Identification of degradation products of indigoids by tandem mass spectrometry

The study concerns identification of photodegradation products of indigotin, indirubin and isoindigo. Experimental methodology consists of degradation of standard solutions of indigoids in a solar box and analysis of samples taken at different aging time by using capillary high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometric and spectrophotometric detectors. Identification of the formed compounds was based on careful interpretation of the electrospray ionization MS/MS spectra. Apart from the well‐known degradation products of indigoids: isatin, isatoic anhydride and anthranilic acid, another seven species were also identified, and their proposed structures were confirmed by high‐resolution molecular masses measurements; according to the best knowledge of authors, they have not been reported so far. The obtained results formed the basis for postulating mechanism of the process. Moreover, the MRM (Multiple Reaction Monitoring) method was developed for the identification of natural dyes and their degradation products in textiles of historical value. Apart from such colorants as indigotin and flavonoids, also presence of degradation products of indigoids was confirmed. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of leucine-enkephalin radical oxidation products by liquid chromatography tandem mass spectrometry

The oxidation of the peptide leucine-enkephalin (YGGFL) induced by the hydroxyl radical (HO*), formed under Fenton-like conditions [Cu (II)/H(2)O(2)], was studied and monitored by LC-MS. The oxidation products identified included products resultant from (a) the insertion of oxygen atoms (1-5), (b) peptide backbone cleavage (short-chain products formed by diamide pathway) and (c) radical-radical crosslinking reactions. In order to identify the modified residues, LC-MS/MS spectra were obtained. The insertion of oxygen atoms into the peptide originated hydroxide, di-hydroxide and/or hydroperoxide derivatives. In addition it was found that the aromatic amino acids are most susceptible to being hydroxylated, while the aliphatic amino acids are more prone to forming hydroperoxides. Oxidation products with double bonds were also identified. The short chain products resulted from the alpha-carbon radical of terminal amino acids (Tyr and Leu). Products resulting from cross-linking reactions between intact carbon-centered peptide radical (with and without one HO group) and a side chain radical (*C(7)H(7)O) were identified. It was found that, although all amino acids residues of the peptide undergo modifications, the N-terminal seems to be prone to oxidative modifications under these conditions.     

Internal standard strategies for relative and absolute quantitation of peptides in biological matrices by liquid chromatography tandem mass spectrometry

The development of LC-MS/MS instruments and related applications improved the large-scale analyses of proteins and peptides in complex biological mixtures. The historical factor limiting these types of studies was the lack of sensitivity and reproducibility. However, the capacity of these analyses to detect proteins and peptides was significantly enhanced to a point where they are routinely performed in specialized laboratories in support to drug development programs as well as prognostic and diagnostic investigations. The analytical strategy used in peptidomic analyses needs to minimize the fluctuation in data measurements that might mask or reduce the precision of the determinations and consequently reduce the sensitivity of the assay. Inherently, it outlines the importance of careful standardization to reduce technical and instrumental variation. Therefore, this review will focus on the strengths and the limitations of the different experimental approaches used for the integration of internal standards in peptidomic studies. This review will examine a wide variety of methods, reagents, instrumentations and data analysis tools available to design peptidomic experiments. Moreover, this review will focus on the importance of precision and accuracy in order to adequately establish analysis threshold to detect peptide expression differences.     

Identification of platelet activating factor by tandem mass spectrometry

Platelet activating factor, a phospholipid (1-O-alkyl-2-O-acetyl-sn-glycerophosphocholine), is a potent mediator of inflammation and acute hypersensitivity reactions. Chemical ionization mass spectra provide useful information for confirmation of structure. However at low levels the confirmation of structure in biological samples is difficult because the chemical noise level is too great. Collisionally activated decomposition daughter spectra of the protonated molecule and major fragment ions of authentic standards were recorded and are discussed. Selected tandem mass spectral scans provided the improvement in signal-to-noise to allow positive confirmation of structure at nanogram levels in partially purified extracts from a biological source, the epidermal cell secretions of the saltwater catfish Arius thalassinus.     

Identification of Barrenwort flavonoids by high-resolution tandem mass spectrometry

Fragmentation of the main Barrenwort flavonoids—icariin, icaritin, icarisides I and II, and epimedins A and B—is studied by tandem mass spectrometry. High-resolution mass spectra of positively charged ions of these compounds are obtained under the conditions of collision-induced dissociation. Characteristic fragment ions are determined, which ensured the classification of unknown compounds as Barrenwort flavonoids. Epimedin C was isolated from raw plant material by preparative liquid chromatography; its structure was confirmed by ¹H and ¹³C NMR spectra.     

Identification of the hydrolysis products of AlCl3.6H2O by electrospray ionization mass spectrometry

The hydrolysis reactions of AlCl3 in 0.1 M aqueous solutions at pH 3.27-4.20 were monitored by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) as a function of time. The cationic and anionic ESI mass spectra of aluminum(III) solutions gave strong evidence of the presence of a variety of monomeric and polymeric complexes. Competition between the OH- and Cl- ligands within the same aluminum core was observed. The influence of the sample cone voltage on the product distribution was also explored. The optimum sample cone voltage for the cationic spectra was 70 V. For the anionic spectra no optimum sample cone voltage was found and the appearance of the anionic spectra was strongly dependent on the sample cone voltage within the whole range explored.     

Identification of components in waste streams by electrospray and tandem mass spectrometry

Highly polar, non-gas-chromatographable compounds have few unambiguous analysis protocols for environmental applications. A recent environmental investigation, concerning the identification of a non-gas-chromatographable yellow component in chemical waste water and in effluents from a biological wastewater treatment plant required the use of a number of analytical approaches. Electrospray mass spectrometry, tandem mass spectrometry, high-performance liquid chromatography, nuclear magnetic resonance, and molecular spectroscopy of commercial and synthesized chlorodinitrophenol isomers were required in order to identify the specific isomer causing the color. The present report summarizes the electrospray ionization and tandem mass spectrometric studies that were used. The mass spectrometric study shows that two different isomers of chlorodinitrophenol exhibit very different collision-induced dissociation (CID) spectra. Differences in the tandem mass spectra can be attributed to the different structures of the anions formed from these two different isomers. Instrumentation that uses electrospray ionization and produces CID mass spectra and optical absorption spectra in a single analysis may be required in order to produce highly specific information on non-gas-chromatographable compounds found in the environment.     

Trace-level quantitation of iralukast in human plasma by microbore liquid chromatography/tandem mass spectrometry

Iralukast (CGP 45715A) is a potent peptido-leukotriene antagonist that is active in various in vitro and animal models for the treatment of asthma. An analytical challenge was to develop a sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method with a lower limit of quantitation (LLOQ) of 10 pg/mL for the analysis of iralukast when administered at low doses during clinical trials. Several issues had to be addressed in order to devise a LC/MS/MS assay for the above compound. First, iralukast appeared to be light sensitive and unstable at room temperature under acidic conditions. Second, a LLOQ of 10 pg/mL was needed to support several clinical trials. Third, positive electrospray ionization of iralukast did not yield the necessary sensitivity required for studies in humans. Consequently, LC/MS/MS conditions were optimized for the negative ion mode of detection. Fourth, sample preparation steps proved to be critical to reduce the possibility of microbore HPLC column (50 mm x 1.0 mm i.d.) obstruction, chromatographic deterioration, and matrix-mediated electrospray ion suppression. While our validated method addressed the above challenges, its major drawback was limited sample throughput capability. Nonetheless, plasma concentration-time profiles for patients with moderate asthma after oral administration of 200, 500, 1000, and 5000 microgram/kg/day of iralukast were successfully obtained.     

Rapid classification of enzymes in cleaning products by hydrolysis, mass spectrometry and linear discriminant analysis

A method for the rapid classification of proteases, lipases, amylases and cellulases used as enhancers in cleaning products, based on precipitation with acetone, hydrolysis with HCl, dilution of the hydrolysates with ethanol, and direct infusion into the electrospray ion source of an ion-trap mass spectrometer, has been developed. The abundances of the ([M+H]+ ions of the amino acids, from the hydrolysates of both the enzyme industrial concentrates and the detergent bases spiked with them, were used to construct linear discriminant analysis models, capable of distinguishing between the enzyme classes. For this purpose, the variables were normalized as follows: (A) the ion abundance of each amino acid was divided by the sum of the ion abundances of all the amino acids in the corresponding mass spectrum; (B) the ratios of pairs of ion abundances were obtained by dividing the ion abundance of each amino acid by each one of the ion abundances of the other 17 amino acids in the corresponding mass spectrum. Using normalization procedure B, excellent class-resolution between proteases, lipases, amylases and cellulases was achieved. In all cases, enzymes in industrial concentrates and manufactured cleaning products were correctly classified with >98% assignment probability.     

Identification and quality evaluation of different processed products of Aconitum carmichaelii by ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry and ultra-high-performance liquid chromatography-tandem mass spectrometry

Aconitum carmichaelii is widely used to treat chronic and intractable diseases due to its remarkable curative effect, but it is also a highly toxic herb with severe cardiac and neurotoxicity. It has been combined with honey for thousands of years to reduce toxicity and enhance efficacy, but there has been no study on the chemical constituent changes in the honey-processing so far. In this study, the chemical constituents of A. carmichaelii before and after honey-processing were characterized by ultra-high-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry. The results showed that a total of 118 compounds were identified, of which six compounds disappeared and five compounds were newly produced after honey-processing, and the cleavage pathway of main components was elucidated. At the same time, 25 compounds were found to have significant effects on different products, among which four compounds with the biggest difference were selected for quantitative analysis by ultra-high-performance liquid chromatography-tandem mass spectrometry. This study not only explained the chemical differences between the different products, but also helped to control the quality of the honey-processed products more effectively, and laid a foundation for further elucidating the mechanism of chemical constituent change during the honey-processing of A. carmichaelii.     

Identification and quantification of domoic acid by UHPLC/QTOF tandem mass spectrometry,with simultaneous identification of non-target photodegradation products

Amnesic shellfish poisoning is a potentially lethal human toxic syndrome which is caused by domoic acid (DA), a neurotoxin produced by marine phytoplankton, principally from Pseudonitzschia genus. In this report, a method to identify and quantify the DA toxin, with simultaneous identification of its photodegradation products, has been developed. It uses an ultra high performance liquid chromatography coupled to a quadrupole-time-of-flight tandem mass spectrometer (UHPLC–QTOF) after solid-phase extraction (SPE). An unambiguous identification of DA was carried out by considering both the retention time of DA in UHPLC and the exact mass of protonated DA molecule ([M + H]⁺ = 312.1447 m/z) and of the most intense fragment ion (m/z 266.1391). The quantification was conducted using protonated DA molecule with protonated Glafenin as internal standard, obtaining a limits of detection of 0.75 µg L^?1. Large screening with UHPLC–QTOF could also give structural information about degradation products of DA present in samples after UV-irradiation. This method was applied for the determination of DA in complex liquid samples after SPE and is applicable for environmental monitoring of this toxic substance in the aquatic environment.     

Characterization of novel hydrolysis products of carbapenems by electrospray ionization mass spectrometry

Carbapenems, including meropenem and imipenem, exhibit low stability against acid or base reagents. The fragmentation behavior of meropenem and its acid hydrolysis products was investigated by Fourier transform ion cyclotron resonance electrospray ionization tandem mass spectrometry and ion trap tandem multi‐stage mass spectrometry in both positive and negative ion mode. Only one neutral loss of CO₂ was observed from the precursor ion to the MS⁴ product ions for the acid hydrolysis product and this behavior did not correspond to that expected for the previously accepted 1‐pyrroline or 2‐pyrroline structure with two carbonyl acid units. The unknown product was then proposed to be 2‐(4‐(5‐(dimethylcarbamoyl)pyrrolidin‐3‐ylthio)‐5‐imino‐3‐methyl‐6‐oxotetrahydro‐2H‐pyran‐2‐yl)‐3‐hydroxybutanoic acid on the basis of the multi‐stage mass spectrometric and accurate mass data. A similar acid hydrolysis product of imipenem was also identified by mass spectrometry, confirming that these carbapenems had the same acid hydrolysis behavior. The proposed structures were further confirmed by NMR experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of by-products from an orthogonal peptide ligation by oxime bonds using mass spectrometry and tandem mass spectrometry

Synthetic proteins with unusual architecture are obtained through chemoselective ligation, a method based on the condensation of unprotected peptides under mild aqueous conditions. The last step of a new procedure leading to a tri-branched conjugate consists of the chemoselective ligation reaction between an (aminooxy)acetyl peptide and a peptide aldehyde resulting from a first ligation via an oxime bond. In order to optimize the reaction conditions, electrospray ionization mass spectrometry combined with liquid chromatography and tandem mass spectrometry has been used. In addition to the target tri-branched conjugate, two other conjugates were characterized allowing documentation of transoximation reactions in peptide chemistry. A fourth conjugate was identified as a side product appearing after the first ligation. Data obtained by low-energy collision-induced dissociation led to a rapid and reliable identification of impurities observed in the (aminooxy)acetyl peptide despite a previous high performance liquid chromatography (HPLC) purification. This highlights the great reactivity of the aminooxy group towards carbonyl-containing compounds.     

Identification of RP-HPLC peaks of bisphenol F and of bisphenol F diglycidyl ether and its hydrolysis products by thermospray mass spectrometry and gas chromatography/mass spectrometry

Summary The need to determine the migration of toxic unreacted compounds in bisphenol diglycidyl ether epoxy resins prompted us to investigate the HPLC properties of bisphenol F diglycidyl ether and its hydrolysis products in the water-based food simulants 3% (w/v) acetic acid, distilled water and 15% (v/v) ethanol. Peaks were identified by reversed-phase HPLC thermospray mass spectrometry and gas chromatography/mass spectrometry.     

Identification of dimethylarsinoyl-riboside derivatives in seaweed by pneumatically assisted electrospray tandem mass spectrometry

Pneumatically-assisted electrospray tandem mass spectrometry (ES MS/MS) was proposed as a technique for the identification of dimethylarsinoyl-riboside derivatives (arsenosugars) in seaweed (Laminaria). Conditions for the acquisition of MS and MS/MS spectra were optimized. A size-exclusion HPLC (SE HPLC) step was developed for the purification of algal extracts prior to ES MS. The arsenosugar fraction was found to elute prior to the majority of other arsenic compounds. The identity of the compounds expected to be arsenosugar compounds was confirmed by the collision induced dissociation (CID) of the relevant protonated molecule ions. An independent confirmation of the identity of analytes was obtained by two-dimensional (size-exclusion–anion exchange) HPLC–ICP MS with signal identification by spiking with the appropriate arsenosugar standards.     

Identification and fragmentation of hydrolyzed aluminum species by electrospray ionization tandem mass spectrometry

Earlier characterization of some hydrolysis products of AlCl₃·6H₂O was confirmed by electrospray ionization tandem mass spectrometry with increasing collision energy of projectile ions. At lower collision energies, the aqua ligands were stripped off. At higher energies, two hydroxo groups formed a bridging oxo group with loss of one water molecule. Aluminum complexes could also capture aqua ligands in the collision chamber so long as the parent ion did not fragment, and the fragment ion spectra broadened toward higher m/z values. The chloro ligands were eliminated as hydrochloric acid. The aluminum cores remained highly intact. Copyright © 2004 John Wiley & Sons, Ltd.     

Rapid determination of fumonisins in corn-based products by liquid chromatography/tandem mass spectrometry

A simple, fast, and robust method was developed for the determination of fumonisin B1 (FB1), fumonisin B2 (FB2), and fumonisin B3 (FB3) in corn-based human food and animal feed (cornmeal). The method involves a single extraction step followed by centrifugation and filtration before analysis by ultra-performance liquid chromatographylelectrospray ionization (UPLC/ESI)-MS/MS. The LC/MS/MS method developed here represents the fastest and simplest procedure (<30 min) among both conventional HPLC methods and other LC/MS methods using SPE cleanup. The potential for high throughput analysis makes the method particularly beneficial for regulatory agencies and analytical laboratories with a high sample volume. A single-laboratory validation was conducted by testing three different spiking levels (200, 500, and 1000 ng/g for FB1 and FB2; 100, 250, and 500 ng/g for FB3) for accuracy and precision. Recoveries of FB1 ranged from 93 to 98% with RSD values of 3-8%. Recoveries of FB2 ranged from 104 to 108%, with RSD values of 2-6%. Recoveries of FB3 ranged from 94 to 108%, with RSD values of 2-5%.     

Electrospray tandem mass spectrometry of mixed-sequence RNA/DNA oligonucleotides

The fragmentation of electrospray-generated multiply deprotonated RNA and mixed-sequence RNA/DNA pentanucleotides upon low-energy collision-induced dissociation (CID) in a hybrid quadrupole time-of-flight mass spectrometer was investigated. The goal of unambiguous sequence identification of mixed-sequence RNA/DNA oligonucleotides requires detailed understanding of the gas-phase dissociation of this class of compounds. The two major dissociation events, base loss and backbone fragmentation, are discussed and the unique fragmentation behavior of oligoribonucleotides is demonstrated. Backbone fragmentation of the all-RNA pentanucleotides is characterized by abundant c-ions and their complementary y-ions as the major sequence-defining fragment ion series. In contrast to the dissociation of oligodeoxyribonucleotides, where backbone fragmentation is initiated by the loss of a nucleobase which subsequently leads to the formation of the w- and [a-base]-ions, backbone dissociation of oligoribonucleotides is essentially decoupled from base loss. The different behavior of RNA and DNA oligonucleotides is related to the presence of the 2'-hydroxyl substituent, which is the only structural alteration between the DNA and RNA pentanucleotides studied. CID of mixed-sequence RNA/DNA pentanucleotides results in a combination of the nucleotide-typical backbone fragmentation products, with abundant w-fragment ions generated by cleavage of the phosphodiester backbone adjacent to the deoxy building blocks, whereas backbone cleavage adjacent to ribonucleotides induces the formation of c- and y-ions.     

Identification and assay of underivatized urinary acylcarnitines by paper spray tandem mass spectrometry

A new analytical approach, using paper spray tandem mass spectrometry, has been developed for assay of carnitine and acylcarnitines in urine. Paper spray (PS) is a very promising technique, especially in clinical investigations, because of its simplicity, low cost, and rapid sample preparation. A home-made paper spray device was used for assay of urinary acylcarnitines (C2–C18). The performance of solvents with different elution efficiency and paper substrates with different porosity grade and structure were tested by use of spiked synthetic urine. Tandem mass spectrometry in multiple reaction monitoring (MRM) mode was optimized to obtain better specificity and sensitivity. Analyte signals were evaluated for stability and reproducibility. Calibration with [²H₃]propionylcarnitine (C3-d3), [²H₃]octanoylcarnitine (C8-d3), and [²H₃] palmitoylcarnitine (C16-d3) as internal standards was used for quantification. Very good linearity was obtained, with correlation coefficients >0.99 for C0–C12 and C16 acylcarnitines and >0.96 for C14 and C18 acylcarnitines. Accuracy and precision (RSD, %) of the proposed procedure were tested at concentrations of 0.8, 8, and 20 mg L^?1 with very satisfactory results: overall mean accuracy was 98.9 % and overall mean relative standard deviation 1 %. Limits of detection (LOD) between 6 and 208 μg L^?1 for propionylcarnitine and tetradecanoylcarnitine, respectively, can be regarded as very satisfactory. Application of the method to real urine proved that paper spray tandem mass spectrometry is a simple, rapid, and direct tool (no derivatization is required) for assay of carnitine and C2–C12 acylcarnitines in urine.     

Determination of phthalates in milk and milk products by liquid chromatography/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric method using pneumatically assisted electrospray ionisation (LC/ESI-MS/MS) was developed for determination of dibutyl phthalate (DBP), benzyl butyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP), di-'isononyl' phthalate (DINP) and di-'isodecyl' phthalate (DIDP) in milk and milk products including infant formulas. The phthalates were extracted by a mixture of tert-butyl methyl ether and hexane from liquid samples. DBP, BBP and DEHP were removed from fats by liquid/liquid extraction into acetonitrile while DINP and DIDP were cleaned up on deactivated silica. The phthalates were detected in positive ion mode after separation on a reversed-phase C5 analytical column. Two transition products were monitored for each compound. The detection limits related to the transition products of lowest abundance were in the range 5-9 microg/kg.