the TPB-method is much more sensitive to packing heterogeneities than the eddy dispersion (H_eddy)-contribution measured under open-pore conditions via B- and C- term subtraction. Typically, differences in H_eddy on the order of 0.1-0.5μm translate into a difference on the order of 0.5-2μm in the TPB mode. This confirms the TPB as a powerful technique to make very sensitive measurements of the homogeneity of packed beds.

Hyphenation of high-temperature liquid chromatography with high-pressure electrospray ionization for subcritical water LC-ESI-MS

High-pressure electrospray ionization (HP-ESI) performed under super-atmospheric pressure allows a stable and efficient electrospray of pure aqueous and/or superheated solutions even under a μL min-1 flow rate regime. In this paper, we report the direct coupling of the HP-ESI source to high-temperature liquid chromatography (HT-LC) operated at ≤30 μL min-1 flow rates. In addition to ESI, the ion source functions as a back-pressure regulator to keep the mobile phase in the liquid phase when the column is heated to >100 °C. Under an ion source pressure of 7 bar, the LC column can be operated up to 160 °C. LC is performed under isocratic elution, and besides the isothermal mode, the temperature of the column can also be programmed to increase the selectivity while keeping the ion source at a constant temperature. For a given solution flow rate, the analytical time can be shortened by increasing the column temperature. HT-LC-ESI-MS using pure water as the mobile phase with a capillary column is also demonstrated.

A Microwave Flow Detector for Gradient Elution Liquid Chromatography

This study presents a microwave flow detector technique for liquid chromatography (LC) application. The detector is based on a tunable microwave interferometer (MIM) with a vector network analyzer (VNA) for signal measurement and a computer for system control. A microstrip-line-based 0.3 μL flow cell is built and incorporated into the MIM. With syringe pump injection, the detector is evaluated by measuring a few common chemicals in DI water at multiple frequencies from 0.98 to 7.09 GHz. Less than 30 ng minimum detectable quantity (MDQ) is demonstrated. An algorithm is provided and used to obtain sample dielectric permittivity at each frequency point. When connected to a commercial HPLC system and injected with a 10 μL aliquot of 10 000 ppm caffeine DI-water solution, the microwave detector yields a signal-to-noise ratio (SNR) up to 10 under isocratic and gradient elution operations. The maximum sampling rate is 20 Hz. The measurements show that MIM tuning, aided by a digital tunable attenuator (DTA), can automatically adjust MIM operation to retain detector sensitivity when mobile phase changes. Furthermore, the detector demonstrates a capability to quantify coeluted vitamin E succinate (VES) and vitamin D₃ (VD₃).

Size exclusion chromatography with superficially porous particles

A comparison is made using size-exclusion chromatography (SEC) of synthetic polymers between fully porous particles (FPPs) and superficially porous particles (SPPs) with similar particle diameters, pore sizes and equal flow rates. Polystyrene molecular weight standards with a mobile phase of tetrahydrofuran are utilized for all measurements conducted with standard HPLC equipment. Although it is traditionally thought that larger pore volume is thermodynamically advantageous in SEC for better separations, SPPs have kinetic advantages and these will be shown to compensate for the loss in pore volume compared to FPPs. The comparison metrics include the elution range (smaller with SPPs), the plate count (larger for SPPs), the rate production of theoretical plates (larger for SPPs) and the specific resolution (larger with FPPs). Advantages to using SPPs for SEC are discussed such that similar separations can be conducted faster using SPPs. SEC using SPPs offers similar peak capacities to that using FPPs but with faster operation. This also suggests that SEC conducted in the second dimension of a two-dimensional liquid chromatograph may benefit with reduced run time and with equivalently reduced peak width making SPPs advantageous for sampling the first dimension by the second dimension separator. Additional advantages are discussed for biomolecules along with a discussion of optimization criteria for size-based separations.

Measurement of caffeine and its three primary metabolites in human plasma by HPLC-ESI-MS/MS and clinical application

Caffeine is a mild stimulant with significant potential for abuse, being consumed in larger doses with the widespread availability of energy drinks and by novel routes of administration such as inspired powder, oral sprays and electronic cigarettes. How these recent changes in caffeine consumption affecting caffeine disposition and abuse potential is of growing concern. In the study of caffeine disposition in humans, it is common to only measure the caffeine concentration; however, caffeine's three major metabolites (paraxanthine, theobromine and theophylline) retain central nervous system stimulant activity that may contribute to the overall pharmacological activity and toxicity. Therefore, it would be scientifically more rigorous to measure caffeine and its major metabolites in the evaluation of caffeine disposition in human subjects. Herein, we report a method for the simultaneous quantification of caffeine and its three major metabolites in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). Human plasma samples were treated by simple protein precipitation and the analytes were separated using a 6 min gradient program. Precision and accuracy were well within in the 15% acceptance range. The simple sample preparation, short runtime, sensitivity and the inclusion of caffeine's major metabolites make this assay methodology optimal for the study of caffeine's pharmacokinetics and pharmacodynamics in human subjects.

Graphical Method for Choosing Optimized Conditions Given a Pump Pressure and a Particle Diameter in Liquid Chromatography

The general limitations on liquid chromatographic performance in isocratic and gradient elution are now well understood. Many workers have contributed to this understanding and to developing graphical methods, or plots, to illustrate the capabilities of chromatographic systems over a wide range of values of operational parameters. These have been invaluable in getting a picture, in broad strokes, about the value of changing an operational parameter or the value of one separation approach over another. Here we present a plotting approach more appropriate for determining how to use chromatography most efficiently in one's own laboratory. The axes are linear: column length vertical and mobile phase velocity horizontal. In this coordinate system, straight lines with intercept zero correspond to different values of t₀. Hyperbolas correspond to values of pressure as the product of length and velocity is proportional to pressure. For a given relationship between theoretical plate height and velocity (e.g., van Deemter), the number of theoretical plates as a function of column length and mobile phase velocity is a surface (z direction) to the x and y of velocity and length. By representing the surface as contours, a two-dimensional plot results. Any point along a constant pressure hyperbola represents the best one can do given the particle diameter, solute diffusion coefficient, and temperature. The user can quickly see how to use the pressure for speed or for more theoretical plates. Sets of such plots allow for comparisons among particle diameters or temperatures. Analogous plots of peak capacity for gradient elution are equally revealing. The plots lead instantly to understanding liquid chromatographic optimization at a practical level. They neatly illustrate the value (or not) of changing pump pressure, particle diameter, or temperature for fast or slow separations in either isocratic or gradient elution. They are illustrated with a focus on maximizing plate count with a given analysis time (isocratic), the effect of volume overload (isocratic), and separations of a limited number of peptides with a peak capacity coming from statistical peak overlap theory (gradient).

Optimized high performance liquid chromatography-ultraviolet detection method using core-shell particles for the therapeutic monitoring of methotrexate

Methotrexate (MTX) is an antineoplastic drug, and due to its high toxicity, the therapeutic drug monitoring is strictly conducted in the clinical practice. The chemometric optimization and validation of a high performance liquid chromatography (HPLC) method using core-shell particles is presented for the determination of MTX in plasma during therapeutic monitoring. Experimental design and response surface methodology (RSM) were applied for the optimization of the chromatographic system and the analyte extraction step. A Poroshell 120 EC-C18 (3.0 mm×75 mm, 2.7 μm) column was used to obtain a fast and efficient separation in a complete run time of 4 min. The optimum conditions for the chromatographic system resulted in a mobile phase consisting of acetic acid/sodium acetate buffer solution (85.0 mM, pH=4.00) and 11.2% of acetonitrile at a flow rate of 0.4 mL/min. Selectivity, linearity, accuracy and precision were demonstrated in a range of 0.10-6.0 µM of MTX. The application of the optimized method required only 150 µL of patient plasma and a low consumption of solvent to provide rapid results.

A Metabolomic Approach to Understanding the Metabolic Link between Obesity and Diabetes

Obesity and diabetes arise from an intricate interplay between both genetic and environmental factors. It is well recognized that obesity plays an important role in the development of insulin resistance and diabetes. Yet, the exact mechanism of the connection between obesity and diabetes is still not completely understood. Metabolomics is an analytical approach that aims to detect and quantify small metabolites. Recently, there has been an increased interest in the application of metabolomics to the identification of disease biomarkers, with a number of well-known biomarkers identified. Metabolomics is a potent approach to unravel the intricate relationships between metabolism, obesity and progression to diabetes and, at the same time, has potential as a clinical tool for risk evaluation and monitoring of disease. Moreover, metabolomics applications have revealed alterations in the levels of metabolites related to obesity-associated diabetes. This review focuses on the part that metabolomics has played in elucidating the roles of metabolites in the regulation of systemic metabolism relevant to obesity and diabetes. It also explains the possible metabolic relation and association between the two diseases. The metabolites with altered profiles in individual disorders and those that are specifically and similarly altered in both disorders are classified, categorized and summarized.

Two variables dominating the retention of intact proteins under gradient elution with simultaneous ultrafast high-resolution separation by hydrophobic interaction chromatography

The retention of proteins under gradient elution in HIC is dominated by two variables of steady and migration regions.

Sub-2 μm fully porous and partially porous (core–shell) stationary phases for reversed phase liquid chromatography

The need for increased throughput and superior performance has increased the demand for stationary phases with improved kinetic performance.

Preparation and evaluation of a hydrophilic poly(2-hydroxyethyl methacrylate-co-N,N'-methylene bisacrylamide) monolithic column for pressurized capillary electrochromatography

A polar polymethacrylate-based monolithic column was introduced and evaluated as a hydrophilic interaction CEC stationary phase. The monolithic stationary phase was prepared by in situ copolymerization of a neutral monomer 2-hydroxyethyl methacrylate and a polar cross-linker N,N'-methylene bisacrylamide in a binary porogenic solvent consisting of dodecyl alcohol and toluene. The hydroxyl and amino groups at the surface of the monolithic stationary phase provided polar sites which were responsible for hydrophilic interactions. The composition and proportion of the polymerization mixture was investigated in detail. The mechanical stability and reproducibility of the obtained monolithic column preformed was satisfied. The effects of pH and organic solvent content on the EOF and the separation of amines, nucleosides, and narcotics on the optimized monolithic column were investigated. A typical hydrophilic interaction CEC was observed on the neutral polar stationary phase. The optimized monolithic column can obtain high-column efficiencies with 62,000-126,000 theoretical plates/m and the RSDs of column-to-column (n = 9), run-to-run (n = 5), and day-to-day (n = 3) reproducibility were less than 6.3%. The calibration curves of these five narcotics exhibited good linearity with R in the range of 0.9959-0.9970 and linear ranges of 1.0-200.0 μg/mL. The detection limits at S/N = 3 were between 0.2 and 1.2 μg/mL. The recoveries of the separation of narcotics on the column were in the range of 84.0-108.6%. The good mechanical stability, reproducibility, and quantitation capacity was suitable for pressure-assisted CEC applications.