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Abstract
A simple, quick, and accurate new method for the determination of quinine (6′-methoxycinchonan-9-ol) in soft drinks is presented. The analysis is carried out using high performance liquid chromatography (HPLC), coupled laser induced fluorescence (LIF) that consisted of a 325 nm He-Cd laser and a ZETALIF detector. The chromatographic separation was performed on a Phenomenex Synergi Fusion-Reversed Phase (RP) column and allows good peak shape and symmetry in less than 1.5 min. A calibration curve ranging from 1 to 100 ng/mL was shown to be linear with a correlation coefficient (R) of 0.9999. The limit of detection of quinine was 3.2 pg on the column. The method was applied to the analysis of several beverages (n = 43) containing quinine, whose analysis required minimum pretreatment before direct injection, and can therefore be used for quality control in comparison to the classical methods. Data obtained from different commercial beverages containing quinine show no homogeneous concentration of this compound. This article describes, for the first time, the successful application of HPLC coupled LIF detection for quinine determination in common beverages.
ACKNOWLEDGMENTS
Mr. Feás acknowledges a scholarship within the program “Formación de Personal Investigador” from MINISTERIO DE CIENCIA Y TECNOLOGÍA, Spain. Also, we wish to thank José Pedro Araujo, Ananias Pascual, José Antonio Abelenda, Tobias Bister, Pablo Iglesias, Pierre Riollet, and Amada Moreno-Cid for providing us soft drinks samples, and Ana Carreira for technical collaboration.
Notes
Acronyms for sample preparation: So, sonication; SD, soft drinks; bf, buffer; C, crystalization; iv, injection volume; H, heated; D, dilution; LL, liquid-liquid extraction; nr, not reported.
Acronyms for methods: FIA-AASid, reversed flow-injection with atomic absorption spectrometry (indirect determination); FIA-OP C18, flow-injection analysis with silica C18 optosensor; PVCm-DP, plasticized poly(vinyl chloride) membrane electrode with direct potentiometry; SP, spectrophotometric; Fl, fluorimetric; ITP-UV-CD isotachophoresis with ultraviolet and conductivity detection; FS-Fl, flow-through sensor with fluorimetric transduction; HPLC-LIF, high-performance liquid chromatography with laser-induced fluorescence detection; HPLC-Fl, high-performance liquid chromatography-fluorimetric detection; 4thSP, 4th-order derivative spectrophotometric; IP-RP-HPLC, ion-pair reversed-phase high performance liquid chromatography.