Pressure Photoionization Mass Spectrometry Research Articles

Laser ablation atmospheric pressure photoionization mass spectrometry imaging of phytochemicals from sage leaves.

Despite fast advances in ambient mass spectrometry imaging (MSI), the study of neutral and nonpolar compounds directly from biological matrices remains challenging. In this contribution, we explore the feasibility of laser ablation atmospheric pressure photoionization (LAAPPI) for MSI of phytochemicals in sage (Salvia officinalis) leaves. Sage leaves were studied by LAAPPI-time-of-flight (TOF)-MSI without any sample preparation. Leaf mass spectra were also recorded with laser ablation electrospray ionization (LAESI) mass spectrometry and the spectra were compared with those obtained by LAAPPI. Direct probing of the plant tissue by LAAPPI efficiently produced ions from plant metabolites, including neutral and nonpolar terpenes that do not have polar functional groups, as well as oxygenated terpene derivatives. Monoterpenes and monoterpenoids could also be studied from sage by LAESI, but only LAAPPI was able to detect larger nonpolar compounds, such as sesquiterpenes and triterpenoid derivatives, from the leaf matrix. Alternative MSI methods for nonpolar compounds, such as desorption atmospheric pressure photoionization (DAPPI), do not achieve as good spatial resolution as LAAPPI (<400 µm). We show that MSI with LAAPPI is a useful tool for concurrently studying the distribution of polar and nonpolar compounds, such as phytochemicals, directly from complex biological samples, and it can provide information that is not available by other, established methods.

The formation of [M-H]+ ions in N-alkyl-substituted thieno[3,4-c]-pyrrole-4,6-dione derivatives during atmospheric pressure photoionization mass spectrometry.

The formation of ions during atmospheric pressure photoionization (APPI) mass spectrometry in the positive mode usually provides radical cations and/or protonated species. Intriguingly, during the analysis of some N-alkyl-substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) derivatives synthesized in our laboratory, unusual [M-H](+) ion peaks were observed. In this work we investigate the formation of [M-H](+) ions observed under APPI conditions. Multiple experimental parameters, including the type of ionization source, the composition of the solvent, the type of dopant, the infusion flow rate, and the length of the alkyl side chain were investigated to determine their effects on the formation of [M-H](+) ions. In addition, a comparison study of the gas-phase tandem mass spectrometric (MS/MS) fragmentation of [M + H](+) vs [M-H](+) ions and computational approaches were used. [M-H](+) ions were observed under APPI conditions. The type of dopant and the length of the alkyl chain affected the formation of these ions. MS/MS fragmentation of [M-H](+) and [M + H](+) ions exhibited completely different patterns. Theoretical calculations revealed that the loss of hydrogen molecules from the [M + H](+) ions is the most favourable condition under which to form [M-H](+) ions. [M-H](+) ions were detected in all the TPD derivatives studied here under the special experimental conditions during APPI, using a halogenated benzene dopant, and TPD containing substituted N-alkyl side chains with a minimum of four carbon atoms. Density functional theory calculations showed that for [M-H](+) ions to be formed under these conditions, the loss of hydrogen molecules from the [M + H](+) ions is proposed to be necessary.

Analysis of oxysterols and vitamin D metabolites in mouse brain and cell line samples by ultra-high-performance liquid chromatography-atmospheric pressure photoionization–mass spectrometry

We have developed an ultra-high-performance liquid chromatography-atmospheric pressure photoionization-tandem mass spectrometric (UHPLC-APPI–MS/MS) method for the simultaneous quantitative analyses of several oxysterols and vitamin D metabolites in mouse brain and cell line samples. An UHPLC-APPI-high resolution mass spectrometric (UHPLC-APPI-HRMS) method that uses a quadrupole-time of flight mass spectrometer was also developed for confirmatory analysis and for the identification of non-targeted oxysterols. Both methods showed good quantitative performance. Furthermore, APPI provides high ionization efficiency for determining oxysterols and vitamin D related compounds without the time consuming derivatization step needed in the conventionally used electrospray ionization method to achieve acceptable sensitivity. Several oxysterols were quantified in mouse brain and cell line samples. Additionally, 25-hydroxyvitamin D3 was detected in mouse brain samples for the first time.

Analysis of C60-fullerene derivatives and pristine fullerenes in environmental samples by ultrahigh performance liquid chromatography–atmospheric pressure photoionization-mass spectrometry

In this work, a method is proposed for the simultaneous analysis of several pristine fullerenes (C60, C70, C76, C78, and C84) and three C60-fullerene derivatives (N-methyl fulleropyrrolidine, [6,6]-phenyl C61 butyric acid methyl ester and [6,6]-phenyl C61 butyric acid butyl ester) in environmental samples. The method involves the use of ultrahigh performance liquid chromatography coupled to atmospheric pressure photoionization mass spectrometry (UHPLC–APPI-MS) and allowed the chromatographic separation in less than 4.5min. The product ions from tandem mass spectrometry studies of fullerene derivatives were characterized and the most abundant one (m/z 720), corresponding to [C60]−, was selected for quantitation. Selected reaction monitoring (SRM at 0.7m/z FWHM) by acquiring two transitions using both isotopic cluster ions [M]− and [M+1]− as precursor ions was proposed for quantitation and confirmation purposes. For pristine fullerenes, highly selective selected ion monitoring (H-SIM) acquisition mode by monitoring the isotopic cluster ions [M]− and [M+1]− was used. Pressurized solvent extraction conditions were optimized in order to improve recoveries of the studied fullerene compounds from sediment samples. Values up to 87–92% for C60-fullerene derivatives and lower but still acceptable, 70–80%, for pristine fullerenes were obtained. Method limits of quantitation (MLOQs) ranging from 1.5pgL−1 to 5.5ngL−1 in water samples and from 0.1ngkg−1 to 523ngkg−1 in sediments were obtained with good precision (relative standard deviations always lower than 13%). The applicability of the developed method was evaluated by analyzing several environmental samples such as sediments and pond water and the detected levels for C60-fullerene derivatives were of 0.1–2.7ngkg−1 and 1.5–8.5pgL−1, respectively. C60 and C70 were the only pristine fullerenes detected in the analyzed samples (0.1–7.2ngkg−1 in sediments and 9–330pgL−1 in water pond samples).

Application of a novel metabolomic approach based on atmospheric pressure photoionization mass spectrometry using flow injection analysis for the study of Alzheimer׳s disease

The use of atmospheric pressure photoionization is not widespread in metabolomics, despite its considerable potential for the simultaneous analysis of compounds with diverse polarities. This work considers the development of a novel analytical approach based on flow injection analysis and atmospheric pressure photoionization mass spectrometry for rapid metabolic screening of serum samples. Several experimental parameters were optimized, such as type of dopant, flow injection solvent, and their flows, given that a careful selection of these variables is mandatory for a comprehensive analysis of metabolites. Toluene and methanol were the most suitable dopant and flow injection solvent, respectively. Moreover, analysis in negative mode required higher solvent and dopant flows (100µlmin−1 and 40µlmin−1, respectively) compared to positive mode (50µlmin−1 and 20µlmin−1). Then, the optimized approach was used to elucidate metabolic alterations associated with Alzheimer׳s disease. Thereby, results confirm the increase of diacylglycerols, ceramides, ceramide-1-phosphate and free fatty acids, indicating membrane destabilization processes, and reduction of fatty acid amides and several neurotransmitters related to impairments in neuronal transmission, among others. Therefore, it could be concluded that this metabolomic tool presents a great potential for analysis of biological samples, considering its high-throughput screening capability, fast analysis and comprehensive metabolite coverage.

Changes in proximate composition and oil characteristics during flaxseed development

Atmospheric Pressure Photoionization-Mass Spectrometry (APPI-MS) and High Performance Liquid Chromatography (HPLC) are the two analytical methods that were used to characterize Triacylglycerols (TAGs) during flaxseed development. The HPLC method of the oils showed the presence of 15 TAG species. In contrast to the HPLC chromatograms, the APPI-MS showed 17 peaks of TAG. APPI-MS is more rapid than the HPLC method (11 min). The iodine value of the oils showed a gradual increase, while the oil stability continuously decreased. Proximate composition during flaxseed development revealed that flaxseed is potentially a good source of dietary energy and protein. At full maturity, flaxseed contained 37% oil and 24% protein on a dry-weight basis; albumin was the major storage protein (53% of total storage proteins) followed by globulin (33%) and glutelin fractions (11%). Prolamins had the lowest percentage with 3%. α-amylase activity was higher in the mature seeds than the young ones.

Analysis of the Products from the Oxidation of Geting Bituminous Coal by Atmospheric Pressure Photoionization–Mass Spectrometry

Geting bituminous coal was directly oxidized in aqueous sodium hypochlorite. The reaction mixture was sequentially extracted with ethyl ether and ethyl acetate. Both extracts were esterified with diazomethane to obtain methyl esterified products, which were analyzed using high performance liquid chromatography–mass spectrometry with electrospray ionization or atmospheric pressure photoionization. A large number of low- and nonpolar products with relatively high molecular masses were determined using atmospheric pressure photoionization mass spectrometry. Toluene and a toluene/anisole mixture (vol/vol = 95:5) were added to the atmospheric pressure photoionization system as dopants. Toluene induced better ionization than the toluene/anisole mixture in both ion signal intensity and number of detected species. Most of the molecular associated compounds contained heteroatoms.

Atmospheric Pressure Photo Ionization Hydrogen/Deuterium Exchange Mass Spectrometry—a Method to Differentiate Isomers by Mass Spectrometry

In this report, a method for in-source hydrogen/deuterium (H/D) exchange at atmospheric pressure is reported. The method was named atmospheric pressure photo ionization hydrogen/deuterium exchange mass spectrometry (APPI HDX MS). H/D exchange was performed by mixing samples dissolved in toluene with CH3OD solvent and analyzing the mixture using atmospheric pressure photo ionization mass spectrometry (APPI-MS). The APPI HDX spectra obtained with contact times between the analyte solution and methanol-OD (CH3OD) of < 0.5 s or 1 h showed the same pattern of H/D exchange. Therefore, it was concluded that APPI HDX occurred in the source but not in the solution. The proposed method does not require a specific type of mass spectrometer and can be performed at atmospheric pressure. H/D exchange can be performed in any laboratory with a mass spectrometer and a commercial APPI source. Using this method, multiple H/D exchanges of aromatic hydrogen and/or H/D exchange of active hydrogen were observed. These results demonstrated that H/D exchange can be used to distinguish between isomers containing primary, secondary, and tertiary amines, as well as pyridine and pyrrole functional groups.

Analysis of anabolic steroids in urine by gas chromatography–microchip atmospheric pressure photoionization-mass spectrometry with chlorobenzene as dopant

A gas chromatography–microchip atmospheric pressure photoionization-tandem mass spectrometry (GC–μAPPI-MS/MS) method was developed for the analysis of anabolic androgenic steroids in urine as their trimethylsilyl derivatives. The method utilizes a heated nebulizer microchip in atmospheric pressure photoionization mode (μAPPI) with chlorobenzene as dopant, which provides high ionization efficiency by producing abundant radical cations with minimal fragmentation. The performance of GC–μAPPI-MS/MS was evaluated with respect to repeatability, linearity, linear range, and limit of detection (LOD). The results confirmed the potential of the method for doping control analysis of anabolic steroids. Repeatability (RSD<10%), linearity (R2≥0.996) and sensitivity (LODs 0.05–0.1ng/mL) were acceptable. Quantitative performance of the method was tested and compared with that of conventional GC–electron ionization-MS, and the results were in good agreement.

Liquid chromatography–dopant‐assisted atmospheric pressure photoionization–mass spectrometry: Application to the analysis of aldehydes in atmospheric aerosol particles

A complete methodology based on LC-anisole-toluene dopant-assisted atmospheric pressure photoionization-IT-MS was developed for the determination of aldehydes in atmospheric aerosol particles. For the derivatization, ultrasound was used to accelerate the reaction between the target analytes and 2,4-dinitrophenylhydrazine. The developed methodology was validated for three different samples, gas phase, ultrafine (Dp = 30 ± 4 nm; where Dp stands for particle diameter) and all-sized particles, collected on Teflon filters. The method quantitation limits ranged from 5 to 227 pg. The accuracy and the potential matrix effects were evaluated using standard addition methodology. Recoveries ranged between 91.7 and 109.9%, and the repeatability and the reproducibility of the method developed between 0.5 and 8.0% and between 2.9 and 11.1%, respectively. The results obtained by the developed methodology compared to those provided by the previously validated method revealed no statistical differences. The method developed was applied to the determination of aldehydes in 16 atmospheric aerosol samples (30 nm and all-sized samples) collected at the Station for Measuring Forest Ecosystem-Atmosphere Relations II during spring 2011. The mean concentrations of aldehydes, and oxidation products of terpenes were between 0.05 and 82.70 ng/m(3).

Direct analysis of cannabis samples by desorption atmospheric pressure photoionization‐mass spectrometry

Fast analysis of cannabis samples without prior sample preparation or chromatography was performed using desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). The MS(2) spectra of the molecular ions of tetrahydrocannabinol (THC) and cannabidiol (CBD) formed in DAPPI-MS showed distinct product ions, unlike the protonated molecules formed with other ambient mass spectrometry techniques, making possible the reliable identification of THC from cannabis samples.

New approach to complex organic compounds mixtures analysis based on gas chromatography–atmospheric pressure photoionization–mass-spectrometry

The mass-spectra of a number of different hydrocarbons were obtained using atmospheric pressure photoionization (APPhI) and photochemical ionization (APPhCI) mass-spectrometry. The respective mass-spectra consisted mainly of molecular (M+) or quasimolecular (MH+) ion peaks or both. The composition of aromatic hydrocarbons in straight-run gasoline was investigated using standard PIONA method, based on capillary GC and retention time indexes, and GC/MS (APPhI). 56 aromatic hydrocarbons were identified using GC/MS (APPhI) and 43-using standard PIONA method. The opportunities of MS (APPHCI) for determination of impurities in pure hydrocarbons and for direct analysis of complex mixtures without separation were demonstrated when MS (APPhCI) analysis for GC standards of benzene and toluene was carried out (main component vapor was reagent gas). The targeted PAHs and phtalates were registered selectively in 44 component model mixture of semivolatiles with partial or without separation of the components, using GC/MS (APPhI).

Atmospheric pressure photoionization mass spectrometry as a valuable method for the identification of polyisoprenoid alcohols

The aim of this study was to determine whether Atmospheric Pressure Photoionization (APPI) was better suited for the mass spectrometric (MS) analysis of polyisoprenoid alcohols than the commonly used Electrospray Ionization (ESI) method. The APPI method should make possible the use of non-polar solvents without any of the additives required by ESI, together with improved detection limits. The liquid chromatography (LC)/APPI-MS and LC/ESI-MS spectra of polyisoprenoid alcohol standards were acquired in both positive and negative ion mode, in methanol and hexane, using a triple quadrupole/linear ion trap tandem mass spectrometer equipped with both an ESI and an APPI ion source. In the positive ion mode peaks corresponding to [M + H - H(2)O](+) and [M + H](+) ions were observed in the APPI-MS spectra of polyprenols and dolichols, respectively. In the negative ion mode peaks corresponding to [M + O(2)](-•) and [M + Cl](-) ions were observed for both classes of polyisoprenoid alcohols. The detection limit of polyisoprenoid alcohols was established at the level of 10 pg. APPI turned out to be a method of choice for the identification and quantitation of polyisoprenoid alcohols by MS using both polar and non-polar solvents. APPI also enabled greater differentiation of polyprenols and dolichols occurring together in natural samples and gave much better TIC chromatograms without the need for the post-column salt addition required by ESI.

Multicomponent mixed dopant optimization for rapid screening of polycyclic aromatic hydrocarbons using ultra high performance liquid chromatography coupled to atmospheric pressure photoionization high‐resolution mass spectrometry

To enhance the ionization efficiencies in atmospheric pressure photoionization mass spectrometry a dopant with favorable ionization energy such as chlorobenzene is typically used. These dopants are typically toxic and difficult to mix with water-soluble organic solvents. In order to achieve a more efficient and less toxic dopant, a multicomponent mixed dopant was explored. A multicomponent mixed dopant for non-targeted rapid screening of polycyclic aromatic hydrocarbons (PAHs) was developed and optimized using ultra high performance liquid chromatography (UPLC) coupled to atmospheric pressure photoionization high-resolution mass spectrometry. Various single and multicomponent mixed dopants consisting of ethanol, chlorobenzene, bromobenzene, anisole and toluene were evaluated. Fourteen out of eighteen PAHs were successfully separated and detected at low pg/μL levels within 5 min with high mass accuracy ≤4 ppm. The optimal mixed multicomponent dopant consisted of ethanol/chlorobenzene/bromobenzene/anisole (98.975:0.1:0.9:0.025, v/v %) and it improved the limit of detection (LOD) by 2- to 10-fold for the tested PAHs compared to those obtained with pure chlorobenzene. A novel multicomponent dopant that contains 99% ethanol and 1% mixture of chlorobenzene, bromobenzene and anisole was found to be an effective dopant mixture to ionize PAHs. The developed UPLC multicomponent dopant assisted atmospheric pressure photoionization high-resolution mass spectrometry offered a rapid non targeted screening method for detecting the PAHs at low pg/μL levels within a 5 min run time with high mass accuracy ≤4 ppm.

Comparison of Direct and Alternating Current Vacuum Ultraviolet Lamps in Atmospheric Pressure Photoionization

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production.

Changes in the triacylglycerol content of flaxseeds during development using liquid chromatography- atmospheric pressure photoionization-mass spectrometry (LC-APPI-MS)

Changes in the triacylglycerol content of flaxseeds during development using liquid chromatography- atmospheric pressure photoionization-mass spectrometry (LC-APPI-MS)

Ultra high performance liquid chromatography–atmospheric pressure photoionization-mass spectrometry for high-sensitivity analysis of US Environmental Protection Agency sixteen priority pollutant polynuclear aromatic hydrocarbons in oysters

In response to Gulf of Mexico deepwater horizon oil spill, we have developed an atmospheric pressure photoionization (APPI) based ultra high performance liquid chromatography–mass spectrometry (UHPLC–MS) method for high-sensitivity analysis of United States Environmental Protection Agency (US EPA) 16 priority pollutant polynuclear aromatic hydrocarbons (PAHs) in oysters. Analyses were performed on an Agilent's Infinity 1290 UHPLC system coupled with a G6140A single quadrupole MS detector with Syagen's PhotoMate® APPI® source. Column separation was achieved using Zorbax Eclipse PAH column. Chlorobenzene was used as an APPI dopant for maximum overall sensitivity. Dynamic linear ranges were evaluated and found to cover 3.6–5.1 (Ave. 4.4) orders of magnitude with R2 of at least 0.995. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and cleanup procedure was used. The spike recoveries ranged from 77% to 110% with %RSD of 0.6–6.7 at spike concentrations below or substantially below the US Food and Drug Administration (FDA) level of concern in oysters. The on-column instrument detection limits (IDLs, 6σ S/N=3) ranged from 8 to 106pg with an average of 23pg for 16 PAHs. The method detection limits (MDLs, 6σ S/N=3) ranged from 0.013 to 0.129ppm with an average of 0.040ppm for all analytes. These MDLs were about 5 times to over 4 orders of magnitude lower than US FDA levels of concern in oysters.

Trimethoxyarene as a Highly Ionizable Tag for Reaction Analysis by Atmospheric Pressure Photoionization Mass Spectrometry (APPI/MS): Exploration of Heterocyclic Synthesis

AbstractA mass spectrometry (MS) method was developed to rapidly analyze crude reaction mixtures. This method relies on highly effective ionization by atmospheric pressure photoionization (APPI) of molecules with a prosthetic trimethoxyarene (TMOA) residue. In a crude reaction mixture, products resulting from the reaction of the TMOA‐labeled substrate will be selectively ionized to afford an easily readable mass spectrum. Interestingly, we noticed that TMOA‐labeled molecules were not fragmented and gave the preferred [M + H]+ ion peak. This APPI‐MS reaction mixture analysis method was used for the optimization of heterocycle synthesis. By comparing results obtained by APPI/MS, GC, and HPLC analysis, it appeared that a semi‐quantification could be achieved by integrating the MS peak intensities.

Cutaneous water loss and lipids of the stratum corneum in two syntopic species of bats

The lipid matrix of the stratum corneum (SC), the outer layer of the epidermis of mammals and birds, constitutes the barrier to diffusion of water vapor through the skin. The lipids of the SC are structured in the intercellular spaces of the mammalian epidermis in ordered layers, called lamellae, which have been postulated to prevent water loss. Lipids in the mammalian SC are mainly cholesterol, free fatty acids and ceramides, the latter forming the structural support for the lamellae. However, knowledge on how the lipid composition of the SC alters cutaneous water loss (CWL) in mammals is rudimentary, and is largely derived from studies on laboratory animals and humans. We measured CWL of individuals of two species of syntopic bats, Tadarida brasiliensis and Myotis velifer. In the first study of its kind on wild mammals, we correlated CWL with the lipid composition of the SC, measured using thin layer chromatography and high performance liquid chromatography coupled with atmospheric pressure photoionization mass spectrometry. Surface-specific CWL was 20.6% higher in M. velifer than in T. brasiliensis, although differences were not significant. Compared with individuals of M. velifer, individuals of T. brasiliensis had more classes, and a higher proportion, of polar ceramides in the SC, a feature associated with lower CWL. Individuals of T. brasiliensis also had a class of non-polar ceramides that presumably spans the lamellae and gives more cohesiveness to the lipid matrix of the SC. We conclude that qualitative and quantitative modifications of the lipid composition of the SC contribute to regulate CWL of these two species of bats.

Analysis of Indigo-type compounds in natural dyes by negative ion atmospheric pressure photoionization mass spectrometry

Atmospheric Pressure Photoionization (APPI) in Mass Spectrometry (MS) has been utilized for a number of indigo-related compounds and was found to exhibit an excellent response. All structures were ionized in negative ion mode yielding almost exclusively deprotonated molecules. Their product ion mass spectra were also recorded and showed characteristic losses mainly of small neutrals such as CO, HBr and CONH 2. APPI-MS was applied further to the analysis of indigo dyestuffs of historical importance. HPLC with single ion monitoring (SIM) was employed for the separation and detection of the compounds. A simple HPLC gradient that separated the components in less than 10 min was developed. MS/MS spectra of the colouring components were also recorded and compared to that of the reference substances. The composition of Tyrian purple originating from Murex trunculus ( Hexaplex trunculus), was by far the most complex, whereas some of the structures were also detected in Purpura haemastoma ( Stramonita haemastoma) and Plicopurpura pansa ( Plicopurpura patula subs. pansa). Further, a number of synthetic indigo dyes, produced at different times of the 19thcentury by different manufacturers, were analyzed; similar spectra were obtained suggesting that these were highly pure. Overall, the developed analytical procedure was very efficient offering high sensitivity and selectivity. APPI was proved suitable for ionizing the species under investigation producing clear mass spectra with characteristic fragment ions and may be used successfully in the future for the characterization of similar structures in historical art objects.