Methane Negative Ion Chemical Ionization Research Articles

Development of a method for measuring mass concentration of cyanides in soil samples using gas chromatography and tandem mass-selective detection

The Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction places CN-containing toxic chemicals like tabun and its numerous homologues and analogues (around 10.000 organic compounds), hydrogen cyanide, cyanogen chloride etc., under the international control in the field of arms control, disarmament and non-proliferation. Moreover, CN-containing toxic chemicals are hazardous industrial and environmental pollutants. Soils are the most widely-spread and complex environmental objects for the detection and analysis of cyanides. The aim of this work is to elaborate the method for measuring mass concentration of cyanides in soil samples, which is more sensitive and less labor-intensive, than photometric method, adopted in the Russian Federation. The developed method involves the use of 2,3,4,5,6-pentafluorobenzyl bromide as a derivatizing agent and GC/MS/MS with methane negative ion chemical ionization. It enables the identification and quantification of cyanide ions in soil in the range of 0.7 ng/g – 10.0 μg/g. This method is much more sensitive than the photometric method, included in the federal registry. It does not require the use of potassium cyanide isotopes with radioactive labels of carbon and potassium as an internal standard, and it requires less implementation time

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.

Organic Contaminants in Canadian Municipal Sewage Sludge. Part II. Persistent Chlorinated Compounds and Polycyclic Aromatic Hydrocarbons

Abstract Thirty-five sewage sludge samples collected across Canada were analyzed for 18 polycyclic aromatic hydrocarbons (PAHs), 17 congeners of polychlorinated biphenyls (PCBs) and seven selected chlorinated compounds. Samples were prepared by accelerated solvent extraction and standard column cleanup procedures using silica gel and Florisil. Gas chromatography with electron-capture detection was used for the determination of PCBs. Gas chromatography/mass spectrometry with electron-impact ionization and methane negative ion chemical ionization were used for the detection of PAHs and the chlorinated compounds, respectively. PAHs were detected in nearly all samples, with a total concentration ranging from 0.14 to 209 µg/g (median 3.65 µg/g) on a dry weight basis. Phenanthrene, fluoranthene and pyrene were present at the highest concentrations, with medians ranging from 0.56 to 0.58 µg/g. PCBs were also found in all samples, with a total PCB concentration ranging from 31 to 323 ng/g. The most abundant PCBs (congeners 52, 101 and 110) had median concentrations of 12 ng/g or above. While pentachlorobenzene and hexachlorobenzene were observed in all sludge, at low ng/g levels, no other less chlorinated benzenes have been detected in the same samples. Octachlorostyrene was only found in the Ontario samples, with concentrations ranging from 0.3 to 11.5 ng/g (median 0.9 ng/g). For the chlorinated insecticides, only p,p'-DDE, α- and γ-chlordane were found on a more regular basis, with median concentrations of 12.0, 0.4 and 0.8 ng/g, respectively. These results suggest that the above toxic chemicals are occurring in Canadian sewage samples and are persistent enough to survive the existing sewage treatment processes.

Occurrence of Polycyclic and Nitro Musk Compounds in Canadian Sludge and Wastewater Samples

Abstract Fragrances such as synthetic musk compounds are commonly used as additives in a wide range of consumer and personal-care products. At the end of their life cycle, most of these compounds will end up in municipal sewage systems. In this work, we report the occurrence of selected polycyclic and nitro musk compounds in sewage sludge, influent, effluent, as well as some industrial wastewater samples collected in Canada. A newly developed supercritical carbon dioxide extraction technique was used for the extraction of residual musk fragrances in the sludge. Final analysis was performed by gas chromatography/ mass spectrometry (GC/MS) using electron-impact and methane negative ion chemical ionization techniques. The results indicated that Galaxolide® (HHCB), Tonalide® (AHTN), musk xylene (MX), and musk ketone (MK) were the most common musk compounds in the Canadian environment, as they were found in every sample in this study. In the same sludge sample, levels of HHCB and AHTN (ranging from 1.3 to 26.7 μg/g) were often found to be about 1000 times higher than those of MX and MK (ranging from 1.4 to 422 ng/g). Similarly, in the sewage influent and effluent collected in Ontario, the levels of HHCB and AHTN (ranging from 159 to 2411 ng/L) were much higher than those of MX and MK (ranging from 1 to 84 ng/L). The levels of musk compounds varied widely in industrial wastewaters. In one sample collected from a detergent manufacturer, the levels of HHCB, AHTN, MX, and MK were found to be 54,200, 13,300, 5480, and 2.2 ng/L, respectively. It was also noted that the levels of MX and MK observed in the samples collected from the commercial laundries in Toronto were significantly higher than those found in domestic sewage.

Confirmation of multiple tetracycline residues in milk and oxytetracycline in shrimp by liquid chromatography–particle beam mass spectrometry

A confirmation procedure is described for detection of residues of six tetracyclines in bovine milk, and oxytetracycline in shrimp. Residues are extracted from milk or shrimp tissue using metal chelate affinity chromatography. The extracts are desalted, further concentrated using polymeric solid-phase extraction, and chromatographed on a polymeric reversed-phase column. Analysis is by methane negative ion chemical ionization on a quadrupole mass spectrometer using a particle beam interface. Data are acquired in partial scan mode, monitoring from m/ z 378 to m/ z 480. The procedure was validated with control milk and shrimp, fortified milk (30 ng/ml) and shrimp (100 ng/g), and milk and tissue from animals treated with the drugs.

Quantitation of the enantiomers of rimantadine and its hydroxylated metabolites in human plasma by gas chromatography/mass spectrometry.

A gas chromatographic/mass spectrometric procedure has been developed for the quantitation in human plasma of the enantiomers of rimantadine and its three hydroxylated metabolites. The assay utilized derivatization of all analytes with the optically active reagent S-alpha-methyl-alpha-methoxy(pentafluorophenyl)acetic acid, selective ion monitoring, methane negative ion chemical ionization mass spectrometry and stable isotope dilution techniques. This method has been used to measure plasma concentrations of the enantiomers of rimantadine, m-hydroxyrimantadine and p-hydroxyrimantadine (equatorial and axial epimers) in the ranges 2.5-250, 2.5-50, 1.25-62.5 and 1.25-62.5 ng/mL, respectively, in six subjects given a single 200 mg dose of racemic rimantadine. Although there are no significant differences in the concentration-time profiles of R- and S-rimantadine, large stereospecific differences in the disposition of their metabolites are observed.

Negative ions generated by reactions with oxygen in the chemical ionization source. I. Characterization of gas‐phase and wall‐catalyzed reactions of fluorene, anthracene and fluoranthene

AbstractThe methane negative ion chemical ionization (NICI) mass spectra of polycyclic aromatic hydrocarbons are usually dominated by molecular, M− ˙ or M  H− ions; however, ions resulting from additions to M have also been reported. Some of these ions have been observed at [M + 14]− ˙, [M + 15]−, [M + 30]− and [M + 32]−˙ and have been attributed to reactions with either oxygen‐containing impurities in the buffer gas or alkyl radical species generated by ionization of a hydrocarbon buffer gas. In this study, the NICI spectra of fluorene, anthracene and fluoranthene were studied in detail using quadrupole and Fourier transform mass spectrometers. Spectra were acquired when reactive species such as oxygen, water, nitrous oxide and carbon dioxide were added to the nitrogen buffer gas. Experiments with deuterated methane were also carried out. These studies indicated that buffer gas impurities affect the NICI spectra; however, gas‐phase ion‐molecule reactions were not responsible for all of the observed products. In addition to electron‐ and ion‐molecule reactions, ions were observed that resulted from wall‐catalyzed oxidation reactions followed by electron capture. These reactions were enhanced by the addition of oxygen and elevated ion source temperatures. Depending upon the parent PAH structure, oxidation products such as ketones, quinones and anhydrides were formed.

Determination of rimantadine and its hydroxylated metabolites in human plasman and urine

A gas chromatographic-mass spectrometric procedure has been developed for the quantitation of the antiviral agent rimantadine and its meta- and para-hydroxylated metabolites in human plasma and urine. The assay utilizes an extractive pentafluorobenzoylation at alkaline pH with cyclohexane saturated with triethanolamine-chloroform (2:1) containing pentafluorobenzoyl chloride, selective ion monitoring, methane negative ion chemical ionization mass spectrometry and stable isotope dilution. The method has been used to measure plasma concentrations of rimantadine, m-hydroxyrimantadine and the two epimers of p-hydroxyrimantadine between 5-250, 5-100 and 2.5-50 ng/ml, respectively. Similarly, the urine concentrations of these measured were between 25-1250, 25-500 and 12.5-250 ng/ml, respectively.

Obtaining structural information of perfluoro‐1,3‐dimethyladamantane from collisionally activated decomposition mass spectra

AbstractCyclic, high molecular weight perfluorocarbons (PFC's) are very electronegative, and can be detected by methane negative ion chemical ionization (NICI); however only molecular ions are detected. Electron ionization (EI) of PFC's, on the other hand, yields little or no molecular ion but very intense low mass fragment ions such as CF (m/z 69), C3F (m/z 131) and C4F (m/z 181), which are not structurally characteristic. High‐energy collisionally activated decomposition (CAD) of positive, molecular ions of perfluoro‐1,3‐dimethyladamantane yields important structural information by providing more intense high mass fragment ions. Fragments of the following formulae and abundances (in brackets): C5F (100), C11F (73), C7F (67), C8F (43), C4F (26), C7F (18), and CF (14) are detected by this method.

Methane chemical ionization mass spectrometry of the pentafluorobenzyl derivatives of abscisic acid, its metabolites and other plant growth regulators

Tetraethyl ammonium hydroxide has been used as a catalyst for the pentafluorobenzylation of abscissic acid and its metabolites, as well as zeatin, gibberellic acid and indole acetic acid. These derivatives, acetylated where necessary, were subjected to methane negative ion chemical ionization mass spectrometry. The spectra were quite simple and are therefore ideally suited for selected ion monitoring at high sensitivity with heavy isotope labelled internal standards. The sensitivity for pentafluorobenzyl abscisate was 20 fg with a signal to noise ratio of greater than 10:1. The other compounds were within an order of magnitude of this. It is thus feasible, at least in principle, to quantify components from all four groups of plant growth regulators from the same tissue.

The fragmentation of methyl abscisate and its 2E isomer in methane positive and negative chemical ionization mass spectrometry

The fragmentation pathways of methyl abscisate and its 2E isomer in methane positive ion chemical ionization (PICI) and methane negative ion chemical ionization (NICI) mass spectrometry have been elucidated using isotopically labelled analogues. It is shown that in PICI the most abundant ions are formed by the loss of water, methanol, both methanol and water and of methyl formate. The PICI mass spectrum of methyl 2E abscisate differs significantly in that the loss of water is much less important. In NICI, the most abundant ions from methyl abscisate are due to the molecular anion, [M – H2O]− and [M – CH3OH]−. It is shown, however, that the methyl ester methyl is not lost in this last fragmentation. Two other significant ions contain the side chain and the ring of methyl abscisate, respectively. In contrast, the NICI mass spectrum of methyl 2E abscisate differs principally in showing an abundant loss of a hydrogen atom.

Quantitation of the enantiomers of rimantadine in human plasma and urine by gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric procedure has been developed for the quantitation in plasma and urine of the enantiomers of rimantadine, an antiviral drug effective against type A influenza. The assay utilizes derivatization with an optically active reagent, selective ion monitoring, methane negative-ion chemical ionization (NICI) mass spectrometry and stable isotope dilution. The method has been used to measure concentrations of each rimantadine enantiomer over a range of 2.5-250 and 12.5-1250 ng/ml in the plasma and urine, respectively, of four male volunteers administered rimantadine. In plasma and urine, no differences were observed in the disposition of the unconjugated enantiomers. In urine, one enantiomer, but not both, was released following enzymatic hydrolysis.

Quantitative determination of rimantadine in human plasma and urine by GC-MS.

A GC-MS procedure has been developed for the quantitation in plasma and urine of rimantadine, an antiviral drug effective against type A influenza. The assay utilizes selective ion monitoring, methane negative ion chemical ionization (NCI) and stable isotope dilution. Sensitivity to NCI is effected by derivation of rimantadine with pentafluorobenzoyl chloride. The method has been used to quantitate plasma concentrations of rimantadine over a range from 4.2 ng/ml to 416 ng/ml, and urinary concentrations of rimantadine over a range of 21 ng/ml to 2077 ng/ml.

Quantitation of toxaphene in environmental samples using negative ion chemical ionization mass spectrometry

A method for quantitating toxaphene in environmental samples using methane negative ion chemical ionization (NICI) mass spectrometry in the selected ion mode is given. NICI is highly selective and sensitive for measuring toxaphene. This method monitors ions from each of the homologue groups in the toxaphene mixture having 6 to 10 chlorines corresponding to the M/sup -/ or the (M - Cl)/sup -/ ion clusters (m/z 340, 341, 342, 343, 375, 377, 411, 413, 447, 449). Additional ions are monitored to correct for interferences from chlorinated pesticides (m/z 336, 338, 371, 373, 376, 412, 444, 448). Quantitation is done relative to an internal standard, 2,2',3,4,4',5,6,6'-octachlorobiphenyl (m/z 428 and 430). The NICI response was linear over 4 orders of magnitude, and the detection limit was 75 pg. This method is accurate and reproducible for measuring toxaphene in the presence of a major interferent, technical chlordane. The method is successful at measuring toxaphene in complex environmental matrices such as fish, and it can also be used to evaluate the changes in the relative homologue distribution that may have resulted from environmental transformations.

Analysis of kava resin by gas chromatography and electron impact and methane negative ion chemical ionization mass spectrometry. New trace constituents of kava resin

Electron impact (EI) and methane negative ion chemical ionization (NICI) gas chromatographic/mass spectrometric analyses of kava resin, derived from commercial Piper methysticum, are described. The resulting mass spectra are correlated with the known major and trace constituents of this resin. Several of the kava lactones (kawain, methysticin, desmethoxyyangonin and yangonin) produced abundant molecular anions when analysed by methane NICI mass spectrometry, in contrast to their 7,8-dihydro analogues which ionized with poor efficiency to yield weak [M − H]− anions. Deuterium labelling established that the origin of the [M − CH3]− anion in the methane NICI mass spectrum of yangonin resulted from the elimination of a methyl radical from the 4-methoxyl substituent. As a result of the present study, an additional four trace components of kava have been identified.

Methane negative ion chemical ionization fragmentation processes of deuterated analogues ofOrtho-,meta- andpara-tyramine-N,O-dipentafluoropropionate derivatives

The methane negative ion chemical ionization (NICI) mass spectra of the three isomeric tyramine-N-O-dipentafluoropropionate derivatives are unique insofar as each has a different base peak in contrast to their methane positive ion chemical ionization (PICI) mass spectra which are very similar in appearance. Deuterium-labelling studies in the three isomeric tyramine derivatives have elucidated the fragmentation processes accompanying the electron capture NICI process for each derivatized compound.

Positive and negative ion chemical ionization mass spectra of amino acid carboxy-n-butyl EsterN-Pentafluoropropionate Derivatives

The positive and negative chemical ionization mass spectra of 29 amino acid carboxy-n-butyl ester N-(O,S)-Pentafluoropropionate derivatives hae been determined. The positive ion (PI) mass spectra conform to the expected fragmentation patterns for this amino acid derivative but their methane negative ion chemical ionization (NICI) mass spectra displayed marked differences between various amino acid classes and bvetween positional isomers within the same class. Isomeric butyric acid (α, β and γ) and tyrosine (o, m amd p-hydroxylation) derivatives all had remarkably difterent NICI mass spectra. Aliphatic amino acid CO2-n-butyl-N-PFP derivatives (except glycine) can be readily recognized by a characteristic fragmentation process corresponding to [M–H–C4CO2H]−. Deuterium labellung studies were used to delineate some of the major NICI fragmentation processes. While the PICI mass spectra all gave comparable detection responses differences were observed with various amino acids when operating in the NICI mode. The order of sensitivity of detection for six representative amino acid-carboxy-n-butyl-N-PFP derivatives were: hydroxyproline > lysine > cysteine > glycine=leucine=methionine in the ratio of 100:20:7:1. In PICI mass spectrometry derivatized leucine yielded a response 25 times less than its NICI mass spectrometric value.

A site specific rearrangement in electron capture negative ion CI mass spectrometry of pentafluoropropionyl derivatives of some β-hydroxyamines

This study reports a rearrangement process observed in electron capture negative ion chemical ionization mass spectrometry of pentafluoropropionate and heptafluorobutyrate derivatives of some β-hydroxylated amines. The pentafluoropropionate derivatives of a number of these substituted amines yield a prominent anion of mass 145 (195 in the corresponding heptafluorobutyrate derivatives). In the pentafluoropropionate derivatives of ethanolamine and β-hydroxyphenethylamine this anion was quantitatively displaced to m/z 146 when the γ-hydrogen (relative to the derivatized hydroxyl group) was substituted by deuterium. We postulate an initial 6-membered transition state to produce a pentafluoropropionic acid anion (not observed) which then eliminates either a hydrogen atom to give m/z 163 or a fluorine atom to give m/z 145. The former remains at mass 163 in the γ-deuterated compounds examined. The proposed rearrangement is the negative ion analogue of the McLafferty rearrangement process of positive ion electron impact mass spectrometry. However, the negative ion rearrangement is not as general as its positive ion electron impact counterpart because the former is critically dependent upon the substitution present on the α and β carbon and nitrogen atoms, respectively, of the β-hydroxyamine-PFP (or HFB) derivatives. In this regard we examined the effects on m/z 145 anion formation of methyl substitution on the nitrogen and α and β carbon atoms of these pentafluoropropionate derivatives. The results suggest that electron capture methane negative ion chemical ionization mass spectra of β-hydroxylated PFP derivatives could be used as diagnostic tool for structural assignments within this group of compounds.

Nitrated polycyclic aromatic hydrocarbons in urban air particles

The organic extract of urban air particles from St. Louis, MO, was fractionated by high-performance liquid chromatography. The moderately polar fraction was characterized by gas chromatography-electron impact and methane negative ion chemical ionization mass spectrometry. The compounds identified in the sample included nitronaphthalene, 9-nitroanthracene, 3-nitrofluoranthene, 1-nitropyrene, arenecarbonitriles, and several polycyclic ketones, quinones, and anhydrides. These studies represent the first mass spectrometric evidence of nitroaromatics in urban air particles.