HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

K3

Jul. 14,
2020

Purity determination of citric acid

Organic acid
1. Abstract

Citric acid is oxycarboxylic acid which has carboxy group (-COOH) and alcoholic hydroxyl group (-OH).
It can be dissolved in water and has acidic property. Citric acid is produced as raw material of organic
compound or food additive.
“JIS K8283” prescribes the determination method for the purity of citric acid by the neutralization
titration using phenolphthalein indicator. This report introduces an example of the potentiometric titration(formula (1)) with sodium hydroxide standard solution for the purity determination of citric acid monohydrate
according to “JIS K8283”.

CH2COOH
C(OH)COOH
CH2COOH+

3NaOH→

CH2COONa
C(OH)COONa
CH2COONa+

3H2O ・・・(1)2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrodes:

Glass electrodeGE-101B

Reference electrodeRE-201Z*Instead of the above electrodes, the following electrodes are usable.
・Glass reference combination electrode GR-501BZ…Fixed sleeve type・Glass reference combination electrode GR-511BZ…Moveable sleeve type(2) Reagents
Titrant:

1 mol/L Sodium hydroxide standard solution

3. Measurement procedure(1) Add about 2.0 g of sample to a beaker and weigh accurately with 0.1 mg digit.
(2) Add 40 mL of DI water and stirring bar to the beaker. Dissolve the sample by stirring.
(3) Immerse electrodes and start titration with 1 mol/L sodium hydroxide standard solution.

4. Measurement conditions and results
Example of titration condition
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto
11pH
52000
3000
0.3
40sec
mLsec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL
Unit
Formula12.000 g
0 mL
1.000 mol/L
1.004
70.05
0%
(D-B)*K*F*M/(S*10)

Decimal Places
Auto In Pram.

3Non

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

50
503
3
240

Measurement results
Number of
Measurement

123Size(g)2.00062.00052.0014

Titrant
Volume (mL)

28.43128.42928.443Purity(%)
99.94899.94699.950

Example of titration curve

Statistic calculation

Avg.
SDRSD

99.95
0.002
0.002%%%

secmV
secmV

5. Note(1) Collection of sample
The sample is collected directly to the beaker and weighed accurately. The accuracy of sample collection
influences the measurement accuracy. Please note that the sample should be carefully taken and accurately
weighed.
(2) Control of titrant
The concentrated sodium hydroxide standard solution is used as titrant in this report. The carbon dioxide
gas absorber (soda lime) on reagent bottle has to be regularly exchanged because sodium hydroxide readily
absorbs carbon dioxide gas in the air (formula (2)). The standard solution of sodium hydroxide that hasabsorbed carbon dioxide contains sodium carbonate, and the inflection point on titration curve may beunclear due to buffer capacity of sodium hydrogen carbonate generated in the reaction with an acidic sample(formula (3)).
2NaOH+CO2→

Na2CO3Na2CO3+RCOOH→

NaHCO3 ++H2 O・・・(2)

RCOONa・・・(3)(3) Reduction of measurement time
The titrant volume was about 28 mL in this report. When the titrant volume is large as described in thisreport, “CP mL” function can be utilized to reduce the measurement time. It was set to “20 mL” in thisreport to continuously add the sodium hydroxide standard solution.

Keywords: Citric acid, Sodium hydroxide, Neutralization titration, JIS K8283*Some measurement would not be possible depending on optional configuration of system.