Quadrupole Linear Ion Trap Mass Research Articles

Formation of Phosphatidylethanol and Its Subsequent Elimination During an Extensive Drinking Experiment Over 5 Days

For almost 30 years, phosphatidylethanol (PEth) has been known as a direct marker of alcohol consumption. This marker stands for consumption in high amounts and for a longer time period, but it has been also detected after 1 high single intake of ethanol (EtOH). The aim of this study was to obtain further information about the formation and elimination of PEth 16:0/18:1 by simulating extensive drinking. After 3 weeks of alcohol abstinence, 11 test persons drank an amount of EtOH leading to an estimated blood ethanol concentration of 1 g/kg on each of 5 successive days. After the drinking episode, they stayed abstinent for 16 days with regular blood sampling. PEth 16:0/18:1 analysis was performed using liquid chromatography-tandem mass spectrometry (high-performance liquid chromatography 1100 system and QTrap 2000 triple quadrupole linear ion trap mass spectrometer. Values of blood alcohol were obtained using a standardized method with headspace gas chromatography flame ionization detector. Maximum measured concentrations of EtOH were 0.99 to 1.83 g/kg (mean 1.32 g/kg). These values were reached 1 to 3 hours after the start of drinking (mean 1.9 hours). For comparison, 10 of 11 volunteers had detectable PEth 16:0/18:1 values 1 hour after the start of drinking, ranging from 45 to 138 ng/ml PEth 16:0/18:1. Over the following days, concentrations of PEth 16:0/18:1 increased continuously and reached the maximum concentrations of 74 to 237 ng/ml between days 3 and 6. This drinking experiment led to measurable PEth concentrations. However, PEth 16:0/18:1 concentrations stayed rather low compared with those of alcohol abusers from previous studies.

HPLC/APCI Mass Spectrometry of Saturated and Unsaturated Hydrocarbons by Using Hydrocarbon Solvents as the APCI Reagent and HPLC Mobile Phase

Saturated and unsaturated, linear, branched, and cyclic hydrocarbons, as well as polyaromatic and heteroaromatic hydrocarbons, were successfully ionized by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as reagents in a linear quadrupole ion trap (LQIT) mass spectrometer. Pentane was proved to be the best reagent among the hydrocarbon reagents studied. This ionization method generated different types of abundant ions (i.e., [M + H](+), M(+•), [M - H](+) and [M - 2H](+ •)), with little or no fragmentation. The radical cations can be differentiated from the even-electron ions by using dimethyl disulfide, thus facilitating molecular weight (MW) determination. While some steroids and lignin monomer model compounds, such as androsterone and 4-hydroxy-3-methoxybenzaldehyde, also formed abundant M(+•) and [M + H](+) ions, this was not true for all of them. Analysis of two known mixtures as well as a base oil sample demonstrated that each component of the known mixtures could be observed and that a correct MW distribution was obtained for the base oil. The feasibility of using this ionization method on the chromatographic time scale was demonstrated by using high-performance liquid chromatography (HPLC) with hexane as the mobile phase (and APCI reagent) to separate an artificial mixture prior to mass spectrometric analysis.

Liquid chromatography–electrospray quadrupole linear ion trap mass spectrometry method for the quantitation of palonosetron in human plasma and urine: Application to a pharmacokinetic study

The new analytical method for the determination of palonosetron in human plasma and urine has been developed based on liquid chromatography–mass spectrometry. The method utilized tramadol as the internal standard (IS). Separation was carried out on a Zorbax Eclipse TC-C18 column using methanol–1mM ammonium formate in water (containing 0.1% formic acid, v/v, pH=2.8) as mobile phase for gradient elution. Detection is carried out by multiple reaction monitoring (MRM) on 3200Qtrap™ mass spectrometry. The method has a chromatographic run time of 5.5min and is linear within the concentration range 0.01–5.00ng/mL for plasma and 0.10–30.00ng/mL for urine both with a LOD of 0.003ng/mL. Intra- and inter-day RSD of the concentration was 3.66–6.60%, 1.29–7.71% for plasma and 2.39–5.76%, 2.06–7.13% for urine. The relative error (RE) was −4.58% to 3.26% for plasma and −1.47% to 2.53% for urine. The recovery rates of palonosetron and IS both for plasma and urine were more than 90%. Palonosetron was stable under all the conditions tested. The method was successfully used to analyze palonosetron in human plasma and urine over a period of 168h after intravenously pumping a single dose of 0.25mg to volunteers. No significant differences were found between the pharmacokinetic parameters and urine accumulated excretory rate for male and female volunteers (P>0.05). A two-compartment model was obtained after administrations. Palonosetron was eliminated at a slow rate in volunteers. The mean urine accumulated excretory rate was 25.97±12.87%. Inter-individual differences could not be neglected due to the high coefficient of variety in several pharmacokinetic parameters and the urine accumulated excretion.

Simultaneous Screening of Glutathione and Cyanide Adducts Using Precursor Ion and Neutral Loss Scans-Dependent Product Ion Spectral Acquisition and Data Mining Tools

Drugs can be metabolically activated to soft and hard electrophiles, which are readily trapped by glutathione (GSH) and cyanide (CN), respectively. These adducts are often detected and structurally characterized using separate tandem mass spectrometry methods. We describe a new method for simultaneous screening of GSH and CN adducts using precursor ion (PI) and neutral loss (NL) scans-dependent product ion spectral acquisition and data mining tools on an triple quadrupole linear ion trap mass spectrometry. GSH, potassium cyanide, and their stable isotope labeled analogues were incubated with liver microsomes and a test compound. Negative PI scan of m/z 272 for detection of GSH adducts and positive NL scans of 27 and 29 Da for detection of CN adducts were conducted as survey scans to trigger acquisition of enhanced resolution (ER) spectrum and subsequent enhanced product ion (EPI) spectrum. Post-acquisition data mining of EPI data set using NL filters of 129 and 27 Da was then performed to reveal the GSH adducts and CN adducts, respectively. Isotope patterns and EPI spectra of the detected adducts were utilized for identification of their molecular weights and structures. The effectiveness of this method was evaluated by analyzing reactive metabolites of nefazodone formed from rat liver microsomes. In addition to known GSH- and CN-trapped reactive metabolites, several new CN adducts of nefazodone were identified. The results suggested that current approach is highly effective in the analysis of both soft and hard reactive metabolites and can be used as a high-throughput method in drug discovery.

Simultaneous Determination of Bisphenol Compounds in Canned Food by Matrix Solid-Phase Dispersion and Liquid Chromatography-Tandem Quadrupole Linear Ion Trap Mass Spectrometry

A method based on matrix solid-phase dispersion and liquid chromatography-quadrupole/linear ion trap-mass spectrometry(MSPD-LC/QqLIT) for qualitative and quantitative determination of bisphenol compounds in canned food was presented.Bisphenol residues were extracted with acetonitrile solution containing 0.1% formic acid,followed by a further clean-up procedure using QuEChERS method.Bisphenol compounds were separated upon a C18 column and detected by liquid chromatographic-tandem mass spectrometry.Information dependent acquisition scan function(IDA) combined with enhanced product ion scan(EPI) library was used to confirm the bisphenol compounds,while quantification analysis was operated by MRM mode using external standard method simulta-neously.The recoveries ranged from 49.3%-128.4%(n=6) with RSD from 3.2% to 14.4%(n=6) in 4 kinds of canned food matrices respectively.The method is proved to be quick and effective for simultaneosly qualitative and quatitative determination of bisphenol residues in canned foodstuffs.

DESI-MS2: a rapid and innovative method for trace analysis of six cytostatic drugs in health care setting

With the aim of establishing exposure levels for hospital personnel preparing and administering cytostatic drugs (CDs), here, we present an innovative screening method based on the use of the desorption electrospray ionization (DESI) interface coupled with a hybrid quadrupole linear ion trap mass spectrometer. A rapid, simple, and sensitive procedure was developed for the simultaneous surface monitoring of cyclophosphamide, dacarbazine, methotrexate, vincristine, gemcitabine, and cytarabine. Since analytes were in the solid state, a novel approach based on the use of passive samplers was combined with the direct analysis of wipes. A PTFE-printed glass slide was used as a passive sampler, while hydrophobic centers of Swiffer® cloths were judged extremely efficient as wipe samplers. After the sampling period, the CD collectors were directly processed with the DESI-MS system without any further treatment. MS/MS confirmatory analysis was conducted using selected reaction monitoring in the positive ion mode and detection limits were evaluated. Values were at the picograms per square millimeter levels on the passive collector and at the picograms per square centimeter levels for the wipe ones. Direct determination on solid-state samples combined with mass spectrometry selectivity provided a powerful tool so far unapplied to occupational hygiene.

Quality Evaluation of a Herbal Prescription Through Quantification of 40 Components by HPLC–ESI–MS/MS

The Kang-nao-shuai (KNS) capsule is a combined herbal prescription used in the treatment of insomnia, amnesia, neurasthenia, age-related dementia and brain injuries. Multiple constituents are considered to be responsible for the therapeutic effects of this herbal prescription. However, the quality control of the multicomponents is limited. To establish a liquid chromatography-electrospray ionisation-mass spectrometry method for the analysis of 40 constituents in KNS capsules. The optimal chromatographic conditions were achieved on an Agilent C₁₈-column with a gradient elution that consisted of methanol and 0.1% formic acid in water. The precursor and product ions of analytes were monitored on a hybrid quadrupole linear ion trap mass spectrometer in positive and negative mode respectively using multiple-reaction monitoring. A total of 40 constituents including organic acid, flavonoid, quinone, terpene, alkaloid and saponin were quantified, most of the 40 components were determined for the first time in the KNS capsule. A quantitative HPLC-ESI-MS/MS method allowing the quantification of 40 marker compounds was optimised and validated for linearity, precision, accuracy, stability, specificity and limits of detection and quantification. The method was successfully applied to analyse 10 batches of KNS capsule. The established method is simple and can be used as a tool for quality evaluation and control of this natural product.

Identification of Epoxide Functionalities in Protonated Monofunctional Analytes by Using Ion/Molecule Reactions and Collision-Activated Dissociation in Different Ion Trap Tandem Mass Spectrometers

A mass spectrometric method has been delineated for the identification of the epoxide functionalities in unknown monofunctional analytes. This method utilizes gas-phase ion/molecule reactions of protonated analytes with neutral trimethyl borate (TMB) followed by collision-activated dissociation (CAD) in an ion trapping mass spectrometer (tested for a Fourier-transform ion cyclotron resonance and a linear quadrupole ion trap). The ion/molecule reaction involves proton transfer from the protonated analyte to TMB, followed by addition of the analyte to TMB and elimination of methanol. Based on literature, this reaction allows the general identification of oxygen-containing analytes. Vinyl and phenyl epoxides can be differentiated from other oxygen-containing analytes, including other epoxides, based on the loss of a second methanol molecule upon CAD of the addition/methanol elimination product. The only other analytes found to undergo this elimination are some amides but they also lose O = B-R (R = group bound to carbonyl), which allows their identification. On the other hand, other epoxides can be differentiated from vinyl and phenyl epoxides and from other monofunctional analytes based on the loss of (CH(3)O)(2)BOH or formation of protonated (CH(3)O)(2)BOH upon CAD of the addition/methanol elimination product. For propylene oxide and 2,3-dimethyloxirane, the (CH(3)O)(2)BOH fragment is more basic than the hydrocarbon fragment, and the diagnostic ion (CH(3)O)(2)BOH (2) (+) is formed. These reactions involve opening of the epoxide ring. The only other analytes found to undergo (CH(3)O)(2)BOH elimination are carboxylic acids, but they can be differentiated from the rest based on several published ion/molecule reaction methods. Similar results were obtained in the Fourier-transform ion cyclotron resonance and linear quadrupole ion trap mass spectrometer.

Quantitative analysis of a quaternary ammonium drug: ipratropium bromide by LC/ESI-MSn in horse plasma and urine

A quantitative method, using LC/ESI-MS(n) with a quadrupole linear ion trap mass analyzer, has been developed for the analysis of ipratropium cation in horse plasma and urine. The method applies solid-phase extraction with WCX cartridges for plasma and MM2 cartridges for urine, prior to analysis by LC/ESI-MS(n). The efficiency of extraction combined with the sensitivity and the selectivity of MS(n) allows for the quantification of ipratropium cation at picogram per milliliter levels. The analytical capabilities of the method have been successfully checked by the quantitative analysis of ipratropium cation in post-administration samples collected from horses treated by nebulization.

Mass Spectrometric Characterization of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine N-Oxidized Metabolites Bound at Cys34 of Human Serum Albumin

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic aromatic amine that is formed during the cooking of meats and poultry. PhIP is a carcinogen in rodents and a potential human carcinogen. Several short-term biomarkers of PhIP have been established for human biomonitoring, but validated long-term biomarkers of the biologically effective dose of PhIP remain to be developed. Metabolites of PhIP have been reported to covalently bind to human serum albumin (SA), which is the most abundant protein in plasma; however, the chemical structures of PhIP-SA adducts are unknown. Cysteine(34) is one of 35 conserved Cys residues in SA across species. Thirty-four of these Cys are involved in 17 disulfide bonds. The single unpaired Cys(34) residue in SA is well-known to react with carcinogenic metabolites and toxic electrophiles. 2-Nitro-1-methyl-6-phenylimidazo[4,5-b]pyridine (NO(2)-PhIP), 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (HONH-PhIP), and 2-nitroso-1-methyl-6-phenylimidazo[4,5-b]pyridine (NO-PhIP), three genotoxic metabolites of PhIP, were reacted with purified human SA or human plasma, and the SA adduction products, following enzymatic digestion, were separated by ultra performance liquid chromatography and characterized with a linear quadrupole ion trap mass spectrometer. The major adduct of NO(2)-PhIP was formed at the Cys(34) of SA with bond formation occurring between the sulfhydryl group of Cys and the C-2 imidazole atom of PhIP. The major adducts formed between SA and HNOH-PhIP or NO-PhIP were identified as acid-labile sulfinamide linkages at Cys(34). These PhIP-SA adducts represent a measure of bioactivation of PhIP and may serve as long-term biomarkers of the biologically effective dose of PhIP.

Mass spectrometric analysis of amino acid/di-peptide modified gemini surfactants used as gene delivery agents: Establishment of a universal mass spectrometric fingerprint

Lipid based gemini surfactant nanoparticles have been extensively studied as non-viral vectors for gene therapy. Novel amino acid substituted gemini surfactants have been recently developed with a molecular structure consisting of two positively charged quaternary ammonium head groups, symmetrical saturated dodecyl tails, and a spacer region containing a secondary amine group. Various amino acids were attached to the amine functional group. The purpose of this work was to confirm the molecular structure of six novel amino acid substituted gemini surfactants and to establish a universal fragmentation (MS/MS) pattern of the tested compounds (i.e., fingerprint). This was accomplished by using a hybrid quadrupole orthogonal time-of-flight mass spectrometer (QqToF-MS) and a triple quadrupole linear ion trap mass spectrometer (QqQ-LIT MS) equipped with electrospray ionization (ESI) source. The single stage QqToF-MS data obtained in the positive ion mode verified the molecular composition of all tested gemini surfactants. Tandem mass spectrometric (MS/MS) analysis showed common fragmentation behaviour among all tested compounds, allowing for the establishment of a universal fragmentation pattern. The fragmentation pathway was confirmed by MS/MS/MS experiments utilizing a Q-Trap™ 4000 LC/MS/MS system. Unique product ions, originating from the loss of one or both head groups along with the attached tail region(s), confirmed the chemical structure of the tested compounds. The established MS/MS fingerprint will be used for qualitative purposes as well as the development of future multiple reaction monitoring (MRM) HPLC–MS/MS quantification methods.

The use of a triple quadrupole linear ion trap mass spectrometer with electrospray ionisation for fragmentation studies of selected antifungal drugs

Fragmentation studies of three antifungal drugs, clotrimazole, fluconazole and clioquinol ,were performed. A triple quadrupole linear ion trap mass spectrometer was used for this purpose. This type of equipment enables MS(3) spectra to be obtained which lead to better understanding of fragmentation pathways. Nevertheless, it is rarely used for fragmentation studies. The results obtained here for the antifungal drugs gave further insight into fragmentation pathways of clotrimazole and fluconazole. Moreover, fragmentation of clioquinol was investigated which had not been presented before.

Identification and Counting of Oxygen Functionalities in Aromatic Analytes Related to Lignin by Using Negative-Mode Electrospray Ionization and Multiple Collision-Activated Dissociation Steps

Identification and counting of different oxygen-containing functional groups in 40 small aromatic analytes, including a lignin monomer, was explored using a linear quadrupole ion trap (LQIT) mass spectrometer. The analytes were evaporated and ionized by negative-mode electrospray ionization (ESI). In an effort to cleave off all of the functionalities, one at a time, the deprotonated analytes were then subjected to multiple consecutive collision-activated dissociation (CAD) events until no more fragmentation was observed (up to MS5). In most cases, the number and types of functionalities could be determined. This approach was demonstrated to be feasible on the high-performance liquid chromatographic (HPLC) time scale. Hence, valuable structural information can be obtained for previously unknown aromatic analytes directly in complex mixtures, such as lignin degradation products.

Simultaneous quantification of flavonoids and phenolic acids in Herba Scutellariae barbatae and its confused plants by high performance liquid chromatography-tandem mass spectrometry

A sensitive and selective high performance liquid chromatography–tandem mass spectrometric method (HPLC–MS/MS) has been developed for simultaneous analysis of 11 components (7 flavonoids and 4 phenolic acids) in Herba Scutellariae barbatae. Simultaneous separation of these 11 compounds was achieved on a C18 analytical column with gradient elution of methanol and 0.1‰ acetic acid (v/v) at a flow rate of 0.8mL/min. The precursor and product ions of analytes were monitored on a hybrid quadrupole linear ion trap mass spectrometer equipped with a turbo ion spray interface in negative mode using multiple-reaction monitoring (MRM). Full validation of the assay was carried out including linearity, precision, accuracy, limits of detection and quantification. The results demonstrated that the method developed was reliable, rapid and specific. Then the method was successfully applied to differentiate 18 batches of Herba Scutellariae barbatae samples and 3 batches of its confused plants from different sources.

Identification of metabolites of crude and processed Fructus Corni in rats by microdialysis sampling coupled with electrospray ionization linear quadrupole ion trap mass spectrometry

A microdialysis (MD) sampling coupled with electrospray ionization linear quadrupole ion trap mass spectrometry (LTQ-MS n ) method has been developed for rapid and sensitive analysis of rat microdialysate metabolite profile of Fructus Corni, a well-known Traditional Chinese Medicine (TCM). The purified samples were separated by a reversed-phase HPLC with C 18 column under a gradient elution. Parent compounds and metabolites of crude and processed Fructus Corni of Jiu Zheng Pin (JZP, JZP is produced after steaming the crude drug pre-steeped in wine) were detected by the on-line MS n detector in negative scan model. The identification of the metabolites and their structural elucidation were performed by comparing the changes in molecular mass and defining sites of biotransformation based on the accurate MS n spectral information of diagnostic fragment ions. In this work, we used such strategies for the identification of the parent compounds and metabolites of crude and processed Fructus Corni in rats, and seven parent compounds and three new metabolites of Fructus Corni were found in rats for the first time. This study provides important structural information regarding to the metabolism of crude Fructus Corni and its JZP. Furthermore, this work also demonstrated the possibilities of using microdialysis sampling coupled with LC–MS n approach for identification of bioactive compounds from TCM in vivo.

DNA Adduct Formation of 4-Aminobiphenyl and Heterocyclic Aromatic Amines in Human Hepatocytes

DNA adduct formation of the aromatic amine, 4-aminobiphenyl (4-ABP), a known human carcinogen present in tobacco smoke, and the heterocyclic aromatic amines (HAAs), 2-amino-9H-pyrido[2,3-b]indole (AαC), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), potential human carcinogens, which are also present in tobacco smoke or formed during the high-temperature cooking of meats, was investigated in freshly cultured human hepatocytes. The carcinogens (10 μM) were incubated with hepatocytes derived from eight different donors for time periods up to 24 h. The DNA adducts were quantified by liquid chromatography-electrospray ionization mass spectrometry with a linear quadrupole ion trap mass spectrometer. The principal DNA adducts formed for all of the carcinogens were N-(deoxyguanosin-8-yl) (dG-C8) adducts. The levels of adducts ranged from 3.4 to 140 adducts per 10(7) DNA bases. The highest level of adduct formation occurred with AαC, followed by 4-ABP, then by PhIP, MeIQx, and IQ. Human hepatocytes formed dG-C8-HAA-adducts at levels that were up to 100-fold greater than the amounts of adducts produced in rat hepatocytes. In contrast to HAA adducts, the levels of dG-C8-4-ABP adduct formation were similar in human and rat hepatocytes. These DNA binding data demonstrate that the rat, an animal model that is used for carcinogenesis bioassays, significantly underestimates the potential hepatic genotoxicity of HAAs in humans. The high level of DNA adducts formed by AαC, a carcinogen produced in tobacco smoke at levels that are up to 100-fold higher than the amounts of 4-ABP, is noteworthy. The possible causal role of AαC in tobacco-associated cancers warrants investigation.

Rapid quantification of four major bioactive alkaloids in Corydalis decumbens (Thunb.) Pers. by pressurised liquid extraction combined with liquid chromatography-triple quadrupole linear ion trap mass spectrometry

A new method based on pressurised liquid extraction (PLE) followed by liquid chromatography–triple quadrupole linear ion trap mass spectrometry (LC–QTrap-MS) analysis has been developed for the identification and quantification of four major alkaloids in extracts of Corydalis decumbens (Thunb.) Pers. PLE extractions were performed using 90% ethanol; temperature was set at 100°C and pressure at 1500psi. HPLC analysis was performed on a Waters XBridge™ C18 column (150mm×2.1mm i.d., 3.5μm) eluted by a mobile phase of acetonitrile and 0.2% acetic acid. Data acquisition was carried out in multiple reaction monitoring transitions (MRMs) mode, monitoring two MRM transitions to ensure an accurate identification of target compounds in the samples. Additional identification and confirmation of target compounds were performed using the enhanced product ion modus (EPI) of the linear ion trap. The novel LC–QTrap-MS platform offers the best sensitivity and specificity for characterization and quantitative determination of the four alkaloids in C. decumbens (Thunb.) Pers. and fulfils the quality criteria for routine laboratory application.

Differentiation of Regioisomeric Aromatic Ketocarboxylic Acids by Positive Mode Atmospheric Pressure Chemical Ionization Collision-Activated Dissociation Tandem Mass Spectrometry in a Linear Quadrupole Ion Trap Mass Spectrometer

Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS(n)) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer. Energy-resolved collision-activated dissociation (CAD) experiments carried out on the protonated analytes revealed fragmentation patterns that varied based on the location of the functional groups. Unambiguous differentiation between the regioisomers was achieved in each case by observing different fragmentation patterns, different relative abundances of ion-molecule reaction products, or different relative abundances of fragment ions formed at different collision energies. The mechanisms of some of the reactions were examined by H/D exchange reactions and molecular orbital calculations.

Comparison of Functional Group Selective Ion–Molecule Reactions of Trimethyl Borate in Different Ion Trap Mass Spectrometers

We report here a comparison of the use of diagnostic ion-molecule reactions for the identification of oxygen-containing functional groups in Fourier-transform ion cyclotron resonance (FTICR) and linear quadrupole ion trap (LQIT) mass spectrometers. The ultimate goal of this research is to be able to identify functionalities in previously unknown analytes by using many different types of mass spectrometers. Previous work has focused on the reactions of various boron reagents with protonated oxygen-containing analytes in FTICR mass spectrometers. By using a LQIT modified to allow the introduction of neutral reagents into the helium buffer gas, this methodology has been successfully implemented to this type of an ion trap instrument. The products obtained from the reactions of trimethyl borate (TMB) with various protonated analytes are compared for the two instruments. Finally, the ability to integrate these reactions into LC-MS experiments on the LQIT is demonstrated.

Laser-induced acoustic desorption/atmospheric pressure chemical ionization mass spectrometry.

Laser-induced acoustic desorption (LIAD) was successfully coupled to a conventional atmospheric pressure chemical ionization (APCI) source in a commercial linear quadrupole ion trap mass spectrometer (LQIT). Model compounds representing a wide variety of different types, including basic nitrogen and oxygen compounds, aromatic and aliphatic compounds, as well as unsaturated and saturated hydrocarbons, were tested separately and as a mixture. These model compounds were successfully evaporated into the gas phase by using LIAD and then ionized by using APCI with different reagents. From the four APCI reagent systems tested, neat carbon disulfide provided the best results. The mixture of methanol and water produced primarily protonated molecules, as expected. However, only the most basic compounds yielded ions under these conditions. In sharp contrast, using APCI with either neat benzene or neat carbon disulfide as the reagent resulted in the ionization of all the analytes studied to predominantly yield stable molecular ions. Benzene yielded a larger fraction of protonated molecules than carbon disulfide, which is a disadvantage. A similar but minor amount of fragmentation was observed for these two reagents. When the experiment was performed without a liquid reagent (nitrogen gas was the reagent), more fragmentation was observed. Analysis of a known mixture as well as a petroleum cut was also carried out. In summary, the new experiment presented here allows the evaporation of thermally labile compounds, both polar and nonpolar, without dissociation or aggregation, and their ionization to predominantly form stable molecular ions.