EN 1133-1994 pdf download.Fruit and vegetable juices-Determination of the formol number.
5 Reagents
5.1 General
Use only reagents of recognized analytical grade
and only water in accordance with at least grade 3
of ISO 3696:1987.
5.2 Sodium hydroxide solution,
c (NaOH) = 0,25 molIl.
5.3 Formaldehyde solution, pH 8,1.
Formaldehyde solution. w (CH2O) = at least 350 gIl.
adjusted precisely to pH 8,1 on the pH meter
with 0,25 mol/l sodium hydroxide (5.2.). This
solution shall be prepared freshly on the day of use.
5.4 Hydrogen peroxide, w(H2O2 = 300 g/l.
6 Apparatus
Usual laboratory equipment and, in particular, the following:
6.1 p11 meter, accurate to at least 0,05 PH units.
6.2 pH glass electrode
6.3 Reference electrode, for example calomel electrode.
6.4 corn bination pH glass electrode (alternative to 6.2 and 6.3).
‘h pH meter and electrode(s) shall be calibrated and serviced according to the manufacturer’s instructions.
7 Procedure
7.1 Preparation of the test sample Normally products shall not be pretreated and their analysis by this method shall be on a volumetric basis, results being expressed per 100 millilitres of sample. The analysis of concentrated products may also he carried out on a volumetric basis, after dilution to a known relative density. In this case, the relative density shall be indicated. Based on a weighed sample and taking the dilution factor for analysis into account, the results may also be expressed per 100 grams of product. In products with high viscosity andlor very high content of cells (for example pulp), determination on the basis of a weighed test sample is the usual procedure. In the case of lemon juice or other high acidic juices, take 5 ml of juice and 20 ml water and continue as below. If the sample contains sulfur dioxide, it shall be treated with a few drops of hydrogen peroxide solution (5.4) before titration.
7.2 Determination
While stirring, adjust 25 ml of test sample in a beaker to pH = 8,1 using solution (5.2) and the pH meter. Add 10 ml solution (5.3) and continue stirring. Leave to stand for 1 minute, then titrate the solution to pH = 8,1 using solution (5.2). while continuing stirring. Note the number of ml (n) of solution (5.2) required for the tiration. If the number of ml required exceeds 20 ml. repeat the titration using 15 ml solution (5.3) in place of 10 ml.
Use only sodium hydroxide solution c (NaOH) = 0,25 molIl (5.2) for the determination, irrespective of the formol number of the test sample.
8 Calculation
Calculate the formol number as follows:
Formol number = 10 x
Any additional dilution and the relation of the value to mass or volume (see 7.1) shall be taken into account if applicable. If a concentrated product, has been diluted to single strength, report the relative density of the single strength sample. The formol number can he calculated per 100 g of test sample, taking into account the relative density.
Report the formol number in millimetres of sodium hydroxide solution c (NaOH) = 0,1 molIl per 100 ml of test sample, to one decimal place.
9 Precision
Details of the interlaboratory test on the precision of the method are summarized in Annex B. The values derived from the interlaboratory test may not be.
9.1 Repeatability
The absolute difference between two single test results found on identical test material by one operator using the same apparatus within the shortest feasible time interval will exceed the repeatability value r in not more than 5 % of the cases.
The value is: r 0.4 mmol NaOH/100 ml.
9.2 Reproducibility
The absolute difference between two single test results on identical test material reported by two laboratories will exceed the reproducibility value R in not more than 5 % of the cases.
The value is: R = 1,1 mmol NaOH/100 ml.
10 Test report
The test report shall contain the following data:
— all information necessary for the identification
of the sample (kind of sample, origin of sample,
designation):
— a reference to this European Standard;
— date and type of sampling procedure
(if possible);
— date of receipt:
— date of test;
— test results and units in which they have been
expressed;
— whether the repeatability has been verified;
— any particular points observed in the course of the test:EN 1133-1994 pdf download.