ISO 592:1998 pdf download – Essential oils – Determination of optical rotation
1 Scope
This International Standard specifies a method for determining the optical rotation of essential oils. When dealing with solid oils, partially solid oils, oils that are highly viscous at room temperature, or highly coloured oils, this determination is carried out on a solution of the oil.
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, any of these publications 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 356, Essential oils — Preparation of test samples .
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. 3.1 optical rotation of an essential oil, a angle, expressed in milliradians and/or degrees of angle, described by the polarization plane of a luminous radiation whose wavelength is 589,3 nm ± 0,3 nm, corresponding to the lines of sodium, when such light travels through a thickness of 1 00 mm of essential oil under given conditions of temperature NOTE When the determination is carried out on different thickness, the value of D t a should be computed by reference to a thickness of 1 00 mm. Also measurements according to the Faraday magneto-optical principle are possible. The thickness of the sample is approximately 1 0 mm in that case.
4 Reagents
Reagents shall be of analytical grade. Use distilled water or water of at least equivalent purity.
4.1 Solvent (only for essential oils that need to be tested in solution).
Use preferably 95 % ethanol by volume. It is advisable to check that the optical rotation of the solvent used is nil.
5 Apparatus
5.1 Polarimeter, having a precision of at least ± 0,5 mrad (± 0,03°) and adjusted to give 0° and 1 80° with water. The polarimeter shall be checked with a quartz plate of known optical rotation or, if that is unavailable, with an aqueous solution containing 26,00 g of anhydrous pure saccharose per 1 00 ml of solution. The optical rotation of this solution shall be +604 mrad (+34,62°) in a 200 mm layer, at a temperature of 20 °C. The instrument shall be under conditions of stability when in use, and non-electronic instruments shall be used in the dark.
5.3 Polarimeter tubes, usually 1 00 mm ± 0,5 mm long.
When testing slightly coloured samples of low optical rotation, tubes of length 200 mm + 0,5 mm may be used. Tubes of length 50 mm ± 0,05 mm or 1 0 mm ± 0,05 mm or even less may be used, if necessary, for strongly coloured samples. For determination at 20 °C or at another specified temperature, use double-walled tubes, equipped with a thermometer (5.4) to ensure water circulation at the required temperature. For determination at ambient temperature, any type of tube may be used, although it is advisable to use the type described above in this case too.