A new procedure for the formation of isotachysterol derivatives of subnanomole quantities of ergocalciferol, cholecalciferol and its metabolites prior to gas liquid chromatography

Quantitative analysis of vitamin D using m/MALDI-TOF mass spectrometry based on a parylene matrix chip

Vitamin D deficiency is associated with various disorders and is diagnosed based on the concentration of 25-hydroxy vitamin D3 (25(OH)D3) in serum. The parylene matrix chip was fabricated to reduce the matrix background noise, and the homogenous distribution of the matrix was retained for the quantitative analysis of 25(OH)D3. The Amplex Red assay was performed to confirm that the sample-matrix mixing zone of the parylene matrix chip was formed below the surface of the parylene-N film. The homogeneous distribution of the matrix was verified from the fluorescence image. For effective analysis using a parylene matrix chip, 25(OH)D3 was modified through the nucleophilic addition of betaine aldehyde (BA) to form a hemiacetal salt. Such modified 25(OH)D3 with a positive charge from BA could be effectively analyzed using MALDI-TOF mass spectrometry. Serum 25(OH)D3 was extracted by liquid–liquid extraction (LLE) and quantified using MALDI-TOF mass spectrometry based on the parylene matrix chip. The intensity of the mass peak of 25(OH)D3 was linearly correlated (r2 = 0.992) with the concentration of 25(OH)D3 spiked in serum, and the LOD was 0.0056 pmol/μL. Energy drinks and vitamin D3 tablets were also employed for the real sample analysis. Finally, the results of the chemiluminescence binding assay and MALDI-TOF mass spectrometry were statistically analyzed to determine the applicability of the method using the Bland–Altman test and Passing–Bablok regression.

Vitamin D analyses in veterinary feeds by gas chromatography-tandem mass spectrometry

This report examines the feasibility of determination of Vitamin D3, D2 and their 25-hydroxy metabolites utilizing Gas Chromatography Tandem Mass Spectrometry (GC/MS/MS) as a potential alternative to popular Liquid Chromatography Tandem Mass Spectrometric (LC/MS/MS) methodologies. The GC/MS/MS approach was found to operate reasonably well despite long-standing concerns that gas-liquid chromatography of vitamin D compounds invoke thermal rearrangements owing to the relatively high inlet and capillary column temperatures used. The workup procedure involved incubation of feed samples with concentrated potassium hydroxide for overnight fat saponification, extraction of D Vitamins in n-hexane and reaction with N,O-bis(trimethylsilyl)trifluoroacetamide at 70 °C for 30 mins. In addition to parent compounds, small amounts of pyro-, isopyro-, and iso-vitamin D and isotachysterol3 variants were obtained from each Vitamin D-related compound upon extraction and GC/MS/MS analysis. Mass spectral and chromatographic behavior of these compounds are herein described and interpreted. Multiple Reaction Monitoring settings on GC/MS/MS included m/z 456→351 for Vitamin D3 and m/z 486→363 for Vitamin D2. Trimethylsilylation enabled single predominant peaks for Vitamins D3 and D2, and sample workup in the presence of deuterated Vitamin D analogs enabled accurate and precise sensitivity to 1 ppb (ng/g) in feeds. The method could be extended with reasonable accuracy to 25-hydroxy (25OH) compounds, but accuracies would be significantly improved by inclusion of respective 25OH-specific deuterated internal standards. The method was applied to 27 submissions of suspect dog foods of which 22% were discovered elevated and 44% were discovered to contain toxic levels of Vitamin D3. The described method was thus discovered to provide a suitable mass spectrometric approach for Vitamin D, proving itself here specifically of value in detection of ergocalciferol and cholecalciferol in animal feeds. The specificity and sensitivity of the tandem quadrupole approach can enable suitable applicability to serum determination if desired.

Stability of vitamin D in foodstuffs during cooking

We investigated the retention of vitamin D3 and 25-hydroxyvitamin D3 in eggs, vitamin D3 in margarine, and vitamin D3 and vitamin D2 in bread. Our set-up illustrated the cooking methods usually performed in households i.e. boiling, frying in pan and oven, and baking. All experiments were performed three times independently of one another. The retention of vitamin D compounds in eggs and margarine during heat treatment in an oven for 40 min at normal cooking temperature showed retention at 39-45%, while frying resulted in retention at 82-84%. Boiled eggs were found to have a similar level of retention (86-88%). For bread baked, as recommended in the recipe, the retention of vitamin D3 in rye bread at 69% was lower than the retention in wheat bread at 85%. A similar observation was made for vitamin D2, although the retention was slightly higher, 73% and 89%. No difference between retention of vitamin D3 and 25-hydroxyvitamin D3 in eggs was shown. Cooking may cause detrimental loss of vitamin D, but it depends on the actual foodstuffs and the heating process. Further research is needed to optimise cooking procedures to enhance retention of vitamin D. Vitamin D retention should be taken into account in future calculations of dietary intake of vitamin D.

A new procedure for the isomerization of vitamin D and its metabolites

A new procedure for the isomerization of vitamin D and its metabolites is described. Vitamin D or its metabolites are dissolved in 100 microliters methanol and 10 M HC1 in 2-butanol is used as the reagent for isomerization. The isomerization reaction is carried out at 5 degrees C for 2-3 min which gives quantitative yields of isotachysterols down to 10 ng level without use of any carrier.

Measurement of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2 and 25,26-dihydroxyvitamin D2 in a single plasma sample by mass fragmentography

A specific and sensitive assay for the measurement of the concentration of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2 and 25,26-dihydroxyvitamin D2 in a single plasma sample is described, using stable isotope dilution mass fragmentography. After addition of appropriate deuterium-labelled internal standards, plasma samples were treated with acetonitrile to precipitate protein, and vitamin D metabolites were extracted on prepacked microparticulate reverse-phase cartridges. Further purification was achieved using straight-phase cartridges and high-performance liquid chromatography. Gas chromatography-mass spectrometry was carried out after appropriate derivatisation of samples and standards. The method has been evaluated in terms of specificity, recovery of added standards, and reproducibility.

Chromatography of fat-soluble vitamins in clinical chemistry

A review is presented of current gas and liquid chromatographic methods for the determination of the fat-soluble vitamins A, D, E and K and the provitamin A beta-carotene in biological samples of human origin. For each vitamin, the discussion successively focuses on procedures for sample preparation, gas and liquid chromatographic systems and principles of detection. The emphasis is on liquid chromatography, which is gradually becoming a standard technique in fat-soluble vitamin assays. New trends in the liquid chromatography of these compounds include the use of smaller particles and shorter columns, to improve speed, and the advance of electrochemical detection as an alternative to absorbance and fluorescence detection. Bonded phases, both normal and reversed phase, tend to be preferred over underivatized silica as column supports. Gas chromatography remains of particular value in combination with mass spectrometry, a technique which may form the basis of reference methods. In general, despite the availability of well established analytical methods for fat-soluble vitamins, the wealth of recent literature in this area indicates that there continues to be a need for new assays with enhanced speed, specificity and sensitivity.

Rapid automated high-performance liquid chromatographic assay for ercalcidiol and calcidiol (25-hydroxyvitamins D2 and D3) using trans-calcidiol as an ultraviolet-absorbing internal standard

A system is described using high-performance liquid chromatography to separate and quantify, by spectrophotometry in a simple one-stage procedure, ercalcidiol (25-hydroxyvitamin D2) and calcidiol (25-hydroxyvitamin D3). The novel feature of the method is the employment of an ultraviolet-absorbing internal standard to monitor recovery. This has the advantage of permitting total automation of the quantification by eliminating the need for radioactivity counting. The method gives results that compare well with those obtained in other systems and has particular application in clinical studies where rapid separate determination of ercalcidiol and calcidiol is required.

Gas chromatography-mass spectrometry and the measurement of vitamin D metabolites in human serum or plasma

Although methods for the measurement of vitamin D metabolites continue to be developed, few have been properly validated by comparison with methods based on gas chromatography-mass spectrometry, widely accepted as being the definitive methodology. To the best of our knowledge, only three such comparisons have been carried out (14, 42, 83), all three examining HPLC assays for 25-OH-D. This lack of proper validation leads to lack of certainty as to the specificity of many assays widely used for clinical investigation. In our view there is an obvious need for the continuing development of mass fragmentographic assays for vitamin D and its metabolites, primarily for use as reference procedures for the evaluation of less rigorous methodologies. Provided standards, both labeled and unlabeled, become more widely available, development of specific mass fragmentographic assays for any metabolite of vitamin D should be possible. For metabolites where no specific binding protein or antiserum is available, mass fragmentography may be the only alternative.

The physiology and pathophysiology of vitamin D

The vitamin D endocrine system plays an important role in the maintenance of normal calcium homeostasis. Abnormalities of this system occur in many conditions, such as rickets, osteomalacia, hypoparathyroidism, and hyperparathyroidism. The diagnosis and treatment of these disorders will be facilitated if the clinician understands the general mechanisms by which defects in vitamin D metabolism and action occur. We review this information and discuss the use and limitations of vitamin D metabolite assays for diagnosis of clinical disorders of mineral metabolism.

A rapid and simple method for the measurement of plasma 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 using Sep-Pak C18 cartridges and a single high-performance liquid chromatographic step

A simple one step high-performance liquid chromatographic (HPLC) procedure for the analysis of plasma concentrations of 25-hydroxyvitamin D3 (25-OHD3) and 25-hydroxyvitamin D2 (25-OHD2) is described. Plasma (2-4 ml) was extracted with methyl cyanide which was passed through a Sep-Pak C18 cartridge, washed with methanol:water (70:30, v/v) and the 25-OHD fraction eluted with methyl cyanide. After isomerisation to their isotachysterol derivatives, the secosteroids were estimated using a straight-phase HPLC system, monitoring the eluent at 301 nm. Radioactive 25-OHD3, added to plasma at the start of the procedure, was used to correct for losses. Recovery of added 25-OHD3 was quantitative and values obtained using this method were similar to those obtained on the same plasma samples using a mass fragmentographic technique. Normal ranges were similar to those described by other workers and within- (5.8% for 25-OHD3) and between-(8.0% for 25-OHD3) batch reproducibilities were satisfactory.

High-performance liquid chromatography of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human plasma. Use of isotachysterols and a comparison with gas chromatography--mass spectrometry

A high-performance liquid chromatographic (HPLC) method for estimating plasma 25-hydroxyvitamin D2 (25-OHD2) and 25-hydroxyvitamin D3 (25-OHD3) is described. The method involves plasma extraction, Lipidex 5000 chromatography and HPLC on straight-phase Zorbax-SIL, collecting the 25-OHD2 + 25-OHD3 fractions. These secosteroids are isomerised to their isotachysterol derivatives and re-run in the same HPLC system, monitoring at 290 nm. 3H-Labelled 25-OHD3 is used as an internal standard. The method was evaluated in terms of reproducibility, and recovery of added secosteroids was quantitative. Values obtained using this method were in close agreement with those values obtained on the same plasma sample using gas chromatography--mass spectrometry.

The estimation of vitamin D and some metabolites in human plasma by mass fragmentography

A mass fragmentographic assay for vitamin D3, 25-hydroxyvitamin D3, 25-hydroxyvitamin D2 and 24,25-dihydroxyvitamin D3 is described. After extraction of plasma with methanol and dichloromethane, Lipidex 5000 chromatography was used to separate the plasma extract into three fractions (a vitamin D fraction, a 25-hydroxyvitamin D fraction and a 24,25-dihydroxyvitamin D fraction). Cholesterol was removed from the vitamin D fractio by thin-layer chromatography. :After addition of vitamin D2 to each fraction, isotachysterol trimethylsilyl ethers were formed. Recoveries prior to gas chromatography-mass spectrometry were assessed by the use of tritiated standards added to the plasma before extraction. Using this procedure, normal ranges were established (vitamin D3: 3--17.7, 25-hydroxyvitamin D3: 5.9--35.2, 25-hydroxyvitamin D2: 0.6---1.0 and 24,25-dihydroxyvitamin D3: 0.6--2.9 micrograms/l).