Determination of Sulfur Compounds in Water Samples by Ion Chromatography Dynamic Reaction Cell Inductively Coupled Plasma Mass Spectrometry

An ion chromatography‐inductively coupled plasma mass spectrometric (IC‐ICP‐MS) method for the speciation of sulfur compounds, namely sulfite [SO₃^2?], sulfate [SO₄^2?] and thiosulfate [S₂O₃^2?], was described. Ionic sulfur compounds were well separated in about 3 min by ion chromatography with a Hamilton PRP‐X100 column as the stationary phase and 60 mmol L^?1 NH₄NO₃ and 0.1% v/v formaldehyde (HCHO) solution (pH = 7) as the mobile phase. The analyses were carried out using dynamic reaction cell (DRC) ICP‐MS. The sulfur‐selective chromatogram was determined at m/z 48 as ³²S¹⁶O⁺ by using its reaction with O₂ in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by ¹⁶O¹⁶O⁺ and ¹⁴N¹⁸O⁺ on ³²S⁺ by detecting ³²S⁺ as the oxide ion ³²S¹⁶O⁺ at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 3.6–4.6 ng S mL^?1. The accuracy of the method has been verified by comparing the sum of the concentrations of individual sulfur compounds obtained by the present procedure with the total concentration of sulfur in several natural water samples. The recovery was in the range of 97–102% for various compounds studied.     

Matrix effects during phosphorus determination with quadrupole inductively coupled plasma mass spectrometry

A quadrupole inductively coupled plasma mass spectrometer was evaluated for use in the detection of phosphorus. The influences of nitric acid and methanol (simulating the composition of a sample solution after nitric acid digestion) on phosphorus determination were studied using two different measuring methods at different plasma conditions: detection of phosphorus ions at m/z 31 and detection of phosphorus oxide ions at m/z 47. The existence of polyatomic interferences at m/z 31 and 47 was explored. Nitric acid and methanol are shown to be the sources of polyatomic ions and therefore cause poorer detection limits. Better detection limits were achieved in such matrices when phosphorus was detected as ³¹P⁺. The presence of methanol improves the system sensitivity towards phosphorus sevenfold; however, this positive effect is hindered by the high background signal due to carbon-based polyatomic ions. For samples with an organic matrix an appropriate mineralization procedure should be applied (high excess of nitric acid and high temperature) to quantitatively oxidize organic compounds to carbon dioxide, which is easily removed from the sample, in order to achieve correct results.     

Determination of the ratio of calcium to phosphorus in foodstuffs by dynamic reaction cell inductively coupled plasma mass spectrometry

An inductively coupled plasma mass spectrometer (ICP–MS) equipped with a dynamic reaction cell (DRC) was used for the determination of Ca and P in foodstuffs. In this study, two different reaction gases, CH₄ and O₂, were introduced successively through the different channels to alleviate different interferences in the same analysis run. The effect of the operating conditions of the DRC system was studied to get the best signal-to-noise ratio for each element. The interfering ⁴⁰Ar⁺ at m/z 40 was reduced in intensity by up to five orders of magnitude by using 1.0 mL min^–1 CH₄ as reaction cell gas in the DRC. On the other hand, by using O₂ as the reaction gas, ³¹P⁺ was converted to ³¹P¹⁶O⁺ that could be detected at m/z 47 where there was less interference. The limits of detection for Ca and P were 0.2 ng mL^–1 and 0.3 ng mL^–1, respectively. This method was used to determine the concentrations of Ca and P and the ratio of Ca to P in NIST SRM 1549 non-fat milk powder and NIST RM 8345 whole milk powder reference materials and an infant milk powder and an infant cereal-rice sample purchased locally. The results for the reference samples agreed satisfactorily with the reference values. The accuracy of the determination was better than 4.1 and 0.9% for Ca and P, respectively. The results for infant milk powder and infant cereal were also found to be in good agreement with the value on the bottle label. Precision (RSD) between sample replicates was better than 4.8% for all the determinations.     

Characterization and determination of chlorophacinone in plasma by ion chromatography coupled with ion trap electrospray ionization mass spectrometry

Plasmatic chlorophacinone is commonly measured with liquid chromatographic assay, which convenient but lacks sensitivity and selectivity and usually requires ion pair reagents to reduce the chromatographic tailed peak. In this paper, a novel method using eluent generator reagent‐free ion chromatography coupled with electrospray ionization ion trap mass spectrometric detection for the determination of chlorophacinone in plasma has been developed. After samples were extracted with 10% (v/v) methanol in acetonitrile and cleaned by solid‐phase extraction, chromatographic separation was performed on an IonPac^® AS11 analytical column (250 × 4.0 mm) using 40.0 mmol/L KOH containing 10% (v/v) methanol as organic modifier. Quantification was performed by negative electrospray ionization in multiple reaction monitoring mode. The transition m/z 373 → 201 was for the quantification ion; the transitions m/z 373 → 172 and m/z 373 → 145, as well as the isotope ions m/z 375 and m/z 203, were for the qualitative ions. All the method parameters were validated. It was confirmed that this method can be used in clinical diagnosis and forensic toxicology. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of the degradation of arsenobetaine during its contact with natural zeolites and the identification of metabolites using HPLC coupled with ICP-MS and ESI-MS

Combined detection by inductively coupled mass spectrometry (ICP-MS) for elemental information (quantification) and electrospray ionization mass spectrometry (ESI-MS) for molecular information (identification) by means of splitting of the eluent after chromatographic separation is a suitable means of analysis for unknown and not commercially available arsenic species. Simultaneous parallel ESI-MS and ICP-MS detection was applied to identify possible metabolites during the interaction of arsenobetaine (AsB) with natural zeolites. AsB, mainly produced by freshwater and marine organisms, is known to be a candidate of low toxicity. To estimate the possible toxicological risk originating from AsB in contact with natural and synthetic zeolites, small particles of a naturally occurring zeolite were mixed with an AsB solution. After a contact time of 56 days the degradation of AsB proceeded with different yields in the case of the natural Mexican zeolites. In contrast, no additional components were detected in the control samples. It was possible to clearly identify the degradation products dimethylarsinate (m/z 139) and dimethylarsinoylacetate (m/z 181) by comparison of the peaks monitored by ESI-MS and ICP-MS. In some other cases the unknown arsenic species could not be identified so clearly from their molecular masses.     

Reactivity of gaseous sodiated ions derived from benzene dicarboxylate salts toward residual water in the collision gas

The sodium adduct of disodium salts of benzene dicarboxylic acids (m/z 233), when subjected to collision‐induced dissociation (CID), undergoes a facile loss of CO₂ to produce an ion of m/z 189, which retains all the three sodium atoms of the precursor. The CID spectrum of this unusual m/z 189 ion shows significant peaks at m/z 167, 63 and 85. The enigmatic m/z 167 ion, which appeared to represent a loss of a 22‐Da neutral fragment from the precursor ion is in fact a fragment produced by the interaction of the m/z 189 ion with traces of water present in the collision gas. The change of the m/z 167 peak to 168, when D₂O vapor was introduced to the collision gas of a Q‐ToF instrument, proved that such an intervention of water could occur even in collision cells of tandem‐in‐space mass spectrometers. The m/z 189 ion has such high affinity for water; it forms an ion/molecule complex even during the brief residence time of ions in collision cells of triple quadrupole instruments. The complex formed in this way then eliminates elements of NaOH to produce the ion observed at m/z 167. In an ion trap, the relative intensity of the m/z 167 peak increases with longer activation time even at the lowest possible collision energy setting. Similarly, the m/z 145 ion (which represents the sodium adduct of phenelenedisodium, formed by two consecutive losses of CO₂ from the m/z 233 ion of meta‐ and para‐isomers) interacts with water to produce a fragment ion at m/z 123 for the sodium adduct of phenylsodium. Other uncommon ions that originate also from water/ion interactions are observed at m/z 85 and 63 for [Na₃O]⁺ and [Na₂OH]⁺, respectively. Tandem mass spectrometric experiments conducted with appropriately deuterium‐labeled compounds confirmed that the proton required for the formation of the [Na₂OH]⁺ ion originates from traces of water present in the collision gas and not from the ring protons of the aromatic moiety. Copyright © 2010 John Wiley & Sons, Ltd.     

Complementary precursor ion and neutral loss scan mode tandem mass spectrometry for the analysis of glycerophosphatidylethanolamine lipids from whole rat retina

A “shotgun” tandem mass spectrometry (MS) approach involving the use of multiple lipid-class-specific precursor ion and neutral loss scan mode experiments has been employed to identify and characterize the glycerophosphatidylethanolamine (GPEtn) lipids that were present within a crude lipid extract of a normal rat retina, obtained with minimal sample handling prior to analysis. Characterization of these lipids was performed by complementary analysis of their protonated and deprotonated precursor ions, as well as their various ionic adducts (e.g., Na⁺, Cl^-), using a triple-quadrupole mass spectrometer. Notably, the application of novel precursor ion and neutral loss scans of m/z 164 and m/z 43, respectively, for the specific identification of sodiated GPEtn precursor ions following the addition of 500 μM NaCl to the crude lipid extracts was demonstrated. The use of these novel MS/MS scans in parallel provided simplified MS/MS spectra and enhanced the detection of 1-alkenyl, 2-acyl (plasmenyl) GPEtn lipids relative to the positive ion mode neutral loss m/z 141 commonly used for GPEtn analysis. Furthermore, the novel use of a “low energy” neutral loss scan mode experiment to monitor for the exclusive loss of 36m/z (HCl) from [M+Cl]^- GPEtn adducts was demonstrated to provide a more than 25-fold enhancement for the detection of GPEtn lipids in negative ion mode analysis. Subsequent “high-energy” pseudo MS³ product ion scans on the precursor ions identified from this experiment were then employed to rapidly characterize the fatty acyl chain substituents of the GPEtn lipids. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Sensitivity of Positive Ion Mode Electrospray Ionization Mass Spectrometry in the Analysis of Thiol Metabolites

High signal intensities of glutathione (GSH), [GSH+H]⁺ (m/z 308), cysteine (CySH), [CySH+H]⁺ (m/z 122), and homocysteine (hCySH), [hCySH+H]⁺ (m/z 136), are observed in ESI MS with on‐line electrochemistry (EC). Dimers formed by H‐bonding, which are not electrochemical products, are detected as [2GSH+H]⁺ (m/z 615), [2CySH+H]⁺ (m/z 243) and [2hCySH+H]⁺ (m/z 271) together with disulfide dimers GSSG, CySSCy and hCySSCyh, [GSSG+H]⁺ (m/z 613), [CySSCy+H]⁺ (m/z 241) and [hCySSCyh+H]⁺ (m/z 269). When dopamine is present a thiol/dopamine quinone (DAQ) adduct is observed. Formation of this adduct is proposed to occur by an electrochemical mechanism during ESI. Catalysis of thiol oxidation and analysis of thiol mixtures is addressed.     

Atmospheric pressure chemical ionization of explosives using alternating current corona discharge ion source

The high‐sensitive detection of explosives is of great importance for social security and safety. In this work, the ion source for atmospheric pressure chemical ionization/mass spectrometry using alternating current corona discharge was newly designed for the analysis of explosives. An electromolded fine capillary with 115 µm inner diameter and 12 mm long was used for the inlet of the mass spectrometer. The flow rate of air through this capillary was 41 ml/min. Stable corona discharge could be maintained with the position of the discharge needle tip as close as 1 mm to the inlet capillary without causing the arc discharge. Explosives dissolved in 0.5 µl methanol were injected to the ion source. The limits of detection for five explosives with 50 pg or lower were achieved. In the ion/molecule reactions of trinitrotoluene (TNT), the discharge products of NO_x^? (x = 2,3), O₃ and HNO₃ originating from plasma‐excited air were suggested to contribute to the formation of [TNT ? H]^? (m/z 226), [TNT ? NO]^? (m/z 197) and [TNT ? NO + HNO₃]^? (m/z 260), respectively. Formation processes of these ions were traced by density functional theory calculations. Copyright © 2015 John Wiley & Sons, Ltd.     

Sensitive measurement of vinorelbine in dog plasma by liquid chromatography–electrospray ionization tandem mass spectrometry utilizing transitions from double‐charged precursor ions

A sensitive high‐performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for measuring vinorelbine was developed. A 100 µL aliquot of plasma was spiked with deuterium‐labeled internal standard and subjected to solid‐phase extraction using an Oasis HLB μ‐elution plate. Two microliters of the extracted samples was directly injected into LC/MS/MS. Chromatographic separation was achieved on a Capcell Pak C18 UG column (2 × 75 mm) with a gradient elution of methanol (mobile phase B) against 0.05% formic acid in aqueous 10 mm ammonium formate (mobile phase A). The LC flow rate was set to 0.28 mL/min and the gradient (solvent B concentration) was processed from 40 to 90%. In mass spectrometric detection, observation of the reaction from a double‐charged precursor ion [M + 2H]²⁺ (m/z 390) to product ion m/z 122 provided very high sensitivity. The method was validated with a lower limit of detection of 0.2 ng/mL with 0.1 mL of plasma, and the method was used to determine the plasma pharmacokinetics of vinorelbine in dogs. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of glutathione adducts of patulin by means of liquid chromatography (HPLC) with biochemical detection (BCD) and electrospray ionization tandem mass spectrometry (ESI-MS/MS)

Abstract  A novel method for the identification of glutathione/electrophile adducts that are inhibiting glutathione-S-transferase (GST) activity was developed and applied for the analysis of the mycotoxin patulin. The method is based on high-performance liquid chromatography (HPLC) coupled to a continuous-flow enzyme reactor serving as biochemical detector (BCD) in parallel to electrospray mass spectrometric detection (ESI-MS). This HPLC-BCD technique combines a separation step and the detection of the inhibition and is therefore ideally suited for the analysis of the activity of single patulin/glutathione adducts within a complex mixture of adducts. Two out of at least 15 detected patulin–glutathione adducts showed strong GST inhibition. In ESI-MS, the inhibitory active adducts were characterized by [M + H]⁺ ions with m/z 462.1138 and m/z 741.2011, respectively. They could be identified as a dihydropyranone adduct containing one molecule glutathione and a ketohexanoic acid bearing two glutathione molecules. Graphical Abstract  OnlineAbstractFigure Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of sulfur and selected trace elements in metallothionein-like proteins using capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry with an octopole reaction cell

The determination of sulfur in biologically relevant samples such as metalloproteins is described. The analytical methodology used is based on robust on-line coupling between capillary electrophoresis (CE) and octopole reaction cell inductively-coupled plasma mass spectrometry (ORC–ICP–MS). Polyatomic ions that form in the plasma and interfere with the determination of S at mass 32 are minimised by addition of xenon to the collision cell. The method has been applied to the separation and simultaneous element-specific detection of sulfur, cadmium, copper, and zinc in commercially available metallothionein preparations (MT) and metallothionein-like proteins (MLP) extracted from liver samples of bream (Abramis brama L.) caught in the river Elbe, Germany. Instrumental detection limits have been calculated according to the German standard procedure DIN 32645 for the determination of sulfur and some simultaneously measured trace elements in aqueous solution. For sulfur detection limits down to 1.3 g L^–1 (³⁴S) and 3.2 g L^–1 (³²S) were derived. For the other trace elements determined simultaneously detection limits ranging from 300 ng L^–1 (⁵⁸Ni) to 500 ng L^–1 (⁶⁶Zn, ⁵⁵Mn) were achieved. For quantification of sulfur and cadmium in a commercially available MT preparation under hyphenated conditions the use of external calibration is suggested. Finally, the need for proper sample-preparation technique will be discussed.     

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products

A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step ³⁴S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental ³⁴S-enriched sulfur. Thiophene was determined in gasoline, ‘sulfur-free’ gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 μg g⁻¹ was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.     

Identification and quantification of oleanolic acid and ursolic acid in Chinese herbs by liquid chromatography-ion trap mass spectrometry

A rapid and sensitive method for the identification and quantification of ursolic acid (UA) and oleanolic acid (OA) in Chinese herbs is described. The method combines liquid chromatography (LC) with ion trap‐mass spectrometry (IT‐MS) detection. The UA and OA standard solution were directly infused into IT‐MS for collecting MSⁿ spectra. The major fragment ions of UA and OA were confirmed by MSⁿ at m/z 455, 407, 391, 377 and 363 in negative ion mode, and m/z 457, 439, 411 and 393 in positive mode, respectively. The possible main cleavage pathway of fragment ions was studied. UA and OA provided good signals corresponding to the deprotonated molecular ion [M − H]⁻. The method is reliable and reproducible, and the detection limit is 5 ng/mL. The method was validated in the concentration range of 0.04–40 μg/mL; intra‐ and inter‐day precisions ranged from 0.78 to 2.15%, and the accuracy was 96.5–108.2% for UA and OA. The mean recovery of UA and OA was 97.1–106.2% with RSD less than 1.86%. An LC‐IT‐MS method was successfully applied to determine the UA and OA in nine Chinese herbs. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of cadmium in oyster tissue using isotope dilution inductively coupled plasma mass spectrometry: comparison of results obtained in the standard and He/H2 cell modes

An inductively coupled plasma quadrupole mass spectrometer equipped with an octopole collision/reaction cell was used for the determination of cadmium in oyster tissue samples using isotope dilution inductively coupled plasma mass spectrometry. The oyster samples in question were found to contain Mo and Zr. In our feasibility study on a Cd standard solution (10 μg L⁻¹) containing a matrix of Mo (1000 μg L⁻¹) or Zr (250 μg L⁻¹), the potentially interfering species (MoO⁺ or ZrO⁺) present at the analytical mass of cadmium concerned (m/z 111, 112 or 114) was reduced effectively through the use of a mixture of He and H₂ as cell gases. The accuracy of the method was validated by the analysis of a matrix-matched certified reference material (CRM) of NIST SRM 1566b. The CRM was analyzed under the standard and He/H₂ cell modes. Two isotopic pairs of ¹¹⁴Cd/¹¹¹Cd and ¹¹²Cd/¹¹¹Cd were selected for quantification purposes. The recoveries of cadmium obtained in the two cell modes were compared with each other. The validated method was applied successfully to the APMP.QM-P5 pilot study for international comparability purposes.     

Sensitive Determination of Felodipine in Human and Dog Plasma by Use of Liquid–Liquid Extraction and LC–ESI–MS–MS

Summary A sensitive and selective liquid chromatographic method coupled with electrospray ionization tandem mass spectrometry (LC–ESI–MS–MS) has been developed for quantification of felodipine in human and dog plasma. Compounds were separated on a 2.0 mm × 150 mm, 5.0 m particle, C₈ column with 1 m m ammonium acetate–acetonitrile, 20:80, pH 6.0, as mobile phase at a flow rate of 200 L min^–1. Nifedipine was used as internal standard. Plasma samples were extracted with diethyl ether, the centrifuged upper layer was evaporated, the residue was reconstituted with mobile phase, and the reconstituted samples were injected. The analytical column lasted for at least 1000 injections. By use of multiple reaction monitoring (MRM) mode in MS–MS felodipine and nifedipine were detected without severe interference from the human or dog plasma matrix. Felodipine produced a protonated precursor ion ([M + H]⁺) at m/z 384 and a corresponding product ion at m/z 338. And internal standard (nifedipine) produced a protonated precursor ion ([M + H]⁺) at m/z 347 and a corresponding product ion at m/z 315. Detection of felodipine in human and dog plasma was accurate and precise, with a limit of quantification of 0.05 ng mL^–1. The method has been successfully applied to preliminary pharmacokinetic study of felodipine in human and dog plasma.     

Simultaneous Element-Selective Detection of C,F, Cl,Br, and I by Capillary Gas Chromatography Coupled with Microplasma Mass Spectrometry

Simultaneous element-selective detection of the halogens and carbon was accomplished with capillary gas chromatography coupled with microplasma mass spectrometry. The microplasma ion source was a radio frequency plasma contained inside the last 4–5 cm of the 0.32 mm i.d. fused silica capillary column. The ion source was located inside the high vacuum housing of the MS, and only the GC carrier gas (2.3 mL min⁻¹ of helium) was used for plasma generation. Atomic ions were detected in the positive mode. Detection limits were in the low picogram area, and the selectivity to carbon ranged from 8×10² for fluorine to higher than 10⁴ for the other halogens. By introduction of both hydrogen and oxygen as reagent gases, peak tailing was avoided by suppression of analyte reactions with the silica walls of the ion source. Special attention was given to the fluorine-selective detection due to an interfering background species at m/z 19, assumed to be H₃O⁺ originating from the reagent gases. The background signal was minimized by careful control of the power level.     

Ultra‐performance liquid chromatography tandem mass spectrometry method for the determination of AZ66, a sigma receptor ligand,in rat plasma and its application to in vivo pharmacokinetics

Methamphetamine abuse continues as a major problem in the USA owing to its powerful psychological addictive properties. AZ66, 3‐[4‐(4‐cyclohexylpiperazine‐1‐yl)pentyl]‐6‐fluorobenzo[d]thiazole‐2(3H)‐one, an optimized sigma receptor ligand, is a promising therapeutic agent against methamphetamine. To study the in vivo pharmacokinetics of this novel sigma receptor ligand in rats, a sensitive ultra‐performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed in rat plasma and validated. The developed method requires a small volume of plasma (100 μL) and a simple liquid–liquid extraction. The chromatographic separations were achieved in 3.3 min using an Acquity UPLC BEH Shield RP₁₈ column. The mass spectrophotometric detection was carried out using a Waters Micromass Quattro MicroTM triple‐quadrupole system. Multiple reaction monitoring was used for the quantitation with transitions m/z 406 → m/z 181 for AZ66 and m/z 448 → m/z 285 for aripiprazole. The method was validated over a concentration range of 1–3500 ng/mL and the lower limit of quantitation was determined to be 1 ng/mL. Validation of the assay demonstrated that the developed UPLC/MS/MS method was sensitive, accurate and selective for the determination of AZ66 in rat plasma. The present method has been successfully applied to an i.v. pharmacokinetic study in Sprague–Dawley rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Identification of in vitro metabolites of JWH-015, an aminoalkylindole agonist for the peripheral cannabinoid receptor (CB2) by HPLC-MS/MS

The in vitro microsomal metabolism of JWH-015, a ligand that exhibits a high binding affinity at the peripheral cannabinoid receptor CB₂, has been studied. A total of 22 metabolites were identified and structurally characterized. The metabolites are products of: 1) monohydroxylation on the naphthalene ring (m/z 344, M20 and M21), indole ring (m/z 344, M17 and M18), or the N-alkyl group (m/z 344, M14); 2) arene oxidation leading to dihydrodiols (m/z 362, M12 and M15); 3) dihydroxylation on the naphthalene ring (m/z 360, M7) or indole ring (m/z 360, M13), resulting from a combination of monohydroxylations on both the naphthalene and indole rings (m/z 360, M16), or a combination of monohydroxylations on the naphthalene ring and on the N-propyl group (m/z 360, M9); 4) trihydroxylation (m/z 378, M1, M3, M4, M6, and M10); 5) N-dealkylation (m/z 286, M19); 6) N-dealkylation and monohydroxylation on the naphthalene ring (m/z 302, M11); 7) N-dealkylation and dihydrodiol formation from arene oxidation (m/z 320, M2 and M5); 8) dehydrogenation after monohydroxylation on the N-alkyl group (m/z 326, M22); 9) dehydrogenation and monohydroxylation on the indole ring (m/z 342, M8).     

Identification and quantification of atractylenolide I and atractylenolide III in Rhizoma Atractylodes Macrocephala by liquid chromatography–ion trap mass spectrometry

Rhizoma Atractylodes Macrocephala (RAM) is an important traditional Chinese medicinal herb that is used for treatment of dyspepsia and anorexia. The active ingredients, atractylenolide I (AO‐I) and atractylenolide III (AO‐III), were identified by direct‐injection ion trap‐mass spectrometry (IT‐MS) for collecting MSⁿ spectra. The major fragment ions of AO‐I and AO‐III were confirmed by MSⁿ both in negative ion mode and in positive ion mode. The possible main cleavage pathway of fragment ions was studied. The determinations of AO‐I and AO‐III were accomplished by liquid chromatography (LC) with UV and MS. The analytes provided good signals corresponding to the protonated molecular ions [M + H]⁺ and product ions. The precursor ions and product ions for quantification of AO‐III and AO‐I were m/z 249 → 231 and m/z 233 → 215, respectively, using selected ion monitoring by LC‐IT‐MS. Two methods were evaluated for a number of validation characteristics (repeatability, limit of detection, calibration range, and recovery). MS provides a high selectivity and sensitivity for determination of AO‐III and AO‐I in positive mode. After optimization of the methods, separation, identification and quantification of the two components in RAM were comprehensively tested by HPLC with UV and MS. Copyright © 2012 John Wiley & Sons, Ltd.