HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

A6

Jun 6,
2017

Continuous measurement of acid(citric acid) and amino nitrogen in grapefruit juice

FOOD

1. Abstract
Successive measurement of acid (citric acid) and amino nitrogen in grapefruit juice and its titration
process will be introduced.
The amino nitrogen.is determined by Formol method which is simplified method of Van Slyke method.
Firstly, measure the acid (citric acid) in sample solution by the titration with sodium hydroxide standard
solution until the pH reaches 8.1 as described in the formula (1). After that, add sodium hydroxide standard
solution to adjust the pH to 8.4. Add neutral buffered formalin solution to react amino nitrogen with formalinfor generating carboxylic acid (formula (2)). Titrate the carboxylic acid with sodium hydroxide until the pHreaches 8.4, and measure amino nitrogen based on formula (3). Figure 1 shows measurement flowchart on thisprocedure.
CH2COOH∣C(OH)COOH∣CH2COOH

CH2COONa∣
C(OH)COONa∣
CH2COONa+

3NaOH

→

RCHCOOH∣
NH2+HCHO→RCHCOOH∣
N=CH2+H 2O･･･(2)

RCHCOOH∣
N=CH2+NaOH→RCHCOONa∣
N=CH2+H 2O･･･(3)+3H 2O･･･(1)SampleMeasurement of acid ( End point: pH 8.1 )Buret I (Sodium hydroxide standard solution)

pH Adjustment (End point: pH 8.4)

Buret I (Sodium hydroxide standard solution)
Optional buret II(Neutral buffered formalin is automatically added.)

Measurement of amino nitrogen ( End point: 8.4 )Figure 1

Buret I (Sodium hydroxide standard solution)

Flowchart of measurement

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

Hiranuma Automatic Titrator COM series

Option：One buretElectrodes：

Glass electrodeGE-101B

Reference electrode RE-201Z
Thermistor electrode TE-403

※Glass reference combination electrode can be used instead of glass electrode andreference electrode. The glass reference combination electrodes are listed below.
・GR-501BZ (Fixed sleeve type)・GR-511BZ (Movable sleeve type )(2) Reagents
Titrant：

0.1 mol/L sodium hydroxide standard solution

Additive solution：

Neutral buffered formalin solution

15mL(Formalin adjusted to pH 8.4 by adding 1 mol/L or 0.1 mol/L sodiumhydroxide solution)

3. Measurement procedure(1) pH calibration
The pH calibration should be performed with neutral phosphate (pH 6.86) and borate (pH 9.18) pHstandard solution.
(2) Measurement of acidi) Dispense 5 g of sample into a 200 mL beaker and accurately weigh it.
ii) Add pure water to make about 100 mL of solution.
iii) Immerse the electrodes and start to titrate with sodium hydroxide standard solution. Perform it until thepH reaches 8.1.
iv) Add 0.1 mol/L sodium hydroxide standard solution to adjust the pH to 8.4.
v) After the above process, 15 mL of neutral buffered formalin solution is automatically dispensed.
(Option: Buret)vi) Titrate with 0.1 mol/L sodium hydroxide standard solution until the pH reaches 8.4.
vii) Measure the blank with the procedure ① ~ ③ without sample.

4. Measurement conditions and results
Examplesof titration
conditions
Measurementof Blank
Measurement of blank
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
D.P. mL
End Point pH
Over mL
Max.Vol.

1
Set
11
pH
50.0
↑
0.0
8.10
0.0
1sec
mL
mL
pHmL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

10.00.0
0.1
1.005
0.00.0Unit
FormulaDigits
Auto In Pram.

mL
D3g
mL
mol/L

Non

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

140003328sec
mV
sec
mV

Measurement of sample(1) Titration of acid (citric acid) with sodium hydroxide standard solution
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. pH
Direction
T Timer
D.P. pH
End Point pH
Over mL
Max.Vol.

2Set
11pH
106.50↑1508.10
0.020

sec
pHsec
pHpH
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

24.6569
0.016
0.1
1.005
640Unit
FormulaDigits
Auto In Pram.

%(D-B)*K*F*M/(S*10)
3NongmLmol/L

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

2005033440

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

2100033220sec
mV
sec
mV

(2) Addition of sodium hydroxide standard solution to adjust the pH to 8.4
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
D.P. mL
End Point pH
Over mL
Max.Vol.

3Set
11pH00.00
↑0.0
8.40
0.020

sec
mL
mLpH
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKL

34.6569
0.00.0000Unit
FormulaDigitsAuto In Pram.

mL
D
3g
mL
mol/L

sec
mV
sec
mV

Non

(3) Dispense neutral buffered formalin solution.
Cndt No.
MethodBuret No.
S-Timer
Disp Vol.

4
Disp
2015.00

secmL(4) Titration of amino nitrogen with sodium hydroxide standard solution
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-TimerC.P. pH
Direction
T Timer
D.P. pH
End Point pH
Over mL
Max.Vol.

5Set
11pH30
6.00
↑15
6.5
8.40
0.1
20

sec
pHsec
pHpHmLmL

ConstantNo.
SizeBlank
Molarity
FactorKL

54.6569
0.0
0.1
1.005
140Unit
FormulaDigitsAuto In Pram.

mg/100(D-B)*K*M*F/(S*10)*1000
3Nong
mLmol/L

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

50
503
3240

sec
mV
sec
mV

Measurement results
Measurement of blank
Number of measurement
123Average (Blank)

Number ofmeasurement

Size(g)1
4.6181
2
4.70463
4.6569AverageStandard deviation
Coefficient of variation

Size(g)―――Measurement of sample
Acid (Citric acid)
Titer
Concentration
(mL)
(%)
6.799
0.945
6.922
0.944
6.874
0.947
0.945 %
0.002 %
0.162 %

Measurement of blank

Titer(mL)
0.015
0.017
0.017
0.016 mL

Amino nitrogen
Titer
Concentration(mL)(mg/100g)
0.785
23.9170.796
23.8060.791
23.89923.874 mg/100g
0.060 mg/100g
0.250 %

Measurement of sample

Examples of titration curves

5. NoteSimplified method of Van Slyke method is utilized in this article. However, please make sure whether it isapplicable for your standard-compliant when using this method.
Procedure for the determination of taurine described in Japanese Pharmacopoeia (rev. 17) is similar tothis method.
Keyword：Grapefruit juice, Amino nitrogen, Citric acid, Van Slyke method, Formol method, Formaldehyde*Some measurement would not be possible depending on optional configuration of system.