Supercritical fluid chromatography for the 21st century

Discrimination of plastic waste pyrolysis oil feedstocks using supercritical fluid chromatography

Advanced chemical recycling techniques provide new avenues for handling and recycling mixed plastic waste; pyrolysis is a prominent approach involving heating plastic waste in an oxygen-free environment to create pyrolysis oils. Pyrolysis oils must be thoroughly characterized before being refined into fuels and chemical feedstocks. Here, a method based on supercritical fluid chromatography with ultraviolet detection was developed to analyze plastic waste pyrolysis oils. Multiple stationary phases were examined, and 2-ethyl pyridine was chosen as the best stationary phase for resolving pyrolysis oil components. Different standards and different plastic waste pyrolysis oils were compared across the different stationary phases. Up to three columns were serially coupled to increase efficiency and column capacity. It was found that a general method using ethanol as a modifier and two 2-ethyl pyridine columns could effectively resolve plastic waste pyrolysis oils. The potential for differentiating polyethylene and polypropylene feedstocks was demonstrated using principal component analysis.

A nitrogenous heterocyclic ring-bonded stationary phase for separating alkaloids in supercritical fluid chromatography

A novel silica stationary phase was designed and prepared through thiol-epoxy click chemistry for supercritical fluid chromatography (SFC). The developed stationary phase was characterized by elemental analysis, Fourier transform infrared spectrometry and solid-state 13C/CP MAS NMR spectroscopy. In order to evaluate the chromatographic performance and retention mechanisms of the prepared column, a variety of alkaloids were used, including indoles, isoquinolines, pyrrolidines, piperidines, quinolizidines and organic amines. The stationary phase showed more symmetrical peak shapes and better performance for these compounds compared to the conventional SFC stationary phases. The investigations on the effects of pressure and temperature on retention provided information that the selectivity of the compounds can be improved by changing the density of the supercritical fluids. Moreover, it shows improved separation efficiency of three natural products with alkaloids as the main components at high sample loading. In conclusion, the developed stationary phase could offer flexible selectivity toward alkaloids and complex samples.

Process Mass Intensity (PMI): A Holistic Analysis of Current Peptide Manufacturing Processes Informs Sustainability in Peptide Synthesis

Small molecule therapeutics represent the majority of the FDA-approved drugs. Yet, many attractive targets are poorly tractable by small molecules, generating a need for new therapeutic modalities. Due to their biocompatibility profile and structural versatility, peptide-based therapeutics are a possible solution. Additionally, in the past two decades, advances in peptide design, delivery, formulation, and devices have occurred, making therapeutic peptides an attractive modality. However, peptide manufacturing is often limited to solid-phase peptide synthesis (SPPS), liquid phase peptide synthesis (LPPS), and to a lesser extent hybrid SPPS/LPPS, with SPPS emerging as a predominant platform technology for peptide synthesis. SPPS involves the use of excess solvents and reagents which negatively impact the environment, thus highlighting the need for newer technologies to reduce the environmental footprint. Herein, fourteen American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable (ACS GCIPR) member companies with peptide-based therapeutics in their portfolio have compiled Process Mass Intensity (PMI) metrics to help inform the sustainability efforts in peptide synthesis. This includes PMI assessment on 40 synthetic peptide processes at various development stages in pharma, classified according to the development phase. This is the most comprehensive assessment of synthetic peptide environmental metrics to date. The synthetic peptide manufacturing process was divided into stages (synthesis, purification, isolation) to determine their respective PMI. On average, solid-phase peptide synthesis (SPPS) (PMI ≈ 13,000) does not compare favorably with other modalities such as small molecules (PMI median 168-308) and biopharmaceuticals (PMI ≈ 8300). Thus, the high PMI for peptide synthesis warrants more environmentally friendly processes in peptide manufacturing.

Analytical Strategies to Investigate Molecular Signaling, Proteomics, Extraction and Quantification of Withanolides - A Comprehensive Review

Withanolides are the class of steroidal molecules getting greater emphasis in recent years. Quality control throughout the manufacturing and storage period is often one of the key problems that have restricted their broad use in India's indigenous and Ayurvedic medical systems for thousands of years. Because of their diverse clinical potential, withanolides have received a great deal of scientific attention. Analytical techniques are being devised for the automated isolation, identification, and estimation of every single protein within the cell as well as in herbal extracts of withanolides, due to which now researchers are interested in determining the effects of metabolism as well as various stimuli on protein expression, which made the study easier. This study discusses the potential use of hyphenated analytical methods that are reliable in understanding the molecular signaling features, proteome evaluation and characterization of withanolides, in addition to examining existing methodological limitations. The choice of analytical techniques for the withanolides analysis, however, relies on the nature of the sample matrix, the aim of the analysis, and the sensitivity of the technique.

A Method for High Throughput Free Fatty Acids Determination in a Small Section of Bovine Liver Tissue Using Supercritical Fluid Extraction Combined with Supercritical Fluid Chromatography-Medium Vacuum Chemical Ionization Mass Spectrometry

A novel ionization technique named medium vacuum chemical ionization (MVCI) mass spectrometry (MS), which is a chemical ionization using oxonium (H3O+) and hydroxide (OH-) formed from water, has excellent compatibility with the supercritical fluid extraction (SFE)/supercritical fluid chromatography (SFC). We have studied a method to determine free fatty acids (FFAs) in a small section of bovine liver tissue using SFE/SFC-MVCI MS analysis without further sample preparation. A series of FFA molecules interact with the C18 stationary phase, exhibiting broad chromatographic peaks when using a non-modified CO2 as the mobile phase. It can be optimized by adding a small content of methanol to the mobile phase as a modifier; however, it may dampen the ionization efficiency of MVCI since the proton affinity of methanol is slightly higher than water. We have carefully evaluated the modifier content on the ion detection and column efficiencies. The obtained result showed that an optimized performance was in the range of 1 to 2% methanol-modified CO2 mobile phase for both column efficiency and peak intensity. Higher methanol content than 2% degrades both peak intensity and column efficiency. Using optimized SFC conditions, a section of bovine liver tissue sliced for 14 µm thickness by 1 mm square, which is roughly estimated as about 3300 hepatocytes, was applied to determine 18 FFAs amounts for carbon chains of C12-C24. An amount of each tested FFA was estimated as in the range of 0.07 to 2.6 fmol per cell.

A novel switchable water stationary phase for supercritical fluid chromatography

A novel pH switchable water stationary phase is presented for use in supercritical fluid chromatography (SFC). By adding NH4OH to the water coating and system hydration, changes in CO2 pressure and temperature allow a wide range of stationary phase pH conditions (∼3-9) to be achieved, which impact analyte retention properties. For example, 100 atm and 50 °C produces an acidic water stationary phase (pH near 4.0) where octanoic acid readily elutes while the base caffeine does not. Conversely, at 80 atm and 120 °C a basic water stationary phase (pH near 8.0) is obtained and the opposite occurs. Further, under constant pressure and temperature conditions, simply adding or removing NH4OH from the system is also found to readily allow switching between the basic and acidic water stationary phase modes and demonstrates control over ionizable analyte elution. For instance, hexanoic acid elution is near 40 times more delayed on a basic water stationary phase and, as such, it can be eluted at later points in time as desired by removing the NH4OH and switching to an acidic stationary phase. Experiments indicate that stationary phase pH switching occurs uniformly across the 15 m column length within about 18 s and that analyte retention times are very reproducible upon performing a switch (1.4% RSD; n = 3). Results demonstrate the selectivity factor between acidic and neutral analytes can be reversed and increased about 35 times, while in other trials resolution also similarly increased near 40-fold. By rapidly switching the stationary phase pH back and forth between acidic and basic modes, the selectivity between ionizable analytes could also be increased as desired. Various applications with the system show that it can vastly increase the separation between target analytes and matrix components as required by the dynamics of a particular separation.

Mass spectrometry-based approaches to assess the botanical authenticity of dietary supplements

Dietary supplements are legally considered foods despite frequently including medicinal plants as ingredients. Currently, the consumption of herbal dietary supplements, also known as plant food supplements (PFS), is increasing worldwide and some raw botanicals, highly demanded due to their popularity, extensive use, and/or well-established pharmacological effects, have been attaining high prices in the international markets. Therefore, botanical adulteration for profit increase can occur along the whole PFS industry chain, from raw botanicals to plant extracts, until final PFS. Besides the substitution of high-value species, unintentional mislabeling can happen in morphologically similar species. Both cases represent a health risk for consumers, prompting the development of numerous works to access botanical adulterations in PFS. Among different approaches proposed for this purpose, mass spectrometry (MS)-based techniques have often been reported as the most promising, particularly when hyphenated with chromatographic techniques. Thus, this review aims at describing an overview of the developments in this field, focusing on the applications of MS-based techniques to targeted and untargeted analysis to detect botanical adulterations in plant materials, extracts, and PFS.

Comparison of Data-Dependent Acquisition, Data-Independent Acquisition, and Parallel Reaction Monitoring in Trapped Ion Mobility Spectrometry-Time-of-Flight Tandem Mass Spectrometry-Based Lipidomics

The parallel accumulation-serial fragmentation (PASEF) approach based on trapped ion mobility spectrometry (TIMS) enables mobility-resolved fragmentation and a higher number of fragments in the same time period compared to conventional MS/MS experiments. Furthermore, the ion mobility dimension offers novel approaches for fragmentation. Using parallel reaction monitoring (prm), the ion mobility dimension allows a more accurate selection of precursor windows, while using data-independent aquisition (dia) spectral quality is improved through ion-mobility filtering. Owing to favorable implementation in proteomics, the transferability of these PASEF modes to lipidomics is of great interest, especially as a result of the high complexity of analytes with similar fragments. However, these novel PASEF modes have not yet been thoroughly evaluated for lipidomics applications. Therefore, data-dependent acquisition (dda)-, dia-, and prm-PASEF were compared using hydrophilic interaction liquid chromatography (HILIC) for phospholipid class separation in human plasma samples. Results show that all three PASEF modes are generally suitable for usage in lipidomics. Although dia-PASEF achieves a high sensitivity in generating MS/MS spectra, the fragment-to-precursor assignment for lipids with both, similar retention time as well as ion mobility, was difficult in HILIC-MS/MS. Therefore, dda-PASEF is the method of choice to investigate unknown samples. However, the best data quality was achieved by prm-PASEF, owing to the focus on fragmentation of specified targets. The high selectivity and sensitivity in generating MS/MS spectra of prm-PASEF could be a potential alternative for targeted lipidomics, e.g., in clinical applications.

First proof-of-concept of UC/HILIC for extending the versatility of the current art of supercritical fluid separation

Supercritical Fluid Chromatography (SFC), a high-throughput separation technique, has been widely applied as a promising routine method in pharmaceutical, pesticides, and metabolome analysis in the same way as conventional liquid chromatography and gas chromatography. Unified chromatography (UC), an advanced version of SFC, which applied gradient elution with mobile phase changing continuously from supercritical to subcritical and to liquid states, can further extend the SFC applications. UC mostly applying the popular mobile phase of 95%:5%/Methanol:Water with additives allows to analyze many hydrophilic compounds. However, many of phosphorylated metabolites or multi carboxylic acids show very poor peak shapes or even can't be eluted under UC conditions, thus hampering the UC's metabolome coverage. In this study, we proposed the first proof-of-concept of UC/HILIC, a novel strategy to extend the current UC metabolome coverage by employing an aqueous gradient right after the UC gradient on a single packed column in a single measurement. The proposed method showed significant improvement regarding the chromatographic performance and metabolome coverage, while still maintaining the precision and high throughput in comparison with conventional UC methods.

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.

Supercritical Fluid Nanospray Mass Spectrometry

Supercritical fluids are typically electrosprayed using an organic solvent makeup flow to facilitate continuous electrical connection and enhancement of electrospray stability. This results in sample dilution, loss in sensitivity, and potential phase separation. Premixing the supercritical fluid with organic solvent has shown substantial benefits to electrospray efficiency and increased analyte charge state. Presented here is a nanospray mass spectrometry system for supercritical fluids (nSF-MS). This split flow system used small i.d. capillaries, heated interface, inline frit, and submicron emitter tips to electrospray quaternary alkyl amines solvated in supercritical CO₂ with a 10% methanol modifier. Analyte signal response was evaluated as a function of total system flow rate (0.5-1.5 mL/min) that is split to nanospray a supercritical fluid with linear flow rates between 0.07 and 0.42 cm/sec and pressure ranges (15-25 MPa). The nSF system showed mass-sensitive detection based on increased signal intensity for increasing capillary i.d. and analyte injection volume. These effects indicate efficient solvent evaporation for the analysis of quaternary amines. Carrier additives generally decreased signal intensity. Comparison of the nSF-MS system to the conventional SF makeup flow ESI showed 10-fold signal intensity enhancement across all the capillary i.d.s. The nSF-MS system likely achieves rapid solvent evaporation of the SF at the emitter point. The developed system combined the benefits of the nanoemitters, sCO₂, and the low modifier percentage which gave rise to enhancement in MS detection sensitivity.

A new quantitative method for pseudouridine and uridine in human serum and its clinical application in acute myeloid leukemia

Pseudouridine, a C-C glycosidic isomer of uridine, is derived from uridine via isomerization, and pseudouridylation is the most common post-transcriptional modification. Our previous study shows pseudouridine may serve an important role in acute myeloid leukemia (AML). The clinical value of pseudouridine and uridine is hampered by the lack of a quantitative methods with high sensitivity, specificity, and stability. Here, we established a supercritical fluid chromatography-tandem triple quadrupole mass spectrometry (SFC-TQ-MS)-based method to quantitate serum pseudouridine and uridine simultaneously. The procedure involves protein precipitation of sample, extraction with solid phase extraction (SPE) plate, 5-min SFC separation by applying gradient elution on a Acquity UPC2 Torus DIOL column, and analysis by TQ-MS using well-characterized calibration standards. After validation, the method was used to measure pseudouridine and uridine concentrations in 143 serum samples from healthy controls (HCs) and AML patients to evaluate their prognostic potential. The successfully validated assay had a linear range of 5-5000 ng/mL, accuracies between 97 % and 102 %, and intra- and inter-assay imprecision <10 %. Compared to HCs, pseudouridine was raised significantly, while uridine was curtailed severely in patients with AML. With a median concentration of 671.4 ng/mL as the prognostic cut-off value, high level pseudouridine independently predicted poor survival of AML patients. Quantification of serum pseudouridine and uridine by SFC-TQ-MS provides an analytically sensitive and reproducible method for clinical diagnosis, and high concentration of pseudouridine is an independent prognostic factor for patients with AML.

Assessment of greenness for the determination of voriconazole in reported analytical methods

Analytical research with adverse environmental impact has caused a severe rise in concern about the ecological consequences of its strategies, most notably the use and emission of harmful solvents/reagents into the atmosphere. Nowadays, industries are searching for the best reproducible methods. Voriconazole is a second-generation azole derivative used effectively in the treatment of Candida and Aspergillus species infections and oropharyngeal candidiasis in AIDS patients. Recently it has become the drug of choice in treating mucormycosis in several countries, which raises the need for production in large quantities. The present review deals with various recent important analytical techniques used to estimate voriconazole and its combination in pharmaceutical formulations and biological fluids. The methods show their own unique way of analyzing voriconazole in different matrices with excellent linearity, detection, and quantification limits. Additionally, this article deals with methods and solvents analyzed for their impact on the environment. This is followed by estimating the degree of greenness of the methods using various available assessment tools like analytical eco-scale, national environmental method index, green analytical procedure index, and AGREE metrics to confirm the environmental impact. The scores obtained with the evaluation tools depict the quantum of greenness for the reported methods and provide an ideal approach adopted for VOR estimation. Very few methods are eco-friendly, which shows that there is a need for the budding analyst to develop methods based on green analytical principles to protect the environment.

Analysis of short-chain bioactive peptides by unified chromatography-electrospray ionization mass spectrometry. Part I. Method development

A method to analyse short-chain bioactive peptides (MW < 800 Da) and their impurities was developed with a unified chromatography (UC) analysis, including a wide mobile phase gradient ranging from supercritical fluid to near-liquid conditions, with UV and electrospray ionization mass spectrometry detection (ESI-MS). Four stationary phases and three mobile phase compositions were examined. Ten model peptides were first selected to identify the best operating conditions, including five linear tripeptides and five cyclic pentapeptides, with log P values ranging from -5.9 to 3.6, and including isomeric species. Derringer desirability functions were designed to identify optimal operating conditions based on 7 criteria, namely the number of peaks detected (including all impurities resolved), the proportion of the chromatogram occupied by target peaks, the least favourable resolution observed between the main peptide and impurities, peak shape features (asymmetry and peak width at half height), and finally the signal-to-noise ratio observed both with UV (210 nm) and ESI-MS in positive ionization mode. The optimum conditions were obtained on Ascentis Express OH5 stationary phase, with a mobile phase composed of carbon dioxide and methanol, comprising 2% water and 20 mM ammonium hydroxide. The final gradient program ranged from 5 to 80% co-solvent in CO₂, with a reversed flow rate gradient ranging from 3.0 to 1.5 mL/min. Back-pressure was set at 120 bar and the column oven temperature at 60°C. Optimal conditions were applied to a large set of 76 peptides (34 linear tripeptides and 42 cyclic pentapeptides) and provided adequate scattering of the peaks in the retention space, together with some separation of isomeric species, particularly for the cyclic peptides.

Chiral Resolution, Absolute Configuration Assignment, and Genotoxicity Evaluation of Racemic 3,4-Dihydroquinazoline as a Novel Anticancer Agent

If a new drug candidate will be a mixture of enantiomers, both enantiomers should be separately studied for at least latent genotoxicity as early as possible since the thalidomide tragedy. Our group has recently reported that KCP-10043F (OZ-001) as a racemate (±)-3,4-dihydroquinazoline derivative strongly represses the proliferation of human A549 lung cancer cells by caspase-mediated apoptosis via STAT3 inactivation. To investigate the possible teratological effects of the two enantiomers of a racemic KCP-10043F, therefore chiral resolution of (±)-KCP-10043F was performed and subsequently followed by a series of chemical processes to afford the corresponding chiral diastereomers. By using 1H NMR anisotropy method, the absolute configuration (+)-KCP-10043F and (−)-KCP-10043F could be assigned as S and R configuration, respectively. The bacterial reverse mutation test (Ames test) for racemate (±)-KCP-10043F and its two enantiomers exhibited that all three stereoisomers were found to be nongenotoxic against five bacterial strains with/without metabolic activation. In addition, (R)-(−)-KCP-10043F displayed almost equal anticancer activity to (S)-(+)-KCP-10043F against three cancer cell lines. Based on these overall results, racemate KCP-10043F (OZ-001) could be used for our ongoing preclinical and clinical studies without the expensive asymmetric process and/or chiral separation.

An enhanced strategy integrating offline two-dimensional separation with data independent acquisition mode and deconvolution: Characterization of metabolites of Uncaria rhynchophylla in rat plasma as a case

The importance to clarify the drug metabolites is beyond doubt in view of their potential efficacy and safety. However, due to the complex matrix interference, relatively low content and the co-eluting effect, it is of a great challenge to comprehensively and systematically characterize the metabolites in vivo, especially for the traditional Chinese medicines (TCMs) due to the numerous types of components. In the present study, a comprehensive off-line two-dimensional separation system combining with data independent acquisition (DIA) mode and multi-dimensional data deconvolution method was established for chromatographic separation, data acquisition and data procession of indole alkaloids in rat plasma after intragastrically administrated with the extract of Uncaria rhynchophylla at the dose of 1 g/kg. The orthogonality of the off-line 2D separation system consisting of HILIC for first-dimensional separation and the PRLC for second-dimensional separation was valuated with the "asterisk" equations, and the results showed that off-line 2D separation system had passable orthogonality (A₀ = 53.3%). Furthermore, the DIA mode was applied to capture MS/MS spectra in view of its advantage in acquiring MS data, and an effective multi-dimensional deconvolution method integrating the calculation of chemical formula, the extraction of diagnostic ion, the filter of ring double bond (RDB) and the judgement of neutral loss was established to parse the spectra for the complicated DIA data for comprehensive analysis of metabolites in rat plasma. Ultimately, a total of 127 indole alkaloids were tentatively characterized, and the main metabolic pathways were inferred as demethylation, dehydrogenation, hydroxylation and deglycosylation. The off-line two-dimensional separation system was applied for the comprehensive characterization of metabolites in vivo for the first time. This study suggested a new approach to enable the enrichment, separation and analysis of the low content components in vivo.

Determination of Saccharides in Honey Using Supercritical Fluid Chromatography Coupled with Single Quadrupole Mass Spectrometry

Saccharides are one of the most important biomoleculars in the world, which are responsible for various roles in living organisms. In this work, a combined use of mass spectrometry (MS) together with supercritical fluid chromatography (SFC) was applied for the separation of eight saccharides. A satisfactory separation was achieved within 15 min on a Unitary Diol column using 10 mM ammonium acetate in methanol as mobile phase additive at a temperature of 60°C. Compared to liquid chromatography-MS (LC-MS), the SFC-MS presented faster running time and better selectivity. The SFC-MS was validated and applied to the analysis of three saccharides (fructose, glucose and sucrose) present in different honey samples. The limits of detection (LODs) and limits of quantification (LOQs) of SFC-MS method for fructose, glucose and sucrose were 5.2, 4.5, 7.4 μg/mL and 17.2, 14.9, 24.1 μg/mL, respectively. The relative standard deviations for intrabatch and interbatch precision were <2.5% and the recoveries ranged from 97.6% to 103.1% for three concentration levels. The values of LODs and LOQs using SFC-MS method were lower (1.5-2.4-fold) than using LC-MS method. The results demonstrated the potential of SFC-MS for fast and sensitive determination of saccharides in honey.

Promising Green Technology in Obtaining Functional Plant Preparations: Combined Enzyme-Assisted Supercritical Fluid Extraction of Flavonoids Isolation from Medicago Sativa Leaves

To elaborate a complete extraction protocol for the enhanced release of biologically active compounds from plant cells, this study aimed to optimize together the parameters of the supercritical fluid extraction (SFE) process (temperature, pressure, and percentage of cosolvent) and enzymatic treatment of plant material (pH, enzyme concentration, time, and temperature) by response surface methodology (RSM). Medicago sativa L. was selected as a plant material due to its richness in phenolics and flavonoids. HPLC-MS/MS analysis allowed evaluating the content of individual bioactive compounds in obtained extracts. The total content of polyphenolic compounds in the extract obtained after two-step optimization was much higher (546 ± 21 µg/g) than in the extract obtained from non-hydrolyzed material (275 ± 23 µg/g) and in the extract obtained by maceration (162 ± 20 µg/g). Furthermore, it was evidenced that extract with the highest content of polyphenolic compounds can support the cellular antioxidant system both as a free radical scavenger and by stimulating the antioxidant enzyme system.

A review of retention mechanism studies for packed column supercritical fluid chromatography

The packed column supercritical fluid chromatography has risen as a promising alternative separation technique to the conventional liquid chromatography and gas chromatography. Although the packed column supercritical fluid chromatography has many advantages compared to other chromatographic techniques, its separation mechanism is not fully understood due to the complex combination effects of many chromatographic parameters on separation quality and the lacking of global strategies for studying separation mechanisms. This review aims to provide recent information regarding the chromatographic behaviors and the effects of the parameters on the separation, discuss the results, and point out the remaining bottlenecks in the packed column supercritical fluid chromatography retention mechanism studies.

The simultaneous determination of naringenin and its valine carbamate prodrug in rat plasma using supercritical fluid chromatography -tandem mass spectrometric method

To enhance the oral bioavailability of naringenin, a valine carbamate prodrug was firstly synthesized. It is essential to measure naringenin and its carbamate prodrug simultaneously for evaluating their pharmacokinetic behavior in Sprague-Dawley rats. Here, the samples were analyzed by a supercritical fluid chromatography-tandem mass spectrometric (SFC-MS/MS) method after extracting by liquid-liquid extraction with ethyl acetate. The analytes were eluted completely on an ACQUITY UPC^2TM BEH 2-EP column (3.0 × 100 mm, 1.7 μm) within 2.5 min by gradient elution. The mass transition ion pairs were m/z 273.2→153.0, 416.0→153.1, and 271.2→91.0 for naringenin, the prodrug, and genistein (the internal standard), respectively. Naringenin and the prodrug had excellent linear correlations over the range of 2-1000 ng/mL (r > 0.995) and 4-2000 ng/mL (r > 0.998), with lower limits of quantification of 2 ng/mL and 4 ng/mL, respectively. The intra-day and inter-day precision and accuracy for all quality control samples were within ± 15 %. The high-throughput, sensitive, and economical SFC-MS/MS method was successfully applied to the pharmacokinetic study of naringenin and its carbamate prodrug for the first time. The pharmacokinetic study results showed the total C_max of naringenin in prodrug group was 4.14-fold higher than naringenin group. The higher total AUC value observed with prodrug group indicated increased bioavailability of naringenin as compared to naringenin suspension. The present work provides some helpful information for future studies of naringenin and its carbamate prodrug.

Development of a novel method for polar metabolite profiling by supercritical fluid chromatography/tandem mass spectrometry

Supercritical carbon dioxide (scCO₂), the main fluid in the mobile phase for supercritical fluid chromatography (SFC), is non-polar. The majority of polar compounds are little soluble in scCO₂, thereby rendering them poor candidates for achieving separation by carbon dioxide-based SFC. There is no reported method for the comprehensive analysis of hydrophilic metabolites by SFC with mobile phases comprising a high CO₂ ratio. In this study, we investigated the effect of additives in the modifier for enabling the application of SFC to profile diverse polar compounds for metabolomics. Eleven types of columns were screened by using proteinogenic amino acids as the model compounds. The addition of water and acids (formic acid and trifluoroacetic acid (TFA)) to the modifier was also investigated to improve the solubility of the polar compounds and mitigate the unfavorable interaction between the stationary phase and the polar compounds. A significant improvement in the peak shapes of the amino acids was observed upon addition of TFA. The CO₂/modifier ratio and TFA concentration in the mobile phases were investigated using the CROWNPAK CR-I (+) column, which showed the best performance during the column-screening. The CO₂/methanol/water/TFA ratio of 70/27/3/0.15 (v/v/v/v) was determined as the optimized mobile phase composition. Furthermore, the applicability of the optimized analytical method to other polar compounds was examined; 100 cationic and amphoteric compounds with predicted logP_ow values that ranged from -5.9 to 1.7 could be simultaneously analyzed without derivatization. Anionic compounds such as organic acids, phosphates, and sugars were excluded from the target analytes. Most of the previously reported SFC methods for analyzing polar compounds employ a gradient elution and require the use of high modifier ratios at 40% or more. In the proposed method, the use of water and TFA enabled the rapid and simultaneous analysis under isocratic elution within 10 min, even with a high CO₂ ratio of 70%. Additionally, a rat serum extract was analyzed using the optimized conditions, and 43 polar metabolites were successfully detected. This result demonstrates the applicability of the SFC/tandem mass spectrometry method to real samples.

Determination of neurosteroids in human cerebrospinal fluid in the 21st century: A review

Determination of steroid hormones synthesized by the human body plays an important role in various fields of endocrinology. Neurosteroids (NS) are steroids that are synthesized in the central (CNS) or peripheral nervous system (PNS), which is not only a source but also a target for neurosteroids. They are discussed as possible biomarkers in various cognitive disorders and research interest in this topic raises continuously. Nevertheless, knowledge on functions and metabolism is still limited, although the concept of neurosteroids was already introduced in the 1980s. Until today, the analysis of neurosteroids is truly challenging. The only accessible matrix for investigations of brain metabolism in living human beings is cerebrospinal fluid (CSF), which therefore becomes a very interesting specimen for analysis. However, neurosteroid concentrations are expected to be very low and the available amount of cerebrospinal fluid is limited. Further, high structural similarities of endogenous neurosteroids challenges analysis. Therefore, comprehensive methods, highly selective and sensitive for a large range of concentrations for different steroids in one aliquot are required and under continuous development. Although research has been increasingly intensified, still only few data are available on reference levels of neurosteroids in human cerebrospinal fluid. In this review, published literature of the last twenty years, as a period with relatively contemporary analytical methods, was systematically investigated. Considerations on human cerebrospinal fluid, different analytical approaches, and available data on levels of in analogy to periphery conceivable occurring neurosteroids, including (pro-) gestagens, androgens, corticoids, estrogens, and steroid conjugates, and their interpretation are intensively discussed.

A rapid method for quantification of persistent and mobile organic substances in water using supercritical fluid chromatography coupled to high-resolution mass spectrometry

Persistent and mobile organic substances (PM substances) are a threat to the quality of our water resources. While screening studies revealed widespread occurrence of many PM substances, rapid trace analytical methods for their quantification in large sample sets are missing. We developed a quick and generic analytical method for highly mobile analytes in surface water, groundwater, and drinking water samples based on enrichment through azeotrope evaporation (4 mL water and 21 mL acetonitrile), supercritical fluid chromatography (SFC) coupled to high-resolution mass spectrometry (HRMS), and quantification using a compound-specific correction factor for apparent recovery. The method was validated using 17 PM substances. Sample preparation recoveries were between 60 and 110% for the vast majority of PM substances. Strong matrix effects (most commonly suppressive) were observed, necessitating a correction for apparent recoveries in quantification. Apparent recoveries were neither concentration dependent nor dependent on the water matrix (surface or drinking water). Method detection and quantification limits were in the single- to double-digit ng L⁻¹ ranges, precision expressed as relative standard deviation of quadruplicate quantifications was on average < 10%, and trueness experiments showed quantitative results within ± 30% of the theoretical value in 77% of quantifications. Application of the method to surface water, groundwater, raw water, and finished drinking water revealed the presence of acesulfame and trifluoromethanesulfonic acid up to 70 and 19 μg L⁻¹, respectively. Melamine, diphenylguanidine, p-dimethylbenzenesulfonic acid, and 4-hydroxy-1-(2-hydroxyethyl)-2,2,6,6-tetramethylpiperidine were found in high ng L⁻¹ concentrations.

Analytical techniques for metabolomic studies: a review

Metabolomics is the comprehensive study of small-molecule metabolites. Obtaining a wide coverage of the metabolome is challenging because of the broad range of physicochemical properties of the small molecules. To study the compounds of interest spectroscopic (NMR), spectrometric (MS) and separation techniques (LC, GC, supercritical fluid chromatography, CE) are used. The choice for a given technique is influenced by the sample matrix, the concentration and properties of the metabolites, and the amount of sample. This review discusses the most commonly used analytical techniques for metabolomic studies, including their advantages, drawbacks and some applications.

Defining a system suitability limit to decide on column deterioration and to facilitate column transfers in chiral supercritical fluid chromatography

The separation of enantiomers is an important requirement during the entire drug life cycle in the pharmaceutical industry. High-performance liquid chromatography and supercritical fluid chromatography (SFC) are the main chromatographic techniques used to separate enantiomers. Since chiral stationary phases are often extensively used once a method has been developed, columns will age and must be replaced after a certain period. However, no practical guidelines exist to determine when a column is deteriorated or to decide whether a transfer to another column (with the same chiral selector) is successful. In this study, a system suitability limit for resolution was defined, based on an intermediate (time-different) precision study in SFC on four immobilized polysaccharide-based columns that only differed in manufacturer or particle size. This system suitability limit could be used to decide on column deterioration or as a requirement to evaluate whether a separation transfer was successful. Some method adaptations may be necessary to obtain successful transfers. An approach was proposed, which helped the analyst to make successful transfers. Graphical abstract.

Adjustable column length using a water stationary phase in supercritical fluid chromatography

A novel method for adjusting the column length during analysis in capillary supercritical fluid chromatography (SFC) is introduced. The approach is based on using a water stationary phase that can be partially ejected (or replenished) from the column as desired, without physically removing the supporting hardware elements. By flowing cool air through a sleeve surrounding the column in a heated oven, an axial thermal gradient along the length of the column was formed. This established a cooler region where the water stationary phase could be maintained and a hotter region where the coating was removed through dehydration. As such, the effective column length could be easily adjusted by changing the gradient via the air flow rate. Using this prototype arrangement, column lengths could be readily varied between 1.4 and 10 m. System response was also fairly rapid and changes took effect in under 1 min. Once a given length was established, retention times were highly reproducible with a relative standard deviation of 1.8% (n = 3). The method is cheaper and faster than the conventional method of storing numerous columns for manual switching. Further, it avoids the convolution of system pressure and flow rate that accompanies the pressure adjustments normally used to optimize capillary SFC separations. Results indicate that this approach could be a useful alternative for adjusting column length to optimize separation speed and resolution.

Supercritical fluid chromatography coupled to mass spectrometry for lipidomics

Supercritical fluid chromatography (SFC) has experienced a particular revival in recent years thanks to the development of robust and efficient commercial systems. Because of its physico-chemical properties, supercritical carbon dioxide (CO₂ ) mixed with cosolvents and additives is particularly suitable for SFC to allow the elution of compounds of different polarities and more particularly complex lipids. Hyphenation with mass spectrometry (MS) is increasingly described in the literature but still requires many further developments in order to be as user-friendly as coupling with liquid chromatography. The basic concepts of SFC and MS hyphenation will be first considered. Then a representative example of method development in lipidomics will be introduced. In conclusion, the challenges and future needs in this field of research will be discussed.

Supercritical fluid chromatography-a technical overview and its applications in medicinal plant analysis: an update covering 2012-2018

Medicinal plants with complex matrices are endowed with a wide scope of biological activities. The separation, quantification, characterization and purification of bioactive components from herbal medicine extracts have always challenged analysts. Fortunately, the advancement of various emerging techniques has provided potent support for improving the method selectivity, sensitivity and run speeds in medicinal plant analyses. In recent years, the advent of new-generation supercritical fluid chromatography (SFC) instruments and a wide diversity of column chemistries, coupled with the intrinsic technical features of SFC, have made it an alternative and prominent analytical platform in the medicinal plant research area. This work aims to give a comprehensive overview of the fundamentals, technical advancement and investigating parameters of SFC in combination with three prevalent detectors. Moreover, the latest research progress of SFC applications in medicinal plant analyses is illuminated, with focus on herbal medicine-related SFC papers on the analytical and preparative scale that were published during the period of 2012 to December 2018. The most relevant applications were classified based on the constituents to be analysed. As for the respective research cases, analytical protocols and data processing strategies were provided, along with the indicated restrictions or superiority of the method; thus, the current status of SFC in medicinal plant analysis was presented.

Fast super/subcritical fluid chromatographic enantioseparations on superficially porous particles bonded with broad selectivity chiral selectors relative to fully porous particles

Superficially porous particles (SPPs) have shown advantages in enantiomeric separations in HPLC by conserving selectivity while providing higher efficiency separations with significantly reduced analysis times. The question arises as to whether the same advantages can be found to the same extent in super/subcritical fluid chromatography. In this work, the low viscosity advantage of carbon dioxide/MeOH mixtures is coupled with high-efficiency 2.7 μm superficially porous particles for enantiomeric separations. Given the fact that the viscosity of the mobile phase is typically ten times lower than liquid mobile phases it is possible to use flow rates as high as 14 mL/min on 5 cm packed columns. Superficially porous particles (SPPs) were grafted with teicoplanin (TeicoShell), a chemically modified macrocyclic glycopeptide (NicoShell), vancomycin (VancoShell), and isopropyl derivatized cyclofructan-6 (LarihcShell-P). One hundred chiral analytes were separated in a very short time frame, as little as 0.2 min (13 s). Even shorter separations can be obtained with advances in SFC instrumentation. The LarihcShell-P is the only chiral crown ether-based selector which showed high selectivity for primary amines. The Teicoshell column offered unique separations for acidic and neutral analytes. The NicoShell and the VancoShell were useful in separating amine (secondary and tertiary) containing pharmaceutical drugs and controlled substances. By chemically modifying a macrocyclic glycopeptide (NicoShell) we report the first enantiomeric separation of nicotine under SFC conditions within 3 min with a resolution of >3. Additionally, van Deemter plots are constructed comparing the fully porous particles and superficially porous particles bonded with the same chiral selectors. In toto the SPP advantages also were found for SFC. However instrumental shortcomings involving extra column effects and pressure limitations need to be addressed by instrument manufacturers to realize the full advantages of SPPs and other smaller particle supports.