ISO 592:1998 download.Essential oils – Determination of optica rotation.
1 Scope
ISO 592 specthes a method for determinirç the oplEal rotation of essential 0i15
When dealing with solid oils. partially solid oê oils that are highly viscous at room temperature, or highly coloured
oils, this determination te carried out on a solution of the of.
2 NormatIve reference
The following normative document conlains provisions which, through reference in this text, constitute provisions of ISO 592, For dated references, subsequent amendments to, or revisions ci. any of these publications do not apuly. However, parties to agreements based on ISO 592 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 apphes. Members CA ISO and IEC maintain registers of currently valid International Standards.
ISO 356, Essential ode — Preparation of test sanip(es.
3 Terms and detinWons
For the pueposes of ISO 592, the tollo’nw’ig terms and definitions apply.
optical rotation of an essential oIl. of,, angle, expressed in milliradians and/or degrees of angle, described by the polarization plane of a kiimnous radiation
whose wavelength is 589,3 nm ± 0.3 nm. corresponding to the Dines of sodium, when such light travels through a thickness of 100mm of essential oil under given conditions of temperature
NOTE When the determination canted out on diflerent thickness, the yak,. of oi,, shou be computed by reference to a thickness of 100 men, Also rreasurements according to the Faraday magreto-opeical pnnaple are posslbIe The ttwckness Cf the sample Is approxImately 10 men ii that case.
3.2
optical rotation of an essential oil In solution specific rotation, a
optical rotation c4, of a solution of essential od divided by the mass of essential oil lithe unit of volume
4 Reagents
Reagents shal 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 acMsable to check that the optical rotation at the soiveni used Is nil.
5 Apparatus
51 Polarlmeter, having a preosion of at least ± 0,5 mrad (± 0.03°) and adjusted to give 0° and 180° with water.
The polarwneter shal be checked with a quartz plate of known optical rotation or, if that is unavailable, with an aqueous solution containing 26.00 g of antly&ous pure saccharose per 100 ml of solution. The optical rotation of this solution shall be +604 mmd (+34,62°) in a 200mm layer, at a temperature of 20°C.
The instrument shall be under contions of slabihly when in use, and non-electronic instruments shall be used in the dark.
5.2 Light source, comprising any device giving a lht of wavelength 589,3 nm ± 0,3 rwn, preferably a sodium vapour lamp.
5.3 Polarlrneter tubes, usually 100 rrwn ±0,5mm long.
When testing sbghtty coloured samples of low optical rotation, tubes of length 200 mm ± 0,5 mm may be used. Tubes ci length 50 mm ± 0.05 mm or 10 mm ± 0,05 mm or even less may be used, It necessary, for strongly coloured samples.
For determination at 20 ‘C or at another specified temperature, use double.walled tubes, equipped with a thermometer (54) to ensure waler circulation at the required temperature.
For determination at ambient temperature, any type of tube may be used, although it i5 advisable to use the type described above in this case too.
5.4 Thermomeler. graduated In 0,2 ‘C or 0,1 ‘C, allowing determination of temperatures between 10°C and
30°C.
5.5 Thermostatically controlled device, for maintaining the temperature of the sample at 20 ‘C ± 0.2 ‘C or any other specified temperature.
6 SamplIng
It is important that the laboratory receive a representative sample which has not been damaged or modified di.iring transportation or storage.
Samp5ng does not constitute a part 01 the method specified In this International Standard A recommended sampling method is given in ISO 212.11
7 Procedure
7.1 Preparalion of test sample
See ISO 356 if it is necessary to dry the sample.
When determining specific rotation (see 3.2), prepare the oil solution in the appropriate solvent (4.1), at the concentration specified in the corresponding appropriate International Standard icr the essential oil being analysed 7.2 DetermInation
Switch on the light source (5.2) and wait until full kimenosity is obtained.
If necessary, bring the temperature of the test sample (7.1)to 20 Cii C er to another specified temperature (see the note), then pour the sample into the appropriate poimeter tube (5.3), which should be at approximately the same temperature. Start waler ciraulabon under thermostatic control so as to keep the whole at the specified temperature (± 02 C) during the deter,tanation.
Fdl the tube with the test sample, and ensure the absence of air bubbles.
Place the tube In the polarimeter (5.1) and read the deictrorotatory (+) or laevcrotatory (—) optical rotation of the oil on the scale of the instrument.
MOTE As a rate, the determination will be carried out at 20 C. exceptIons 10 that being set out in the specifications ooncen.ig a number at paniciiw ails.
7.3 Number of determInations
Carry out at least three determinations with the same test sample.
Take as the result the mean of the values obtained for three measurements, provided that they do not differ by more
than 1,4 mrad (0,089.
8 Expression of results
8.1 CalculatIon and formulae
8.1.1 Optical rotation
The optical rotation, expressed in miliradians and/or degrees of angle, is given by the equation:
where
af is the optical rotation of the oil solution, calculated eccording to 8.1.1;
c Is the concentration of the Cd solution, m grave of oil per mdlilltre of soiuion.
8.2 PrecisIon
The precision of the test method is ± 3 mrad ( ± 0.1 7).
9 Test report
The test report shall state
— all deals necessary for the complete identification of the sample;
— the sampling method used, if known:
— the test method used, with reference to ISO 592:
— whether an oil in solution was used in the test, specifying the nature of the solvent and the concentration of the oil:
— all operating detaAs not specified in ISO 592, or regarded as optional, together with details of any incidents whidi may have influenced the test result:
— the test result obtarned:
— if repeatability has been chedied, the final c,oted result obtained.