Background-correction methods for the determination of caffeine in beverages, coffee and tea by using second-derivative ultraviolet spectrophotometry

Abstract

Background-correction methods have been developed for the determination of caffeine in beverages, coffee and tea by second-derivative ultraviolet spectrophotometry. The second derivatives of caffeine were measured at 298.6 nm. Interference from tannins in beverages and tea was minimized by treating the sample with 0.1 m o l dm-3 sodium hydroxide and by precipitating tannins with copper(ti) acetate, respectively. Coffee samples were treated with sodium hydroxide (0.25-0.75 m m o l dm-3). The calibration graphs for the three types of sample had slightly different slopes (0.00146-0.00152 A nm-2 ppm-1) and linear ranges. The precision for the determination ranged from 0.3 t o 0.9%, at the 10 pg ml-1 level of caffeine. A number of cola drinks, energy drinks, lemon tea drinks, coffee samples and tea samples were analysed.

Influence of different coffee drink preparations on ochratoxin A content and evaluation of the antioxidant activity and caffeine variations

“…In particular Lau, Luk, Cheng, and Chiu (1992), studied the presence of this bioactive compound in different coffee samples divided in instant coffees and regular coffe utilizing the technique of the ultraviolet spectrophotometry. In the instant coffee samples, as Espresso, Extra, Gold blend, Jacobs, Moccona, Maxim the authors evidenced a concentration of caffeine variables from 2.16 to 4.30 mg/mL.…”

Effects of Preparation Techniques on the Antioxidant Capacity of Coffee Brews

“…According to the results of Santini et al (2011) caffeine content was the highest in 'Moka' coffee (5.4 mg/ml), followed by espresso (3.33 mg/ml), Turkish (1.94 mg/ml), and Neapolitan coffee (1.89 mg/ml), while the lowest value was observed for the American coffee that had a caffeine content of 0.44 mg/ml. Lau et al (1992) studied the presence of this bioactive compound in different coffee samples divided in instant and regular coffees. In the instant coffee samples the authors determined a content of caffeine varying from 2.16 to 4.30 mg/ ml.…”

Determination of caffeine in tea samples by Fourier transform infrared spectrometry

“…Caffeine has been determined in drinks by different analytical techniques such as UV-VIS spectrophotometry [2,3,4] or amperometry [5] and most frequently by using separation methods like high performance liquid chromatography (HPLC) [6,7,10], ion chromatography [11], capillary electrophoresis [12,13,14], as well as high performance thin layer chromatography (HPTLC) [15,16,17] and micellar capillary electrophoresis [18,19,20]. The official method for caffeine determination in tea leaves [21] is based on low-pressure column chromatography and spectrophotometric determination at 276 nm.…”