Capture Negative Ionization Mass Spectrometry Research Articles

Determination of Short-Chain Polychlorinated Paraffins in Fish Samples by Short-Column GC/ECNI-MS

A new analytical method has been developed for quantification of C10−C13 polychlorinated paraffins in fish samples. After a cleanup procedure with a silica gel minicolumn and gel permeation chromatography, detection has been achieved by a short-column gas chromatography/electron capture negative ion mass spectrometry. The quantification was performed by reintegration of selected ions from full-scan spectra. Without chromatographic separation, all short-chain polychlorinated paraffins eluated from the column as only one peak. Consequently, this leads to better sensitivity and makes it more easy to survey the spectra. For the first time, a great number of C10, C11, C12, and C13 polychlorinated alkanes with different chlorine contents were used as standards. Detection limits in the full-scan mode varied between 10 and 100 pg depending on the chlorination grade of the alkanes. The results show, that polychlorinated decanes are the dominant residues in the most of investigated fish samples.

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives.

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C14O2H8) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M−· (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy ∼0.5 eV corresponds to a shape resonance with lifetime 1–2·10−13 s in the f-partial wave (ℓ = 3) of the incident electron. The next resonant state of MNI at the energy ∼1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet nπ* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright © 1999 John Wiley & Sons, Ltd.

An Improved Method for the Measurement of Urinary and Plasma F2-Isoprostanes Using Gas Chromatography–Mass Spectrometry

We have developed an improved method for the measurement of F2-isoprostanes using stable isotope dilution capillary gas chromatography/electron capture negative ionization mass spectrometry (GC-ECNI-MS). The F2-isoprostane family consists of a series of chemically stable prostaglandin F2(PGF2)-like compounds generated during peroxidation of arachidonic acid in phospholipids. There is evidence that measurement of F2-isoprostanes represents a reliable and useful index of lipid peroxidation and oxidant stressin vivo.Furthermore, 8-epi-PGF2α, which is one of the more abundant F2-isoprostanes, is biologically active, being a potent mitogen and vasoconstrictor of rat and rabbit lung and kidney, as well as a partial agonist of platelet aggregation. Measurement of F2-isoprostanes in biological samples is complex and has involved methods which utilize multiple chromatographic steps, including separation by thin-layer chromatography, leading to poor sample recovery. We now present an improved method for the measurement of plasma and urinary F2-isoprostanes using a combination of silica and reverse-phase extraction cartridges, high-performance liquid chromatography (HPLC), and GC-ECNI-MS. Different approaches to the derivatization of the F2-isoprostanes prior to GC-ECNI-MS are also addressed. The overall recovery of F2-isoprostanes is improved (approx 70% for urine) and the within and between assay reproducibility is 6.7% (n= 23) and 3.7% (n= 3), respectively. The mean urinary excretion of F2-isoprostanes in eight healthy males was 365 ± 5 pmol/mmol creatinine and in three smokers 981 ± 138 pmol/mmol creatinine. The mean total (free + esterified) plasma F2-isoprostane concentration was 952 ± 38 pmol/liter, with a within and between assay reproducibility of 8% (n= 13) and 5.6% (n= 3), respectively. This improved method for the measurement of F2-isoprostanes represents a significant advance in terms of the rapidity and yield in the purification of biological samples. The inclusion of HPLC separation enables improved analysis of F2-isoprostanes by GC-MS. This methodology will assist in defining the role of F2-isoprostanes asin vivomarkers of oxidant stress in clinical and experimental settings.

Electron Energy Dependence of Regioselective Chloride Ion Loss from Polychlorodibenzo-p-dioxins. Relationship between Resonance Electron Energies and Virtual Orbital Energies

Regiospecifically chlorine-37-labeled polychlorodibenzo-p-dioxins (PCDDs) undergo electron energy-dependent regioselective chloride ion loss when analyzed by electron capture negative ion mass spectrometry using an electron monochromator to supply the slow monoenergetic electrons. Three negative ion resonances, produced with electrons of energies <0.5, ∼1, and ∼4 eV are associated with the production of chloride ions from PCDDs. Negative ion resonances for the production of molecular ions of higher PCDDs were recorded with electrons of energies <0.2 eV. Dichlorodibenzo-p-dioxins and some trichlordibenzo-p-dioxins showed no molecular ions. A correlation was found between the experimental electron attachment energies and the virtual orbital energies calculated by modified density functional theory methods using the B3LYP/D95//B3LYP/D95 level of theory. The results from these correlations strongly suggest that all negative ion-forming processes for this class of compounds are initiated from π* states. The loss of chloride ion from transient negative PCDD ions requires π*−σ* orbital mixing.

Interlaboratory Study on Quantitative Methods of Analysis of C10−C13 Polychloro-n-alkanes

Seven laboratories participated in an international interlaboratory comparison exercise to compare the quantitative methods used for measuring C10−C13 polychloro-n-alkanes (PCAs). Participants were supplied with two solutions (PCA-1, PCA-70) containing PCAs of “known” but unstated concentrations, and two real world samples (fish extracts FE1 and FE2) each consisting of a cleaned up extract (lipid-free) of a fish tissue known to contain PCAs. A well-characterized commercial formulation, PCA-60, of stated concentration was also supplied and was used as the external standard for the exercise. Participants having other commercially available C10−C13 PCA mixtures were encouraged to use them as external standards for the study, and the choice of the quantitative method employed was left to participants, though all were based on high-resolution gas chromatography with detection by electron capture negative ion mass spectrometry (plus electron capture detection in one case). The results of the study met with mixe...

Electron capture negative ion (ECNI) mass spectrometry of complex mixtures of chlorinated decanes and dodecanes: An approach to ECNI mass spectra of chlorinated paraffins in technical mixtures

The electron capture negative ion (ECNI) mass spectra of two complex mixtures of polychlorinated decanes (PCDe) and polychlorinated dodecanes (PCDo) are presented. The number of isomers in these mixtures is still high but is drastically reduced in comparison to technical products of chlorinated paraffins (CP), due to their fixed chain length. As a result, the mass spectra are simplified and less complex. Different modes of negative ion formation were observed in the spectra of the PCDe and PCDo. [M+Cl]– adduct ions were the most abundant ions in the spectra of lower chlorinated molecules. Higher chlorinated isomers formed prominently [M-Cl]– and [M-HCl]– fragments besides [M+Cl]–. Possible consequences for the determination of chlorinated paraffins by ECNI-MS that result from the variation in ion formation are addressed.

Deuterium enrichment of retinol in humans determined by gas chromatography electron capture negative chemical ionization mass spectrometry

A new application of electron capture negative chemical ionization mass spectrometry method has been developed for detecting vitamin A enrichment in human serum. Octadeuterated all-trans retinyl acetate 1.5 mg was fed to a volunteer and blood samples were collected over a period of 32 days. Serum samples were extracted and isolated by high performance liquid chromatography to collect the fraction containing retinol. The retinol fraction was derivatized to a trimethylsilyl ether, which was analyzed by gas chromatograph (GC)/mass spectrometry using a capillary column coated with DB-1 followed by methane electron capture negative chemical ionization/mass spectrometry (ECNCI-MS). Although ECNCI-MS of derivatized retinol produced no molecular ion, it produced a single negatively charged fragment ion at m/z 268 for natural retinol (m/z 276 for octadeuterated retinol) due to loss of the silyl group. The serum enrichment of labeled retinol was detectable at 7 hours, reached a maximum of 2.6% at 24 hours, and declined thereafter but was still at 0.07% at 32 days. In 200 μL of serum, the minimum detectable enrichment of retinol- d 8 was 0.01%. The GC/ECNCI-MS method for detecting retinol in serum is at least 10 times more sensitive than any previously published mass spectrometry method.

Characterization of three major toxaphene congeners in arctic ringed seal by electron ionization and electron capture negative ion mass spectrometry

Three environmentally significant chlorinated bomane (CHB) congeners were extracted from Arviat ringed seal blubber and identified by using gas chromatography/mass spectrometry (HRGC/HRECNIMS (CH 4), low resolution EIMS, and linked field scanning). They are referred to as TS2 (Parlar#39, B8-531) [2- exo,3- endo,5- exo,6,6,8b,9c,10c (or 10a)-octachlorobonane], TS3 (Parlar#40, B8-1414) [2- endo,3- exo,5- endo,6- exo,8c,9b,10a,10c (or 10b)-octachlorobornane] and TS4 (Parlar#42, Toxicant A, B8-806/809) [2- exo,3- endo,6,6,8b,8c,9c,10c (or 10a)-octachlorobonane/2- exo,3- endo,6,6,8b,9b,9c,10a (or 10b)-octachlorobonane]. This is the first time Toxicant A, known to be the most toxic CHB congener in technical toxaphene, has been found in any significant concentration in a marine mammal.

Determination of Chlordane in Soil by LC/GC/ECD and LC/GC/EC NIMS with Comparison of ASE, SFE, and SOXHLET Extraction

Chlordane is a polychlorinated mixture that was used as a long-lived pesticide and now is considered a potential endocrine-disrupting compound. The Environmental Sciences Division is involved in modernizing methods for a number of analytes that are potential target substances for dietary studies, endocrine disrupter studies, Superfund site monitoring, and human exposure studies. In this work, chlordane is determined in soils using each of three different liquid phase/supercritical fluid (CO2) extractions followed by a two-dimensional chromatographic separation based on high performance gel permeation chromatography (HPGPC) followed by GC/electron capture detection (GC/ECD) and GC/electron capture negative ion mass spectrometry (GC/EC NIMS). Liquid phase extractions were carried out using accelerated solvent extraction, supercritical fluid extraction, and Soxhlet extraction. The preparative liquid chromatographic part of the work is used in an off-line fractionation mode of HPGPC. Further cleanup is afforded by solid-phase extraction using silica cartridges. Soils spiked at 2 ppm, 0.2 ppm, and 0.02 ppm were quantitated using GC/ECD and GC/EC NIMS with recoveries usually greater than 80%. Soil from a Superfund site and a standard reference material sediment were analyzed as examples of real samples. The modernized methodology developed in this work should offer improved approaches for Superfund analyses and for monitoring methods used in determining potential exposure to endocrine-disrupting compounds while minimizing solvent usage compared to previous methodology.

Amino Acid Analysis of Peptides and Proteins on the Femtomole Scale by Gas Chromatography/Mass Spectrometry

Amino acid analysis (AAA) is a useful aid in protein chemistry, but its routine application is limited by a modest limit of detection. Typically, 10 pmol of material is required, but even at this level the reproducibility can be poor. We have employed isotope dilution gas chromatography electron capture negative ionization mass spectrometry (GC/ECNI/MS) to provide accurate and reliable data on less than 100 fmol of material. Precision and accuracy are good, and all 20 non-hydrolyzed amino acids can be determined in this manner. The protein is hydrolyzed (HCl), and then a cocktail, composed of all 20 amino acids as stable isotope-labeled forms (i.e., (13)C and (2)H), is added. The mixture of protein-derived and stable isotope-labeled amino acids is then converted to volatile electron-capturing derivatives with a multistep approach employing heptafluorobutyric anhydride (HFBA), pentafluorobenzyl bromide (PFBBr), and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). These derivatives are then injected directly into the GC/MS system. Groups of selected ions, characteristic of each derivatized amino acid, are thereafter monitored at appropriate time intervals. The ratios of the ion current for the selected ions for the native amino acid and its labeled form are determined and converted to absolute amounts of the native amino acids in the protein hydrolyzate by reference to standard samples prepared at the time of the analysis.

Simplified Determination of Imidazolinone Herbicides in Soil at Parts-per-Billion Level by Liquid Chromatography/ Electrospray Ionization Tandem Mass Spectrometry

Abstract Imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for protection of a wide variety of agricultural commodities. Because of their low rates of application, residues of imidazolinones in soil need to be monitored at low parts-per-billion (ppb) levels. Greatly simplified cleanup procedures were reported recently for determining imidazolinones in soil at the 1 ppb level by combining microwave-assisted extraction (MAE) with gas chromatography/electron capture negative chemical ionization mass spectrometry (GC/ECNCI) and for determining imidazolinones in water by using liquid chromatography/electrospray ionization mass spectrometry (LC/ESMS) and liquid chromatography/electrospray ionization tandem MS (LC/ESMS/MS). By merging the extraction and cleanup procedures for determining imidazolinones in soil with LC/ESMS/MS, instrumental analysis time was reduced to that approximating sample preparation time, and the drawbacks of in situ methylation required for GC/ECNCI were eliminated. Recoveries of imazethapyr, the most widely used imidazolinone, from a variety of soil types fortified at 1–50 ppb averaged 92% with a standard deviation of 9.7%. Control soil extracts gave apparent residues of &amp;lt;0.2 ppb. These results were almost identical to those previously reported for GC/ECNCI.

Trace Quantification of the Oxidative Damage Products,meta- andortho-Tyrosine, in Biological Samples by Gas Chromatography–Electron Capture Negative Ionization Mass Spectrometry

Oxygen radicals damage biomolecules and may contribute to cellular aging and degenerative disease. We describe a sensitive method for the quantification of two endogenous biomarkers of oxidative damage:meta-tyrosine (m-Tyr) andortho-tyrosine (o-Tyr). The assay can be applied to direct analysis of free amino acids or protein-bound amino acids following hydrolysis. The assay involves derivatization with pentafluorobenzyl bromide and extraction inton-decane, followed by gas chromatography–mass spectrometry. Stable isotope labeledm- ando-Tyr (2H4) and phenylalanine [i.e., Phe (2H5)] were added as internal standards to improve analytical accuracy. Quantification of as little as 50 pg ofm- ando-Tyr in 100 μg protein is possible and the data are expressed as a molar ratio ofm- ando-Tyr to native Phe. The assay was used to determine the levels ofm- ando-Tyr in freshly isolated human plasma protein (4.05 ± 0.67m-Tyr per 104Phe, 0.35 ± 0.07o-Tyr per 104Phe). Exposure of human plasma to reactive oxygen species significantly increased the levels ofm-Tyr (56.4 ± 1.1m-Tyr per 104Phe,P< 0.0001) ando-Tyr (48.9 ± 1.3o-Tyr per 104Phe,P< 0.0001). The mild hydrolysis and derivatization conditions caused no artifactual formation of eitherm- oro-Tyr.

Enantiomeric resolution of persistent compounds of technical toxaphene (CTTs) on t-butyldimethylsilylated β-cyclodextrin phases

Eight of the most important single compounds of technical toxaphene were separated on t-butyldimethylsilylated β-cyclodextrin (β-BSCD) diluted in a medium polar phase using gas chromatography with electron capture detectors (GC-ECD). The enantiomeric resolution of all compounds was obtained in one GC run. The β-BSCD phase also separated the enantiomers of oxychlordane, cis- and trans-chlordane as well as α-HCH. Problems in the enantioselective determination of CTTs in biological samples are discussed. Finally, the enantioselective determination of the two most recalcitrant CTTs in biological samples was achieved using electron capture negative ionization mass spectrometry (GC-ECNI-MS) in the single ion monitoring (SIM) mode.

13] Atmospheric pressure chemical ionization and electron capture negative chemical ionization mass spectrometry in studying β-carotene conversion to retinol in humans

This chapter proposes a method that uses flow injection atmospheric pressure chemical ionization–mass spectrometry (FI/APCI–MS) to measure the enrichment of β-C-d8 in the serum of a subject who was orally supplemented with β-C-d8. The kinetics of the metabolism of β-C-d8 to retinol-d4 is investigated using gas chromatography–mass spectrometry with electron capture negative chemical ionization (GC/ECNCI–MS) to measure the enrichment of derivatized retinol-d4 in the serum. Under APCI conditions, β-C is readily ionized by proton transfer from protonated ethanol to a protonated molecule with a molecular mass of 537 Da. β-C analyzed by APCI–MS exhibits a linear correlation between concentration and signal response. The APCI analysis for β-C extracted from a blood sample is presented as replicate flow injection profiles. The detection limit was 50 pg of standard β-C. The absolute concentration of labeled β-C-d8 in serum reached 329 nM in 2 days after the administration of β-C-d8 while unlabeled β-C-d8 in serum peaked at 1 day after the β-C-d8dose. The highest enrichment of labeled β-C-d8 was 30.9%, which occurred at 2 days after the β-C-d8 dose.

Assessment of DNA Oxidative Damage by Quantification of Thymidine Glycol Residues Using Gas Chromatography/Electron Capture Negative Ionization Mass Spectrometry

A technique to assess DNA oxidative damage by quantification of thymidine glycol residues is described. 2-Methylglycerate was released from thymidine glycol in DNA by alkaline cleavage/borodeuteride reduction, then derivatized to form a combined pentafluorobenzyl–tertbutyldimethylsilyl (PFB–TBDMS) derivative and analyzed by gas chromatography/electron capture negative ionization mass spectrometry. [2H4]Thymine glycol was used as an internal standard. The derivatization chemistry was assessed by using [14C-methyl]glycerate. Successful esterification was achieved with 75–80% yield using tetrabutylammonium sulfate-assisted anhydrous pentafluorobenzylation. The PFB–TBDMS derivative exhibits excellent chromatographic and detection properties with a detection limit of 41 amol injected on column. Freshly dissolved calf thymus DNA was used to test the method performance. The background level of thymidine glycol detected in this DNA was 11.7 ± 0.3 × 10−6mol thymidine glycol per 1 mol thymidine. The thymidine glycol background in undamaged DNA establishes a lower limit of oxidative damage below which biological oxidation events would not be measured by this method. The method was linear for 4–20 μg DNA added per tube. The minimum measurable amount of thymidine glycol in DNA sample was 36 fmol. An increased level of thymidine glycol was measured in salmon sperm DNA which had autoxidized during storage in a refrigerated aqueous solution, 71.2 ± 14.3 × 10−6mol thymidine glycol per 1 mol thymidine.

GC/MS analysis of toxaphene: A comparative study of different mass spectrometric techniques

Electron capture negative ion (ECNI) mass spectrometry has been recognized as the most sensitive and specific method for toxaphene analysis. Our recent analysis of 17 individual chlorobornane congeners indicated that the production of [MCl] − from some congeners was highly susceptible to ECNI conditions and may result in very weak or totally absent responses in selected ion monitoring (SIM) mode. These congeners have two common features: all have 2,2,5,5-chlorine substitutions and no chlorine substitution at C-3 and C-6 positions. On the other hand, electron impact ionization combined with high resolution mass spectrometry (EI-MS) produces responses (based on the characteristic ions at m/z 159, 161 and 163) similar to that from the electron capture GC for all congeners. Evidence will be presented to illustrate the difference in responses between these two mass spectrometric methods from a nonachlorobornane (congener #62, based on Parlar's numbering system) which is one of the abundant congeners in cod liver oil, fish, as well as monkey blood/tissues in our toxicology studies. Advantages and disadvantages of both methods in trace analysis of toxaphene are discussed.

Analysis of Amino Acids in Biological Fluids by Pentafluorobenzyl Chloroformate Derivatization and Detection by Electron Capture Negative Ionization Mass Spectrometry

Pentafluorobenzyl chloroformate (PFBCF) has been utilized as a derivatization reagent for amino acids (AAs) in biological fluids with subsequent detection by electron capture negative ionization mass spectrometry (ECNI/MS). AAs were derivatized in one step in aqueous solution, plasma, and whole blood at room temperature. To demonstrate quantitative analysis, phenylalanine concentrations were determined in human plasma. AAs were derivatized in one step using PFBCF and a mixture of water, ethanol, and pyridine/dimethylaminopyridine. TheN-pentafluorobenzyloxycarbonyl amino acid ethyl esters (fφ-AA-OEt) exhibited good GC properties and the ECNI mass spectra are dominated by the [M-181]−ion. Thefφ-AA-OEt derivatives can be easily detected at the femtomole level by selected ion monitoring. Phenethyl alcohol was also derivatized, using anhydrous conditions, and the resulting PFB carbonate's ECNI mass spectrum was dominated by the [M-181]−ion. The ECNI molar response of the PFB carbonate derivative is two times that of the corresponding pentafluorobenzoate.

Microwave-Assisted Extraction Coupled with Gas Chromatography/Electron Capture Negative Chemical Ionization Mass Spectrometry for the Simplified Determination of Imidazolinone Herbicides in Soil at the ppb Level

The imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for protection of a wide variety of agricultural commodities. Because of their low rates of application, residues of the imidazolinones in soil need to be monitored at the low ppb level. Current methodology for this purpose involves an exhaustive base extraction followed by a laborious, time-consuming cleanup procedure to permit analysis at the 5 ppb level. Using imazethapyr, the most widely utilized member of the class, as a representative, we have achieved not only a limit of quantitation of 1 ppb but also a greatly simplified cleanup procedure by combining microwave-assisted extraction technology with gas chromatography/electron capture negative chemical ionization mass spectrometry. On a variety of soil types covering a fortification range of 1−50 ppb, an average recovery of 92% with a standard deviation of 13% was achieved. Control soil extracts gave apparent residues of <0.2 ppb. Sample preparation time per sample was reduced from 2 h to 10 min.

Electron capture negative chemical ionization mass spectrometry and tandem mass spectrometry analysis of β‐carotene, α‐tocopherol and their oxidation products

AbstractThe biological antioxidants α‐tocopherol, 1, and β‐carotene, 4, and products of their antioxidant reactions are potentially important indicators of biological antioxidant status and functions. Electron capture by compounds 1 and 4 and their oxidation products yields intense molecular anions with little fragmentation. Collision‐induced dissociation of the molecular anions was studied by linked‐scaning (B/E = constant) on a reverse‐geometry magnetic‐sector mass spectrometer. Both 1 and 4 and their products undergo extensive diagnostic cleavages of their hydrocarbon chains, apparently via charge‐remote fragmentation. Electron capture negative chemical ionization mass spectrometry appears uniquely suited to structure identification studies of antioxidants and their oxidation products. This methodology is used to identify oxidation products of 1 and 4 from a model biological membrane system subjected to peroxyl radical attack.