Determination of caffeine and identification of adulteration in coffee by capillary electrophoresis with capacitively coupled contactless conductivity detection / Determinação de cafeína e identificação de adulterações no café empregando a eletroforese capilar com detecção condutométrica sem contato

AUTOR(ES)

Thiago Nogueira

DATA DE PUBLICAÇÃO

2006

RESUMO

In this work, methods based on capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) for the determination of caffeine in coffee as well as for the identification of its adulteration by addition of some other vegetal products were developed. Caffeine is a neutral species, and the proposed method was based on its mobilization by the formation of a complex with the anion 3,4 dimethoxycinnamate. The experiments were carried out in buffer Tris/3,4 dimethoxycinnamic acid (pH 8.5) and the migration of the complex was done in counter electroosmotic flow. The running time was less than 5 minutes. In addition, theobromine and theophylline (two caffeine analogues) were completely separated. The new method was compared to a standard method based on HPLC, and similar results were obtained. Samples of integral, soluble, and decaffeinated coffees were analyzed and the limit of quantification (0.33 mg/g) was low enough to fulfill the Brazilian norm. The proposed approach for the identification of adulteration was based on the controlled hydrolysis of xylan and starch present in some vegetable adulterants, followed by the analysis of the resulting xylose and glucose, which are the monosaccharides that compose, respectively, the two polysaccharides. Although the monosaccharides are neutral species in ordinary conditions, they form anionic species in high values of pH. The best separations were obtained in NaOH 80 mmol L-1, CTAB 0.5 mmol L-1, and methanol 30% (v/v). The results showed that it is possible to identify levels of contamination below tolerable limits.

ASSUNTO(S)

eletroforese cafeína g coffee glucose capacitively coupled contactless conductivity detection caffeine xilose detecção condutométrica sem contato xylose electrophoresis café

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