RESUMO
The main goal of this work is to expand the availability of chiral columns for the analysis of agrochemicals by gas chromatography. A broader offer of chiral stationary phases would allow shifting toward enantioselective analytical techniques environmentally more friendly for those compounds. We prepared seven chiral capillary columns based on derivatives of either, ß-cyclodextrin or γ-cyclodextrins dissolved at high concentrations, in two typical polysiloxanes with different polarities, demonstrating not only the significance of the chiral selector but also of the polymer solvent for achieving adequate enantioseparation of some agrochemicals. The enantiorecognition ability of each column was evaluated with 20 volatile and semivolatile agrochemicals, possessing one or two chiral centers. Besides, to elute more polar agrochemicals, as well as to enhance enantioselectivity, three derivatization procedures targeting the carboxyl and/or amine group were evaluated. The results revealed that the prepared column consisting of octakis(2,3-di-O-acetyl-6-O-tertbutyldimethylsilyl)-γ-cyclodextrin dissolved in (14%-cyanopropyl-phenyl)-86%-methyl-polysiloxane provides the broadest enantiorecognition capacity. This column allowed the enantioseparation of seventeen chiral agrochemicals, including metalaxyl, furalaxyl, and four imidazolinones, which were not enantioseparated in the remaining columns. To the best of our knowledge, glufosinate, fluorochloridone, fenarimol, furalaxyl, and four imidazolinones were enantioseparated by gas chromatography for the first time.
RESUMO
Terpenes and terpenoids are the principal responsible for the aroma of Cannabis, playing an important role in the interaction with the environment. Analytical determination of these compounds can be done by headspace coupled to solid phase micro-extraction (HS-SPME) and then injected in a gas chromatograph. In the present study, we determined distribution constants between gas and polydimetylsiloxane (PDMS), a conventional SPME liquid phase, at three temperatures between 303.15 and 343.15 K for major Cannabis terpenes and terpenoids employing a method based in gas chromatography using four capillary columns for monoterpenes and five columns for sesquiterpenes. In addition, van't Hoff regressions (logKfg vs T-1) were obtained in order to estimate logKfg at 298.15 K aiming to compare with bibliographic values (experimental or estimated ones). An excellent agreement was found between them. The method, based on chromatographic theory is robust and relatively simple. It is expected that the herein obtained data could be useful for selecting SPME fiber type and dimensions, estimating extraction efficiencies, as well as to develop prediction models and validate them.
Assuntos
Cannabis , Terpenos , Terpenos/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Microextração em Fase Sólida/métodos , Cromatografia Gasosa , Dimetilpolisiloxanos/químicaRESUMO
Absolute content of terpenes in inflorescences of two strains of Cannabis sativa L., CAT 1 and CAT 3, has been determined. Twenty terpenes commonly present in these samples were quantified by solid phase microextraction combined with gas chromatography and flame ionization detection (SPME/GC-FID). High amounts of ß-myrcene, α-pinene, ß-pinene, limonene, (E)-ß-ocimene, ß-caryophyllene, α-humulene, (E)-nerolidol, and linalool, were found in both strains. Lower concentrations (< 20 µg·g-1) of other terpenes were also determined. Only (E)-ß-ocimene was detected at 50 µg·g-1 in CAT 3 whereas it was below the LOD in CAT 1. Concentrations of other compounds for which standards were not available, were estimated based on a response factor obtained from the calibration curves of compounds with similar chemical structures. Fingerprints of both CAT strains were obtained and the identities of most volatile compounds were assigned using gas chromatography coupled to mass spectrometer detector (GC-MS). Additionally, an assessment of variability of terpenes was achieved by analyzing ten plants of each strain grown under controlled conditions and harvested at the same time. This variability was about 20%, considering terpenes at concentration above 20 µg·g-1.