BS EN ISO 6320:2000 pdf – Animal and vegetable fats and oils Ð Determination of refractive index.
1? Scope This International Standard specifies a method for the determination of the refractive index of animal and vegetable fats and oils. 2? Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, this publication do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 661 , Animal and vegtable fats and oils — Preparation of test sample . 3? Terms and definitions For the purposes of this International Standard, the following term and definition apply. 3.1 refractive index (of a medium) ratio of the velocity of light of a definite wavelength in a vacuum to its velocity in the medium NOTE 1 ? In practice, the velocity of light in air is used in place of that in a vacuum and, unless otherwise specified, the selected wavelength is the mean wavelength of the sodium D lines (589,6 nm). NOTE 2? The refractive index of a given substance varies with the wavelength of the incident light and with temperature. The notation used? , D t n? where t is the temperature in degrees Celsius. 4 Principle By means of a suitable refractometer, the refractive index of a liquid sample is measured at a specified temperature. 5? Reagents Use only reagents of recognized analytical grade, and distilled or demineralized water or water of equivalent purity. 5.1? Ethyl laurate , of quality suitable for refractometry, and of known refractive index.
5.2? Hexane, or other suitable solvents, such as light petroleum, acetone or toluene, for cleaning the prism of the refractometer. 6? Apparatus Usual laboratory equipment and, in particular, the following. 6.1? Refractometer, for example of the Abbé type, suitable for measurements of refractive index to within ? 0,000 1 over the range n D = 1 ,300 to n D = 1 ,700. 6.2? Light source: sodium vapour lamp White light can also be used if the refractometer is fitted with an achromatic compensation system. 6.3? Glass plate, of known refractive index. 6.4? Water bath, thermostatically controlled, with a circulation pump, and capable of being maintained to the nearest ? 0,1 °C. 6.5? Water bath, capable of being maintained at the temperature at which the measurements are to be made (in the case of solid samples). 7? Sampling It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transportation or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO 5555. 8? Preparation of test sample Prepare the test sample in accordance with ISO 661 . The refractive index shall be determined on dried and filtered fats and oils. In the case of a solid sample, transfer the sample prepared in accordance with ISO 661 to a suitable container and place it in the water bath (6.5), set at the temperature at which the measurements are to be made. Allow sufficient time for the temperature of the sample to stabilize.
Maintain the temperature of the prism of the refractometer at the required constant value by circulating through the instrument water from the water bath (6.4). Monitor the temperature of the water issuing from the refractometer using a suitable precision thermometer. Immediately before the measurement, lower the movable part of the prism to a horizontal position. Wipe the surface of the prism with a soft cloth and then with a piece of cotton wool moistened with a few drops of the solvent (5.2). Allow to dry. Carry out the measurement acccording to the operating instructions for the instrument being used. Read the refractive index to the nearest 0,000 1 as an absolute value, and record the temperature of the prism of the instrument. Immediately after the measurement, wipe the surface of the prism with a soft cloth and then with a piece of cotton wool moistened with a few drops of the solvent (5.2). Allow to dry.