Analytical Method: Ascorbic Acid in Fruit Juices

Photometric Determination with Tillmann's Reagent

Materials and Reagents:

Reagents

Cat. No. 100546 meta-Phosphoric acid for analysis
Cat. No. 106267 Sodium acetate trihydrate for analysis
Cat. No. 100063 Acetic acid 100 % for analysis
Cat. No. 103028 2.6-Dichlorphenolindophenol sodium salt dihydrate for analysis
Cat. No. 108661 Xylene for analysis
Cat. No. 116754 Water for analysis

Instruments

Cat. No. 173016 Spectroquant^® Vis Spectrophotometer Prove 100 or
Cat. No. 173017 Spectroquant^® UV/Vis Spectrophotometer Prove 300 or
Cat. No. 173018 Spectroquant^® UV/Vis Spectrophotometer Prove 600 or
Cat. No. 109748 Spectroquant^® Nova 30 or
Cat. No. 109751 Spectroquant^® Nova 60

Materials

Cat. No. 114946 Rectangular cells 10 mm

Measurement Range

20 - 600 mg/l ascorbic acid at cell length 10 mm and 525 nm

Preparing the Reagents

Reagent 1:
Dissolve 3 g meta-phosphoric acid in 100 ml of water for analysis.

Reagent 2:
Dissolve 25 g sodium acetate trihydrate and 50 ml Acetic acid 100 % in water and make up to 500 ml with water for analysis.

Reagent 3:
Dissolve 0.25 g 2,6-dichlorophenolindophenol sodium salt dihydrate in 500 ml water for analysis.

Analysis

Homogenize the juice by shaking well in the package and analyse immediately. Place 2.0 ml sample in a 50 ml separating funnel and add 2.0 ml reagent 1 1.0 ml reagent 2 and 5.0 ml reagent 3. To extract, add 15 ml xylene and shake for 30 s. When the phases have separated, remove the lower aqueous phase and dispose of and place the upper organic phase in a test tube containing anhydrous sodium sulphate. Carry out the analysis immediately against a reagent blank using one of the above mentioned photometers.