Isabel Gibbs’s research while affiliated with Virginia Commonwealth University and other places

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Publications (1)

Excitation and emission spectra of the 1 ppm quinine standard solution. The spectra collected, one excitation and two emissions, are color-coded to designate the different data sets. Spectra were obtained with monochromator slit widths of 5.0 nm and a PMT voltage of 600 V. The λmax values for the first excited singlet state (S1), second excited singlet state (S2), first emission (E1), and second emission (E2) are listed. Five replicates were recorded for excitation and emission spectra (n = 5). Spectra were collected at room temperature.
(A) Plot of fluorescence intensity vs. PMT voltage for five different data sets. Data points were best fit with the power function (second order), and the corresponding correlation coefficient R² values are provided. (B) Plot of the mean fluorescence intensity and PMT voltage. The mean intensity was calculated by averaging out the five intensity values at each voltage, and the corresponding standard deviation is represented by the error bars (n = 5). The correlation coefficient for the best-fit line is shown on the plot.
(A) Plot of fluorescence intensity vs. excitation monochromator slit width for the five groups. The linear best-fit lines, linear regression equations, and correlation coefficients are displayed for each group. (B) Plot of the mean fluorescence intensity as a function of excitation slit width. Error bars represent standard deviations from five datasets (n = 5). Data were collected at a PMT voltage of 600 V with an emission monochromator slit width of 5 nm.
(A) Plot of the square root of fluorescence intensity vs. emission monochromator slit width for the five groups. The polynomial best-fit lines, quadratic equations, and correlation coefficients are displayed for each group. (B) Plot of the mean square root of intensity as a function of emission slit width. Error bars denote standard deviations from five datasets (n = 5). Data were collected at a PMT voltage of 600 V with an excitation monochromator slit width of 5 nm.
Calibration curves prepared from the quinine standard solutions using the external (A) and the internal (B) standard addition methods. The linear best-fit lines, linear regression equations, and correlation coefficients are displayed for each group in panel A (n = 5). Data were collected at excitation and emission wavelengths of 350 nm and 450 nm, respectively, with a PMT voltage of 600 V and slit widths set to 5 nm each. The Canada Dry tonic water sample was used for the internal standard (Si) method in panel B, and the fluorescence intensity is an average of two replicates (n =2). Standard deviations are represented by the error bars.
Fluorescence Analysis of Quinine in Commercial Tonic Waters
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  • Full-text available

January 2025

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185 Reads

Artturi Harcher

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Connor Ricard

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Danielle Connolly

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Quinine is known for treating malaria, muscle cramps, and, more recently, has been used as an additive in tonic water due to its bitter taste. However, it was shown that excessive consumption of quinine can have severe side effects on health. In this work, we utilized fluorescence spectroscopy to measure the concentration of quinine in commercial tonic water samples. An external standard method was used to calculate the concentrations of quinine in two commercially available tonic water brands, namely Canada Dry and Schweppes, and compare them to the maximum allowable concentration of quinine in beverages. Upon analysis of the data collected by five different groups, the levels of quinine were found to be above the average concentration in most commercial tonic water samples, but below the maximum permitted concentration. Moreover, the five replicate sets of data demonstrated high reproducibility of the method employed in this study. The simple yet instructive protocol that we developed can be adapted to determine the concentration of other fluorescent compounds in foods and beverages. Further, the presented method and detailed protocol can be easily adopted for undergraduate labs and in chemical education.

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