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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.


Flow diagram used. S, sample (standard solutions or samples), C1 and C2, carrier streams (phosphate buffer solution), R, reagent stream (ferricyanide solution), IC, injector, LS and LR, sample and reagent loops, W, waste, B1 and B2, coiled reactors, a and b, confluent points, R′, confluent stream (EDTA solution), FC, flow cell (model FC2), and W, waste. The boxed part relates to the movable bar of the commutator, the dashed lines indicating the next commutating state. The sites where pumping is applied are indicated by arrows. For system dimensioning, see text.
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fig2: Flow diagram used. S, sample (standard solutions or samples), C1 and C2, carrier streams (phosphate buffer solution), R, reagent stream (ferricyanide solution), IC, injector, LS and LR, sample and reagent loops, W, waste, B1 and B2, coiled reactors, a and b, confluent points, R′, confluent stream (EDTA solution), FC, flow cell (model FC2), and W, waste. The boxed part relates to the movable bar of the commutator, the dashed lines indicating the next commutating state. The sites where pumping is applied are indicated by arrows. For system dimensioning, see text.

Mentions: The preoxidation of gallic acid by ferricyanide and the employment of EDTA were put here as strategic to prevent the passivation of the working electrode during the oxidation of phenolic compound. The proposed FI system represents an interesting alternative for developing robust systems for routine analysis. Before using the flow injection system of Figure 2, gallic acid, ferricyanide, and EDTA solutions were observed by cyclic voltammetry.


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)

Flow diagram used. S, sample (standard solutions or samples), C1 and C2, carrier streams (phosphate buffer solution), R, reagent stream (ferricyanide solution), IC, injector, LS and LR, sample and reagent loops, W, waste, B1 and B2, coiled reactors, a and b, confluent points, R′, confluent stream (EDTA solution), FC, flow cell (model FC2), and W, waste. The boxed part relates to the movable bar of the commutator, the dashed lines indicating the next commutating state. The sites where pumping is applied are indicated by arrows. For system dimensioning, see text.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Flow diagram used. S, sample (standard solutions or samples), C1 and C2, carrier streams (phosphate buffer solution), R, reagent stream (ferricyanide solution), IC, injector, LS and LR, sample and reagent loops, W, waste, B1 and B2, coiled reactors, a and b, confluent points, R′, confluent stream (EDTA solution), FC, flow cell (model FC2), and W, waste. The boxed part relates to the movable bar of the commutator, the dashed lines indicating the next commutating state. The sites where pumping is applied are indicated by arrows. For system dimensioning, see text.
Mentions: The preoxidation of gallic acid by ferricyanide and the employment of EDTA were put here as strategic to prevent the passivation of the working electrode during the oxidation of phenolic compound. The proposed FI system represents an interesting alternative for developing robust systems for routine analysis. Before using the flow injection system of Figure 2, gallic acid, ferricyanide, and EDTA solutions were observed by cyclic voltammetry.

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.