Fully automated method for the determination of 24,25(OH)2 and 25(OH) D3 hydroxyvitamins, and Vitamins A and E in human serum by HPLC

Effective, convenient, and green sample preparation for the determination of retinol and retinol acetate in human serum using pipette tip microextraction

An efficient sample preparation based on pipette tip microextraction that can be used for the analysis of retinol in human serum has been developed. Altogether, nine commercial pipette tips were compared based on recovery, sample volume, use of organic solvent, handling difficulty, duration of the preparation process, price, and greenness of the method. Retinol acetate was used as the internal standard. The extraction efficiency for both compounds was evaluated to optimize and select the best pipette tip for sample preparation, which was the WAX-S XTR pipette tip containing an ion exchanger and salt. This tip combined solid phase extraction and salting-out assisted liquid‒liquid extraction. Satisfying recoveries of 100 and 80% for retinol and retinol acetate, respectively, and good repeatability were demonstrated. The action of this pipette tip was based on the clean-up workflow in which the interferences were retained on the sorbent. The presence of residual interferences in the extracted samples did not affect the HPLC separation of compounds of interest. The simplicity of the clean-up workflow reduced the time of the sample preparation compared to the bind-wash-elute counterpart workflow. The advantages of our technique are its environmental friendliness and cost effectiveness. The selected pipette tip with an excellent microextraction efficiency enables sample preparation in both clinical research and practice.

Vitamin D metabolites and analytical challenges

Vitamin D is an essential micronutrient for bone health and the general cellular functions of the body. Its insufficiency/deficiency leads to the pathophysiology of disorders like diabetes, cancer, autoimmune, neurodegenerative, and cardiovascular diseases. Clinical interest in Vitamin D metabolites and their role in various medical disorders have contributed to an increase in laboratory demands for vitamin D measurements. For clinical and research laboratories worldwide, analysis of vitamin D and associated metabolites is a significant problem. The best way for determining vitamin D levels is constantly being debated. Various methods such as immunoassays and chromatographic techniques are available for determining vitamin D levels. Additionally, biosensors have recently been considered promising options for routine vitamin D analysis. The existing methods and other developments in the measurement of vitamin D metabolites and associated analytical challenges are discussed in this review.

Vitamin A Update: Forms, Sources, Kinetics, Detection, Function, Deficiency, Therapeutic Use and Toxicity

Vitamin A is a group of vital micronutrients widely present in the human diet. Animal-based products are a rich source of the retinyl ester form of the vitamin, while vegetables and fruits contain carotenoids, most of which are provitamin A. Vitamin A plays a key role in the correct functioning of multiple physiological functions. The human organism can metabolize natural forms of vitamin A and provitamin A into biologically active forms (retinol, retinal, retinoic acid), which interact with multiple molecular targets, including nuclear receptors, opsin in the retina and, according to the latest research, also some enzymes. In this review, we aim to provide a complex view on the present knowledge about vitamin A ranging from its sources through its physiological functions to consequences of its deficiency and metabolic fate up to possible pharmacological administration and potential toxicity. Current analytical methods used for its detection in real samples are included as well.

Measurement of plasma 25-hydroxyvitamin D2, 25-hydroxyvitamin D3 and 3-epi-25-hydroxyvitamin D3 in population of patients with cardiovascular disease by UPLC-MS/MS method

Vitamin D has a potential role in protecting against cardiovascular disease (CVD). Serum 25-hydroxyvitamin D (25D) is the most widely used indicator of vitamin D status in the human body. 25D is estimated as total of 25-hydroxyvitamin D2 (25D2) and 25-hydroxyvitamin D3 (25D3). However, the presence of 3-epi-25-hydroxyvitamin D3 (3epi25D3) can affect 25D measurement. In this research a novel validated UPLC-MS/MS technique was developed to measure three vitamin D metabolites, 25D2, 25D3 and 3epi25D3 in human plasma. A liquid-liquid extraction using hexane was applied for isolation of the analytes from the samples. A chromatographic separation was achieved in a Kinetex F5 analytical column with isocratic elution (water and methanol with 0.1% methanoic acid, 20:80 v/v). Mass spectrometry detection of the metabolites was performed in a triple-quadruple tandem mass spectrometer under positive ion mode. Concentrations of the analytes were estimated in plasma samples of 54 patients. Validation parameters of the UPLC-MS/MS method, including linearity, precision, accuracy, and stability, fulfilled the requirements for bioanalytical assays. The deficient concentration of 25D (<20 ng/mL) was stated in over 60% of patients. 3epi25D3 was present in 78% of samples and its relative amount ranged from 0 to 54.1% of 25D concentration. The analysis of 25D2, 25D3 and 3epi25D3 by the validated UPLC-MS/MS method in plasma of patients with CVD permitted the classification of the patients with insufficient levels of 25D. 3epi25D3 might be relevant in the classification of vitamin D status.

Liquid chromatography as candidate reference method for the determination of vitamins A and E in human serum

BACKGROUND

Owing to the increasing interest in public health research of antioxidant micronutrients and the inaccuracy of routine serum concentrations of the fat-soluble vitamins A (retinol) and E (DL-α-tocopherol) measurements, we developed a reliable, highly sensitive, robust and rapid method for the quantification of two clinically important lipophilic antioxidants in serum using a reverse-phase HPLC/DAD method.

METHOD

Sample preparation and analytical conditions that would affect extraction efficiency and quantitative results of vitamins A and E were investigated and optimized. Vitamins A and E were extracted from serum via liquid-liquid extraction (LLE). After adequate sample preparation, the samples were injected directly into the HPLC system with diode-array detector (DAD). Chromatographic separation was completed in 7 minutes for vitamins A and E. With vitamin A acetate and vitamin E acetate as internal standards, the method was applied to the measurement of vitamins A and E in human serum.

RESULTS

We evaluated method linearity, accuracy (recovery rate and trueness), precision, carryover, limit of quantitation and limit of detection, and measurement uncertainty. The method was evaluated for trueness using NIST Standard Reference Material SRM 968f. The serum concentration of the studied compounds had a good linear relationship in the range of 0.05 ~ 3.0 μg/mL concentration (r ＝ 0.9998), with 0.0077 μg/mL detection limit and 0.025 μg/mL quantitative limit for vitamin A, respectively, and 1.0 ~ 60.0 μg/mL concentration (r ＝ 0.9999), with 0.40 μg/mL detection limit and 0.50 μg/mL quantitative limit for vitamin E, respectively. The intra- and inter-assay coefficients of variation were calculated by using three concentrations (1, 2, and 3) of the studied compounds in human serum samples. Intra-assay and inter-assay precision were 1.23%-4.97% and 0.97%-3.79% for vitamin A, respectively, and 0.64%-4.07% and 0.81%-5.96% for vitamin E, respectively. The average recovery rates were 100.98% for vitamin A, and 99.21% for vitamin E, respectively. The carryover rate of vitamins A and E was below 1%. As for the evaluation of accuracy, the biases were <± 5% by comparing with NIST standard reference material SRM 968f.

CONCLUSION

The method is a simple sample treatment procedure for the determination of fat-soluble vitamins A and E in human serum with high sensitivity and specificity. The proposed method could be recommended as a candidate reference method for the determination of serum concentrations of the fat-soluble vitamins A and E in human serum.

Development and optimization of simultaneous determination of fat soluble vitamins by liquid chromatography tandem mass spectrometry

OBJECTIVE

Fat-soluble vitamins (A, D, E and K) are isoprene derived apolar molecules. While deficiencies of these vitamins have been associated with various diseases such as type 2 diabetes and cancer, high doses of Vitamin A and D can cause toxic effects. Accurate detection of serum levels of these vitamins have critical importance. In this study, it is aimed to develop and validate a sensitive and specific Liquid Chromatography Tandem Mass Spectrometry (LC-MS / MS) method that allows simultaneous analysis of fat-soluble vitamins.

MATERIALS AND METHODS

Serum samples were deproteinized with methanol and chromatographic separation of analytes were performed by LC-MS/MS system (Agilent Technologies 6420 Triple Quadrapole LC-MS), Agilent Pursuit PFP column (100 mm × 3.0 mm; 3.0 μm), in gradient mode using Mobile phase A (milli-Q+0.1 % formic acid) and Mobile phase B (Methanol+0.1 % formic acid). Ion scan was performed in MRM (multiple reaction monitoring) mode with positive ion selectivity in ESI ion source.

RESULTS

The retention times were 6.93 min, 6.94 min and 9.34 min while concentrations were linear in the ranges between 10-150 ng/mL, 3-90 μg /dL and 6-90 μg/mL for 25-hydroxy vitamin D₃ (25-OHD₃), Vitamin A and Vitamin E, respectively. Inter-day Coefficient Variation (CV%) values for Vitamin A, Vitamin E and 25-OHD₃ were; 9.08 %, 9.85 % and 3.07 % and intra-day CV% values were; 2.98 %, 5.05 % and 5.01 %. LOD and LOQ results were 2.11 μg/dL and 3.50 μg/dL for Vitamin A; 1.71 μg/mL and 2.45 μg/mL for Vitamin E; 1.47 ng/mL and 2.50 ng/mL for 25-OHD₃, respectively.

CONCLUSION

In this study, a LC-MS/MS method that can analyze fat soluble vitamins in 13 min was developed and validated. This method will be useful for clinical purposes by replacing low specificity immunoassay methods and High Performance Liquid Chromatography (HPLC) methods that can not allow simultaneous analysis.

Simultaneous determination of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human serum by ultra performance liquid chromatography: An economical and validated method with bovine serum albumin

A simple and economical method has been developed for simultaneous determination of human serum 25-hydroxyvitamin D₂ (25OHD₂) and 25-hydroxyvitamin D₃ (25OHD₃) using Ultra Performance Liquid Chromatography (UPLC). Non-human matrix of 4% BSA was used to construct the calibration curve and in quality control samples' preparation to avoid interference of the endogenous 25-hydroxyvitamin D (25OHD) present in the human serum. 25OHD₂, 25OHD₃ and dodecanophenone (internal standard, IS) were separated on a CORTECS solid-core particle column and monitored by photodiode array detector at wavelength of 265 nm within five min run time. The relationship between 25OHD concentration and peak area ratio (25OHD:IS) was linear over the range of 12.5 - 200 nM with mean correlation coefficients (r²) >0.998. The limit of detection (LOD) for 25OHD₂ and 25OHD₃ was 3.00 nM and 3.79 nM, while the lower limit of quantification (LLOQ) was 9.11 nM and 11.48 nM, respectively. High repeatability was obtained for both isomers with intra-day CV% <5.6% and <5.3% for inter-day assay. This method was further tested with a commercial lyophilized serum control with an accuracy of 92.87-108.31% and applied on 214 human serum samples. In summary, this validated method with BSA can be reliably applied for routine quantification of 25OHD in adults.

Analysis of retinol, α-tocopherol, 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in plasma of patients with cardiovascular disease by HPLC-MS/MS method

Fat-soluble vitamins play a pivotal role in the progression of atherosclerosis and the development of cardiovascular disease. Therefore, plasma monitoring of their concentrations may be useful in the diagnosis of these disorders as well as in the process of treatment. The study aimed to develop and validate an HPLC-MS/MS method for determination of retinol, α-tocopherol, 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in plasma of patients with cardiovascular disease. The analytes were separated on an HPLC Kinetex F5 column via gradient elution with water and methanol, both containing 0.1% (v/v) formic acid. Detection of the analytes was performed on a triple-quadrupole MS with multiple reaction monitoring via electrospray ionization. The analytes were isolated from plasma samples with liquid-liquid extraction using hexane. Linearity of the analyte calibration curves was confirmed in the ranges 0.02-2 μg/mL for retinol, 0.5-20 μg/mL for α-tocopherol, 5-100 ng/mL for 25-hydroxyvitamin D2 and 2-100 ng/mL for 25-hydroxyvitamin D3. Intra- and inter-assay precision and accuracy of the method were satisfactory. Short- and long-term stabilities of the analytes were determined. The HPLC-MS/MS method was applied for the determination of the above fat-soluble vitamin concentrations in patient plasma as potential markers of the cardiovascular disease progression.

Determination of vitamins A, D and E in a small volume of human plasma by a high-throughput method based on liquid chromatography/tandem mass spectrometry

We have developed an automated high-throughput assay for the determination of vitamin A (retinol), ergocalciferol (25-OH D2), cholecalciferol (25-OH D3) and vitamin E (α-tocopherol) in a small volume of human plasma. Sample preparation involved mixing 50 μL of plasma with 100 μL of ethanol containing isotope-labelled internal standards, followed by mixing with isooctane/chloroform (3:1, 300 μL). The organic phase was evaporated, and the sample reconstituted in 50 μL methanol. The analysis was performed using reversed-phase liquid chromatography with a gradient mobile phase containing water, methanol and ammonium formate. Chromatographic run-time was 5 min, and positive mode electrospray tandem mass spectrometry (MS/MS) was used for detection. The limits of detection were 0.10 μM for all-trans retinol and 3.3 nM for 25-OH D2 and 25-OH D3. Recoveries were 91.9-105.0%, and within- and between-day coefficients of variance (CVs) 2.4-5.3 and 3.1-8.2, respectively. The assay is presently being used in large-scale studies.

Measurement of 25-hydroxyvitamin D in the clinical laboratory: current procedures, performance characteristics and limitations

In this review we describe procedures, performance characteristics and limitations of methods available for the measurement of 25-hydroxyvitamin (25OHD) since the year 2000. The two main types of methods are competitive immunoassay and those based on chromatographic separation followed by non-immunological direct detection (HPLC, LC-MS/MS). Lack of a reference standard for 25OHD has, until recently, been a major issue resulting in poor between-method comparability. Fortunately this should soon improve due to the recent introduction of a standard reference material in human serum (SRM 972) from the National Institute of Standards and Technology (NIST). For immunoassay, specificity can be an issue especially in relation to the proportion of 25OHD2 that is quantified whereas HPLC and LC-MS/MS methods are able to measure the two major vitamin D metabolites 25OHD2 and 25OHD3 independently. HPLC and LC-MS/MS require more expensive equipment and expert staff but this can be offset against lower reagent costs. Increasingly procedures are being developed to semi-automate or automate HPLC and LC-MS/MS but run times remain considerably longer than for immunoassays especially if performed on automated platforms. For most HPLC and LC-MS/MS methods extraction and procedural losses are corrected for by the inclusion of an internal standard which, in part, may account for higher results compared to immunoassay. In general precision of immunoassay, HPLC and LC-MS/MS are comparable and all have the required sensitivity to identify severe vitamin D deficiency. Looking to the future it is hoped that the imminent introduction of a standard reference method (or methods) for 25OHD will further accelerate improvements in between method comparability.

HPLC method for simultaneous determination of retinoids and tocopherols in human serum for monitoring of anticancer therapy

A simple and rapid HPLC method requiring small volumes (250 microL) of human serum after C18 SPE sample preparation was developed using monolithic technology for simultaneous determination of all-trans-retinoic acid, 13-cis-retinoic acid, retinol, gamma- and alpha-tocopherol. The monolithic column, Chromolith Performance RP-18e (100x4.6 mm), was operated at ambient temperature. The mobile phase consisted of a mixture of acetonitrile (ACN) and 1% ammonium acetate in water (AMC) at pH 7.0. The mobile phase started at 98:2 (v/v) ACN/AMC (column pre-treatment) at a flow rate of 2 mL/min, then changed to 95:5 (v/v) ACN/AMC for 4 min at a flow rate of 1.5 mL/min and a further 3 min at a flow rate of 3.2 mL/min. Detection and identification were performed using a photodiode array detector. Retinol, 13-cis- and all-trans-retinoic acid were monitored at 325 nm. Both alpha- and gamma-tocopherol were detected at 295 nm. The total analysis time was 7.2 min. Tocol (synthesized tocopherol, not occurring in humans) was used as internal standard. The method was linear in the range of 0.125-10.00 micromol/L for all-trans-retinoic acid, 0.125-5.00 micromol/L for 13-cis-retinoic acid, 0.25-10.00 micromol/L for retinol, 0.5-50.00 micromol/L for gamma-tocopherol, and 0.5-50.00 micromol/L for alpha-tocopherol. The present method may be useful for monitoring of retinoids and tocopherols in clinical studies.

Comparison of a novel ultra-performance liquid chromatographic method for determination of retinol and α-tocopherol in human serum with conventional HPLC using monolithic and particulate columns

Retinol and alpha-tocopherol are biologically active compounds often monitored in blood samples because of their evident importance in human metabolism. In this study a novel ultra-performance liquid chromatographic (UPLC) method used for determination of both vitamins in human serum has been compared with conventional HPLC with particulate and monolithic C(18) columns. In UPLC a sub-two-micron particle-hybrid C(18) stationary phase was used for separation, in contrast with a five-micron-particle packed column and a monolithic column with a highly porous structure. Methanol, at flow rates of 0.48, 1.5, and 2.5 mL min(-1), respectively, was used as mobile phase for isocratic elution of the compounds in the three methods. Detection was performed at 325 nm and 290 nm, the absorption maxima of retinol and alpha-tocopherol, respectively. Analysis time, sensitivity, mobile-phase consumption, validation data, and cost were critically compared for these different chromatographic systems. Although cost and mobile-phase consumption seem to make UPLC the method of choice, use of the monolithic column resulted in almost the same separation and performance with a slightly shorter analysis time. These methods are alternatives and, in routine laboratory practice, more economical means of analysis of large numbers of biological samples than use of a traditional particulate column.

Identification and determination of fat-soluble vitamins and metabolites in human serum by liquid chromatography/triple quadrupole mass spectrometry with multiple reaction monitoring

A method for determination of fat-soluble vitamins K(1), K(3), A, D(2), D(3) and E (as alpha- and delta-tocopherol) and metabolites 25-hydroxyvitamin D(2) and D(3) and 1,25-dihydroxyvitamin D(3) in human serum by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) in positive mode is proposed. Highly selective identification of the target compounds in serum was confirmed by the most representative transitions from precursor ion to product ion. Quantitative MS/MS analysis was carried out by multiple reaction monitoring optimizing the most sensitive transition for each analyte in order to achieve low detection limits (from 0.012 to 0.3 ng/mL estimated with serum). The analysis was performed with 1 mL of serum, which was subjected to protein precipitation, liquid-liquid extraction to an organic phase, evaporation to dryness and reconstitution with methanol. The precision of the overall method ranged from 3.17-6.76% as intra-day variability and from 5.07-11.53% as inter-day variability. The method, validated by the standard addition method, provides complete information on the fat-soluble vitamins profile, which is of interest in clinical and metabolomics studies.

HPLC method for simultaneous determination of retinol, alpha-tocopherol and coenzyme Q10 in human plasma

A simple HPLC method with UV detection is proposed for the simultaneous determination of three lipophilic vitamins: all-trans-retinol, alpha-tocopherol and coenzyme Q(10) (ubiquinone) in human plasma. The following chromatographic conditions were used: RP-18 column, a mobile phase consisted of methanol -n-hexane 72:28 (v/v) and UV detector set at 324, 292 and 276 nm for all-trans-retinol, alpha-tocopherol and coenzyme Q(10), respectively. The linearity range was 0.35-70 microM for all-trans-retinol, 0.23-44 microM for alpha-tocopherol and 0.12-23 microM for coenzyme Q(10). Deproteinised plasma samples were extracted with n-hexane prior to the analysis. The within-day and between day reproducibilities were 1.5 and 3.7% for all-trans-retinol, 4.0 and 5.8% for alpha-tocopherol and 2.3 and 3.1% for coenzyme Q(10), respectively. Using the proposed method the following recoveries were achieved: 91% for all-trans-retinol, 86% for alpha-tocopherol and 88% for coenzyme Q(10). The method was applied to the determination of the levels of retinol, tocopherol and coenzyme Q(10) in plasma of healthy children and children treated by elimination diet.

Quantification of sifuvirtide in monkey plasma by an on-line solid-phase extraction procedure combined with liquid chromatography/electrospray ionization tandem mass spectrometry

A simple, automated and rapid method has been developed for the determination of a novel antiviral peptide sifuvirtide in monkey plasma. Raw plasma samples were directly loaded onto an on-line solid-phase extraction (SPE) column, which removes the time-consuming and laborious sample pretreatment. Following a timed valve-switching event, the analyte was eluted on-line to a reversed-phase high-performance liquid chromatography (RP-HPLC) column and subsequently introduced into a linear ion trap mass spectrometer, LTQ-MS, via an electrospray ionization (ESI) interface. The multiply charged peptides were specified and quantitatively analyzed using selective reaction monitoring (SRM). A highly pure four iodine-sifuvirtide was synthesized using an optimized iodogen method and proved to be a suitable internal standard (IS). A single analysis run takes about 18 min. Validation of the method demonstrated that the linear calibration curves covered the range of 4.88-5000 ng/mL, and the correlation coefficients were above 0.9923. The limit of detection (LOD) with the signal-to-noise (S/N) ratio higher than 12 was calculated as 1.22 ng/mL. The intra- and inter-batch precisions were less than 12.7% and 9.1%, and the mean accuracy ranged from -5.2% to 3.6%, respectively. Any carry-over effect from the system was negligible. In a pharmacokinetic (PK) study of sifuvirtide after a single intravenous or subcutaneous dose in monkeys, the on-line SPE-LC/MS/MS system was successfully utilized to determine hundreds of samples with only one extraction column, which indicated the feasibility and the reliability of this method for application in preclinical and clinical PK studies of peptide drugs.

Analysis of vitamin E derivatives in serum using coordinated ion spray mass spectrometry

A method for the extraction and analysis of tocopherols from serum using coordinated ion spray (CIS) mass spectrometry was developed and tested. The tocopherols were extracted from serum and analyzed by direct infusion into the mass spectrometer, bypassing the need for a liquid chromatography step. CIS is a method for improving the ionization efficiency of non-polar compounds by adding metal ions to the electrospray solvent. The non-polar analytes appear as metal adducts in the resulting mass spectrum. Silver was used as the metal ion for the CIS, causing analyte masses to be increased by 107 and 109 Da from the two main silver isotopes. Vitamin E succinate was added to the samples before extraction and was used as an internal standard to compensate for any variations in the extraction efficiency or mass spectrometric response. alpha-Tocopherol and an ether-linked analogue known as alpha-TEA were analyzed in concentrations from 1.25-40 microg/mL (1.9-60 pg consumed). The response curve was constructed by comparing the response of the analytes to the internal standard and gave linear results with r2 values greater than 0.98. This new method was shown to be sensitive, reproducible, fast and required very small amounts of analyte.