Fundamental and practical aspects of ultrahigh pressure liquid chromatography for fast separations

Green chromatography-carbon footprint of columns packed with core–shell materials

Acetonitrile and methanol are the most popular organic solvents employed in RP HPLC, so it is important to minimize the environmental impact of organic solvent and the use of environmentally friendly solvents.

Monodisperse sphere-on-sphere silica particles for fast HPLC separation of peptides and proteins

One-pot synthesis of monodisperse sphere-on-sphere (SOS) silica microspheres is developed for fast separation of peptide and protein mixtures by HPLC.

Detection and quantification of neurotransmitters in dialysates

Sensitive analytical methods are needed for the separation and quantification of neurotransmitters obtained in microdialysate studies. This unit describes methods that permit quantification of nanomolar concentrations of monoamines and their metabolites (high-performance liquid chromatography [HPLC] electrochemical detection), acetylcholine (HPLC-coupled to an enzyme reactor), and amino acids (HPLC-fluorescence detection, capillary electrophoresis with laser-induced fluorescence detection).

Determination of mycophenolic acid in human plasma by ultra performance liquid chromatography tandem mass spectrometry

A simple, sensitive and high throughput ultra performance liquid chromatography tandem mass spectrometry method has been developed for the determination of mycophenolic acid in human plasma. The method involved simple protein precipitation of MPA along with its deuterated analog as an internal standard (IS) from 50 µL of human plasma. The chromatographic analysis was done on Acquity UPLC C18 (100 mm×2.1 mm, 1.7 µm) column under isocratic conditions using acetonitrile and 10 mM ammonium formate, pH 3.00 (75:25, v/v) as the mobile phase. A triple quadrupole mass spectrometer operating in the positive ionization mode was used for quantitation. In-source conversion of mycophenolic glucuronide metabolite to the parent drug was selectively controlled by suitable optimization of cone voltage, cone gas flow and desolvation temperature. The method was validated over a wide concentration range of 15-15000 ng/mL. The mean extraction recovery for the analyte and IS was >95%. Matrix effect expressed as matrix factors ranged from 0.97 to 1.02. The method was successfully applied to support a bioequivalence study of 500 mg mycophenolate mofetil tablet in 72 healthy subjects.

Analytical methodologies for the determination of endocrine disrupting compounds in biological and environmental samples

Endocrine-disruptor compounds (EDCs) can mimic natural hormones and produce adverse effects in the endocrine functions by interacting with estrogen receptors. EDCs include both natural and synthetic chemicals, such as hormones, personal care products, surfactants, and flame retardants, among others. EDCs are characterised by their ubiquitous presence at trace-level concentrations and their wide diversity. Since the discovery of the adverse effects of these pollutants on wildlife and human health, analytical methods have been developed for their qualitative and quantitative determination. In particular, mass-based analytical methods show excellent sensitivity and precision for their quantification. This paper reviews recently published analytical methodologies for the sample preparation and for the determination of these compounds in different environmental and biological matrices by liquid chromatography coupled with mass spectrometry. The various sample preparation techniques are compared and discussed. In addition, recent developments and advances in this field are presented.

Simultaneous analysis of the non-canonical amino acids norleucine and norvaline in biopharmaceutical-related fermentation processes by a new ultra-high performance liquid chromatography approach

In this study, a precise and reliable ultra-high performance liquid chromatography (UHPLC) method for the simultaneous determination of non-canonical (norvaline and norleucine) and standard amino acids (aspartic acid, glutamic acid, serine, histidine, glycine, threonine, arginine, tyrosine, methionine, valine, phenylalanine, isoleucine, leucine) in biopharmaceutical-related fermentation processes was established. After pre-column derivatization with ortho-phthaldialdehyde and 2-mercaptoethanol, the derivatives were separated on a sub-2 μm particle C18 reverse-phase column. Identification and quantification of amino acids were carried out by fluorescence detection. To test method feasibility on standard HPLC instruments, the assay was properly transferred to a core-shell particle C18 reverse-phase column. The limits of detection showed excellent sensitivity by values from 0.06 to 0.17 pmol per injection and limits of quantification between 0.19 and 0.89 pmol. In the present study, the newly established UHPLC method was applied to a recombinant antibody Escherichia coli fermentation process for the analysis of total free amino acids. We were able to specifically detect and quantify the unfavorable amino acids in such complex samples. Since we observed trace amounts of norvaline and norleucine during all fermentation phases, an obligatory process monitoring should be considered to improve quality of recombinant protein drugs in future.

Clinical applications of fast liquid chromatography: a review on the analysis of cardiovascular drugs and their metabolites

One of the major challenges facing the medicine today is developing new therapies that enhance human health. To help address these challenges the utilization of analytical technologies and high-throughput automated platforms has been employed; in order to perform more experiments in a shorter time frame with increased data quality. In the last decade various analytical strategies have been established to enhance separation speed and efficiency in liquid chromatography applications. Liquid chromatography is an increasingly important tool for monitoring drugs and their metabolites. Furthermore, liquid chromatography has played an important role in pharmacokinetics and metabolism studies at these drug development stages since its introduction. This paper provides an overview of current trends in fast chromatography for the analysis of cardiovascular drugs and their metabolites in clinical applications. Current trends in fast liquid chromatographic separations involve monolith technologies, fused-core columns, high-temperature liquid chromatography (HTLC) and ultra-high performance liquid chromatography (UHPLC). The high specificity in combination with high sensitivity makes it an attractive complementary method to traditional methodology used for routine applications. The practical aspects of, recent developments in and the present status of fast chromatography for the analysis of biological fluids for therapeutic drug and metabolite monitoring, pharmacokinetic studies and bioequivalence studies are presented.

One-pot synthesis of spheres-on-sphere silica particles from a single precursor for fast HPLC with low back pressure

Spheres-on-sphere (SOS) silica particles are prepared in a one-pot scalable synthesis from mercaptopropyltrimethoxysilane with hydrophilic polymer and cationic surfactant under alkaline conditions. The SOS particles exhibit solid-core porous-shell properties. The fast separation of small molecules and proteins with low back pressure are demonstrated by high-performance liquid chromatography (HPLC) for the columns packed with SOS-particles.

Improved Chromatographic Methods for Determination of Bioactive Compounds from Aloe vera Leaves

In this work three chromatographic methods were developed to reduce the total time of the analysis of main compounds in Aloe vera extracts. The first method was developed in a regular reverse phase chromatographic system using a particulate reverse phase C-18 column. Methods already published were used as a starting point for the development of the new method. All the compounds were separated in 32 minutes. The second method was developed in a regular reverse phase chromatographic system employing a monolithic type column. Using a 4.5 mL min−1 flow, the total time of analysis was reduced to 6 minutes with very similar resolution values. The third method was developed in an ultraperformance liquid chromatographic system, and the final time for the analysis of the phenolic compounds was reduced to 4 minutes. The analytical properties of the three chromatographic methods were compared for the main compounds in the chromatograms. Robustness of the three new methods was also checked with regard to the injection volume and the amount of methanol in the sample. A fast method (4 min) is then available for bioactive compounds from Aloe vera determination.

A new approach for cytokinin isolation from Arabidopsis tissues using miniaturized purification: pipette tip solid-phase extraction

BACKGROUND

We have developed a new analytical approach for isolation and quantification of cytokinins (CK) in minute amounts of fresh plant material, which combines a simple one-step purification with ultra-high performance liquid chromatography-fast scanning tandem mass spectrometry.

RESULTS

Plant tissue samples (1-5 mg FW) were purified by stop-and-go-microextraction (StageTip purification), which previously has only been applied for clean-up and pre-concentration of peptides. We found that a combination of two reverse phases and one cation-exchange phase, was the best tool, giving a total extraction recovery higher than 80%. The process was completed by a single chromatographic analysis of a wide range of naturally occurring cytokinins (bases, ribosides, O- and N-glucosides, and nucleotides) in 24.5 minutes using an analytical column packed with sub-2-microne particles. In multiple reaction monitoring mode, the detection limits ranged from 0.05 to 5 fmol and the linear ranges for most cytokinins were at least five orders of magnitude. The StageTip purification was validated and optimized using samples of Arabidopsis thaliana seedlings, roots and shoots where eighteen cytokinins were successfully determined.

CONCLUSIONS

The combination of microextraction with one-step high-throughput purification provides fast, effective and cheap sample preparation prior to qualitative and quantitative measurements. Our procedure can be used after modification also for other phytohormones, depending on selectivity, affinity and capacity of the selected sorbents.

Streamlined approach to high-quality purification and identification of compound series using high-resolution MS and NMR

Automated medicinal chemistry (parallel chemistry) has become an integral part of the drug-discovery process in almost every large pharmaceutical company. Parallel array synthesis of individual organic compounds has been used extensively to generate diverse structural libraries to support different phases of the drug-discovery process, such as hit-to-lead, lead finding, or lead optimization. In order to guarantee effective project support, efficiency in the production of compound libraries has been maximized. As a consequence, also throughput in chromatographic purification and analysis has been adapted. As a recent trend, more laboratories are preparing smaller, yet more focused libraries with even increasing demands towards quality, i.e. optimal purity and unambiguous confirmation of identity. This paper presents an automated approach how to combine effective purification and structural conformation of a lead optimization library created by microwave-assisted organic synthesis. The results of complementary analytical techniques such as UHPLC-HRMS and NMR are not only regarded but even merged for fast and easy decision making, providing optimal quality of compound stock. In comparison with the previous procedures, throughput times are at least four times faster, while compound consumption could be decreased more than threefold.

Comprehensive two-dimensional separation of hydroxylated polybrominated diphenyl ethers by ultra-performance liquid chromatography coupled with ion mobility-mass spectrometry

A comprehensive two-dimensional system coupling ultra-performance liquid chromatography (UPLC) and ion mobility-mass spectrometry (IM-MS) has been applied for the separation and analysis of hydroxylated polybrominated diphenyl ethers (OH-PBDEs). A complex mixture containing 23 OH-PBDE congeners ranging from hydroxylated monobromodiphenyl ether (OH-monoBDE) to hydroxylated octabromodiphenyl ether (OH-octaBDE) was satisfactorily separated within 16 min of analysis time. The first-dimensional reversed-phase UPLC was performed on a sub-2 μm BEH C(18) chromatographic column using acetonitrile-water gradient elution program with a flow rate ramp. It enabled excellent chromatographic separation for both between-class and within-class OH-PBDEs based on their differences in hydrophobicity. Following the pre-ionization resolution in the first dimension, the second-dimensional IM-MS employed a hybrid electrospray quadrupole ion mobility time-of-flight mass spectrometer and added an extra post-ionization separation for between-class OH-PBDE congeners on account of their relative mobility disparity during a very short period of 8.80 ms. The orthogonality of the developed two-dimensional system was evaluated with the correlation coefficient of 0.9665 and peak spreading angle of 14.87°. The peak capacity of the system was calculated to be approximately 2 and 15 times higher than that of the two dimensions used alone, respectively. The two-dimensional separation plane also contributed to the removal of background interference ions and the enhanced confidence in the characterization of OH-PBDEs of interest.

Practical comparison of LC columns packed with different superficially porous particles for the separation of small molecules and medium size natural products

Commercial C(18) columns packed with superficially porous particles of different sizes and shell thicknesses (Ascentis Express, Kinetex, and Poroshell 120) or sub-2-μm totally porous particles (Acquity BEH) were systematically compared using a small molecule mixture and a complex natural product mixture as text probes. Significant efficiency loss was observed on 2.1-mm id columns even with a low dispersion ultra-high pressure liquid chromatography system. The Kinetex 4.6-mm id column packed with 2.6-μm particles exhibited the best overall efficiency for small molecule separations and the Poroshell 120 column showed better performance for mid-size natural product analytes. The Kinetex 2.1-mm id column packed with 1.7-μm particles did not deliver the expected performance and the possible reasons besides extra column effect have been proved to be frictional heating effect and poor column packing quality. Different column retentivities and selectivities have been observed on the four C(18) columns of different brands for the natural product separation. Column batch-to-batch variability that has been previously observed on the Ascentis Express column was also observed on the Kinetex and Poroshell 120 column.

Rapid simultaneous determination of isoflavones in Radix puerariae using high-performance liquid chromatography-triple quadrupole mass spectrometry with novel shell-type column

A high-performance liquid chromatography (HPLC) coupled with triple quadrupole mass spectrometry (MS/MS) method was developed for rapid determination of 13 isoflavones in Radix puerariae. A novel shell-type column, namely Kinetex core-shell C(18) column (50 mm×2.1 mm id, 2.6 μm), and gradient elution were used during the analysis. The chromatographic peaks of 13 investigated compounds were identified by comparing their retention time and MS data with the related reference compounds. Multiple-reaction monitoring (MRM) was employed for the quantitative analysis with negative ionization mode. All calibration curves showed good linearity (r(2)>0.9990) within test ranges. The LOD and LOQ were lower than 0.017 and 0.873 μg/mL on column, respectively. The intra- and inter-day precisions for 13 analytes were <1.17 and 2.17%, respectively, and the recoveries were 93.1-104.4%. The validated method was applied for quantitative analysis of 13 isoflavones in 7 species of Radix puerariae. The result demonstrated that HPLC-MS/MS system with Kinetex column could be a promising analytical tool for the determination of isoflavones in traditional Chinese medicines, which is helpful for comprehensive evaluation of quality of R. puerariae.

Application of a validated ultra performance liquid chromatography-tandem mass spectrometry method for the quantification of darunavir in human plasma for a bioequivalence study in Indian subjects

A simple, precise and rapid ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed and validated for the quantification of darunavir, a protease inhibitor, using darunavir-d9 as internal standard (IS). The method involved liquid-liquid extraction of darunavir and IS in methyl-tert-butyl ether from 50 μL human plasma. The chromatographic separation was achieved on an Acquity UPLC BEH C18 (50 mm × 2.1mm, 1.7 μm particle size) analytical column under gradient conditions, in a run time of 1.6 min. The precursor → product ion transitions for darunavir (m/z 548.1 → 392.0) and IS (m/z 557.1 → 401.0) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. The method was extensively validated for its selectivity, sensitivity, carryover check, linearity, precision and accuracy, reinjection reproducibility, recovery, matrix effect, ion suppression/enhancement, stability and dilution integrity. The linearity of the method was established in the concentration range of 1.0-5000 ng/mL. The mean relative recovery for darunavir (100.8%) and IS (89.8%) from spiked plasma samples was consistent and reproducible. The application of this method for routine measurement of plasma darunavir concentration was demonstrated by a bioequivalence study conducted in 40 healthy Indian subjects for a 600 mg tablet formulation along with 100mg ritonavir as booster under fast and fed conditions. To demonstrate the reproducibility in the measurement of study data, an incurred sample reanalysis was done with 400 subject samples and the % change in concentration was within ± 12%.

Multivariate analysis of phenol in freeze-dried and spray-dried insulin formulations by NIR and FTIR

Dehydration is a commonly used method to stabilise protein formulations. Upon dehydration, there is a significant risk the composition of the formulation will change especially if the protein formulation contains volatile compounds. Phenol is often used as excipient in insulin formulations, stabilising the insulin hexamer by changing the secondary structure. We have previously shown that it is possible to maintain this structural change after drying. The aim of this study was to evaluate the residual phenol content in spray-dried and freeze-dried insulin formulations by Fourier transform infrared (FTIR) spectroscopy and near infrared (NIR) spectroscopy using multivariate data analysis. A principal component analysis (PCA) and partial least squares (PLS) projections were used to analyse spectral data. After drying, there was a difference between the two drying methods in the phenol/insulin ratio and the water content of the dried samples. The spray-dried samples contained more water and less phenol compared with the freeze-dried samples. For the FTIR spectra, the best model used one PLS component to describe the phenol/insulin ratio in the powders, and was based on the second derivative pre-treated spectra in the 850-650 cm(-1) region. The best PLS model based on the NIR spectra utilised three PLS components to describe the phenol/insulin ratio and was based on the standard normal variate transformed spectra in the 6,200-5,800 cm(-1) region. The root mean square error of cross validation was 0.69% and 0.60% (w/w) for the models based on the FTIR and NIR spectra, respectively. In general, both methods were suitable for phenol quantification in dried phenol/insulin samples.

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

Perhaps the most consistent trend in the development of high-performance liquid chromatography (HPLC) since its inception in the 1960s has been the continuing reach for ever faster analyses. The pioneering work of Knox, Horvath, Halasz, and Guiochon set forth a theoretical framework that was used early on to improve the speed of HPLC, primarily through the commercialization of smaller and smaller particles. Over the past decade, approaches to improving the speed of HPLC have become more diverse, and now practitioners of HPLC are faced with the difficult task of deciding which of these approaches will lead them to the fastest analysis for their application. Digesting the rich literature on the optimization of HPLC is a difficult task in itself, which is further complicated by contradictory marketing messages from competing commercial outlets for HPLC technology. In this perspectives article we provide an overview of the theoretical and practical aspects of the principal modern approaches to improving the speed of HPLC. We present a straightforward theoretical basis, informed by decades of literature on the problem of optimization, that is useful for comparing different technologies for improving the speed of HPLC. Through mindful optimization of conditions, high-performance separations on the subminute timescale are now possible and becoming increasingly common under both isocratic and gradient elution conditions. Certainly the continued development of ultrafast separations will play an important role in the development of two-dimensional HPLC separations. Despite the relatively long history of HPLC as an analytical technique, there is no sign of a slow-down in the development of novel HPLC technologies.

Recent developments in the HPLC separation of phenolic compounds

Phenolic compounds represent a class of highly complex naturally occurring molecules that possess a range of beneficial health properties. As a result, considerable attention has been devoted to the analysis of phenolics in a variety of samples. HPLC is the workhorse method for phenolic separation. However, conventional HPLC methods provide insufficient resolving power when faced with the complexity of real-world phenolic fractions. This limitation has been traditionally circumvented by extensive sample fractionation, multiple analysis methods and/or selective detection strategies. On the other hand, there is an increasing demand for improved throughput and resolving power from the chromatographic methods used for phenolic analyses. Fortunately, during the last decade, a number of important technological advances in LC have demonstrated significant gains in terms of both speed and resolution. These include ultra high-pressure liquid chromatography (UHPLC), high-temperature liquid chromatography (HTLC), multi-dimensional separations as well as various new stationary phase chemistries and morphologies. In recent years, these technologies have also found increasing application for phenolic analysis. This review seeks to provide an updated overview of the application of recent advances in HPLC to phenolic separation, with the emphasis on how these methodologies can contribute to improve performance in HPLC analysis of phenolics.

Fast liquid chromatography combined with mass spectrometry for the analysis of metabolites and proteins in human body fluids

In the last decade various analytical strategies have been established to enhance separation speed and efficiency in high performance liquid chromatography applications. Chromatographic supports based on monolithic material, small porous particles, and porous layer beads have been developed and commercialized to improve throughput and separation efficiency. This paper provides an overview of current developments in fast chromatography combined with mass spectrometry for the analysis of metabolites and proteins in clinical applications. Advances and limitations of fast chromatography for the combination with mass spectrometry are discussed. Practical aspects of, recent developments in, and the present status of high-throughput analysis of human body fluids for therapeutic drug monitoring, toxicology, clinical metabolomics, and proteomics are presented.

Development and characterization of "push-pull" sampling device with fast reaction quenching coupled to high-performance liquid chromatography for pharmaceutical process analytical technologies

A push-pull sampling system interfaced on-line to high-performance liquid chromatography (HPLC) was developed for micro-volume real-time monitoring of reaction mixtures. The device consists of concentric tubes wherein sample was continuously withdrawn through the outer tube and reaction quenchant continuously delivered through a recessed inner tube. The device allowed sampling rates of 0.1-6.0 μL/min from a reaction vessel and stopped the reaction by passive mixing with quenchant to preserve the conditions observed in the reaction vessel. A finite element model of the system showed that reaction mixtures could be completely mixed with quenchant within 4.3s at a flow rate of 1.0 μL/min. The model also showed that an offset distance of 1mm between the push capillary and sample capillary tips is sufficient to avoid leakage of quenchant/diluent into the bulk sample for push flow rates up to 95% of the pull flow rate. The maximum relative push flow rate was determined to be 90% of the pull flow rate experimentally. Delay between sampling and delivery to the HPLC was from 111±3s to 317±9s for pull flow rates from 1.0 to 3.0 μL/min in agreement with expected delays based on tubing volume. Response times were from 27±1s to 52±6s over the same flow rate range. The sampler was tested to determine the effects of sample viscosity. The sampler was also used to demonstrate periodic sampling capabilities. As a test of the system, it was used to monitor the base-catalyzed hydrolysis of aspirin for 1.5h, demonstrating its utility for monitoring an ongoing reaction.

Capillary ultrahigh performance liquid chromatography with elevated temperature for sub-one minute separations of basal serotonin in submicroliter brain microdialysate samples

Improving the time resolution in microdialysis coupled to high performance liquid chromatography (HPLC) requires that the volume of the separation system be decreased. A low-volume separation permits smaller microdialysate volumes to be injected without suffering a sensitivity loss from dilution. Thus, improved time resolution can be achieved with offline analysis simply by decreasing the separations system volume. For online (near real-time) analysis, there is a further requirement. The separation speed must be at least as fast as the sampling time. Here, the combined use of high column pressures and temperatures, sub-2-μm stationary phase particles, capillary columns, and sensitive, low dead-volume detection resulted in a retention time for the neurotransmitter serotonin of less than 1 min in a 500 nL dialysate sample volume. Two sensitive detectors, photoluminescence following electron transfer (PFET) and electrochemical, were used for the detection of subnanomolar concentrations of serotonin in brain microdialysate samples. The general principles developed are applicable to a wide range of separations with the additional advantages of increases in sample throughput and decreases in mobile phase usage.

Fourier transform ion cyclotron resonance mass spectrometer with coaxial multi-electrode cell ('O-trap'): first experimental demonstration

The conceptual design of the O-trap Fourier transform ion cyclotron resonance (FT-ICR) cell addresses the speed of analysis issue in FT-ICR mass spectrometry. The concept of the O-trap includes separating the functions of ion excitation and detection between two different FT-ICR cell compartments. The detection compartment of the O-trap implements additional internal coaxial electrodes around which ions with excited cyclotron motion revolve. The expected benefits are higher resolving power and the lesser effect of the space charge. In this work we present the first experimental demonstration of the O-trap cell and its features, including the high ion transfer efficiency between two distinct compartments of an ICR cell after excitation of the coherent cyclotron motion. We demonstrate that utilization of the multiple-electrode detection in the O-trap provides mass resolving power enhancement (achieved over a certain time) equal to the order of the frequency multiplication. In an O-trap installed in a 5 T desk-top cryogen-free superconducting magnet, the resolving power of R = 80,000 was achieved for bradykinin [M + 2H](2+) (m/z 531; equivalent to 100,000 when recalculated for m/z 400) in 0.2 s analysis time (transient length), and R = 300,000 at m/z 531 for a 1 s transient. In both cases, detection on the third multiple of the cyclotron frequency was implemented. In terms of the acquisition speed at fixed resolving power, such performance is equivalent to conventional FT-ICR detection using a 15 T magnet.

Analysis of amphetamines and metabolites in urine with ultra performance liquid chromatography tandem mass spectrometry

A simple, rapid and sensitive ultra performance liquid chromatography tandem mass spectrometry method was developed and fully validated for the quantitative determination of seven amphetamines and metabolites in urine. The method was validated for selectivity, linearity, LOQ, LOD, imprecision, bias, analyte and processed sample stability, matrix effect, recovery, carryover and dilution integrity. A classic liquid-liquid extraction with ethyl acetate was used as sample preparation procedure. The compounds were separated on an Acquity UPLC HSS C18 column in 6.8 min. The linear dynamic range was established from 25 to 500 ng/mL. The limit of quantification was fixed to the lowest calibrator level and the limit of detection ranged from 0.125 to 2.5 ng/mL. The method presented an excellent intra- and inter-assay imprecision and bias (<10.7%) at each measured concentration of two external quality controls (QC) and three "in house" QC. No matrix effects were observed and good recoveries (>70%) were obtained for all the compounds. No carryover was observed after the analysis of high concentrated samples (8000 ng/mL). The method was subsequently applied to authentic samples.