Determination of caffeine in coffee products by dynamic complexation with 3,4‐dimethoxycinnamate and separation by CZE

Abstract

A method based on the formation of pi-complexes with chlorogenate-like species was proposed for the determination of caffeine in regular (nondecaffeinated) and decaffeinated coffee. Both caffeate and 3,4-dimethoxycinnamate were able to transform caffeine--a neutral species in aqueous solutions--into an anionic species. The usage of 3,4-dimethoxycinnamate in the running electrolyte is advantageous, because of its greater chemical stability and the improved resolution of the peaks of caffeine, theobromine, and theophylline. Negative peaks were registered with a capacitively coupled contactless conductivity detector when solutions of these alkylxanthines were analyzed with a BGE composed of 20 mmol/L 3,4-dimethoxycinnamic acid and pH adjusted to 8.5 with Tris. This behavior was expected, because the complex is larger and thus should move slower than the free anion. Caffeine was determined in ground and instant coffee with precision and accuracy that meet Brazilian norms about such products. The LOD was estimated as 33 mg/L, which corresponds to 0.8 and 0.3 mg of caffeine per gram of dry instant coffee and ground coffee, respectively. For the case of decaffeinated coffee, ten times preconcentration with dichloromethane was carried out to allow the quantitation of caffeine, which should not exceed the concentration of 1 mg/g in dry matter.

A compact and high‐resolution version of a capacitively coupled contactless conductivity detector

“…The procedure for the determination of caffeine in instant coffee was similar to that previously described [21]. For decaffeinated instant coffee, the procedure using organic solvent was replaced.…”

“…To prevent misinterpretations, no software filter was applied to the data. The limits of detection based on the 3 criterion (without baseline filtering) were 0.6, 0.4, 0.3, 0.5, 0.6, and 0.8 mmol/L for K 1 , Ba 21 , Ca 21 , Na 1 , Mg 21 , and Li 1 , respectively. These results are comparable with those from other implementations.…”

“…Of course, the sensitivity of a C 4 D is not directly related to the difference of the analyte and co-ion mobilities [18], but this principle functions as a rule of thumb. Even better examples of the capabilities of C 4 D are found in its use in MEKC [19], detection of synthetic polymers in non-aqueous size-exclusion electrokinetic chromatography [20], and in detection of caffeine by pi-complex formation [21]. In this last example, a neutral analyte and an ionic species from the BGE -both of them with an appropriate pi-system -form an ionic complex that migrates.…”

Investigating the formation and the properties of monoalkyl carbonates in aqueous medium using capillary electrophoresis with capacitively coupled contactless conductivity detection

“…C 4 D by its turn is a suitable detection scheme in the present case, because not only it dismisses the need for absorbing groups but it allows to evaluate the concentration of unstable species as will be shown. This application augments the pool of applications where this reliable electrochemical-detection scheme can be used [14][15][16][17][18][19][20][21][22].…”

Identification and chromatographic determination of bioactive components in the instant coffee samples

“…Определение кофеина и суммарного содержа-ния ХГК в кофе проводят спектрофотометрически [25][26][27] и электрофоретически [22,28,29]. Индиви-дуальные кофеилхинные кислоты в этом продукте определяют методом мицеллярной электрокинети-ческой хроматографии [24], а разделение практи-чески всех известных изомеров ХГК достигается методом ВЭЖХ (табл.…”