BS EN 13196:2000 – Fruit and vegetable juices Determination of total sulfur dioxide by distillation
5.7 Sodium hydroxide solution, c (NaOH) 0,01 mol. Dilute an appropriate standardized soluion of sodium hydroxide solution (0.1 mol or 1,0 mol) to 0.01 mo/I in freshly boiled water. This solution should be prepared freshly every week or standard ized against a known mass of potassium hydrogen phthalate using pheniphalein 88 the indicator,
5.8 Purified nitrogen gas or air supply 6 Apparatus Uual laboratory apparatus and. in particular, the fllowing
6.1 isillation system A disllation system similar to the one shown in FigureC.1 is used to carry out this determinaton. The condenser of this type is a critical feature of the method. NOTE Sodium hydroryetylsulfonate can be used to assess the rlabililyl of the apparatus.
6.2 10 ml burette graduated in 0,02 ml units.
7 Procedure
7.1 Preparation of the test sample Normally produds shall not be pre treated and their analysis by this method shall be on a volumetnic basis, results being expressed per ire of sample. The analysis of concentraled samples may also be carried out on a volumetric basls, arter dilution to a known relative density. In this case, the relatve density shall be indicated. Based on a weighed sample and taking the diluion factor for analysis into account, the resuts may also be expressed per klogram of produdt. In produdts with a high viscosity and/lor a very high content of cells (tor example pulp), determination on the basis of a weighed test sample is the usual procedure. Mix doudy samples well before dilution.
7.2 Test procedure Ifa fuit or vegetable Juice or related product preserved with sulftur doixide P 50mg/) is analysed, place 20 ml of the test sample in a 100 ml round bottom flsk. Connect this flask to the distilation system as shown in Figure C.1 in annex C.5 ml of phosphoric acid (5see 5.2) is placed in the dropping furnel. IfFa fuit or vegetable juice or rabed product, unpresorved with sulur dioxide (e 50 mgM. is analysed place 50 ml of the test sample in the 250 ml round bottom flask. Conned this flask to the dist ation system as shown in Figure C.1 in amnex c.15 ml of phosphorie add (8ee 52) is placed in the dropping funnel. 2 or 3ml of the hydrogen peroxide solution (see 5.6) is added to the absorption receiver, shown asB in FigureC.1 in annexC. To this solution is added 2 drops of the mixed indicator solution (see 5.4) and the hydrogen peroxide solution is netralized with the sodium hydroxide solution (see 5.7).
This fask is then conneded to the disllalion system. Allow the phosphoric acid (see 5.2) to enter the distlation fask from the droping funnel. The dillation fask is then heated to biling with a small flame (4 cm to 5 cm) postined directly beneath the flask. The flask is heated over a suitable disk with a small hole cult in it (30 mm diameter) to stop the product from burning in the flask. A wire g8uze should not be used.
BS EN 13196:2000 – Fruit and vegetable juices Determination of total sulfur dioxide by distillation