Pressure Ion Source Research Articles

Energy‐resolved mass spectrometry: a comparison of quadrupole cell and cone‐voltage collision‐induced dissociation

Collision-induced dissociation (CID) can be effected in the interface region between atmospheric pressure ionization sources and single quadrupole mass analyzers. By varying the electric field in these cone-voltage CID experiments energy-resolved mass spectra can be obtained leading to breakdown graphs exploring the energy evolution of the fragmentation pathways. The breakdown graphs obtained from these cone-voltage CID studies are very comparable to those obtained by varying the collision energy in the quadrupole collision cell of a BEqQ mass spectrometer. The comparison has been made for the protonated peptides H-Leu-Gly-Gly-OH, H-Gly-Leu-Gly-OH, H-Gly-Gly-Leu-OH and Leu-enkephalin Copyright © 1999 John Wiley & Sons, Ltd.

Energy-resolved mass spectrometry: a comparison of quadrupole cell and cone-voltage collision-induced dissociation.

Collision-induced dissociation (CID) can be effected in the interface region between atmospheric pressure ionization sources and single quadrupole mass analyzers. By varying the electric field in these cone-voltage CID experiments energy-resolved mass spectra can be obtained leading to breakdown graphs exploring the energy evolution of the fragmentation pathways. The breakdown graphs obtained from these cone-voltage CID studies are very comparable to those obtained by varying the collision energy in the quadrupole collision cell of a BEqQ mass spectrometer. The comparison has been made for the protonated peptides H-Leu-Gly-Gly-OH, H-Gly-Leu-Gly-OH, H-Gly-Gly-Leu-OH and Leu-enkephalin

Evaluation of a dual electrospray ionization/atmospheric pressure chemical ionization source at low flow rates (∼50 μl/min) for the analysis of both highly and weakly polar compounds

The atmospheric pressure ionization (API) source for a commercial mass spectrometer was modified to operate as a dual source in both the electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) techniques by simultaneously utilizing the electrospray probe and the corona discharge needle. A switching box was designed to operate in either manual or programmable modes to permit rapid switching between ionization techniques without changing sources, probes, or breaking vacuum. The source can be operated using the following ionization techniques: ESI only, APCI only, ESI/APCI simultaneously, and ESI/APCI alternatingly. The optimum operating conditions for these ionization techniques were similar to the manufacturer’s original specifications except that the APCI flow rate was lower (∼50 μL/min versus 1000 μL/min) and externally heated nebulizing gas was found to be desirable. A four-component mixture, introduced by flow injection, was used to demonstrate the versatility of the dual ESI/APCI source.

Detection of a thermally unstable intermediate in the Wittig reaction using low-temperature liquid secondary ion and atmospheric pressure ionization mass spectrometry

The signal of an extremely air sensitive and thermally unstable intermediate, four-membered ring oxaphosphetane in the Wittig reaction was detected for the first time at subambient temperature using liquid secondary ion mass spectrometry (LSIMS) and atmospheric pressure ionization (API) mass spectrometry. A copper probe and interface were constructed to perform LSIMS analysis at the temperature below −70 °C. A stable signal from a oxaphosphetane ion [in dry tetrahydrofolate (THF)] was obtained by LSIMS without using a viscous matrix. The signal of the oxaphosphetane was also detected using a low-temperature API source (−40 °C) connected to a reaction vessel.

Detection of reactive 1,2,3-hexatriene-5-one monomer by low-temperature atmospheric pressure ionization mass spectrometry

This study detected the extremely reactive carbenoid, 1,2,3-hexatriene-5-one (HTO), by low-temperature atmospheric pressure ionization (API) mass spectrometry. During the analysis the sample solution was maintained at −78 °C in the API source to prevent the analyte molecule from polymerizing. At this low temperature a strong protonated HTO signal was detected. At room temperature the compound polymerized rapidly and the mass spectrum was dominated by dimer ions. Signals due to protonated HTO- (H2O)2 adducts were also detected, and can possibly be attributed to trace water in the organic solvent, or to ionization of the moisture as in atmospheric pressure chemical ionization. © 1998 John Wiley & Sons, Ltd.

Ion-spray mass spectrometry for identification of the nonreducing terminal sugar of glycosaminoglycan.

Various oligosaccharides from hyaluronic acid, which have glucuronic acid or N- acetylglucosamine at the nonreducing terminal, were prepared by digestion with a combination of testicular hyaluronidase and beta-glucuronidase. These oligo saccharides were analyzed by negative-mode ion-spray mass spectrometry (MS) with an atmospheric pressure ion source. Introduction of collisionally activated dissociation tandem mass spectrometry (CAD-MS/MS) produced ions derived from cleavage of the glycosidic bonds, allowing the structure to be analyzed. The CAD-MS/MS spectrum showed an intense and characteristic fragment ion at m/z 193 for oligosaccharides having glucuronic acid at the nonreducing terminal. On the other hand, this ion was not observed in the spectra of oligosaccharides having N- acetylglucosamine at the nonreducing terminal. Therefore, the fragmentation pattern revealed by CAD-MS/MS provides useful information for distinguishing glucuronic acid and N- acetylglucosamine at the nonreducing terminal of oligosaccharides derived from hyaluronic acid and other glycosaminoglycans. This ion-spray CAD-MS/MS technique was also applied successfully to the characterization of glycosaminoglycans reconstructed by glycotechnology.

Determination of Diarrheic Shellfish Toxins in Mussels b Microliquid Chromatography-Tandem Mass Spectrometry

A fast, sensitive, and specific procedure for determining toxins that cause diarrheic shellfish poisoning (DSP) using microliquid chromatography coupled with tandem mass spectrometry (micro-LC-MS-MS) is reported. The lipophylic polyether acidic toxins okadaic acid (OA), its isomer dinophysistoxin-2 (DTX-2), the 35-methylokadaic acid dinophysistoxin-1 (DTX-1), and the novel toxin dinophysistoxin-1B (DTX-2B; recently isolated from Irish mussels) were extracted from shellfish tissues with acetone and chromatographed by isocratic elution at 10 microL/min with CH3 CN-H2O, 80 + 20 (v/v), containing 0.1% trifluoroacetic acid, through a C18 reversed-phase column (1.0 mm id). The chromatograph is coupled via an ion spray interface to an atmospheric pressure ionization source. Collision-induced-dissociation (CID) ion mass spectra of the protonated molecule, [M + H]+, at m/z 805 for OA, DTX-2, and DTX-2B and at m/z 819 for DTX-1, were obtained in MS-MS experiments to identify 2 diagnostic fragment ions for each analyte that could be used for selected-reaction-monitoring (SRM) micro-LC-MS-MS analysis. The CID spectrum of DTX-2B confirmed it to be a new OA isomer, like DTX-2. Standard curves obtained by SRM micro-LC-MS-MS were linear (r2 > or = 0.9992) over the range 0.05-1.00 micrograms/mL (i.e., 0.10-2.00 micrograms toxin/g hepatopancreas), and a detection limit of 15 pg/injection was obtained for each DSP toxin. Average recoveries ranged from 95 to 101%, and coefficients of variation ranged from 1.8 to 3.4%. This novel SRM micro-LC-MS-MS method was used to confirm acidic DSP toxins in Irish and Italian toxic mussels. It offers a high degree of specificity because analyte confirmation is based on retention time, molecular weight, structural information obtained from the presence of 2 diagnostic fragments for each analyte, and ion ratios. OA was found in both Irish (< or = 0.7 micrograms/g hepatopancreas) and Italian (< or = 1.5 micrograms/g hepatopancreas) mussels. DTX-1 was found only in Italian mussels (< or = 0.3 micrograms/g hepatopancreas). DTX-2 (< or = 6.1 micrograms/g hepatopancreas) and DTX-2B (< or = 0.08 micrograms/hepatopancreas) were unique to Irish shellfish.

Development of a simple liquid chromatographic method with UV and mass spectrometric detection for the separation of substances related to amoxicillin sodium

The development of a selective method for the separation and identification of amoxicillin sodium-related substances is described. It is based on reversed-phase liquid chromatography followed either by UV detection (LC–UV) or by mass spectrometry (LC–MS). Mass detection was carried out by an atmospheric pressure ionization source and ionspray interface. Flow injection analyses–MS gave positive-ion mass spectra exhibiting abundant peaks due to their protonated molecules without significant fragmentation. The protonated molecules were used for selected ion monitoring LC–MS analyses. The method allowed the resolution of 13 available potential impurities from amoxicillin and from each other. Its applicability to an MS detector also permits a rapid identification of the impurities in the lack of the corresponding reference substances.

Binding Energies of Silver Ion−Ligand, L, Complexes AgL2+ Determined from Ligand-Exchange Equilibria in the Gas Phase

The free energy ΔG°, entropy ΔS°, and enthalpy ΔH° for the reaction: AgL2+ = Ag+ + 2L in the gas phase were determined for 16 different ligands L which included oxygen bases such as H2O, MeOH, EtOH, Me2CO, and Me2SO, nitrogen bases NH3 and MeCN, and sulfur bases Me2S. The determinations were based on measurements of the exchange equilibria AgA2+ + B = AgAB+ + A and AgAB+ + B = AgB2 + A where A and B are different ligands L. The exchange equilibria were determined in a “high”-pressure ion source at 10 Torr bath gas containing A and B in the 10−100 mTorr range and using Ag(MeOH)2+ ions produced by electrospray. A scale of ΔG° values for the exchange reaction AgA2+ + 2B = AgB2+ + 2A was established and calibrated to the ΔG° for Ag(H2O)2+ = Ag+ + 2H2O, due to Holland and Castleman, obtaining thus absolute ΔG° values for all ligands involved. Theoretically calculated ΔS° values led to ΔH°. Comparison of the ΔG° and ΔH° results with binding energies for the same ligands in complexes with the alkali ions Li+ and K+ showed that while a good correlation is observed for the alkali ions as a group, only a very poor correlation is observed between the alkali ions and Ag+. In particular, the “soft” base Me2S showed, relative to the “hard” oxygen bases, a much stronger bonding to Ag+. The comparison was extended to CuL2+ on the basis of additional exchange equilibria determinations. The CuL2+ and AgL2+ results combined with earlier determinations of MnL2+, CoL2+ and CuL2+ by Jones and Staley provide a partial confirmation of the hard and soft acid−base (HSAB) concept for these systems. However, a more detailed comparison on the basis of the absolute hardness, η, scale developed by Pearson and co-workers indicates only a very limited agreement when a larger variety of bases is included.

Determination of nitrofuran residues in avian eggs by liquid chromatography–UV photodiode array detection and confirmation by liquid chromatography–ionspray mass spectrometry

A high-performance liquid chromatographic–UV–Vis photodiode-array detection (HPLC–DAD) method for the determination of nitrofuran residues, nitrofurazone, furazolidone and furaltadone, in chicken eggs is described. Confirmation of the identity of nitrofurazone, furazolidone and furaltadone was performed by high-performance liquid chromatography–mass spectrometry (HPLC–MS) using an atmospheric pressure ionization (API) source and an ionspray interface. The nitrofuran residues were extracted from eggs with acetonitrile and the extracts purified by liquid–liquid partitioning. Analytes were chromatographed isocratically with an octadecylsilyl (ODS) column and an UV–Vis detector set at 362 nm and identified by comparing the retention times and UV–Vis spectra of the sample peaks with the reference compounds. The HPLC–DAD limit of detection based on a signal-to-noise ratio (S/N) of 3, was estimated to be 2.5 μgkg−1 for nitrofurazone and furazolidone and 5.0 μgkg−1 for furaltadone. The ionspray HPLC–MS was carried out on the purified extracts. The HPLC–MS method involved the separation of analytes on a C18 column with acetonitrile–water (50:50, v/v), containing 1 mM ammonium acetate and 0.025% acetic acid, with selected-ion monitoring (SIM) of only protonated molecules, [M+H]+ of the analytes. The overall average recovery in nitrofuran fortified eggs was 85.3±3.8% for nitrofurazone, 88.1±3.9% for furazolidone and 87.1±3.7% for furaltadone. The HPLC–MS limit of detection, based on a S/N of 3, was estimated to be 3.2, 1.6 and 1.0 μgkg−1 for nitrofurazone, furazolidone and furaltadone, respectively. HPLC–MS has shown itself to be a sensitive, selective and rapid method and was successfully used for the confirmation analysis of nitrofurazone, furazolidone and furaltadone in avian eggs for regulatory purposes.

Liquid chromatography with fluorimetric, mass spectrometric and tandem mass spectrometric detection for the investigation of the seafood-toxin-producing phytoplankton, Dinophysis acuta

The diarrhoeic shellfish poisoning (DSP) toxins, okadaic acid (OA) and its isomer, dinophysistoxin-2 (DTX-2), were determined in the marine phytoplankton, Dinophysis acuta, harvested in Ireland. Unialgal samples (22–100 cells) were extracted and derivatised using 9-anthryldiazomethane (ADAM) or 1-bromoacetylpyrene (BAP) and analysed by liquid chromatography (LC). Isocratic elution on a C18 reversed-phase column, with fluorimetric detection, was used to determine OA (58±7 pg/cell) and DTX-2 (78±14 pg/cell). The detection limit was 0.1 ng OA/20 μl injection using ADAM. Gradient LC, using a polymeric bonded phase, successfully separated mixtures containing both the ADAM and BAP derivatised toxins. Identification of DSP toxins was confirmed using isocratic micro LC with tandem mass spectrometric (μLC–MS–MS) analysis of the free toxins and μLC–MS of the BAP-derivatised toxins with an ionspray (IS) interface, coupled to an atmospheric pressure ionisation (API) source. Collision induced dissociation (CID) ion mass spectra of the protonated molecule, [M+H]+, at m/z 805 for OA and DTX-2, identified three diagnostic fragment ions for each analyte which were used for selected reaction monitoring (SRM) LC–MS–MS analysis. The detection limit for OA and DTX-2 was 0.025 ng/0.2 μl injected. These studies showed that D. acuta was the progenitor of DTX-2 in shellfish.

On cluster ions, ion transmission, and linear dynamic range limitations in electrospray (ionspray) mass spectrometry

The ion transmission in Electrospray (Ionspray) Mass Spectrometry (ESMS) was studied in order to examine the instrumental factors potentially contributing to observed ESMS linear dynamic range (LDR) limitations. A variety of means used for the investigation of ion transmission demonstrated that a suspected loss in tetraalkylammonium ion signal in favour of formation of analyte ion-analyte ion-pair clusters is negligible. The ion/ion-pair cluster abundance continues to rise after the core analyte ion reaches the 10 −5M concentration LDR plateau. The relative cluster ion abundance changes observed with increasing concentration appear to reflect solution phase ion/molecule clustering reactions at the surface of charged droplets produced in the electrospray. The simultaneous measurement of the ES capillary spray current and ion currents at the first three stages of ion sampling revealed that the nozzle orifice which separates the atmospheric pressure ion source from the first vacuum stage receives a current that rises continuously with sample concentration. The skimmer current rises to a plateau then falls off at higher analyte concentrations, closely matching the final mass spectrometric response. Complete coverage of the charged droplet surface can explain the plateau, but a simple model that explains tetraalkylammonium ion signal suppression cannot be given. Dynamic range limitation was less pronounced with higher atmospheric pressure chemical ionization total ion currents, which showed linearity over greater total MS ion current ranges. MS signal suppression observed at high (> 0.2 mM) analyte concentrations may thus be attributed to unique ES ion formation/instrumental/space charge effects.

Electron CaptureNegative Ionization Mass Spectrometric Characteristics of Bioaccumulating Methyl SulfoneSubstituted Polychlorinated Biphenyls

Gas chromatography/electron-capture negative ionization mass spectrometry (GC/ECNI-MS) was used to separate and detect a mixture of 24, 3-and 4-methyl sulfone-substituted polychlorinated biphenyls (MeSO2-PCBs). The dominant fragment ions were [M-CH3]- and [M-Cl+H]-, and to a lesser extent [M-2Cl]-, [M-2Cl+2H]-, [M-CH3-Cl+H]- and [M-SO2CH3+H]-). The structures of the 3-and 4-MeSO2-PCBs varied in the degree (i.e. tetrachloro-to heptachloro-) and position of chlorine substitution. With the assistance of multivariate statistical analysis, the abundance of several isotopic clusters of fragment ions relative to that of the molecular ion (M-) was found to vary as a function of MeSO2-PCB structure. Compared with other congeners, the relative abundance of [M-CH3]- was significantly lower for MeSO2-PCBs containing the 4-MeSO2-2,5-dichloro moiety, and the hexachloro-and heptachloro-MeSO2-PCBs had higher relative abundances of [M-Cl+H]-. Subtle ECNI mass spectral fragmentation rules therefore exist for 3-and 4-MeSO2-PCBs with respect to congener structure; however, both ion source temperature and pressure must be controlled. Increasing the ion source temperature from 100 to 260°C resulted in an large increase in the abundance of [M-CH3]- relative to M- from <20% to >100%, for all the MeSO2-PCBs studied. For the set of ten 3-/4-MeSO2-PCB pairs, the [M-CH3]- relative abundance ratio was independent of ion source temperature, and was ∽4.5 and ∽1.5 for congeners possessing 2,5-dichloro and 2,5,6-trichloro substitution on the MeSO2-containing phenyl ring, respectively. The effect of an increase in ion source temperature, over the same temperature range, on the relative abundance of hydrogen inclusion-type fragment ions was much less dramatic. [M-CH3-Cl+H]- and [M-Cl+H]- abundance often increased, but never exceeded ∽40%. Decreasing the methane reagent gas pressure from 0.5 to 0.05 mbar did not significantly alter the ion source temperature effect on the relative abundance of the fragment ions. However, the ECNI response sensitivity decreased by an order of magnitude. © 1997 by John Wiley & Sons, Ltd.

Electron Capture/Negative Ionization Mass Spectrometric Characteristics of Bioaccumulating Methyl Sulfone-Substituted Polychlorinated Biphenyls

Gas chromatography/electron-capture negative ionization mass spectrometry (GC/ECNI-MS) was used to separate and detect a mixture of 24, land 4-methyl sulfone-substituted polychlorinated biphenyls (MeSO 2 PCBs). The dominant fragment ions were [M-CH 3 ] - and [M - Cl + H] - , and to a lesser extent [M - 2Cl] - , [M - 2Cl + 2H] , [M - CH 3 -Cl + H] - and [M -SO 2 CH 3 + H] - ). The structures of the 3-and 4-MeSO 2 -PCBs varied in the degree (i.e. tetrachloro-to heptachloro-) and position of chlorine substitution. With the assistance of multivariate statistical analysis, the abundance of several isotopic clusters of fragment ions relative to that of the molecular ion (M - ) was found to vary as a function of MeSO 2 -PCB structure. Compared with other congeners, the relative abundance of (M-CH 3 ] - was significantly lower for MeSO 2 -PCB 8 containing the 4-MeSO 2 -2,5-dichloro moiety, and the hexachloro-and heptachloro-MeSO2-PCBs had higher relative abundances of [M - Cl + H] - . Subtle ECNI mass spectral fragmentation rules therefore exist for land 4-MeSO2-PCBs with respect to congener structure; however, both ion source temperature and pressure must be controlled. Increasing the ion source temperature from 100 to 260°C resulted in an large increase in the abundance of [M - CH 3 ] - relative to M - from 100%, for all the MeSO 2 -PCBs studied. For the set of ten 3-/4-MeSO 2 -PCB pain, the [M - CH 3 ] - relative abundance ratio was independent of ion source temperature, and was ∼4.5 and ∼1.5 for congeners possessing 2,5-dichloro and 2,5,6-trichloro substitution on the MeSO 2 -containing phenyl ring, respectively. The effect of an increase in ion source temperature, over the same temperature range, on the relative abundance of hydrogen inclusion-type fragment ions was much less dramatic. [M-CH 3 -Cl+ H] - and [M - Cl + H] - abundance often increased, but never exceeded 40%. Decreasing the methane reagent gas pressure from 0.5 to 0.05 mbar did not significantly alter the ion source temperature effect on the relative abundance of the fragment ions. However, the ECNI response sensitivity decreased by an order of magnitude.

Identification of Carbamates by Particle Beam/Mass Spectrometry

The possibility of analysing 33 carbamate pesticides and 14 of their transformation products was investigated utilizing flow injection particle beam/mass spectrometry (PBMS) with electron impact (EI) ionization and ammonia and methane positive and negative chemical ionization (CI). Optimum operating conditions of the interface and mass spectrometer in each mode were determined, with special attention given to spectrum quality; variables investigated included ion source temperature and ion source pressure in CI experiments. Ammonia, as a reagent gas, provided less fragmentation and better quantitative results than methane. The CI response was generally higher with positive ion detection (PCI) than with negative ion detection (NCI), but NCI was found to be highly selective for compounds such as aminocarb, asulam and thiophanate-methyl. As regards analyte detectability, EI performed best for most compounds, with the spectra providing relevant structure information. The response of more polar degradation products is generally larger by 2–3 orders of magnitude compared with the parent compounds. When analysing real samples, the combined use of CI for molecular mass determination and EI for structure elucidation is required. The spectral information from this study and additional chromatographic data were used for the determination of low- and sub-μg l-1 levels of the test carbamates in surface water. © 1997 by John Wiley & Sons, Ltd.

Performance of a Low Cost Atmospheric Pressure Chemical Ionization-interfaced Thermospray Ion Source

The combination of a custom-made atmospheric pressure chemical ionization interface with a thermospray (TSP) ion source is described. The sensitivity is comparable with normal specifications of commercially available interfaces. The TSP ion source is used as an intermediate pressure region to force ions by means of a repeller into the mass spectrometer. The TSP ion source pressure has been optimized with respect to transmission and ion energy distribution and has been used, in conjunction with optimization of the repeller voltage, to increase the sensitivity of the interface. Using optimal conditions, 50 pg of reserpine can be detected with a signal-to-noise ratio of 20 in selected-ion monitoring. The performance of the interface coupled with liquid chromatography in negative ionization mode for the analysis of some steroids is also described. In this case absolute detection limits of 40 pg, corresponding to a sample concentration detection limit of 2 ng/mL, have been obtained.

First report of pectenotoxin-2 (PTX-2) in algae ( Dinophysis fortii) related to seafood poisoning in Europe

Pectenotoxin-2 (PTX-2), a polyether-lactone included in the neutral class of diarrhoetic shellfish poisoning (DSP) toxins, has been unambiguously detected in Dinophysis fortii collected in the northern Adriatic Sea (Emilia Romagna coasts). This is the first report of such a toxin in Europe. This lipid soluble toxin was identified both in crude methanolic phytoplankton extract and in the neutral fraction obtained by extract chromatography on a basic alumina column. The techniques used were reversed phase high-performance liquid chromatography followed either by UV diode-array detection (LC-UV-DAD) or by mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS-MS) using an atmospheric-pressure ionization source and an ionspray interface. Okadaic acid (OA) was also found in the D. fortii specimens and quantified as 15 pg/cell. Although quantitation of PTX-2 was not possible due to the lack of pure toxin, the high PTX-2:OA ratio suggested PTX-2 was significant in the D. fortii specimens. The presence of PTX-2 in a region with no previous report of DSP neutral toxic compounds may indicate a risk of human poisoning. Serious efforts should therefore be made to develop suitable routine methods capable of detecting the presence of PTXs in biological materials of marine origin, in order to assure the wholesomeness of seafood products.

Quantitative Analysis of Thermostable Explosive Compounds by Combined Liquid Chromatography/Tandem Mass Spectrometry

A method for quantitative determination of thermostable explosive compounds is described. This method uses a Perkin Elmer Sciex API III triple-quadrupole mass spectrometer equipped with an atmospheric-pressure ion source, as a detector for liquid chromatography. The explosives were dissolved in dimethylformamide and the quantitative analysis was performed by combined liquid chromatography/tandem mass spectrometry using a phenyl column. Selected reaction monitoring experiments were performed by setting the first quadrupole to pass the [M-H]− or [M+acetate]− ions of a selected explosive, while simultaneously setting the third quadrupole to pass its most characteristic fragment ion. An extensive statistical analysis of results was carried out, which showed a linear response between 0.8 ng and 12.8 ng for hexanitrostilbene, between 0.4 ng and 6.4 ng for hexanitrodiphenylamine, and between 0.1 ng and 1.6 ng for tetranitroacridone. Detection of these compounds with an intra-assay relative standard deviation (RSD) between 0.53% and 5.79% and an inter-assay RSD between 0.08% and 6.61% was obtained with this method. Accuracy, expressed as percentage error, was always better than 7%.

Analysis of Inorganic Species by Capillary Electrophoresis−Mass Spectrometry and Ion Exchange Chromatography−Mass Spectrometry Using an Ion Spray Source

Mixtures of inorganic ions separated by capillary electrophoresis (CE) and ion exchange chromatography (IC) are detected by mass spectrometry (MS) using an ion spray atmospheric pressure ionization source. The selectable degree of ion-adduct declustering and molecular fragmentation in the MS interface region allows the system to be operated as an elemental analyzer or as a molecular detector suitable for oxidation state determinations. Both inorganic anions and cations (including alkalis, alkaline earths, transition metals, and lanthanides) are analyzed by CE-MS. A variety of CE separation buffers are evaluated for the cation analyses (e.g., creatinine, ammonium acetate, and tris[hydroxymethyl]aminomethane). Only one of the buffers (i.e., creatinine) can be used for CE-indirect UV detection. A CE capillary permanently coated with strong anion exchange sites and a pyromellitic acid buffer (suitable for indirect UV detection) is used for the inorganic anion separations. The coated column eliminates the need for buffer modifiers to reverse the flow in the capillary, which then reduces background noise and mass spectral complexity. The separation and detection of 13 inorganic anions are also accomplished by IC using an anion exchange column with a carbonate-bicarbonate mobile phase, on-line suppressed conductivity detection, and mass spectrometric detection.

Limitations and perspectives in the determination of carbofuran with various liquid chromatography-mass spectrometry interfacing systems

Column liquid chromatography with mass spectrometric detection (LC-MS) has been widely accepted as the preferred technique for the identification and quantification of polar and thermally labile compounds at trace levels. Over the last decade many different types of LC-MS interfacing techniques have been used for the determination of carbamate pesticides and especially for the N-methylcarbamate carbofuran. This article addresses the difficulties encountered with the various types of LC-MS interface and discusses recent alternatives for the determination of carbofuran. With thermospray and particle beam interfaces the quantification of carbofuran is affected by both the ion source pressure and temperature, whereas quantification using the recently developed atmospheric pressure ionization interfaces, atmospheric pressure chemical ionization, electrospray, and ionspray, is less dependent on these parameters.