The method used was in accordance to Barba, Cortés, Esteve,and Frígola (2012). Beverage (5 mL) was diluted to 25 mL with the extraction solution (1% w/v oxalic acid, 2% w/v trichloroacetic acid and 1% w/v sodium sulphate). After vigorous shaking, the solution was filtered through a folded filter (Whatman No. 1). 1%(w/v) oxalic acid (9.5 mL) and 2 mL of 2 M acetic acid/sodium acetate buffer (pH = 4.8) were added to an aliquot of 0.5 mL of filtrate and the solution was transferred to the polarographic cell. A Metrohm 746 VA Trace Analyzer (Herisau, Switzerland) equipped with a Metrohm 747 VA stand was used for the polarographic determination. The working electrode was a Metrohm multi-mode electrode operated in the dropping mercury mode. A platinum wire counter electrode and a saturated calomel reference electrode
were used. The following instrumental conditions were applied:
DP50, mode DME, drop size 2, drop time 1 s, scan rate 10 mV/s, initial
potential 0.10 V. Determinations were carried out by using
the peak heights and standard additions method.
The method used was in accordance to Barba, Cortés, Esteve,and Frígola (2012). Beverage (5 mL) was diluted to 25 mL with the extraction solution (1% w/v oxalic acid, 2% w/v trichloroacetic acid and 1% w/v sodium sulphate). After vigorous shaking, the solution was filtered through a folded filter (Whatman No. 1). 1%(w/v) oxalic acid (9.5 mL) and 2 mL of 2 M acetic acid/sodium acetate buffer (pH = 4.8) were added to an aliquot of 0.5 mL of filtrate and the solution was transferred to the polarographic cell. A Metrohm 746 VA Trace Analyzer (Herisau, Switzerland) equipped with a Metrohm 747 VA stand was used for the polarographic determination. The working electrode was a Metrohm multi-mode electrode operated in the dropping mercury mode. A platinum wire counter electrode and a saturated calomel reference electrodewere used. The following instrumental conditions were applied:DP50, mode DME, drop size 2, drop time 1 s, scan rate 10 mV/s, initialpotential 0.10 V. Determinations were carried out by usingthe peak heights and standard additions method.
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