EN 1142-1994 pdf download.Fruit and vegetable juices – Determination of the sulfate content.
This EN 1142 specifies a method for the determination of the sulfate content of fruit and vegetable juices and related products.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. Iso 5725:1986, Precision of test methods — Del erm in at ion of repeatability and reproducibility for a standard test method by inter-laboratory tests. Iso 3696:1987, Water for analytical laboratory use — Specification and test methods.
3 Symbols
For the purposes of this standard, the following symbols apply:
c Substance concentration;
p Mass concentration;
g Acceleration due to gravity at the surface of the earth.
4 Principle
The sulfate ions present in the test sample are precipitated by means of barium chloride. Co.precipitated barium phophate is eliminated by treatment of the precipitate with hydrochloric acid. The precipitate is weighed after ashing.
5 Reagents
Use only reagents of recognized analytical grade
and only water in accordance with at least grade 3
of ISO 3696.
5.1 Barium chloride solution,
r (BaCI2.2H20) = 200 gIl
5.2 hydrochloric acid, c (HCI) = 2 molfl
6 Apparatus
Usual laboratory apparatus and, in particular, the following:
6.1 Centrifuge, capable of producing a centrifugal force of 3 000 x g at the base of the centrifuge tubes (6.2) (the value of g is fixed for the purpose of this European Standard at 9,81).
6.2 centrifuge tubes, 50 ml.
6.3 Platinum dish, minimum volume 30 ml.
6.4 Analytical balance, accurate to 0,1 mg.
6.5 Water bath
6.6 Dessicator. with a drying agent.
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. The analysis of concentrated products may also be carried out on a volumetric basis, after dilution to a known relative density. In this case, the 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 kilogram of product. In products with high viscosity and/or very high content of cells (for example Pull)), determination on the basis of a weighed test sample is the usual procedure.
Clear juices are used without any particular preparation of the sample. Cloudy juices are centrifuged at 3 000 x g and the determination is conducted on the clear supernatant liquid.
7.2 Determination
Pipette 40,0 ml of clear or clarified sample (7.1) into a centrifuge tube, add 2,0 ml of hydrochloric acid (5.1) and 2 ml of barium chloride solution (5.1) and mix thoroughly with a glass rod. Rinse the glass rod with water. Leave the centrifuge tube to stand for 5 mm and then centrifuge for 5 mm at 3 000 g. Carefully decant the clear supernatant solution into a beaker.
The barium sulfate precipitate is then washed as follows. The Precipitate is treated first with 10 znl of hydrochloric acid (5.2) any co-precipitated barium phosphate being dissolved by stirring several times. Centrifuge again for 5 mm at 3 000 x g and carefully decant the supernatant clear liquid. The precipitate is washed twice in the same manner with 15 ml water. Transfer the washed residue quantitively with water to a previously weighed platinum crucible (mass = rn ) and evaporate to dryness on the water bath. Next heat the platinum crucible several times over an open flame, until the residue is white. Weigh the crucible (mass = rn) after cooling to room temperature in a desiccator (6.6).
8 Calculation
Calculate the sulfate content p, expressed in milligrams per litre, using the equation:
p=(rn2_rn1)x 10,29
where:
(rn2 rn1) is the mass of BaSO4, in milligrams. precipitated from 40 ml of sample.
The factor 10,29 results as follows:
10,29 = 25 x 0,4116
(Factor 25 for calculation in 1 litre of sample; factor 0.4116 for conversion of BaSO4 to sulfate content).
Take into account the dilution factor and the relation of the value to mass or volume. EN 1142-1994 pdf download.