A Novel Equipment-Free Paper-Based Fluorometric Method for the Analytical Determination of Quinine in Soft Drink Samples

Abstract

A simple, equipment-free, direct fluorometric method, employing paper-based analytical devices (PADs) as sensors, for the selective determination of quinine (QN) is described herein. The suggested analytical method exploits the fluorescence emission of QN without any chemical reaction after the appropriate pH adjustment with nitric acid, at room temperature, on the surface of a paper device with the application of a UV lamp at 365 nm. The devices crafted had a low cost and were manufactured with chromatographic paper and wax barriers, and the analytical protocol followed was extremely easy for the analyst and required no laboratory instrumentation. According to the methodology, the user must place the sample on the detection area of the paper and read with a smartphone the fluorescence emitted by the QN molecules. Many chemical parameters were optimized, and a study of interfering ions present in soft drink samples was carried out. Additionally, the chemical stability of these paper devices was considered in various maintenance conditions with good results. The detection limit calculated as 3.3 S/N was 3.6 mg L−1, and the precision of the method was satisfactory, being from 3.1% (intra-day) to 8.8% (inter-day). Soft drink samples were successfully analyzed and compared with a fluorescence method.

Development of an image-based fluorometer with smartphone control for paper analytical devices

“…It's important to highlight that, as expected, the analytical performance of the proposed instrument for this determination falls short of that achieved when using a commercial spectro-uorometer, which can yield a detection limit of 0.009 mg L −1 for quinine within a linear calibration range of 0.05 to 1.48 mg L −1 . 25 However, the uorimeter described in this present work has demonstrated superior analytical performance for a similar application combining PADs and digital image detection, as recently described by Tsaari et al 15 In their work, a detection limit of 3.6 mg L −1 (compared to 1.1 mg L −1 in this study) was estimated for a calibration curve ranging from…”

“…Despite this, significative differences in results (95% confidence level t -test) were found for two samples (TW2 and FTW), probably indicating a matrix effect on analysis, which was not investigated in this paper. In fact, only degassing and dilution of samples in H 2 SO 4 solution were performed before analysis, so sugar and other major components on these beverages 15 could affect the image-based detection of PAD by crystallization of substances on the surface of the plates after drying up.…”

“…Recent studies have showcased a range of applications for PADs employing fluorescence-based detection via digital imagery. Tsaftari et al 15 utilized a 365 nm UV lamp for irradiating the PADs and a smartphone for capturing sensor images, which were assessed for their ability to determine quinine levels in beverages. The acquired images were subjected to analysis using specialized software for RGB detection, enabling calibration within the concentration range of 5.0 to 40.0 mg L −1 , with a detection limit of 3.6 mg L −1 .…”

Blue applicability grade index (BAGI) and software: a new tool for the evaluation of method practicality

“…The biggest advantage of BAGI is the simplicity and ease of application, which was achieved by preparing an interesting web application that allows to quickly evaluate the 18 (c) androgens and progestogens in environmental water samples, 19 (d) ibuprofen in milk-containing simulated gastrointestinal media, 20 and (e) quinine in soft drinks. 21 method and copy a colourful pictogram presenting the results of the evaluation. We believe that the BAGI tool will gain attention and acceptance from the chemical community.…”

“…For this purpose, the new tool was used to evaluate the applicability of five different analytical methods dealing with the determination of antidepressants in postmortem whole blood and cerebrospinal liquor, 17 bisphenol A (BPA) in food contact materials' leachates, 18 androgens and progestogens in environmental water samples, 19 ibuprofen in milk-containing simulated gastrointestinal media, 20 and quinine in soft drinks. 21 The BAGI index pictograms for these methods are depicted in Fig. 1.…”