EN 1132-1994 pdf download.Fruit and vegetable juices – Determination of the pH-value.
This EN 1132 specifies a method for the determination of the pH-value 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 — Deternz ination 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 Definition
For the purposes of this standard, the following definition applies:
pH value
the negative common logarithm of the concentration of hydrogen ions in moles per litre of solution
4 Principle
The pH value of the sample is measured potentiometrically.
5 Reagents
5.1 General
Use only reagents of recognized analytical grade and only degassed water in accordance with at least grade 3 of ISO 3696:1987.
5.2 Buffer solution with a pH of 6.88 at 20 °C I)ry anhydrous potassium dihydrogen phosphate, KH9PO4, and anhydrous disodium hydrogen phosphate. Na2HPO, at 120 °C ± 10 °C to constant mass. After cooling in a desiccator (6.5), weigh 3,40 g KH2PO4 and 3,55 g Na2HPO1 and dissolve in approximately 800 ml water, then make up to 1 000 ml at a temperature of 20 °C. This solution is stable for about 1 month.
5.3 Buffer solution with a pH of 3.57 at 20°C Dissolve 30 g potassium hydrogen tartrate, KHC4H4O, in about 11 water. Shake the container vigorously to give a saturated solution. Remove the undissolved residue by filtration. This solution contains at least 5,7 g KHC4H.1O.
use, since it deteriorates. I’he solution may be preserved by the addition of 0,05 g thymol per 100 ml of solution. It is then stable for about 2 months at 20°C.
5.4 Corn mercialiy available buffer solutions (alternative to 5.2 and 5.3)
Commercially available buffer solutions with pH values similar to (5.2) and (5.3) may also be used. Observe the buffer solution manufacturer’s instructions for their preparation, storage and date of expiry.
6 Apparatus
Usual laboratory apparatus and, in particular, the following:
6.1 pH meter accurate to at least 0,05 l)H units.
6.2 pH glass electrode
6.3 Reference electrode e.g. calonwl electrode.
6.4 c’ornbination pH glass electrode (alternative to 6.2 and 6.3.
6.5 Dessicator with drying agent.
7 Procedure
7.1 General
The pH meter and electrodes shall be calibrated and serviced according to the instrument manufacturer’s instructions.
The pH-value of the sample is normally measured at 20 °C ± 2 °C. If the pH meter possesses a temperature compensation facility, the measurement may be made at a temDerature other than 20 °C but in any case between 10 °C and 30 °C and according to the instrument manufacturer’s instruction.
Before each measurement or calibration step, rinse the electrode(s) well with water and remove adhering water with a filter paper.
Calibration and measurement should be carried out while gently stirring the solution or test sample.
7.2 Preparation of the test sample
If the sample contains appreciable quantities of carbon dioxide, degas it by shaking in a stoppered conical flask (remove the stopper from time to time), or by using vacuum or ultrasound treatment, until no more gas evolves.
7.3 Calibration
Perform two-point calibration of the pH meter with buffer solutions (5.2 and 5.3), following the instrument manufacturer’s instructions. The calibration may alternatively be carried out using commercially available buffer solutions (see 5.4).
7.4 Measurement
Measure the pH-value of the test sample, according
to the instrument manufacturer’s instructions.
8 Expression of results
Report the pH-value to two decimal places.
9 Precision
Details of the inter-laboratory test on the precision of the method are summarized in Annex B. The values derived from the inter-laboratory test may not be applicable to analyze concentration ranges and matrices other than given in Annex B.
9.1 Repeatability
The absolute difference between two single 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 0/ of the cases.
The value is: r = 0,03.
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 = 0,12.EN 1132-1994 pdf download.