Surfactant-free microemulsion electrokinetic chromatography (SF-MEEKC) with UV and MS detection - a novel approach for the separation and ESI-MS detection of neutral compounds

Microemulsion electrokinetic chromatography (MEEKC) is a powerful tool to separate neutral species based on differences in their hydrophobic and hydrophilic properties. However, as a major drawback the conventionally used SDS based microemulsions are not compatible with electrospray ionization mass spectrometry (ESI-MS). In this work, a surfactant-free microemulsion (SFME) consisting of water, ethanol, and 1-octanol is used for surfactant-free microemulsion electrokinetic chromatography (SF-MEEKC). Ammonium acetate was added to the SFME enabling electrophoretic separations. The stability of SFMEs containing ammonium acetate was investigated using small-angle X-ray scattering and dynamic light scattering. A method for the separation of a model system of hydrophobic and hydrophilic neutral vitamins, namely the vitamins B₂ and D₃, and the cationic vitamin B₁ was developed using UV/VIS detection. The influence of the ammonium acetate concentration on the separation performance was studied in detail. The method was characterized concerning reproducibility of migration times and peak areas and concerning the linearity of the calibration data. Furthermore, SF-MEEKC was coupled to ESI-MS investigating the compatibility between SFMEs and the ESI process. The signal intensities of ESI-MS measurements of the model analytes were comparable for SFMEs and aqueous systems. Finally, the vitamin D₃ content of a drug treating vitamin D₃ deficiency was determined by SF-MEEKC coupled to ESI-MS using 25-hydroxycholecalciferol as an internal standard. Graphical abstract The concept of surfactant-free microemulsion electrokinetic chromatography coupled to electrospray ionization mass spectrometry.

Simultaneous analysis of circulating 25-hydroxy-vitamin D3, 25-hydroxy-vitamin D2, retinol, tocopherols, carotenoids, and oxidized and reduced coenzyme Q10 by high performance liquid chromatography with photo diode-array detection using C18 and C30 columns alone or in combination

Circulating lipid-phase micronutrients (LPM) such as 25-hydroxylated D vitamers, retinol, tocopherols, carotenoids including their isomers, and coenzyme Q10 play important roles in health maintenance and disease prevention and can serve as useful biomarkers. We developed fast, affordable, and accurate HPLC assays that simultaneously measured all above LPM in a single run using UV/VIS detection at 265nm, 295nm, and 480nm with (1) a C18 column alone; (2) a C30 column alone; or (3) each of these columns connected in series. The C18 column alone could separate all major LPM of interest in less than 17min but insufficiently resolved the lycopene isomers, the 25-hydroxylated D vitamers, lutein from zeaxanthin and β- from γ-tocopherol. The C30 column alone separated all LPM of interest including many isomeric analytes but failed to resolve the Q10 compounds, which co-eluted with carotenoids. Connecting the C18 and C30 columns in series with a detector after the C30 column and a pressure resistant detector between the columns resulted in ideal resolution and accurate quantitation of all LPM of interest but required software capable of processing the acquired data from both detectors. Connecting the C18 and C30 columns in series with exclusively one detector after the C30 column resulted in carotenoid-Q10 interferences, however, this was remedied by heart-cutting 2D-LC with a 6-port valve between the columns, which resolved all analytes in 42min. Faster run times led to some analytes not being resolved. Many variations of these methods are possible to meet the needs of individual requirements while minimizing sample material and turn-around-times.

Feasibility of ionic liquids as extractants for selective separation of vitamin D₃ and tachysterol₃ by solvent extraction

A selective separation of vitamin D₃ and tachysterol₃ by solvent extraction with 7 organic solvents and 11 ionic liquids (ILs) has been reported. Among organic solvents sulfolane showed optimal extraction performance, giving only a selectivity of 1.44 for tachysterol₃ over vitamin D₃. ILs with unsaturated bonds demonstrated high selectivity probably due to their different π-π interactions with the two compounds. A pyrrolidinium-based ionic liquid, for example, [BMPr][NTf2], provided the highest selectivity up to 1.77. Acceptable selectivity and distribution coefficients were observed by a combination of organic solvents and ILs as extracting agents. In this work, the effects of concentrations, anions, cations, and substituent of ILs were investigated, which may provide a rational strategy for the design of novel ILs for extractive separation of structural analogues. The purification and recovery of vitamin D₃3 via continuous multistage extractions were simulated, indicating that IL-based liquid-liquid extraction might be superior to traditional organic solvents in practical production.

Microemulsion electrokinetic chromatography for the separation of retinol, cholecalciferol, δ-tocopherol and α-tocopherol

A microemulsion electrokinetic chromatographic method was used to separate fat-soluble vitamins. The separation of retinol, cholecalciferol, and delta- and alpha-tocopherol was performed using a microemulsion containing 0.75% (v/v) n-heptane, 30 mM bis(2-ethylhexyl)sodium sulfosuccinate (AOT), 5% (v/v) 1-butanol, 15% (v/v) 1-propanol and 15% (v/v) methanol in 20mM boric acid-sodium borate buffer. The effect of the different microemulsion constituents was studied, including the type and concentration of surfactant, buffer, oil and co-surfactants. The presence of methanol in the microemulsion was found to be necessary to achieve the separation of the tocopherols. Detection was carried out at 200, 265 and 325 nm for the tocopherols, cholecalciferol and retinol, respectively. Calibration curves and precision data were obtained for each analyte. Good linear relationships were found between the analytical signal and the analytes concentration in the 25-500 mg L(-1) for retinol and cholecalciferol, and 25-300 mg L(-1) for tocopherols ranges. The precision of the method afforded relative standard deviations in the 4.0-10% range.

Effect of culture conditions on the synthesis of vitamin D(3) metabolites in Solanum glaucophyllum grown in vitro

In cultured Solanum glaucophyllum we have recently described the operation of a light-independent pathway of 1alpha,25-dihydroxy-vitamin D(3) (1alpha,25(OH)(2)D(3)) biosynthesis which involves similar intermediates as in vertebrates. In this work we investigated factors influencing the formation of 1alpha,25(OH)(2)D(3) and related sterols in S. glaucophyllum grown in vitro in darkness. Callus tissue and cells cultured in Murashige and Skoog medium in the absence of light were employed. Lipids were extracted with chloroform-methanol. The remaining water soluble fraction was incubated with beta-glucosidase to release vitamin D(3) compounds from their glycoconjugated derivatives followed by organic solvent extraction. Vitamin D(3) derivatives were isolated by Sephadex LH-20 and high-performance liquid chromatography (HPLC). HPLC or competitive protein binding assays with intestine 1alpha,25(OH)(2)D(3) receptor and serum vitamin D binding protein were used to quantify the metabolites. The levels of 1alpha,25(OH)(2)D(3) in calli varied according to the tissue explant origin, e.g. stem>leaf>fruit. For all organs, the metabolite was mainly present as free sterol (>80% of total). There were larger amounts of 25(OH)D(3) than 1alpha,25(OH)(2)D(3). It was found that Ca(2+), auxin and kinetin are important factors upregulating 1alpha,25(OH)(2)D(3) synthesis in S. glaucophyllum tissue and cells. Irradiation with UV light increased vitamin D(3) but not 1alpha,25(OH)(2)D(3) levels. In agreement with these results, incubation of cells with [3H]25(OH)D(3) revealed a low conversion rate to [3H]1alpha,25(OH)(2)D(3). The operation of a light-dependent pathway formation of vitamin D(3) coupled to higher expression of 25(OH)D(3)-1alpha-hydroxylase may account for the large concentrations of 1alpha,25(OH)(2)D(3) normally found in differentiated field-grown plants.

Microemulsion electrokinetic chromatography in suppressed electroosmotic flow environment. Separation of fat-soluble vitamins

Microemulsion electrokinetic chromatography (MEEKC) was carried out in a pH 2.5 phosphate buffer to effectively suppress the electroosmotic flow (EOF). With 66.6% (w/w) 25 mM phosphate buffer pH 2.5, 20.0% (w/w) 2-propanol, 6.6% (w/w) 1-butanol, 6.0% (w/w) sodium lauryl sulphate (SDS), and 0.8% (w/w) n-octane as the separation medium, the fat-soluble vitamins A palmitate, E acetate, and D3 were baseline separated within 11 min. With strongly suppressed EOF, the polarity of the separation voltage was reversed (positive electrode at the outlet); the n-octane micro droplets surrounded by negatively charged SDS molecules migrated towards the detector. The aqueous part of the microemulsion was modified with 20% (w/w) 2-propanol to improve partition between the n-octane phase and the surrounding aqueous medium. The fat-soluble vitamins were separated in order of decreasing hydrophobicity with a high migration time stability (repeatable within 0.1% RSD). Excellent accuracy and precision were obtained when the system was applied for the determination of vitamin E acetate in commercial vitamin tablets; quantitative data corresponded to 97.0% of label claim, intra-day results varied within 1.72% RSD (n=6), and inter-day results varied within 3.22% RSD (n=5).

Isolation and identification of 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3: metabolites of 1alpha,24(R)-dihydroxyvitamin D3 produced in rat kidney

1alpha,24(R)-Dihydroxyvitamin D3 [1alpha,24(R)(OH)2D3], a synthetic vitamin D3 analog, has been developed as a drug for topical use in the treatment of psoriasis. At present, the target tissue metabolism of 1alpha,24(R)(OH)2D3 is not understood completely. In our present study, we investigated the metabolism of 1alpha,24(R)(OH)2D3 in the isolated perfused rat kidney. The results indicated that 1alpha,24(R)(OH)2D3 is metabolized in rat kidney into several metabolites, of which 1alpha,24(R),25-trihydroxyvitamin D3, 1alpha,25-dihydroxy-24-oxovitamin D3, 1alpha,23(S),25-trihydroxy-24-oxovitamin D3, and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D3 are similar to the previously known metabolites of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. In addition to these aforementioned metabolites, we also identified two new metabolites, namely 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3. The two new metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1alpha,24(R)(OH)2D3 into both 25-hydroxylated and non-25-hydroxylated metabolites suggests that 1alpha,24(R)(OH)2D3 is metabolized in the rat kidney through two pathways. The first pathway is initiated by C-25 hydroxylation and proceeds further via the C-24 oxidation pathway. The second pathway directly proceeds via the C-24 oxidation pathway without prior hydroxylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1alpha-hydroxyvitamin D3 [1alpha(OH)D3] into 1alpha,25(OH)2D3. This finding indicates that the rat kidney does not possess the classical vitamin D3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1alpha(OH)D3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1alpha,24(R)(OH)2D3 is unknown. Our observation that the side chain of 1alpha,24(R)(OH)2D3 underwent 24-ketonization and 23-hydroxylation even in the absence of the C-25 hydroxyl group suggests that 1alpha,25(OH)2D3-24-hydroxylase (CYP24) can perform some steps of the C-24 oxidation pathway without prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1alpha,24(R)(OH)2D3.

Synergistic approaches based on nonchromatographic continuous separation techniques (solid-phase extraction and pervaporation) and chromatography couplings

Approaches based on continuous separation units coupled to either liquid or gas chromatography for improving the features of analytical methods are proposed. Examples of solid-phase separation-liquid chromatography for the determination of fat-soluble vitamins and their metabolites in clinical samples, and pervaporation-gas chromatography for the determination of volatile compounds in solid environmental samples are described. The clean-up and preconcentration effect achieved by the former coupling and the easy and effective solid-sample pretreatment in the latter clearly show their utility. The use of pervaporation as an advantageous alternative to headspace is demonstrated.

Separation from related compounds and assay of calcipotriol by high-performance liquid chromatography

In this paper, two methods are presented. One involves the separation of calcipotriol, a new synthetic analogue, from two related compounds, specifically cholecalciferol (Vitamin D3) and calcitriol (1,25-dihydroxyvitamin D3). The other involves the isolation and assay of calcipotriol from a topical ointment. The study was performed with reversed-phase high-performance liquid chromatography using an RP18 column and ultraviolet detection. Applying the method of Snyder, a mobile phase mixture containing methanol-acetonitrile-water (67:23:10, v/v) was found which achieved a total separation within 18 min. A mobile phase of methanol-water (80:20, v/v) attained a slower elution of calcipotriol. For isolation and assay of calcipotriol from an ointment (Daivonex), dissolution in chloroform gave the highest recovery (> 98%). The isolation and assay process can be performed within 2 h.

Separation and characterization of monoglucuronides of vitamin D(3) and25-hydroxyvitamin D(3) in rat bile by high-performance liquid chromatography

The separation and characterization of vitamin D(3)- and 25-hydroxyvitamin D(3)-monoglucuronides, biliary metabolites obtained from rats dosed with D(3) and 25-hydroxyvitamin D(3) per os, respectively, were carried out by HPLC. The glucuronide fractions were obtained from bile specimens by the combined use of a Bond Elut C18 cartridge, for solid phase extraction, and a lipophilic gel (piperidinohydroxypropyl Sephadex LH-20), for ion-exchange chromatography. Each glucuronide was identified by comparison with an authentic sample in three ways: its chromatographic behavior, that of its fluorescent labeled derivative using 4-[4-(6-methoxy-2-benzoxazolyl)phenyl]-1,2,4-triazoline-3,5- dione and data obtained following enzymatic hydrolysis using beta-glucuronidase.

Retention behavior of conjugated metabolites of vitamin D and related compounds in high-performance liquid chromatography

The retention behavior of sulfates or glucuronides of provitamin D, vitamin D, and 25-hydroxyvitamin D3, together with its fluorescent derivatives, are examined with reversed-phase high-performance liquid chromatography. Inclusion chromatography using cyclodextrin as a mobile-phase additive is also used for this purpose. Conventional reversed-phase high-performance liquid chromatography clearly separates the positionally isomeric conjugates of 25-hydroxyvitamin D3. The addition of the host compound to the mobile phase is effective in separating the pairs of fluorescent derivatives of vitamin-D3 and -D2 conjugates or provitamin-D3 and -D2 conjugates.

Kinetic and thermodynamic studies of the conversion of previtamin D3 to vitamin D3 in human skin

The thermoisomerization of previtamin D3 to vitamin D3 is the last step in the synthesis of vitamin D3 in human skin. Kinetic and thermodynamic studies of this reaction in human skin and an organic solvent revealed that not only the equilibrium of the reaction was shifted in favor of vitamin D3 formation in human skin (equilibrium constant K at 37 degrees C = 11.44) compared to hexane (K = 6.15), but also the rate of the reaction was increased by more than 10-fold in human skin (T1/2 at 37 degrees C = 2.5 h) when compared to hexane (T1/2 = 30 30 h). This extraordinarily fast reaction rate was also confirmed in vitro in chicken skin and in vivo in human subjects. The enthalpy change for the reaction determined by the van't Hoff plot was delta H degree = -21.58 kJ mol-1 in human skin and delta H degree = -15.60 kJ mol-1 in hexane. Arrhenius plots showed that the activation energies for both the forward and the reverse reactions were lower in human skin (Ea1 = 71.05 kJ mol-1 and Ea2 = 92.63 kJ mol-1) than in hexane (Ea1 = 84.90 kJ mol-1 and Ea2 = 100.5 kJ mol-1). Activation parameters for the reaction in human skin and in hexane were also reported. Subcellular fractionation of human epidermal tissue revealed that most epidermal 7-dehydrocholesterol and previtamin D3 were in the membrane fraction, while only 20% were in the cytosol. The interaction of previtamin D3 with intracellular lipids and/or proteins in skin may be responsible for the increased vitamin D3 formation rate in the skin.

Isolation and identification of vitamin D3, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and 1,24,25-trihydroxyvitamin D3 in Solanum malacoxylon incubated with ruminal fluid

It has been shown that Solanum malacoxylon contains 1 alpha,25-dihydroxyvitamin D3-glycoside. The presence of vitamin D3 and 25-hydroxyvitamin D3 has also been suggested. In the present study vitamin D3 and three of its metabolites, including 1 alpha,25-dihydroxyvitamin D3, were detected in plant leaf extracts preincubated with ruminal fluid (SMRF). Extraction of SMRF with non-polar organic solvents and purification of the lipid extract by TLC followed by HPLC yielded nine ultraviolet-absorbing (264 nm) peaks. Four of them comigrated on a Zorbax-Sil HPLC column with synthetic standards of vitamin D3, 25-hydroxyvitamin D3, 1 alpha,25-dihydroxyvitamin D3 and 1,24R,25-trihydroxyvitamin D3, respectively. These compounds were unequivocally identified by means of mass spectrometry. The results confirm that Solanum malacoxylon contains, in addition to 1 alpha,25-dihydroxyvitamin D3, vitamin D3, 25-hydroxyvitamin D3 and possibly other as yet unidentified derivatives. As 1,24,25-trihydroxyvitamin D3 is absent in plant extracts not incubated with ruminal fluid, the data also indicate that rumen microbes may convert 1 alpha,25-dihydroxyvitamin D3 into 1,24,25-trihydroxyvitamin D3.

[Cholecalciferol Reference Standard (Control 901) of the National Institute of Hygienic Sciences]

Cholecalciferol Reference Standard for the Japanese Pharmacopoeia (JP RS) was prepared. The following analytical data were obtained: melting point 85.8 degrees C; UV and IR spectra were in agreement with both of the previous JP RS and USP RS of Cholecalciferol; absorptivity at 265 nm E1%lcm = 476; optical rotation [alpha]20D = + 110.1 degrees; no impurities were detected by TLC and HPLC analyses; assay 100.1% by HPLC against the USP RS. Based on the above results, the raw material was authorized as the Reference Standard of the National Institute of Hygienic Sciences.

The measurement of vitamins D2 and D3 and seven major metabolites in a single sample of human plasma using gas chromatography/mass spectrometry

Selected ion monitoring of vitamin D metabolites has previously been described but there has been only one detailed description of the measurement by gas chromatography/mass spectrometry (GC/MS) of a number of metabolites in a single plasma sample. We describe here a GC/MS method, using stable isotope labelled internal standards, which allows the estimation of vitamins D2 and D3, and their 25-hydroxy, 24,25-dihydroxy and 25,26-dihydroxy metabolites in a single 2 ml sample of plasma, although more is needed for the measurement of 1,25-dihydroxyvitamin D3. Plasma was extracted on Bond Elut C18 cartridges and initial fractionation carried out on Sep-Pak SIL. Straight-phase high-performance liquid chromatography was required for separation of polyhydroxylated metabolites prior to GC/MS using an LKB 2091 mass spectrometer with conventional packed columns. n-Butylboronate esters were formed across vicinal hydroxyls, followed by formation of trimethylsilyl ethers using trimethylsilylimidazole. The [M - 90 - 15]+ ion for each compound was monitored. Deuterated internal standards were not available for all metabolites and it was necessary to use (2H6)D3 and (2H6)25OHD3 as standards for the measurement of D2 and D3, and 25OHD3 and 25OHD2, respectively, and (2H6)24,25(OH)2D3 as a standard for 24,25(OH)2D3 and 25,26(OH)2D2. Although the [M - 90 - 15]+ ion of 24,25(OH)2D and 25,26(OH)2D has the same mass: charge ratio, derivatives of these compounds are completely separated in the GC system used. The intra-assay precision for all these assays is usually less than 5%.

Isolation and identification of 24-dehydroprovitamin D3 and its photolysis to 24-dehydroprevitamin D3 in mammalian skin

Until now it had been assumed that mammalian skin contains only one provitamin D, 7-dehydrocholesterol, that is eventually converted to vitamin D3 after the skin is exposed to sunlight. Examination by reverse phase high performance liquid chromatography of lipid extracts from young rat skin, however, led to the observation that 7-dehydrocholesterol is not the only provitamin D in rat skin. Another provitamin D, accounting for 22 +/- 3% of the total provitamin content of the skin, was resolved from 7-dehydrocholesterol, and, on the basis of ultraviolet spectrophotometry, mass spectrometry, and nuclear magnetic resonance spectrometry, was identified as 24-dehydroprovitamin D3 (cholesta-5,7,24-trien-3 beta-ol). This new cutaneous provitamin D is not unique to the rat because it was also detected in the skin of reptiles, amphibians, birds, aquatic mammals, and humans. To be certain that the cutaneous 24-dehydroprovitamin D3 was as susceptible as 7-dehydrocholesterol to ultraviolet photolysis, rat skin was exposed to ultraviolet radiation. A reverse phase high performance liquid chromatographic analysis of a lipid extract of rat skin previously exposed to ultraviolet radiation demonstrated the presence of both previtamin D3 and 24-dehydroprevitamin D3. Therefore, these observations demonstrate for the first time that mammalian skin has the capacity to produce not one but at least two different vitamin Ds.

The isolation and identification of vitamin D2 and vitamin D3 from Medicago sativa (alfalfa plant)

Vitamin D2 and vitamin D3 were isolated from Medicago sativa (alfalfa) grown under field and laboratory conditions and then irradiated with ultraviolet light. The vitamins were identified by ultraviolet absorption, mass spectroscopy, and comparison with synthetic standards on several chromatographic systems. Sun-cured, field-grown alfalfa contained vitamin D2 at a concentration of 48 ng/g (1920 IU/kg) and vitamin D3 at 0.63 ng/g (25 IU/kg). Laboratory-grown alfalfa, artificially irradiated, contained vitamin D2 at a concentration of 80 ng/g and vitamin D3 at 1.0 ng/g. Therefore, the presence of vitamin D2, as well as vitamin D3, has unequivocally been demonstrated in alfalfa plant tissue.

Liquid chromatographic cleanup and determination of low levels of vitamin D3 in sheep plasma

A liquid chromatographic (LC) method is described for the determination of vitamin D3 in sheep plasma. Samples are extracted by one of 2 different methods, depending on the concentration of vitamin D3. The samples are purified by using either a Sep-Pak silica cartridge or a small alumina column, followed by additional cleanup on a Metalsorb LC column. Final analysis was carried out on a 5 micron C18 column using a radial compression separation system with an acetonitrile-methanol solvent system. Vitamin D3 was completely resolved from any interfering compounds in the plasma; total run time was less than 15 min, using a variable wavelength detector set at 264 nm. The method was successfully applied to samples at levels of 1-10 ng added vitamin D3 mL sheep plasma, with recoveries in the range 90-97%.

An evaluation of the use of Sep-Pak C18 cartridges for the extraction of vitamin D3 and some of its metabolites from plasma and urine

The use of Sep-Pak C18 cartridges for the extraction of vitamin D and some of its metabolites from plasma and urine has been evaluated by studying the recovery of added tritiated secosteroids. The preparation of the cartridges, recoveries, extraction and elution with a number of solvents, effect of varying flow rates for application and elution, and the effect of increasing volumes of plasma and urine have been investigated. Two methods for the application of secosteroids present in plasma to Sep-Pak C18 cartridges have been examined, using methyl cyanide extracts removing precipitated protein by centrifugation, and using acidified methanolic plasma. Methyl cyanide extracts applied to Sep-Pak C18 cartridges and eluted with methanol or methyl cyanide gave the cleanest extracts suitable for direct HPLC. Acidified methanolic plasma, applied to Sep-Pak C18 cartridges and eluted with methanol or methyl cyanide gave extracts which could not be applied directly to an HPLC--further fractionation using Sep-Pak SIL cartridges was necessary. Recoveries of added tritiated secosteroids using both methods were greater than 80% with the exception of vitamin D itself which was poorly recovered--methyl cyanide extraction giving only 30% recovery and use of acidified methanolic plasma giving 66% recovery.

19-nor-10-ketovitamin D derivatives: unique metabolites of vitamin D3, vitamin D2, and 25-hydroxyvitamin D3

Three metabolites were isolated after incubation of vitamin D3, vitamin D2, or 25-hydroxyvitamin D3 with bovine rumen microbes. They are identified as 5(E)-19-nor-10-ketovitamin D3, 5(E)-19-nor-10-ketovitamin D2, and 5(E)-19-nor-10-keto-25-hydroxyvitamin D3, respectively. The identifications were based on ultraviolet absorbance, mass spectroscopy, and chemical reactivity. All 5(E)-19-nor-10-ketovitamin D derivatives examined had an absorbance maximum at 312 nm and a characteristic fragment in their mass spectra corresponding to loss of 43 amu from their molecular ions. The vitamin D3 metabolite was identical in all essential spectral and chromatographic aspects with authentic synthetic 5(E)-19-nor-10-ketovitamin D3. These metabolites represent a unique pathway of vitamin D metabolism and the first characterized products of microbial vitamin D metabolism. The conversion of vitamin D and its metabolites to their 19-nor-10-keto forms likely represents a detoxification mechanism.

Individual quantitation of vitamin D2, vitamin D3, 25-hydroxyvitamin D2, and 25-hydroxyvitamin D3 in human milk

Extraction, lipid-reduction, and chromatographic methods suitable for the resolution and subsequent quantitation of vitamin D2, vitamin D3, 25-hydroxyvitamin D2, and 25-hydroxy-vitamin D3 from human milk are described. This procedure utilizes a methanol:methylene chloride extraction, precipitation of unwanted lipids with cold methanol and ether, backwash with alkaline buffer, silica Sep-Pak preparative chromatography, normal- and reverse-phase high-performance liquid chromatography with final quantitation of the antirachitic sterols by competitive protein binding assay. The described assay was used to determine these antirachitic sterols in milk from women receiving various supplements of vitamin D or undergoing ultraviolet phototherapy.

High-performance liquid chromatography of fat-soluble vitamins. Simultaneous quantitative analysis of vitamins D2, D3 and E. Study of percentage recoveries of vitamins from cod liver oil

Vitamins D2, D3 and E were resolved and quantified by applying reversed-phase high-performance liquid chromatography to extracts of cod liver oil. The method, using two reversed-phase C18 columns and a ternary mixture of acetonitrile, methanol and water as the eluent resolved all fat-soluble vitamins well, including the pair D2-D3. The extraction procedure was studied; the recoveries, using two different solvents (hexane and diethyl ether) for extractions were 60.6 +/- 1.0 and 77.1 +/- 1.1, 56.9 +/- 1.2 and 74.8 +/- 0.8, and 14.1 +/- 0.7 and 89.8 +/- 1.4% for vitamins D2, D3 and E, respectively.

High-performance liquid chromatography of fat-soluble vitamins: separation and identification of vitamins D2 and D3 and their isomers in food samples in the presence of vitamin A, vitamin E and carotene

Vitamins D2 and D3 and their corresponding previtamins and provitamins were resolved by reversed-phase high-performance liquid chromatography using a ternary solvent system (acetonitrile-methanol-water) pumped according to a gradient elution programme. The D vitamins were also resolved in the presence of other lipid-soluble vitamins (A, E and K1) and carotene. The peaks were monitored with a UV-visible variable-wavelength detector and were detected at their maximum absorbance, resulting in maximum sensitivity. Lipid-soluble vitamins and carotene were resolved in extracts obtained from oils and butter, thus permitting their identification in a single chromatographic run.

Determination of vitamin D3 in cod-liver oil by high-performance liquid chromatography

The present British Pharmacopoeia monograph for cod-liver oil requires a bioassay for the vitamin D3 content which is both time-consuming and complex. Alternative assays employing chromatographic procedures have been described but all these involve prior saponification of the oil. A selective extraction for vitamin D3 without the need for saponification is reported in this paper. The extraction utilizes only chromatographic assay using argentation on reversed-phase silica, with vitamin D2 as the internal standard. Reproducibility of injection gave a coefficient of variation of 0.6%, and repeatability of extraction for six samples gave a coefficient of variation of 6.8%.

A simple method for the isolation of vitamin D metabolites from plasma extracts

A simple method has been developed using 'SEP-PAK' disposable silica cartridges to separate the major endogenous vitamin D metabolites, namely vitamin D3, 25-hydroxy vitamin D3 (25OHD3), 1,25 dihydroxy vitamin D3 (1.25 (OH)2D3) and 24,25 dihydroxyvitamin D3 (24,25 (OH) 2D3). After extraction of plasma in isopropanol-toluene (25:75) the dried extract is reconstituted in hexane; this is applied to a SEP-PAK column, and stepwise elution carried out under gravity with 0.1 divided by isopropanol in hexane (neutral lipids), 1% isopropanol in hexane (D3), 3 divided by isopropanol in hexane (25OHD3), 3.125 divided by ethanol in dichloromethane (24,25 (OH) 2D3) and 50 divided ethanol in toluene (1, 25(OH) 2D3). Complete separation of these D3 metabolites is achieved by this process and up to 40 samples can be handled at one time. If combined with a suitable ligand binding assay, the system appears to be suitable for preparation of samples prior to the routine assay of vitamin D metabolites.

Chromatographic separation of vitamin D3 sulfate and vitamin D3

This paper describes a simple chromatographic technique on Sephadex LH20 for the separation of vitamin D3 sulfate from free vitamin D3 and its metabolites. This technique has been used in the study of vitamin D3 sulfate metabolism in rats. Seven hours after injection of vitamin D3 sulfate (35S or 35S and 3H) only the peak of vitamin D sulfoconjugate was found in chromatographic elution of serum extracts.

High pressure liquid chromatographic separation and identification of vitamins D2 and D3 in the presence of fat-soluble vitamins in dosage forms

A simple and rapid qualitative method is described for determining the presence of vitamin D2 (ergocalciferol) and/or vitamin D3 (cholecalciferol) in various preparations by reverse phase high pressure liquid chromatography (HPLC). When both D2 and D3 are present, this method effectively separates and identifies each vitamin D form by its respective retention time. A significant difference between vitamins D2 and D3 exists in their antirachitic activity in poultry. Preparations can be tested rapidly by this method to ascertain that the correct D vitamin form has been added. Fat-soluble vitamins such as vitamins A, E, K1, and K3 do not interfere. Vitamins D2 and D3 were separated at the baseline in model preparations. As little as 2 ng each of vitamin D2 and vitamin D3 can be separated and identified.

High-pressure liquid chromatography: separation of the metabolites of vitamins D2 and D3 on small-particle silica columns

The high-pressure liquid chromatographic separation of all of the known metabolites of vitamin D(2) and vitamin D(3) found in biological fluids has been achieved. This technique has been successfully applied to the analysis of vitamin D mixtures, purification of vitamin D metabolites, and identification of radioactive peaks. Some theoretical bases for the observed resolutions are suggested.

Identification of 1,25-dihydroxycholecalciferol, a form of vitamin D3 metabolically active in the intestine

A biologically active vitamin D(3) metabolite ("peak V metabolite") more polar than 25-hydroxycholecalciferol has been isolated from chicken intestines in pure form as a mono(trimethylsilyl)ether derivative. The molecule has been identified as 1,25-dihydroxycholecalciferol by means of mass spectrometry, ultraviolet absorption spectrophotometry, and specific chemical reactions.

Absorption of vitamin D3-3H in control subjects and patients with intestinal malabsorption

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