Identification of anabolic steroids and derivatives using bioassay-guided fractionation, UHPLC/TOFMS analysis and accurate mass database searching

Biological tests can be used to screen samples for large groups of compounds having a particular effect, but it is often difficult to identify a specific compound when a positive effect is observed. The identification of an unknown compound is a challenge for analytical chemistry in environmental analysis, food analysis, as well as in clinical and forensic toxicology. In this study bioassay-guided fractionation, ultra high performance liquid chromatography combined with time-of-flight mass spectrometry (UHPLC/TOFMS) and accurate mass database searching was tested to detect and identify unknown androgens. Herbal mixtures and sport supplements were tested using an androgen bioassay and modifications in sample preparations were carried out in order to activate inactive pro-androgens, androgen esters and conjugated androgens to enable their detection in the bioassay. Two of the four herbal mixtures tested positive and bioassay-guided fractionation followed by UHPLC/TOFMS of positive fractions resulted in the identification of nortestosterone phenylpropionate, testosterone cyclohexanecarboxylate and methyltestosterone. Three of the four sport supplements reacted toxic in the bioassay or gave inconclusive results and were further investigated using UHPLC/TOFMS in combination with data processing software and an accurate mass database having approximately 40,000 entries. This accurate mass database was derived from the PubChem database on the internet and coupled to the TOFMS software. This resulted in the tentative identification of several androgens, including methylboldenone, testosterone and the androgen esters methyltestosterone propionate or testosterone isobutyrate, testosterone buciclate and methylenetestosterone acetate. The study showed that bioassay-guided fractionation in combination with UHPLC/TOFMS analysis is a useful procedure to detect, isolate and identify unknown androgens in suspected samples. As an alternative, the use of data processing software in combination with an accurate mass database and coupled on-line with the TOFMS instrument software enabled the identification of androgens and androgen esters in the chromatogram even without bioassay-guided fractionation.     

Characterization of forced degradation products of ketorolac tromethamine using LC/ESI/Q/TOF/MS/MS and in silico toxicity prediction

Ketorolac, a nonsteroidal anti‐inflammatory drug, was subjected to forced degradation studies as per International Conference on Harmonization guidelines. A simple, rapid, precise, and accurate high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry (LC/ESI/Q/TOF/MS/MS) method has been developed for the identification and structural characterization of stressed degradation products of ketorolac. The drug was found to degrade in hydrolytic (acidic, basic, and neutral), photolytic (acidic, basic, and neutral solution), and thermal conditions, whereas the solid form of the drug was found to be stable under photolytic conditions. The method has shown adequate separation of ketorolac tromethamine and its degradation products on a Grace Smart C‐18 (250 mm × 4.6 mm i.d., 5 µm) column using 20 mM ammonium formate (pH = 3.2): acetonitrile as a mobile phase in gradient elution mode at a flow rate of 1.0 ml/min. A total of nine degradation products were identified and characterized by LC/ESI/MS/MS. The most probable mechanisms for the formation of degradation products have been proposed on the basis of a comparison of the fragmentation of the [M + H]⁺ ions of ketorolac and its degradation products. In silico toxicity of the drug and degradation products was investigated by using topkat and derek softwares. The method was validated in terms of specificity, linearity, accuracy, precision, and robustness as per International Conference on Harmonization guidelines. Copyright © 2014 John Wiley & Sons, Ltd.     

Automated software-guided identification of new buspirone metabolites using capillary LC coupled to ion trap and TOF mass spectrometry

The identification and structure elucidation of drug metabolites is one of the main objectives in in vitro ADME studies. Typical modern methodologies involve incubation of the drug with subcellular fractions to simulate metabolism followed by LC-MS/MS or LC-MS(n) analysis and chemometric approaches for the extraction of the metabolites. The objective of this work was the software-guided identification and structure elucidation of major and minor buspirone metabolites using capillary LC as a separation technique and ion trap MS(n) as well as electrospray ionization orthogonal acceleration time-of-flight (ESI oaTOF) mass spectrometry as detection techniques.Buspirone mainly underwent hydroxylation, dihydroxylation and N-oxidation in S9 fractions in the presence of phase I co-factors and the corresponding glucuronides were detected in the presence of phase II co-factors. The use of automated ion trap MS/MS data-dependent acquisition combined with a chemometric tool allowed the detection of five small chromatographic peaks of unexpected metabolites that co-eluted with the larger chromatographic peaks of expected metabolites. Using automatic assignment of ion trap MS/MS fragments as well as accurate mass measurements from an ESI oaTOF mass spectrometer, possible structures were postulated for these metabolites that were previously not reported in the literature.     

Cutting-edge LC–MS/MS applications in clinical mass spectrometry: Focusing on analysis of drugs and metabolites

In recent years, liquid chromatography with tandem mass spectrometry (LC–MS/MS) has become a fundamental technology in clinical practice. In Japan, the LC–MS/MS system is used in many large hospitals. It has become popular among pharmacists and laboratory technicians. LC–MS/MS has some advantages in terms of accuracy, speed, and comprehensiveness compared to conventional automated chemical testing equipment. However, LC–MS/MS is by no means a universal method, and it is necessary to understand its characteristics before using it. In the field of therapeutic drug monitoring (TDM), there is an issue with linearity in comprehensive measurement; however, ion-abundance adjustment methods, such as in-source collision-induced dissociation, have been proposed as a solution to this problem. The development of a biomarker analysis includes search, identification, and quantification, and it is necessary to select an appropriate mass spectrometric method for each step. In this paper, we review cutting-edge technologies that can expand the performance of LC–MS/MS in the clinical field and consider current issues and future prospects.     

Identification of photocatalytic degradation products of diazinon in TiO2 aqueous suspensions using GC/MS/MS and LC/MS with quadrupole time-of-flight mass spectrometry

The photocatalytic degradation of the organophosphorus insecticide diazinon in aqueous suspensions has been studied by using titanium dioxide as a photocatalyst. The degradation of the insecticide was a fast process and included the formation of several intermediates that were identified using GC/ion-trap mass spectrometry with EI or CI in positive and negative ionization mode and HPLC/electrospray-QqTOF mass spectrometry. Since primarily hydroxy derivatives were identified in these aqueous suspensions, the mechanism of degradation was probably based on hydroxyl radical attack. The initial oxidative pathways of the degradation of diazinon involved the substitution of sulfur by oxygen on the Pz.dbnd6;S bond, cleavage of the pyrimidine ester bond, and oxidation of the isopropyl group. Exact mass measurements of the derivatives allowed the elemental formula of the molecules to be determined confidently. Similarities to the metabolic pathways occurring in living organisms were observed.     

A validated assay to quantitate serotonin in lamb plasma using ultrahigh-performance liquid chromatography-tandem mass spectrometry: applications with LC/MS3

An ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC/MS/MS) method was developed and validated for the quantification of serotonin (5-HT) in lamb plasma using [²d₄]-serotonin ([²d₄]-5-HT) as an internal standard. Charcoal-stripped human plasma was used as the blank matrix during validation, and 5-HT was quantitated using selected reaction monitoring. The UHPLC/MS/MS system consisted of an Agilent 1290 Infinity ultrahigh-performance liquid chromatograph coupled with an AB SCIEX QTRAP® 5500 hybrid linear ion trap triple quadrupole mass spectrometer. The method was validated for accuracy, precision, linearity, lower limit of quantification (LLOQ), selectivity, and other parameters. The LLOQ was 1.0 ng/mL, requiring 100 μL of sample. The method was applied to monitor the 5-HT levels in lamb plasma after the administration of fluoxetine. Tandem mass spectrometry cubed (MS³) experiments were also performed to investigate the fragmentation pattern of 5-HT and [²d₄]-5-HT. A liquid chromatography-MS³ (LC/MS³) method was developed, and the UHPLC/MS/MS and the LC/MS³ methods were compared for performance.

Evaluation of relative LC/MS response of metabolites to parent drug in LC/nanospray ionization mass spectrometry: potential implications in MIST assessment

There is an increasing demand for quantitative data on metabolite exposure triggered by regulatory guidances. This contribution describes the accuracy of nanoelectrospray ionization mass spectrometry response of drug compounds and their metabolites from biological matrices compared with radiometric quantification. This is a comprehensive investigation of a set of real-life pharmaceutical compounds in relevant matrices such as urine, bile, feces and plasma. The data suggest that nanoelectrospray mass spectrometry can be used for semi-quantitation of metabolites in the absence of reference standards. Therefore, this approach is suitable to screen out non-relevant metabolites early in development as long as an adequate analytical error margin is applied thus balancing risks and resources.     

Multiresidue analysis and probabilistic dietary risk assessment of 241 pesticides in wheatgrass (Triticum sp.) using LC–MS/MS in combination with QuEChERS extraction

Wheatgrass is consumed as an important nutritious herbal food supplement across the globe; however, limited studies have been reported analyzing multiclass pesticides in this complex, nutrient-rich natural product. An analytical method was developed for the estimation of 241 pesticides in random wheatgrass samples collected from Delhi Northern Capital Region (Delhi-NCR). Extraction was performed by QuEChERS, cleaning was performed by dispersive solid-phase extraction and the extracts were analyzed using triple quadrupole liquid chromatography mass spectrometry. The limit of quantification was 0.5 μg/kg, which is well below the European Union Maximum Residue Level. The coefficient of determination was >0.991 across a calibration range of 0.5–100 μg/kg. The relative standard deviation values for 231 pesticides based on 10 replicates of samples spiked at 10 μg/kg were <5%. Among random samples, 54% confirmed the presence of at least one pesticide. The results indicated the presence of eight different pesticides among 38% of the total population with metribuzin at 299.7 μg/kg and carfentrazone-ethyl at 19.47 μg/kg exceeding the permissible limits among 6% of the total estimated population. The chronic and acute risk quotients as calculated were <1, indicating nonsignificant dietary risk to consumers. However, the presence of pesticides above the permissible limit is likely to result in adverse health effects to the consumers of herbal supplements from an urban population and incorporating measures would be useful to ensure the quality and safety of wheatgrass consumption.     

Multiresidue screening of pesticides in foods using retention time locking, GC-AED, database search, and GC/MS identification

Fruit and vegetable extracts were screened for over 400 pesticides by gas chromatography with atomic emission detection (GC-AED) and an experimental database. A technique called retention time locking was used to match GC-AED and GC with mass spectrometry (MS) retention times to those of the database. Samples were analyzed for sulfur, nitrogen, phosphorus, and chlorine by GC-AED. Possible pesticides were suggested by database search and identified by GC/MS. Forty-four pesticide standards were analyzed to determine the precision of retention time matching and the accuracy of the database search. Analytical retention times matched database retention times within 0.32 min. Using elemental criteria, the database search identified the correct compound for 41 of 44 pesticide standards. For blind spikes of fruit and vegetable extracts, the database suggested 22 of 26 spiked pesticides as matches. Nineteen were identified by GC/MS. The combination of retention time locking, GC-AED, database search, and GC/MS can be a powerful tool for identifying pesticides in a complex matrix.     

Development and validation of a high-sensitivity liquid chromatography/tandem mass spectrometry (LC/MS/MS) method with chemical derivatization for the determination of ethinyl estradiol in human plasma

An ultra-sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the analysis of oral contraceptive ethinyl estradiol (EE) was developed and validated over the curve range of 2.5-500 pg/mL using 1 mL of human plasma sample. Ethinyl estradiol and the internal standard, ethinyl estradiol tetra-deuterated (EE-d4), were extracted from the plasma matrix with methyl t-butyl ether, derivatized with dansyl chloride and then back-extracted into hexane. The hexane phase was evaporated to dryness, reconstituted and injected onto the LC/MS/MS system. The chromatographic separation was achieved on a Luna C(18) column (50 x 2 mm, 5 micro m) with an isocratic mobile phase of 20:80 (v/v) water:acetonitrile with 1% formic acid. The offline derivatization procedure introduced the easily ionizable tertiary amine function group to EE. This greatly improved analyte sensitivity in electrospray ionization and enabled us to achieve the desired lower limit of quantitation at 2.5 pg/mL. This high sensitivity method can be used for therapeutic drug monitoring or supporting bio-equivalence and drug-drug interaction studies in human subjects.     

Identification and structural characterization of in vivo metabolites of ketorolac using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS)

In vivo metabolites of ketorolac (KTC) have been identified and characterized by using liquid chromatography positive ion electrospray ionization high resolution tandem mass spectrometry (LC/ESI‐HR‐MS/MS) in combination with online hydrogen/deuterium exchange (HDX) experiments. To identify in vivo metabolites, blood urine and feces samples were collected after oral administration of KTC to Sprague–Dawley rats. The samples were prepared using an optimized sample preparation approach involving protein precipitation and freeze liquid separation followed by solid‐phase extraction and then subjected to LC/HR‐MS/MS analysis. A total of 12 metabolites have been identified in urine samples including hydroxy and glucuronide metabolites, which are also observed in plasma samples. In feces, only O‐sulfate metabolite and unchanged KTC are observed. The structures of metabolites were elucidated using LC‐MS/MS and MSⁿ experiments combined with accurate mass measurements. Online HDX experiments have been used to support the structural characterization of drug metabolites. The main phase I metabolites of KTC are hydroxylated and decarbonylated metabolites, which undergo subsequent phase II glucuronidation pathways. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantitation of cytidine-5′-monophospho-N-acetylneuraminic acid in human leukocytes using LC–MS/MS: method development and validation

The biosynthesis of sialic acid (Neu5Ac) leads to the intracellular production of cytidine-5′-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac), the active sialic acid donor to nascent glycans (glycoproteins and glycolipids) in the Golgi. UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase myopathy is a rare autosomal recessive muscular disease characterized by progressive muscle weakness and atrophy. To quantify the intracellular levels of CMP-Neu5Ac as well as N-acetylmannosamine (ManNAc) and Neu5Ac in human leukocytes, we developed and validated robust liquid chromatography–tandem mass spectrometry methods. A fit-for-purpose approach was implemented for method validation. Hydrophilic interaction chromatography was used to retain three hydrophilic analytes. The human leukocyte pellets were lysed and extracted in a methanol–water mixture and the leukocyte extract was used for LC–MS/MS analysis. The lower limits of quantitation for ManNAc, Neu5Ac and CMP-Neu5Ac were 25.0, 25.0 and 10.0 ng/ml, respectively. These validated methods were applied to a clinical study.     

Studies on the influence of esterase inhibitor to the pharmacokinetic profiles of oseltamivir and oseltamivir carboxylate in rats using an improved LC/MS/MS method

Oseltamivir (O), an ethyl ester prodrug of oseltamivir carboxylate (OC), is currently the drug of choice for avian influenza. Previous studies have found that the addition of esterase inhibitor can inhibit the metabolism of O to OC in plasma samples. The current study aims to evaluate the impact of dichlorvos on the rat plasma concentrations of O and OC and subsequent effect on their pharmacokinetics. The plasma samples of rats after oral administration of O were divided into two equal portions for treatment with/without dichlorvos. O and OC plasma concentrations were analyzed by a sensitive and specific LC/MS/MS method, using cephalexin as internal standard for both two analytes. The samples were extracted with an MCX cartridge and separated on a Nova‐Pak CN HP column eluted with a mobile phase of 0.15% formic acid in 50% methanol. The results showed that dichlorvos significantly inhibited further hydrolysis of O to OC during the period of rat plasma sample treatment. A significant difference in the pharmacokinetic parameters of O (except for T_max and t_1/2,λz) was found when the plasma samples were treated with dichlorvos. The use of dichlorvos is recommended in all rat studies which require plasma concentration determination of O and OC. Copyright © 2009 John Wiley & Sons, Ltd.