Study of active naphtodianthrone St John's Wort compounds by electrospray ionization Fourier transform ion cyclotron resonance and multi‐stage mass spectrometry in sustained off‐resonance irradiation collision‐induced dissociation and infrared multiphoton dissociation modes

Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSⁿ. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]^? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSⁿ experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification and fragmentation pathways of caffeine metabolites in urine samples via liquid chromatography with positive electrospray ionization coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry and tandem mass spectrometry

Liquid chromatography (LC) with positive ion electrospray ionization (ESI+) coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was employed for the simultaneous determination of caffeine and its metabolites in human urine within a single chromatographic run. LC/ESI‐FTICRMS led to the unambiguous determination of the molecular masses of the studied compounds without interference from other biomolecules. A systematic and comprehensive study of the mass spectral behaviour of caffeine and its fourteen metabolites by tandem mass spectrometry (MS/MS) was performed, through in‐source ion trap collision‐induced dissociation (CID) of the protonated molecules, [M+H]⁺. A retro‐Diels‐Alder (RDA) process along with ring‐contraction reactions were the major fragmentation pathways observed during CID. The base peak of xanthine precursors originates from the loss of methyl isocyanate (CH₃NCO, 57 Da) or isocyanic acid (HNCO, 43 Da), which in turn lose a CO unit. Also uric acid derivatives shared a RDA rearrangement as a common fragmentation process and a successive loss of CO₂ or CO. The uracil derivatives showed a loss of a ketene unit (CH₂CO, 42 Da) from the protonated molecule along with the loss of H₂O or CO. To assess the potential of the present method three established metabolite ratios to measure P450 CYP1A2, N‐acetyltransferase and xanthine oxidase activities were evaluated by a number of identified metabolites from healthy human urine samples after caffeine intake. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular mass ranges of coal tar pitch fractions by mass spectrometry and size‐exclusion chromatography

A coal tar pitch was fractionated by solvent solubility into heptane‐solubles, heptane‐insoluble/toluene‐solubles (asphaltenes), and toluene‐insolubles (preasphaltenes). The aim of the work was to compare the mass ranges of the different fractions by several different techniques. Thermogravimetric analysis, size‐exclusion chromatography (SEC) and UV‐fluorescence spectroscopy showed distinct differences between the three fractions in terms of volatility, molecular size ranges and the aromatic chromophore sizes present. The mass spectrometric methods used were gas chromatography/mass spectrometry (GC/MS), pyrolysis/GC/MS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and laser desorption time‐of‐flight mass spectrometry (LD‐TOFMS). The first three techniques gave good mass spectra only for the heptane‐soluble fraction. Only LDMS gave signals from the toluene‐insolubles, indicating that the molecules were too involatile for GC and too complex to pyrolyze into small molecules during pyrolysis/GC/MS. ESI‐FTICRMS gave no signal for toluene‐insolubles probably because the fraction was insoluble in the methanol or acetonitrile, water and formic acid mixture used as solvent to the ESI source. LDMS was able to generate ions from each of the fractions. Fractionation of complex samples is necessary to separate smaller molecules to allow the use of higher laser fluences for the larger molecules and suppress the formation of ionized molecular clusters. The upper mass limit of the pitch was determined as between 5000 and 10 000 u. The pitch asphaltenes showed a peak of maximum intensity in the LDMS spectra at around m/z 400, in broad agreement with the estimate from SEC. The mass ranges of the toluene‐insoluble fraction found by LDMS and SEC (400–10 000 u with maximum intensity around 2000 u by LDMS and 100–9320 u with maximum intensity around 740 u by SEC) are higher than those for the asphaltene fraction (200–4000 u with maximum intensity around 400 u by LDMS and 100–2680 u with maximum intensity around 286 u by SEC) and greater than values considered appropriate for petroleum asphaltenes (300–1200 u with maximum intensity near 700 u). Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of complex assemblages of organic acids in geological samples by negative electrospray ionization mass spectrometry using a double‐focusing magnetic sector field mass spectrometer

Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double‐focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high‐resolution double‐focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition C_nH_2n+zO₂, among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O₂ class. In addition, minor compound classes could be identified using FTICRMS. Copyright © 2010 John Wiley & Sons, Ltd.     

CID of singly charged antioxidants applied in lubricants by means of a 3D ion trap and a linear ion trap-Orbitrap mass spectrometer

The aim of this study was to investigate the fragmentation behavior induced by low‐energy collision‐induced dissociation (LE‐CID) of four selected antioxidants applied in lubricants, by two different types of ion trap mass spectrometers: a three‐dimensional ion trap (3D‐IT) and a linear IT (LIT) Orbitrap MS. Two sterically hindered phenols and two aromatic amines were selected as model compounds representing different antioxidant classes and were characterized by positive‐ion electrospray ionization (ESI) and LE‐CID. Various types of molecular ions (e.g. [M]^+?, [M + H]⁺, [M + NH₄]⁺ or [M + Na]⁺) were used as precursor ions generating a significant number of structurally relevant product ions. Furthermore, the phenolic compounds were analyzed by negative‐ion ESI. For both IT types applied for fragmentation, the antioxidants exhibited the same unusual LE‐CID behavior: (1) they formed stable radical product ions and (2) C? C bond cleavages of aliphatic substituents were observed and their respective cleavage sites depended on the precursor ion selected. This fragmentation provided information on the type of structural isomer usually not obtainable for branched aliphatic substituents utilizing LE‐CID. Comparing the two instruments, the main benefit of applying the LIT‐Orbitrap was direct access to elemental composition of product ions enabling unambiguous interpretation of fragmentation trees not obtainable by the 3D‐IT device (e.g. loss of isobaric neutrals). It should be emphasized that the types of product ions formed do not depend on the type of IT analyzer applied. For characterizing degradation products of antioxidants, the LIT‐Orbitrap hybrid system, allowing the determination of accurate m/z values for product ions, is the method of choice. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of benzofurazan derivatization reagents for short chain carboxylic acids in liquid chromatography/electrospray ionization‐tandem mass spectrometry (LC/ESI‐MS/MS)

Benzofurazan derivatization reagents, 4‐[2‐(N,N‐dimethylamino)ethylaminosulfonyl]‐7‐(2‐aminopentylamino)‐2,1,3‐benzoxadiazole (DAABD‐AP) and 4‐[2‐(N,N‐dimethylamino) ethylaminosulfonyl]‐7‐(2‐aminobutylamino)‐2,1,3‐benzoxadiazole (DAABD‐AB), for short‐chain carboxylic acids in liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) were synthesized. These reagents reacted with short chain carboxylic acids in the presence of the condensation reagents at 60°C for 60 min. The generated derivatives were separated on the reversed‐phase column and detected by ESI‐MS/MS with the detection limits of 0.1–0.12 pmol on column. Upon collision‐induced dissociation, a single and intense product ion at m/z 151 was observed. These results indicated that DAABD‐AP and DAABD‐AB are suitable as the derivatization reagents in LC/ESI‐MS/MS analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of phospholipids using an open‐tubular capillary column with a monolithic layer of molecularly imprinted polymer in capillary electrochromatography‐electrospray ionization‐tandem mass spectrometry

In this study, an open‐tubular capillary electrochromatography (OT‐CEC) column with a monolithic layer of molecularly imprinted polymer (MIP) based on methacrylic acid, ethylene glycol dimethacrylate, and 4‐styrenesulfonic acid was utilized for the simultaneous separation and characterization of phospholipid (PL) molecular structures by interfacing with electrospray ionization‐tandem mass spectrometry (ESI‐MS‐MS). Introducing an MIP‐based monolith along with charged species at the OT column made it possible to separate PL molecules based on differences in head groups and acyl chain lengths in CEC. For the interface of OT‐CEC with ESI‐MS‐MS, a simple nanospray interface utilizing a sheath flow was developed and the resulting OT‐CEC‐ESI‐MS‐MS was able to separate PL standards (phosphatidylserines, phosphatidylethanolamines, phosphatidylglycerols, phosphatidic acid, and lysophosphatidylglycerols). The developed method was applied to human urinary lipid extracts, and resulted in the separation and structural identification of 18 molecules by data‐dependent collision‐induced dissociation.     

Fragmentation behavior of Amadori‐peptides obtained by non‐enzymatic glycosylation of lysine residues with ADP‐ribose in tandem mass spectrometry

Mono‐ and poly‐adenosine diphosphate (ADP)‐ribosylation are common post‐translational modifications incorporated by sequence‐specific enzymes at, predominantly, arginine, asparagine, glutamic acid or aspartic acid residues, whereas non‐enzymatic ADP‐ribosylation (glycation) modifies lysine and cysteine residues. These glycated proteins and peptides (Amadori‐compounds) are commonly found in organisms, but have so far not been investigated to any great degree. In this study, we have analyzed their fragmentation characteristics using different mass spectrometry (MS) techniques. In matrix‐assisted laser desorption/ionization (MALDI)‐MS, the ADP‐ribosyl group was cleaved, almost completely, at the pyrophosphate bond by in‐source decay. In contrast, this cleavage was very weak in electrospray ionization (ESI)‐MS. The same fragmentation site also dominated the MALDI‐PSD (post‐source decay) and ESI‐CID (collision‐induced dissociation) mass spectra. The remaining phospho‐ribosyl group (formed by the loss of adenosine monophosphate) was stable, providing a direct and reliable identification of the modification site via the b‐ and y‐ion series. Cleavage of the ADP‐ribose pyrophosphate bond under CID conditions gives access to both neutral loss (347.10 u) and precursor‐ion scans (m/z 348.08), and thereby permits the identification of ADP‐ribosylated peptides in complex mixtures with high sensitivity and specificity. With electron transfer dissociation (ETD), the ADP‐ribosyl group was stable, providing ADP‐ribosylated c‐ and z‐ions, and thus allowing reliable sequence analyses. Copyright © 2010 John Wiley & Sons, Ltd.     

Dimerization of ionized 4‐(methyl mercapto)‐phenol during ESI,APCI and APPI mass spectrometry

A novel ion/molecule reaction was observed to occur under electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo ionization (APPI) conditions, leading to dimerization of ionized 4‐(methyl mercapto)‐phenol followed by fast H^· loss. The reaction is particularly favored during ESI, which suggests that this ion/molecule reaction can occur both in the solution inside the ESI‐charged droplets and in the gas‐phase environment of most other atmospheric pressure ionization techniques. The dimerization reaction is inherent to the electrolytic process during ESI, whereas it is more by ion/molecule chemistry in nature during APCI and APPI. From the tandem mass spectrometry (MS/MS) data, accurate mass measurements, hydrogen/deuterium (H/D) exchange experiments and density functional theory (DFT) calculations, two methyl sulfonium ions appear to be the most likely products of this electrophilic aromatic substitution reaction. The possible occurrence of this unexpected reaction complicates mass spectral data interpretation and can be misleading in terms of structural assignment as reported herein for 4‐(methyl mercapto)‐phenol. Copyright © 2009 John Wiley & Sons, Ltd.     

Drug impurity profiling by capillary electrophoresis/mass spectrometry using various ionization techniques

Capillary electrophoresis/mass spectrometry (CE/MS) is predominantly carried out using electrospray ionization (ESI). Recently, atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) have become available for CE/MS. With the VUV lamp turned off, the APPI source may also be used for CE/MS by thermospray ionization (TSI). In the present study the suitability of ESI, APCI, APPI and TSI for drug impurity profiling by CE/MS in the positive ion mode is evaluated. The drugs carbachol, lidocaine and proguanil and their potential impurities were used as test compounds, representing different molecular polarities. A background electrolyte of 100 mM acetic acid (pH 4.5) provided baseline separation of nearly all impurities from the respective drugs. APPI yielded both even‐ and odd‐electron ions, whereas the other ionization techniques produced even‐electron ions only. In‐source fragmentation was more pronounced with APCI and APPI than with ESI and TSI, which was most obvious for proguanil and its impurities. In general, ESI and TSI appeared the most efficient ionization techniques for impurities that are charged in solution achieving detection limits of 100 ng/mL (full‐scan mode). APPI and APCI showed a lower efficiency, but allowed ionization of low and high polarity analytes, although quaternary ammonium compounds (e.g. carbachol) could not be detected. Largely neutral compounds, such as the lidocaine impurity 2,6‐dimethylaniline, could not be detected by TSI, and yielded similar detection limits (500 ng/mL) for ESI, APPI and APCI. In many cases, impurity detection at the 0.1% (w/w) level was possible when 1 mg/mL of parent drug was injected with at least one of the CE/MS systems. Overall, the tested CE/MS systems provide complementary information as illustrated by the detection and identification of an unknown impurity in carbachol. Copyright © 2009 John Wiley & Sons, Ltd.     

Practical approaches to the ESI‐MS analysis of catalytic reactions

Electrospray ionization mass spectrometry (ESI‐MS) is a soft ionization technique commonly coupled with liquid or gas chromatography for the identification of compounds in a one‐time view of a mixture (for example, the resulting mixture generated by a synthesis). Over the past decade, Scott McIndoe and his research group at the University of Victoria have developed various methodologies to enhance the ability of ESI‐MS to continuously monitor catalytic reactions as they proceed. The power, sensitivity and large dynamic range of ESI‐MS have allowed for the refinement of several homogenous catalytic mechanisms and could potentially be applied to a wide range of reactions (catalytic or otherwise) for the determination of their mechanistic pathways. In this special feature article, some of the key challenges encountered and the adaptations employed to counter them are briefly reviewed. Copyright © 2014 John Wiley & Sons, Ltd.     

Global detection and identification of components from crude and processed traditional Chinese medicine by liquid chromatography connected with hybrid ion trap and time‐of‐flight‐mass spectrometry

We herein present a chemical profiling method to efficiently process the information acquired by ultra fast liquid chromatography (UFLC)‐electrospray ionization source in combination with hybrid ion trap and high‐resolution time‐of‐flight mass spectrometry (UFLC‐(ESI)‐IT‐TOF/MS), facilitating the structural determination of serial components contained in crude or processed traditional Chinese medicine (TCM). Under the optimized UFLC and IT‐TOF‐MSⁿ conditions, over 39 compounds were separated and detected in crude or processed Fructus corni within 25 min. The components were identified by comparing the mass spectra and retention time with reference compounds, or tentatively assigned by elucidating low‐energy collision‐induced dissociation (CID) fragment ions and matching empirical molecular formula with that of the published compounds. Several factors in the processing procedure were examined. The experimental results demonstrate that the chemical reactions that occurred in the processing procedure can be used to elucidate the processed mechanism of F. corni, which is regularly affected by the processing conditions. This study provides a novel approach and methodology to identify the complicated components from various complex mixtures such as crude TCM, processed TCM, and biological samples. It can be used as a valid analytical method for further understanding the processing mechanism of TCM, along with the intrinsic quality control of TCM and its processed product.     

Evaluation of analytical performance and reliability of direct nanoLC‐nanoESI‐high resolution mass spectrometry for profiling the (xeno)metabolome

Mass spectrometry (MS) profiling techniques are used for analysing metabolites and xenobiotics in biofluids; however, detection of low abundance compounds using conventional MS techniques is poor. To counter this, nanoflow ultra‐high‐pressure liquid chromatography‐nanoelectrospray ionization‐time‐of‐flight MS (nUHPLC‐nESI‐TOFMS), which has been used primarily for proteomics, offers an innovative prospect for profiling small molecules. Compared to conventional UHPLC‐ESI‐TOFMS, nUHPLC‐nESI‐TOFMS enhanced detection limits of a variety of (xeno)metabolites by between 2 and 2000‐fold. In addition, this study demonstrates for the first time excellent repeatability and reproducibility for analysis of urine and plasma samples using nUHPLC‐nESI‐TOFMS, supporting implementation of this platform as a novel approach for high‐throughput (xeno)metabolomics. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of hormones in human urine by ultra‐high‐performance liquid chromatography/triple‐quadrupole mass spectrometry

Steroid hormones play a critical role in maintaining the homeostasis of human metabolism. Urine as a noninvasive sample has been extensively used in clinical diagnosis for hormones homeostasis. In this study, the simultaneous characterization of fourteen hormones in urine was performed based on ultra‐high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPHLC/ESI(+)‐MS/MS) with multiple reaction monitoring in the positive ionization mode. The target hormones were cortisone, cortisol, 11‐deoxycortisol, aldosterone, corticosterone, 11‐deoxycorticosterone, progesterone, 17‐OH‐progesterone, pregnenolone, estrone, estradiol, estriol, testosterone and dehydreopiandrosterone. β‐Glucuronidase/sulfatase deconjugation and liquid–liquid extraction (LLE) were conducted for the determination of urinary hormones (free + conjugated forms). The limits of detection (LODs) ranged from 0.2 ng/mL (11‐deoxycortisol and testosterone) to 1 ng/mL (cortisone). The extraction recovery of the targeted compounds ranged from 87% to 127%, indicating sufficient extraction efficiency for the LLE process. Intraday precision was below 10% and the accuracy ranged from 84% to 122%. The profiling analysis of hormones in urine samples helps to understand the metabolic state of biological systems and can be employed as a diagnostic tool in diseases developed by endocrine‐disrupted systems.     

Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry

Fragmentation reactions of β‐hydroxymethyl‐, β‐acetoxymethyl‐ and β‐benzyloxymethyl‐butenolides and the corresponding γ‐butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) using collision‐induced dissociation (CID). This study revealed that loss of H₂O [M + H ?18]⁺ is the main fragmentation process for β‐hydroxymethylbutenolide (1) and β‐hydroxymethyl‐γ‐butyrolactone (2). Loss of ketene ([M + H ?42]⁺) is the major fragmentation process for protonated β‐acetoxymethyl‐γ‐butyrolactone (4), but not for β‐acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI‐MS/MS spectra of β‐benzyloxymethylbutenolide (5) and β‐benzyloxymethyl‐γ‐butyrolactone (6). The different side chain at the β‐position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas‐phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry. Copyright © 2009 John Wiley & Sons, Ltd.     

Stereochemical differentiation of C‐7 hydroxyltaxane isomers by electrospray ionization mass spectrometry

In this study, different electrospray ionization mass spectrometric (ESI‐MS) methods were utilized to analyze several pairs of taxane stereoisomers including paclitaxel and 7‐epi‐paclitaxel. Both ESI‐MS and tandem mass spectrometry (MS/MS) techniques provided stereochemically dependent mass spectra in negative‐ion mode, and all studied stereoisomers could be easily distinguished based on their characteristic ions or distinct fragmentation patterns. MS/MS experiments for several taxane analogues at various collision energies were performed to elucidate potential dissociation pathways. The gas‐phase deprotonation potentials were also calculated to estimate the most thermodynamically favorable deprotonation site using DFT B3LYP/6‐31G(d). The results of the theoretical studies agreed well with the fragmentation patterns of paclitaxel and 7‐epi‐paclitaxel observed from MS/MS experiments. In addition, it was found that liquid chromatography (LC)/ESI‐MS was a useful and sensitive technique for assignment of C‐7 taxane stereoisomers from realistic samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Combined use of tandem mass spectrometry and computational chemistry to study 2H‐chromenes from Piper aduncum

Natural 2H‐chromenes were isolated from the crude extract of Piper aduncum (Piperaceae) and analyzed by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) applying collision‐induced dissociation. Density functional theory (DFT) calculations were used to explain the preferred protonation sites of the 2H‐chromenes based on thermochemical parameters, including atomic charges, proton affinity, and gas‐phase basicity. After identifying the nucleophilic sites, the pathways were proposed to justify the formation of the diagnostic ions under ESI‐MS/MS conditions. The calculated relative energy for each pathway was in good agreement with the energy‐resolved plot obtained from ESI‐MS/MS data. Moreover, the 2H‐chromene underwent proton attachment on the prenyl moiety via a six‐membered transition state. This behavior resulted in the formation of a diagnostic ion due to 2‐methylpropene loss. These studies provide novel insights into gas‐phase dissociation for natural benzopyran compounds, indicating how reactivity is correlated to the intrinsic acid‐base equilibrium and structural aspects, including the substitution pattern on the aromatic moiety. Therefore, these results can be applied in the identification of benzopyran derivatives in a variety of biological samples.     

ESI-FTICRMS与更换底物保护基团方法联用表征烯醇反应中间体

更换底物保护基团的化学方法与质谱、同位素标记以及核磁方法联用表征钯催化的烯醇环化反应中间体。实验表明更换底物的保护基团方法可以明显降低反应速度,延长关键中间体离子的存活寿命,不仅清晰地观察了反应的整个进程而且成功地捕获检测表征了其中关键中间体离子。进一步,串联质谱(SORI-CAD)方法研究了其中一些中间体离子的气相裂解反应行为,归纳总结其气相裂解反应的途径。结合同位素标记的结构为它们结构的确证提供了丰富信息。     

Real‐time reaction monitoring by probe electrospray ionization mass spectrometry

Probe electrospray ionization (PESI) is a modified version of the electrospray ionization (ESI), where the capillary for sampling and spraying is replaced by a solid needle. High tolerance to salts and direct ambient sampling are major advantages of PESI compared with conventional ESI. In this study, PESI‐MS was used to monitor some biological and chemical reactions in real‐time, such as acid‐induced protein denaturation, hydrogen/deuterium exchange (HDX) of peptides, and Schiff base formation. By using PESI‐MS, time‐resolved mass spectra and ion chromatograms can be obtained reproducibly. Real‐time PESI‐MS monitoring can give direct and detailed information on each chemical species taking part in reactions, and this is valuable for a better understanding of the whole reaction process and for the optimization of reaction parameters. PESI‐MS can be considered as a potential tool for real‐time reaction monitoring due to its simplicity in instrumental setup, direct sampling with minimum sample preparation and low sample consumption. Copyright © 2010 John Wiley & Sons, Ltd.     

Fourier transform ion cyclotron resonance mass spectrometry using atmospheric pressure photoionization for high-resolution analyses of corticosteroids

Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was coupled with atmospheric pressure photoionization (APPI) for the first time and used for the analysis of several corticosteroids.1 The analytes showed excellent response using APPI when compared with both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). APPI has the advantage of requiring less heat for desolvation, resulting in less thermal degradation of the analytes and higher signal-to-noise than APCI. In terms of ultimate sensitivity, APPI is more efficient than either ESI or APCI for the analysis of corticosteroids. With some compounds, the high-resolution capability of FTICRMS was necessary to obtain an accurate mass due to contributions of the M(+.) (13)C isotope in the [M+H](+) ion peak.