Evaluation of trifluoroacetic acid as an ion-pair reagent in the separation of small ionizable molecules by reversed-phase liquid chromatography

Quantitative analysis of residual aurintricarboxylic acid in biotherapeutic process streams using liquid chromatography triple quadrupole mass spectrometry

Aurintricarboxylic acid (ATA) is an excipient that can be added to the therapeutic protein manufacturing process as a component of the Chinese hamster ovary (CHO) cell culture media. ATA inhibits cell apoptosis and promotes cell growth in both serum-free and protein-free media. The addition of ATA is beneficial to the manufacturing process at the cell growth stage, however, residual ATA not consumed by cells can have toxicological effects on patients and its removal is required during downstream processing. To ensure manufacturing control and patient safety, the determination of residual ATA during downstream processing of biotherapeutics is required. The aim of this study was to develop and validate a liquid chromatography triple quadrupole mass spectrometry method for monitoring process clearance of ATA during downstream processing. Chromatographic separation of ATA was achieved using a 50 × 3 mm, 3 µm Imtakt Cadenza HS-C18 column and a triple quadrupole mass spectrometer operated in selected reaction monitoring mode was used for sensitive and specific detection. Linearity was assessed over a range of 62.5 ng/mL to 2000 ng/mL. Accuracy and precision were within 20% of the theoretical spike levels across the three concentration levels evaluated utilising two different antibodies, an IgG1 and an IgG4. Analyte specificity and selectivity were deemed acceptable based on no extraneous peaks detected. The method was successfully applied to monitoring process clearance of ATA in a tangential flow filtration (TFF) unit operation for downstream processing of monoclonal antibodies.

Development and Validation of a Reversed-Phase HPLC Method with UV Detection for the Determination of L-Dopa in Vicia faba L. Broad Beans

L-Dopa (LD), a substance used medically in the treatment of Parkinson’s disease, is found in several natural products, such as Vicia faba L., also known as broad beans. Due to its low chemical stability, LD analysis in plant matrices requires an appropriate optimization of the chosen analytical method to obtain reliable results. This work proposes an HPLC-UV method, validated according to EURACHEM guidelines as regards linearity, limits of detection and quantification, precision, accuracy, and matrix effect. The LD extraction was studied by evaluating its aqueous stability over 3 months. The best chromatographic conditions were found by systematically testing several C18 stationary phases and acidic mobile phases. In addition, the assessment of the best storage treatment of Vicia faba L. broad beans able to preserve a high LD content was performed. The best LD determination conditions include sun-drying storage, extraction in HCl 0.1 M, chromatographic separation with a Discovery C18 column, 250 × 4.6 mm, 5 µm particle size, and 99% formic acid 0.2% v/v and 1% methanol as the mobile phase. The optimized method proposed here overcomes the problems linked to LD stability and separation, thus contributing to the improvement of its analytical determination.

Impurity Profiling of Baclofen Using Gradient HPLC–UV Method

The GABAB receptor agonist baclofen is a medication commonly used for the treatment of muscle spasticity. It is an amino acid and related to the neurotransmitter GABA. In this study, we developed a new, gradient high-performance liquid chromatography (HPLC) method for the impurity assessment of baclofen, which is appropriate for pharmacopoeial purposes. Since the impurities related to the synthesis pathway are acids, zwitterionic, or neutral, the method development is challenging. However, the separation of all components was achieved on a C18 stationary phase using a water–acetonitrile–trifluoroacetic acid gradient. A limit of detection (LOD) of at least 0.02% was registered for all specified impurities. Additionally, CAD detection was performed to detect potential impurities lacking off a chromophore. The baclofen batches analyzed are far more pure than expected. All impurities were found below the specification limit, and thus, they can be regarded as unspecified. Moreover, the required runtime could be significantly reduced compared to the current USP or Ph. Eur. method.

Liquid chromatographic separation of alkaloids in herbal medicines: Current status and perspectives

Alkaloids are a widespread group of basic compounds in herbal medicines and have attracted great interest due to various pharmaceutical activities and desirable druggability. Their distinctive structures make chromatographic separation fairly difficult. Peak tailing, poor resolution, and inferior column-to-column reproducibility are common obstacles to overcome. In order to provide a valuable reference, the methodologies and/or strategies on liquid chromatographic separation of alkaloids in herbal medicines proposed from 2012 to 2019 are thoroughly summarized.

Electromembrane extraction of substances with weakly basic properties: a fundamental study with benzodiazepines

Aim: Electromembrane extraction (EME) of weakly basic benzodiazepines was investigated (-1.47 < pKa < 5.01). Materials & Methods: 96-well EME was performed with strongly acidic conditions in the acceptor solution using 250-mM trifluoroacetic acid to maximize ionization. Results & Conclusion: Recoveries more than 80% were obtained for analytes with pKa > 2, whereas EME was less efficient for substances with pKa < 2. The latter was trapped in the supported liquid membrane due to less acidic pH conditions in the acceptor solution close to the supported liquid membrane. EME followed by UHPLC–MS/MS analysis was evaluated from human plasma, and the results were in compliance with EMA guidelines. Both electrokinetic migration and passive diffusion contributed to mass transfer when performing EME of weakly basic analytes.

Quality control of Lycium chinense and Lycium barbarum cortex (Digupi) by HPLC using kukoamines as markers

Background

Lycii Cortex (LyC), composed of Lycium chinense and Lycium barbarum cortex and having the Chinese name Digupi, is used to treat chronic diseases like cough, hypertension, and diabetes in Eastern Asia. However, chromatographic methods, such as TLC and HPLC, to determine the phytochemical composition of LyC have not been included in any official compendiums. This study aims to establish a validated HPLC method for quality control of LyC.

Methods

Kukoamines A and B (KA and KB, respectively) were selected as markers for the HPLC method. An acetic acid solution was adopted for sample extraction because it facilitated the release of kukoamines and effectively prevented their degradation. Optimal separation of the kukoamine isomers was achieved on hydrophilic ligand-coated C18 columns with a gradient elution of acetonitrile and 0.1% (v/v) trifluoroacetic acid. The average contents and proposed contents for LyC were calculated with a t test and an uncertainty test based on 16 batches of authentic samples.

Results

The method was validated with linearity (r² = 0.9999 for both KA and KB), precision (RSD = 1.29% for KA and 0.57% for KB), repeatability (RSD = 1.81% for KA and 0.92% for KB), and accuracy (recovery of 90.03–102.30% for KA, and 98.49–101.67% for KB), indicating that the method could offer reliable results for quality control analysis of LyC. At the 95% confidence level, the calculated content limits were 1.45 mg/g for KA and 4.72 mg/g for KB.

Conclusion

Compared with conventional morphological identification, the HPLC method involving KA and KB contents offers precise, objective, and quantitative results for quality control of LyC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-016-0121-x) contains supplementary material, which is available to authorized users.

Elucidation of molecular interactions between a DBU based protic ionic liquid and organic solvents: thermophysical and computational studies

Energy profile of 1,8-diazabicyclo[5.4.0]undec-7-en-8-ium trifluoroacetate [DBUTFA].

A semi-automated LC-MS/MS method for the determination of LCI699, a steroid 11β-hydroxylase inhibitor, in human plasma

A novel liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the determination of LCI699 was developed and validated with dynamic ranges of 0.0500-50.0 ng/mL and 1.00-1,000 ng/mL using 0.0500 mL and 0.100mL, respectively, of human plasma. LCI699 and the internal standard, [M+6]LCI699, were extracted from fortified human plasma via protein precipitation. After transfer or dilution of the supernatant followed by solvent evaporation and/or reconstitution, the extract was injected onto the LC-MS/MS system. Optimal chromatographic separation was achieved on an ACE C18 (50 mm × 4.6mm, 3 μm) column with 30% aqueous methanol (containing 0.5% acetic acid and 0.05% TFA) as the mobile phase run in isocratic at a flow rate of 1.0 mL/min. The total analysis cycle time is approximately 3.5 min per injection. The addition of an ion-pair reagent, TFA (0.05%, v/v), to the mobile phases significantly improved the chromatographic retention and resolution of the analyte on silica based reversed-phase column. Although addition of TFA to the mobile phase suppresses the ESI signals of the analyte due to its ion-pairing characteristics in the gas phase of MS source, this negative impact was effectively alleviated by adding 0.5% acetic acid to the mobile phase. The current method was validated for sensitivity, selectivity, linearity, reproducibility, stability and recovery. For the low curve range (0.0500-50.0 ng/mL), the accuracy and precision for the LLOQs (0.0500 ng/mL) were -13.0 to 2.0% bias and 3.4-19.2% CV, respectively. For other QC samples (0.100, 6.00, 20.0 and 40.0 ng/mL), the precision ranged from 1.2 to 9.0% and from 3.8 to 8.8% CV, respectively, in the intra-day and inter-day evaluations. The accuracy ranged from -11.3 to 8.0% and -7.2 to 1.6% bias, respectively, in the intra-day and inter-day batches. For the high curve range (1.00-1,000 ng/mL), the accuracy and precision for the LLOQs (1.00 ng/mL) were 1.0-15.0% bias and 7.4-9.2% CV, respectively. For the other QC samples (3.00, 20.0, 200 and 750 ng/mL), the precision ranged from 0.8 to 7.0% and from 1.9 to 5.2% CV, respectively, in the intra-day and inter-day evaluations. The accuracy ranged from -2.5 to 4.0% and 0.7-1.0% bias, respectively, in the intra-day and inter-day batches. Additional assessments of incurred sample stability (ISS) and incurred sample reanalysis (ISR) were conducted to demonstrate the ruggedness and robustness of the assay method. The absence of adverse matrix effect and carryover was also demonstrated. The validated method was successfully used to support rapid turnaround human pharmacokinetic studies.

Selective separation, detection of zotepine and mass spectral characterization of degradants by LC-MS/MS/QTOF

A simple, precise, accurate stability-indicating gradient reversed-phase high-performance liquid chromatographic (RP–HPLC) method was developed for the quantitative determination of zotepine (ZTP) in bulk and pharmaceutical dosage forms in the presence of its degradation products (DPs). The method was developed using Phenomenex C₁₈ column (250 mm×4.6 mm i.d., 5 µm) with a mobile phase containing a gradient mixture of solvents, A (0.05% trifluoroacetic acid (TFA), pH=3.0) and B (acetonitrile). The eluted compounds were monitored at 254 nm; the run time was within 20.0 min, in which ZTP and its DPs were well separated, with a resolution of >1.5. The stress testing of ZTP was carried out under acidic, alkaline, neutral hydrolysis, oxidative, photolytic and thermal stress conditions. ZTP was found to degrade significantly in acidic, photolytic, thermal and oxidative stress conditions and remain stable in basic and neutral conditions. The developed method was validated with respect to specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness as per ICH guidelines. This method was also suitable for the assay determination of ZTP in pharmaceutical dosage forms. The DPs were characterized by LC–MS/MS and their fragmentation pathways were proposed.

Mitigation of signal suppression caused by the use of trifluoroacetic acid in liquid chromatography mobile phases during liquid chromatography/mass spectrometry analysis via post-column addition of ammonium hydroxide

A method has been developed to reduce the mass spectrometric ion signal suppression associated with the use of TFA as an additive in LC mobile phases. Through post-column infusion of diluted NH(4)OH solution to LC eluents, the ammonium ion introduced causes the neutral analyte-TFA ion pair to dissociate which consequently releases the protonated analyte as free ions into the gas phase (through regular electrospray ionization mechanisms). An ion signal improvement from 1.2 to 20 times for a variety of compounds had been achieved through the application of this method. The molar ratios of NH(4)OH:TFA which result in a reduction of signal suppression were determined to be between 0.5:1 and 50:1. In addition, it was shown that this NH(4)OH infusion method could reduce the level of doubly-charged species and the product ions formed via in-source collision. The use of diluted NH(4)OH solution is favorable since it is compatible with mass spectrometry analysis, and it is applicable in both positive and negative-ion generation mode.

Kinetics of changes in glucosinolate concentrations during long-term cooking of white cabbage (Brassica oleracea L. ssp. capitata f. alba)

Brassica vegetables are the predominant dietary source of glucosinolates (GLS) that can be degraded in the intestinal tract into isothiocyanates, which have been shown to possess anticarcinogenic properties. The effects of pilot-scale long-term boiling on GLS in white cabbage (Brassica oleracea L. ssp. capitata f. alba cv. 'Bartolo') was experimentally determined and mathematically modeled. Cabbage was boiled, resulting in a dramatic decrease of 56% in the total GLS levels within the plant matrix during the first 2 min. After 8-12 min of boiling, the decrease progressed to over 70%. Progoitrin had an exceptionally higher decline rate in comparison to all other GLS. As boiling progressed the concentration of all GLS continued to decrease at a lower rate for the remaining cooking period. A mathematical model was used to describe the concentration profile of the GLS in the plant matrix, based on leaching of GLS to the water phase due to cell lysis and thermal degradation of the GLS both in the plant matrix and in the water phase. The model described the concentration profiles very well. Estimated lysis and degradation rate constants for white cabbage differed from those reported in the literature for red cabbage. The degradation rate constants found were significantly higher in the plant matrix when compared to those in the water phase for all GLS. Identification of the kinetics of decline of GLS during cooking can aid in designing processing and preparation methods and determining the conditions for the optimal effects of ingestion of Brassicaceae toward cancer prevention.

Reversed-phase high-performance liquid chromatography behavior of chaotropic counteranions

The retention behavior of inorganic liophilic anions in reversed-phase HPLC columns was studied. Usually, the addition of these ions to the mobile phase influences the retention of protonated basic analytes similar to the effect of amphiphilic ions (ion-pairing agents). The nature of this influence is the subject of this paper. HPLC retention of perchlorate (ClO4-), tetrafluoroborate (BF4-), and hexafluorophosphate (PF6-) ions was studied on six columns with different bonded phases including alkyl, phenyl and perfluorophenyl phases. The effect of the mobile phase ionic strength on the retention of liophilic ions was investigated. The influence of the type of organic modifier, acetonitrile and methanol, on the retention of inorganic ions was also studied and interpreted on the basis of adsorption from solutions. Semi-empirical expression is suggested for the description of the retention profile of studied liophilic ions versus the eluent composition. Significant retention of these ions is observed in acetonitrile-water eluents. Multilayer-type adsorption of the acetonitrile on the reversed-phase surface and its strong dispersive (or pi-pi) interactions with liophilic ions are responsible for significant retention of these ions. This accumulation of liophilic ions in the adsorbed layer on the surface of reversed-phase material introduces an electrostatic component in the retention of protonated basic analytes.

Intact glucosinolate analysis in plant extracts by programmed cone voltage electrospray LC/MS: performance and comparison with LC/MS/MS methods

We present a comprehensive, sensitive, and highly specific negative ion electrospray LC/MS method for identifying all structural classes of glucosinolates in crude plant extracts. The technique is based on the observation of simultaneous maxima in the abundances of the m/z 96 and 97 ions, generated by programmed cone voltage fragmentation, in the mass chromatogram. The abundance ratios lie in the range 1:2-1:4 ([m/z 96]/[m/z 97]). Examination of the corresponding full-scan mass spectra allows individual glucosinolates of all structural classes to be identified rapidly and with confidence. The use of linearly programmed cone voltage fragmentation enhances characteristic fragment ions without compromising the abundance of the analytically important [M - H]- ion and its associated (and analytically useful) sulfur isotope peaks. Detection limits are in the low nanogram range for full-scan, programmed cone voltage spectra. Comparison of the technique with LC/MS/MS methods (product ion, precursor ion, and constant neutral loss scans) has shown that the sensitivity and selectivity of the programmed cone voltage method is superior. Data obtained on a variety of plant extracts confirmed that the methodology was robust and reliable.