Chemical ionization mass spectrometry of carbamate pesticides:  a major dissociation pathway

Jj, Stamp; Eg, Siegmund; Cairns, Thomas; Chan, KK

doi:10.1021/ac00295a050

Cited by 29 publications

(2 citation statements)

References 34 publications

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“…As can be seen, the intensity ratio of the ammonium adduct ion mjz 239 and the quasimolecular ion mlz 222 varies widely over the TSP mass spectra. Furthermore, the specific fragmentation required to produce mlz 165 from [M + H]+ by loss of methyl isocyanate (CH 3NCO) [11] is observed with desorption CI, nebulizer assisted electrospray (ionspray), and atmospheric pressure chemical ionization (APCn but not with TSP.…”

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confidence: 99%

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

Honing

Barceló

Baar

et al. 1994

J. Am. Soc. Mass Spectrom.

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The effects of three additives-ammonium acetate, ammonium formate, and nicotinic acid-to the liquid chromatographic (LC) eluent and of the vaporizer temperature on the ion formation of N-methyl carbamate pesticides in thermospray (TSP) mass spectrometry was investigated by using filament- or discharge-assisted ionization. Nineteen carbamates and 12 of their known environmental degradation products were used as model compounds. The additives cause a strong reduction in the abundance of the characteristic fragment ions [M + H - CH3NCO](+) and [M - H - CH3NCO](-) for some of the carbamates. The addition of nicotinic acid reduces the quasimolecular ion intensity and, in most cases, produces nicotinic acid adduct ions. The addition of ammonium acetate or ammonium formate increases the intensity of the quasimolecular ion and in most cases produces a base peak for the ammonium adduct ion. The combination of a suppression of fragmentation and an enhancement of quasimolecular ion formation produces an overall gain in sensitivity. As to more specific effects, the addition of the ammonium salts reduces the intensity of M(-•) with the chlorinated carbamate barban and suppresses the formation of "odd" adduct ions in the TSP mass spectra of most other carbamates. Monitoring the intensity of the fragment and the quasimolecular ion signal as a function of the probe stem temperature, and the related probe tip temperature, proved to be an easy method to study the thermal degradation of the carbamates. This monitoring procedure showed that methiocarb and its sulfone already suffer from thermal degradation at a stem temperature of 90°C and that these compounds will therefore present problems in quantitation with LC/TSP mass spectrometry.

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confidence: 99%

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

Honing

Barceló

Baar

et al. 1994

J. Am. Soc. Mass Spectrom.

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“…2(b)) gave, in addition to the m/z 181 ion due to N ‐methylisocyanate loss, a diagnostic ion at m/z 220.0985 (the base peak), not observed for by‐product 2, corresponding to an elemental composition of C 12 H 14 NO

_{3}^{+}

(error 7.6 ppm) deriving from loss of water. Such an ion was also observed during GC/MS analysis in both CI and EI modes,17, 28 although a structure was not proposed. Its formation cannot be attributed (without invoking a rearrangement) to a dehydration process, as is observed for primary and secondary alcohols, since the carbon at position 2 is not bound to any hydrogen.…”

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confidence: 96%

Characterization of carbofuran photodegradation by‐products by liquid chromatography/hybrid quadrupole time‐of‐flight mass spectrometry

Detomaso

Mascolo

López

2005

Rapid Comm Mass Spectrometry

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The structural elucidation of by-products arising from carbofuran photodegradation using a high-pressure UV lamp has been investigated by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) employing a quadrupole time-of-flight mass spectrometer. Exact mass measurements of the [M + H]+ ions of the by-products and of product ions allowed the elemental formulae and related structures of seven photodegradation by-products (resulting, respectively, from photo-Fries rearrangement, hydroxylation of the benzene ring, oxidation of the 2,3-dihydrobenzofuran ring, cleavage of the carbamate group, hydrolysis of the ether group and the newly observed radical coupling and decarboxylation processes) to be determined confidently. Accurate mass measurements of product ions allowed ambiguities to be removed concerning neutral losses having the same nominal mass, namely CO and C2H4, allowing the fragmentation patterns to be rationalized.

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Carbamate and Carbamoyloxime Insecticides: Single‐Class, Multiresidue Analysis of

Honing¹

2000

Encyclopedia of Analytical Chemistry

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Large quantities of modern pesticides such as the N ‐methyl‐ and carbamoyloxime carbamates (over 1000 t of the N ‐methylcarbamate carbaryl) are used for agricultural as well as for nonagricultural purposes. The European Union (EU)‐permitted concentration levels of these insecticides and their related transformation products in drinking water is 0.1 µg L −1 , and the maximum for the total pesticide content has been set to 0.5 µg L −1 . Many analytical procedures, focusing on sample pretreatment, column chromatographic separation, and sensitive detection, have been reported for the trace‐level determination of these compounds. This article surveys the application of these techniques, and their potential with regard to recovery, resolution, sensitivity, and robustness is discussed. For example the reproducibility of results with a variety of carbamates from water samples or pretreated biological/soil samples is an essential criteria during the development of extraction procedures. The percentage of recovery influences the sensitivity of the total analytical method. Good results with solid‐phase extraction (SPE) are obtained with a C 18 /OH phase which is used on a routine basis by various analytical laboratories for the analysis of surface waters and vegetables. This technique is superior to liquid–liquid extraction (LLE) for reasons explained in this article. Chromatographic resolution is most effective, when gas chromatography (GC) is used. Unfortunately, thermal degradation of some carbamates in the injector takes place, making liquid chromatography (LC) the separation technique of choice despite the fact that some carbamates cannot now be separated. Capillary electrophoresis (CE) offers better separation efficiency but is still not a robust technique. Another way to solve the coelution problem is the application of mass spectrometry (MS). Utilizing the selected ion monitoring mode, coeluting compounds can be quantified. MS adds an extra separation step because ionized compounds are separated by the mass‐to‐charge ratio. Application of the ionspray (ISP) and the heated nebulizer (HN) interfacing techniques makes possible the quantification of carbamates at trace levels as low as 0.1 ng L −1 in drinking water, without any sample preconcentration. Furthermore, MS also offers the ability to confirm the identity of the compounds. On‐line SPE in combination with liquid chromatography/mass spectrometry (LC/MS) or, better, liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the best method for the quantification and structural confirmation of carbamate pesticides at concentration levels of 0.1 ng L −1 or lower.

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Chemical ionization mass spectrometry of carbamate pesticides: a major dissociation pathway

Cited by 29 publications

References 34 publications

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

Characterization of carbofuran photodegradation by‐products by liquid chromatography/hybrid quadrupole time‐of‐flight mass spectrometry

Carbamate and Carbamoyloxime Insecticides: Single‐Class, Multiresidue Analysis of

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