LC-tandem mass spectrometry method for the simultaneous determination of metformin and sitagliptin in human plasma after ion-pair solid phase extraction

Analytical quality by design approach for the development of high-performance liquid chromatography method for simultaneous analysis of metformin and sitagliptin in the presence of major degradation products

An analytical quality by design-based high-performance liquid chromatography method for determining metformin (MET) and sitagliptin (SIT) in stress-degraded samples was developed and validated. The analytical target profile and risk assessment-driven critical method variables, for example, pH, % aqueous, and buffer concentration, were studied for their effect on method responses of retention time and resolution using a central composite design. The correlation regression coefficient was more than 0.8, and variables interaction was significant on method responses with curvature effect. The method operable design region afforded an aqueous range of 55%-70% and an ortho-phosphoric acid buffer of 0.1% with a pH of 3.0-4.0 as a robust region for the suitable method performance characteristics. The separation of MET and SIT from their degradants (m/z 85.0509; m/z 193.0694) on the C8 column was achieved using a mobile phase consisting of 0.1% ortho-phosphoric acid and methanol (60:40% v/v; pH 3.0). The optimized method eluted MET and SIT at 4.3 ± 0.2 and 7.1 ± 0.2 min, respectively, with acceptable specificity and resolution. The linearity ranges of 25-250 μg/mL (r2 : 0.9982) and 5-50 μg/mL (r2 : 0.9989) was established for MET and SIT, respectively. The % recovery (98.81%-102.17%), precision (0.55%-1.65%), and robustness study for method variables were acceptable.

In vitro study and pharmacokinetic evaluation of sitagliptin phosphate enantiomers in rat plasma

Background: A chiral HPLC technique was developed to determine sitagliptin phosphate enantiomers in rat plasma in compliance with US FDA regulations. Methods & results: The technique used a Phenomenex column with a mobile phase consisting of a 60:35:5 (v/v/v) blend of pH4, 10-mM ammonium acetate buffer, methanol and 0.1% formic acid in Millipore water. The precision for both (R) and (S) sitagliptin phosphate varied between 0.246 and 1.246%, while the accuracy was 99.6-100.1%. A glucose uptake assay was used to assess enantiomers in 3T3-L1 cell lines through flow cytometry. Conclusion: Investigation of the pharmacokinetic impacts of sitagliptin phosphate racemic enantiomers in rat plasma revealed notable contrasts in R and S enantiomers in female albino Wistar rats, suggesting enantioselectivity for sitagliptin phosphate.

The simultaneous quantification of Sitagliptin and Irbesartan in rat plasma using the validated LC-MS/MS method is applied to a pharmacokinetic study

Irbesartan (IRB), an angiotensin II receptor AT1 blocker, is an antihypertensive agent commonly used with Sitagliptin (STG), a novel antidiabetic agent in diabetes. A finalised and validated LC-MS/MS method was used for the bioanalytical quantification of STG and IRB to be applicable to studies on the P.K drug-drug interactions between STG and IRB. Using a YMC triart C18 column (50 mm × 4.6 mm i.d., 3 µm), both the drugs and the Tolbutamide were separated using a gradient mode with a flow rate of 1 ml/min with run time of 5 min. For analyte detection, an LC-MS/MS system with multiple reaction monitoring (MRM) was used. The technique was validated across a concentration range of 5-1000 ng/ml, with the LLOQ for both analytes being 5 ng/ml. At all QC levels accuracies from spiked samples were > 83% for both drugs and internal standards. The accuracy for STG within-batch and between-batch was found within 98.4-107.2%, and for IRB was found within 92.4-102.5%. The precision for STG within batch and between batches was less than 12.3% CV, and for IRB was less than 10.2% CV at all concentration levels. The pharmacokinetic profiles of STG and IRB were successfully applied on simultaneous oral administration to rats. This method applies to pharmacokinetic multidrug interaction studies.

Development and validation of an HPLC coupled with tandem mass spectrometry method for the determination of HSK7653, a novel super long-acting dipeptidyl peptidase-4 inhibitor, in human plasma and urine and its application to a pharmacokinetic study

HSK7653 is a novel super long-acting dipeptidyl peptidase-4 inhibitor, which is promising for the treatment of type 2 diabetes mellitus with the twice-monthly dosing regimen. In this article, a robust and sensitive HPLC coupled with tandem mass spectrometry method for determining the concentration of HSK7653 in human plasma and urine was developed and validated for the first time. Plasma and urine samples were prepared by protein precipitation. After that, the extracts were analyzed using an LC-20A HPLC system coupled with API 4000 tandem MS equipped with an electrospray ionization source in positive mode. Separation was obtained using an XBridge Phenyl column (2.1 × 50 mm, 3.5 μm) with a gradient elution of acetonitrile and water containing 0.1% formic acid and 5% acetonitrile at room temperature. This bioanalysis method has been fully validated and the results showed good sensitivity and specificity. In brief, the standard curves were linear over the concentration range of 2.00-2000 ng/ml for plasma and 20.0-20,000 ng/ml for urine, respectively. In addition, the precisions of inter- and intra-run of HSK7653 were less than 12.7% and the accuracies were -3.3% to 6.3% for both plasma and urine. Finally, this method was successfully applied to explore the pharmacokinetic characteristics of HSK7653 in Chinese healthy volunteers in a first-in-human study.

Development and Validation of a Simple and Sensitive LC-MS/MS Method for Quantification of Metformin in Dried Blood Spot Its Application as an Indicator for Medication Adherence

OBJECTIVE

Metformin (MET), an oral biguanide agent, can improve insulin resistance and decrease hepatic glucose production, leading to a reduction in blood-sugar levels. The objective of the present study was to develop and validate simple and rapid LC-MS/MS method for analysis of MET in dried blood spot (DBS) sample for patient monitoring studies purposes (drug adherence).

METHODS

The chromatographic separation was achieved with Waters HSS-T3 column using gradient elution of mobile phases of two solvents: 1) solvent A, consisted of 10mM ammonium formate, 0.2% formic acid 1%; and 2) acetonitrile solvent B, contained 0.2% formic acid in acetonitrile at a flow rate of 0.2 mL/min. The total run time was 3.0 min. The effectiveness of chromatographic conditions was optimized, and afatinib was used as the internal standard. The assay method was validated using USP 26 and the ICH guidelines.

RESULTS

The method showed good linearity in the range 8-48 ng/mL for MET with correlation coefficient (r) >0.9907. The intra- and inter‑day precision values for MET met the acceptance criteria as per regulatory guidelines. MET was stable during the stability studies at ambient temperature 25 °C, at refrigerator 4 °C, at 10 °C autosampler, freeze/thaw cycles and 30 days storage in a freezer at -30 ± 0.5 °C.

CONCLUSION

This method has successfully fulfilled all validation requirements referring to EMA and FDA guidelines, and successfully can be applied for MET adherence study. All the six studied patients were approved to metformin adherence.

Validation of a novel UPLC-MS/MS method for estimation of metformin and empagliflozin simultaneously in human plasma using freezing lipid precipitation approach and its application to pharmacokinetic study

A fast, sensitive one step UPLC ESI-MS/MS method was successfully applied for the simultaneous estimation of two concurrently administrated antidiabetic drugs, Metformin (MET) and Empagliflozin (EMPA) in human plasma. Metformin-d6 (MET-d6) and Empagliflozin-d4 (EMPA-d4) were utilized as internal standards. Extraction of the analytes from the human plasma was performed through acetonitrile precipitation technique followed by freezing the precipitated plasma proteins and lipids to minimize the matrix effect. Chromatographic analysis was developed on Acquity UPLC BEH C₁₈ column (1.7 μm, 2.1 × 50 mm) using isocratic elution mode. A mobile phase of formic acid (0.01 %): acetonitrile (70:30 v/v) with a flow rate of 0.3 mL/min achieved optimum separation. Multiple reaction monitoring (MRM) in positive ion mode, with transitions at (m/z) 130.14 →71.08 for (MET), 451.72 →71.29 for (EMPA), 136.03 →77.02 for (MET-d6), and 455.43 → 75.05 for (EMPA-d4) was used for quantification. The obtained linearity covered the concentration ranges of 10-1500 ng/mL and 2.0-250.0 ng/mL for MET and EMPA, respectively. The run time of the proposed Method didn't exceed 3.0 min allowing faster analysis and determination of larger number of samples per day without affecting accuracy and sensitivity. The presented chromatographic method could be successfully applied in pharmacokinetics studies and therapeutic monitoring of MET and EMPA in patients' plasma administrating fixed dose combination of both drug with high reproducibility and ruggedness.

A simple, quantitative method for spectroscopic detection of metformin using gold nanoclusters

We synthesized bovine serum albumin (BSA)-stabilized gold nanoclusters (BSA-GNCs) and confirmed their ultra-small size using HRTEM (High-resolution Transmission Electron Microscope) and DLS (Dynamic Light Scattering). The fluorescence intensity of BSA-GNCs is "turned off" in the presence of Cu(II) metal ions. The resulting Cu(II)-mediated BSA-GNCs were utilized to detect metformin, a drug used to control diabetes. Metformin binds to and displaces Cu(II) ions from the BSA on the surface of the nanoclusters, which turns on the fluorescence of the nanoclusters. The interactions between the protein-stabilized nanoclusters were investigated in the absence and presence of Cu(II) using circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR). Cu(II)-quenched BSA-GNCs had an extremely high sensitivity to detect metformin, with a low limit of detection (LOD) of 0.068 μM and a dynamic range of limit of quantification (LOQ = 10/3 LOD) of 0.22 to 11 μM. The ability of this novel "turn-on" nanosensor to detect metformin in human serum and urine samples was confirmed: the percentage recovery in fluorescence for spiked analyte ranged from 96.00-98.50% and 92.60-96.62% in human serum and urine samples, respectively. Thus, BSA-GNCs provide a valid, sensitive, specific fluorometric methodology for the detection of metformin in biomedical applications.

Sensitive detection of quinoline-derivatized sitagliptin in small volumes of human plasma by MALDI-TOF mass spectrometry

Dipeptidyl peptidase 4 (DPP-4) inhibitors are incretin-based medications used as oral antidiabetic agents for the treatment of type 2 diabetes. However, DPP-4 inhibitors produce side effects like acute pancreatitis, upper respiratory tract infection, nasopharyngitis, urinary tract infection, serious allergies, cardiovascular diseases, hemolysis, and retinopathy. Hence, the development of a fast and simple method to detect DPP-4 inhibitors in body fluids is important. In this study, we developed a derivatization-assisted microextraction method to enhance the detection sensitivity for trace levels of a DPP-4 inhibitor, sitagliptin, from a small volume (10 μL) of human plasma by using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Subjecting the analyte to 100 W microwave irradiation after derivatization using a quinoline alkylating reagent (8-bromomethyl quinilone, BrMQ) shortened the reaction time to ~120 s and allowed the target analyte to be easily extracted to a small volume of the organic layer (20 μL). The analyte was then detected by MALDI-TOF MS using α-cyano-4-hydroxycinnamic acid as the matrix. The relative standard deviation and relative error were below 10% in intra- and inter-day assays. Using sitagliptin-d4 as an internal standard, the limits of quantitation and detection were found to be 0.03 μg/mL and 0.01 μg/mL, respectively. All the derivatization and extraction procedures described herein were of microliter grade. This method could effectively reduce the use of organic chemicals and solvents, thereby proving to be an eco-friendly strategy that will cause no harm to the environment.

Simultaneous ultra-trace quantitative colorimetric determination of antidiabetic drugs based on gold nanoparticles aggregation using multivariate calibration and neural network methods

In this study, a simple and rapid method was investigated for the simultaneous ultra-trace colorimetric determination of Metformin (MET) and Sitagliptin (STG) based on the aggregation of gold nanoparticles (AuNPs). The Morphology and size distribution of synthesized AuNPs before and after adding drug (Zipmet) were monitored using transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. By adding a drug, the absorption peak was shifted from 520 to 650 nm. The colorimetric method along with partial least squares (PLS) as a multivariate calibration method, as well as neural network time series were applied to estimate MET and STG simultaneously. The percentage of the mean recovery and root mean square error (RMSE) of the test set of mixtures related to the MET and STG were obtained 99.96, 1.1301 and 99.77, 1.0106, respectively. On the other hand, the regression coefficient (R²) of the training, validation, and test sets corresponding to the artificial neural network (ANN) were close to one for both components. Eventually, the proposed method was compared with a reference technique named high-performance liquid chromatography (HPLC) by analysis of variance (ANOVA) test and there was no significant difference between them.

Determination of metformin bio-distribution by LC-MS/MS in mice treated with a clinically relevant paradigm

Metformin, an anti-diabetes drug, has been recently emerging as a potential “anti-aging” intervention based on its reported beneficial actions against aging in preclinical studies. Nonetheless, very few metformin studies using mice have determined metformin concentrations and many effects of metformin have been observed in preclinical studies using doses/concentrations that were not relevant to therapeutic levels in human. We developed a liquid chromatography-tandem mass spectrometry protocol for metformin measurement in plasma, liver, brain, kidney, and muscle of mice. Young adult male and female C57BL/6 mice were voluntarily treated with metformin of 4 mg/ml in drinking water which translated to the maximum dose of 2.5 g/day in humans. A clinically relevant steady-state plasma metformin concentrations were achieved at 7 and 30 days after treatment in male and female mice. Metformin concentrations were slightly higher in muscle than in plasma, while, ~3 and 6-fold higher in the liver and kidney than in plasma, respectively. Low metformin concentration was found in the brain at ~20% of the plasma level. Furthermore, gender difference in steady-state metformin bio-distribution was observed. Our study established steady-state metformin levels in plasma, liver, muscle, kidney, and brain of normoglycemic mice treated with a clinically relevant dose, providing insight into future metformin preclinical studies for potential clinical translation.

Development of simultaneous determination of empagliflozin and metformin in human plasma using liquid chromatography-mass spectrometry and application to pharmacokinetics

A rapid and sensitive liquid chromatography-mass spectrometry method was developed, optimized, and validated for simultaneous quantification of empagliflozin and metformin in human plasma using empagliflozin D4and metformin D6 as an internal standard. Analytes and internal standard were extracted from plasma by optimized solid-phase extraction technique using Strata X polymeric reverse phase (30 mg-1cc) solid-phase extraction cartridges. The prepared samples were chromatographed on Orosil C18 column (150 × 4.6 mm, 3 µ). Separation was done by pumping isocratic mobile phase consisting of methanol and 10 mM ammonium trifluoroacetate (90:10, v/v) in positive ion mode at a flow rate of 0.8 mL/min. The API 3200 liquid chromatography-mass spectrometry system having turbo ion spray as an ion source coupled with Shimadzu Prominence ultrafast liquid chromatography system was operated under the selected reaction monitoring mode. Turbo ion spray ionization was used for mass transition of m/z 468.070/355.100 and m/z 130.072/71.200 for empagliflozin and metformin, respectively. A method was successfully validated for concentration range of 10.09-5013.46 ng/mL for both the analytes and according to the United States Food and Drugs Administration guidelines. The linearity was found to be in the range of 10.09-403.46 ng/mL for empagliflozin and 25.44-5013.46 ng/mL for metformin. The limit of quantification was found to be 10.09 ng/mL for empagliflozin and 25.44 ng/mL for metformin. Intra- and inter-day/between batch precision determination for empagliflozin and metformin, expressed as coefficient of variation were within the acceptance limits and ranged below 13.16%. A short run time of 3.3 min allows analysis of more than 400 plasma samples per day. The developed method was successfully applied to fasting pharmacokinetic study in healthy human volunteers. Results of incurred sample re-analysis were within the acceptance range of ±20% of original value, for 97.2% of samples reanalyzed for empagliflozin and 100% of samples reanalyzed for metformin.

A Rapid and Sensitive Method for the Pharmacokinetic Study of Janumet (Sitagliptin and Metformin) Tablets by LC-MS/MS Coupled with Ion-Pair Solid Phase Extraction

Background:

As first-line treatments for diabetes, sitagliptin and metformin have been widely prescribed as a combination to enhance the therapeutic effect.

Objective:

To establish a methodology to simultaneously monitor the two drugs in vivo by a reversedphase Liquid Chromatography-Tandem Mass Spectrometric (LC-MS/MS) method.

Methods:

The two drugs were extracted from 50 μl human plasma by ion-pair solid phase extraction. The separation of the plasma samples was implemented on an Agilent Zorbax SB-CN column (150×4.6 mm, 5.0 µm). The mobile phase was the mixture (80:20, v/v) of methanol and 5.0 mM ammonium formate in water (pH 4.5). An ion trap spectrometer equipped with an electrospray ionization source was utilized to detect the elution in positive mode. Quantification of the analytes was achieved by Multiple Reaction Monitoring (MRM) using the transitions of m/z 408.3→235.1 for sitagliptin and m/z 130.1→ 60.2 for metformin.

Results:

Sitagliptin and metformin demonstrated good linearity among the range of 1.00-1000 ng/mL and 5.00-4000 ng/mL. The intra-day and inter-day investigations displayed precisions of ≤ 3.6% and an accuracy range of -7.5% to 6.0% for the two drugs. The mean recovery of the two drugs was 96.0% and 98.5%. Under mandatory storage conditions, both the drugs gave an acceptable stability. The throughput of the assay was found to be more than 100 plasma samples per day ascribed to the run time of 3.0 min for each sample.

Conclusion:

The developed method was successfully applied to a pharmacokinetic study for a fixeddose tablet formulation containing 50 mg sitagliptin and 500 mg metformin in 12 healthy volunteers.

A HILIC-MS/MS assay for the quantification of metformin and sitagliptin in human plasma and urine: A tool for studying drug transporter perturbation

This article describes the development and validation of a HILIC-MS/MS method for the simultaneous quantification of metformin and sitagliptin from human plasma and urine. The presented method uses quick sample preparation and fast chromatography allowing for high sample throughput. The quantification is performed using multi-reaction monitoring and ESI positive mode with stable isotope labelled internal standards for both metformin and sitagliptin. Excellent linearity in the selected calibrations ranges, low inter-day variability (CV% <6.7%), and high accuracy (95.5-104.1%) were obtained. Adequate retention was attained for both analytes by hydrophilic interaction liquid chromatography using a plain silica column in combination with a mobile phase composed of ammonium formate, acetonitrile, formic acid and water in gradient separation mode.

The role of mass spectrometry in studies of glycation processes and diabetes management

In the last decade, mass spectrometry has been widely employed in the study of diabetes. This was mainly due to the development of new, highly sensitive, and specific methods representing powerful tools to go deep into the biochemical and pathogenetic processes typical of the disease. The aim of this review is to give a panorama of the scientifically valid results obtained in this contest. The recent studies on glycation processes, in particular those devoted to the mechanism of production and to the reactivity of advanced glycation end products (AGEs, AGE peptides, glyoxal, methylglyoxal, dicarbonyl compounds) allowed to obtain a different view on short and long term complications of diabetes. These results have been employed in the research of effective markers and mass spectrometry represented a precious tool allowing the monitoring of diabetic nephropathy, cardiovascular complications, and gestational diabetes. The same approaches have been employed to monitor the non-insulinic diabetes pharmacological treatments, as well as in the discovery and characterization of antidiabetic agents from natural products. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 38:112-146, 2019.

UPLC-MS/MS method for the quantification of ertugliflozin and sitagliptin in rat plasma

In the present study, an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) approach was designed to concurrently measure the levels of ertugliflozin and sitagliptin in rat plasma with diazepam as the internal standard (IS). Acetonitrile-based protein precipitation was applied for sample preparation, then analytes (ertugliflozin and sitagliptin) were subjected to gradient elution chromatography with a mobile phase composed of acetonitrile (A) and 0.1% formic acid in water (B). Ertugliflozin was monitored by m/z 437.2 → 329.0 transition for quantification and m/z 437.2 → 207.5 transition for qualification, and sitagliptin was determined by m/z 408.2 → 235.0 transition for quantification and m/z 408.2 → 174.0 transition for qualification by multiple reaction monitoring (MRM) in positive ion electrospray ionization (ESI) source. When the concentration of ertugliflozin ranged from 1 to 1000 ng/mL and sitagliptin ranged from 2 to 2500 ng/mL, the method exhibited good linearity. For both ertugliflozin and sitagliptin, the intra- and inter-day precision were determined with the values of 1.6-10.9% and 0.8-13.3%, respectively; and the accuracy ranged from -5.7% to 14.6%. Matrix effect, extraction recovery, and stability data were in line with the stipulated FDA guidelines for validating a bioanalytical method. The validity of the designed method was confirmed through the pharmacokinetic experiments.

A high-performance liquid chromatography-tandem mass spectrometry method for simultaneous determination of imigliptin, its five metabolites and alogliptin in human plasma and urine and its application to a multiple-dose pharmacokinetic study

Imigliptin is a novel DPP-4 inhibitor, designed to treat type 2 diabetes mellitus (T2DM). A selective and sensitive method was developed using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) to simultaneously quantify imigliptin, its five metabolites, and alogliptin in human plasma and urine. Solid-phase extraction (SPE) and direct dilution were used to extract imigliptin, its five metabolites, alogliptin from plasma and urine, respectively. The extracts were injected onto a SymmetryShield RP₈ column with a gradient elution of methanol and water containing 10 mM ammonium formate (pH = 7). Ionization of all analytes was performed using an electrospray ionization (ESI) source in positive mode and detection was carried out with multiple reaction monitoring (MRM) mode. The results revealed that the method had excellent selectivity and linearity. Inter- and intra-batch precisions of all analytes were less than 15% and the accuracies were within 85%-115% for both plasma and urine. The sensitivity, matrix effect, extraction recovery, linearity, and stabilities were validated for all analytes in human plasma and urine. In conclusion, the validation results showed that this method was robust, specific, and sensitive and it can successfully applied to a pharmacokinetic study of Chinese T2DM subjects after oral dose of imigliptin and alogliptin.

A sensitive fluorescent sensing strategy for nanomolar levels of metformin using graphitic carbon nitride nanosheets as nanofluoroprobe

A simple and green fluorescence detection system on the basis of the quenching effect of Cu(II) ions on the graphitic carbon nitride nanosheets (g-C₃N₄ NS) fluorescence and recording the changes of restored fluorescence intensity upon the addition of metformin (MET) was developed for the first time. The g-C₃N₄ NS were produced using high-temperature polymerization of melamine followed by ultrasonication-assisted liquid exfoliation. The method exhibited excellent sensitivity and accuracy toward MET with the detection as low as 3 nM and linear calibration curve in the range of 0.01-20 μM. In addition, this assay was successfully applied to the determination of MET concentration in human serum samples. It is robust and is suitable for fast, sensitive and cost effective measurement of MET in biological materials.

Mechanistic study for the simultaneous determination of metformin and teneligliptin in human plasma using hydrophilic interaction liquid chromatography–MS/MS

Aim: A simple, selective and sensitive hydrophilic interaction liquid chromatography-MS/MS method is developed for the simultaneous determination of metformin (MET) and teneligliptin (TEN) in human plasma using deuterated internal standards. The mechanism of retention of analytes was studied by varying the proportion of organic diluent, buffer strength, pH of the mobile phase and temperature. Results: The results showed a mixed-mode mechanism comprising of hydrophilic (partition) and electrostatic interaction (ion exchange) for MET and essentially hydrophilic for TEN. The linear calibration curves were established in the concentration range of 1.0–1000 ng/ml for MET and 0.50–750 ng/ml for TEN. Conclusion: The method was applied to determine plasma concentration of MET and TEN in healthy subjects.

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.