Current state and future perspectives of supercritical fluid chromatography

Economical and rapid enantioselective, diastereoselective and achiral separation of palonosetron hydrochloride and its impurities using supercritical fluid chromatography

Simultaneous separation of compounds with multiple chiral centers and highly similar structures presents significant challenges. This study developed a novel supercritical fluid chromatography (SFC) method with reduced organic solvent consumption and robust separation capabilities to address these challenges. The method was applied to simultaneously achieve enantioselective, diastereoselective, and achiral separation of palonosetron hydrochloride and its six impurities. The effects of the polysaccharide-based chiral stationary phase (CSP), modifier, additive, and column temperature on retention and separation were comprehensively evaluated. It was found that a combination of a polysaccharide-based CSP and a single modifier or a mixture of protonic modifiers could not achieve complete separation due to high structural similarity. However, an ADH column and a ternary solvent mixture containing acetonitrile (methanol: acetonitrile: diethylamine, 60:40:0.2, v/v/v) provided satisfying separation, particularly for the enantiomer and diastereomers of palonosetron. Using the optimized method, the enantioselective, diastereoselective, and achiral separation of palonosetron hydrochloride and its six impurities can be accomplished in 18 min under gradient elution. Thermodynamic results indicated that the separation process was entropy driven. A molecular docking study revealed that the separation was mainly achieved through the differences in hydrogen bond and π - π interactions between the analytes and CSP. This study lays the foundation for SFC analysis of palonosetron hydrochloride and provides a reference for the simultaneous SFC separation of the enantiomers, diastereoisomers and structurally similar compounds.

Characterization of a Soft Ionization by Chemical Reaction in Transfer Ion Source Hyphenated With Supercritical Fluid Chromatography-Tandem Mass Spectrometry

A commercially available dielectric barrier discharge ionization (DBDI) source was tested with supercritical fluid chromatography-mass spectrometry (SFC-MS). The compound mixture investigated comprised caffeine, theobromine, theophylline, uracil, testosterone, and pyrene, diluted in methanol. Dynamic response ranges were evaluated with multiple injections at different concentrations. Precision studies demonstrated the robustness and sensitivity of the ionization source across a concentration range of 10-1000 ng/mL. Results from this experiment showed linear regression of 0.99 or greater for all analytes tested over the range with a relative standard deviation (RSD) of less than 10% down to 10 ng/mL for all analytes except theobromine, which had an RSD of less than 10% down to 25 ng/mL. Notably, this study marks the first investigation of sensitivity for coupling a commercial DBDI source with SFC; a limit of detection less than 1 ng/mL was achieved for all compounds. This study demonstrates chromatographic separation by SFC and MS analysis for compounds that ionize poorly using traditional atmospheric pressure ionization, such as polycyclic aromatic hydrocarbons. Combining SFC with the DBDI source opens promising avenues for analyzing compounds that were previously challenging to characterize with standard atmospheric pressure ionization techniques.

Advancing Fundamental Understanding of Retention Interactions in Supercritical Fluid Chromatography Using Artificial Neural Networks: Polar Stationary Phases with -OH Moieties

The retention behavior in supercritical fluid chromatography and its stability over time are still unsatisfactorily explained phenomena despite many important contributions in recent years, especially focusing on linear solvation energy relationship modeling. We studied polar stationary phases with predominant -OH functionalities, i.e., silica, hybrid silica, and diol columns, and their retention behavior over time. We correlated molecular descriptors of analytes with their retention using three organic modifiers of the CO2-based mobile phase. The differences in retention behavior caused by using additives, namely, 10 mmol/L NH3 and 2% H2O in methanol, were described in correlation to analyte properties and compared with the CO2/methanol mobile phase. The structure of >100 molecules included in this study was optimized by semiempirical AM1 quantum mechanical calculations and subsequently described by 226 molecular descriptors including topological, constitutional, hybrid, electronic, and geometric descriptors. An artificial neural networks simulator with deep learning toolbox was trained on this extensive set of experimental data and subsequently used to determine key molecular descriptors affecting the retention by the highest extent. After comprehensive statistical analysis of the experimental data collected during one year of column use, the retention on different stationary phases was fundamentally described. The changes in the retention behavior during one year of column use were described and their explanation with a proposed interpretation of changes on the stationary phase surface was suggested. The effect of the regeneration procedure on the retention was also evaluated. This fundamental understanding of interactions responsible for retention in SFC can be used for the evidence-based selection of stationary phases suitable for the separation of particular analytes based on their specific physicochemical properties.

Insights on the Extraction and Analysis of Phenolic Compounds from Citrus Fruits: Green Perspectives and Current Status

Citrus fruits (CF) are highly consumed worldwide, fresh, processed, or prepared as juices and pies. To illustrate the high economic importance of CF, the global production of these commodities in 2021 was around 98 million tons. CF's composition is considered an excellent source of phenolic compounds (PC) as they have a large amount and variety. Since ancient times, PC has been highlighted to promote several benefits related to oxidative stress disorders, such as chronic diseases and cancer. Recent studies suggest that consuming citrus fruits can prevent some of these diseases. However, due to the complexity of citrus matrices, extracting compounds of interest from these types of samples, and identifying and quantifying them effectively, is not a simple task. In this context, several extractive and analytical proposals have been used. This review discusses current research involving CF, focusing mainly on PC extraction and analysis methods, regarding advantages and disadvantages from the perspective of Green Chemistry.

Analysis of vitamin D and its metabolites in biological samples - Part I: Optimization and comparison of UHPSFC-MS/MS and UHPLC-MS/MS methods

Fat-soluble vitamin D is an essential bioactive compound important for human health. Insufficient vitamin D levels can result not only in bone disease but also in other disorders, such as cancer, metabolic disorders, and diseases related to poor immune function. The current methods commonly used for vitamin D analysis are often applied to determine the levels of the most abundant metabolite in plasma, i.e., 25-OH-D2/D3. These methods do not consider the presence of other hydroxylated and esterified metabolites, including isomers and epimers, which are typically found in low concentrations. In this study, we developed a fast and selective ultra-high performance supercritical fluid chromatography (UHPSFC) method using a 150 mm long 1-amino anthracene (1-AA) column and a mobile phase consisting of carbon dioxide and methanol/isopropanol (1/1, v/v) mixed with 8 % water. After thorough optimization of column temperature and back pressure, the separation of four vitamin D3 esters, vitamin D3 and D2, and eight mono- and di-hydroxylated metabolites, including three groups of isomers, was achieved in 10 min. Two ion sources, atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization optimized within this study, were compared in tandem mass spectrometry (MS/MS) detection. No significant sensitivity differences were observed. Subsequently, the same 1-AA column chemistry was examined in ultra-high performance liquid chromatography (UHPLC) as the stationary phase that could hypothetically bring different selectivity in the separation of vitamin D and its metabolites. However, this hypothesis was rejected, and C18 was used as a stationary phase in the final optimized UHPLC-MS/MS method. Despite detailed optimization, the final 15 min UHPLC method was not able to separate di-hydroxylated isomers of vitamin D3, while it enabled better resolution of esterified forms compared to UHPSFC. Optimized methods provided similar repeatability of retention times and peak areas, with RSD < 2 % and 10 %, respectively. The lowest limits of quantification were in the range of 1.2 - 4.9 ng/mL for UHPSFC-APCI-MS/MS, while for UHPLC-APCI-MS/MS, they were typically in the range of 2.6 - 9.6 ng/mL. Based on the obtained results, the UHPSFC-APCI-MS/MS method was the most promising approach for fast, selective, and sensitive analysis that could be applied in the analysis of biological samples with emphasis on the separation of both hydroxylated and esterified metabolites, including isomeric forms.

Computer-assisted multifactorial method development for the streamlined separation and analysis of multicomponent mixtures in (Bio)pharmaceutical settings

The (bio)pharmaceutical industry is rapidly moving towards complex drug modalities that require a commensurate level of analytical enabling technologies that can be deployed at a fast pace. Unsystematic method development and unnecessary manual intervention remain a major barrier towards a more efficient deployment of meaningful analytical assay across emerging modalities. Digitalization and automation are key to streamline method development and enable rapid assay deployment. This review discusses the use of computer-assisted multifactorial chromatographic method development strategies for fast-paced downstream characterization and purification of biopharmaceuticals. Various chromatographic techniques such as reversed-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), ion exchange chromatography (IEX), hydrophobic interaction chromatography (HIC), and supercritical fluid chromatography (SFC) are addressed and critically reviewed. The most significant parameters for retention mechanism modelling, as well as mapping the separation landscape for optimal chromatographic selectivity and resolution are also discussed. Furthermore, several computer-assisted approaches for optimization and development of chromatographic methods of therapeutics, including linear, nonlinear, and multifactorial modelling are outlined. Finally, the potential of the chromatographic modelling and computer-assisted optimization strategies are also illustrated, highlighting substantial productivity improvements, and cost savings while accelerating method development, deployment and transfer processes for therapeutic analysis in industrial settings.

Ultrahigh-Performance Supercritical Fluid Chromatography-Multimodal Ionization-Tandem Mass Spectrometry as a Universal Tool for the Analysis of Small Molecules in Complex Plant Extracts

Complex analysis of plant extracts usually requires a combination of several analytical approaches. Therefore, in this study, we developed a holistic two-injection approach for plant extract analysis, which is carried out within one instrument without the need for any manual intervention during the analysis. Ultrahigh-performance supercritical fluid chromatography (UHPSFC) was employed for the analysis of 17 volatile terpenes on a porous graphitic carbon column within 7.5 min, followed by analysis on short diol column where flavonoids, phenolic acids, and terpenoic acids were analyzed within 15.5 min. A multimodal ionization source combining electrospray and atmospheric pressure chemical ionization (ESCi) was selected for mass spectrometry detection as a simultaneous ionization of both lipophilic and polar compounds was required. The quantitative aspects of the final UHPSFC-ESI/ESCi-MS/MS two-injection approach were determined, and it was applied to the analysis of Eucalyptus sp. extracts prepared by supercritical fluid extraction. Current methods reported in the literature typically require a labor-intensive combination of liquid and gas chromatography for the complex analysis of plant extracts. We present for the first time a new UHPSFC approach requiring only a single instrument that provides an alternative approach to the analysis of complex plant extracts.

Comprehensive Single-Platform Lipidomic/Metabolomic Analysis Using Supercritical Fluid Chromatography-Mass Spectrometry

Supercritical fluid chromatography (SFC) is a rapidly expanding technique in the analysis of nonpolar to moderately polar substances and, more recently, also in the analysis of compounds with higher polarity. Herein, we demonstrate a proof of concept for the application of a commercial SFC instrument with electrospray ionization-mass spectrometry (MS) detection as a platform for the comprehensive analysis of metabolites with the full range of polarities, from nonpolar lipids up to highly polar metabolites. The developed single-platform SFC-MS lipidomic/metabolomic method is based on two consecutive injections of lipid and polar metabolite extracts from biphase methyl tert-butyl ether extraction using a diol column and two different gradient programs of methanol-water-ammonium formate modifier. Detailed development of the method focused mainly on the pressure limits of the system, the long-term repeatability of results, and the chromatographic performance, including optimization of the flow rate program, modifier composition and gradient, and injection solvent selection. The developed method enabled fast and comprehensive analysis of lipids and polar metabolites from plasma within a 24 min cycle with two injections using a simple analytical platform based on a single instrument, column, and mobile phase. Finally, the results from SFC-MS analysis of polar metabolites were compared with widely established liquid chromatography MS analysis in metabolomics. The comparison showed different separation selectivity of metabolites using both methods and overall lower sensitivity of the SFC-MS due to the higher flow rate and worse chromatographic performance.

Novel approach to supercritical fluid chromatography-mass spectrometry analysis of metal ions using EDTA complexation

BACKGROUND

Reliable methods enabling detection of metal ions, and especially heavy metals, in different matrices are necessary in various fields such as ecology, pharmaceuticals and toxicology. As some of the currently used methods suffer from spectral and chemical interferences, this study investigates the applicability of SFC-MS/MS for the determination of metal ions.

RESULTS

Effective novel approaches for metal ion analysis using CO2-based mobile phase were developed using three ligands forming metal complexes. As metal-EDTA complexes are prepared by simple addition of EDTA to the solution containing metal ions, this approach to metal ion analysis does not require laborious synthesis and isolation of solid metal-complexes. Besides, two other approaches using diethyldithiocarbamate and acetylacetonate as ligands were compared. Metal complexes of Cu, Co, Cr, Fe, Al, Mn, and Zn with all 3 ligands were synthesized and their identity was confirmed by high-resolution mass spectrometry (HRMS). The suitability of the three developed UHPSFC-MS/MS methods was examined using the determination of calibration range and repeatability of injections. Moreover, the universality of the developed UHPSFC-MS/MS method for the determination of metal-EDTA complexes was proved by analyzing Ni, Bi and Pb as additional metal ions.

SIGNIFICANCE AND NOVELTY

This study demonstrates the extended range of applicability for SFC based separations. For the first time, the possibility to analyze metal complexes with EDTA using a fast and reliable ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) method is reported. The three developed UHPSFC-MS/MS methods are able to separate DDC, acac, and EDTA complexes of various metals very efficiently (total cycle times of 5, 2, and 3 min, respectively). They offer a fast and green alternative to chromatographic methods commonly used for metal ion analysis.

Unified chromatography in drug development: Exploiting chaotropic/kosmotropic salts for an accelerated method development

Recent trends in supercritical fluid chromatography (SFC) introduced an innovative gradient profile called Unified Chromatography (UC), which pushes the amount of liquid modifier up to 80-100 % of the total mobile phase composition. These new conditions allow the full transition from a supercritical to a liquid state, unifying the benefits of both SFC and liquid chromatography. However, to facilitate the use of UC for industrial drug development, a stronger effort is needed to streamline and simplify its method development and optimization. In this work, a quick and novel method development procedure for UC is introduced, enabled by the first-time use of novel additives in SFC/UC that exploit chaotropic/kosmotropic properties. A comprehensive view on some fundamental properties, such as the amount of liquid modifier blended with supercritical CO2 (scCO2) and the percentage of water added in the mobile phase is given, to clarify the benefits of using either a chaotropic salt (NaClO4), kosmotropic (HCOONa) or salt with mixed properties (NaOMs - sodium methanesulfonate). With this expanded knowledge, challenging separations of nucleosides, nucleotide, indoles, triazoles and related derivates have been accomplished with UC. Finally, we provide an example of UC delivering a faster and better method for an AbbVie pipeline compound under accelerated stability study. The combined use of scCO2-based chromatography and the novel additive NaClO4 ensures the retention and elution of all degradation species generated at different conditions, where RP-HPLC failed to provide satisfactory performance.

Simultaneous determination of enantiomeric and organic impurities of vildagliptin on a cellulose tris(3-chloro-4-methylphenylcarbamate) column under revered-phase conditions

A new, reversed-phase HPLC (RP-HPLC) method was developed for the simultaneous determination of the dipeptidyl-peptidase-IV-inhibitor antidiabetic drug vildagliptin (VIL) enantiomeric impurity and four other achiral related impurities. An initial screening was performed on five polysaccharide-type chiral stationary phases (Lux Amylose-1, Lux Amylose-2, Lux-Cellulose-1, Lux-Cellulose-2, Lux-Cellulose-3) in polar organic mode with methanol, ethanol, 2-propanol, or acetonitrile containing 0,1% diethylamine as mobile phase to identify the best conditions for the separation of VIL enantiomers. Lux-Cellulose-2 column was found to provide the best chiral resolution for VIL enantiomers. Further experiments were conducted using different aqueous-organic mobile phases to achieve the simultaneous chiral-achiral separation of the selected compounds. Experimental design-based optimization was performed by using a face-centered central composite design. The optimal separation conditions (Lux Cellulose-2 stationary phase, 45 °C, mobile phase consisting of methanol/water/diethylamine 80:20:0.2 (v/v/v), and 0.45 mL/min flow rate) provided baseline separation for all 6 compounds. The optimized method was validated according to the ICH guideline and proved to be reliable, specific, linear, precise, and accurate for the determination of at least 0.1% for all impurities in VIL samples. The validated method was applied for determinations from a commercially available drug formulation and proved to be suitable for routine quality control of both enantiomeric and organic impurities of VIL.

Columns in analytical-scale supercritical fluid chromatography: From traditional to unconventional chemistries

Within this review, we thoroughly explored supercritical fluid chromatography (SFC) columns used across > 3000 papers published from the first study carried out under SFC conditions in 1962 to the end of 2022. We focused on the open tubular capillary, packed capillary, and packed columns, their chemistries, dimensions, and trends in used stationary phases with correlation to their specific interactions, advantages, drawbacks, used instrumentation, and application field. Since the 1990s, packed columns with liquid chromatography and SFC-dedicated stationary phases for chiral and achiral separation are predominantly used. These stationary phases are based on silica support modified with a wide range of chemical moieties. Moreover, numerous unconventional stationary phases were evaluated, including porous graphitic carbon, titania, zirconia, alumina, liquid crystals, and ionic liquids. The applications of unconventional stationary phases are described in detail as they bring essential findings required for further development of the supercritical fluid chromatography technique.

Revisiting Disinfection Byproducts with Supercritical Fluid Chromatography-High Resolution-Mass Spectrometry: Identification of Novel Halogenated Sulfonic Acids in Disinfected Drinking Water

High resolution mass spectrometry (HRMS) coupled to either gas chromatography or reversed-phase liquid chromatography is the generic method to identify unknown disinfection byproducts (DBPs) but can easily overlook their highly polar fractions. In this study, we applied an alternative chromatographic separation method, supercritical fluid chromatography-HRMS, to characterize DBPs in disinfected water. In total, 15 DBPs were tentatively identified for the first time as haloacetonitrilesulfonic acids, haloacetamidesulfonic acids, and haloacetaldehydesulfonic acids. Cysteine, glutathione, and p-phenolsulfonic acid were found as precursors during lab-scale chlorination, with cysteine providing the highest yield. A mixture of the labeled analogues of these DBPs was prepared by chlorination of ¹³C₃-¹⁵N-cysteine and analyzed using nuclear magnetic resonance spectroscopy for structural confirmation and quantification. A total of 6 drinking water treatment plants utilizing various source waters and treatment trains produced sulfonated DBPs upon disinfection. Those were widespread in the tap water of 8 cities across Europe, with estimated concentrations up to 50 and 800 ng/L for total haloacetonitrilesulfonic acids and haloacetaldehydesulfonic acids, respectively. Up to 850 ng/L haloacetonitrilesulfonic acids were found in 3 public swimming pools. Considering the stronger toxicity of haloacetonitriles, haloacetamides, and haloacetaldehydes than the regulated DBPs, these newly found sulfonic acid derivatives may also pose a health risk.

The Enantioselective Potential of NicoShell and TeicoShell Columns for Basic Pharmaceuticals and Forensic Drugs in Sub/Supercritical Fluid Chromatography

The enantioselective potential of two macrocyclic glycopeptide-based chiral stationary phases for analysis of 28 structurally diverse biologically active compounds such as derivatives of pyrovalerone, ketamine, cathinone, and other representatives of psychostimulants and antidepressants was evaluated in sub/supercritical fluid chromatography. The chiral selectors immobilized on 2.7 μm superficially porous particles were teicoplanin (TeicoShell column) and modified macrocyclic glycopeptide (NicoShell column). The influence of the organic modifier and different mobile phase additives on the retention and enantioresolution were investigated. The obtained results confirmed that the mobile phase additives, especially water as a single additive or in combination with basic and acidic additives, improve peak shape and enhance enantioresolution. In addition, the effect of temperature was evaluated to optimize the enantioseparation process. Both columns exhibited comparable enantioselectivity, approximately 90% of the compounds tested were enantioseparated, and 30% out of them were baseline enantioresolved under the tested conditions. The complementary enantioselectivity of the macrocyclic glycopeptide-based chiral stationary phases was emphasized. This work can be useful for the method development for the enantioseparation of basic biologically active compounds of interest.

Gradient elution of hydroxyacetophenones by supercritical fluid chromatography with electrochemical detection

Linear gradient elution supercritical fluid chromatography with electrochemical detection was developed using hydroxyacetophenones as analytes. Separation was carried out with a diol column (4.6 mm id × 250 mm length, 5 μm) as a stationary phase and a mixture of supercritical carbon dioxide and methanol as a mobile phase, where the ratio of carbon dioxide and methanol was changed from 99:1 (v/v) to 60:40 (v/v). For the electrochemical detection, methanol containing 1.0 mol L^-1 ammonium acetate was used as a supporting electrolyte solution and + 1.2 V was applied to the electrochemical cell. We compared the performance of the present method to isocratic elution supercritical fluid chromatography, and the repeatability, linearity, and detection capability all showed better analytical parameters in the gradient elution. As such, we found that gradient elution supercritical fluid chromatography can achieve the faster separation and save resources compared to isocratic elution. Thus, the present method may contribute to the development of green analytical methods.

Optimization and validation of a fast supercritical fluid chromatography tandem mass spectrometry method for the quantitative determination of a large set of PFASs in food matrices and human milk

An Ultra-High Performance Supercritical Fluid Chromatography coupled with tandem Mass Spectrometry analytical method (UHPSFC-MS/MS) was developed for the determination of 34 perfluoroalkylated substances (PFASs) in food-related matrices. Two parameters (i.e. stationary phase and co-solvent) were selected and optimized using a step-by-step method, while a design of experiment (DoE) method using a central composite design (CCD) was implemented to optimize column temperature, mobile phase flow rate, co-solvent concentration and automated back pressure regulator (ABPR). The Torus 2-PIC column was selected along with ammonium acetate AcoNH₄ as additive in the co-solvent. DoE optimization of both peak width and resolution enabled validating an optimized model (desirability 0.613) and setting column temperature at 38.7 °C, AcoNH₄ concentration at 8 mM, mobile phase flow rate of 1.9 mL/min and ABPR at 1654 psi. The validated resulting method enabled reaching limits of quantification below 0.2 ng/g (w.w.) for 97 % PFASs in accordance with current EU requirements. The strategy was successfully applied to the characterization of a range (n > 30) of food-related matrices (red meat, poultry meat, eggs, fish and breast milk) collected in Algeria in 2019. PFOA and PFBA were observed as the most frequently detected PFASs, i.e. in 96.96 % and 90.9 % of the samples respectively. The highest concentrations were determined in fishery products up to 4.42 ng/g (w.w.) for PFTeDA and 0.75 ng/g (w.w.) for PFOS.

Supercritical fluid chromatography coupled to high-resolution tandem mass spectrometry: an innovative one-run method for the comprehensive assessment of chocolate quality and authenticity

To assess chocolate quality and authenticity comprehensively, a combination of various analytical procedures is involved, thereby making the process time-consuming and costly. Thus, we investigated the potential of ultra-high performance supercritical fluid chromatography coupled to quadrupole-time of flight mass spectrometry (UHPSFC-QTOF-MS) as an alternative to "classic" methods. By combining hexane and aqueous extracts from sequential extraction, a single 8-min analytical run enabled us (i) to determine cocoa butter equivalents (CBEs) and milk fat content based on the detection of selected triacylglycerols, (ii) to calculate dry non-fat cocoa solids based on determined theobromine and caffeine content, and (iii) to profile contained sugars. To obtain the most comprehensive information about sample composition, the MS method comprised a full MS scan for non-target screening and several time-scheduled targeted MS/MS functions ("parallel reaction monitoring") optimized according to the possible concentration ranges of the analytes. For 40 different chocolate samples, our results and those obtained by using standard methods (LC-UV for non-fat cocoa solids, and GC-FID for CBEs) were in good agreement. Compared to the conventional approach for chocolate quality and authenticity control, the presented SFC-MS method is a fast, cost-effective, and efficient alternative, and only samples suspicious for the presence of CBE should be referred to the standard GC-FID method for exact CBE quantification. In the study, also some challenges offered by SFC-MS have been addressed.