The importance of both charge exchange and proton transfer in the analysis of polycyclic aromatic compounds using atmospheric pressure chemical ionization mass spectrometry

The feasibility of atmospheric pressure chemical ionization (APCI) as an alternative ionization technique for capillary electrophoresis-mass spectrometry (CE-MS) was investigated using a grounded sheath-flow CE-MS sprayer and an orthogonal APCI source. Infusion experiments indicated that highest analyte signals were achieved when the sprayer tip was in close vicinity of the vaporizer entrance. The APCI-MS set-up enabled detection of basic, neutral, and acidic compounds, whereas apolar and ionic compounds could not be detected. In the positive ion mode, analytes could be detected in the entire transfer voltage range (0 -5 kV), whereas highest signal intensities were observed when the corona discharge current was between 1000 and 2000 nA. In the negative ion mode, the transfer voltage typically was 500 V and the optimum corona discharge current was 6000 nA. Analyte signals were raised with increasing nebulizing gas pressure, but the pressure was limited to 25 psi to avoid siphoning and current drops. Signal intensities appeared to be optimal and constant over a wide range of sheath liquid flow rate (5-25 L/min) and vaporizer temperature (200 -350°C). APCI-MS signals were unaffected by the composition of the background electrolyte (BGE), even when it contained sodium phosphate and sodium dodecyl sulfate (SDS). Consequently, BGE composition, sheath-liquid flow rate, and vaporizer temperature can be optimized with respect to the CE separation without affecting the APCI-MS response. The analysis of a mixture of basic compounds and a steroid using volatile and nonvolatile BGEs further demonstrates the feasibility of CE-APCI-MS. Detection limits (S/N ϭ 3) were 1.6 -10 M injected concentrations. (J Am Soc Mass

Section: Corona Current and Transfer Voltagementioning

confidence: 99%

Capillary electrophoresis-atmospheric pressure chemical ionization-mass spectrometry using an orthogonal interface: Set-up and system parameters

Hommerson

Khan

Jong

et al. 2009

“…The observation that ionization efficiency differs markedly among solvents argues against both significant amounts of direct analyte ionization in the discharge, Reaction (7), or analyte ionization by collision with a high-energy nitrogen ion, Reaction (8), even though such ionization is highly energetically favored. If either were the case, analyte ionization would be independent of solvent.…”

Section: Formation Of Analyte Molecular Ions a ϩ·mentioning

confidence: 99%

“…Gas chromatography (GC) and GC coupled with electron ionization (EI) mass spectrometry (GC/ MS) are normally employed for samples containing robust, thermally stable analytes [4,5]. Atmospheric pressure ionization methods [6]-electrospray ionization (ESI) [7], atmospheric pressure chemical ionization (APCI) [8], and atmospheric pressure photoionization (APPI) [9]-in conjunction with liquid chromatography (LC) have been used for samples of more problematic analytes.It is generally believed that ESI suffers more from nonlinear response and matrix effects than APCI. Linear response over a wide concentration range is an attractive feature of APCI and has been reported by several authors [10,11].…”

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confidence: 99%

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confidence: 99%

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Quantitative aspects of and ionization mechanisms in positive-ion atmospheric pressure chemical ionization mass spectrometry

Herrera

Grossert

Ramaley

2008

Self Cite

The behavior in atmospheric pressure chemical ionization of selected model polycyclic aromatic compounds, pyrene, dibenzothiophene, carbazole, and fluorenone, was studied in the solvents acetonitrile, methanol, and toluene. Relative ionization efficiency and sensitivity were highest in toluene and lowest in methanol, a mixture of molecular ions and protonated molecules was observed in most instances, and interferences between analytes were detected at higher concentrations. Such interferences were assumed to be caused by a competition among analyte molecules for a limited number of reagent ions in the plasma. The presence of both molecular ions and protonated analyte molecules can be attributed to charge-transfer from solvent radical cations and proton transfer from protonated solvent molecules, respectively. The order of ionization efficiency could be explained by incorporating the effect of solvation in the ionization reactions. Thermodynamic data, both experimental and calculated theoretically, are presented to support the proposed ionization mechanisms. The analytical implications of the results are that using acetonitrile (compared with methanol) as solvent will provide better sensitivity with fewer interferences (at low concentrations), except for analytes having high gas-phase basicities. (J Am Soc Mass Spectrom 2008, 19, 1926 -1941) © 2008 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry T he analysis of polycyclic aromatic compounds (PACs) in petroleum and environmental samples has been the subject of many investigations [1-3], due to their impact on the environment, refining processes, and product quality. However, success is often hindered by the number and low concentration of these compounds in such samples, as well as by the lack of standards. Gas chromatography (GC) and GC coupled with electron ionization (EI) mass spectrometry (GC/ MS) are normally employed for samples containing robust, thermally stable analytes [4,5]. Atmospheric pressure ionization methods [6]-electrospray ionization (ESI) [7], atmospheric pressure chemical ionization (APCI) [8], and atmospheric pressure photoionization (APPI) [9]-in conjunction with liquid chromatography (LC) have been used for samples of more problematic analytes.It is generally believed that ESI suffers more from nonlinear response and matrix effects than APCI. Linear response over a wide concentration range is an attractive feature of APCI and has been reported by several authors [10,11]. Recently, Roussis and Fedora compared the ability of APCI and ESI to quantify polar and ionic compounds in petroleum products [12]. They obtained linear ranges of three orders of magnitude for both techniques, and higher sensitivity for ESI. However, the ESI response was nonlinear over the concentration range of interest, and they recommended the use of APCI for quantitative LC/MS applications.In the course of a study of the application of APCI to the analysis of nitrogen-and particularly sulfurcontaining PACs in petroleum samples, we observe...

“…The most common approach utilizes collision-activation dissociation (CAD) to generate structurally characteristic fragmentation patterns. This is sometimes carried out in an energyresolved manner in order to obtain more detailed structural information [9,[12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

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

Amundson

Owen

Gallardo

et al. 2011

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.