Reversed-phase Liquid Chromatographic System Research Articles

Evaluation of the Goss-modified solvation parameter model for the characterization of biphasic systems and descriptor assignments

The solvation parameter model uses six descriptors identified as excess molar refraction, E, dipolarity/polarizability, S, overall hydrogen-bond acidity, A, overall hydrogen-bond basicity, B, McGowan's characteristic volume, V, and the gas-liquid partition constant on hexadecane at 25 °C, L to model the distribution of neutral compounds in biphasic systems. Abraham's version of this model uses all six descriptors with two separate linear free energy relationship models for the transfer of compounds from a gas phase to a condensed phase and between condensed phases. Goss proposed a modification to this model that uses a single calibration model regardless of the physical state for each phase and five of the descriptors employed in Abraham's model (E descriptor is eliminated). The capability of Abraham's model and the Goss-modified model to characterize the contribution of intermolecular interaction to retention for gas and reversed-phase liquid chromatographic systems and distribution in liquid-liquid partition systems is evaluated using the WSU compound descriptor database. These more accurate values for the Abraham descriptors have not been utilized previously for the evaluation of the Goss-modified model and should be more capable of discerning subtle differences in model performance. It is shown that model quality defined by statistical parameters favors Abraham's model over the Goss-modified model with differences in model quality greater for systems in which Abraham's model indicates a significant contribution from electron lone pair interactions and for systems in which one phase is a solvent containing perfluoroalkyl substituents. There is a small systematic difference for the terms describing the combined contributions of cavity formation and dispersion interactions and for interactions of a dipole-type. The contribution of hydrogen-bonding interactions is virtually identical for the two models. The model intercepts are generally different and potentially assigned to a larger contribution from lack-of-fit for the Goss-modified model. Although the Abraham model descriptors have been routinely employed for applications using the Goss-modified model the possibility that Goss-model specific descriptors should be employed was evaluated. Using the Solver method and Goss-model specific calibration models for chromatographic and liquid-liquid partition systems a new set of Goss-specific descriptors was calculated for 28 varied compounds. These descriptors show good statistical agreement with the Abraham descriptor values with an average deviation of 0.009, -0.003, -0.004, and -0.023, respectively, for the S, A, B, and L descriptors, corresponding to a relative absolute deviation in percent of 2.2 %, 3.9 %, 4.3 %, and 1.2 %, respectively.

A polemic on the use of reversed-phase liquid chromatography to determine descriptors for the solvation parameter model

Revised descriptors for 74 varied compounds recommended for the characterization of reversed-phase silica columns using the solvation parameter model are assigned by the Solver method from experimental retention factors for calibrated gas-liquid and reversed-phase liquid chromatographic (RPLC) and biphasic liquid-liquid partition systems. These descriptors are taken as the best estimate of the true descriptor values and used to evaluate several RPLC systems as a single-technique approach for descriptor assignments. Various combinations of isocratic single column and multiple mobile phase compositions, multiple columns with a single mobile phase composition, and multiple columns and multiple mobile phase compositions are evaluated. A multiple column (Discovery HS C18 and HS F5, Fluophase-RP, and XBridge Shield RP18, Phenyl, and C18) with acetonitrile- and methanol-water mobile phases provided the best results with an absolute average deviation (AAD) of 0.043 for the electron lone pair interaction descriptor E, 0.047 for the dipole-type interaction descriptor S, 0.020 for the hydrogen-bond acid descriptor A, and 0.010 for the hydrogen-bond base descriptor B° for 46 varied compounds. These values compare favorably with the larger all columns and mobile phase composition RPLC dataset with the best estimate of the true descriptors, or all data set, with AAD = 0.026 for E, 0.044 for S, 0.027 for A, and 0.011 for B° for 74 varied compounds. The preferred RPLC systems for descriptor assignments contain columns identified as belonging to different selectivity groups that maximize the relative magnitude of the dipole-type contribution, s system constant, hydrogen-bond basicity, a system constant, and electron lone pair interactions, e system constant. RPLC systems are well suited to assigning the B° descriptor and, with proper system selection, the A and S descriptors. The E descriptor for compounds unavailable by calculation is more problematic and a few extreme values with an AAD > ± 0.1 were observed and can affect the reliability of the S descriptor assignments for these compounds. The likelihood of poor descriptor assignments using the Solver method can be identified by evaluating descriptor wells.

Chemometrics of anisotropic lipophilicity of anticancer androstane derivatives determined by reversed-phase ultra high performance liquid chromatography with polar aprotic and protic modifiers

The research of the use of steroid compounds in the treatment of various types of cancer has a history of more than 50 years. Numerous steroid derivatives have expressed significant anticancer activity, however the thorough analysis of their physicochemical and toxicological properties is required prior to their clinical application. The present study is focused on the characterization of physicochemical properties of a series of previously synthesized new androstane derivatives (16E-hydroxyimino derivatives, D-homo lactones and D-seco dinitriles) with anticancer activity applying reversed-phase ultra high performance liquid chromatography (RP-UHPLC) system under isocratic conditions and chemometric tools, including in silico determination of their absorption, distribution, metabolism, excretion and toxicity (ADMET) properties. The chromatographic analysis was carried out applying two two-component and one ternary mobile phases with aprotic (acetonitrile) and protic (water and methanol) solvents. The conducted quantitative structure-retention relationship modeling resulted in two univariate and nine multivariate linear mathematical models that successfully correlate the retention parameters (logk) with descriptors of molecular polarity/lipophilicity (tPSA, REF, Average LogP, ClogP, ALOGP, LogS-SILICOS-IT, AClogS), descriptors that mainly depend on intermolecular interactions (BP, CP, CT, DE, HL) and ADMET descriptors (SWISSLogKpSP, GPCR, HIA, EI). The quality of the models was proved by the internal and external validation, while the robustness of the models was confirmed by Y-randomization test. Considering the established meaningful relationships between physicochemical/ADMET properties and retention parameters, the determined logk parameters of the analyzed series of steroid derivatives can be considered to be a biopharmaceutical property from the perspective of lipophilicity.

Comprehensive profiling of Sanguisorba officinalis using offline two-dimensional mixed-mode liquid chromatography × reversed-phase liquid chromatography, tandem high-resolution mass spectrometry, and molecular network.

The profiling of natural products is important in modern biological sciences and new drug development. However, the separation and characterization of complex herbal extracts are significantly challenging for researchers in the biochemical field. Herein, an offline two-dimensional mixed-mode liquid chromatography × reversed-phase liquid chromatography system is developed. Our system exhibits high orthogonality and is composed of a newly prepared stationary phase in the first dimension and a traditional C18 phase in the second dimension, and is operated in combination with a high-resolution mass spectrometry and molecular network. Sanguisorba officinalis L. is studied using the proposed method owing to its bioactivity. With the aid of orthogonal separation, the ionization of the individual components is improved. The number of detected compounds and separated peaks are significantly increased when one-dimensional liquid chromatography is upgraded to two-dimensional liquid chromatography. In addition, 270 compounds (127 of which are tentatively characterized as new compounds, and further confirmation is needed) are successfully characterized based on their fragmentation patterns under the guidance of molecular network, while only 95 compounds are characterized using one-dimensional liquid chromatography and high-resolution mass spectrometry. The results indicate that the developed offline two-dimensional mixed-mode liquid chromatography × reversed-phase liquid chromatography, tandem high-resolution mass spectrometry, and molecular network method are effective for profiling complex samples.

Chemical profiling of Qingfei Paidu Decoction by triplex off-line two-dimensional liquid chromatography coupled with quadrupole time-of-flight mass spectrometry.

Qingfei Paidu Decoction is a Chinese medicine formula that has been proved effective in the treatment of coronavirus disease 2019. However, the comprehensive separation and characterization of Qingfei Paidu Decoction are of a great challenge due to the diversity of chemical components in a wide range of polarity. In this study, a triplex off-line two-dimensional liquid chromatography coupled with quadrupole time-of-flight mass spectrometry is developed for the analysis of Qingfei Paidu Decoction. One reversed-phase liquid chromatography×hydrophilic interaction liquid chromatography system and two reversed-phase liquid chromatography×reversed phase liquid chromatography systems were constructed to separate polar components and weak-polar components in Qingfei Paidu Decoction, respectively. Benefiting from the good orthogonality of two-dimensional liquid chromatography and high sensitivity of quadrupole time-of-flight MS, chemical components with different polarities and content were discovered. A total of 749 peaks were detected in positive and negative ionization mode and presented as a four-dimensional data plot. Meanwhile, 498 compounds belonging to 14 categories were tentatively identified. These results provide good supplementary to elucidate the material basis of Qingfei Paidu Decoction. The triplex off-line two-dimensional liquid chromatography-quadrupole time-of-flight mass spectrometry strategy can be a powerful and efficient tool for the separation and characterization of chemical substances in traditional Chinese medicine formulas.

Discovery of Polar Ozonation Byproducts via Direct Injection of Effluent Organic Matter with Online LC-FT-ICR-MS.

Effluent organic matter (EfOM), a major ozone consumer during wastewater ozonation, is a complex mixture of natural and anthropogenic organic molecules. Ozonation of EfOM adds to molecular complexity by introducing polar and potentially mobile ozonation byproducts (OBPs). Currently, nontargeted direct infusion (DI) ultrahigh resolution mass spectrometry (e.g. FT-ICR-MS) is used to study OBPs but requires sample extraction, limiting the accessible polarity range of OBPs. To better understand the impact of ozonation on EfOM and the formation of polar OBPs, nonextracted effluent was analyzed by direct injection onto a reversed-phase liquid chromatography system (RP-LC) online hyphenated with an FT-ICR-MS. Over four times more OBPs were detected in nonextracted EfOM compared to effluent extracted with solid phase extraction and measured with DI-FT-ICR-MS (13817 vs 3075). Over 1500 highly oxygenated OBPs were detected exclusively in early eluting fractions of nonextracted EfOM, indicating polar OBPs. Oxygenation of these newly discovered OBPs is higher than previously found, with an average molecular DBE-O value of -3.3 and O/C ratio of 0.84 in the earliest eluting OBP fractions. These polar OBPs are consistently lost during extraction but may play an important role in understanding the environmental impact of ozonated EfOM. Moreover, 316 molecular formulas classified as nonreactive to ozone in DI-FT-ICR-MS can be identified with LC-FT-ICR-MS as isomers with varying degrees of reactivity, providing for the first time experimental evidence of differential reactivity of complex organic matter isomers with ozone.

An offline two-dimensional supercritical fluid chromatography × reversed phase liquid chromatography tandem quadrupole time-of-flight mass spectrometry system for comprehensive gangliosides profiling in swine brain extract

Gangliosides, widely distributed in tissues and body fluid, have been connected to the therapy of cancer and brain related diseases. The complexity of the gangliosides structures with different polar moieties coexisting, a carbohydrate moiety and a ceramide chain, make it a great challenge in separation and analysis science. This study aimed to develop a strategy on the basis of high-accuracy data collected by an offline two-dimensional (2D) supercritical fluid chromatography (SFC) × reversed phase liquid chromatography (RPLC)/quadrupole time-of-flight (Q-ToF) system, and to integrate an in-house library with self-developed software for fast screening and identification of gangliosides from a complex sample (swine brain extract). Subsequent positive-mode MS/MS was used to validate the identified gangliosides. Finally, 153 gangliosides were separated and 79 of them were identified by the in-house library and self-developed software, 4-fold more than those by manual identification (18 gangliosides). Among the identified ones, 20 were detected in swine brain for the first time. This study established an offline 2D SFC × RPLC system and provided a new method for fast screening and automatic identification of gangliosides in complex mixtures. It will be conducive to further study of biological functions of gangliosides.

Automated Nanoflow Two-Dimensional Reversed-Phase Liquid Chromatography System Enables In-Depth Proteome and Phosphoproteome Profiling of Nanoscale Samples.

Two-dimensional reversed-phase capillary liquid chromatography (2D RPLC) separations have enabled comprehensive proteome profiling of biological systems. However, milligram sample quantities of proteins are typically required due to significant losses during offline fractionation. Such a large sample requirement generally precludes the application samples in the nanogram to low-microgram range. To achieve in-depth proteomic analysis of such small-sized samples, we have developed the nanoFAC (nanoflow Fractionation and Automated Concatenation) 2D RPLC platform, in which the first dimension high-pH fractionation was performed on a 75-μm i.d. capillary column at a 300 nL/min flow rate with automated fraction concatenation, instead of on a typically used 2.1 mm column at a 200 μL/min flow rate with manual concatenation. Each fraction was then fully transferred to the second-dimension low-pH nanoLC separation using an autosampler equipped with a custom-machined syringe. We have found that using a polypropylene 96-well plate as collection device as well as the addition of n-Dodecyl β-d-maltoside (0.01%) in the collection buffer can significantly improve sample recovery. We have demonstrated the nanoFAC 2D RPLC platform can achieve confident identifications of ∼49,000-94,000 unique peptides, corresponding to ∼6,700-8,300 protein groups using only 100-1000 ng of HeLa tryptic digest (equivalent to ∼500-5,000 cells). Furthermore, by integrating with phosphopeptide enrichment, the nanoFAC 2D RPLC platform can identify ∼20,000 phosphopeptides from 100 μg of MCF-7 cell lysate.

Reversed-phase liquid chromatography system constant database over an extended mobile phase composition range for 25 siloxane-bonded silica-based columns

The solvation parameter model is used to characterize the retention properties of 25 siloxane-bonded type-B silica columns under typical reversed-phase liquid chromatography conditions with binary aqueous mobile phases containing 10–70% (v/v) methanol and acetonitrile. To further explore the affect of solvent type on column selectivity complementary information is presented for aqueous phases containing 10–70% (v/v) tetrahydrofuran for two columns. Columns were selected to include examples of all common column packing morphologies for small molecule separations (totally porous particles, superficially porous particles, organic–inorganic hybrid particles, and a monolith) and common topologies octadecylsiloxane-bonded (including phases with a polar-embedded group, mixed-mode phases with a short-chain siloxane-bonded polar functional group, sterically crowded, positive shield, and fluorine-containing phases); octylsiloxane-bonded; and various phenyl-containing stationary phases with different linker arms, pentafluorophenylalkyl and biphenyl groups. The column properties are reported as a system constant database and as system maps for the full range of mobile phase compositions. Selectivity differences are evaluated using principal component factor analysis to classify the columns into selectivity groups and correlation plots of the system constants for compared columns at all mobile phase compositions. The later is shown to be a suitable technique to identify (near) selectivity equivalent columns and varied columns suitable for method development. Contributions to retention from steric resistance and cation-exchange interactions not parameterized in the solvation parameter model are identified for columns and conditions where they may be important. It is shown that the interaction parameters employed in the hydrophobic-subtraction model have little overlap with those of the solvation parameter model and a quantitative comparison of column properties delineated by both models is not possible.

Multi-Parametric Characterization of Amino Acid- and Peptide-Silica Stationary Phases

Amino acids and peptides (di- and tripeptides) as chemically bonded ligands in liquid chromatography were investigated. The comparison between 9 home-made amino acid- and peptide-silica stationary phases in hydrophilic interaction liquid chromatography (HILIC) and reversed-phase liquid chromatography (RP HPLC) systems has been presented. The investigated stationary phases were modified by the following amino acids: phenylalanine, leucine, alanine, glycine, and aspartic acid. Desired interactions were derived from the retention variation between pairs of similar solutes differing with particular structure properties. In the case of HILIC mode, the characterization was performed in terms of the degree of hydrophilicity, selectivity for hydrophilic–hydrophobic compounds, selectivity for the regio and configurational substituents, anion and cation exchange properties, and acidic or basic nature of the stationary phase surface. Under RP HPLC conditions, following features were elucidated: hydrophobicity, hydrophobic selectivity, shape selectivity, hydrogen bonding, electrostatic interactions at pH values 2.7 and 7.6. The results of the selectivity for partial structural differences were presented as radar-shaped plots and in tabular format. The factor analysis (FA) based on the principal component analysis (PCA) was also used in the stationary phase comparison. The performed research assisted in the evaluation of the relation between the chemical properties of bonded amino acid sequence and their role in the retention mechanism.

Synthesis and chromatographic evaluation of phenyl/tetrazole bonded stationary phase based on thiol-epoxy ring opening reaction.

A silica-based reversed-phase stationary phase bonding with phenyl and tetrazole groups was synthesized by thiol-epoxy ring opening reaction. The bonded groups could not only provide hydrophobic interaction, but also π-π, hydrogen bonding, electrostatic interactions, and so on. The results of characterization with elemental analysis and solid-state 13 C cross-polarization magic-angle-spinning NMR spectroscopy indicated the successful preparation of phenyl/tetrazole sulfoether bonded stationary phase. Chromatographic evaluation revealed that phenyl/tetrazole sulfoether bonded stationary phase behaved well under the reversed-phase mode. The column parameters (H, S*, A, B, and C) showed different selectivity compared with some typical commercial columns, and it was validated by the separation of estrogen, ginsenoside, alkaloid samples. Based on the different selectivity between phenyl/tetrazole sulfoether bonded stationary phase and C18 columns, phenyl/tetrazole sulfoether bonded stationary phase also showed potential to construct a 2D reversed-phase liquid chromatography system with C18. And it was verified by the separation of corydalis tuber and curcuma zedoary extracts.

Comprehensive two-dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography for analysis of toad skin

An analytical two–dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography (2D NPLC × RPLC) system was constructed with a newly developed thermal evaporation assisted adsorption (TEAA) interface. This novel TEAA interface with heating temperature above solvent boiling point allowed fast removal of organic NPLC solvent and successfully solved the solvent incompatibility problem between NPLC and RPLC. The system achieved rapid on-line solvent exchange between the two dimensions within a short modulation time of 190 s and was applied in the analysis of an extract from the skin of Bufo bufo gargarizans. This is the first time to realize the on-line comprehensive analysis of a moderate polar natural product by coupling NPLC with reversed phase ultra-high performance liquid chromatography (UHPLC). To be highlighted, with the TEAA interface, the 2D NPLC × RPLC system provided excellent resolution and orthogonality (75.2%), when compared with that of 2D RPLC × RPLC.

Quantitative structure—retention relationships modeling and multivariate data analysis of lipophilicity data of new spirohydantoin derivatives

Modeling properties of newly synthesized compounds is important for both understanding their activity and predicting their interactions. This paper describes the evaluation of the lipophilicity of the newly synthesized cycloalkylspiro-5-hydantoins by experimental and calculation methods. The chromatographic lipophilicity (RM0) of the analyzed compounds was determined by reversed-phase liquid chromatographic system consisting of RP-18 stationary phase and methanol—water mobile phase. Correlation coefficients between RM0 values and the predicted log P were above 0.93, indicating a strong linear relationship between the variables. Multivariate data analysis applied in this study enabled the comparison of the lipophilicity and the structure of the investigated compounds using solely information obtained from thin-layer chromatography. Hierarchical clustering analysis (HCA) reveals a high similarity between RM0 and miLogP whereas squared log Ps such as ALOGP2 and MLOGP2 were distinct from RM0. HCA classifies t...

On-line comprehensive two-dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography for preparative isolation of toad venom

An on-line comprehensive preparative two–dimensional normal-phase liquid chromatography×reversed-phase liquid chromatography (2D NPLC×RPLC) system was constructed with a newly developed vacuum evaporation assisted adsorption (VEAA) interface, allowing fast removal of NPLC solvent in the vacuum condition and successfully solving the solvent incompatibility problem between NPLC and RPLC. The system achieved on-line solvent exchange within the two dimensions and its performance was illustrated by gram-scale isolation of crude extract from the venom of Bufo bufo gargarizans. Within separation time of ∼20h, 19 compounds were obtained with high purity in a single run. With the VEAA interface, the 2D system exhibited apparent advantages in separation efficiency and automation compared with conventional methods, indicating its promising application in the routine separation process for complicated natural products.

A simple and rapid HPLC-DAD method for simultaneously monitoring the accumulation of alkaloids and precursors in different parts and different developmental stages of Catharanthus roseus plants.

A rapid and simple reversed phase liquid chromatographic system has been developed for simultaneous analysis of terpenoid indole alkaloids (TIAs) and their precursors. This method allowed separation of 11 compounds consisting of eight TIAs (ajmalicine, serpentine, catharanthine, vindoline, vindolinine, vincristine, vinblastine, and anhydrovinblastine) and three related precursors i.e., tryptophan, tryptamine and loganin. The system has been applied for screening the TIAs and precursors in Catharanthus roseus plant extracts. In this study, different organs i.e., flowers, leaves, stems, and roots of C. roseus were investigated. The results indicate that TIAs and precursor accumulation varies qualitatively and quantitatively in different organs of C. roseus. The precursors showed much lower levels than TIAs in all organs. Leaves and flowers accumulate higher level of vindoline, catharanthine and anhydrovinblastine while roots have higher level of ajmalicine, vindolinine and serpentine. Moreover, the alkaloid profiles of leaves harvested at different ages and different growth stages were studied. The results show that the levels of monoindole alkaloids decreased while bisindole alkaloids increased with leaf aging and upon plant growth. The HPLC method has been successfully applied to detect TIAs and precursors in different types of C. roseus samples to facilitate further study of the TIA pathway and its regulation in C. roseus plants.

Liquid chromatography-tandem mass spectrometric assay for the tyrosine kinase inhibitor afatinib in mouse plasma using salting-out liquid-liquid extraction.

A quantitative bioanalytical liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay for afatinib, an irreversible inhibitor of the ErbB (erythroblastic leukemia viral oncogene homolog) tyrosine kinase family, was developed and validated. Plasma samples were pre-treated using salting-out assisted liquid-liquid extraction (SALLE) with acetonitrile, magnesium chloride and a stable isotopically labeled internal standard. After dilution, the extract was directly injected into the reversed-phase liquid chromatographic system. The eluate was transferred into the electrospray interface with positive ionization and compounds were detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was completely validated for plasma in a 0.5-500ng/ml calibration range with r(2)=0.995±0.002 (n=6) using linear regression with the inverse square of the concentration as the weighting factor for the calibration. Within-run precisions (n=18) were 2.7-11.7% and between-run (3 runs; n=18) precisions 3.0-14.5%. Accuracies were between 96-109% for the whole calibration range. The drug was sufficiently stable under all relevant analytical conditions. Finally, the assay was successfully applied to determine plasma drug levels and study pharmacokinetics after oral administration of afatinib to female FVB mice.

Identification of urinary proteins potentially associated with diabetic kidney disease.

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease. Although several parameters are used to evaluate renal damage, in many instances, there is no pathological change until damage is already advanced. Mass spectrometry-based proteomics is a novel tool to identify newer diagnostic markers. To identify urinary proteins associated with renal complications in diabetes, we collected urine samples from 10 type 2 diabetes patients each with normoalbuminuria, micro- and macro-albuminuria and compared their urinary proteome with that of 10 healthy individuals. Urinary proteins were concentrated, depleted of albumin and five other abundant plasma proteins and in-gel trypsin digested after prefractionation on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The peptides were analyzed using a nanoflow reverse phase liquid chromatography system coupled to linear trap quadrupole-Orbitrap mass spectrometer. We identified large number of proteins in each group, of which many were exclusively present in individual patient groups. A total of 53 proteins were common in all patients but were absent in the controls. The majority of the proteins were functionally binding, biologically involved in metabolic processes, and showed enrichment of alternative complement and blood coagulation pathways. In addition to identifying reported proteins such as α2-HS-glycoprotein and Vitamin D binding protein, we detected novel proteins such as CD59, extracellular matrix protein 1 (ECM1), factor H, and myoglobin in the urine of macroalbuminuria patients. ECM1 and factor H are known to influence mesangial cell proliferation, and CD59 causes microvascular damage by influencing membrane attack complex deposition, suggestive their biological relevance to DN. Thus, we have developed a proteome database where various proteins exclusively present in the patients may be further investigated for their role as stage-specific markers and possible therapeutic targets.

On-line comprehensive two-dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography for preparative isolation of Peucedanum praeruptorum

A new on-line comprehensive preparative two-dimensional normal-phase liquid chromatography×reversed-phase liquid chromatography (2D NPLC×RPLC) system was developed for the separation of complicated natural products. It was based on the use of a silica gel packed medium-pressure column as the first dimension and an ODS preparative HPLC column as the second dimension. The two dimensions were connected with normal-phase (NP) and reversed-phase (RP) enrichment units, involving a newly developed airflow assisted adsorption (AAA) technique. The instrument operation and the performance of this NPLC×RPLC separation method were illustrated by gram-scale isolation of ethanol extract from the roots of Peucedanum praeruptorum. In total, 19 compounds with high purity were obtained via automated multi-step preparative separation in a short period of time using this system, and their structures were comprehensively characterized by ESI-MS, 1H NMR, and 13C NMR. Including two new compounds, five isomers in two groups with identical HPLC and TLC retention values were also obtained and identified by 1D NMR and 2D NMR. This is the first report of an NPLC×RPLC system successfully applied in an on-line preparative process. This system not only solved the interfacing problem of mobile-phase immiscibility caused by NP and RP separation, it also exhibited apparent advantages in separation efficiency and sample treatment capacity compared with conventional methods.

Liquid chromatography-tandem mass spectrometric assay for the PI3K/mTOR inhibitor GSK2126458 in mouse plasma and tumor homogenate

A quantitative bioanalytical liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay for GSK2126458, a dual PI3K/mTOR inhibitor, was developed and validated. Plasma and tumor homogenate samples were pre-treated using protein precipitation with acetonitrile containing dabrafenib as internal standard. After dilution with water, the extract was directly injected into the reversed-phase liquid chromatographic system. The eluate was transferred into the electrospray interface with positive ionization and compounds were detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer.The assay was completely validated for plasma in a 4–4000ng/ml calibration range with r2=0.9996±0.0003 using double logarithmic calibration (n=5). Within-run precisions (n=6) were 2.0–5.3% and between-run (3 runs; n=18) precisions 2.7–5.8%. Accuracies were between 101 and 105% for the whole calibration range. The drug was sufficiently stable under all relevant analytical conditions. Finally, the assay was successfully applied to determine plasma and tumor drug levels after oral administration of GSK2126458 to mice with AMC711T neuroblastoma xenografts.

Double Off-line Two-dimensional Liquid Chromatography for Separation and Identification of Compounds in Salvia Miltiorrhiza (Danshen)

Background: Danshen is an important traditional Chinese medicine (TCM) used for the treatment of cardiovascular and cerebrovascular diseases. Separation and analysis of its components have been widely investigated. However, the systematical two dimensional liquid chromatography (2D-LC) methods have not been developed to comprehensively separate and characterize its components. Objective: In this work, double off-line 2D-LC methods were aimed to develop for the systematical separation of compounds from Danshen. Methods: Using solid phase extraction (SPE), the Danshen extract was divided into a medium-polar fraction (Sample I) and a weak-polar fraction (Sample II) according to their polarities. Based on reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) modes, a 2D-HILIC × RPLC system and a 2D-RPLC × RPLC system were designed for the separation of Sample I and Sample II, respectively. According to reversed-phase and HILIC columns selectivities characterized in our previous reports, ZIC-HILIC and XTerra C18 were employed to build the 2D-HILIC × RPLC system and Click TE-CD and XTerra C18 for the 2D-RPLC × RPLC system, respectively. Results: The 2D-HILIC × RPLC and 2D-RPLC × RPLC systems exhibited excellent orthogonality for the separation of Sample I and Sample II, respectively. Their orthogonalities were 88.42% and 63.24%. Based on these double 2D-LC systems combined with mass spectrometry, at least 200 compounds were found and 33 compounds of them were identified, including 16 phenolic acids and 17 diterpenoid quinines. Conclusion: These results suggest that these two off-line 2D-LC methods are effective for the separation and characterization of components in Danshen.