Letter: characterisation and identification of spermine and spermidine derivatives in Microdesmis keayana and Microdesmis puberula roots by electrospray ionisation tandem mass spectrometry and high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

Three new N(1),N(5),N(14)-tris(4- hydroxycinnamoyl)spermines were identified in hydromethanolic root extracts of Microdesmis keayana J. Léonard and Microdesmis puberula Hook f. The electrospray ionisation tandem mass spectrometry (ESI-MS/MS) technique with specific nuclear magnetic resonance analysis of hydrolysed products made it possible to identify N(1),N(5),N(14)-tris(p-coumaroyl)spermine, N(1)-feruloyl,N(5),N(14)-di(p-coumaroyl)spermine and N(1),N(5),N(14)-tris(feruloyl)spermine, named keayanines B, C and D, respectively. ESI-MS/MS analysis most effectively provided structural data although high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry was also used to characterise four other compounds from Microdesmis puberula-keayanidines A, B, C and keayanine A-which had already been identified in M. keayana. This chemical data is the first to be published for M. puberula which is a commonly used plant in Central African traditional medicine.     

A derivatisation and liquid chromatography/electrospray ionisation multistage mass spectrometry method for the characterisation of naphthenic acids

Naphthenic acids (NAs) are partially uncharacterised complex mixtures of carboxylic acids, resulting from the microbial oxidation of petroleum hydrocarbons. They are associated with the fouling of pipelines and process equipment in oil production and with corrosion in oil refineries. As by-products of the rapidly expanding oil (tar) sands industries, NAs are also pollutants and have proved to be toxic to a range of organisms. They also have important beneficial uses as fungicides, tyre additives and, paradoxically, also in the manufacture of corrosion inhibitors. These features make the characterisation of NAs an important goal for analytical chemists. Here we describe the synthesis of amide derivatives of NAs for characterisation by liquid chromatography/electrospray ionisation multistage mass spectrometry (LC/ESI-MS(n)). The method was applied to commercially available carboxylic acids, novel synthetic NAs, commercial NAs refined from crude oils, crude oil NAs and Athabasca oil sands NAs. In addition to confirming the number of alicyclic rings and length of alkyl side chain substituents (confirming information from existing methods), the MS(n) results provided further structural information. Most important of these was the finding that bi- to polycyclic acids containing ethanoate side chains, in addition to alkyl substituents, were widespread amongst the oil and oil sands NAs. The latter NAs are known end members of the beta-oxidation of NAs with even carbon number alkanoate chains. Since such NA mixtures are toxic, they should be targets for bioremediation. Bioremediation of NAs can also be monitored better by application of the methods described herein.     

The characterisation of selected antidepressant drugs using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their determination by high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

The electrospray ionisation ion trap tandem mass spectrometry (ESI-MS(n)) of selected antidepressant drugs, i.e., citalopram, fluoxetine, mirtazapine, paroxetine, sertraline, and venlafaxine, has been investigated. Sequential product ion fragmentation experiments (MS(n)) have been performed in order to elucidate the degradation pathways for the [M+H](+) ions and their predominant product ions. These MS(n) experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as molecules such as H(2)O, amines and phenols. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with mirtazapine, fragmentation initially occurs at the latter ring with the former being predictably resistant to fragmentation. Also, when an amine-containing drug molecule such as fluoxetine also contains a functional group, which liberates a phenol with a significantly lower DeltaH(f) (0) value than that of the corresponding amine, the phenol is preferentially liberated. The structures of product ions proposed for ESI-MS(n) can be supported by electrospray ionisation quadrupole-time-of-flight tandem mass spectrometry (ESI-QToF-MS/MS). These molecules can be identified and determined in mixtures at low ng/mL concentrations by the application of high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry (HPLC/ESI-MS(2)), which can also be used for their analysis in hair samples.     

A novel approach for identification and measurement of hemoglobin adducts with 1,2,3,4-diepoxybutane by liquid chromatography/electrospray ionisation mass spectrometry and matrix-assisted laser desorption/ionisation tandem mass spectrometry

The structural characterisation of the adducts formed by in vitro interaction of hemoglobin (Hb) with 1,2,3,4-diepoxybutane (DEB), the most reactive 1,3-butadiene (BD) metabolite, was obtained by liquid chromatography/electrospray ionisation mass spectrometry (LC/ES-MS) analysis of modified tryptic peptides of human hemoglobin chains. The reactive sites of human hemoglobin towards DEB and its hydroxylated derivatives (trihydroxybutyl (THB)-derivatives) were identified through the characterisation of alkylated tryptic peptides by matrix-assisted laser desorption/ionisation tandem mass spectrometry (MALDI-MS/MS). Based on this characterisation, a procedure was set up to measure the Hb-adducts of THB-derivatives by isotope dilution mass spectrometry with the use of a deuterated peptide standard. The results obtained here could permit optimisation of molecular dosimetry of BD-adducts, and extension of the analysis to the biological monitoring of occupational exposure to butadiene.     

Photocatalytic degradation of the herbicide isoproturon: characterisation of by-products by liquid chromatography with electrospray ionisation tandem mass spectrometry

By-products arising from immobilised TiO2-catalysed photodegradation of the herbicide isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] in aqueous solution under solar radiation were analysed by reversed-phase liquid chromatography combined with electrospray ionisation ion trap mass spectrometry. Structural information on by-products, formed at different degradation times, was then obtained from interpretation of the relevant MS/MS spectra. Several species were identified through this approach, and in many cases several isomers were found. As expected, most by-products resulted from single or multiple hydroxylation (by photo-generated OH* radicals) of the isoproturon molecule at different positions. However, substitution of some functional groups of the herbicide (isopropyl or methyl) by OH* was also observed. A possible degradation scheme is hypothesised.     

A new method for the analysis of styrene mercapturic acids by liquid chromatography/electrospray tandem mass spectrometry

A new method based on liquid chromatography/tandem mass spectrometry has been developed for the direct determination of specific urinary mercapturic acids arising from the conjugation of (R)-and (S)-enantiomers of styrene 7,8-oxide with glutathione (GSH), i.e. (R,R)- and (S,R)-N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (R,R-M1 and S,R-M1) and (R,R)- and (S,R)-N-acetyl-S-(2-phenyl-2-hydroxyethyl)-cysteine (R,R-M2 and S,R-M2). The four diastereoisomers were separated on a C18-DB (7.5 cm, 3 microm) column using variable proportions of 20 mM aqueous ammonium formate buffer and methanol at a flow-rate of 0.5 mL/min. The analytes were ionized by electrospray, in negative-ion mode. Operating in selected-reaction monitoring mode, linearity of the MS response versus analyte concentration was established over 4 orders of magnitude, the detection limits being 0.7-1.0 microg/L for all the mercapturates. Precision of the method determined at 50 microg/L (n = 12), expressed as relative standard deviation, was respectively 3.1, 4.8 and 6.9% within the run, intra-day and inter-day. The corresponding figures at 1.0 mg/L (n = 12) were respectively 2.0, 3.6 and 5.5%. The method was applied to the quantitative analysis of conjugated metabolites in urine samples from workers occupationally exposed to styrene. The diastereoisomers R,R-M1 and S,R-M2 accounted respectively for 50 and 40% of total mercapturates, whereas the proportion of R,R-M2 was 7% and only minor amounts of S,R-M1 were detectable. Styrene mercapturates represented a minor fraction of total styrene metabolites, less than 1% on average. The ratio mercapturates/main metabolites (mandelic + phenylglyoxylic acid) showed a bimodal distribution, the medians of the two subgroups being 0.2 and 1%, respectively. Such subgroups are probably characterized by the genetic polymorphisms of the drug-metabolizing enzymes to be identified.     

Acrylamide determination in atmospheric particulate matter by high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

A method has been developed for the determination of acrylamide at the picogram per cubic metre level in particulate-phase outdoor aerosol using high-performance liquid chromatography with triple quadrupole tandem mass spectrometric detection. Acrylamide was identified by positive ion electrospray mass spectrometry using m/z 72.00/54.90 as monitoring ion transition. The limit of detection, defined as three times the standard deviation of the procedural blanks, was 0.4?pg?m^?3 (173?pg absolute amount injected); the repeatability was 8% (evaluated as the relative standard deviation of five consecutive measurements on cleaned quartz fibre filters of acrylamide standard spikes) and the recovery was 52?±?4%. The accuracy of the method (evaluated as relative error) has been estimated to be ?2%. This methodology was used to determine acrylamide concentrations in particulate-phase outdoor aerosol in the Venice Lagoon with concentrations ranging between 0.4 and 12.9?pg?m^?3 with an average value of 3.1?pg?m^?3.     

An electrospray ionisation tandem mass spectrometric investigation of selected psychoactive pharmaceuticals and its application in drug and metabolite profiling by liquid chromatography/electrospray ionisation tandem mass spectrometry

A tandem mass spectrometric investigation of the collision-induced dissociation of five commonly prescribed psychoactive pharmaceuticals, risperidone, sertraline, paroxetine, trimipramine, and mirtazapine, and their metabolites has been carried out. Quadrupole ion trap mass spectrometry was employed to generate tandem mass spectrometric (MS/MS) data of the compounds under investigation and structural assignments of product ions were supported by quadrupole time-of-flight mass spectrometry. These fragmentation studies were then utilised in the development of a liquid chromatographic method to identify the drugs and their metabolites in human hair and saliva samples, thus providing relevant profiling information.     

Rapid identification of saponins in plant extracts by electrospray ionization multi-stage tandem mass spectrometry and liquid chromatography/tandem mass spectrometry

Electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)) and liquid chromatography coupled with on-line mass spectrometry (LC/MS/MS) were applied to characterize saponins in crude extracts from Panax ginseng. The MS(n) data of the [M - H](-) ions of saponins can provide structural information on the sugar sequences of the saccharide chains and on the sapogins of saponins. By ESI-MS(n), non-isomeric saponins and isomeric saponins with different aglycones can be determined rapidly in plant extracts. LC/MS/MS is a good complementary analytical tool for determination of isomeric saponins. These approaches constitute powerful analytical tools for rapid screening and structural assignment of saponins in plant extracts.     

The characterisation of coumarins from selected structural classes by electrospray ionisation quadrupole time-of-flight tandem mass spectrometry

Electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) has been used for characterisation of a selection of naturally occurring and synthetic coumarins from different structural classes. The product ions, suggested in earlier studies by electrospray ionisation ion trap mass spectrometry (ESI-MS(n)), are unequivocally established for the representative coumarins by virtue of accurate mass measurement. Synthetic coumarins that are unsubstituted in the heterocyclic ring give rise to a major product ion by loss of CO(2), whereas those substituted in the heterocyclic ring generally undergo alternative fragmentation releasing neutral species such as ketene or methyl ketene. Naturally occurring coumarins, unsubstituted in the heterocyclic ring and substituted in the benzene ring with chains or rings of hydrocarbons and oxygen, principally fragment at the side chain releasing unsaturated hydrocarbons. The ESI-QTOF-MS/MS behaviour of some naturally occurring and synthetic quinolines which are structurally similar or fragment similarly are included where appropriate.     

Quantitative analysis of surfactant deposits on human skin by liquid chromatography/electrospray ionisation tandem mass spectrometry

Surfactants are commonly used as cleansing agents and yet there are concerns that they may also have a role in skin irritation. The lack of suitable methods for the quantitative and qualitative analysis of surfactant deposition on skin has hindered the in‐depth investigation of such effects. Here, we report the application of reversed‐phase liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI‐MS/MS) assays for two surfactants commonly used in consumer products, namely sodium lauryl ether sulfate (SLES) and laurylamidopropyl betaine (LAPB), to a baseline study aiming to assess deposition levels on human skin. The linearity of the assays was established at 3–20 ng, with coefficient of variation below 5%. The detection limits were 100 pg for LAPB and 1 ng for SLES; quantitation limits were 500 pg for LAPB and 2.5 ng for SLES. The baseline study was conducted using a panel of 40 healthy volunteers. Skin extract samples were taken in triplicate from forearms, using ethanol. SLES was detected on most volunteers, with 75% of them having SLES deposits in the range of 100–600 ng/cm². LAPB was detected on the skin of all volunteers with 85% of them having deposit levels within the concentration range of 1–100 ng/cm². These results demonstrate the extent to which commonly used surfactants remain on the skin during the day. The analytical methods reported here can be applied to the investigation of surfactants in relation to general skin condition and to the development and optimisation of new consumer wash products. Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous determination of alkylphenol ethoxylates and their biotransformation products by liquid chromatography/electrospray ionisation tandem mass spectrometry

Reversed-phase LC-MS/MS is used to determine major estrogenic alkylphenol ethoxylates (APEOs) and their biotransformation products. It allows the simultaneous analysis of eight APEOs, alkylphenoxy carboxylates (APECs) and alkylphenols (APs) in sewage treatment plant (STP) effluents in the same extract after solid-phase enrichment on polymeric Oasis HLB. As precursor ions, [APEO + NH4]+, [APEC - H]- and [AP - H]- were monitored. Instrumental limits of detection (LOD) were 2-600 pg, corresponding to sample concentrations of 0.04-12 ng l(-1), without correction for overall method recoveries. Matrix-induced signal suppression during electrospray ionisation (ESI) and extraction as well as overall method recoveries were assessed and the suitability of deuterated surrogates as internal standards was evaluated.     

Simultaneous determination of parabens,triclosan and triclocarban in water by liquid chromatography/electrospray ionisation tandem mass spectrometry

A method for the determination of several household biocides in water by liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI‐MS/MS) is presented. It permits the simultaneous determination of triclosan (TCS), triclocarban (TCC) and seven parabens, including the distinction between branched and linear isomers of propyl (i‐PrP and n‐PrP) and butyl parabens (i‐BuP and n‐BuP). Prior to LC/MS/MS, analytes are preconcentrated by solid‐phase extraction (SPE) on Oasis HLB (60 mg) cartridges at natural sample pH and subsequently eluted with 4 mL of methanol. This simple SPE procedure provides extraction recoveries above 85% except for raw wastewater, where it falls to 65% for TCC. The performance of the method was tested with two triple‐quadrupole LC/MS instruments from a low/mid and mid/high market range: a Varian 1200L and an API‐4000. The latter system provided between 3 and 80 times lower limits of quantification (LOQs) than the first one, in the 0.08–0.44 ng/L range for surface water. Moreover, a comparison of matrix effects on both instruments showed a very different behaviour, particularly in the case of parabens. For these compounds signal suppression was observed in the 1200L instrument and signal enhancement with the 4000 instrument. As a result, different calibration approaches were chosen for them and this pointed to the need of matrix effect re‐evaluation in method transfer between different LC/MS systems. The application of the method to real samples showed the ubiquity of methyl paraben (MeP) and n‐PrP (at the 1–6 µg/L in raw wastewater) and the coexistence of i‐BuP and n‐BuP at similar levels (ca. 100–200 ng/L in raw wastewater). Copyright © 2009 John Wiley & Sons, Ltd.     

Rapid characterisation and identification of compounds in Saposhnikoviae Radix by high-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight mass spectrometry

Saposhnikoviae Radix (SR), the dried root of Saposhnikovia divaricata (Turcz.) Schischk. (Umbelliferae), is commonly used as a traditional Chinese medicine. In this study, a rapid and accurate method was firstly, developed for the qualitative analysis of SR by high-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight mass spectrometry (HPLC-ESI-Q-TOF-MS/MS). A total of 45 compounds were identified or tentatively characterised, including 13 chromones, 28 coumarins and four others. Among them, 16 compounds were identified from SR for the first time. In addition, six chromones reference standards, including two isolated compounds of 3′-O-angeloylhamaudol and norcimifugin from the extraction of SR, were used to study the fragmentation pathways of chromones. The developed method was effective for characterising the compounds of SR, and the results of the study enriched the understanding of the chemical connotation.     

Quantitative determination of ochratoxin A by liquid chromatography/electrospray tandem mass spectrometry

Mass spectrometry of ochratoxin A (OTA) and B (OTB) under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) was studied. ESI offers higher sensitivities and less fragmentation than APCI. A sensitive LC/MS/MS method for the determination of ochratoxin A (OTA) in human plasma samples was developed. The absolute minimum detection limit was around 10-20 pg per injection, corresponding to 0.5 ppb in an injection equivalent to 20-40microg of human plasma. Ochratoxin B (OTB) was used as an internal standard and its absence in real-life samples was carefully checked before samples were spiked with the internal standard. It was found that these two ochratoxins are susceptible to sodium adduct formation. Fragment ions from the [M + H](+) and [M + Na](+) ions of both OTA and OTB were monitored in the multiple reaction monitoring mode. Three quantitative approaches, standard addition method, internal standard method (using ochratoxin B as an internal standard) and external standard method, were compared in the analysis of human blood plasma. Results from the mass spectrometric method were comparable to those from a conventional LC/fluorescence method. The LC/MS/MS method was also applied to the analysis of contaminated coffee samples.     

Detection and identification of sulphonamide drugs in municipal waste water by liquid chromatography coupled with electrospray ionisation tandem mass spectrometry.

High-performance liquid chromatography coupled with positive-ion electrospray ionisation tandem mass spectrometry was used for the determination and confirmation of 13 sulphonamide drugs in environmental water samples in the low ng/L-range. Enrichment with concentration factors of 130-670 was performed by solid phase extraction, achieving recoveries of 50 to 90%. After gradient elution HPLC, detection and quantification was performed using selected reaction monitoring (SRM) with limits of detection between 0.2 and 3.7 microg/L. Confirmation was obtained by either SRM transitions of collision induced dissociation reactions or daughter ion mass spectra. Primary and secondary effluents of municipal waste water treatment plants and different surface waters were examined. The compounds sulphamethoxazole and sulphadiazine were detected and confirmed with concentrations ranging between 30-2000 ng/L and 10-100 ng/L, respectively. The compound sulphamethizole was detected in low amounts but could not be positively confirmed.     

Development of a multi-residue method for the determination of 18 carbamates in tobacco by high-performance liquid chromatography/positive electrospray ionisation tandem mass spectrometry

A multi-residue method for the determination of carbamates in tobacco was developed by high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometry (MS). A rapid sample preparation consisted of an extraction step with methanol, centrifugation and 1:1 dilution with aqueous 10 mM ammonium acetate. After filtration these extracts were directly analysed by reversed-phase HPLC coupled to positive electrospray ionisation tandem mass spectrometry operated in the multiple reaction monitoring mode. Capillary voltage and dwell times were optimised to reduce matrix effects and to increase sensitivity. The method was validated for the determination of 18 carbamates in three main types of raw tobacco and three tobacco products. The interday accuracy ranged between 80 and 110% with a relative standard deviation (RSD) of <30%. The limits of quantification (LOQs) ranged between 0.01 and 0.04 ppm for almost all carbamates, except aldicarb sulfone, carbofuran, and pebulate, with LOQs between 0.10 and 0.20 ppm. These LOQs were clearly below the guidance residue levels defined by the Agrochemical Advisory Committee of CORESTA, an association of organisations having scientific research relative to tobacco.     

A novel arsenical in clam kidney identified by liquid chromatography/electrospray ionisation mass spectrometry.

Kidneys of clams of the genus Tridacna accumulate metabolic products from symbiotic unicellular algae that grow in the mantles of the clams. These metabolites include organoarsenic compounds that are biosynthesised by algae from arsenate in seawater. The arsenic compounds in aqueous extracts of the kidney of the giant clam T. derasa were investigated by liquid chromatography/electrospray ionisation mass spectrometry. About 50% of the water-soluble arsenic was present as dimethylarsinoylribosides and dimethylarsinate which are common algal metabolites. The major compound in the kidney (50% of water-soluble arsenic) was identified as a 5-dimethylarsinoyl-2,3,4-trihydroxycarboxylic acid, a new natural product.     

Derivatization reagents in liquid chromatography/electrospray ionization tandem mass spectrometry

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is one of the most prominent analytical techniques owing to its inherent selectivity and sensitivity. In LC/ESI-MS/MS, chemical derivatization is often used to enhance the detection sensitivity. Derivatization improves the chromatographic separation, and enhances the mass spectrometric ionization efficiency and MS/MS detectability. In this review, an overview of the derivatization reagents which have been applied to LC/ESI-MS/MS is presented, focusing on the applications to low molecular weight compounds.