A simple, rapid atmospheric pressure chemical ionization liquid chromatography tandem mass spectrometry method for the determination of 25-hydroxyvitamin D2 and D3

Quantification of 25-Hydroxyvitamin D2 and D3 Using Liquid Chromatography-Tandem Mass Spectrometry

Vitamin D plays an important role not only in bone health but also in many other body functions. Vitamin D deficiency is very common in the general population. Measurement of blood 25-hydroxyvitamin D is a common practice to evaluate vitamin D deficiency. Immunoassays and liquid chromatography tandem mass spectrometry (LC-MS/MS) are the most commonly used methods for the measurement of 25-hydroxyvitamin D. Immunoassays suffer from specificity issues and do not distinguish between 25-hydroxyvitamin D2 and D3. Therefore, LC-MS/MS is a preferred method for quantification of 25-hydroxyvitamin. We describe an LC-MS/MS method, which involves protein precipitation and analysis of the extract using atmospheric pressure chemical ionization and multiple reaction monitoring. 25-hydroxyvitamin D3-d6 is used as an internal standard. The method is linear from 1-100 ng/mL for both 25-hydroxyvitamin D2 and D3 and has imprecision of <10%.

Comparison of two LC-MS/MS methods for the quantification of 24,25-dihydroxyvitamin D3 in patients and external quality assurance samples

OBJECTIVES

In-house developed liquid-chromatography mass spectrometry (LC-MS/MS) methods are used more and more frequently for the simultaneous quantification of vitamin D metabolites. Among these, 24,25-dihydroxyvitamin D3 (24,25(OH)₂D₃) is of clinical interest. This study assessed the agreement of this metabolite in two validated in-house LC-MS/MS methods.

METHODS

24,25(OH)₂D₃ was measured in 20 samples from the vitamin D external quality assurance (DEQAS) program and in a mixed cohort of hospital patients samples (n=195) with the LC-MS/MS method at the Medical University of Graz (LC-MS/MS 1) and at the University of Liège (LC-MS/MS 2).

RESULTS

In DEQAS samples, 24,25(OH)₂D₃ results with LC-MS/MS 1 had a proportional bias of 1.0% and a negative systemic difference of -0.05%. LC-MS/MS 2 also showed a proportional bias of 1.0% and the negative systemic bias was -0.22%. Comparing the EQA samples with both methods, no systemic bias was found (0.0%) and the slope was 1%. The mean difference of 195 serum sample measurements between the two LC-MS/MS methods was minimal (-0.2%). Both LC-MS/MS methods showed a constant bias of 0.31 nmol/L and a positive proportional bias of 0.90%, respectively.

CONCLUSIONS

This study is the first to assess the comparability of 24,25(OH)₂D₃ concentrations in a mixed cohort of hospitalized patients with two fully validated in-house LC-MS/MS methods. Despite different sample preparation, chromatographic separation and ionization, both methods showed high precision measurements of 24,25(OH)₂D₃. Furthermore, we demonstrate the improvement of accuracy and precision measurements of 24,25(OH)₂D₃ in serum samples and in the DEQAS program.

25-Hydroxyvitamin D Testing: Immunoassays Versus Tandem Mass Spectrometry

Vitamin D has been associated with many health conditions. Because of widespread deficiency in the general population, laboratory testing of vitamin D has increased exponentially in recent years. Currently, 25-hydroxyvitamin D (25[OH]D) is considered the best marker of vitamin D status. Automated immunoassays and tandem mass spectrometry are the most widely used assays for the measurement of 25(OH)D. Because a medical decision of vitamin D deficiency and treatment are made based on specific levels, it is important that different 25(OH)D assays are harmonized. Despite standardization efforts, significant differences remain among various methods and laboratories for the measurement of 25(OH)D.

Determination of Serum 25-Hydroxyvitamin D3 by LC/MS/MS and Its Monthly Variation in Sapporo Indoor Workers

25-Hydroxyvitamin D₃ (25(OH)D₃) as the metabolite of vitamin D, is connected with various of diseases, and important to people with limited sunshine. Thus, the investigation of serum 25-hydroxyvitamin D and its variation in these people is necessary. In this study, a simple, precise, and accurate method for serum 25(OH)D₃ determination by LC/MS/MS was developed. Serum samples were obtained monthly for one year from 11 male and 11 female indoor workers in Sapporo, Japan, and the overall 25(OH)D₃ concentration was 12.9 ± 4.7 ng/mL. The 25(OH)D₃ in females was significantly lower than that in males (14.0 ± 5.0 vs. 11.9 ± 4.3 ng/mL). The serum 25(OH)D₃ concentration in males and females were both strongly correlated to UV-B radiation (r² = 0.8477 and 0.7384, respectively), with a two-month's lag. Also the monthly change in 25(OH)D₃ in males was more significant than that in females.

Determination of ergocalciferol in human plasma after Diels-Alder derivatization by LC-MS/MS and its application to a bioequivalence study

An accurate, sensitive and selective method is developed for determination of ergocalciferol (vitamin D₂) in human plasma using LC-MS/MS. After liquid-liquid extraction with n-hexane, ergocalciferol was derivatized by reacting with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), a strong dienophile based on Diels-Alder reaction. Ergocalciferol and its deuterated internal standard, ergocalciferol-d6, were analyzed on X Select CSH C₁₈ (100 mm×4.6 mm, 2.5 µm) column using acetonitrile and 0.1% (v/v) formic acid in water containing 0.14% methylamine within 6.0 min under gradient elution mode. Tandem mass spectrometry in positive ionization mode was used to quantify ergocalciferol by multiple reaction monitoring (MRM). Entire data processing was done using Watson LIMS™ software which provided excellent data integrity and high throughput with improved operational efficiency. The major advantage of this method includes higher sensitivity (0.10 ng/mL), superior extraction efficiency (≥83%) and small sample volume (100 µL) for processing. The method was linear in the concentration range of 0.10-100 ng/mL for ergocalciferol. The intra-batch and inter-batch accuracy and precision (% CV) values varied from 97.3% to 109.0% and 1.01% to 5.16%, respectively. The method was successfully applied to support a bioequivalence study of 1.25 mg ergocalciferol capsules in 12 healthy subjects.

Vitamin D, Low-Grade Inflammation and Cardiovascular Risk in Young Children: A Pilot Study

Vitamin D has anti-inflammatory properties, and deficiency is prevalent in children. There is a paucity of data regarding vitamin D status and its correlation with low-grade inflammation and vasculature. We prospectively enrolled 25 children, 9-11 years old (13 male); 21 obese. Eight atherosclerosis-promoting risk factors were scored as categorical variables with the following thresholds defining abnormality: body mass index Z score ≥ 1.5; systolic blood pressure ≥ 95th percentile (for age, sex, and height); triglyceride ≥ 100 mg/dL; low-density lipoprotein cholesterol (LDL-C) ≥ 110 mg/dL; high-density lipoprotein cholesterol ≤ 45 mg/dL; hemoglobin A1C (HBA1C) ≥ 5.5; 25-hydroxyvitamin D [25(OH) D] ≤ 30 ng/mL, and tobacco smoke exposure. High-sensitivity C-reactive protein (hsCRP) was measured to assess low-grade inflammation and classified as low- (<1 mg/L), average- (1-3 mg/L), and high-risk (>3 to <10 mg/L) groups. The proportion of children within each hsCRP group who had above threshold risk factors was calculated. Carotid artery ultrasound was performed to measure carotid artery intima-media thickness (CIMT). Median (range) for 25(OH) D was 24 (17-45) ng/mL. Eighteen were either 25 (OH) D deficient (<20 ng/mL) or insufficient (20-30 ng/mL), and seven were sufficient (>30 ng/mL). hsCRP was 1.7 (0.2-9.1) mg/L, with 11 being <1.0 mg/L, 8 between 1.0-3.0 and 6 > 3.0 to < 10.0 mg/L. Risk factor score was 3.9 ± 1.7 out of eight. 25(OH) D levels did not correlate with hsCRP or CIMT. While vitamin D deficiency, inflammation, and risk factors coexist at a very young age, causative mechanisms remain unclear.

Recent trends in the determination of vitamin D

The occurrence of vitamin D deficiency has become an issue of serious concern in the worldwide population. As a result numerous analytical methods have been developed, for a variety of matrices, during the last few years to measure vitamin D analogs and metabolites. This review employs a comprehensive search of all vitamin D methods developed during the last 5 years for all applications, using ISI Web of Science(®), Scifinder(®), Science Direct, Scopus and PubMed. Particular emphasis is given to sample-preparation methods and the different forms of vitamin D measured across different fields of applications such as biological fluids, food and pharmaceutical preparations. This review compares and critically evaluates a wide range of approaches and methods, and hence it will enable readers to access developments across a number of applications and to select or develop the optimal analytical method for vitamin D for their particular application.