Optimization and Validation of RP-LC/UV–VIS Detection Method for Simultaneous Determination of Fat-Soluble Anti-Oxidant Vitamins, all-trans-Retinol and α-Tocopherol in Human Serum: Effect of Experimental Parameters

New Insights into Vitamin K-From Its Natural Sources through Biological Properties and Chemical Methods of Quantitative Determination

Vitamin K is one of the many health-promoting substances whose impact on the human body has been underestimated until recently. However, recently published research results have changed this situation, prompting some researchers to consider it a new panacea for diseases of old age. The result is a significant increase in interest in the accurate analysis of vitamin K in various types of samples, ranging from food, through dietary supplements, to biological matrices and clinical trials, both observational and interventional. This review summarizes the current state of knowledge about the proven and speculated biological activity of vitamin K and its importance for the world's aging societies, including the methods used for its isolation and analysis in various matrices types. Of all the analytical methods, the currently preferred methods of choice for the direct analysis of vitamin K are chromatographic methods, in particular liquid chromatography-tandem mass spectrometry. This technique, despite its sensitivity and selectivity, requires an appropriate stage of sample preparation. As there is still room for improvement in the efficiency of these methods, especially at the sample preparation stage, this review shows the directions that need to be taken to make these methods faster, more efficient and more environmentally friendly.

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.

A Review of the Extraction and Determination Methods of Thirteen Essential Vitamins to the Human Body: An Update from 2010

Vitamins are a class of essential nutrients in the body; thus, they play important roles in human health. The chemicals are involved in many physiological functions and both their lack and excess can put health at risk. Therefore, the establishment of methods for monitoring vitamin concentrations in different matrices is necessary. In this review, an updated overview of the main pretreatments and determination methods that have been used since 2010 is given. Ultrasonic assisted extraction, liquid–liquid extraction, solid phase extraction and dispersive liquid–liquid microextraction are the most common pretreatment methods, while the determination methods involve chromatography methods, electrophoretic methods, microbiological assays, immunoassays, biosensors and several other methods. Different pretreatments and determination methods are discussed.

Analyte stability during the total testing process: studies of vitamins A, D and E by LC-MS/MS

Background:

There are limited evidence based studies demonstrating the stability of fat-soluble vitamins (FSV) measured in blood. This study aimed to examine the effects of light, temperature and time on vitamins A, D and E throughout the total testing process.

Methods:

Four experiments were conducted. Three investigated the sample matrix, of whole blood, serum and the extracted sample, against the variables of temperature and light; and the fourth experiment investigated the sample during the extraction process against the variable of light. All samples were analysed via our simultaneous FSV method using liquid chromatography-tandem mass spectrometry technology. The allowable clinical percentage change was calculated based on biological variation and desirable method imprecision for each analyte. The total change limit was ±7.3% for 25-OH-vitamin D3, ±11.8% for retinol and ±10.8% for α-tocopherol.

Results:

Vitamins D and E were stable in the investigated conditions (concentration changes <4%) in the pre-analytical and analytical stages. Vitamin A showed photosensitivity in times >48 h with concentration changes of −6.8% (blood) and −6.5% (serum), both are within the allowable clinical percentage change. By contrast, the extracted retinol sample demonstrated a concentration change of −18.4% after 48 h of light exposure. However, vitamin A in the serum and extracted solution was stable for one month when stored at −20°C.

Conclusions:

Blood samples for vitamins D and E analyses can be processed in normal laboratory conditions of lighting and temperature. The required conditions for vitamin A analysis are similar when performed within 48 h. For longer-term storage, serum and vitamin A extracts should be stored at −20°C.

Robust measurement of vitamin A status in plasma and blood dried on paper

Vitamin A deficiency is the leading cause of preventable blindness in children and increases the risk of disease and death from severe infections. In addition, fat soluble vitamin A and associated retinoids directly regulate the expression of genes involved in fatty acid metabolism. Conventional methods for measuring vitamin A involve venipuncture, centrifugation and refrigeration all of which make measuring vitamin A in nutritional surveys expensive. We aimed to develop a simple and robust system for measurement of retinol (biomarker for vitamin A) using dried blood spot (DBS) samples. Low recoveries and inconsistent results reported by others were found to be due to poor extraction efficiency rather than retinol instability. Maintaining acid conditions during extraction resulted in recoveries >95% with <6.5% of coefficient of variation. Using isocratic high performance liquid chromatography, separation was achieved in <3.5 min. Detector response was linear (R(2)=0.9939) within a range of 0.05-2 μg/mL, with a limit of quantification of 0.05 μg/mL. Retinol in DBS was shown to be stable (>95%) at room temperature for up to 10 weeks. DBS values for retinol were highly correlated with venous blood samples from 24 healthy subjects (r=0.9724) and were consistent with results from a commercial laboratory. This simple and reliable method for the determination of vitamin A status should prove particularly valuable for population studies and large clinical trials.

Simultaneous determination of the endogenous free α-lipoic acid and dihydrolipoic acid in human plasma and erythrocytes by RP-HPLC coupled with electrochemical detector

A highly sensitive, precise, and accurate reversed-phase high performance liquid-chromatography/electrochemical detection method for simultaneous determination of the endogenous free α-lipoic acid and dihydrolipoic acid in biological matrices is presented. The two analytes are extracted from samples with acetonitrile-10% m-phosphoric acid solution(aqueous) (50:50 v/v). To determine the total lipoic acid, samples are treated with tris(2-carboxyethyl)phosphine solution in phosphate buffer: pH 2.5 with 85% o-phosphoric acid prior to deproteination. The two analytes are separated on a C18 (150 × 4.6 mm, 5 μm) analytical column using acetonitrile-50 mM phosphate buffer: pH 2.5 with 85% o-phosphoric acid (35:65 v/v) as the isocratic mobile phase pumped at a flow rate of 2.0 ml/min at the column oven temperature of 35 °C. The column eluents are monitored at a potential of 0.9 V. These analytes are efficiently resolved in <7 min.

Quantification of the level of fat-soluble vitamins in feed based on the novel microemulsion electrokinetic chromatography (MEEKC) method

BACKGROUND

Simultaneous quantification of liposoluble vitamins is not a new area of interest, since these compounds co-determine the nutritional quality of food and feed, a field widely explored in the human and animal diet. However, the development of appropriate methods is still a matter of concern, especially when the vitamin composition is highly complex, as is the case with feed designated for laboratory animals, representing a higher health and microbiological status.

RESULTS

A method combining microemulsion electrokinetic chromatography (MEEKC) with liquid-liquid extraction was developed for the determination of four fat-soluble vitamins in animal feed. A separation medium consisting of 25 mmol L⁻¹ phosphate buffer (pH 2.5), 2-propanol, 1-butanol, sodium dodecyl sulfate and octane allowed the simultaneous determination of vitamins A, D, E and K within a reasonable time of 25 min. The polarity of the separation voltage was reversed in view of the strongly suppressed electro-osmotic flow, and the applied voltage was set at 12 kV. The fat-soluble vitamins were separated in the order of decreasing hydrophobicity.

CONCLUSION

It was proved that the proposed MEEKC method was sufficiently specific and sensitive for screening fat-soluble vitamins in animal feed samples after their sterilization.

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.

Analysis of circulating lipid-phase micronutrients in humans by HPLC: review and overview of new developments

Retinol, tocopherols, coenzyme Q10, carotenoids, and vitamin D are lipophilic compounds shown to function as important health-protective agents by mitigating the damaging effects of oxidative and other injury. Scientific interest in evaluating these compounds has resurfaced in recent years, particularly in the nutritional, clinical and epidemiologic fields, and has precipitated the development of a multitude of new analytical techniques. This review considers recent developments in HPLC-based assays since 2007 for the simultaneous determination of these lipid-phase compounds utilizing exclusively serum or plasma as these matrices are mostly used in clinical and epidemiological investigations. We also provide an overview of blood measurements for selected carotenoids, tocopherols, coenzyme Q10 and retinol from the last 15years of healthy umbilical cord blood, children, and adults.

Application of core-shell technology for determination of retinol and alpha-tocopherol in breast milk

Breast milk is a main source of fat-soluble vitamins for newborns and it is needful to monitor the nutritional status prior to its application. In this work a novel, high-throughput and low-cost method for monitoring of retinol and alpha-tocopherol in breast milk was developed, validated and compared with reference method using monolithic column. For this purpose five various porous shell and monolithic columns were tested on the basis of relationship between HETP and linear mobile phase velocity, analysis time and consumption of solvents. Finally the core-shell analytical column Kinetex C18 (2.6 μm, 100 Å, 100×4.6 mm) was chosen as the best and optimal values of flow rate, injection volume and temperature of analysis were established. The detection of retinol and alpha-tocopherol was carried out at 325 and 295 nm, respectively by diode array detector. The LOD 0.004 μmol/L and 0.078 μmol/L, the LOQ 0.012 μmol/L and 0.182 μmol/L for retinol and alpha-tocopherol, respectively were calculated. The validation data showed good linearity, repeatability of retention time with RSD 0.22% and 0.12%, repeatability of peak area with RSD 6.94% and 1.75%, recovery 114.1-116.3% and 99.0-108.6% for retinol and alpha-tocopherol, respectively. Moreover, the newly developed method substantially decreased the solvent consumption by about 263 mL per 100 samples with the total time of analysis 1.75 min in comparison with analysis time 1.80 of the reference method.