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.

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.

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.

Fast Optimization of Supercritical Fluid Chromatography-Mass Spectrometry Interfacing Using Prediction Equations.

The effect of makeup solvent composition in ultrahigh-performance supercritical fluid chromatography-triple quadrupole mass spectrometry using electrospray ionization was studied using a set of 91 compounds, 3 stationary phases, and 2 organic modifiers of the mobile phase. The 24 tested makeup solvents included pure alcohols and methanol in combination with commonly used additives such as water, formic and acetic acid, ammonia, and ammonia salts with varying molarity. The behavioral trends for different makeup solvent additives were established in the first step. Subsequently, the correlations between physicochemical properties and the MS responses were calculated using the Pearson correlation test and matrix plots. The regression analysis was performed using five descriptors: molecular weight, pKa, log P, number of hydrogen donors/acceptors, and the MS responses obtained with methanol as the makeup solvent. The resulting regression equations had a high prediction rate calculated as R2-predicted coefficient, especially when 10 mmol/L ammonium in methanol was used as an organic modifier of the mobile phase in positive mode. The trueness of these equations was tested via the comparison between experimental and predicted responses expressed as R2. Values of R2 > 0.8 were found for 88% of the proposed equations. Thus, the MS response could be measured using only one makeup solvent and the responses of other makeup solvents could be easily estimated. The suitability and applicability of determined regression equations was confirmed by the analysis of 13 blind probes, i.e., compounds not included in the original set of analytes. Moreover, the predicted and experimental responses followed the same increasing/decreasing trend enabling one to predict makeup solvent compositions leading to the highest sensitivity.

Ion mobility-high resolution mass spectrometry in doping control analysis. Part II: Comparison of acquisition modes with and without ion mobility.

In the second part of this study, a systematic comparison was made between two ion fragmentation acquisition modes, namely data-independent acquisition (DIA) and DIA with ion mobility spectrometry (IMS) technology. These two approaches were applied to the analysis of 192 doping agents in urine. Group I included 102 compounds such as stimulants, diuretics, narcotics, and ß2-agonists, while Group II contained 90 compounds included steroids, glucocorticoids, and hormone and metabolic modulators. Important method parameters were examined and compared, including the fragmentation, sensitivity, and assignment capability with the minimum occurrence of false positive hits. The results differed between Group I and II in number of detected fragments when exploring the MS/MS spectra. In Group I only 13%, while in the Group II 64% of the substances had a higher number of fragments in DIA-IMS mode vs. DIA. In terms of sensitivity, the performance of the two modes with and without activated IMS dimension was identical for about 50% of the doping agents. The sensitivity was higher without IMS, i.e. in simple DIA mode, for 20-40% of remaining doping agents. Despite this sensitivity reduction with IMS, 82% of compounds from both Groups met the minimum required performance level (MRPL) criteria of the World Anti-Doping Agency (WADA) when the DIA-IMS mode was applied. Automated data processing is important in routine doping analysis. Therefore, processing methods were optimized and evaluated for the prevalence of false peak assignments by analysing the target substances at different concentrations in urine samples. Overall, a significantly higher number of misidentified compounds was observed in Group II, with an almost 2-fold higher number of misidentifications in DIA compared to DIA-IMS. This result highlights the benefit of the IMS dimension to reduce the rate of false positive in screening analysis. The optimized UHPLC-IM-HRMS method was finally applied to the analysis of urine samples from administration studies including nine doping agents from both Groups. However, to limit the number of interferences from the biological matrix, an emphasis is needed on the adequate settings of the data processing method.

The effect of column history in supercritical fluid chromatography: Practical implications.

Long-term stability of retention times of a wide range of analytes has been evaluated using eight different stationary phases. These were from a single manufacturer to minimize the differences in silanol activity caused by the manufacturing process. The tested stationary phases included bridge ethylene hybrid, 2-ethylpyridine bridge ethylene hybrid with direct modification of silica particles, bidentate crosslinked charged surface hybrid fluorophenyl, bidentate crosslinked high strength silica C18, and propanediol linked phases including diol (pure propanediol linker), and three phases based on diol further modified with 2-picolylamine, diethylamine, and 1-aminoanthracene group. Retention times were monitored at the first injection, after three, nine, twelve months, and after the column regeneration via washing with pure water. The analyses were carried out using three different mobile phases, including methanol, methanol with 10 mmol/L ammonium formate, and methanol with 0.1% ammonium hydroxide. No overall decreasing or increasing trends were observed after evaluating individual contributing parameters such as analyte, stationary phase, and organic modifier. Our results suggest that the silyl-ether formation is not the only factor contributing to changes in the stationary phase pore surface. Indeed, the adsorption of mobile phase additives is probably another significant factor. That was also confirmed by the regeneration procedure using water, which is likely to reverse the silyl-ether formation to achieve the original retention. However, the retention times returned to the original values for all analytes only on three columns. Retention times on other columns remained shifted within ± 15 % RSD depending on the analyte properties and the nature of organic modifier. The retention time variations observed for each analyte group, i.e., acids, bases, and neutrals, were interpreted for each stationary phase. We concluded that the sterically protected surfaces exhibited significantly smaller changes in the retention times. Although the regeneration procedure effect depended on the column type, the results suggested beneficial effect of water. However, as the adsorption of additives on the column surface is an additional factor leading to retention time variations, the recommendation of using only one additive and/or organic modifier in each column will clearly improve the long-term repeatability of the retention times.

Ion mobility-high resolution mass spectrometry in anti-doping analysis. Part I: Implementation of a screening method with the assessment of a library of substances prohibited in sports.

In this series of two papers, 192 doping agents belonging to the classes of stimulants, narcotics, cannabinoids, diuretics, ß2-agonists, ß-blockers, anabolic agents, and hormone and metabolic modulators were investigated, with the aim to assess the benefits and limitations of ion mobility spectrometry (IMS) in combination with ultra-high performance liquid chromatography (UHPLC) and high resolution mass spectrometry (HRMS) in anti-doping analysis. In this first part, a generic UHPLC-IM-HRMS method was successfully developed to analyze these 192 doping agents in standard solutions and urine samples, and an exhaustive database including retention times, TWCCSN2 values, and m/z ratios was constructed. Urine samples were analyzed using either a simple "dilute and shoot" procedure or a supported liquid-liquid extraction (SLE) procedure, depending on the physicochemical properties of the compounds and sensitivity criteria established by the World Anti-Doping Agency (WADA) as the minimum required performance levels (MRPL). Then, the precision of the generic UHPLC-IM-HRMS method was assessed as intraday, interday as well as interweek variation of UHPLC retention times and TWCCSN2 values, for which RSD the values were always lower than 2% in urine samples. The possibility to filter MS data using IMS dimension was also investigated, and in average, the application of IMS filtration provided low energy MS spectra with 86% less interfering peaks in both standard and urine samples. Therefore, the filtered MS spectra allowed for an easier interpretation and a lower risk of false positive result interpretations. Finally, IMS also offers additional selectivity to the UHPLC-HRMS enabling to separate isobaric and isomeric substances. Among the selected set of 192 doping agents, there were 30 pairs of isobaric or isomeric compounds, and only two pairs could not be resolved under the developed conditions. This illustrates the potential of adding ion mobility to UHPLC-HRMS in anti-doping analyses.

Ultra-high performance supercritical fluid chromatography coupled to tandem mass spectrometry for antidoping analyses: Assessment of the inter-laboratory reproducibility with urine samples.

The aim of this study was to assess the interlaboratory reproducibility of ultra-high performance supercritical fluid chromatography coupled with tandem mass spectrometry method for routine antidoping analyses. To do so, a set of 21 doping agents, spiked in urine and analyzed after dilute and shoot treatment, was used to assess the variability of their retention times between four different laboratories, all equipped with the same chromatographic system and with the same ultra-high performance supercritical fluid chromatography stationary phase chemistry. The average relative standard deviations (RSD%) demonstrated a good reproducibility of the retention times for 19 out of 21 analytes, with RSD% values below 3.0%. Only for two substances, namely fenbutrazate and niketamide, the retention was not repeatable between laboratories, with RSD% of approximately 15% in both cases. This behaviour was associated with (a) the low organic modifier percentage (around 2-4%) in the mobile phase at the corresponding retention times, and (b) the influence of the system volume on poorly retained analytes. An analysis on seven "blind" urines was subsequently carried out in the same four laboratories. In these blind samples, either one, two, or none of the 21 doping agents previously analyzed were present at an unknown concentration. Each laboratory had to perform the identification of the compounds in the samples and estimate their concentrations. All laboratories assigned all target analytes correctly in all blind urine samples and provide a comparable estimation of their concentrations.

Ultra-high performance supercritical fluid chromatography in impurity control II: Method validation.

In our previous study we proposed a screening approach using ultra-high performance supercritical fluid chromatography for the determination of 10 pharmaceutical quality control mixtures. Most of resulting methods offered baseline separation of all analytes. However, some of these methods had to be further optimized to ensure their successful validation and applicability to impurity control in drug substance and drug products. Several challenges occurred during the optimization including: (i) the necessity of the resolution of active pharmaceutical ingredient and following impurity equaling at least 3, which was especially difficult to achieve for mixtures of structurally close compounds, (ii) unrepeatable elution of compounds eluting close to the dead volume or at the end of the gradient elution, and (iii) shifts in retention times due to the column aging and effects of additive. The most frequent optimization adjustments involved changes in gradient program. Other adjustments such as the substitution of Viridis UPC2 HSS C18 SB column with a slightly different Acquity UPLC HSS C18 SB column, the addition of acetonitrile in the modifier, and the column coupling also led to beneficial changes in selectivity. Subsequently, validation of all 10 methods was carried out to prove the applicability of ultra-high performance supercritical fluid chromatography methods for the impurity control in pharmaceuticals. Parameters recommended by ICH guidelines Q2 and Q3 including specificity, linearity, range, lower and upper limit of quantification, limit of detection, accuracy, and precision were examined. In addition, intermediate precision and the accuracy profiles were determined for selected methods. Overall, only two impurities did not meet the validation criteria due to low resolution and low sensitivity, respectively. Only identification threshold and not reporting threshold was met for this impurity.

Ultra-high performance supercritical fluid chromatography in impurity control: Searching for generic screening approach.

In this study, 63 compounds measured as 10 individual mixtures containing in each case an active pharmaceutical ingredient and its relevant impurities, and additional set of 7 basic beta blockers were analyzed using ultra-high performance supercritical fluid chromatography with UV and mass spectrometry detection. The separations were accomplished using 8 different stationary phases (diol, diethylamine, 2-picolylamine, 1-aminoanthracene, BEH 2-ethylpyridine, BEH, CSH pentafluorophenyl, and HSS C18 SB), 6 modifiers (methanol, ethanol, isopropanol, methanol/acetonitrile, methanol/ethanol, ethanol/acetonitrile) and 5 additives in methanol (0.1% formic acid, 10 mmol/L ammonium formate, 10 mmol/L ammonium acetate, 0.4% ammonium hydroxide, and 2% water). The resulting chromatograms were evaluated using 6 selected parameters: number of eluted peaks, number of separated peaks, resolution between active pharmaceutical ingredient and following impurity, peak symmetry, peak width at 50% of the peak height, and selectivity. Volatile additives such as ammonium formate, ammonium acetate, and especially ammonium hydroxide provided overall generic approach with very good chromatographic performance. Combined modifier methanol/acetonitrile (1:1) was important for separations of some critical pairs in case of neutral compounds. Diol stationary phase proved its suitability for wide range of applications when the separations of all mixtures were satisfactory on this column, except for vardenafil and beta blockers mixture. HSS C18 SB stationary phase offered unique complementary selectivity especially for analysis of structurally close compounds and/or isomers.

First inter-laboratory study of a Supercritical Fluid Chromatography method for the determination of pharmaceutical impurities.

Supercritical Fluid Chromatography (SFC) has known a strong regain of interest for the last 10 years, especially in the field of pharmaceutical analysis. Besides the development and validation of the SFC method in one individual laboratory, it is also important to demonstrate its applicability and transferability to various laboratories around the world. Therefore, an inter-laboratory study was conducted and published for the first time in SFC, to assess method reproducibility, and evaluate whether this chromatographic technique could become a reference method for quality control (QC) laboratories. This study involved 19 participating laboratories from 4 continents and 9 different countries. It included 5 academic groups, 3 demonstration laboratories at analytical instrument companies, 10 pharmaceutical companies and 1 food company. In the initial analysis of the study results, consistencies within- and between-laboratories were deeply examined. In the subsequent analysis, the method reproducibility was estimated taking into account variances in replicates, between-days and between-laboratories. The results obtained were compared with the literature values for liquid chromatography (LC) in the context of impurities determination. Repeatability and reproducibility variances were found to be similar or better than those described for LC methods, and highlighted the adequacy of the SFC method for QC analyses. The results demonstrated the excellent and robust quantitative performance of SFC. Consequently, this complementary technique is recognized on equal merit to other chromatographic techniques.

Simultaneous determination of quercetin and its metabolites in rat plasma by using ultra-high performance liquid chromatography tandem mass spectrometry.

Fast, selective, and sensitive ultra-high performance liquid chromatography method with tandem mass spectrometry detection for the determination of quercetin and its metabolites with various physico-chemical properties such as molecular weight, lipophilicity, and acid-base properties has been developed. These compounds included small hydrophilic phenolic acids and more lipophilic metabolites with preserved flavonoid structure in small amount of rat plasma. The developed method enables selective separation of phenolic acids and a pair of isomers tamarixetin and isorhamnetin with satisfactory peak shapes and a high sensitivity using mass spectrometry detection. In addition, two sample preparation procedures including protein precipitation and microextraction in packed sorbent (MEPS) were optimized. The sample acidification included in protein precipitation as well as optimizing of MEPS sorbents and elution solvents improved isolation of quercetin and related compounds from rat plasma. Finally, both methods developed for sample preparation were fully validated to demonstrate sufficient accuracy and precision and acceptable matrix effects. Both sample preparation approaches combined with mass spectrometry-based quantification allowed the simultaneous determination of quercetin and its metabolites from a small amount of biological samples of only 50 µL. Due to the fast and non-selective parallel sample preparation, the protein precipitation was eventually applied to plasma samples derived from pharmacokinetic studies.

Development of matrix effect-free MISPE-UHPLC-MS/MS method for determination of lovastatin in Pu-erh tea, oyster mushroom, and red yeast rice.

Matrix effect-free UHPLC-MS/MS method was developed and validated for the determination of cholesterol-lowering lovastatin in food samples represented by Pu-erh tea, oyster mushroom, and red yeast rice. The resulting method was fully validated in terms of intra-day and inter-day precision, accuracy, linearity, range, LOD, LOQ, and matrix effects. The matrix effect phenomenon evaluated by comparison of slopes of calibration curves was completely eliminated by solid-phase extraction based on the technique of molecularly imprinted polymers (MIPs). Comparison of elution profiles obtained on the MIP and corresponding control non-imprinted polymer (NIP) showed selectivity of the extraction procedure. In addition, selectivity of the MIP material and the molecularly imprinted solid-phase extraction (MISPE) was also proved by experiments evaluating retention of analytes physico-chemically similar to the target molecule. Extraction recoveries of these analytes represented by estrogen derivatives (estrone, estriol, 17α-ethinylestradiol, and ß-estradiol) were very low or even null. Synthesis and preparation of the resulting MIP sorbent was characterized by excellent repeatability expressed as RSD 7.7% (n=9) of extraction recoveries. The determined capacity of the MIP material reaching 375ng/mg is sufficient for analysis of the evaluated statin in its natural sources. Suitability of the resulting MISPE-UHPLC-MS/MS procedure for real sample analysis was verified by the determination of lovastatin in one dietary supplement based on the red yeast rice with a given amount of the target analyte. Finally, three mushroom and fifteen tea samples obtained in Czech food stores and tearooms were subjected to analysis. Low or null amount of lovastatin was found in these samples.

Development, validation and comparison of UHPSFC and UHPLC methods for the determination of agomelatine and its impurities.

Agomelatine is one of the newest antidepressants. Due to a different mechanism of action it offers a completely new approach in the treatment of depressive disorders. Two chromatographic methods for determination of agomelatine and its impurities were developed. The separations on UHPSFC system were accomplished using stationary phase based on BEH 2-EP and gradient elution with CO2 and methanol containing 20mM ammonium formate and 5% of water. The UHPLC separations were performed on stationary phase BEH Shield RP18. The mixture of acetonitrile and methanol in ratio 1:1 and ammonium acetate buffer pH 9.5 were used as mobile phase. Both developed methods were properly validated in terms of linearity, sensitivity (LOD, LOQ), accuracy and precision according to ICH guidelines. The UHPSFC method was linear in the range 0.25-70µg/ml for all analytes with method accuracy ≥97.4% and ≥100.2% and method intra-day precision RSD ≤2.4 and ≤0.8 for impurities and API (active pharmaceutical ingredient), respectively. The UHPLC method was linear in the range 0.1-10µg/ml for all analytes except three impurities for which the linear range was larger 0.1-25µg/ml. Method accuracy ≥95.7% and ≥95.2% and method intra-day precision RSD ≤2.6 and ≤1.5 were found for impurities and API, respectively. The measurement of tablet samples was performed and the selected parameters of the methods were compared. In conclusion, both methods were appropriate for the determination of agomelatine and its impurities in pharmaceutical quality control (QC), although the UHPSFC method was found as more convenient especially in the method development phase. The advantages of newly developed UHPSFC-PDA (photo diode array detector) method were its environmental friendliness due to the mobile phase used, a very good resolution, selectivity and high speed of analysis (total time of separation was 4.1min).