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Caffeine belongs to a group of alkaloids that stimulates the central nervous system, affecting breathing and the cardiovascular system. Due to its popular performance-enhancing effects, caffeine is considered the world's most consumed pharmacologically active substance.

Iodometric back titration is a simple and accurate method for the determination of caffeine in aqueous solutions or water-soluble samples. In acidic solution, caffeine reacts with iodine to form an insoluble, brown-red complex. Excess iodine is then back titrated with sodium thiosulfate. This method is suitable for food and substances from which caffeine can be extracted with water (e.g., coffee).

In this Application Note, the caffeine content in aqueous samples is accurately and reliably analyzed by iodometric back titration using the OMNIS Titrator equipped with a dPt Titrode.

This application is demonstrated on caffeine standard, guarana extract, guarana extract concentrate, ground coffee, and an energy drink.

An appropriate amount of sample is weighed into an amber glass beaker. Deionized water, iodine solution, and sulfuric acid are added, and the caffeine-iodine complex is formed. Afterwards, the solution is filtered.

Exemplary titration curve of caffeine in an energy drink (Table 1) with sodium thiosulfate as titrant.
Figure 1. Exemplary titration curve of caffeine in an energy drink (Table 1) with sodium thiosulfate as titrant.

An aliquot of the filtrate is titrated until after the first equivalence point with standardized sodium thiosulfate solution (Figure 1). The determination is carried out with an OMNIS Titrator equipped with a dPt Titrode (Figure 2).

Figure 2. OMNIS Titrator equipped with a dPt Titrode electrode for the determination of caffeine content in aqueous samples.

This method offers very accurate results, as displayed in Table 1.

Table 1. Results of caffeine determination in different aqueous samples.
Sample (n = 6) Caffeine in % SD(rel) in %
Caffeine standard 100.1 0.9
Guarana extract 4.2 2.0
Guarana extract concentrate 40.7 2.1
Ground coffee (roasted) 1.3 2.9
Energy drink 0.07 2.4

The iodometric back titration is a precise method used to accurately measure the caffeine content in various aqueous samples. Reliable determinations are made easy using the OMNIS Titrator equipped with a dPt Titrode. This system offers flexible analyses combined with high-end software. The dPt Titrode is maintenance-free and suitable for redox titrations like iodometry when the pH value remains constant.

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