Analysis of pharmaceutical impurities using multi-heartcutting 2D LC coupled with UV-charged aerosol MS detection

Two-dimensional liquid chromatography with reversed phase in both dimensions: A review

Two-dimensional liquid chromatography (2D-LC), and in particular comprehensive two-dimensional liquid chromatography (LC×LC), offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal; however, the use of similar separation mechanisms in both dimensions has been gaining popularity as it helps avoid difficulties related to mobile phase incompatibility and poor column efficiency. The remarkable advantages of using reversed phase in both dimensions (RPLC×RPLC) over other separation mechanisms made it a promising technique in the separation of complex samples. This review discusses some physical and practical considerations in method development for 2D-LC involving the use of RP in both dimensions. In addition, an extensive overview is presented of different applications that relied on RPLC×RPLC and 2D-LC with reversed phase column combinations to separate components of complex samples in different fields including food analysis, natural product analysis, environmental analysis, proteomics, lipidomics and metabolomics.

In-silico method development and optimization of on-line comprehensive two-dimensional liquid chromatography via a shortcut model

Comprehensive two-dimensional liquid chromatography (LCxLC) represents a valuable alternative to conventional single column, or one-dimensional, liquid chromatography (1D-LC) for resolving multiple components in a complex mixture in a short time. However, developing LCxLC methods with trial-and-error experiments is challenging and time-consuming, which is why the technique is not dominant despite its significant potential. This work presents a novel shortcut model to in-silico predicting retention time and peak width within an RPLCxRPLC separation system (i.e., LCxLC systems that use reversed-phase columns (RPLC) in both separation dimensions). Our computationally effective model uses the hydrophobic-subtraction model (HSM) to predict retention and considers limitations due to the sample volume, undersampling and the maximum pressure drop. The shortcut model is used in a two-step strategy for sample-dependent optimization of RPLCxRPLC separation systems. In the first step, the Kendall's correlation coefficient of all possible combinations of available columns is evaluated, and the best column pair is selected accordingly. In the second step, the optimal values of design variables, flow rate, pH and sample loop volume, are obtained via multi-objective stochastic optimization. The strategy is applied to method development for the separation of 8, 12 and 16 component mixtures. It is shown that the proposed strategy provides an easy way to accelerate method development for full-comprehensive 2D-LC systems as it does not require any experimental campaign and an entire optimization run can take less than two minutes.

Determination of genotoxic impurities of aromatic aldehydes in pharmaceutical preparations by high performance liquid chromatography after derivatization with N-Cyclohexyl-4-hydrazino-1,8-naphthalenediimide

The detection of aromatic aldehydes, considered potential genotoxic impurities, holds significant importance during drug development and production. Current analytical methods necessitate complex pre-treatment processes and exhibit insufficient specificity and sensitivity. This study presents the utilization of naphthalenediimide as a pre-column derivatisation reagent to detect aromatic aldehyde impurities in pharmaceuticals via high-performance liquid chromatography (HPLC). We screened a series of derivatisation reagents through density functional theory (DFT) and investigated the phenomenon of photoinduced electron transfer (PET) for both the derivatisation reagents and the resulting products. Optimal experimental conditions for derivatisation were achieved at 40 °C for 60 min. This approach has been successfully applied to detect residual aromatic aldehyde genotoxic impurities in various pharmaceutical preparations, including 4-Nitrobenzaldehyde, 2-Nitrobenzaldehyde, 1,4-Benzodioxane-6-aldehyde, and 5-Hydroxymethylfurfural. The pre-column derivatisation method significantly enhanced detection sensitivity and reduced the limit of detection (LOD), which ranged from 0.002 to 0.008 μg/ml for the analytes, with relative standard deviations < 3 %. The correlation coefficient (R2) >0.998 demonstrated high quality. In chloramphenicol eye drops, the concentration of 4-Nitrobenzaldehyde was measured to be 8.6 µg/mL below the specified concentration, with recoveries ranging from 90.0 % to 119.2 %. In comparison to existing methods, our work simplifies the pretreatment process, enhances the sensitivity and specificity of the analysis, and offers comprehensive insights into impurity detection in pharmaceutical preparations.

Trapping mode two-dimensional liquid chromatography for quantitative low-level impurity enrichment in pharmaceutical development

Trapping mode two-dimensional liquid chromatography (2D-LC) has recently found applications in pharmaceutical analysis to clean, refocus, and enrich analytes. Given its enrichment capability, 2D-LC with multiple trappings is appealing for low-level impurity monitoring that cannot be solved by single dimensional LC (1D-LC) or unenriched 2D-LC analysis. However, the quantitative features of multi-trapping 2D-LC remain largely unknown at impurity levels from parts-per-million (ppm) to 0.15% (w/w). We present a simple heart-cutting trapping mode 2D-LC workflow using only common components and software found in typical off-the-shelf 1D-LC instruments. This robust, turn-key system's quantitative capabilities were evaluated using a variety of standard markers, demonstrating linear enrichment for up to 20 trapping cycles and achieving a recovery of over 97.0%. Next, the trapping system was applied to several real-world low-level impurity pharmaceutical case studies including (1) the identification of two unknown impurities at sub-ppm levels resulting in material discoloration, (2) the discovery of a new impurity at 0.05% (w/w) co-eluted with a known impurity, making the undesired summation above the target specification, and (3) the quantification of a potential mutagenic impurity at 10-ppm level in a poorly soluble substrate. The recovery in all studies was better than 97.0% with RSD lower than 3.0%, demonstrating accuracy and precision of the 2D-LC trapping workflow. As no specialized equipment or software is required, we envision that the system could be used to develop low-impurity monitoring methods suitable for validation and potential execution in quality-control laboratories.

Separation and structural characterization of unknown impurity in vancomycin by two-dimensional preparative liquid chromatography, LC-MS and NMR

Vancomycin is an effective antibiotic used for the treatment of Gram-positive bacterial infections. During the analysis of vancomycin, an unknown impurity at the level of 0.5% was detected by high-performance liquid chromatography (HPLC). To characterize the structure of the impurity, a new two-dimensional preparative liquid chromatography (2D-Prep-LC) method was developed to separate the impurity from the vancomycin sample. After further analysis including liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy, the structure of the unknown impurity was identified as a vancomycin analog in which the N-Methyl-leucine residue on the side chain is replaced by an N-methylmethionine residue. In this study, we established a reliable and efficient method for separating and identifying vancomycin impurities, which will provide a valuable contribution to the field of pharmaceutical analysis and quality control.

Two-dimensional reversed phase-normal phase liquid chromatography for simultaneous achiral-chiral analysis to support high-throughput experimentation

Typical chromatographic analysis of chiral compounds requires the use of achiral methods to evaluate impurities or related substances along with separate methods to evaluate chiral purity. The use of two-dimensional liquid chromatography (2D-LC) to support simultaneous achiral-chiral analysis has become increasingly advantageous in the field of high-throughput experimentation where low reaction yields or side reactions can lead to challenging direct chiral analysis. Advancements in multi-dimensional chromatography have led to the development of robust 2D-LC instrumentation with reversed phase solvent systems (RPLC-RPLC) enabling this simultaneous analysis, eliminating the need to purify crude reaction mixtures to determine stereoselectivity. However, when chiral RPLC cannot separate a chiral impurity from the desired product, there are few viable commercial options. The coupling of NPLC to RPLC (RPLC-NPLC) continues to remain elusive due to solvent immiscibility between the two solvent systems. This solvent incompatibility leads to lack of retention, band broadening, poor resolution, poor peak shapes, and baseline issues in the second dimension. A study was conducted to understand the effect of various water-containing injections on NPLC and applied to the development of robust RPLC-NPLC methods. Following thoughtful consideration and modifications to the design of a 2D-LC system in regards to mobile phase selection, sample loop sizing, targeted mixing, and solvent compatibility, proof of concept has been demonstrated with the development of reproducible RPLC-NPLC 2D-LC methods to perform simultaneous achiral-chiral analysis. Second dimension NPLC method performance proved comparable to corresponding 1D-NPLC methods with excellent percent difference in enantiomeric excess results ≤ 1.09% and adequate limits of quantitation down to 0.0025 mg/mL for injection volumes of 2 µL, or 5 ng on-column.

Simplification of pharmacopoeial liquid chromatography methods for related substances of statins by hyphenated ultraviolet and charged aerosol detection

For a more comprehensive characterization of a drug substance and its impurities, multidetector approaches are a helpful tool in liquid chromatography. In particular, the relatively inexpensive hyphenation of the ultraviolet (UV) with the charged aerosol detector (CAD) extends the scope from UV-active to non- or weak chromophore analytes, respectively. In this study, the chromatographic methods of the test for related substances of simvastatin and lovastatin in the European Pharmacopoeia were adapted to UV-CAD and thus allowing a more sophisticated detection of the weak chromophore dihydro impurity besides the other UV-active impurities. The compendial gradient program for simvastatin had to be modified (lowered initial acetonitrile percentage and increased gradient slope) because an additional critical peak pair emerged with the Hypersil C₁₈ BDS column used here. Therefore, a Plackett-Burman design with 11 factors (including 4 dummy factors) was chosen to evaluate robustness of the adapted method. The flow rate, initial acetonitrile percentage, and column temperature were identified as three critical parameters that had to be carefully observed. Finally, the validity of the method for simultaneous detection of dihydrosimvastatin with CAD and of lovastatin and simvastatin as examples of UV detection was verified according to ICH Q2 (R1). In the case of lovastatin, the direct comparison with the pharmacopoeial method reveal that a determination with CAD is the more sensitive method.

Multi-2D LC × LC as a Novel and Powerful Implement for the Maximum Separation of Complex Samples

Achieving complete information about the chemical composition of complex samples requires the use of multianalytical platforms able to maximize the acquisition of high-quality data for unequivocal identification. However, this process requires long analysis times and several instruments. Food analysis is one of the analytical fields where the analysis of very complex samples has a huge impact. One of these complex samples is vermouth, a fortified wine based on the maceration of a large number of herbs, fruits, barks, seeds, and leaves. The application of conventional or even advanced analytical techniques like comprehensive two-dimensional (2D) liquid chromatography (LC × LC) does not provide enough separation power to resolve the complete profile of this sample. In this work, a novel 2DLC strategy called multi-²D LC × LC is developed. This new setup consists of the use of two different columns with different separation properties in the second dimension (²D) that can be selected during the LC × LC analysis accordingly to the chemical nature of the compounds eluted from the first dimension (¹D). The vermouth sample was analyzed using a ¹D-PFP and a combination of HILIC (from 0 to 30 min) and C18 (from 30 to the end) columns in the ²D. This setup increased both the peak capacity and the orthogonality of the analysis in comparison to the use of only one of the columns in the ²D. Multi-²D LC × LC is presented as an integrated 2DLC tool that maximizes the separation capacity for very complex samples.

Multiple Heart-Cutting Two-Dimensional HPLC-UV Achiral–Chiral Analysis of Branched-Chain Amino Acids in Food Supplements under Environmentally Friendly Conditions

A multiple heart-cutting (mLC-LC) two-dimensional HPLC-UV achiral–chiral method for the direct analysis of branched-chain amino acids (BCAAs) in food supplements under environmentally friendly conditions was developed to cope with the very well-known limited chemoselectivity of chromatographic media for enantioselective analysis. Both achiral and chiral methods were developed in compliance with the main principles of green chromatography. The achiral analysis was performed isocratically with an optimized ion-pair reversed-phase (IP-RP) method based on a water/EtOH (95:5, v/v) mobile phase containing heptafluorobutyric acid (7 mM) as the IP agent. The achiral method was characterized by a very appreciable performance and was validated before the analysis of the real sample. High recovery values for all compounds (from 97% to 101%) were found in the interday evaluation. Additionally, low RSD% values in the long-term period were measured, in the range between 1.1% and 4.8%. Still, an LOQ value of 0.06 mg/mL was established for all compounds. The quantitative analysis of a commercial food supplement revealed that BCAAs were present in amounts very close to those declared by the producer. The enantioselective analysis was carried out through the application of the chiral ligand-exchange chromatography (CLEC) approach, using O-benzyl-(S)-serine ((S)-OBS, 0.5 mM) as the chiral selector and Cu(II) nitrate (0.25 mM) as the metal source in the eluent. Resolution and separation factor values up to 2.31 and 1.43, respectively, were obtained. The two chromatographic systems were connected through a six-port switching valve, and the developed two-dimensional mLC-LC method confirmed the absence of D-enantiomers of BCAAs in the food supplement, as reported in the manufacturer’s label.

Liquid chromatography coupled with photodiode array and a multivariate curve resolution - Alternating least square algorithm for identification and quantification of co-eluting impurities in pharmaceutical analysis

This paper systematically investigated and reported for the first time the identification and quantification of co-eluting impurities as low as 0.05 area% by PDA with i-PDeA II deconvolution software in the LabSolutions Chromatographic Data System (CDS) using an integrated multivariate curve resolution-alternating least squares (MCR-ALS) algorithm with a bidirectional exponentially modified Gaussian (BEMG) model function. The algorithm was able to consistently identify 0.05% impurities when co-eluting with the main component (Rs ≥ 0.8) as well as when co-eluting with another impurity (Rs ≥ 0.5). In the case of two co-eluting impurities from 0.05% to 1% (Rs ≥ 0.5), the quantification error ranged from +10.6% to -16.7%. In the case of an impurity co-eluting with the main component (Rs ≥ 0.8), the quantification error was 4.4-8.9% for 1% impurity and 109-184% for 0.05% impurity. The precision was excellent for the range of 0.05-1.0% impurities with the RSD being 1.4-3.0% for 1% impurity and 4.0-8.7% for 0.05% impurity. The identification rate and quantitation accuracy were not affected by the spectral similarity of the molecules, as comparable results were obtained by analyzing two molecules with low similarity (4,4-difluorobenzophenone and valerophenone) and two molecules with high similarity (diazepam and oxazepam) based on simulated data. This peak resolution by MCR-ALS approach provides fast and robust identification and quantification of co-eluting impurities even when method development efforts do not provide complete separation of the target peaks, and could therefore find a wide range of applications in pharmaceutical and other types of analyses.

Characterization of positional isomers of drug intermediates by off-line RPLC x SFC hyphenated to high resolution MS

Many steps are needed in the synthesis of a new active pharmaceutical ingredient (API). In a practical case proposed by a French pharmaceutical company, an intermediate synthesis step, needed to protect 8 hydroxyl groups before oxidation, could produce a mixture of neutral compounds containing up to 652 structures being positional isomers of 18 molecular formulas. Some mixtures allowed obtaining the desired API, others did not. An efficient analytical method was needed to characterize these neutral positional isomers and identify the mixtures to reject. Two samples were provided by the pharmaceutical company: Sample A was conform, Sample B was not. 8 RPLC columns were used with different gradients to screen Sample A. Next, the best RPLC separation was used as the second dimension fast analysis in a comprehensive 2D-RPLC systems. Two columns were used as first dimension: a fluorinated one and a zirconium based one. An order of magnitude was gained in peak capacity, but a better sample characterization was still needed. An off-line RPLC x SFC x Q-TOF/MS analysis was performed collecting 96 RPLC fractions and analyzing them by SFC with Q-TOF/MS detection. A home-made software associated the 96 SFC MS chromatograms to produce either base peak (BPC) or extract ion (EIC) contour plots that allowed for a satisfying characterization of the samples. Subtracting the EIC of expected m/z compounds from the Sample B BPC contour plot produced a unique new contour plot clearly pointing out unexpected compounds explaining the failure of the synthesis and possibly allowing improving the synthesis process.

Achiral-Chiral Two-Dimensional Liquid Chromatography Platform to Support Automated High-Throughput Experimentation in the Field of Drug Development

Automated high-throughput experimentation (HTE) is a powerful tool for scientists to explore and optimize chemical transformations by simultaneously screening yield, stereoselectivity, and impurity profiles. To analyze the HTE samples, high-throughput analysis (HTA) platforms must be fast, accurate, generic, and specific at the same time. A large amount of high-quality data is critical for the success of machine learning models in the era of big data. Conventional chiral liquid chromatography-mass spectrometry (LC/MS) HTE methods are hampered by compound co-eluting, possible ion suppression, and limited chiral column lifetime in the presence of crude reaction mixtures or complex sample matrices. To overcome these limitations, a generic and fast achiral-chiral heart-cutting two-dimensional (2D)-LC method has been developed to determine both the yield and stereoselectivity of chemical transformations within a 10 min run time. Successful implementation of the 2D-LC HTA platform in a routine drug development environment was achieved for real-world project support, with the analysis so far of over 2000 reaction mixtures prepared in the 96-well plate format. Excellent performance of the method was demonstrated by relative standard deviation (RSD) lower than 0.83% for the ¹D and ²D retention times, and determination coefficients higher than 0.99. The presented HTA 2D-LC platform has had a significant impact on drug development by analyzing the HTE samples rapidly with unambiguous peak tracking and providing a robust approach for accurately generating a large amount of high-quality data in a short time.

Enhancing online protein isolation as intact species from soy flour samples by actively modulated two-dimensional liquid chromatography (2D-LC)

In this study, an enhanced fully automated approach is described for the protein isolation from soy flour samples by two-dimensional liquid chromatography with active modulation interface. The use of two multi-port switching valves is proposed to on-line connect the first to the second dimension column, thus overcoming the problems associated with the re-mixing effects and incompatibility of eluent composition and pH. A 5-cm long C4 analytical column installed in the interface device allows to focus the proteins coming from the first column (size exclusion chromatography), before their selective elution in the second column (reversed-phase). A trap washing step was included in the total workflow, as a desalting step to remove buffer residues from the eluent of the first column and to enhance the chromatographic performances of the second column. The experimental conditions were optimized by analyses of mixed standard solutions of bovine serum albumin, glucose oxidase, immunoglobulin A, thyroglobulin and myoglobin. Then, the optimized 2D-LC method was applied to the protein analysis in extracts of soy flour, known worldwide as one of the major food allergen sources, with the final aim to recovery sufficient protein amounts for the molecular characterization and the assessment of the pattern of allergenic components.

Quality control and testing evaluation of pharmaceutical aerosols

Drug delivery to the respiratory tract locally has become an increasingly effective and important therapeutic method for treating a variety of pulmonary disorders, including chronic abstractive disease, asthma, bronchitis, pneumonia, and cystic fibrosis. Increase in prevalence respiratory disorders is a major factor driving the growth of global respiratory inhaler devices market. The effectiveness of pharmaceutical aerosols therapeutic performance is affected by various factors such as type and characteristics of propellants, whose properties are vapor pressure of propellants, viscosity and density flash point and also other factors such as type and characteristics of active ingredients, containers, valves, and actuators, along with percentage of moisture content and mechanism of emitted dose deposition, spray pattern, efficiency of valve crimping, and measurement of particle size aerosols. The purpose of this book chapter is to discuss the in-process and finished product quality control tests for pharmaceutical aerosols based on pharmacopeia standards and specifications.

Seeking universal detectors for analytical characterizations

It is highly desirable to have a universal detector that can detect all types of compounds and give a uniform response regardless of the physiochemical properties of the compounds. With such a universal detector, all components in a sample can be accurately quantified without the need for individual standards. This is especially needed for the characterization of unknowns and for non-targeted analysis, or for samples that have no isolated standards available for each component. Over the years, much effort has been put into seeking a universal detection technology. In this review, we discuss the commonly used detectors for analytical characterization, including UV, RI, ELSD, CAD, CLND, FID, VUV, MS, NMR, and hyphenated detection, with the focuses on the "universal" features of these detectors regarding the types of molecules they can detect and the uniformity of responses.

The use of online heart-cutting high-performance liquid chromatography coupled with linear ion trap mass spectrometry in the identification of impurities in vidarabine monophosphate

It is difficult to identify unknown impurities in nucleotide analogues by mass spectrometry because mass-spectrometry-incompatible mobile phases need to be used to separate the major ingredient from impurities. In this study, vidarabine monophosphate was selected, and unknown impurities were identified by online heart-cutting two-dimensional high-performance liquid chromatography and linear ion trap mass spectrometry. The one-dimensional reversed-phase column was filled with a mobile phase containing nonvolatile salt. In two-dimensional high-performance liquid chromatography, we used an Acclaim Q1 column with volatile salt, and the detection wavelength was 260 nm. The mass spectrum was scanned in positive- and negative-ion mode. The online heart-cutting and online demineralization technique ensured that the mobile phase was compatible with mass spectrometry; seven impurities were identified by MS² and MS³ fragments. The mass fragmentation patterns of these impurities were investigated. The two isomers were semiprepared and complemented by nuclear magnetic resonance. The results were further compared with those of normal-phase high-performance liquid chromatography with mass spectrometry. The online heart-cutting two-dimensional high-performance liquid chromatography with mass spectrometry was superior in identifying more impurities. The method solves the problem of incompatibility between the mobile phase and mass spectrometry, so it is suitable for identifying unknown impurities. This method may also be used for investigating impurities in other nucleotide analogues.

Restriction capillaries as an innovative mixing unit for intermediate mobile phase exchange in multidimensional analysis

A novel mixing unit is proposed for the serial coupling of orthogonal columns to analyze polar and non-polar compounds in a single run. The principle relies on the isolation of unretained peaks eluting from a first dimension column in a sample loop, before directing them to a second column for separation. Since the mobile phases employed in highly orthogonal separations are not directly compatible, a mixing unit is required to alter the mobile phase composition before executing the second dimension separation. The mixing unit proposed in this work is based on the use of two restriction capillaries with different flow resistances to dilute the mobile phase eluting from the first dimension with a solvent appropriate for the second dimension separation. The restriction capillaries are implemented in an ultra-high performance liquid chromatography set-up using three high-pressure switching valves and two T-pieces. It is demonstrated that the dilution ratio can be adequately predicted using the law of Hagen-Poiseuille and can be adjusted easily by changing the dimensions of the restriction capillaries. The dilution volume required to obtain acceptable recoveries is investigated and the use of different column diameters in the first and second dimension is proposed to increase the sensitivity of the analysis. Under optimum dilution conditions, recoveries ranging between 82% and 99% are always obtained, while repeatability values are excellent. The proof-of-concept of the different set-ups is demonstrated for the separation of 20 pharmaceuticals with log D-values ranging between -5.75 and 4.22.

Validation of a two-dimensional liquid chromatography method for quality control testing of pharmaceutical materials

Despite the advantages of 2D-LC, there is currently little to no work in demonstrating the suitability of these 2D-LC methods for use in a quality control (QC) environment for good manufacturing practice (GMP) tests. This lack of information becomes more critical as the availability of commercial 2D-LC instrumentation has significantly increased, and more testing facilities begin to acquire these 2D-LC capabilities. It is increasingly important that the transferability of developed 2D-LC methods be assessed in terms of reproducibility, robustness and performance across different laboratories worldwide. The work presented here focuses on the evaluation of a heart-cutting 2D-LC method used for the analysis of a pharmaceutical material, where a key, co-eluting impurity in the first dimension (¹D) is resolved from the main peak and analyzed in the second dimension (²D). A design-of-experiments (DOE) approach was taken in the collection of the data, and the results were then modeled in order to evaluate method robustness using statistical modeling software. This quality by design (QBD) approach gives a deeper understanding of the impact of these 2D-LC critical method attributes (CMAs) and how they affect overall method performance. Although there are multiple parameters that may be critical from method development point of view, a special focus of this work is devoted towards evaluation of unique 2D-LC critical method attributes from method validation perspective that transcend conventional method development and validation. The 2D-LC method attributes are evaluated for their recovery, peak shape, and resolution of the two co-eluting compounds in question on the ²D. In the method, linearity, accuracy, precision, repeatability, and sensitivity are assessed along with day-to-day, analyst-to-analyst, and lab-to-lab (instrument-to-instrument) assessments. The results of this validation study demonstrate that the 2D-LC method is accurate, sensitive, and robust and is ultimately suitable for QC testing with good method transferability.

Compatibility study of a parenteral microdose polyethylene glycol formulation in medical devices and identification of degradation impurity by 2D-LC/MS

Polyethylene glycol (PEG) based formulation and polyvinylchloride (PVC) tubing are frequently used for drug delivery and administration. The compatibility of a parenteral drug microdose formulation in intravenous infusion (IV) devices was studied to support the clinical determination of absolute bioavailability by the microdosing method. The investigational microdose formulation containing PEG was found prone to significant loss of potency within hours of storage in the PVC IV tubing due to degradation. Degradation occurred only when both PEG and PVC tubing were present. The degradation product could not be detected by LC/MS due to the significant interference from the high concentration of PEG (4%) matrix and the extremely low level of drug (0.6ppm). To obtain structural information of the degradation impurity and understand the cause of the degradation, a simple heart-cutting 2D-LC/MS approach was utilized to effectively separate the impurity from the complex PEG oligomers and overcome the matrix interference, enabling mass spectrometric analysis of the impurity. An oxidation- dominated mechanism was proposed in which the combination of PEG auto-oxidation and dehydrochlorination of the PVC tubing yielded an oxidative environment that enhanced radical propagation and accelerated degradation of the investigational parent drug.

Antibody-drug conjugate characterization by chromatographic and electrophoretic techniques

Due to the inherent structure complexity and component heterogeneity of antibody drug conjugates (ADCs), separation technologies play a critical role in their characterization. In this review, we focus on chromatographic and electrophoretic approaches used to characterize ADCs with respect to drug-to-antibody ratio, drug distribution and conjugation sites, free small molecule drugs, charge variants, aggregates and fragments, etc. Chromatographic techniques including reversed-phase, ion exchange, size exclusion, hydrophobic interaction, two-dimensional liquid chromatography, and gas chromatography as well as capillary electrophoretic techniques including capillary electrophoresis sodium dodecyl sulfate, capillary zone electrophoresis and capillary isoelectric focusing are reviewed for their applications in the characterization of ADCs.

A sensitive multidimensional method for the detection, characterization, and quantification of trace free drug species in antibody-drug conjugate samples using mass spectral detection

Conjugation processes and stability studies associated with the production and shelf life of antibody-drug conjugates (ADCs) can result in free (non-conjugated) drug species. These free drug species can increase the risk to patients and reduce the efficacy of the ADC. Despite stringent purification steps, trace levels of free drug species may be present in formulated ADCs, reducing the therapeutic window. The reduction of sample preparation steps through the incorporation of multidimensional techniques has afforded analysts more efficient methods to assess trace drug species. Multidimensional methods coupling size-exclusion and reversed phase liquid chromatography with ultra-violet detection (SEC-RPLC/UV) have been reported, but offer limited sensitivity and can limit method optimization. The current study addresses these challenges with a multidimensional method that is specific, sensitive, and enables method control in both dimensions via coupling of an on-line solid phase extraction column to RPLC with mass spectral detection (SPE-RPLC/MS). The proposed method was evaluated using an antibody-fluorophore conjugate (AFC) as an ADC surrogate to brentuximab vedotin and its associated parent maleimide-val-cit-DSEA payload and the derived N-acetylcysteine adduct formed during the conjugation process. Assay sensitivity was found to be 2 orders more sensitive using MS detection in comparison to UV-based detection with a nominal limit of quantitation of 0.30 ng/mL (1.5 pg on-column). Free-drug species were present in an unadulterated ADC surrogate sample at concentrations below 7 ng/mL, levels not detectable by UV alone. The proposed SPE-RPLC/MS method provides a high degree of specificity and sensitivity in the assessment of trace free drug species and offers improved control over each dimension, enabling straightforward integration into existing or novel workflows.

Recent advances in 2D-LC for bioanalysis

This article summarizes the most important developments in the use of 2D-LC for bioanalysis in the last 5 years. While several interesting and powerful applications have been developed recently, this work has been supported by continued, significant development of theoretical concepts, instrument development and practical aspects of method development. Some of the most exciting applications have been focused on the use of 2D-LC and characterize proteins both as biotherapeutic drug substances, and in formulations. These materials are inherently complex, difficult to resolve chromatographically and present problems that are essentially unknown (e.g., aggregation) in the small molecule world, thus 2D-LC can be leveraged very effectively to address these challenges.

A rapid on-line method for mass spectrometric confirmation of a cysteine-conjugated antibody-drug-conjugate structure using multidimensional chromatography

Cysteine-conjugated antibody-drug conjugates (ADCs) are manufactured using controlled partial reduction and conjugation chemistry with drug payloads that typically occur in intervals of 0, 2, 4, 6, and 8. Control of heterogeneity is of particular importance to the quality of ADC product because drug loading and distribution can affect the safety and efficacy of the ADC. Liquid chromatography ultra-violet (LC-UV)-based methods can be used to acquire the drug distribution profiles of cysteine-conjugated ADCs when analyzed using hydrophobic interaction chromatography (HIC). However, alternative analysis techniques are often required for structural identification when conjugated drugs do not possess discrete ultra-violet absorbance properties for precise assessment of the drug-to-antibody ratio (DAR). In this study, multidimensional chromatography was used as an efficient method for combining non-compatible techniques, such as HIC, with analysis by mass spectrometry (LC/LC/QTOF-MS) for rapid on-line structural elucidation of species observed in HIC distribution profiles of cysteine-conjugated ADCs. The methodology was tested using an IgG1 mAb modified by cysteine conjugation with a non-toxic drug mimic. Structural elucidation of peaks observed in the HIC analysis (1^st dimension) were successfully identified based on their unique sub-unit masses via mass spectrometry techniques once dissociation occurred under denaturing reversed phase conditions (2^nd dimension). Upon identification, the DAR values were determined to be 2.83, 4.44, and 5.97 for 3 drug load levels (low-, medium-, and high-loaded ADC batches), respectively, based on relative abundance from the LC-UV data. This work demonstrates that multidimensional chromatography coupled with MS, provides an efficient approach for on-line biotherapeutic characterization to ensure ADC product quality.