ISO 11021 pdf download.Essential oils — Determination of water content — Karl Fischer method
1 Scope
This International Standard specifies a method for the determination of the water content of essential oils by the Karl Fischer method.
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 760, Determination of water content — Karl Fischer method (General method).
3 Terms and definitions
For the purposes of this International Standard, the following term and definition apply. 3.1 water content amount of water present in the essential oil considered, determined in accordance with the procedure specified in this International Standard NOTE Water content is expressed as a mass fraction in percent [formerly designated as % (m/m)].
4 Principle
The water present in a test portion is absorbed with dried methanol. The water is allowed to react with the Karl Fischer reagent without pyridine, previously standardized by titration using a Karl Fischer apparatus. The endpoint of the reaction is obtained by an electrometric method.
5 Reactions
During the determination of water according to the Karl Fischer method, the water present in the sample reacts, in the presence of an amine and an alcohol, with iodine and sulfur dioxide: H 2 O + I 2 + SO 2 + ROH + 3R n NH 3–n → 2R n NH 3–n HI + R n NH 3–n HSO 4 R where R is an alkyl or alkoxyl group. The endpoint of the reaction is obtained electrometrically by a surplus of iodine.
6 Reagents and materials
Use only reagents of recognized analytical quality and distilled or demineralized water or water of equivalent purity. 6.1 Methanol, containing not more than 0,05 % of water by mass. If the reagent contains more than this quantity of water, dry it by distillation in an inert atmosphere (nitrogen, helium etc.) with magnesium turnings activated with iodine. Collect the distillate in a flask protected from atmospheric moisture by means of a guard tube with a desiccant. Alternatively, use 2-methoxyethanol (6.2). 6.2 2-Methoxyethanol (ethylene glycol monomethyl ether or methylcellosolve), containing not more than 0,05 % of water by mass. If the reagent contains more than this quantity of water, dry it by distillation, rejecting the first few millilitres of the distillate which contains water. 6.3 Karl Fischer reagent, 1 ) free from pyridine, having a titre lower than 4,0 mg/ml; one or two component system. The titre shall be determined daily. If carbonyl compounds are present, an adapted Karl Fischer reagent shall be used. 6.4 Tartaric acid, dipotassium salt (C 4 H 4 O 6 K 2 • ½H 2 O), or water.
7 Apparatus
See ISO 760. All the glassware used shall be previously dried for 30 min in an oven maintained at approximately 1 30 °C, then stored in a desiccator containing a desiccant then allowed to cool to room temperature. The automatic burettes should not be heated in an oven. They should be dried with absolute ethanol or acetone and a dry air stream. Usual laboratory apparatus and, in particular, the following. 7.1 Titration apparatus There is commercially available apparatus for the automatic determination of the water content according to the Karl Fischer method, which consists of the items given in 7.1 .1 to 7.1 .5. 7.1.1 Endpoint indicator, for titration according to the electrometric method. 7.1.2 Platinum double electrode. 7.1.3 Magnetic stirrer, fitted with a stirring rod covered with polytetrafluoroethytlene, operating at a rotational frequency of 1 50 r/min to 300 r/min. 7.1.4 Titration vessel, of approximately 200 ml capacity, with at least three ground glass sockets. Connect one of the ground glass sockets to the automatic burette. Place the platinum double electrode in the automatic burette, and the platinum double electrode in the second one, and use the third one to add the reagents and the sample. A discharge tap at the bottom of the vessel is an advantage. Connect it to the vessel with a capillary tube having a volume of not more than 0,5 ml. Close all ventilation sockets in the titration vessel either with drying tubes which have been charged with an effective drying agent or molecular sieves, or with drying receivers filled with the reagent (6.3) in order to avoid the influence of moisture from the air.