Negative Chemical Ionization Mass Spectrometry Research Articles

Determination of polybrominated diphenyl ethers in human milk samples in the Czech Republic: Comparative study of negative chemical ionisation mass spectrometry and time-of-flight high-resolution mass spectrometry

In the Czech Republic no study on the levels of brominated flame retardants in human milk has been conducted, yet. In the first step analytical method for determination of PBDEs in this bioindicator matrix was implemented. Liquid–liquid extraction (LLE) (hexane, diethyl ether), followed by gel permeation chromatography was employed for isolation of PBDEs. Identification and quantification of PBDEs was carried out by GC–MS operated in negative chemical ionisation (NCI). Two mass spectrometric technologies, one employing quadrupole and the other one high resolution (HR) time-of-flight (TOF) analyzer, etc. were used in our study. Detection limits (LODs) obtained by quadrupole analyzer ranged from 0.02 to 0.05 ng g −1 lipid weight, using high resolution time-of-flight analyzer LODs were significantly lower, ranging from 0.002–0.005 ng g −1 lipid weight, what enabled detection of minor PBDE congeners. Within this pilot study 103 breast milk samples, obtained from mothers living in Olomouc region, were examined. Ten PBDE congeners were determined. All samples examined till now contained PBDEs residues, the dominating contaminant representing this group was congener BDE 47. In most of analysed samples levels of this compound ranged from 0.2 to 2 ng g −1 of lipid weight. Three exceptionally contaminated samples, containing levels of PBDEs 5–10 times higher than other samples, were found.

Determination of perfluorocarboxylic acids in aqueous matrices by ion-pair solid-phase microextraction–in-port derivatization–gas chromatography–negative ion chemical ionization mass spectrometry

A rapid, selective and simple analytical procedure using tetrabutylammonium as ion pair in conjunction with solid-phase microextraction followed by in-port derivatization–GC–negative ion chemical ionization mass spectrometry was developed. The procedure allows an accurate determination of perfluoroalkylcarboxylic acids in aqueous samples at ng L −1 levels (i.e. method detection limit 20 ng L −1 for perfluorodecanoic acid) improving previous GC methods in terms of analysis time and sensitivity. Ammonia as reagent gas in the negative ion chemical ionization mass spectrometry increased the sensitivity at least 3-fold compared to methane for perfluorocarboxylic acid butyl esters. The developed procedure was successfully applied to effluents from wastewater treatment plants (i.e. 0.05–8.2 μg L −1) and harbor seawaters.

Identification and quantification of astaxanthin esters in shrimp (Pandalus borealis) and in a microalga (Haematococcus pluvialis) by liquid chromatography-mass spectrometry using negative ion atmospheric pressure chemical ionization.

Negative ion liquid chromatography-atmospheric pressure chemical ionization mass spectrometry [negative ion LC-(APCI)MS] was used for the identification of astaxanthin esters in extracts of commercial shrimp (Pandalus borealis) and dried microalga (Haematococcus pluvialis) samples. A cleanup step using a normal phase solid phase extraction (SPE) cartridge was applied prior to analysis. Recovery experiments with astaxanthin oleate as model compound proved the applicability of this step (98.5 +/- 7.6%; n = 4). The assignment of astaxanthin esters in negative ion LC-(APCI)MS was based on the detection of the molecular ion (M*-) and the formation of characteristic fragment ions, resulting from the loss of one or two fatty acids. Quantification of individual astaxanthin esters was performed using an astaxanthin calibration curve, which was found to be linear over the required range (1-51 micromol/L; r2 = 0.9996). Detection limits, based on the intensity of M*-, a signal-to-noise ratio of 3:1, and an injection volume of 20 microL, were estimated to be 0.05 microg/mL (free astaxanthin), 0.28 microg/mL (astaxanthin-C16:0), and 0.78 microg/mL (astaxanthin-C16:0/C16:0), respectively. This LC-(APCI)MS method allows for the first time the characterization of native astaxanthin esters in P. borealis and H. pluvialis without using time-consuming isolation steps with subsequent gas chromatographic analyses of fatty acid methyl esters. The results suggest that the pattern of astaxanthin-bound polyunsaturated fatty acids of P. borealis does not reflect the respective fatty acid pattern found in triacylglycerides. Application of the presented LC-(APCI)MS technique in common astaxanthin ester analysis will forestall erroneous xanthophyll ester assignment in natural sources.

The branching ratio of anions in thermal electron attachment to chlorinated fluorobenzenes

The temperature dependences of the formation of negative ions from C 6F 6− x Cl x , CF 3C 6F 5− x Cl x , and NC 5F 5− x Cl x ( x=1,2) were studied using negative chemical ionization mass spectrometry. Cl − and the parent negative ion were produced. The ( M−Cl) −(M: parent molecule) was also observed for CF 3C 6F 5− x Cl x and NC 5F 5− x Cl x . The temperature dependence of the relative intensity, ( M−Cl) −/Cl −, suggested that the electron affinity of the fragment radicals decreases in the order, CF 3C 6F 4>C 5F 4N>C 6F 5. On the other hand, the relative intensity, Cl −/ M −, suggested that the electron affinity of the parent molecules decreases in the order, CF 3C 6F 5− x Cl x ⪢NC 5F 5− x Cl x >C 6F 6− x Cl x . Geometries of the parent anions were also calculated using with B3LYP/6-31+G method. The parent anions have an out-of-plane deformed structure and the extent of the deformation corresponds to that of the electron affinity for the parent molecule.

Determination of picogram levels of midazolam, and 1- and 4-hydroxymidazolam in human plasma by gas chromatography–negative chemical ionization–mass spectrometry

Midazolam is a widely accepted probe for phenotyping cytochrome P4503A. A gas chromatography–mass spectrometry (GC–MS)–negative chemical ionization method is presented which allows measuring very low levels of midazolam (MID), 1-OH midazolam (1OHMID) and 4-OH midazolam (4OHMID), in plasma, after derivatization with the reagent N- tert-butyldimethylsilyl- N-methyltrifluoroacetamide. The standard curves were linear over a working range of 20 pg/ml to 5 ng/ml for the three compounds, with the mean coefficients of correlation of the calibration curves ( n=6) being 0.999 for MID and 1OHMID, and 1.0 for 4OHMID. The mean recoveries measured at 100 pg/ml, 500 pg/ml, and 2 ng/ml, ranged from 76 to 87% for MID, from 76 to 99% for 1OHMID, from 68 to 84% for 4OHMID, and from 82 to 109% for N-ethyloxazepam (internal standard). Intra- ( n=7) and inter-day ( n=8) coefficients of variation determined at three concentrations ranged from 1 to 8% for MID, from 2 to 13% for 1OHMID and from 1 to 14% for 4OHMID. The percent theoretical concentrations (accuracy) were within ±8% for MID and 1OHMID, within ±9% for 4OHMID at 500 pg/ml and 2 ng/ml, and within ±28% for 4OHMID at 100 pg/ml. The limits of quantitation were found to be 10 pg/ml for the three compounds. This method can be used for phenotyping cytochrome P4503A in humans following the administration of a very low oral dose of midazolam (75 μg), without central nervous system side-effects.

Determination of quinoxaline-2-carboxylic acid, the major metabolite of carbadox, in porcine liver by isotope dilution gas chromatography–electron capture negative ionization mass spectrometry

A sensitive and robust method using isotope dilution gas chromatography–electron capture negative chemical ionization mass spectrometry (GC–ECNI-MS) was developed and validated for the analysis of quinoxaline-2-carboxylic acid (QCA) in porcine liver. [ 2H 4]QCA was added to liver samples which were then deproteinated with 2% metaphosphoric acid in 20% methanol. Followed by sequential extraction with water-saturated ethyl acetate and phosphate buffer, the buffer extracts were subject to solid-phase extraction clean-up by mixed mode anion-exchange columns. QCA was derivatized with N-methyl- N- tert-butyldimethylsilyltrifluoroacetamide (MTBSTFA) prior to GC–ECNI-MS determination. For unambiguous identification, a second GC–ECNI-MS experiment was performed on suspected positive samples which were derivatized independently with another derivatization agent, trimethylsilyldiazomethane. Excellent recovery and precision were obtained and the limit of quantitation was 0.7 μg/kg (S/N>60). Method ruggedness by Taguchi orthogonal array technique is also presented.

Validation of a simple, sensitive method for the determination of beta-estradiol in bovine urine using gas-chromatography negative-ion chemical ionization mass spectrometry.

A new method is presented for the analysis of 17[small beta]-estradiol in bovine urine. After deconjugation, the sample is cleaned up using an OASIS[trade mark sign] HLB disposable cartridge and extracted into 1-chlorobutane. The hormone is derivatized using pentafluorobenzoyl chloride. The derivatized estradiol is quantitated using gas-chromatography negative-ion chemical ionization mass spectrometry. Calibrations, obtained using spiked blank urine, are linear in the range of 100-1000 pg mL(-1) with CC[small alpha] approximately 170 pg mL(-1) and CC[small beta] of 287 pg mL(-1). Recoveries are in the range of 80 to 130%. The method is rugged, rapid and sensitive when compared to other hormone methods.

負イオン化学イオン化質量分析法による多環芳香族炭化水素の分析とコールタール分析への応用

負イオン化学イオン化質量分析法による多環芳香族炭化水素の分析とコールタール分析への応用

Volatile fatty acids as malodorous compounds in wool scouring water and lanolin. Origin and characterisation

Volatile fatty adds (C2‐C7) analysis in wool scouring water and lanolin is presented. These substances are of major interest as malodorous compounds in urban and industrial wastewaters. In this work, they have been analysed in wool scouring water by headspace solid‐phase microextraction followed by gas chromatography negative chemical ionisation mass spectrometry. Most of the volatile fatty adds have been identified at μg g−1 levels. In addition, since lanolin is a major impurity of raw wool, volatile fatty add patterns of wool scouring water and lanolin have been compared in order to establish the origin of these compounds in the wastewater. Finally, the efficiency of the deodorization step, mandatory to obtain commerdal lanolin, has been assessed taking into account the decrease in volatile fatty add content from the raw wool to the lanolin.

Solid-phase extraction versus solid-phase microextraction for the determination of chlorinated paraffins in water using gas chromatography–negative chemical ionisation mass spectrometry

Solid-phase extraction (SPE) and solid-phase microextraction (SPME) were evaluated for the analysis of short-chain chlorinated paraffins (SCCPs) in water samples using gas chromatography coupled to negative chemical ionisation mass spectrometry (GC-NCI-MS). For SPE optimisation, four commercially available SPE cartridges were tested and several SPE parameters, such as the elution solvent, elution volume and breakthrough volume were studied. The best results were obtained with Varian Bond Elut-C 18. In order to achieve a high selectivity in the determination of SCCPs, GC-NCI-MS was used. Quality parameters of the optimised SPE and SPME procedures were determined, and the best results were obtained for the SPE/GC-NCI-MS method with LODs of 5 and 20 ng l −1 for tap and river water, respectively. This method was successfully applied to the analysis of SCCPs in river water samples at concentrations below the μg l −1 level.

Quantification of F-ring isoprostane-like compounds (F 4-neuroprostanes) derived from docosahexaenoic acid in vivo in humans by a stable isotope dilution mass spectrometric assay

Lipid peroxidation has been implicated in the pathophysiological sequelae of human neurodegenerative disorders. It is recognized that quantification of lipid peroxidation is best assessed in vivo by measuring a series of prostaglandin (PG) F 2-like compounds termed F 2-isoprostanes (IsoPs) in tissues in which arachidonic acid is abundant. Unlike other organs, the major polyunsaturated fatty acid (PUFA) in the brain is docosahexaenoic acid (DHA, C22:6 ω-6), and this fatty acid is particularly enriched in neurons. We have previously reported that DHA undergoes oxidation in vitro and in vivo resulting in the formation of a series of F 2-IsoP-like compounds termed F 4-neuroprostanes (F 4-NPs). We recently chemically synthesized one F 4-NP, 17-F 4c-NP, converted it to an 18O-labeled derivative, and utilized it as an internal standard to develop an assay to quantify endogenous production of F 4-NPs by gas chromatography (GC)/negative ion chemical ionization (NICI) mass spectrometry (MS). The assay is highly precise and accurate. The lower limit of sensitivity is approximately 10 pg. Levels of F 4-NPs in brain tissue from rodents were 8.7±2.0 ng/g wet weight (mean±S.D.). Levels of the F 4-NPs in brains from normal humans were found to be 4.9±0.6 ng/g (mean±S.D.) and were 2.1-fold higher in affected regions of brains from humans with Alzheimer’s disease ( P=0.02). Thus, this assay provides a sensitive and accurate method to assess oxidation of DHA in animal and human tissues and will allow for the further elucidation of the role of oxidative injury to the central nervous system in association with human neurodegenerative disorders.

Pyrethroid soil extraction, properties of mixed solvents and time profiles using GC/MS-NICI analysis

Ultrasonic extraction was used to develop a suitable binary solvent system for the analysis of synthetic pyrethroid pesticides and mirex on soil. The analysis was carried out by gas chromatography with negative ion chemical ionization mass spectrometry (GC/MS-NICI). In the initial experiments, accurately weighed soil samples were spiked with a mixture of standard solution pyrethroids and mirex and shaken for 24 h to ensure homogeneity, then extracted with solvent. The extracts were evaporated to dryness before the volumetric internal standard was added. The binary solvents used in this study were various mixtures of hexane : acetone, hexane : dichloromethane (DCM), isooctane : acetone and isooctane : dichloromethane, representing different classes of polarity. The recoveries of all pyrethroids and mirex were satisfactory over three solvent systems: hexane : acetone, hexane : DCM and isooctane : acetone, but results of isooctane : DCM produced low recoveries. The average recovery increased with the extraction time, but the increase was not statistically significant. A 30-min optimum extraction was deemed sufficient for recovering pyrethroids from soil. After 30 min, extraction decreased owing to the re-distribution of the analyte on the soil matrix.

Sorption–desorption studies of six pyrethroids and mirex on soils using GC/MS-NICI

Sorption–desorption equilibria of six pyrethroids (permethrin, cyfluthrin, cypermethrin, λ-cyhalothrin, deltamethrin and fenvalerate) and mirex were determined in soils possessing a range of organic content (1.15–2.46%). Solutions (in deionized water, pH 6.5–7.4) of the samples were shaken using a mechanical shaker for 24 h. The suspensions were centrifuged and aliquots of clear supernatant were passed through a C-18 column (SPE extraction). The eluates were concentrated to dryness before a volumetric standard was added. The analytes were determined by gas chromatography with negative ion chemical ionization mass spectrometry (GC/MS-NICI) either in SIR or SCN mode. Sorption isotherm parameters (n and k) were calculated according to the Freundlich equation. The values of n are around unity. Permethrin and cyfluthrin were the least sorbed pyrethroids, k<2, mirex and fenvalerate the most. The effect of the pH on sorption was examined also (at pH values 2, 4, 6 and 9). Sorption behaviour on different soils and silica was also examined. Desorption studies were conducted on the same pyrethroid solutions. After sorption, the supernatant was replaced with a similar volume of deionized water. Desorption was achieved by removing all the supernatant from the centrifuged samples and then replacing it with deionized water. This equilibration process was repeated five times. Each time the suspension was centrifuged, concentrated and analyzed using GC/MS analysis. The residual amount of pyrethroid on the soil was calculated as the difference between the initial amount and the desorbed amount (mass balance).

HPLC-MS investigations of acidic contaminants in ammunition wastes using volatile ion-pairing reagents (VIP-LC-MS).

In order to hyphenate ion pairing chromatography and MS detection we used several types of formates as volatile ion pairing reagents (IPRs) instead of common tetraalkylammonium salts, as these salts tend to precipitate in the ion source. The formates were prepared by mixing formic acid with the corresponding amine. Both tributyl- and trihexylammonium formate proved to be valuable IPRs for the separation of acidic compounds like nitrobenzoic acids, nitrobenzenesulfonic acids and nitrated phenols. Due to the weaker retention of the ion-pairs with trialkylammonium formates compared with tetraalkylammonium compounds, either less organic modifier or a higher concentration of the IPR had to be used. With negative atmospheric pressure chemical ionization mass spectrometry and electrospray ionization mass spectrometry it was possible to unambiguously identify several acidic oxidation products of 2,4,6-trinitrotoluene (TNT) in ammunition wastewater and soil extracts. 2-amino-4,6-dinitrobenzoic acid was often found to be the main metabolite of TNT in such water samples.

5-Chlorouracil, a Marker of DNA Damage from Hypochlorous Acid during Inflammation: A GAS CHROMATOGRAPHY-MASS SPECTROMETRY ASSAY

Hypochlorous acid (HOCl), generated from H2O2 and Cl- by myeloperoxidase in activated neutrophils, causes tissue damage during inflammation. We have developed a simple, sensitive (approximately 0.2 fmol on column) and specific GC-MS assay for the detection of 5-chlorouracil (5-ClUra), a signature product of HOCl-mediated damage to nucleobases. In this assay, 5-ClUra is released from isolated DNA by a digestion with nuclease P1, alkaline phosphatase, and thymidine phosphorylase (TP), or from chlorinated nucleosides in biological fluids by TP. The freed 5-ClUra is derivatized with 3, 5-bis-(trifluoromethyl)-benzyl bromide, which is detected by negative chemical ionization mass spectrometry. The assay can be used to simultaneously detect other halogenated uracils including bromouracil. Using this assay, we showed that 5-ClUra is generated by the reaction of low micromolar HOCl with (deoxy)cytidine, (deoxy)uridine, and DNA. In cell cultures, an increase of 5-ClUra was detected in DNA when cells were treated with sublethal doses of HOCl and allowed to proliferate. The elevation of 5-ClUra was markedly accentuated when physiologically relevant concentrations of (deoxy)uridine, (deoxy) cytidine, uracil, or cytosine were present in the medium during HOCl treatment. In the carrageenan-induced inflammation model in rats, chlorinated nucleosides was significantly increased, compared with controls, in the exudate fluid isolated from the inflammation site. Our study provides the direct evidence that chlorinated nucleosides are found in the inflammation site and can be incorporated in DNA during cell/tissue proliferation. These findings may be relevant to the carcinogenesis associated with chronic inflammation.

Determination of dexamethasone in urine by gas chromatography with negative chemical ionization mass spectrometry

Dexamethasone, as some other synthetic corticosteroids, is licensed for therapy in veterinary practice, but its misuse as a growth promotor, often in combination with beta-agonists, is forbidden. In this report an analytical method is described for the detection and confirmation of very low concentrations of dexamethasone in urine. The influence of enzymatic hydrolysis time of samples with glucuronidase was studied. The proposed method consisted of the enzymatic hydrolysis of urine samples, which were then extracted and concentrated using solid-phase cartridges with mixed reversed-phase materials (OASIS). No further clean-up step was found to be necessary. Eluates were derivatized following a previously described method [Analyst 119 (1994) 2557]. Detection, identification and quantification of residues of this compound was carried out by gas chromatography with mass spectrometry in the negative chemical ionization mode. The proposed procedure permits the determination of dexamethasone in urine at levels as low as 0.2 ng ml −1

Identification of Trimer and Dimer of 4-hydroxy-3-methoxy benzaldehyde in crystal structure of Vanillin

The effect of intermolecular hydrogen bonding on the molecular structure of vanillin has been studied using negative ion chemical ionization (NICl) mass spectrometry methods. The [Trimer-H2O] and [Dimer-H2O] were observed at m/z 438 and 286 respectively in NICl (CH4) mass spectrum of vanillin. The NICl (Cl) mass spectrum of vanillin differs where deprotonated molecular ion peak, [monomer-H] at m/z,151 was the second most abundant ion peak. The base ion peak was observed at m/z,187 due to the presence of monomer+35Cl. The [Trimer-H2O] and [Dimer - H2O] were not detected due to the presence of chloride ion. The results obtained support that the crystal of vanillin consists of trimer and dimer of 4-hydroxy-3-methoxy benzaldehyde. Keywords 4-hydroxy-3-methoxy benzaldehyde, vanillin, intermolecular hydrogen bonding. (Global Journal of Pure and Applied Sciences: 2002 9(1): 101-104)

APPLICATIONS OF NEGATIVE ION CHEMICAL IONIZATION MASS SPECTROMETRY TECHNIQUE IN ENVIRONMENTAL ANALYSIS

With the availability of Negative Ion Chemical Ionization (NCI) mode of ionization on most bench top Mass Spectrometry (MS), many analytical problems involving the analysis of electron capturing organic compounds can be easily resolved. The Negative Ion Chemical Ionization Mass Spectrometry (NCI/MS) technique has been utilized for many types of analysis at the Environmental Protection Laboratory on a regular basis for routine analysis and resolving sensitivity, matrix and interference problems. NCI/MS is shown to provide inroads in the identification and lowering of detection limits for halogenated pesticides, polychlorinated biphenyls (PCBs), dioxins and furans. NCI/MS specificity and selectivity are shown to eliminate interferences caused by substances such as plasticizers and other nonhalogenated compounds including petroleum products when analyzing contaminated sample extracts.

The pharmacokinetics of the prostaglandin E1 analogue misoprostol in plasma and colostrum after postpartum oral administration

Objective: To study pharmacokinetics of prostaglandin E1 analogue, misoprostol in plasma and colostrum after postpartum oral administration. Study design: Twenty women received 600 μg doses of misoprostol orally after delivery. Plasma levels of the principal metabolite, misoprostol acid, were measured at 2, 10, 20, 30, 40, 50, 60, 90, 120, 180, 240 and 300 min (48 samples). Colostrum was expressed from the breasts to measure misoprostol acid at 60, 120, 180, 240, and 300 min (24 samples). Assay was done using isotope dilution gas chromatography (GC)/negative ion chemical ionisation mass spectrometry (MS). Results: The plasma concentration of misoprostol acid rose quickly. Two minutes after oral administration its mean level was 91.5 pg/ml, peaked at 20 min (344 pg/ml), then fell steeply by 120 min (27.8 pg/ml) and remained low for the duration of the study. Misoprostol acid in colostrum reached maximum concentration of 20.9 pg/m within 1 h after oral administration. It then declined gradually to 17.8 pg/ml at 2 h, 2.8 pg/ml at 4 h and to <1 pg/ml at 5 h. Areas under misoprostol concentration versus time curves up to 5 h were 290.1 pg h/ml in the plasma and 51.4 pg h/ml in colostrum, respectively. Conclusion: Misoprostol acid is secreted in colostrum within 1 h of oral administration of 600 μg of misoprostol; the pharmacokinetics of misoprostol after oral administration during postpartum is similar to that of other pregnancy periods.

Negative-ion CIMS: analysis of volatile leaf wound compounds including HCN

Chemical-ionization mass spectrometry (CIMS) using flow-reactor mass spectrometers has flourished as a sensitive, on-line method of analyzing trace volatile organic compounds (VOCs) in air. In this work, the OH− anion is explored as the ionizing reagent in a flowing-afterglow selected ion flow tube (FA-SIFT) instrument for its utility in detecting VOCs and HCN released by cut and wounded plant material. Reaction rate coefficients and products for reactions between OH− anion and 17 plant VOCs and some structural isomers are reported. These results are also compared to reactions between H3O+ and these same VOCs. Fragmentation products from collision-induced dissociation (CID) of the [M−1]− anion of each species are also given to aid in ion identification. H/D exchange was successfully used to distinguish ionized aldehyde/ketone products that are structural isomers for two different isomeric aldehyde/ketone pairs. Simultaneous emissions of acetone, butanone, and HCN were observed from several plants and the emissions of acetone and butanone were confirmed from one plant using H/D exchange. The utility of this technique as a screening tool for cyanogenesis in plants is discussed.