Automatic determination of the formol number in fruit and vegetable juices

Automatic determination of the formol number in fruit and vegetable juices

Summary

The determination of the formol number in fruit and vegetable juices represents a further parameter for the characterisation of these drinks. As this is merely an index (it does not deal with molecular size, nor with the quantity of amino acids), the conditions of this titration can be adapted to practical needs. This concerns mainly the pH value of the endpoint (pH = 8.5, 9.0, 9.2 etc.).

Apparatus and accessories

• Titrino 702 or 716 or 719 or 736 or 751 or 785 or Titroprocessor 726 with Dosino 700 or Dosimat 685

• Second Dosimat (addition of formaldehyde) 765 or 776

• Magnetic Swing-out Stirrer 2.728.0040

• Exchange units 6.3014.223

• Comb. glass electrode 6.0219.100 with electrode cable 6.2104.020

Reagents

• Titrant: c(NaOH) = 0.1 mol/L

• Formaldehyde: w(HCHO) = 35 %, adjusted to pH = 8.5 with NaOH

Analysis

25.0 mL sample solution are pipetted into a glass beaker and titrated in a first SET titration to pH = 8.5. Then through activation pulse, the second SET titration is automatically started under the following parameters:

Addition of 15 mL formaldehyde (second Dosimat), 60 s waiting time, titration to pH = 8.5.

Calculation

Formol number (FN) = EP1 * C01; mL

c(NaOH) = 0.1 mol/L per 100 mL sample

EP1 = mL NaOH second SET titration

C01 = 4 (with 25 mL sample size)

Answer :

719 S Titrino 0P1/110 719.0020

pHc(init) 7.04 SET pH Formal2

EP1 4.842 ml 8.50

FZ 19.368

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Literature

Metrohm, Application Bulletin No. 180 /2 e