HIRANUMA APPLICATION DATA

Data No. A12

Automatic Titrator

Sep. 12,2018

Measurement of vitamin C in soft drink withindophenol method

FOOD

1. Abstract
Many soft drinks contain vitamin C (ascorbic acid). Vitamin C is included as not only nutrient factor but
also an antioxidant for drinks. There are iodine titration method and indophenol method for analysis of vitaminC, this report introduces indophenol method.
Firstly, acidify the sample with mixed solution of metaphosphoric acid and acetic acid. After that, titratewith indophenol standard solution. The endpoint of the titration is detected as color change from colorless tored-purple with photometric probe.
OClOH
ClCl

O＝C

Cl

O＝C
O＝C

HO－CN

HO－C＋O

H－C

O＝C
→NH

O

H－C
HO－C－H

HO－C－H

CH2OH

CH2OH
OHOH
Indophenol＋

Reduced Vitamin C

Leucoindophenol(Red-purple)

Oxidized Vitamin C(Colorless)

2. Configuration of instruments and Reagents(1) Instruments
Main unit：

Hiranuma Automatic Titrator COM series with Photometric unit (M-Type)Electrode：

Probe for photometric detection with optical filter 530 nm：

Indophenol standard solution(2) Regents
Titrant

Dissolve 50 mg of 2,6-dichlorophenol-indophenol sodium salt dehydrate
into 200 mL of DI water containing 50 mg of sodium hydrogen carbonate.
Filter the solution with No. 42 grade of Whatman filter (2.5 µm).
Additive solvent：

Mixed solution of metaphosphoric acid and acetic acid
Take 30 g of metaphosphoric acid and dissolve with 80 mL of acetic acidand 800 mL of DI water. Obtain 1 L of the solution by filling the volumetricflask with DI water.

Standard solution ：Ascorbic acid standard solution (for use of factor determination of titrant)
Weigh 50 mg of L(+)‐ascorbic acid precisely and dissolve with additivesolvent. Obtain 100 mL of the solution by filling the volumetric flask withthe mixed additive solvent.

3. Measurement procedure
3.1. Factor measurement for indophenol standard solution(1) Take 1 mL of standard solution into 100 ml tall-beaker with volumetric pipet.
(2) Add 60 mL of additive solvent.
(3) Immerse the probe and start titration with indophenol standard solution.
3.2. Measurement of vitamin C in sample(1) Take 2 mL of sample into 100 ml tall-beaker with volumetric pipet.
(2) Add 60 mL of additive solvent.
(3) Immerse the probe and start titration with indophenol standard solution.

4. Measurement conditions and results
Examples of titration conditions
Factor measurement for indophenol standard solution
Condition No. 1
MethodF-Cross

Constant No.

1Mode No.

20Buret No.

1Size

0.0503g

Pre Int

0Amp No.

2Blank0mL

Del K

0D.UnitT%

S-Timer

5sec

Molality

0mol/LDel Sens

0mV

Factor0Int time

15sec

CP mL

3mLK0Int Sens

15mVT Timer

15sec

L0Buret Speed

4D.P. mL

0.5mLUnit

mg/mL

End Sens

100Formula

S*10/DOver mL

0.5

mLDigits

Max. Vol.

10mL

Auto input Parameter

Pulse

sec

160
0.2

mL

4None

Measurement of vitamin C in sample
Condition No. 2Method

F-Cross

Constant No.

2Buret No.
Amp No.

Mode No.

20

1Size

22Blank0g

Pre Int

0mL

Del K

0D.Unit

T%Molality

0mol/LDel Sens

0mV

S-Timer

5sec

Factor

0.0965Int time

15

sec

CP mL

0mL

T Timer15

sec

K0Int Sens

15mVL

0Buret Speed

4D.P. mL

0mL

Unit

mg/mL

End Sens100

FormulaD*F/SOver mL

0.5mL

DigitsMax. Vol.

20mL

Auto input Parameter

Pulse

160
0.2

4
NonesecmL

Measurement results

Examples of titration curve

Factor measurement for indophenol standard solution
Measurement

Size

Titrant

FactorNo.

(g)volume (mL)

(mg/mL)

5.224

0.09635.200

0.09675.217

0.0964

Avg. (mg/mL)

0.0965SD (mg/mL)

0.0002120.0503 (*)

3
Statisticalresult

RSD (%)
0.22(* Weighed amount of vitamin C at preparation of standardsolution)

Measurement of vitamin C in sample
Measurement

SizeTitrant

Conc.

No.

(g)

volume (mL)

(mg/mL)

2.343

0.11302.337

0.11282.335

0.1127

Avg. (mg/mL)

0.1128SD (mg/mL)

0.0002

RSD (%)

0.14

123
Statisticalresult

25. Note
In this measurement, indophenol titrant tends to gradually become clear on each dropping when each drop
has a small volume (0.05 mL. etc.), the titration doesn’t proceed well in this case. Therefore the amount of eachtitrant dropping was set to relatively large volume (0.2 mL), and the waiting time with each dropping was set tolonger than normal titration condition.
When measuring the color sample like a grapefruit juice, the measurement of vitamin C by photometrictitration is possibly affected by the sample color. In that case, you can reduce the influence by diluting thesample.

Keywords：Food, Soft drink, Vitamin C, Indophenol method, Photometric titration*Some measurement would not be possible depending on optional configuration of system.