Direct separation and quantitative analysis of thyroxine and triiodothyronine enantiomers in pharmaceuticals by high-performance liquid chromatography

Nanopore surface engineering of molecular imprinted mesoporous organosilica for rapid and selective detection of L-thyroxine

To develop a biosensing platform for precise diagnosis and management of thyroid-related diseases, the sensitive and selective recognition and identification of L-thyroxine (T4), a thyroid hormone, remains challenging. We herein introduce T4-imprinted mesoporous organosilica (T4-IMO) for sensitive and specific detection of T4 via the sophisticated engineering of pore surfaces using additives with different polarities. The pore surface of T4-IMO emitting a stable fluorescence signal is simply modified by fixed additives. Additives embedded in the pore surface promote the rebinding response of T4 into the recognized cavities, subsequently sensitizing T4 detection. Notably, T4-IMO containing abundant fluorine elements on the pore surface shows a high affinity toward T4, remarkably boosting the rebinding capacity. In addition to good selectivity to T4, the "turn-off" fluorescent signal exhibits a linear relationship with the logarithm of T4 concentration in a range of 0-500 nM with a detection limit of 0.47 nM in synthetic urine samples. Our findings can establish an insightful strategy for the rational design of molecular-recognition-based sensor systems for the selective and sensitive detection of target analytes.

Chiral LC-MS/MS method for the discrimination of triiodothyronine enantiomers on a crown ether-based chiral stationary phase

Considering the greater pharmaceutical and clinical interest of triiodothyronine (T3 ) thyroid hormone, an effective D/L-T3 enantiomer separation was performed on a crown ether-based chiral stationary phase by LC-MS/MS. In optimal analytical condition and selected reaction monitoring mode, the two enantiomers of T3 were baseline separated within 10 min. The limit of detection and limit of quantitation were found to be 0.05 and 0.10 ng/μl; 0.20 and 0.50 ng/μl for D- and L-T3 , respectively. During validation, this method proved to be feasible, accurate as well as enantioselective and sensitive for the resolution of T3 enantiomers. For commercial D- and L-T3 chemicals, the enantiomeric impurities as the other enantiomer were 0.11% and 4.61%. On the other hand, the impurity as D-T3 for commercial pharmaceutical products (liothyronine sodium tablets, two suppliers) was 0.68% and 6.57%.

Simultaneous enantioselective separation method for thyroid hormones using liquid chromatography-tandem mass spectrometry and its applications

An analytical method for the simultaneous determination of chiral thyroxine and the related iodinated chiral compounds using LC-MS/MS is introduced in this study. D-Thyroid hormones (THs), which are not commercially available, were produced through the racemization reaction of the L-THs in acetic acid solution containing salicylaldehyde. The solution containing D- and L-THs after the reaction was used for optimizing the chiral separation. The D- and L-THs were well separated enantiomerically under isocratic conditions in 70 % acetonitrile containing 0.1 % formic acid on a CROWNPAK® CR-I (+) column, but some peaks, such as those of diiodo-D-tyrosine (D-DIT)/monoiodo-L-tyrosine, diiodo-D-thyronine/diiodo-L-tyrosine and D-thyroxine/triiodo-L-thyronine, overlapped chromatographically, causing misinterpretation in impurity analysis. This was overcome by using the gradient condition providing the best chiral selectivity (α) and resolution (Rs) ranging from 1.14 to 1.37 and from 2.39 to 4.52, respectively. The linearity was above 0.999 and the detection limits ranged from 8.2 to 57.7 ng/mL by the separation method. This method was applied to identify and quantify chiral impurities in authentic standards and pharmaceuticals. As a result, D-enantiomers corresponding to the L-THs standards as well as L-DIT were commonly observed as impurities. In the stability test of DL-thyroxine under acidic conditions for identifying the distribution of chiral products, it was observed that the formation of DIT by hydrolysis increased over time. Additional products formed through esterification, including thyroxine methyl ester and diiodo-tyrosine methyl ester, were newly separated and identified using a C18 column.

Quantification of triiodothyronine and thyroxine in rat serum using liquid chromatography tandem mass spectrometry

Thyroid hormones act on almost every tissue in the body to promote catabolism in cells and are important for regulating many biological processes. Accurate quantification of endogenous thyroid hormones has become essential for clinical and non-clinical applications in the development of new drugs according to the OECD Guideline (2018). However, there are difficulties in quantitative analysis of thyroid hormones because no analyte-free biological matrices are available for analysis of endogenous substances. In this study, surrogate matrix and surrogate analyte methods were compared and validated to quantify endogenous triiodothyronine (T₃) and thyroxine (T₄) in rat serum using LC-MS/MS. Separation of analytes was performed using an Xbridge™ C18 (2.1 × 50 mm, 2.5 μm) column. In the surrogate matrix, 3,3'5-triiodo- l-thyronine-¹³C₆ (cT₃) and l-thyroxine-¹³C₆ (cT₄) were used as the internal standard (IS), and in the surrogate analyte, l-3,3'-diiodothyronine-¹³C₆ (cT₂) was used as the IS. The mobile phases consisted of 0.1 % acetic acid in purified water (A) and 0.1 % acetic acid in acetonitrile (B). Both analytical methods were suitable for selectivity, matrix effect, carryover, lower limit of quantification, linearity, accuracy, precision, recovery, stability and parallelism. The surrogate matrix method was more accurate than using the surrogate analyte method, including evaluation of parallelism at low concentrations. Additionally, the surrogate matrix is cost-effective for T₃ and T₄ analysis in biological samples because it consists only of deionized water. However, surrogate analytes difficult to evaluate parallelism by obtaining response factors for mass spectrometric signal differences between the actual and surrogate analytes. Therefore, the results of this study indicate that it is more cost-effective to use the surrogate matrix method for endogenous thyroid hormone, T₃ and T₄, analysis in biological samples.

A feasible method for indirect quantification of L-T4 in drugs by iodine determination

In this work, a method combining microwave-induced combustion (MIC) for sample preparation of commercial levothyroxine sodium (L-T₄) drugs (L-T₄: 25-200µg/tablet), and potentiometry with ion selective electrode (ISE) for iodine determination and subsequent indirect quantification of L-T₄ was proposed. The type and concentration of the absorbing solution were evaluated to select the most suitable conditions for this study. Using the MIC method, it was possible to use solutions as diluted as 150mmolL^-1 (NH₄)₂CO₃ (for samples containing 25-200µg of L-T₄/tablet) for I absorption. In these conditions, recoveries for L-T₄ were between 99% and 101%, and relative standard deviations were lower than 10%. The limit of detection for L-T₄ was 11.2µg/tablet, which is almost two times lower than the minimum concentration of L-T₄ in commercially available drugs. Thus, the MIC was suitable for the digestion of several L-T₄ drugs for subsequent I determination by ISE and indirect quantification of L-T₄. Furthermore, the proposed method presents high throughput with low reagent consumption and consequently lower waste generation, making it suitable for routine determination of L-T₄ in drugs. From the obtained results, it was possible to observe that one of the analyzed samples is not in agreement with the limits established by the United States Pharmacopeia, indicating the importance of the drug quality control. The United States Pharmacopeia establishes that each tablet must contain between 90% and 110% of the amount of active substance declared by the manufacturer.

Levothyroxine sodium revisited: A wholistic structural elucidation approach of new impurities via HPLC-HRMS/MS, on-line H/D exchange, NMR spectroscopy and chemical synthesis

The structural elucidation of unknown pharmaceutical impurities plays an important role in the quality control of newly developed and well-established active pharmaceutical ingredients (APIs). The United States Pharmacopeia (USP) monograph for the API Levothyroxine Sodium, a synthetic thyroid hormone, features two high pressure liquid chromatography (HPLC) methods using UV-VIS absorption detection to determine organic impurities in the drug substance. The impurity profile of the first USP method ("Procedure 1") has already been extensively studied, however for the second method ("Procedure 2"), which exhibits a significantly different impurity profile, no wholistic structural elucidation of impurities has been performed yet. Applying minor modifications to the chromatographic parameters of USP "Procedure 2" and using various comprehensive structural elucidation methods such as high resolution tandem mass spectrometry with on-line hydrogen-deuterium (H/D) exchange or two-dimensional nuclear magnetic resonance spectroscopy (NMR) we gained new insights about the complex impurity profile of the synthetic thyroid hormone. This resulted in the characterization of 24 compounds previously unknown to literature and the introduction of two new classes of Levothyroxine Sodium impurities. Five novel compounds were unambiguously identified via isolation or synthesis of reference substances and subsequent NMR spectroscopic investigation. Additionally, Collision-Induced Dissociation (CID)-type fragmentation of identified major impurities as well as neutral loss fragmentation patterns of many characterized impurities were discussed.

Ultrahigh-performance liquid chromatography-ultraviolet absorbance detection-high-resolution-mass spectrometry combined with automated data processing for studying the kinetics of oxidative thermal degradation of thyroxine in the solid state

Levothyroxine as active pharmaceutical ingredient of formulations used for the treatment of hypothyroidism is distributed worldwide and taken by millions of people. An important issue in terms of compound stability is its capability to react with ambient oxygen, especially in case of long term compound storage at elevated temperature. In this study we demonstrate that ultrahigh-performance liquid chromatography coupled to UV spectrometry and high-resolution mass spectrometry (UHPLC-UV-HRMS) represent very useful approaches to investigate the influence of ambient oxygen on the degradation kinetics of levothyroxine in the solid state at enhanced degradation conditions. Moreover, the impurity pattern of oxidative degradation of levothyroxine is elucidated and classified with respect to degradation kinetics at different oxygen levels. Kinetic analysis of thyroxine bulk material at 100 °C reveals bi-phasic degradation kinetics with a distinct change in degradation phases dependent on the availability of oxygen. The results clearly show that contact of the bulk material to ambient oxygen is a key factor for fast compound degradation. Furthermore, the combination of time-resolved HRMS data and automated data processing is shown to allow insights into the kinetics and mechanism of impurity formation on individual compound basis. By comparing degradation profiles, four main classes of profiles linked to reaction pathways of thyroxine degradation were identifiable. Finally, we show the capability of automated data processing for the matching of different stressing conditions, in order to extract information about mechanistic similarities. As a result, degradation kinetics is influenced by factors like availability of oxygen, stressing time, or stressing temperature, while the degradation mechanisms appear to be conserved.

Rapid and comprehensive impurity profiling of synthetic thyroxine by ultrahigh-performance liquid chromatography-high-resolution mass spectrometry

Rapid and efficient quality control according to the public authority regulations is mandatory to guarantee safety of the pharmaceuticals and to save resources in the pharmaceutical industry. In the case of so-called "grandfather products" like the synthetic thyroid hormone thyroxine, strict regulations enforce a detailed chemical analysis in order to characterize potentially toxic or pharmacologically relevant impurities. We report a straightforward workflow for the comprehensive impurity profiling of synthetic thyroid hormones and impurities employing ultrahigh-performance liquid chromatography (UHPLC) hyphenated to high-resolution mass spectrometry (HRMS). Five different batches of synthetic thyroxin were analyzed resulting in the detection of 71 impurities within 3 min total analysis time. Structural elucidation of the compounds was accomplished via a combination of accurate mass measurements, computer based calculations of molecular formulas, multistage high-resolution mass spectrometry (HRMS(n)), and nuclear magnetic resonance spectroscopy, which enabled the identification of 71 impurities, of which 47 have been unknown so far. Thirty of the latter were structurally elucidated, including products of deiodination, aliphatic chain oxidation, as well as dimeric compounds as new class of thyroid hormone derivatives. Limits of detection for the thyroid compounds were in the 6 ng/mL range for negative electrospray ionization mass spectrometric detection in full scan mode. Within day and day-to-day repeatabilities of retention times and peak areas were below 0.5% and 3.5% R.SD. The performance characteristics of the method in terms of robustness and information content clearly show that UHPLC-HRMS is adequate for the rapid and reliable detection, identification, and semiquantitative determination of trace levels of impurities in synthetic pharmaceuticals.

Investigation of reaction mechanisms of drug degradation in the solid state: a kinetic study implementing ultrahigh-performance liquid chromatography and high-resolution mass spectrometry for thermally stressed thyroxine

A reaction scheme was derived for the thermal degradation of thyroxine in the solid state, using data obtained from ultrahigh-performance liquid chromatography and high-resolution mass spectrometry (UHPLC-HRMS). To study the reaction mechanism and kinetics of the thermal degradation of the pharmaceutical in the solid state, a workflow was developed by generating compound-specific, time-dependent degradation or formation curves of at least 13 different degradation products. Such curves allowed one to distinguish between first- and second-generation degradation products, as well as impurities resulting from chemical synthesis. The structures of the degradation products were derived from accurate molecular masses and multistage mass spectrometry. Deiodination and oxidative side chain degradation were found to be the major degradation reactions, resulting in the formation of deiodinated thyroxines, as well as acetic acid, benzoic acid, formaldehyde, acetamide, hydroxyacetic acid, oxoacetic acid, hydroxyacetamide, or oxoacetamide derivatives of thyroxine or deiodinated thyroxine. Upon additional structural verification of mass spectrometric data using nuclear magnetic resonance spectroscopy, this comprehensive body of data sheds light on an elaborate, radical-driven reaction scheme, explaining the presence or formation of impurities in thermally stressed thyroxine.

Autoantibodies against thyroid hormones and their influence on thyroxine determination with chemiluminescence immunoassay in dogs

Autoantibodies against thyroxin (T4AA) and triiodothyronine (T3AA) are present in dogs with autoimmune thyroiditis and have been reported to interfere with immunoassays. The objectives of this study were to determine the frequency of autoantibodies and to determine whether interference occurs by T4AA, using a non-immunological method (high performance liquid chromatography, HPLC) for thyroxin (T4) measurement. Based on clinical symptoms, T4 and thyroid stimulating hormone (TSH) concentration, 1,339 dogs were divided into six groups: Group 1: hypothyroid (n = 149); Group 2: subclinical thyroiditis (n = 110); Group 3: suspicious for non thyroidal illness (n = 691); Group 4: biochemical euthyroid (n = 138); Group 5: hypothyroid dogs under substitution therapy (n = 141); Group 6: healthy dogs (n = 110). The incidence of T4AA and T3AA, determined using radiometric assay, was low (0.5% and 3.8%) and higher in hypothyroid dogs compared to dogs suspicious for hypothyroidism (Group 2-4) (p < 0.05). T4AA was not detected in dogs with normal T4 and elevated TSH. T4 concentrations of T4AA positive samples determined using HPLC were comparable to results obtained by chemiluminescence immunoassay. These findings indicate that the probability of interference of T4AA leading to falsely elevated T4 concentration in the T4 assay seems to be low.

Development and application of a validated HPLC method for the analysis of dissolution samples of levothyroxine sodium drug products

A rapid, selective, and sensitive gradient HPLC method was developed for the analysis of dissolution samples of levothyroxine sodium tablets. Current USP methodology for levothyroxine (L-T(4)) was not adequate to resolve co-elutants from a variety of levothyroxine drug product formulations. The USP method for analyzing dissolution samples of the drug product has shown significant intra- and inter-day variability. The sources of method variability include chromatographic interferences introduced by the dissolution media and the formulation excipients. In the present work, chromatographic separation of levothyroxine was achieved on an Agilent 1100 Series HPLC with a Waters Nova-pak column (250 mm × 3.9 mm) using a 0.01 M phosphate buffer (pH 3.0)-methanol (55:45, v/v) in a gradient elution mobile phase at a flow rate of 1.0 mL/min and detection UV wavelength of 225 nm. The injection volume was 800 μL and the column temperature was maintained at 28°C. The method was validated according to USP Category I requirements. The validation characteristics included accuracy, precision, specificity, linearity, and analytical range. The standard curve was found to have a linear relationship (r(2)>0.99) over the analytical range of 0.08-0.8 μg/mL. Accuracy ranged from 90 to 110% for low quality control (QC) standards and 95 to 105% for medium and high QC standards. Precision was <2% at all QC levels. The method was found to be accurate, precise, selective, and linear for L-T(4) over the analytical range. The HPLC method was successfully applied to the analysis of dissolution samples of marketed levothyroxine sodium tablets.

Enatioselective quantitative separation of D- and L-thyroxine by molecularly imprinted micro-solid phase extraction silver fiber coupled with complementary molecularly imprinted polymer-sensor

Thyroxine is a known disease biomarker which demands a highly sensitive and selective technique to measure ultratrace level with enantiodifferentiation of its optical isomers (d- and l-), in real samples. In this work, an approach of hyphenation between molecularly imprinted micro-solid phase extraction and a complementary molecularly imprinted polymer-sensor was adopted for enantioseparation, preconcentration, and analysis of d- and l-thyroxine. In both techniques, the same imprinted polymer, coated on a vinyl functionalized self-assembled monolayer modified silver wire, was used as the respective extraction fiber as well as sensor material. This combination enabled enhanced preconcentration of test analyte substantially so as to achieve the stringent limit [limit of detection: 0.0084 ng mL(-1), RSD=0.81%, S/N=3 (d-thyroxine); 0.0087 ng mL(-1), RSD=0.63%, S/N=3 (l-thyroxine)] of clinical detection of thyroid-related diseases, without any problems of non-specific false-positive contribution and cross-reactivity.

HPLC-MS analysis of iodotyrosines produced by sample hydrolysis: A simple method for monitoring iodinated casein in feed premixes

A new and simple HPLC-MS method was developed for monitoring iodinated casein in feed premixes. In this method, feed premixes were hydrolyzed, and the iodotyrosines thus released were analyzed. Sample pretreatment included precipitation of transition metals ions with Na(2)S, hydrolysis with sodium hydroxide, and cleaning up with an Oasis SAX cartridge. Gradient elution was carried out on a C(18) column with water (containing 0.1% formic acid) and acetonitrile. Ion detection was performed using ESI positive SIM at m/z 262, 308, 388, and 434. Iodinated casein levels were monitored by qualitative analysis of the iodotyrosines released upon sample hydrolysis and by quantifying the 3,5-diiodotyrosine released. The validation data demonstrated that the method was selective and sensitive (<or=0.2mgg(-1)) for iodinated casein and had acceptable accuracy (recoveries: 81.3-106.7%) and precision (RSD: 1.7-16.0%).

Flow-injection determination of thyroxine using immobilized enzyme with tris(2,2'-bipyridyl)ruthenium(III) chemiluminescence detection

A flow-injection method is reported for the determination of thyroxine based on its enhancement effect on the tris(2,2'-bipyridyl)ruthenium(III) chemiluminescence reaction in the presence of NADH using immobilized alcohol dehydrogenase purified from baker yeast. The limit of detection (3 sigma blank) was 5.0 x 10(-8) M with a sample throughput of 80 h(-1). The calibration graph was linear over the range 0.5 - 10 x 10(-7) M (r2= 0.9988) with the relative standard deviation in the range 1.4 - 3.5% (n = 4). The effect of common excipients used in pharmaceutical preparations, some organic compounds and metal ions was studied. The method was applied to pharmaceutical thyroxine tablets, and the obtained results were not significantly different from the amount quoted.

Aptamer-based enantioselective competitive binding assay for the trace enantiomer detection

The development of highly enantioselective assays and sensors has received much attention for the determination of enantiomeric impurities at a low level. For chiral compounds, the efficient monitoring of the in selection procedure has allowed the isolation of nucleic acid aptamers which are able to strongly discriminate the target enantiomers. In this paper, we demonstrated for the first time that an aptamer can be successfully used to design a highly enantioselective tool for the trace enantiomer detection. The aptamer-based stereoselective assay was developed using an affinity capillary electrophoresis-based competitive, homogeneous format and an on-capillary mixing approach. Detection of as low as 0.01% of the minor enantiomer in a nonracemic mixture can be achieved, in a short analysis time (<5 min).

Enantioselective resolution of thyroxine hormone by high-performance liquid chromatography utilizing a highly fluorescent chiral tagging reagent

A highly fluorescent chiral tagging reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole, [R(-)-DBD-PyNCS], was employed to develop an indirect resolution method for efficient separation of thyroxine enantiomers,D-T(4) and L-T(4). The reaction of R(-)-DBD-PyNCS with the thyroxine enantiomers proceeds effectively at 40 degrees C for 20 min in the presence of basic medium to produce the corresponding pair of diastereomers. No racemization occurs during the tagging reaction under the optimized conditions. Various experimental parameters for derivatization reaction including the species of catalyst, the concentration of tagging reagent and reaction temperatures, have been examined to get a highest yield for T(4) derivatives. The structure of T(4) derivatives was identified based on ESI-MS/MS measurements in negative mode. The efficient separation of D-, L-T(4) derivatives was achieved by isocratic elution with water-acetonitrile mobile phase containing 1% AcOH on a reversed phase column utilizing a conventional fluorescence detector. The resolution (Rs) value of the diastereomers derived from thyroxine was 5.1. The calibration curves of both the D-T(4) and L-T(4) were linear over the concentration range of 0.1-20 microg/ml. The limits of detection (S/N = 3) for both D-T(4) and L-T(4) were 0.2 ng per injection. The proposed method was applied to the determination of D-T(4) and L-T(4) in pharmaceutical formulations and human serum samples.

Chiral separation of T3 enantiomers using stereoselective antibodies as a selector in micro-HPLC

This work deals with the application of stereoselective antibodies against L-T3 as a tailor-made chiral selector in micro-HPLC. The separations were performed in microbore columns using commercially available anti-L-T3 antibodies chemically bonded to 5 microm silica gel. The enantiomers of T3 were baseline separated under mild continuous isocratic elution conditions using 10 mM phosphate buffer, pH 7.4. The D-enantiomer eluted with the void volume, while the L-enantiomer was retained by the antibody phase and eluted second. An indirect competitive and non-competitive enzyme linked immunosorbent assay (ELISA) was used for testing the stereoselectivity of anti-L-T3 antibodies.