Simultaneous Determination of Vitamin D and Its Hydroxylated and Esterified Metabolites by Ultrahigh-Performance Supercritical Fluid Chromatography-Tandem Mass Spectrometry

Supercritical Fluid Chromatography in Bioanalysis-A Review

In the last decade, the instrumentation improvements in supercritical fluid chromatography (SFC) and the hyphenation to mass spectrometry (MS), have increased the SFC acceptance between scientists, becoming today a valuable tool in analytical chemistry. The unique selectivity, short analysis times, low consumption of organic solvents, and the greener mobile phase, have contributed to expanding its applicability which has led to an increase in the number of publications especially in the bioanalysis area. This work reviews the advantages and main applications of SFC in bioanalysis during the last 5 years. Fundamental aspects concerning mobile phase composition, stationary phase, hyphenation to MS as well as matrix effect have been discussed. Finally, the most relevant applications have been summarized.

Comprehensive analysis of vitamin D3 impurities in oily drug products using supercritical fluid chromatography-mass spectrometry

Vitamin D3, an essential micronutrient, often requires supplementation via medicines or food supplements, which necessitate quality control (QC). This study presents the development of a method for detecting and quantifying seven impurities of vitamin D3 in oily drug products using supercritical fluid chromatography-mass spectrometry (SFC-MS). Targeted impurities include two esters of vitamin D3 and five non-esters including four that are isobaric to vitamin D3. Firstly, a screening study highlighted the Torus 1-AA column and acetonitrile modifier as adequate for the separation, followed by optimization of the SFC conditions. Secondly, make-up solvent composition and MS settings were optimized to reach high sensitivity. For both the separation and MS response, the screening design of experiments proved useful. Lastly, a fast saponification and liquid-liquid extraction method was developed, enabling efficient sample cleanup and impurities recovery from the complex oily matrix. The SFC-MS method suitability was assessed in two validation studies. The first study employed the ICH Q2 guideline for impurity limit test to demonstrate method specificity and establish a limit of detection (LOD) and a limit of quantification (LOQ) at 0.2% and 0.5%, respectively, for ester impurities. The second study conducted a comprehensive quantitative assessment for three non-ester impurities using a total error approach, determining method validity through accuracy profiles. The validated method exhibited reliable performance across impurity concentrations from 0.1% to 2.0%, with estimated LODs ranging from 2 to 7 ng/mL. This study further promotes SFC-MS as a valuable, versatile, and green tool for routine pharmaceutical QC.

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.

Analysis of vitamin D and its metabolites in biological samples - Part II: Optimization of a sample preparation method for liver tissue

Extraction of vitamin D, including its hydroxylated and esterified metabolites, from soft tissues such as the liver is challenging due to the lipophilic character of matrix and analytes that are expected in very low concentration levels. In this study, we aimed at the optimization of two-step extraction using solid-liquid extraction as the first step, followed by solid-phase extraction. Various solvents, including ethanol, acetonitrile, methanol, acetone, heptane, and heptane with isopropanol, were investigated to isolate vitamin D compounds from liver tissue in the first step. Acetone was finally selected as the most suitable solvent for the solid-liquid extraction, with the highest recovery in the range of 67 - 98% for polar hydroxylated forms and 3 - 28% for lipophilic vitamin D and esters. Two solid phase extraction (SPE) based on the (i) "bind and elute strategy" and (ii) "removal strategy" using hydrophilic-lipophilic balanced SPE sorbent were optimized as a proceeding step for acetone extracts to increase the method selectivity. Finally, two optimized methods, combining solid-liquid extraction and individual SPE strategy, were examined in terms of sensitivity, recovery, matrix effect, accuracy, and precision. The limits of quantification were in the range of 1 - 10 ng/mL and 3 - 20 ng/mL analyzed by ultra-high performance supercritical fluid chromatography and ultra-high performance liquid chromatography hyphenated a with tandem mass spectrometer, respectively. The absolute recovery determined for the "bind and elute strategy" protocol was in the range of 3 - 24 %. Nevertheless, this method was free of matrix effects, which were determined to be in the 73 - 120 % range. On the contrary, the "removal strategy" approach provided higher recovery values for all compounds (47 - 123 %), but the results for nonpolar vitamin D and esters were strongly affected by signal suppression (matrix effects 3 - 51 %). Both methods fulfilled the criteria for accuracy and precision requested by the European Medicine Agency Guideline on Bioanalysis. "Removal strategy" SPE with decreased manual intervention and lower solvent consumption was finally applied to mouse liver tissue to determine vitamin D and its hydroxylated and esterified metabolites for the first time. The results, i.e., vitamin D esters detected in liver tissue, supported the notion that esters of vitamin D can be stored in lipophilic tissues to release vitamin D.

Accurate Clinical Detection of Vitamin D by Mass Spectrometry: A Review

Vitamin D deficiency is thought to be associated with a wide range of diseases, including diabetes, cancer, depression, neurodegenerative diseases, and cardiovascular and cerebrovascular diseases. This vitamin D deficiency is a global epidemic affecting both developing and developed countries and therefore qualitative and quantitative analysis of vitamin D in a clinical context is essential. Mass spectrometry has played an increasingly important role in the clinical analysis of vitamin D because of its accuracy, sensitivity, specificity, and the ability to detect multiple substances at the same time. Despite their many advantages, mass spectrometry-based methods are not without analytical challenges. Front-end and back-end challenges such as protein precipitation, analyte extraction, derivatization, mass spectrometer functionality, must be carefully considered to provide accurate and robust analysis of vitamin D through a well-designed approach with continuous control by internal and external quality control. Therefore, the aim of this review is to provide a comprehensive overview of the development of mass spectrometry methods for vitamin D accurate analysis, including emphasis on status markers, deleterious effects of biological matrices, derivatization reactions, effects of ionization sources, contribution of epimers, standardization of assays between laboratories.

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.

Analysis of the ability of vitamin D3-metabolizing cytochromes P450 to act on vitamin D3 sulfate and 25-hydroxyvitamin D3 3-sulfate

25-Hydroxyvitamin D3 (25(OH)D3) is present in the human circulation esterified to sulfate with some studies showing that 25(OH)D3 3-sulfate levels are almost as high as unconjugated 25(OH)D3. Vitamin D3 is also present in human serum in the sulfated form as are other metabolites. Our aim was to determine whether sulfated forms of vitamin D3 and vitamin D3 metabolites can be acted on by vitamin D-metabolizing cytochromes P450 (CYPs), one of which (CYP11A1) is known to act on cholesterol sulfate. We used purified, bacterially expressed CYPs to test if they could act on the sulfated forms of their natural substrates. Purified CYP27A1 converted vitamin D3 sulfate to 25(OH)D3 3-sulfate with a catalytic efficiency (k_cat/K_m) approximately half that for the conversion of vitamin D3 to 25(OH)D3. Similarly, the rate of metabolism of vitamin D3 sulfate was half that of vitamin D3 for CYP27A1 in rat liver mitochondria. CYP2R1 which is also a vitamin D 25-hydroxylase did not act on vitamin D3 sulfate. CYP11A1 was able to convert vitamin D3 sulfate to 20(OH)D3 3-sulfate but at a considerably lower rate than for conversion of vitamin D3 to 20(OH)D3. 25(OH)D3 3-sulfate was not metabolized by the activating enzyme, CYP27B1, nor by the inactivating enzyme, CYP24A1. Thus, we conclude that 25(OH)D3 3-sulfate in the circulation may act as a pool of metabolically inactive vitamin D3 to be released by hydrolysis at times of need whereas vitamin D3 sulfate can be metabolized in a similar manner to free vitamin D3 by CYP27A1 and to a lesser degree by CYP11A1.

Comparison of Validation Parameters for the Determination of Vitamin D3 in Commercial Pharmaceutical Products Using Traditional and Greener HPTLC Methods

Several analytical methods are documented for the estimation of vitamin D3 (VD3) in pharmaceuticals, food supplements, nutritional supplements, and biological samples. However, greener analytical methods for VD3 analysis are scarce in the literature. As a consequence, attempts were made to design and validate a greener “high-performance thin-layer chromatography (HPTLC)” method for VD3 estimation in commercial pharmaceutical products, as compared to the traditional HPTLC method. The greenness indices of both approaches were predicted by utilizing the “Analytical GREENness (AGREE)” method. Both traditional and greener analytical methods were linear for VD3 estimation in the 50–600 ng band−1 and 25–1200 ng band−1 ranges, respectively. The greener HPTLC strategy outperformed the traditional HPTLC strategy for VD3 estimation in terms of sensitivity, accuracy, precision, and robustness. For VD3 estimation in commercial tablets A–D, the greener analytical strategy was better in terms of VD3 assay over the traditional analytical strategy. The AGREE index of the traditional and greener analytical strategies was estimated to be 0.47 and 0.87, respectively. The AGREE analytical outcomes suggested that the greener analytical strategy had a superior greener profile to the traditional analytical strategy. The greener HPTLC strategy was regarded as superior to the traditional HPTLC methodology based on a variety of validation factors and pharmaceutical assays.

Differentiation of Dihydroxylated Vitamin D3 Isomers Using Tandem Mass Spectrometry

Vitamin D compounds are a group of secosteroids derived from cholesterol that are vital for maintaining bone health in humans. Recent studies have shown extraskeletal effects of vitamin D, involving vitamin D metabolites such as the dihydroxylated vitamin D₃ compounds 1,25-dihydroxyvitamin D₃ and 24,25-dihydroxyvitamin D₃. Differentiation and characterization of these isomers by mass spectrometry can be challenging due to the zero-mass difference and minor structural differences between them. The isomers usually require separation by liquid chromatography (LC) prior to mass spectrometry, which adds extra complexity to the analysis. Herein, we investigated and revisited the use of fragmentation methods such as collisional induced dissociation (CID), infrared multiphoton dissociation (IRMPD), electron induced dissociation (EID), and ultraviolet photodissociation (UVPD), available on a 12T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) to generate characteristic fragments for the dihydroxylated vitamin D₃ isomers that can be used to distinguish between them. Isomer-specific fragments were observed for the 1,25-dihydroxyvitamin D₃, which were clearly absent in the 24,25-dihydroxyvitamin D₃ MS/MS spectra using all fragmentation methods mentioned above. The fragments generated due to cleavage of the C-6/C-7 bond in the 1,25-dihydroxyvitamin D₃ compound demonstrate that the fragile OH groups were retained during fragmentation, thus enabling differentiation between the two dihydroxylated vitamin D₃ isomers without the need for prior chromatographic separation or derivatization.