Analysis of lipids with desorption atmospheric pressure photoionization‐mass spectrometry (DAPPI‐MS) and desorption electrospray ionization‐mass spectrometry (DESI‐MS)

In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat‐soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization‐MS (DESI‐MS) and desorption atmospheric pressure photoionization‐MS (DAPPI‐MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M‐H]⁺ ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a targeted adductomic method for the determination of polycyclic aromatic hydrocarbon DNA adducts using online column‐switching liquid chromatography/tandem mass spectrometry

Human exposure to polycyclic aromatic hydrocarbons (PAHs) from sources such as industrial or urban air pollution, tobacco smoke and cooked food is not confined to a single compound, but instead to mixtures of different PAHs. The interaction of different PAHs may lead to additive, synergistic or antagonistic effects in terms of DNA adduct formation and carcinogenic activity resulting from changes in metabolic activation to reactive intermediates and DNA repair. The development of a targeted DNA adductomic approach using liquid chromatography/tandem mass spectrometry (LC/MS/MS) incorporating software‐based peak picking and integration for the assessment of exposure to mixtures of PAHs is described. For method development PAH‐modified DNA samples were obtained by reaction of the anti‐dihydrodiol epoxide metabolites of benzo[a]pyrene, benzo[b]fluoranthene, dibenzo[a,l]pyrene (DB[a,l]P) and dibenz[a,h]anthracene with calf thymus DNA in vitro and enzymatically hydrolysed to 2′‐deoxynucleosides. Positive LC/electrospray ionisation (ESI)‐MS/MS collision‐induced dissociation product ion spectra data showed that the majority of adducts displayed a common fragmentation for the neutral loss of 116 u (2′‐deoxyribose) resulting in a major product ion derived from the adducted base. The exception was the DB[a,l]P dihydrodiol epoxide adduct of 2′‐deoxyadenosine which resulted in major product ions derived from the PAH moiety being detected. Specific detection of mixtures of PAH‐adducted 2′‐deoxynucleosides was achieved using online column‐switching LC/MS/MS in conjunction with selected reaction monitoring (SRM) of the [M+H]⁺ to [M+H–116]⁺ transition plus product ions derived from the PAH moiety for improved sensitivity of detection and a comparison was made to detection by constant neutral loss scanning. In conclusion, different PAH DNA adducts were detected by employing SRM [M+H–116]⁺ transitions or constant neutral loss scanning. However, for improved sensitivity of detection optimised SRM transitions relating to the PAH moiety product ions are required for certain PAH DNA adducts for the development of targeted DNA adductomic methods. Copyright © 2010 John Wiley & Sons, Ltd.     

HPLC‐DAD and HPLC‐ESI‐MS separation,determination and identification of the spin‐labeled diastereoisomers of podophyllotoxin

Spin‐labeled nitroxide derivatives of podophyllotoxin had better antitumor activity and less toxicity than that of the parent compounds. However, the 2‐H configurations of these spin‐labeled derivatives cannot be determined by nuclear magnetic resonance (NMR) methods. In the present paper, a high‐performance liquid chromatography‐diode array detection (HPLC‐DAD) and a high‐performance liquid chromatography‐electrospray ionization tandem mass spectrometry (HPLC‐ESI/MS/MS) method were developed and validated for the separation, identification of four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 position. In the HPLC‐ESI/MS spectra, each pair of diastereoisomers of the spin‐labeled derivatives in the mixture was directly confirmed and identified by [M+H]⁺ ions and ion ratios of relative abundance of [M‐ROH+H]⁺ (ion 397) to [M+H]⁺. When the [M‐ROH+H]⁺ ions (at m/z 397) were selected as the precursor ions to perform the MS/MS product ion scan. The product ions at m/z 313, 282, and 229 were the common diagnostic ions. The ion ratios of relative abundance of the [M‐ROH+H]⁺ (ion 397) to [M+H]⁺, [A+H]⁺ (ion 313) to [M‐ROH+H]⁺, [A+H‐OCH₃]⁺ (ion 282) to [M‐ROH+H]⁺ and [M‐ROH‐ArH+H]⁺ (ion 229) to [M‐ROH+H]⁺ of each pair of diastereoisomers of the derivatives specifically exhibited a stereochemical effect. Thus, by using identical chromatographic conditions, the combination of DAD and MS/MS data permitted the separation and identification of the four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 in the mixture.     

Influence of reversed- and normal-phase liquid chromatographic eluents in the fragmentation of selected chlorinated herbicides in thermospray liquid chromatography-mass spectrometry

The effect of two completely different mobile phase compositions, reversed-phase acetonitrile-water + ammonium acetate and normal-phase cyclohexane, were compared in filament-on thermospray liquid chromatography-mass spectrometry (LC-MS) for the determination of selected chlorinated herbicides such as chloroatrazines and chlorinated phenoxyacetic acids. By using acetonitrile-water + 0.05 M ammonium acetate mixtures in positive ion mode thermospray LC-MS, the chloroatrazine herbicides showed the acetonitrile adduct ion [M + (CH₃CN)H]⁺ as the base peak, whereas the chlorinated phenoxyacetic acids showed no signal. In contrast, when cyclohexane, which is reported for the first time as an eluent in the thermospray technique, was used as the mobile phase the chlorinated phenoxyacetic acid herbicides exhibited [M – H]⁺, [M – Cl]⁺ and M⁺˙ as the main ions. Negative ion mode thermospray LC-MS showed [M – H]^? as the base peak for the chloroatrazines in the different mobile phases, whereas the chlorinated phenoxyacetic acids exhibited [M + H]^?, [M + Cl]^? or [M – HCl]^? as the base peaks in cyclohexane and [M + acetate]^? in acetonitrile-water-ammonium acetate.     

Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH₄Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]^? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄]⁺, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^? into a Cl^? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄]⁺ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.     

Acidic metabolite profiling analysis of catecholamine and serotonin as O‐ethoxycarbonyl/tert‐butyldimethylsilyl derivatives by gas chromatography–mass spectrometry

A novel derivatization method was developed for the simultaneous determination of six acidic metabolites of catecholamine and serotonin by gas chromatography–mass spectrometry (GC‐MS). The metabolites were converted to O‐ethoxycarbonyl/tert‐butyldimethylsilyl (EOC/TBDMS) derivatives for the direct GC‐MS analysis in selected ion monitoring mode. Their mass spectral pattern as EOC/TBDMS derivatives showed characteristic fragment ions of [M – 15]⁺ and [M – 57]⁺, which permitted rapid and accurate structural confirmation of acidic metabolites. The present method was linear (r ≥ 0.998), reproducible (percentage relative standard deviation = 1.0–10.0) and accurate (% relative error = ?9.7–9.8) with detection limits of 0.001–4.7 ng/mL. When applied to human urine samples, the method allowed simultaneous determination of six acidic metabolites of catecholamine and serotonin. Copyright © 2012 John Wiley & Sons, Ltd.     

Relationships between structure,ionization profile and sensitivity of exogenous anabolic steroids under electrospray ionization and analysis in human urine using liquid chromatography–tandem mass spectrometry

The relationships between the ionization profile, sensitivity, and structures of 64 exogenous anabolic steroids (groups I–IV) was investigated under electrospray ionization (ESI) conditions. The target analytes were ionized as [M + H]⁺ or [M + H–nH₂O]⁺ in the positive mode, and these ions were used as precursor ions for selected reaction monitoring analysis. The collision energy and Q3 ions were optimized based on the sensitivity and selectivity. The limits of detection (LODs) were 0.05–20 ng/mL for the 64 steroids. The LODs for 38 compounds, 14 compounds and 12 compounds were in the range of 0.05–1, 2–5 and 10–20 ng/mL, respectively. Steroids including the conjugated keto‐functional group at C3 showed good proton affinity and stability, and generated the [M + H]⁺ ion as the most abundant precursor ion. In addition, the LODs of steroids using the [M + H]⁺ ion as the precursor ion were mostly distributed at low concentrations. In contrast, steroids containing conjugated/unconjugated hydroxyl functional groups at C3 generated [M + H ? H₂O]⁺ or [M + H ? 2H₂O]⁺ ions, and these steroids showed relatively high LODs owing to poor stability and multiple ion formation. An LC‐MS/MS method based on the present ionization profile was developed and validated for the determination of 78 steroids (groups I–V) in human urine. Copyright © 2015 John Wiley & Sons, Ltd.     

APCI as an innovative ionization mode compared with EI and CI for the analysis of a large range of organophosphate esters using GC‐MS/MS

Organophosphate esters (OPEs) are chemical compounds incorporated into materials as flame‐proof and/or plasticizing agents. In this work, 13 non‐halogenated and 5 halogenated OPEs were studied. Their mass spectra were interpreted and compared in terms of fragmentation patterns and dominant ions via various ionization techniques [electron ionization (EI) and chemical ionization (CI) under vacuum and corona discharge atmospheric pressure chemical ionization (APCI)] on gas chromatography coupled to mass spectrometry (GC‐MS). The novelty of this paper relies on the investigation of APCI technique for the analysis of OPEs via favored protonation mechanism, where the mass spectra were mostly dominated by the quasi‐molecular ion [M + H]⁺. The EI mass spectra were dominated by ions such as [H₄PO₄]⁺, [M–R]⁺, [M–Cl]⁺, and [M–Br]⁺, and for some non‐halogenated aryl OPEs, [M]^+● was also observed. The CI mass spectra in positive mode were dominated by [M + H]⁺ and sometimes by [M–R]⁺, while in negative mode, [M–R]⁻ and more particularly [X]^‐ and [X₂]^‐● were mainly observed for the halogenated OPEs. Both EI and APCI techniques showed promising results for further development of instrumental method operating in selective reaction monitoring mode. Instrumental detection limits by using APCI mode were 2.5 to 25 times lower than using EI mode for the non‐brominated OPEs, while they were determined at 50‐100 times lower by the APCI mode than by the EI mode, for the two brominated OPEs. The method was applied to fish samples, and monitored transitions by using APCI mode showed higher specificity but lower stability compared with EI mode. The sensitivity in terms of signal‐to‐noise ratio varying from one compound to another. Copyright © 2016 John Wiley & Sons, Ltd.     

Direct analysis of Salvia divinorum leaves for salvinorin A by thin layer chromatography and desorption electrospray ionization multi‐stage tandem mass spectrometry

Salvia divinorum is widely cultivated in the US, Mexico, Central and South America and Europe and is consumed for its ability to produce hallucinogenic effects similar to those of other scheduled hallucinogenic drugs, such as LSD. Salvinorin A (SA), a kappa opiod receptor agonist and psychoactive constituent, is found primarily in the leaves and to a lesser extent in the stems of the plant. Herein, the analysis of intact S. divinorum leaves for SA and of acetone extracts separated using thin layer chromatography (TLC) is demonstrated using desorption electrospray ionization (DESI) mass spectrometry. The detection of SA using DESI in the positive ion mode is characterized by several ions associated with the compound – [M+H]⁺, [M+NH₄]⁺, [M+Na]⁺, [2M+NH₄]⁺, and [2M+Na]⁺. Confirmation of the identity of these ions is provided through exact mass measurements using a time‐of‐flight (ToF) mass spectrometer. The presence of SA in the leaves was confirmed by multi‐stage tandem mass spectrometry (MSⁿ) of the [M+H]⁺ ion using a linear ion trap mass spectrometer. Direct analysis of the leaves revealed several species of salvinorin in addition to SA as confirmed by MSⁿ, including salvinorin B, C, D/E, and divinatorin B. Further, the results from DESI imaging of a TLC separation of a commercial leaf extract and an acetone extract of S. divinorum leaves were in concordance with the TLC/DESI‐MS results of an authentic salvinorin A standard. The present study provides an example of both the direct analysis of intact plant materials for screening illicit substances and the coupling of TLC and DESI‐MS as a simple method for the examination of natural products. Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous quantitation of metformin and dapagliflozin in human plasma by LC–MS/MS: Application to a pharmacokinetic study

A single LC–MS/MS assay has been developed and validated for the simultaneous determination of metformin and dapagliflozin in human plasma using ion‐pair solid‐phase extraction. Chromatographic separation of the analytes and their internal standards was carried out on a reversed‐phase ACE 5CN (150 × 4.6 mm, 5 μm) column using acetonitrile–15 mm ammonium acetate, pH 4.5 (70:30, v/v) as the mobile phase. To achieve higher sensitivity and selectivity for the analytes, mass spectrometric analysis was performed using a polarity switching approach. Ion transitions studied using multiple reaction monitoring mode were m/z 130.1 [M + H]⁺/60.1 for metformin and m/z 467.1 [M + CH₃COO]^?/329.1 for dapagliflozin in the positive and negative modes, respectively. The linear calibration range of the assay was established from 1.00 to 2000 ng/mL for metformin and from 0.10 to 200 ng/mL for dapagliflozin to achieve a better assessment of the pharmacokinetics of the drugs. The limit of detection and limit of quantitation for the analytes were 0.39 and 1.0 ng/mL for metformin and 0.03 and 0.1 ng/mL for dapagliflozin, respectively. There was no interference of plasma matrix obtained from different sources, including hemolyzed and lipemic plasma. The method was successfully applied to study the effect of food on the pharmacokinetics of metformin and dapagliflozin in healthy subjects.     

Mass spectrometry of 3-substituted 4-hydroxyisoquinolines and their derivatives

Under electron impact, 3-aryl-4-hydroxyisoquinolines form [M – H]⁺, [M – CO]⁺ and [M – H – CO]⁺ ions with a subsequent elimination of HCN or CH₃CN. A cyclic structure for the [M – H]⁺ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH₃?, as well as H?; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]⁺, [M – OH]⁺ and [M – CH₅?]⁺ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.     

The unusual fragmentation of long‐chain feruloyl esters under negative ion electrospray conditions

Long‐chain ferulic acid esters, such as eicosyl ferulate ( 1 ), show a complex and analytically valuable fragmentation behavior under negative ion electrospay collision‐induced dissociation ((?)‐ESI‐CID) mass spectrometry, as studied by use of a high‐resolution (Orbitrap) mass spectrometer. In a strong contrast to the very simple fragmentation of the [M + H]⁺ ion, which is discussed briefly, the deprotonated molecule, [M – H]^?, exhibits a rich secondary fragmentation chemistry. It first loses a methyl radical (MS²) and the ortho‐quinoid [M – H – Me]^‐? radical anion thus formed then dissociates by loss of an extended series of neutral radicals, C_nH_2n + 1^? (n = 0–16) from the long alkyl chain, in competition with the expulsion of CO and CO₂ (MS³). The further fragmentation (MS⁴) of the [M – H – Me – C₃H₇]^? ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M – H – Me – CO]^‐? and [M – H – Me – CO₂]^‐? ions provide some mechanistic and structural insights.     

Critical assessment of ionization patterns and applications of ambient desorption/ionization mass spectrometry using FAPA–MS

Ambient desorption/ionization mass spectrometry (MS) has gained growing interest during the last decade due to its high analytical performance and yet simplicity. Here, one of the recently developed ambient desorption/ionization MS sources, the flowing atmospheric‐pressure afterglow (FAPA) source, was investigated in detail regarding background ions and typical ionization patterns in the positive as well as the negative ion mode for a variety of compound classes, comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides and alkaloids. A broad range of signals for adducts and losses was found, besides the usually emphasized detection of quasimolecular ions, i.e. [M + H]⁺ and [M ? H]^? in the positive and the negative mode, respectively. It was found that FAPA–MS is best suited for polar analytes containing nitrogen and/or oxygen functionalities, e.g. carboxylic acids, with low molecular weights and relatively high vapor pressures. In addition, the source was used in proof‐of‐principle studies, illustrating the capabilities and limitations of the technique: Firstly, traces of cocaine were detected and unambiguously identified on euro banknotes using FAPA ionization in combination with tandem MS, suggesting a correlation between cocaine abundance and age of the banknote. Secondly, FAPA–MS was used for the identification of acidic marker compounds in organic aerosol samples, indicating yet‐undiscovered matrix and sample surface effects of ionization pathways in the afterglow region. Copyright © 2016 John Wiley & Sons, Ltd.     

[C]+· and [CH]+ from doubly charged ions formed from malononitrile

The metastable ions [M]²⁺, [M – H]²⁺· and [M – H₂]²⁺ from malononitrile fragment by loss of [CH]⁺, [C]⁺· and [C]⁺·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M – H]²⁺· involves exclusively the nitrile carbon and that of [M ? H₂]²⁺ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.     

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

2,3‐Dimethyl‐2,3‐dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour‐phase detection systems. In this study, the formation and detection of gas‐phase [M+H]⁺, [M+Li]⁺, [M+NH₄]⁺ and [M+Na]⁺ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]⁺ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]⁺ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision‐induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source‐formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]⁺ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.     

[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines

The N₂ negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [M + 11]^?˙. This addition is also observed in the N₂ positive chemical ionization (PCI) mass spectra. An ion at [M – 15]^? is found in the NICI spectra of aminoaromatics such as aniline, 1- and 2-aminonaphthalene and 1- and 2-aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [M + 11]^?˙, [M – 15]^?˙ and [M + 11]^+˙ ions result from the ionization of analytes altered by surface-assisted reactions. Experiments with ¹⁵N₂, [¹⁵N] aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆] aniline show that the [M + 11]^?˙ ion corresponds to [M + N – 3H]^?˙. The added nitrogen originates from the N₂ buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N₂ PCI mass spectrum of aniline suggest that the neutral product of the surface-assisted reaction is 1,4-dicyanobuta-1,3-diene. Experiments with diamino-substituted aromatics show analogous reactions resulting in the formation of [M – 4H]^?˙ ions for aromatics with ortho-amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.     

Collision-Induced Dissociation Analysis of Negative Atmospheric Ion Adducts in Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry

Collision-induced dissociation (CID) experiments were performed on atmospheric ion adducts [M + R]^– formed between various types of organic compounds M and atmospheric negative ions R^- [such as O₂ ^–, HCO₃ ^–, COO^–(COOH), NO₂ ^–, NO₃ ^–, and NO₃ ^–(HNO₃)] in negative-ion mode atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. All of the [M + R]^– adducts were fragmented to form deprotonated analytes [M – H]^– and/or atmospheric ions R^–, whose intensities in the CID spectra were dependent on the proton affinities of the [M – H]^– and R^– fragments. Precursor ions [M + R]^– for which R^- have higher proton affinities than [M – H]^– formed [M – H]^– as the dominant product. Furthermore, the CID of the adducts with HCO₃ ^– and NO₃ ^-(HNO₃) led to other product ions such as [M + HO]^– and NO₃ ^–, respectively. The fragmentation behavior of [M + R]^– for each R^– observed was independent of analyte type (e.g., whether the analyte was aliphatic or aromatic, or possessed certain functional groups).      

Studies on the Mass Spectra of Monocyclic N‐Aryl‐δ‐Valerolactams

The fragmental behavior of some monocyclic N‐aryl‐δ‐valerolactams in EI‐MS was studied. Their molecular ion peak, together with some characteristic fragments such as [M‐29]⁺, [M‐56]^+?, [M‐69]⁺, and [M‐98]⁺, were always found in a series of N‐aryl‐δ‐valerolactams in EI‐MS spectra. Furthermore, the mechanism for the interpretation of each fragment is described.     

Electrospray ionization and atmospheric pressure matrix‐assisted laser desorption/ionization mass spectrometry of antioxidants applied in lubricants

The aim of this study was to investigate the utility of ion trap mass spectrometry (ITMS) in combination with the two desorption/ionization methods, electrospray (ESI) and atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI), for the detection of antioxidants which are applied in lubricants. These experiments should form the base for future investigations of antioxidants in tribologically formed thin layers on the surface of frictional systems. Seventeen different antioxidants were selected out of the group of hindered phenolic and aromatic aminic compounds. Practically all antioxidants could be characterized by positive ion ESI‐ and AP‐MALDI‐ITMS, forming various types/species of molecular ions (e.g. [M]^{+ .} , [M+H]⁺, [M+Na]⁺ or [M–2H+H]⁺). A few compounds could be analyzed by negative ion ESI‐MS, too, but none by negative ion AP‐MALDI‐MS. The influence of target materials in AP‐MALDI‐MS (gold‐ and titanium nitride (TiN)‐covered stainless steel, micro‐diamond‐covered hard metal, hand‐polished and sand‐blasted stainless steel targets) with respect to the molecular ion intensity and type of molecular ion of two selected antioxidants was evaluated. The surface properties are of particular interest because in friction tests different materials with different surface characteristics are used. However, the MS results indicate that optimal target surfaces have to be found for individual antioxidants in AP‐MALDI‐MS but in general smooth surfaces were superior to rough surfaces. Finally the gold‐covered stainless steel MALDI target provided the best mass spectra and was selected for all the antioxidants investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigation of endogenous corticosteroids profiles in human urine based on liquid chromatography tandem mass spectrometry

The accurate and precise measurement of endogenous corticosteroids in urine is a powerful tool to understand the biochemical state in several diseases. In this study, a rapid, accurate, and sensitive method based on liquid chromatography-tandem mass spectrometry (LC–MS/MS) for the quantification of 67 endogenous gluco- and mineralo-corticosteroids and progestins has been developed and validated. Sample preparation, chromatographic separation, and mass spectrometric detection were optimized. Urine samples (0.5 mL) were hydrolyzed with β-glucuronidase and the released analytes were extracted by liquid–liquid extraction. The chromatographic separation was performed in 20 min after redisolution of the extract. MS behavior of endogenous corticosteroids was evaluated in order to select the most specific precursor ion ([M+H]⁺, [M+NH₄]⁺, or [M+H-nH₂O]⁺) for the detection. MS/MS determination was performed under selected reaction monitoring mode using electrospray ionization in positive mode. The method was shown to be linear (r > 0.99) in the range of endogenous concentrations for all studied metabolites. Limits of detection (LOD) below 1 ng mL⁻¹ were typically obtained for analytes with a 3-oxo-4-ene structure whereas LODs below 15 ng mL⁻¹ were common for the rest of analytes. Recoveries were higher than 80% and intra-assay precisions below 20%, evaluated at three concentration levels, were found for most steroids. No significant or moderate matrix effect, ranging from 54 to 155%, was observed for most of the analytes. The applicability of the method was confirmed by analyzing 24 h urine samples collected from twenty healthy volunteers and comparing the results with previously established normal ranges. The wide coverage of corticosteroid metabolism, together with short analysis time, low sample volume, simple sample preparation, and satisfactory quantitative results make this method useful for clinical purposes.