Electron-capture Negative-ion Mass Spectrometry Research Articles

Enantioselective determination of various chlordane components and metabolites using high-resolution gas chromatography with a β-cyclodextrin derivative as chiral selector and electron-capture negative ion mass spectrometry detection

Enantioenriched fractions of various chiral chlordane compounds (heptachlor, cis-chlordane, trans-chlordane) and metabolites (cis- and trans-heptachlorepoxide, oxychlordane) were used to evaluate a high-resolution gas chromatography (HRGC) column with heptakis-[2,3-dimethyl-6-t-butyldimethylsilyl]-β-cyclodextrin (TBDM) as chiral selector and enantiomer elution sequences were determined. The enantioenriched fractions were previously isolated from the racemates by enantioselective high-performance liquid chromatography (HPLC) using a permethylated β-cyclo-odextrin. Additionally, two octachlordanes, U82 and MC5, were isolated as racemates from technical chlordane using HRGC and then used for reference purposes. The TBDM column enantiomerically resolved cis- and trans-chlordane, MC5, cis- and trans-heptachlorepoxide, and oxychlordane; it did not enantiomerically resolve heptachlor, the octachlordane U82 and the nonachlordane MC6. A 12-m column resulted in a better enantiomer resolution than a longer (23-m) column of the same type due to a lower elution temperature. The TBDM column was used to analyze technical chlordane and chlordane residues in the fish oil reference material SRM 1588, a cod liver oil. Isomer and enantiomer ratios of chlordane residues in this reference material are reported and compared to those reported in earlier studies on the same material and to data on other fish species from the Baltic.

Evaluation of fluorinated indole derivatives for electron-capture negative ionization mass spectrometry: application to the measurement of endogenous 5-methoxyindole-3-acetic acid in rat.

A series of N-trifluoroacetyl/pentafluoropropionyl-O-trifluoroethyl/ pentafluoropropyl/heptafluorobutyl ester derivatives of 5-methoxyindole-3-acetic acid (5MIAA) were synthesized. Under electron-capture negative ionization conditions, the N-trifluoroacetyl derivatives were found to yield relatively abundant, analyte-specific M-. molecular ions and [M-HF]-., [M-HF-CF2CO]-. and [M-CF3CO]- fragment ions, while the N-pentafluoropropionyl derivatives yielded predominantly the reagent-specific pentafluoroacylium C2F5CO- ion. 5-[2H3]Methoxyindole-3-acetic acid was prepared in high yield by a new synthetic procedure and used as the internal standard in subsequent gas chromatographic/mass spectrometric analysis. Using the N-trifluoroacetyl-O-pentafluoropropyl ester derivative, femtomole to low picomole per gland/organ per g ml-1 levels of endogenous 5MIAA were identified and determined in the rat pineal gland, retina, whole brain and serum.

Evaluation of Fluorinated Indole Derivatives for Electroncapture Negative Ionization Mass Spectrometry: Application to the Measurement of Endogenous 5-Methoxyindole-3-Acetic Acid in Rat

Evaluation of Fluorinated Indole Derivatives for Electroncapture Negative Ionization Mass Spectrometry: Application to the Measurement of Endogenous 5-Methoxyindole-3-Acetic Acid in Rat

Determination of aromatic amines at trace levels by derivatization with heptafluorobutyric anhydride and gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry

A procedure for the simultaneous identification of seventy-three primary and secondary aromatic amines (including alkyl-, chloro- and nitro-substituted anilines, benzidines, aminoaphtalenes and aminobiphenyls) is described. The amines were derivatized by reaction with heptafluorobutyric anhydride to form the corresponding heptafluorobutyramides. The electrophoric derivatives were analyzed by gas chromatography combined with electron-capture negative-ion chemical ionization mass spectrometry. Linearity was satisfactory for all the compounds examined. Detection limits were in the range 0.3–66.3 pg the injected in full-scan acquisition mode and 0.01–0.57 pg injected in the selected ion monitoring acquisition mode. Application of the procedure to contaminated groundwater samples was also attempted.

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.

An Integrated Analytical Method for Determination of Polychlorinated Aryl Methyl Sulfone Metabolites and Polychlorinated Hydrocarbon Contaminants in Biological Matrixes

A simple column chromatography method was developed for separation and cleanup in the determination of chlorinated hydrocarbon contaminants and their methyl sulfone (MeSO2-) metabolites in biological tissues. The method was validated for determination of 11 polychlorinated biphenyls (PCBs), 15 tetra- to heptachloro 3- and 4-MeSO2-PCBs, 3-MeSO2-DDE, and tris(4-chlorophenyl)-methanol spiked to herring gull egg, smelt, and polar bear liver and adipose tissue using gas chromatography with electron-capture detection (GC-ECD). The overall mean recovery relative to the internal standard was 103% +/- 8%, independent of analyte, substrate type, and lipid extract weights up to approximately 0.7 g. Precision of replicate analyses of individual congeners was good. There were no significant residual biogenic or xenobiotic interferences in the aryl methyl sulfone fraction of any substrate. Sensitivity and linearity of molar response of MeSO2-PCBs and MeSO2-DDE was tested for ECD and electron-capture negative ion mass spectrometry monitoring the total ion current (TIC) and the molecular ion (SIM). The mean practical quantitation limit among MeSO2-PCBs and 3-MeSO2-DDE was lowest for SIM (2.1 +/- 0.9 pg) and similar for ECD and TIC (24.2 +/- 4.6 and 44.4 +/- 17.1 pg, respectively). Response factors were linear above the practical quantitation limit to at least the nanogram level for all three techniques. In spite of superior sensitivity, there was more inherent variability in the response factors for SIM (approximately 18%-56% CV) than for ECD (approximately 7%-12% CV) or TIC (approximately 11%-18% CV); therefore, ECD or TIC is recommended for quantitative analysis.

A potential problem in the analysis of toxaphene by electron-capture negative-ion mass spectrometry

On analyzing 11 pure individual toxaphene congeners, it was noted that a nonachloro congener (2,2,5,5,8,8,9,10,10-nonachlorobornane, Parlar's No. 62) failed to produce a reasonable [M–Cl]− response under our electron-capture negative-ion (ECNI) chemical ionization conditions. On the other hand, this congener gave a stronger response than other nonachlorobornane congeners in electron impact (EI) mode. Based on EI mass spectra data as well as electron capture gas chromatographic results, this congener is one of the major components in commercial toxaphene and is also present in fish and cod liver oil samples. This congener-specific discriminatory effect raises concern about possible false negative results from the ECNI/selective-ion monitoring analyses.

Determination of toxaphene in soil by electron-capture negative-ion mass spectrometry and capillary column gas chromatography

Although toxaphene is now limited in use, interest in its analysis continues because of its persistence and widespread atmospheric transport in the environment and its presence in many dump-sites all over the world. Top soil samples collected from a dump site were analyzed for toxaphene residues. Analyses were performed by wall-coated open tubular column gas chromatography in tandem with electron-capture negative-ion mass spectrometry. Since the concentrations of toxaphene residues were at mg/kg levels, the application of a mass spectrometer as a substance-selective detector has been applied. Advantages of this mode of real-time acquisition in continuous repetitive scanning of mass spectra has significant advantages in comparison to the selected-ion monitoring technique. An average R.S.D. of 10% and recoveries of 90 to 109% were obtained. Levels down to 50 μg/kg are obtainable.

Quantification of fg-pg amounts by electron capture negative ion mass spectrometry ? Parameter optimisation and practical advices

Electron capture negative ion mass spectrometry (ECNI-MS) is a very suitable and popular technique for the identification and quantification of fg-pg amounts of compounds with a sufficiently high electron affinity. Many users of the ECNI mode have faced a lot of frustrating problems due to instrument contamination and wrong recommendations concerning instrument optimisation. This article summarises 14 years of experience with ECNI-MS using a large number of different instruments. Recommendations are given concerning optimisation procedures of important parameters such as ion source pressure and temperature as well as electron energy. An ion pressure optimisation method is proposed using a gas chromatograph. ECNI-MS is very sensitive against trace amounts of contaminants in the mass spectrometer and requires very clean components in the reagent gas line. Recommendations are given concerning suitable parts. Different other contamination sources are also discussed. The construction of a simple and clean gas inlet system is presented. Furthermore, contamination-free cleaning methods for the ion source are suggested. A test method based on the detection of hexachlorobenzene in the full scan mode (m/z 34–300) is proposed. It allows to evaluate both the background level in the mass spectrometer and the overall system performance. Clean instruments should show a signal-to-noise ratio of the total ion current GC signal of at least 20:1 without applying any mass signal area reject threshold. A linearity test procedure is also suggested. It shows that the linear range of a clean and optimised instrument is at least 3 orders of magnitude in the ECNI mode.

Toxaphene contamination in Lake Baikal's water and food web

Water and biological samples were obtained from Lake Baikal in June 1991 and analyzed for toxaphene and other organochlorines. Dissolved toxaphene concentration ranged from 34 pg/L to 143 pg/L and were similar in magnitude to ∑DDT (47 pg/L; sum of 2,4′-DDT, 4,4′-DDT, and 4,4′-DDE) and ∑chlordanes (28 pg/L; sum of cis- and trans-chlordane and cis- and trans-nonachlor). Toxaphene in biota was 1.9 mg/kg-lipid in the pelagic sculpin Comephorus dybowskii, 1.1 mg/kg-lipid in the omul ( Coregonus autumnalis migratorious) and 2.3 mg/kg-lipid in Baikal seal (Phoca siberica) blubber. Toxaphene chromatographic patterns, determined by gas chromatography electron capture negative ion-mass spectrometry, were transformed in the seal relative to either of the fish, which is likely due to the seal's greater ability to metabolize some toxaphene congeners. The major peak in the Baikal seal toxaphene chromatogram was an 8-chlorinated bornane unlike that found by other investigators for narwhal or beluga whale blubber, but similar to ringed seals from the Canadian Arctic.

Toxaphene: Analytical chemistry

The working group on analytical chemistry of toxaphene the Toxaphene Workshop (Burlington Ont Feb. 4–6, 1993) recommended that the “shorthand” term of “chlorobornanes” be adopted when referring to toxaphene related compounds. Analytical standards for several important chlorobornanes are now available but the working group concluded that there was a need to identify the remaining environmentally significant congeners. It was recommended that total chlorobornanes be reported using existing methods such as electron capture negative ion mass spectrometry (ECNIMS), as well as individual congeners. No standard reference materials have yet been certified for analysis of chlorobornanes but several (e.g. fish oils, whale blubber) may be suitable.

Determination of toxaphene in soil by electron-capture negative ion mass spectrometry after fractionation by high-performance gel permeation chromatography

Toxaphene is extracted from soil by standard procedures using Soxhlet or sonication methods. The extract is fractionated by high-performance gel permeation chromatography (HPGPC), which separates toxaphene from the bulk of co-extractives including polychlorinated biphenyls. This HPGPC fractionation has broad application to many problems of environmental analysis. A solid-phase extraction cleanup with silica gel further removes any polar components present in the collected fraction. Determination of toxaphene is accomplished by electron-capture negative ion mass spectrometry (ECNI-MS) after introduction by capillary gas chromatography. Levels down to 100 μg/kg in soil are obtainable. Brief mention is made of high-resolution ECNI-MS carried out at a resolution of 10 000.

Primary contribution of the injector to carryover of a trace analyte in high-performance liquid chromatography

When a low-nanogram amount of N1,N3-bis-(pentafluorobenzyl)-N7-(2-[pentafluorobenzyloxy]ethyl) xanthine was subjected to HPLC, low-picogram amounts of the compound could be detected subsequently (off-line by gas chromatography—electron-capture negative-ion mass spectrometry) after injection of pure mobile phase. This was in spite of significant, intermediate washing of the injector and column. It was determined that essentially 99.9% of this analyte contamination came from the injector. Use of two injectors is a practical remedy for this problem.

High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7-(2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide: (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.

Enantioselective determination of chlordane components using chiral high-resolution gas chromatography-mass spectrometry with application to environmental samples

Technical chlordane was examined using both achiral and chiral high-resolution gas chromatography (HRGC) with detection by electron capture, negative ionization mass spectrometry (ECNI-MS). The enantiomer separation of several chiral octachlordanes including cis- and trans-chlordane was achieved and enantiomeric ratios of approximately 1:1 were determined using a modified β-cyclodextrin as the chiral selector. The method was then applied to tissue extracts of several aquatic vertebrate species collected from the Baltic Sea (herring, salmon, and seal) and from Antarctica (penguin).

Superoxide chemical transformation of diolepoxide polyaromatic hydrocarbon DNA adducts: Determination of benzo[α]pyrene- r-7, t-8,9, c-10-tetrahydrotetrol by gas chromatography

Benzo[α]pyrene- r-7, t-8,9, c-10-tetrahydrotetrol (100 pg, 342 fmol) was measured using the following sequence of steps: (1) chemical transformation with potassium superoxide to 2,3-pyrenedicarboxylic acid; (2) electrophore derivatization with pentafluorobenzyl bromide; (3) sample clean-up by high-performance liquid chromatography and (4) measurement by gas chromatography with electron-capture detection and by gas chromatography with electron-capture negative-ion mass spectrometry. The overall, absolute yields obtained by the two procedures were 69% and 60%, respectively. This work completes the first stage towards the establishment of a general method for detecting diolepoxide polyaromatic hydrocarbon DNA adducts by gas chromatography.

Application of reversal electron attachment for ultrasensitive detection of thermal electron-attaching molecules: carbon tetrachloride and nitrobenzene

A standard gas-dilution method was used to determine the selective response of the reversal electron attachment detector to carbon tetrachloride concentrations in nitrogen. Data are provided that determine the lowest concentration of sample detectable with the present instrumental configuration as being below 1.0 part per trillion by volume. The incorporation of a 90-deg electrostatic deflector with the quadrupole mass spectrometer is shown to be vital, and with it, negative-ion quadrupole mass spectrometry is used to characterize the ionization process. Observations are also made of the reversal electron attachment response to nitrobenzene. The analytical potential of reversal electron capture negative-ion mass spectrometry is examined, and areas for future development are discussed.

Comparison of tandem and conventional mass spectrometry using electron capture negative ionization in the detection of chemically oxidized dexamethasone in human plasma

Dexamethansone, a synthetic steroid, can be oxidized chemically to a ketonic steroid structure that is readily detected by electron capture negative ionization mass spectrometry (ECNI/MS). Previous work from this laboratory has demonstrated that the chemical oxidation procedure provides advantages of low detection limits and high selectivity for detection of oxidized dexamethasone against chemical background that would otherwise interfere with detection of this steroidal drug in biological samples using more conventional methodology. This report describes the extent to which tandem mass spectrometry (MS/MS) can further enhance the selectivity of the oxidation/ECNI methodology for the detection of dexamethasone during the analysis of human plasma and presents evidence that sample introduction by direct inlet probe (DIP) can be used successfully under ECNI conditions. For purposes of comparing the methodologies, the same human plasma samples are analyzed by ECNI, first with detection by conventional mass spectrometry using selected ion monitoring (SIM) and then by MS/MS using selected reaction monitoring (SRM) with sample introduction by the gas chromatographic (GC) inlet and by the DIP. The results indicate that use of the DIP is a viable means of sample introduction for ECNI when sample processing involves the specialized oxidation procedure described herein because the sample matrix does not compete significantly for the thermal electrons in the ion source. Whereas SIM and SRM provide comparable results when sample introduction is achieved by the GC inlet, the MS/MS approach offers the possibility for sample introduction using the DIP, which significantly simplifies and shortens the analysis.

Selection of electrophoric derivatives of 1-aminopyrene and 2-aminofluorene for determination by gas chromatography with electron-capture negative-ion mass spectrometry

Several electrophone derivatives of 1-aminopyrene and 2-aminofluorene were prepared. Reagents such as heptafluorobutyryl chloride, pentafluorobenzoyl chloride, pentafluorobenzyl bromide and pentafluorobenzaldehyde, alone and in certain combinations, were employed. The ease of formation, yield, stability and fragmentation by gas chromatography with electron-capture negative-ion (ECNI) mass spectrometry of the derivatives were compared. This allowed the most promising ones to be selected for future work on the sensitive detection of aminopolyaromatics by this detection technique. Pentafluorobenzylidene (first choice) and N-pentafluorobenzylN-heptafluorobutyryl (second choice) derivatives emerged as the best ones. The origins of losses of HF and 2HF from some of the derivatives were elucidated in the ECNI mass spectra by studies of deuterium-labeled analogues.

Electron-capture negative ionization calibrants for magnetic sector mass spectrometers

Fomblin [poly(perfluoropropylene oxide)], PFK (perfluorokerosene) and FC-43 (perfluorotributylamine) are investigated as mass calibrants in electron-capture negative ionization mass spectrometry on a magnetic sector hybrod mass spectrometer. This work provides exact negative ion mass tables of these three calibrants obtained using high-resolution peak matching of representative ions of the calibrants against ions of known mass. The suitability of these calibrants for full data system control in the negative ionization mode is demonstrated for the techniques of high-resolution scanning, selected ion recording and calibration of the quadrupole sector of a hybrid instrument.