Development of new capillaries coated with ionic liquids for in-tube SPME-UHPLC-MS / MS and comprehensive two-dimensional gas chromatography (GC × GC)

Author(s)

Israel Donizéti de Souza

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-08-15

Examining board members

Maria Eugenia Queiroz Nassur; Andréa Rodrigues Chaves; Eduardo Costa de Figueiredo; Leandro Wang Hantao; Fernando Mauro Lanças; Luiz Alberto Beraldo de Moraes

• Advisor: Maria Eugenia Queiroz Nassur

Abstract

Considering the advances in chromatographic techniques, the development of new stationary phases has improved the selectivity and detectability of analytical methods. In this context, ionic liquids have been in the spotlight as innovative compounds of the 20th century: they are mainly applied as stationary phases for gas chromatography (GC), high-performance liquid chromatography (HPLC), and solid-phase microextraction (SPME). The benefits of ionic liquids are related to their unique retention/separation mechanisms (hydrophobic, hydrophilic, ionic interactions, hydrogen bonding, and complexation, among others) and to the possibility of tuning their physicochemical properties during the synthesis procedure. In the first part of this study, polymeric ionic liquids were synthesized, characterized, and chemically immobilized on the internal surface of fused silica capillaries. These innovative capillaries were used for capillary microextraction in line with ultra-high performance liquid chromatography coupled to tandem mass spectrometry (in-tube SPME-UHPLC-MS/MS) for online determination of endocannabinoids, anandamide (AEA), and 2-aracdonoylglycerol (2-AG) in plasma samples from patients with Parkinson\'s Disease (PD). Introducing long alkyl chains in the imidazole cation favored hydrophobic interactions; on the other hand, combining the imidazole rings with the halide anions elicited polar interactions and hydrogen bonds with the endocannabinoids. These capillaries promoted exclusion of endogenous compounds from the biological matrix and low backpressures in the analytical system. The linearity of this innovative method ranged from 0.05 to 100 ng mL-1, whereas the precision and accuracy ranged from 1.6 to 14% (coefficient of variation) and from 19.6 to 13.2% (standard error deviation), respectively. Therefore, the in-tube SPME-UHPLC-MS/MS method is adequate for AEA and 2-AG determination in plasma samples from patients with PD. In the second part of this study, high thermal stability capillary columns containing silver-based ionic liquid stationary phases were developed, characterized, and applied in the second dimension of a comprehensive two-dimensional gas chromatograph (GC × GC) with flame ionization detector (FID) to separate alkanes, alkenes, alkynes, dienes, esters, ketones, aldehydes, terpenes, and polyunsaturated fatty acids. When the Rtx-5MS × [(CSUB>10MIM)(MIM)Ag+][NTf2-]/[C10MIM+][NTf2-] column set was employed, the separation in the first dimension was based on the volatility of each analyte; the separation mechanism in the second dimension was strongly influenced by -complexation between the silver ions and the double or triple bonds of the analytes. Compared to the SUPELCOWAX10 column, the [(C10MIM)(MIM)Ag+] [NTf2-]/[C10MIM+][NTf2-] (1.2 m x 0.25 mm x 0.15 m) and (0.9 m x 0.25 mm x 0.15 m) columns provided narrow peaks and unique selectivity, which improved separation of the analytes in the second dimension. The chromatographic separations using the silver-based ionic liquid columns presented exceptional chromatographic resolution in the second dimension for the separation of the analytes 1-hexyne and 3-hexyne, n-pentane and 3-methyl-1,4-pentadiene, and butanal and 2-butanone, which coelute when the commercial benchmark column is used. The retention times of the polyunsaturated fatty acids (PUFAs of C14: 0 to C18: 3) were proportional to the number of unsaturation within the structure of these analytes. In summary, this study presented the development of a promising generation of silver-based capillary columns for GC × GC experiments (AU)

• FAPESP's process: 16/01082-9 - Column switching liquid chromatography coupled to tandem mass spectrometry for the analysis of endocannabinoids in plasma samples
• Grantee: Israel Donizeti de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate