Acid Mobile Phase Research Articles

NEW STABILITY-INDICATING ULTRA PERFORMANCE LIQUID CHROMATOGRAPHY METHOD DEVELOPMENT AND VALIDATION OF LENVATINIB MESYLATE IN BULK DRUG AND PHARMACEUTICAL DOSAGE FORMS

Objective: The objective of the present study was to develop and validate a new stability-indicating method for the quantification of lenvatinib mesylate in bulk drug and pharmaceutical dosage form using ultra performance liquid chromatography (UPLC).Methods: The optimized chromatographic conditions for elution of drug included UPLC HSS C18 (100 mm × 2.1 mm, 1.8 m) column, mixture of 0.1% orthophosphoric acid and acetonitrile (50:50 v/v%) mobile phase run on an isocratic mode at a flow rate of 0.3 mL/min, 240 nm detection wavelength, and column oven temperature maintained at 30°C.Results: The retention time for lenvatinib was found to be 1.24 min. The developed method was validated for various validation parameters in accordance with the International Conference on Harmonization guidelines. The method obeyed Beer’s law in the concentration range of 2.5– 15 μg/mL with a correlation coefficient of 0.9996. The percentage relative standard deviation and percentage recovery were determined to be 0.4 and 99.66–100.30%, respectively. The developed method was found to be accurate, precise, specific, linear, rugged, and robust. Forced degradation studies were conducted by exposing the drug to diverse stress conditions such as acidic, basic, peroxide, neutral, photolytic, and thermal conditions. The net degradation was obtained within the limits.Conclusion: The developed method for the estimation of lenvatinib can be employed to routine analysis of pharmaceutical dosage form.

HPLC determination of Metronidazole in pure form, pharmaceutical dosage form and spiked urine.

A new HPLC method for the determination of Metronidazole was established. The determination was performed by using a Kinetex C18 analytical column with a gradient mobile phase system consisting of 0.05M KH₂PO4 (pH 3.5), pH adjusted with ortho phosphoric acid (mobile phase A) and Acetonitrile (mobile phase B). The flow rate was 1ml/min. and quantitation was achieved with UV detection at 230 nm, based on peak area. The retention time obtained was 5.35 ± 0.004 and the method was validated according to ICH guidelines regarding linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy, robustness, and selectivity. Excellent linearity was observed for the calibration curve with an excellent correlation coefficient 0.9999. Limit of detection was 0.78 μg mL−1; limit of quantitation 2.37 μg mL−1. The developed method was found to be accurate and sensitive and is ideally suited for analysis of MTZ in pure form, pharmaceutical dosage form and spiked urine samples.

Separation of Triacylglycerols from Edible Oil Using a Liquid Chromatography–Mass Spectrometry System with a Porous Graphitic Carbon Column and a Toluene–Isopropanol Gradient Mobile Phase

AbstractThis study presented a rapid and practical method of separating triacylglycerol (TAG) from edible oil using high‐performance liquid chromatography (LC) coupled with atmospheric‐pressure chemical ionization (APCI)/mass spectrometry (MS) system with a porous graphitic carbon column (150 mm × 2.1 mm, 5 μm) and a toluene–isopropanol–formic acid mobile phase. After investigating the experimental conditions, the gradient toluene–isopropanol mobile phase containing 0.1% formic acid was changed from 50:50 to 80:20 in 30 min; the column temperature was set to 35 °C, and APCI/MS was used in the positive‐ion acquisition mode. The TAG retention displayed a special order and was summarized to fit as follows: S‐ECN (special equivalent carbon number) = 2CN (carbon number) − 3dB (double bond number) – 5uFA (unsaturated fatty‐acid number). Then, the LC–MS method was applied to separate TAG in 6 vegetable oils, resulting in the recognition of 27 TAG in corn oil, 21 TAGs in olive oil, 22 TAG in sunflower seed oil, 28 TAG in soybean oil, 25 TAG in sesame oil, and 31 TAG in peanut oil. The TAG separation through the LC–MS method was rapid, reproducible, and durable.

A Stability-Indicating UPLC Method for the Determination of Potential Impurities and Its Mass by a New QDa Mass Detector in Daclatasvir Drug Used to Treat Hepatitis C Infection.

A stability-indicating ultraperformance liquid chromatographic method has been developed for the quantitative determination of degradation products and process-related impurities of daclatasvir in a pharmaceutical dosage form. Chromatographic separation was achieved on a polar Waters ACQUITY BEH phenyl 100 × 2.1 mm, 1.7-μm column using the gradient program consisting of mobile phase A: 0.03 M sodium perchlorate with 0.002 M of 1-octanesulfonic acid sodium salt (pH 2.5 buffer) and mobile phase B: 0.03 M sodium perchlorate with 0.02 M of 1-octanesulfonic acid sodium salt (pH 2.5 buffer) with acetonitrile in the ratio of 20:80% v/v. A flow rate of 0.4 mL/min is maintained under ultraviolet detection at 305 nm. The run time was 15 min, within which daclatasvir, its related impurities and unknown degradants were well resolved. The method was found to produce symmetric and sharp peaks with good separation between process-related impurities and degradation impurities. Samples were subjected to hydrolysis (acid and base), oxidative, photolytic and thermal stress conditions to prove the stability-indicating nature of the method. The unknown degradation products were identified by PDA/QDa mass detector. This mass spectrum reveals protonated molecular ion peaks [M + H]+ at m/z DP1-582.4 in acid and base hydrolyses and m/z DP2-778.5 in peroxide hydrolysis. The method was validated in terms of specificity, precision, linearity, accuracy, limit of detection, limit of quantification and robustness as per ICH guidelines.

Fast and sensitive method for the determination of trace 1,2,4-triazole and 4-amino-1,2,4-triazole by hydrophilic interaction liquid chromatography (HILIC) in antifungal drug substance

An HILIC method was developed to quantitatively determine trace amounts of 1,2,4-triazole and 4-amino-1,2,4-triazole in fluconazole drug substance. Separation was achieved on HILIC column using isocratic elution with mixture of water, acetonitrile and phosphoric acid mobile phase and UV detection at 205 nm. The method was validated according to ICH guideline requirements and was determined to be linear in the range of 0.6–22.0 μg/mL. Method accuracy and precision were assessed by spiking 1,2,4-triazole and 4-amino-1,2,4-triazole at three levels over the range of 2.5–15 μg/mL, the recoveries ranged from 78.6% to 95.7% for 1,2,4-triazole and 94.6% to 103.4% for 4-amino-1,2,4-triazole. The intermediate precision was represented by the overall %RSD of 6.9% (n = 9) for 1,2,4-triazole and 3.6% (n = 9) for 4-amino-1,2,4-triazole. The method was also shown to be repeatable at concentration levels of 2.5, 12.5 and 15 μg/mL with n = 3 %RSD values of 3.7%, 1.0% and 1.3% for 1,2,4-triazole, and 0.3%, 1.2% and 0.6% for 4-amino-1,2,4-triazole. The method was found to be specific, stability-indicating and has a detection limit of 0.8 μg/mL and a quantitation limit of 2.5 μg/mL. Finally, the method was demonstrated to be robust to small variations of key chromatographic parameters.

An effective validated method for HPTLC-fingerprinting of alkaloids and glycosides from multiple plant parts of three Terminalia spp.

Our study developed a HPTLC fingerprint profile of alkaloids and glycosides obtained from the methanol extracts of four different plant parts of Terminalia arjuna, T. bellerica and T. chebula, trees with cardio-protective values. The multiple qualitative phytochemical analyses of water, acetone, petroleum ether and methanol extracts from all the plant parts of Terminalia spp. detected the presence of alkaloids and glycosides, wherein the methanol extracts exhibited the presence of maximum alkaloids and glycosides. The chromatographic analysis of methanol extracts was carried out on silica gel 60F254HPTLC aluminium sheets with CAMAG Linomat 5 applicator. The plates were developed using ethyl acetate:toluene:formic acid (10:10:1; v/v/v) mobile phase. Alkaloids and glycosides were detected at 254 nm, 366 nm and 540 nm (after derivatization). These developed fingerprints would eventually be of great benefit in identifying or differentiating the alkaloids and glycosides in the form of marker compounds in the three Terminalia spp. mentioned.

Development and Validation of a High-performance Liquid Chromatography-Diode-array Detection Method for the Determination of Eight Phenolic Constituents in Extracts of Different Wine Species.

A new HPLC method was developed and validated for the determination of some phenolic compounds; gallic acid, chlorogenic acid, epigallocatechin, caffeic acid, vanillin, p-coumaric acid, rutin, and quercetin in some local wine and fruit wine samples. Analyses were performed on a Zorbax Eclipse C18 column (4.6 x 150 mm, 3.5-µm particle size) using a gradient system. Mobile phase A was a 10-mM phosphoric acid solution and mobile phase B was methanol using a flow rate of 1 mL/min. Phenolic components were monitored using a DAD at three different wavelengths. The developed and validated method was generally linear between the 1-100 ppm concentration range. Recovery values were obtained in the range of 95-105% and repetitive. The method was successfully applied to investigate the phenolic profiles of different wine samples. As a result of the study, an accurate, sensitive and reliable HPLC-DAD method was developed. The method was successfully used to determine the concentrations of antioxidant phenolic constituents from some local wine extracts.

Improved LC-MS/MS method for the quantification of hepcidin-25 in clinical samples.

Mass spectrometry-based methods play a crucial role in the quantification of the main iron metabolism regulator hepcidin by singling out the bioactive 25-residue peptide from the other naturally occurring N-truncated isoforms (hepcidin-20, -22, -24), which seem to be inactive in iron homeostasis. However, several difficulties arise in the MS analysis of hepcidin due to the "sticky" character of the peptide and the lack of suitable standards. Here, we propose the use of amino- and fluoro-silanized autosampler vials to reduce hepcidin interaction to laboratory glassware surfaces after testing several types of vials for the preparation of stock solutions and serum samples for isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS). Furthermore, we have investigated two sample preparation strategies and two chromatographic separation conditions with the aim of developing a LC-MS/MS method for the sensitive and reliable quantification of hepcidin-25 in serum samples. A chromatographic separation based on usual acidic mobile phases was compared with a novel approach involving the separation of hepcidin-25 with solvents at high pH containing 0.1% of ammonia. Both methods were applied to clinical samples in an intra-laboratory comparison of two LC-MS/MS methods using the same hepcidin-25 calibrators with good correlation of the results. Finally, we recommend a LC-MS/MS-based quantification method with a dynamic range of 0.5-40μg/L for the assessment of hepcidin-25 in human serum that uses TFA-based mobile phases and silanized glass vials. Graphical abstract Structure of hepcidin-25 (Protein Data Bank, PDB ID 2KEF).

Development of an analytical method for urocanic acid isomers in fish based on reactive extraction cleanup and chaotropic chromatography techniques

Urocanic acid (UA), existing in trans- or cis-isoform, is of fairly recent interest to food researchers because of its potential public health hazards of scombrotoxicity and immunotoxicity, as well as associating with fish spoilage. This work is among the first efforts to study the analytical chemistry of UA in fish. With 0.6 M perchloric acid UA was extracted, and co-extracted fish matrix components were efficiently removed through a reactive extraction of UA. The optimum conditions for the reactive extraction, which allowed an 80% recovery of UA, were sample pH adjustment to 9, twice extractions with 32% (w/w) di (2-ethylhexyl) phosphate in hexanol, and a back-extraction with 0.1 M hydrochloric acid at 1:1 phase ratio. A chaotropic hexafluorophosphate salt was added to acidic water-acetonitrile mobile phases to improve the reversed-phase chromatography of UA, which otherwise was poorly retained. Optimum separation conditions were obtained for fish samples and enabled a fast (10 min), convenient-to-use chromatography that clearly outperforms cumbersome legacy ion-pair chromatography. Intended for routine use in our laboratory, the proposed method passed an in-house validation test for linearity, matrix effect (on reactive extraction), accuracy, precision, and detectability.

Determination of Mycophenolic Acid and Mycophenolic Acid Glucuronide Using Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS).

Mycophenolic acid (MPA) is an immunosuppressant that is used in renal, liver, and heart transplantation. Due to its narrow therapeutic range, monitoring of MPA levels is essential to avoid toxicity and organ rejection. Although immunoassays are available for the determination of MPA, due to their higher specificity, mass spectrometry methods are preferred. In this unit, we describe a liquid chromatography tandem mass spectrometry (LC/MS/MS) method utilizing positive ionization electrospray and multiple reaction monitoring (MRM) for the quantification of levels of MPA and its conjugate MPA glucuronide (MPAG). Blood collected in a plain, EDTA, or heparin-containing tube is centrifuged to separate the serum or plasma. Proteins are precipitated using a solution containing zinc sulfate and acetonitrile that has been spiked with deuterated internal standards. The resulting protein-free supernatant is injected into the LC/MS/MS system for analysis. The chromatography involves the use of a C18 column and ammonium acetate/water/formic acid and ammonium acetate/methanol/formic acid mobile phases. Quantification of MPA and MPAG levels is achieved by comparing the MRM peak area ratios of analytes and internal standards, consisting of specific precursor/product pairs, with those of calibrators at various concentrations. Calibration curves are constructed from the MRM peak area ratios of calibrators and internal standards versus concentration. © 2018 by John Wiley & Sons, Inc.

Improving Mass Spectral Quality of Monoclonal Antibody Middle-Up LC-MS Analysis by Shifting the Protein Charge State Distribution.

Monoclonal antibodies (mAbs) are experiencing accelerated development in the pharmaceutical industry. Utilization of middle-up LC-MS methodology can provide detailed characterization of mAbs via reduction and/or enzymatic cleavage of the mAb into smaller protein fragments. However, under typical LC-MS conditions, these fragments, especially the more heterogeneous heavy chain, can present charge state distributions (CSD) featuring a severe interference in the low mass-to-charge (m/z) region in the mass spectrum, adversely impacting spectral quality of these proteins and ultimately the deconvoluted mass spectrum. Here, we introduce a novel method to characterize protein fragments by partially reducing mAbs and using acidic mobile phases (MPs) with a trace amount of base additive. Gas-phase charge stripping occurs with the basic MP additive, causing the CSD to shift to a higher m/z region resulting in high-quality mass spectra with enhanced resolution of protein charge states. Subsequently, high-quality deconvoluted spectra and accurate mass measurement of the fragments are achieved. This method has been applied to the intact mass measurement of mAbs and antibody drug conjugates.

Using High Performance Thin Layer Chromatography-Densitometry to Study the Influence of the Prion [RNQ+] and Its Determinant Prion Protein Rnq1 on Yeast Lipid Profiles.

The baker’s yeast Saccharomyces cerevisiae harbors multiple prions that allow for the creation of heterogeneity within otherwise clonal cell populations. However, in many cases, the consequences of prion infection are entirely unclear. Predictions of prion-induced changes in cell physiology are complicated by pleotropic effects, and detection is often limited to relatively insensitive cell growth assays that may obscure many physiological changes. We previously showed that silica gel high performance thin-layer chromatography-densitometry (HPTLC) can be used to empirically determine prion-induced changes in lipid content in yeast. Here, we conduct pair-wise quantifications of the relative levels of free sterols, free fatty acids, and triacylglycerols [petroleum ether-diethyl ether-glacial acetic acid (80:20:1, v/v/v) mobile phase and phosphomolybdic acid (PMA) detection reagent]; steryl esters, methyl esters, and squalene [hexane-petroleum ether-diethyl ether-glacial acetic acid (50:20:5:1, v/v/v/v) and PMA]; and phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol (chloroform-diethyl ether-acetic acid (65:25:4.5, v/v/v) and cupric sulfate-phosphoric acid) in otherwise clonal prion-infected ([RNQ+]) and prion-free ([rnq−]) cells in both stationary- and logarithmic-growth phases. We detected multiple statistically significant differences between prion-infected and prion-free cells that varied by growth phase, confirming our pr evious observations that prions exert distinct influences on cell physiology between stationary- and log-phase growth. We also found significant differences between cells expressing or lacking the Rnq1 protein which forms the [RNQ+] prion, providing new clues to the as yet unresolved normal biological function of this prion-forming protein. This investigation further emphasizes the utility of HPTLC-densitometry to empirically determine the effects of prions and other presumed innocuous gene deletions on lipid content in yeast, and we expect that additional analyses will continue to resolve the physiological effects of prion infection.

Offline derivatization LC-MS/MS method for simultaneous estimation of vanillin and vanillic acid in guinea pig plasma.

Vanillin used as a positive control substrate of aldehyde oxidase activity gets metabolized to vanillic acid. Low MW and low sensitivity in negative ion mode are challenges with these analytes. Our objective was to develop a simple offline derivatization LC-MS/MS method to address these challenges. A simple dansyl chloride derivatization of the phenolic groups on vanillin and vanillic acid was adopted to enable easy ionization in commonly used acidic mobile phases. Calibration curves were linear over the concentrations of 4.88-1250nM with an LLOQ of 0.64 fmoles on column for both analytes. The qualified method was successfully applied to simultaneously measure vanillin and vanillic acid in plasma and urine from a guinea pig pharmacokinetic study.

DEVELOPMENT AND VALIDATION OF HPTLC METHOD FOR SIMULTANEOUS ESTIMATION OF ERDOSTEINE, GUAIPHENESIN AND TERBUTALINE SULPHATE USING BOX-BEHNKEN DESIGN

The present study was aimed to develop and validate a simple, rapid, accurate, precise, and sensitive HPTLC method using DoE approach for the simultaneous estimation of erdosteine, guaiphenesin and terbutaline sulphate in syrup formulations. HPTLC separation was performed on aluminium plates precoated with silica gel 60 F254 as the stationary phase, three different factors like methanol content, chamber saturation time and distance travelled were optimized using Box-Behnken Design Good separation was obtained with toluene:dichloromethane:methanol:glacial acetic acid (4:4:1.81:0.2; % V/V/ V/V) mobile phase. Quantification was achieved by densitometric analysis of erdosteine, guaiphenesin and terbutaline sulphate over the concentration range of 500-3000, 200-1200 and 25-150 ng/band, respectively, at 225 nm. The method was validated for precision, accuracy, robustness, specificity, limit of detection and limit of quantitation as per ICH guideline. The method was successfully applied for the quantitative determination of erdosteine, guaiphenesin and terbutaline sulphate in in-house dosage form, i.e. syrup.

Determination of Acetaminophen, Dexchlorpheniramine, Caffeine, Cotinine and Salicylic acid in 100 μL of Whole Blood by UHPLC–MS/MS

A sensitive and robust ultra-high-performance liquid chromatography-tandem mass spectrometry method has been developed and validated for the quantification of acetaminophen, dexchlorpheniramine, caffeine, cotinine and salicylic acid in postmortem blood samples from children younger than 4 years. The sample was prepared by a protein precipitation with ice-cold methanol/acetonitrile mixture (85:15, v/v). The organic phase was evaporated to dryness and the residue was dissolved in the mobile phase. Separation, with gradient elution and an acidic mobile phase, was achieved on an Acquity UPLC® HSS T3 column. The compounds were quantified using a multiple reaction-monitoring mode. Two transitions were monitored for each compound and one for the deuterated internal standards. The mass spectrometric detection in the positive ion mode was performed for all the compounds except salicylic acid which was detected in the negative ionization mode. The limits of quantification were as follows: acetaminophen 0.30 mg/L, dexchlorpheniramine 0.0050 mg/L, caffeine 0.099 mg/L, cotinine 0.00035 mg/L and salicylic acid 1.3 mg/L. Between-assay and within-assay precisions were ≤15% (biases: -10% to 26%) and ≤10%, respectively. Extraction recoveries varied from 93% to 137%. The matrix effects in blood, corrected with deuterated internal standards, were 100% ± 10% for all compounds except dexchlorpheniramine (111%) and caffeine (138%).

High-performance Liquid Chromatographic Method for the Quantification of Gallic Acid in Simhanada Guggulu

Marker compounds quantification with new analytical tools and methods is necessary for establishing the authenticity and usage of Ayurvedic or herbal formulations. Simhanada guggulu or guggul is one of the supportive Ayurvedic medicines for treatment of rheumatoid arthritis and used in various disorders in Ayurveda such as limping, anemia, gout, disease of skin, cough, abdominal lump, pain digestive impairment. Simhanada guggulu is an Ayurvedic herbal formulation made by some selected herbs. The rejuvenating and tonic properties of ‘Simhanada guggulu’ are considered majorly due to their antioxidant principles, which in turn is due to the presence of phenolic compounds. A high-performance liquid chromatography (HPLC) method has been developed for quantitative determination of the gallic acid in ‘Simhanada guggulu’. The acidic mobile phase used in RP18 column which enabled efficient separation of gallic acid. A binary gradient with mobile phase containing solvent A (Acetonitrile) and solvent B (water: 0.3% O-Phosphoric Acid) was used for analysis. Elution was carried out at flow rate of 0.8 mL/min. Pure gallic acid Rt was found to be 5.29 min and peak with same Rt was also observed in prepared formulation. Gallic acid content of prepared formulation was found to be 2.28 %. The developed HPLC-UV method is simple, rapid and help as tool for the standardization of Simhanda guggulu.

Semisynthesis and spectral characterization of 5-methylpyranopelargonidin and 4-methylfuropelargonidin and their separation and detection in strawberry fruit wine

Condensation of anthocyanins and their aglycons with small organic molecules yields more stable natural dyes, e.g. pyranoanthocyanins arising spontaneously in various food products. Reaction of pelargonidin with acetone produces two isomeric anthocyanidin dyes − 5-methylpyranopelargonidin and 4-methylfuropelargonidin. A robust semipreparative liquid chromatographic method was developed to isolate both derivatives from a simple aged solution of pelargonidin in methanol: acetone: 37% aqueous hydrochloric acid (1:1:0.008, v/v/v). Detailed interpretation of mass and nuclear magnetic resonance spectra allowed to assign structures of both dyes in isolated fractions. A fast UHPLC–MS method was optimized for the control of their production in the reaction mixture. Use of reversed stationary phase and acidic mobile phases in gradient mode allowed separation of both isomers in less than one minute. Fragmentation of both dyes after collision activated dissociation in collision cell was studied comprehensively and the observed processes were compared with data from quantum calculations (computational chemistry utilizing DFT methods). When comparing both isomers, retro-Diels-Alder fragmentation appears preferred in furo-derivative, while small losses (i.e. methane and water molecules) were more pronounced in pyrano-derivative. Both studied isomeric dyes were found in laboratory prepared strawberry fruit wine and their content was compared with major present anthocyanins and their derivatives.

High-Efficiency Microflow and Nanoflow Negative Electrospray Ionization of Peptides Induced by Gas-Phase Proton Transfer Reactions.

Liquid chromatography coupled with electrospray ionization mass spectrometry (ESI-MS) is routinely used in proteomics research. Mass spectrometry-based peptide analysis is performed de facto in positive-ion mode, except for the analysis of some post-translationally modified peptides (e.g., phosphorylation and glycosylation). Collected mass spectrometry data after peptide negative ionization analysis is scarce, because of a lack of negatively charged amino acid side-chain residues that would enable efficient ionization (i.e., on average, every 10th amino acid residue is negatively charged). Also, several phenomena linked to negative ionization, such as corona discharge, arcing, and electrospray destabilization, because of the presence of polar mobile-phase solutions or acidic mobile-phase additives (e.g., formic or trifluoroacetic acid), reduce its use. Named phenomena influence microflow and nanoflow electrospray ionization (ESI) of peptides in a way that prevents the formation of negatively charged peptide ions. In this work, we have investigated the effects of post-column addition of isopropanol solutions of formaldehyde, 2,2-dimethylpropanal, ethyl methanoate, and 2-phenyl-2-oxoethanal as the negative-ion-mode mobile-phase modifiers for the analysis of peptides. According to the obtained data, all four modifiers exhibited significant enhancement of peptide negative ionization, while ethyl methanoate showed the best results. The proposed mechanism of action of the modifiers includes proton transfer reactions through oxonium ion formation. In this way, mobile phase protons are prevented from interfering with the process of negative ionization. To the best of our knowledge, this is the first study that describes the use and reaction mechanism of aforementioned modifiers for enhancement of peptide negative ionization.

Development and validation of liquid chromatography tandem mass spectrometry method quantitative determination of polymyxin B1, polymyxin B2, polymyxin B3 and isoleucine-polymyxin B1 in human plasma and its application in clinical studies

Polymyxin B (PB) is an antibiotic consisting of a cyclic heptapeptide and a tripeptide side chain used in treatment of infections caused by Gram-negative bacteria. Commercial formulations of PB contain multiple structurally related components with major constituents of PB1, PB2, PB3 and ile-PB1. To understand the pharmacokinetics of these major components, we have developed and validated a LC–MS/MS method to quantify PB1, PB2, PB3 and ile-PB1 in human plasma. PB was extracted from plasma by protein precipitation using trichloroacetic acid followed by chromatographic separation on Zorbax Bonus-RP column (100mm×2.1mm, 1.8μm) using stepwise gradient elution of water containing 0.1% of formic acid and 0.1% of trichloroacetic acid (mobile phase A) and 90% acetonitrile with 0.1% formic acid (mobile phase B). Despite of structural similarities, these PBs were completely resolved in the analytical run time of 6.5min. Detection and quantification of PBs were performed by selected reaction monitoring (SRM) under positive ionization mode in the mass spectrometer. Separation of PB1 and ile-PB1, as well as PB2 and PB3, before quantification is crucial because they are structural isomers detected based the same SRM. Excellent linearity was achieved (r2>0.99) in the calibration curves of PB. The developed method was accurate (95.3–111.7%) and precise (CV<5.1%). Recovery of PB from the plasma extraction was between 53 and 76% and reproducible (CV<4.5%). Matrix effect was not observed by post-column infusion of PB in the mass spectrometer. This methodology has been successfully applied to clinical study of patients dosed with intravenous infusions of PB.

Separation of peptides on superficially porous particle based macrocyclic glycopeptide liquid chromatography stationary phases: consideration of fast separations

Macrocyclic glycopeptide based liquid chromatography stationary phases are known for their highly selective peptide separations. Fast and ultrafast (t R < 1min) high-efficiency separations were achieved with superficially porous particle (SPP)-based stationary phases. Separations of pharmaceutically important classes of peptides such as enkephalins and bradykinins have been achieved in less than 5min in isocratic elution modes. Selectivity for peptides structurally similar to one another was increased with use of teicoplanin-based stationary phases compared with commercial C18 stationary phases. Ultrafast isocratic separations of structurally related peptides were achieved with teicoplanin- and vancomycin-based short SPP columns. Acidic mobile phases produced better separations. Ammonium formate was the optimal mobile phase buffer additive. Use of an appropriate combination of a macrocyclic glycopeptide stationary phase and a mobile phase permits faster and more electrospray ionization mass spectrometry compatible isocratic separations than previous gradient approaches. The tryptic peptide separation characteristics of the teicoplanin stationary phase are demonstrated. Additionally, compared with commercial C18 stationary phases, teicoplanin showed tryptic peptide separations with different selectivities. Graphical Abstract Ultrafast separation of enkephalin peptide epimers.