Determination of the Formaldehyde Number in Fruit Juices with Potentiometric Method

Determination of the Formaldehyde Number in Fruit Juices with Potentiometric Method

Equipment

Potentiometer = 751 GPD Titrino / Titroprocessor

Electrodes = 6.0232.100 combined pH glass electrode; input 1

Reagents

c(NaOH) = 0.1 mol/L; D0

w(HCHO) = 0.35 (35%), adjusted to pH = 8.5 with NaOH; D1

Sample

25 mL sample (orange juice)

Electrodes

6.0232.100 combined pH glass electrode; input 1

Remarks

· Determination reaction:

OH

H2C=O + H2N-R Þ H2C + H+

NHR

Amino groups of amino acid react according to the above reaction.

· Calculations:

Formol No = C70*C01;1;

Formol No = formol number as mL NaOH 0.1 mol/L for 100 mLsample solution

C01 = factor for 100 mL sample solution (4)

· Calibrate the electrode for the SET titration.

. Answer

Formol No = 5.634 x 4 = 22.5

C70 = 5.634

Literature

· Metrohm Application Bulletin No. 180: Automatic determination of the

formol number in fruit and vegetable juices

Method documentation

'pa

751 GPD Titrino 15215 751.0010

TIP FormolNo

parameters

>sequence

1.stirrer: ON

2.method: FormoPre

3.method: FormoDos

4.pause 60 s

5.method: FormoDet

>statistics

status: OFF

>preselections

req.ident: OFF

req.smpl size: OFF

meas.mode: OFF

temperature 25.0 °C

------------

'fm

751 GPD Titrino 15215 751.0010

TIP FormolNo

>calculations

FormolNo=C70*C01;1;

C01= 4

C70= 5.634

------------

'fr

751 GPD Titrino 15215 751.0010

TIP FormolNo

smpl size 25 ml

C70 5.634

FormolNo 22.5

TIP terminated

============

'cr

751 GPD Titrino 15215 751.0010

meas.input: 1 CAL

pH U/mV

buffer 1 7.00 -5

buffer 2 9.00 -122

cal.temp 21.7 °C

slope(rel) 0.999 pH(as) 6.91