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  • Time-of-flight accurate mass spectrometry identification of quinoline alkaloids in honey.

Time-of-flight accurate mass spectrometry identification of quinoline alkaloids in honey.

Analytical and bioanalytical chemistry (2015-06-05)
Tamara Rodríguez-Cabo, Mohammed Moniruzzaman, Isaac Rodríguez, María Ramil, Rafael Cela, Siew Hua Gan
ABSTRACT

Time-of-flight accurate mass spectrometry (TOF-MS), following a previous chromatographic (gas or liquid chromatography) separation step, is applied to the identification and structural elucidation of quinoline-like alkaloids in honey. Both electron ionization (EI) MS and positive electrospray (ESI+) MS spectra afforded the molecular ions (M(.+) and M+H(+), respectively) of target compounds with mass errors below 5 mDa. Scan EI-MS and product ion scan ESI-MS/MS spectra permitted confirmation of the existence of a quinoline ring in the structures of the candidate compounds. Also, the observed fragmentation patterns were useful to discriminate between quinoline derivatives having the same empirical formula but different functionalities, such as aldoximes and amides. In the particular case of phenylquinolines, ESI-MS/MS spectra provided valuable clues regarding the position of the phenyl moiety attached to the quinoline ring. The aforementioned spectral information, combined with retention times matching, led to the identification of quinoline and five quinoline derivatives, substituted at carbon number 4, in honey samples. An isomer of phenyquinoline was also noticed; however, its exact structure could not be established. Liquid-liquid microextraction and gas chromatography (GC) TOF-MS were applied to the screening of the aforementioned compounds in a total of 62 honeys. Species displaying higher occurrence frequencies were 4-quinolinecarbonitrile, 4-quinolinecarboxaldehyde, 4-quinolinealdoxime, and the phenylquinoline isomer. The Pearson test revealed strong correlations among the first three compounds.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methanol, NMR reference standard
Sigma-Aldrich
Ammonium acetate, BioXtra, ≥98%
Sigma-Aldrich
Ammonium acetate solution, for molecular biology, 7.5 M
Sigma-Aldrich
Chloroform, ≥99%, PCR Reagent, contains amylenes as stabilizer
Sigma-Aldrich
Hydroxylamine hydrochloride, 99.999% trace metals basis
Sigma-Aldrich
Ammonium acetate, 99.999% trace metals basis
Sigma-Aldrich
Methanol, anhydrous, 99.8%
Sigma-Aldrich
4-Quinolinecarboxylic acid, 97%
Sigma-Aldrich
4-Chloroquinoline, 99%
Sigma-Aldrich
Diethyl ether
Sigma-Aldrich
Acetone, suitable for HPLC, ≥99.9%
Sigma-Aldrich
2-Quinolinecarboxaldehyde, 97%
Sigma-Aldrich
Carbon tetrachloride, anhydrous, ≥99.5%
Sigma-Aldrich
4-Quinolinecarboxaldehyde, 97%
Sigma-Aldrich
Diethyl ether, contains 1 ppm BHT as inhibitor, anhydrous, ≥99.7%
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Chloroform, anhydrous, ≥99%, contains 0.5-1.0% ethanol as stabilizer
Sigma-Aldrich
Acetone, ≥99%, meets FCC analytical specifications
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Acetone, natural, ≥97%
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Ammonium acetate, reagent grade, ≥98%
Sigma-Aldrich
Ammonium acetate, for molecular biology, ≥98%
Sigma-Aldrich
Chloroform, anhydrous, contains amylenes as stabilizer, ≥99%
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Hydroxylamine hydrochloride, 99.995% trace metals basis
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Methanol-12C, 99.95 atom % 12C
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Methanol solution, NMR reference standard, 4% in methanol-d4 (99.8 atom % D), NMR tube size 3 mm × 8 in.
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Quinoline, reagent grade, 98%
Sigma-Aldrich
Phenylmagnesium chloride solution, 2.0 M in THF
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Quinaldine, ≥95.0% (GC)
Sigma-Aldrich
Lepidine, 99%
Sigma-Aldrich
2-Phenylquinoline, 99%
Sigma-Aldrich
Acetonitrile, anhydrous, 99.8%