GC‐MS of amaryllidaceous galanthamine‐type alkaloids

Galanthamine‐type alkaloids produced by plants of the Amaryllidaceae family are potent acetylcholinesterase inhibitors. One of them, galanthamine, has been marketed as a hydrobromide salt for the treatment of Alzheimer's disease. In the present work, gas chromatography with electron impact mass spectrometry (GC‐EIMS) fragmentation of 12 reference compounds isolated from various amaryllidaceous plants and identified by spectroscopic methods (1D and 2D nuclear magnetic resonance, circular dichroism, high‐resolution MS (HRMS) and EIMS) was studied by tandem mass spectrometry (GC‐MS/MS) and accurate mass measurements (GC‐HRMS). The studied compounds showed good peak shape and efficient GC separation with a GC‐MS fragmentation pattern similar to that obtained by direct insertion probe. With the exception of galanthamine‐N‐oxide and N‐formylnorgalanthamine, the galanthamine‐type compounds showed abundant [M]^+. and [M‐H]⁺ ions. A typical fragmentation pattern was also observed, depending on the substituents of the skeleton. Based on the fragmentation pathways of reference compounds, three other galanthamine‐type alkaloids, including 3‐O‐(2′‐butenoyl)sanguinine, which possesses a previously unelucidated structure, were identified in Leucojum aestivum ssp. pulchelum, a species endemic to the Balearic islands. GC‐MS can be successfully applied to Amaryllidaceae plant samples in the routine screening for potentially new or known bioactive molecules, chemotaxonomy, biodiversity and identification of impurities in pharmaceutical substances. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of LC‐MS and LC‐MS‐MS to the analysis of photo‐decomposed crystal violet in the investigation of cultural heritage materials aging

In this work, the accurate liquid chromatography‐ultraviolet‐visible (LC‐UV‐Vis), LC‐mass spectrometry (MS) and LC‐MS‐MS analysis of the photo‐degradation products of crystal violet (CV) is reported. CV is a light fugitive early synthetic dye which had a widespread diffusion into the market starting from the end of the XIX century and was used among others by V. Van Gogh and P. Gauguin in their writings, drawings or paintings. On‐line photodiode array detector enabled simultaneous UV‐Vis spectra acquisition. Many degradation compounds were identified through their exact mass (2 ppm accuracy) and MS‐MS technique. In particular, all CV demethylated products, demethylated Michler's ketone and particularly some compounds that most likely contain oxygen, such as N‐oxides, were found. Fragmentation products are all justified by the proposed fragmentation scheme, in term of precursor exact mass and isotopic profile, characteristic losses in fragmentation and rebuilt structure formula. In particular, we hypothesized the presence of N‐imido oxides and hydroxylamine derivates, never reported before, together with the demethylated derivatives of the studied dyes. All these compounds, although at trace level in our samples, contribute to the discoloration and fading of works of arts made with CV. In particular, demethylation of CV by UV light leads to formation of compounds absorbing at shorter wavelengths than CV (blue shift) or no‐absorbing in visible range (yellow‐colourless) with an overall effect that may appear reddish‐brown. This phenomenon justifies drawings appearing grey or brown on aged yellowed paper, when CV‐based inks or paints were used. The final aim was to better characterize the photo‐degradation of early synthetic dyes (in particular of CV) and to gain a better insight into the discoloration and fading of purple ink strokes made of CV. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐resolution MALDI‐TOF MS study on analysis of low‐molecular‐weight products from photo‐oxidation of poly(3‐hexylthiophene)

High‐resolution matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry (TOF MS) was used for the analysis of the low‐molecular‐weight products from the photo‐oxidation of poly(3‐hexylthiophene) (P3HT) in solution and thin film. Eight new peak series were observed in the low‐mass range of the mass spectra of the products degraded in solution, and the formulas of the eight components were determined from the accurate mass. From SEC/MALDI‐TOF MS, two components were identified as the degraded products, and the other six components were derived from the fragmentation of the degraded products during the MALDI process. A mechanism for the formation of these components was proposed on the basis of the results of MALDI‐TOF MS. For the thin film degradation, a part of products in the solution degradation were observed, which supports that the oxidation of P3HT in solution and thin film proceeded in the same mechanism. This study shows that high‐resolution MALDI‐TOF MS is effective for the analysis of the low‐molecular‐weight products from P3HT photo‐oxidation and expected to be feasible for the degradation analyses of other polymers. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of major degradation products of an adenosine A2A receptor antagonist under stressed conditions by LC‐MS and FT tandem MS analysis

Parkinson's disease (PD) is a very serious neurological disorder, and current methods of treatment fail to achieve long‐term control. SCH 420814 is a potent, selective and orally active adenosine A_2A receptor antagonist discovered by Schering‐Plough. Stability testing provides evidence of the quality of a bulk drug when exposed to the influence of environmental factors. Understanding the drug degradation profiles is critical to the safety and potency assessment of the drug candidate for clinical trials. As a result, identification of degradation products has taken an important role in drug development process. In this study, a rapid and sensitive method was developed for the structural determination of the degradation products of SCH 420814 formed under different forced conditions. The study utilizes a combination of liquid chromatography–tandem‐mass spectrometry (LC‐MS/MS) and Fourier Transform (FT) MS techniques to obtain complementary information for structure elucidation of the unknowns. This combination approach has significant impact on degradation product identification. A total of ten degradation products of SCH 420814 were characterized using the developed method. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of forced degradation products of pazopanib hydrochloride by UHPLC‐Q‐TOF/MS and in silico toxicity prediction

Pazopanib (PZ), an anti‐cancer drug, was subjected to forced degradation under hydrolytic (acid, base and neutral), oxidative, photolytic and thermal stress conditions as per International Conference on Harmonization guidelines. A selective stability indicating validated method was developed using a Waters Acquity UPLC HSS T3 (100 × 2.1 mm, 1.7 µm) column in gradient mode with ammonium acetate buffer (10 m m , pH 5.0) and acetonitrile. PZ was found to degrade only in photolytic conditions to produce six transformation products (TPs). All the TPs were identified and characterized by liquid chromatography/atmospheric pressure chemical ionization–quadrupole‐time of flight mass spectrometry experiments in combination with accurate mass measurements. Plausible mechanisms have been proposed for the formation of TPs. In silico toxicity was predicted using TOPKAT and DEREK softwares for all the TPs. The TP, N4‐(2,3‐dimethyl‐2H‐indazol‐6‐yl)‐N4‐methylpyrimidine‐2,4‐diamine, was found to be genotoxic, whereas all other TPs with sulfonamide moiety were hepatotoxic. The data reported here are expected to be of significance as this study foresees the formation of one potential genotoxic and five hepatotoxic degradation/transformation products. Copyright © 2015 John Wiley & Sons, Ltd.     

Metabolic profile of glyburide in human liver microsomes using LC‐DAD‐Q‐TRAP‐MS/MS

The sulfonylurea urea drug glyburide (glibenclamide) is widely used for the treatment of diabetes milletus and gestational diabetes. In previous studies monohydroxylated metabolites were identified and characterized for glyburide in different species, but the metabolite owing to the loss of cyclohexyl ring was identified only in mouse. Glyburide upon incubation with hepatic microsomes resulted in 10 metabolites for human. The current study identifies new metabolites of glyburide along with the hydroxylated metabolites that were reported earlier. The newly identified drug metabolites are dihydroxylated metabolites, a metabolite owing to the loss of cyclohexyl ring and one owing to hydroxylation with dehydrogenation. Among the 10 identified metabolites, there were six monohydroxylated metabolites, one dihydroxylated metabolite, two metabolites owing to hydroxylation and dehydrogenation, and one metabolite owing to the loss of cyclohexyl ring. New metabolites of glyburide were identified and characterized using liquid chromatography–diode array detector–quadruple‐ion trap–mass spectrometry/mass spectrometry (LC‐DAD‐Q‐TRAP‐MS/MS). An enhanced mass scan–enhanced product ion scan with information‐dependent acquisition mode in a Q‐TRAP‐MS/MS system was used to characterize the metabolites. Liquid chromatography with diode array detection was used as a complimentary technique to confirm and identify the metabolites. Metabolites formed in higher amounts were detected in both diode array detection and mass spectrometry detection. Copyright © 2012 John Wiley & Sons, Ltd.     

Development and validation of a stability‐indicating assay including the isolation and characterization of degradation products of metaxalone by LC‐MS

A stability‐indicating reverse‐phase high‐performance liquid chromatography–mass spectrometric method was developed and validated for the assay of metaxalone through forced degradation under acidic, alkaline, photo, oxidative and peroxide stress conditions. Separation of degradation products was accomplished on a reverse‐phase Phenomenex C₁₈ (250 × 4.6 mm, 5 µm) column thermostated at 25°C using 10 mM aqueous ammonium acetate: methanol (35:65 v/v) as mobile phase in an isocratic mode of elution. The eluents were detected at 275 nm by photo diode array detector and mass detectors connected in series. Two unknown base hydrolysis products of metaxalone were identified and characterized as (a) methyl 3‐(3,5‐dimethylphenoxy)‐2‐hydroxypropylcarbamate and (b) 1‐(3,5‐dimethylphenoxy)‐3‐aminopropan‐2‐ol by MS, ¹H NMR and FTIR spectroscopy. The method was validated as per International Conference on Harmonization guidelines and metaxalone was selectively determined in presence of its degradation impurities, demonstrating its stability‐indicating nature. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis and Identification of the Chemical Constituents of Ding‐Zhi‐Xiao‐Wan Prescription by HPLC‐IT‐MSn and HPLC‐Q‐TOF‐MS

Ding‐Zhi‐Xiao‐Wan (DZXW) is a famous traditional Chinese medicine (TCM) formula, which is composed of four herbs, Ginseng Radix, Poria, Polygala Radix and Acori Tatarinowii Rhizoma. It has been popularly used for the treatment of emotional disease, like Alzheimer's disease, Parkinson's disease, depression, anxiety, forgetfulness and neurasthenia. In this research, a high‐performance liquid chromatography coupled with ion‐trap tandem mass spectrometry (HPLC‐IT‐MSⁿ) method along with a high‐performance liquid chromatography coupled with quadrupole time‐of‐flight mass spectrometry (HPLC‐Q‐TOF‐MS) method in negative ion mode was established to investigate the major constitutions in DZXW. The extracts were prepared by ultra‐sonication in ethyl acetate, n‐butanol, 95% ethanol and deionized water sequentially as well as in deionized water directly. A Kromasil C18 column was used to separate the extracts of DZXW. Acetonitrile and 0.1% aqueous formic acid (V/V) were used as the mobile phase. A total of 64 components were characterized, including 16 triterpenoids, 14 Polygala saponins, 10 oligosaccharide esters, 6 sucrose esters, 2 xanthone C‐glycosides and 16 ginsenosides.     

新型除草剂及其杂质的LC-MS和GC-MS分析

High performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) have been utilized to analyze the synthesized 2-(2-arylaminomethylphenoxy)pyrimidine derivatives, which are a new kind of environmentally benign herbicides and have passed the temporary pesticide registration. The identification of main product and impurities has been achieved according to the UV and mass spectra. Moreover, one impurity, introduced by the raw material in the last step of the synthetic route, was identified by GC-MS analysis. It can be concluded that the combination of chromatography and mass spectrometry, including LC-MS and GC-MS, provided a vital tool of the pesticide science.     

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.     

Studies on the metabolism of the Δ9‐tetrahydrocannabinol precursor Δ9‐tetrahydrocannabinolic acid A (Δ9‐THCA‐A) in rat using LC‐MS/MS,LC‐QTOF MS and GC‐MS techniques

In Cannabis sativa, Δ9‐Tetrahydrocannabinolic acid‐A (Δ9‐THCA‐A) is the non‐psychoactive precursor of Δ9‐tetrahydrocannabinol (Δ9‐THC). In fresh plant material, about 90% of the total Δ9‐THC is available as Δ9‐THCA‐A. When heated (smoked or baked), Δ9‐THCA‐A is only partially converted to Δ9‐THC and therefore, Δ9‐THCA‐A can be detected in serum and urine of cannabis consumers. The aim of the presented study was to identify the metabolites of Δ9‐THCA‐A and to examine particularly whether oral intake of Δ9‐THCA‐A leads to in vivo formation of Δ9‐THC in a rat model. After oral application of pure Δ9‐THCA‐A to rats (15 mg/kg body mass), urine samples were collected and metabolites were isolated and identified by liquid chromatography‐mass spectrometry (LC‐MS), liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) and high resolution LC‐MS using time of flight‐mass spectrometry (TOF‐MS) for accurate mass measurement. For detection of Δ9‐THC and its metabolites, urine extracts were analyzed by gas chromatography‐mass spectrometry (GC‐MS). The identified metabolites show that Δ9‐THCA‐A undergoes a hydroxylation in position 11 to 11‐hydroxy‐Δ9‐tetrahydrocannabinolic acid‐A (11‐OH‐Δ9‐THCA‐A), which is further oxidized via the intermediate aldehyde 11‐oxo‐Δ9‐THCA‐A to 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinolic acid‐A (Δ9‐THCA‐A‐COOH). Glucuronides of the parent compound and both main metabolites were identified in the rat urine as well. Furthermore, Δ9‐THCA‐A undergoes hydroxylation in position 8 to 8‐alpha‐ and 8‐beta‐hydroxy‐Δ9‐tetrahydrocannabinolic acid‐A, respectively, (8α‐Hydroxy‐Δ9‐THCA‐A and 8β‐Hydroxy‐Δ9‐THCA‐A, respectively) followed by dehydration. Both monohydroxylated metabolites were further oxidized to their bishydroxylated forms. Several glucuronidation conjugates of these metabolites were identified. In vivo conversion of Δ9‐THCA‐A to Δ9‐THC was not observed. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification and characterization of stress degradation products of sumatriptan succinate by using LC/Q‐TOF‐ESI‐MS/MS and NMR: Toxicity evaluation of degradation products

Sumatriptan succinate, a selective 5‐HT1B receptor agonist, was subjected to forced degradation studies as per to International Conference on Harmonization‐specified conditions. The drug exclusively showed its degradation under basic, photolytic, and oxidative stress conditions, whereas it was found to be stable under acidic, thermal, and neutral conditions. Eight (DP‐1 to DP‐8) degradation products were identified and characterized by UPLC‐ESI/MS/MS experiments combined with accurate mass measurements. The effective chromatographic separation was achieved on Hibar Purospher STAR, C18 (250 × 4.6 mm, 5 μm) column using mobile phase consisting of 0.1% formic acid and methanol at a flow rate of 0.6 mL/minute in gradient elution method. It is noteworthy that 2 major degradation products DP‐3 and DP‐7 were isolated using preparative HPLC and characterized by advanced NMR experiments. The degradation pathway of the sumatriptan was established, which was duly justified by mechanistic explanation. In vitro cytotoxicity of isolated DPs was tested on normal human cells such as HEK 293 (embryonic kidney cells) and RWPE‐1 (normal prostate epithelial cells). This study revealed that they were nontoxic up to 100 μm concentration. Further, in silico toxicity of the drug and its degradation products was determined using ProTox‐II prediction tool. This study revealed that DP‐4 and DP‐8 are predicted for immune toxicity. Amine oxidase A and prostaglandin G/H synthase 1 are predicted as toxicity targets for DP‐3, DP‐4, and DP‐6 whereas DP‐1 and DP‐2 are predicted for amine oxidase A target.     

Analysis of hydroxyl radical‐induced oxidation process of glucagon by reversed‐phase HPLC and ESI‐MS/MS

Structural modification of a polypeptide hormone, glucagon, by a hydroxyl radical in vitro was investigated by reversed‐phase high‐performance liquid chromatography (RP‐HPLC), and the oxidized site of glucagon was detected by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). It was shown that ²⁷methionine (Met) was oxidized to ²⁷Met sulfoxide by hydroxyl radical, and the production rate of ²⁷Met sulfoxide was faster than that by hydrogen peroxide. In addition, production of ²⁷Met sulfoxide enantiomer was confirmed by RP‐HPLC analysis. cAMP production in a HepG2 cell induced by ²⁷Met sulfoxide glucagon was reduced to approximately 75% as compared with that induced by the native form of glucagon. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of autoxidation oligomers of flavan‐3‐ols in model solutions by HPLC‐MS/MS

Autoxidation of flavan‐3‐ols was carried out in aqueous/methanol model solutions under mildly acidic conditions (pH 6.0), and these autoxidation products were analyzed by using high performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS). The results showed that (+)‐catechins and (?)‐epicatechins generated autoxidation reaction with each other to form a series of oligomers that had the same [M ? H]^? molecular ions (MS¹) as those of natural procyanidins, but had completely different fragment ions (MS²). According to MS/MS analysis, the major fragments of these oligomers were derived not only from the retro‐Diels–Alder (RDA) dissociations on the C‐rings of the flavan‐3‐ol units, but also from the quinone‐methide (QM) cleavage of the interflavan linkages (IFL), and thus they were identified as B‐type dehydrodicatechins, B‐type dehydrotricatechins and A‐type dehydrotricatechins, respectively. The potential structures of their [M ? H]^? molecular ions and partial fragment ions were deduced on the basis of the MS/MS characterization and the oxidation of flavan‐3‐ols in previous reports. Some specific fragment ions were found to be very useful for identifying the autoxidation oligomers (the B‐type dehydrodicatechins at m/z 393, the B‐type dehydrotricatechins at m/z 681 and the A‐type dehydrotricatechins at m/z 725). Copyright © 2008 John Wiley & Sons, Ltd.     

2,5‐Dihydroxybenzoic acid solution in MALDI‐MS: ageing and use for mass calibration

2,5‐Dihydroxybenzoic acid (DHB) is one of the most widely used and studied matrix compounds in matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry. However, the influence of ageing of the DHB solution on the MALDI mass spectra has not been yet systematically studied. In this work, the possible changes occurring in the acidified acetonitrile/water solution of the MALDI matrix compound DHB during 1‐year usage period have been monitored with MALDI‐Fourier transform ion cyclotron resonance mass spectrometer (MALDI‐FT‐ICR‐MS) and attenuated total reflectance Fourier transform infrared (ATR‐FT‐IR) spectroscopy. No significant ageing products have been detected. The ability of the aged DHB solution to act as a MALDI matrix was tested with two materials widely used in art and conservation – bone glue (a proteinaceous material) and shellac resin (a resinous material) – and good results were obtained. A number of peaks in the mass spectra measured from the DHB solution were identified, which can be used for internal calibration of the mass axis. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantification issues of trace metals analysis on silicon oxide and nitride films by using VPD‐ICP‐MS and VPD‐GF‐AAS

Vapor phase decomposition (VPD) is a pretreatment technique for collecting trace metal contaminants on the surface of a Si wafer. Such trace metals can be identified and quantified by inductively coupled plasma mass spectrometry (ICP‐MS) or graphite furnace atomic absorption spectroscopy (GF‐AAS). However, the analytical results can be influenced by the Si‐matrix in the VPD samples. This article discusses the approaches to eliminate the interference caused by Si‐matrix. When the thickness of oxide film on wafer surface is less than 100 Å, the quantification results of ICP‐MS analysis will not be affected by Si‐matrix in the VPD samples. Except this, the Si‐matrix must be removed before analysis. An improved heating pretreatment approach has been adopted successfully to eliminate the Si‐matrix. For GF‐AAS analysis, the Si‐matrix will influence the sodium and aluminum analyses. Adding HNO₃ to the graphite furnace tubing after sample injection could also eliminate the interference caused by the Si‐matrix. The method detection limits (MDLs) of VPD‐GF‐AAS and VPD‐ICP‐MS range from 0.04 to 0.55 × 10¹⁰ atoms cm^?2 and 0.05 to 1.73 × 10⁹ atoms cm^?2, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Simultaneous determination of six C21 steroids of Xiao‐Ai‐Ping injection in rat plasma by LC‐MS/MS

Xiao‐Ai‐Ping injection (XAPI) is a traditional Chinese medicine that has been widely used to treat cancer. Modern pharmacological studies have demonstrated that C₂₁ steroids are the main active compounds in XAPI. In this study, a sensitive and specific liquid chromatography tandem mass spectrometry (LC‐MS/MS) method was developed and validated the first time for simultanenous determination of three isomeric pregnane genins (17β‐tenacigenin B, tenacigenin B and tenacigenin A) and their corresponding glycosides (tenacigenoside A, tenacissoside F and marsdenoside I) from XAPI in rat plasma. A simple liquid–liquid extraction technique was used after the addition of dexamethasone acetate as internal standard. The chromatography separation of analytes was achieved on an Agilent Zorbax Eclipse XDB‐C₁₈ column (3.5 µm, 150 × 3 mm i.d.) using methanol–water as mobile phase in a gradient elution program. Detection was performed in multiple reaction monitoring mode using electrospray ionization in the negative ion mode. The method showed satisfactory linearity over a concentration range 5.00–2000.00 ng/mL for tenacigenin B, tenacigenin A, marsdenoside I and tenacissoside F (r² > 0.99), 10.00–4000.00 ng/mL for 17β‐tenacigenin B and tenacigenoside A (r² > 0.99). Intra‐ and inter‐day precisions (valued as relative standard deviation) were <9.00% and accuracies (as relative error) in the range ?6.31 to 7.23%. Finally, this validated method was successfully applied to the pharmacokinetic study of XAPI after intravenous administration to rats. Copyright © 2013 John Wiley & Sons, Ltd.     

DMSO as a mobile phase additive enhances detection of ubiquitination sites by nano‐LC‐ESI‐MS/MS

Large‐scale detection of ubiquitination sites in whole cell proteomes using nano–liquid chromatography coupled to tandem mass spectrometry is a well‐established technique that has deepened the understanding of protein degradation processes in eukaryotic cells. Ubiquitination sites are usually identified by detection of Lys‐ɛ‐Gly‐Gly (K‐ɛ‐GG)‐remnant peptides, which are generated by tryptic digestion of proteomes. We show in this application note that dimethyl sulfoxide addition to the liquid chromatography mobile phase enhances identification rates of K‐ɛ‐GG peptides by more than 100% due to an increase of peptide signal intensities. The gain in the number of ubiquitination site identifications exceeds by far the gain that has been published for other posttranslational modifications, namely, phosphorylation and acetylation.     

Fragmentation pathways of metopimazine and its metabolite using ESI‐MSn,HR‐MS and H/D exchange

Metopimazine (MPZ) is a phenothiazine derivative used to prevent emesis during chemotherapy where few structural analysis of the aforementioned compound have been described in the literature. Thus, this work reports, for the first time, the detailed study of fragmentation pathways of MPZ and its metabolite (AMPZ) using electrospray ionization (EI) with multistage mass spectrometry (ESI‐MSⁿ) in positive‐ion mode. The structures of 21 product ions were identified and their accurate masses were determined using high resolution mass spectrometry (HRMS) experiments. Characteristic product ions of these two phenothiazine derivatives are more particularly displayed along with differences between their relative abundances and their structures checked by H/D exchange experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

On‐line 2D‐LC‐ESI/MS/MS determination of rifaximin in rat serum

A highly sensitive and selective on‐line two‐dimensional reversed‐phase liquid chromatography/electrospray ionization–tandem mass spectrometry (2D‐LC‐ESI/MS/MS) method was developed and validated to determine rifaximin in rat serum by direct injection. The 2D‐LC‐ESI/MS/MS system consisted of a restricted access media column for trapping proteins as the first dimension and a Waters C₁₈ column as second dimension using 0.1% aqueous acetic acid:acetonitrile as mobile phase in a gradient elution mode. Rifampacin was used as an internal standard. The linear dynamic range was 0.5–10 ng/mL (r² > 0.998). Acceptable precision and accuracy were obtained over the calibration range. The assay was successfully used in analysis of rat serum to support pharmacokinetic studies. Copyright © 2009 John Wiley & Sons, Ltd.