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Detection of total phenol in green and black teas by flow injection system and unmodified screen printed electrode.

de Mattos IL, Zagal JH - Int J Anal Chem (2011)

Bottom Line: Results were reported as gallic acid equivalents (GAEs).The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35-40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement.Precise results are in agreement with those obtained by the Folin-Ciocalteu method.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química de Los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Sucursal Matucana, Santiago 9170022, Chile.

ABSTRACT
A flow injection system using an unmodified gold screen-printed electrode was employed for total phenol determination in black and green teas. In order to avoid passivation of the electrode surface due to the redox reaction, preoxidation of the sample was realized by hexacyanoferrate(III) followed by addition of an EDTA solution. The complex formed in the presence of EDTA minimizes or avoids polymerization of the oxidized phenols. The previously filtered tea sample and hexacyanoferrate(III) reagent were introduced simultaneously into two-carrier streams producing two reproducible zones. At confluence point, the pre-oxidation of the phenolic compounds occurs while this zone flows through the coiled reactor and receives the EDTA solution before phenol detection. The consumption of ferricyanide was monitorized at 360 mV versus Ag/AgCl and reflected the total amount of phenolic compounds present in the sample. Results were reported as gallic acid equivalents (GAEs). The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35-40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement. Precise results are in agreement with those obtained by the Folin-Ciocalteu method.

No MeSH data available.


Effect of EDTA solution on the operational stability of the gold screen-printed electrode. High level (100.0 mg·L−1, square) or low level (50.0 mg·L−1, circle) refers to successive injection of standard-solutions of gallic in phosphate buffer.  R′ is the flow rate which depending on the experiments; it is distilled water for 100.0 mg·L−1 gallic acid and 0.25 M EDTA solution for 50.0 mg·L−1 gallic acid.
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fig4: Effect of EDTA solution on the operational stability of the gold screen-printed electrode. High level (100.0 mg·L−1, square) or low level (50.0 mg·L−1, circle) refers to successive injection of standard-solutions of gallic in phosphate buffer. R′ is the flow rate which depending on the experiments; it is distilled water for 100.0 mg·L−1 gallic acid and 0.25 M EDTA solution for 50.0 mg·L−1 gallic acid.

Mentions: We believe that the stabilization of the signals occurs because: (i) the oxidation of gallic acid occurs by hexacyanoferrate(III), outside of the electrode, like a preoxidation and (ii) the oxidized gallic acid reacts with EDTA giving a complex GAox EDTA. The formation of the complex reduces polymerization of the oxidized products formed that passivate the electrode. In fact, Figure 4 shows that in presence of EDTA solution the signals associated to gallic acid was maintained constant after 50 successive injection; in its absence, this signal was deteriorated. Similar results were showed before in experiments using dopamine, catechol, and 4-aminophenol oxidation [21]. Therefore, the preoxidation and the formation of a complex with EDTA can be used to avoid the formation of a passivation layer on the electrode surface and allows the determination of phenolic compounds without the necessity of cleaning the electrode by polishing before each measurement.


Detection of total phenol in green and black teas by flow injection system and unmodified screen printed electrode.

de Mattos IL, Zagal JH - Int J Anal Chem (2011)

Effect of EDTA solution on the operational stability of the gold screen-printed electrode. High level (100.0 mg·L−1, square) or low level (50.0 mg·L−1, circle) refers to successive injection of standard-solutions of gallic in phosphate buffer.  R′ is the flow rate which depending on the experiments; it is distilled water for 100.0 mg·L−1 gallic acid and 0.25 M EDTA solution for 50.0 mg·L−1 gallic acid.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3065041&req=5

fig4: Effect of EDTA solution on the operational stability of the gold screen-printed electrode. High level (100.0 mg·L−1, square) or low level (50.0 mg·L−1, circle) refers to successive injection of standard-solutions of gallic in phosphate buffer. R′ is the flow rate which depending on the experiments; it is distilled water for 100.0 mg·L−1 gallic acid and 0.25 M EDTA solution for 50.0 mg·L−1 gallic acid.
Mentions: We believe that the stabilization of the signals occurs because: (i) the oxidation of gallic acid occurs by hexacyanoferrate(III), outside of the electrode, like a preoxidation and (ii) the oxidized gallic acid reacts with EDTA giving a complex GAox EDTA. The formation of the complex reduces polymerization of the oxidized products formed that passivate the electrode. In fact, Figure 4 shows that in presence of EDTA solution the signals associated to gallic acid was maintained constant after 50 successive injection; in its absence, this signal was deteriorated. Similar results were showed before in experiments using dopamine, catechol, and 4-aminophenol oxidation [21]. Therefore, the preoxidation and the formation of a complex with EDTA can be used to avoid the formation of a passivation layer on the electrode surface and allows the determination of phenolic compounds without the necessity of cleaning the electrode by polishing before each measurement.

Bottom Line: Results were reported as gallic acid equivalents (GAEs).The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35-40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement.Precise results are in agreement with those obtained by the Folin-Ciocalteu method.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química de Los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Sucursal Matucana, Santiago 9170022, Chile.

ABSTRACT
A flow injection system using an unmodified gold screen-printed electrode was employed for total phenol determination in black and green teas. In order to avoid passivation of the electrode surface due to the redox reaction, preoxidation of the sample was realized by hexacyanoferrate(III) followed by addition of an EDTA solution. The complex formed in the presence of EDTA minimizes or avoids polymerization of the oxidized phenols. The previously filtered tea sample and hexacyanoferrate(III) reagent were introduced simultaneously into two-carrier streams producing two reproducible zones. At confluence point, the pre-oxidation of the phenolic compounds occurs while this zone flows through the coiled reactor and receives the EDTA solution before phenol detection. The consumption of ferricyanide was monitorized at 360 mV versus Ag/AgCl and reflected the total amount of phenolic compounds present in the sample. Results were reported as gallic acid equivalents (GAEs). The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35-40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement. Precise results are in agreement with those obtained by the Folin-Ciocalteu method.

No MeSH data available.