HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

K8Feb. 10,
2021

Fractional determination of ascorbic acid andsodium ascorbate

Organic acid
1. Abstract

Ascorbic acid has properties as an acid and a strong reducing agent. On the other hand, sodium ascorbate
doesn’t have a function as an acid but works as a reducing agent as well as ascorbic acid. The quantitative
determination method for ascorbic acid is prescribed in JIS K 9502 and Japanese pharmacopeia. There are twodetermination methods for ascorbic acid; neutralization titration and iodine titration.
The fractional determination method for ascorbic acid and sodium ascorbate is introduced in this report.
First, ascorbic acid is determined by the neutralization titration with sodium hydroxide standard solution(formula (1)). After that, the total amount of ascorbic acid (ascorbic acid and sodium ascorbate) is measured by
the redox titration with iodine standard solution (formula (2) and (3)). The sodium ascorbate is determined by
the subtraction of the ascorbic acid from the total amount of ascorbic acid.
(I) Reaction formula for neutralization titration

C6H8O6 ＋NaOH→C6H7NaO6 ＋・・・(1)

H2O(II) Reaction formulae for redox titration

C6H8O6 ＋→I2

C6H7NaO6 ＋I2

C6H6O6 ＋ 2HI→

C6H5NaO6 ＋・・・(2)・・・(3)

2HI

2. Configuration of instruments and reagents(1) Configuration
Main unit ：Option：

Electrode ：Automatic Titrator COM series
One buret and one buret head
Glass reference electrodeGR-501BZ

Connect to IE-1.

：

Platinum electrodePT-301Connect to IE-2.

：

0.1 mol/L Sodium hydroxide standard solution(2) Reagents
Titrant

0.05 mol/L Iodine standard solutionAdditive ：2 % Metaphosphoric acid solution

3. Measurement procedure。

(1) Measurement for ascorbic acid(i) Take approx. 0.4 g of sample into a 100 mL beaker and weigh it accurately.
(ii) Add approx. 40 mL of DI water.
(iii) Immerse the electrodes to start titration with 0.1 mol/L sodium hydroxide standard solution.
(2) Measurement for sodium ascorbate(i) Take approx. 0.4 g of sample into a 100 mL beaker and weigh it accurately.
(ii) Add 50 mL of 2 % metaphosphoric acid solution.
(iii) Immerse the electrodes to start titration with 0.05 mol/L iodine standard solution with using optional
buret and buret head.

4. Measurement conditions and results
Examples of titration conditions(1) Measurement for ascorbic acidCndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mLMax Vol.

1Auto
11pH
5000200
0.2
20sec
mL
sec
mL
mL
mL

Constant No.
SizeBlank
Molarity
FactorKL
Unit
Formula10.4036 g0 mL
0.1 mol/L
1.004
176.13mg/g(D-B)*K*F*M/S
Decimal places4Auto input parameter
None

Mode No.
Pre Int
Del KDel Sens
Int TimeInt Sens
Brt SpeedPulse

409033240sec
mVsec
mV

(2) Measurement for sodium ascorbate
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mLMax Vol.

2Auto
22mV
30
730
0.5
500
0.2
20Cndt No.
Method

3Calc

sec
mL
sec
mLmL
mL

Constant No.
SizeBlank
Molarity
FactorKL
Unit
Formula20.4042 g
0 mL
0.05 mol/L
1.001
176.130mg/g(D-B)*K*F*M/S
Decimal places
4Auto input parameter
Constant No.
SizeBlank
Molarity
FactorKL
Unit
Formula0.4042000116.92
1.125mg/g

Mode No.
Pre Int
Del KDel Sens
Int Time
Int Sens
Brt Speed
Pulse

2002033240sec
mV
sec
mV

None
3gmLmol/L*1*2(CA-K)*L
Decimal places
4
Auto input parameter
None*1 K (coefficient 1): Result of ascorbic acid by neutralization titration*2 L (coefficient 2): Coefficient to convert ascorbic acid to sodium ascorbate (C6H7NaO6 (198.11) / C6H8O6 (176.13))

Measurement results
Measurement results of ascorbic acid
Ascorbic acid

0.4036

Titrant
volume(mL)
2.671

117.028

Average116.92 mg/g

20.40212.659

116.931

Standard deviation

0.12 mg/g

30.40552.678

116.796

Coefficient of variation

Meas.
No.

Size(g)1

Statistic calculation(mg/g)

0.10 %

Measurement results of sodium ascorbate
Meas.
No.

Size(g)Titrant
volume(mL)

Totalascorbic acid(mg/g)

Sodiumascorbate(mg/g)

Statistic calculation

10.40429.858

215.001110.341

Average

110.70 mg/g20.4056

9.922

215.671

111.095

Standard deviation

0.38 mg/g

30.40649.925

215.275

110.649

Coefficient of variation

0.34 %

Measurement for ascorbic acid

Measurement for sodium ascorbate

Examples of titration curves

5. NoteAnother determination method of ascorbic acid
The iodine titration method is used for the determination of ascorbic acid in this report, but there is anindophenol method as another determination method for ascorbic acid; the color change of indophenol from blue
to red under metaphosphoric acid is detected as the end point of titration in this method. The relatively-highselectivity on the determination of ascorbic acid in fruit juice etc. compared with the iodine titration method isthe character of the indophenol method.
Keywords: Fractional determination of ascorbic acid and sodium ascorbate, Neutralization titration,
Redox titration, Iodine titration*Some measurement would not be possible depending on optional configuration of system.