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)

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