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1、INTERNATIONAL IS0 STANDARD 1279 ,Jxfwl lnternat I9oc set Third edition 1996-12-15 Essential oils - Determination of carbonyl value - Potentiometric methods using hydroxylammonium chloride Huiles essentielles - D a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii Copyright International Or
2、ganization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD 0 IS0 IS0 1279:1996(E) Essential oils - Determinat
3、ion of carbonyl values - Potentiometric methods using hydroxylammonium chloride 1 SCOPE This International Standard specifies two methods for the potentiometric determination of the carbonyl value of essential oils which contain carbonyl compounds, either aldehydes or ketones. Method I (see clause 5
4、), is based on a cold oximation reaction with hydroxylammonium chloride. It applies to essential oils whose main constituents are easily oximable aldehydes and ketones, with the exception of citronella1 which needs a low temperature to avoid cyclization phenomena and acetalization. NOTE 1 In the cas
5、e of citronella1 the free hydroxylamine method described in IS0 1271 should be used. NOTE 2 Examples of essential oils concerned are lemongrass, hesperydus and rue. Method II (see clause 6), is based on a hot oximation reaction with hydroxylammonium chloride. It applies to essential oils whose main
6、constituents are ketones which are in general oximable only with difficulty. NOTE 3 Examples of essential oils concerned are vetiver, Dalmation sage and white artemisia which contain methylketones oximable only with difficulty. The International Standard for a specific essential oil will specify the
7、 method to be used, whether this is the free hydroxylamine method described in IS0 1271 or another method. 2 NORMATIVE REFERENCES The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the ed
8、itions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of current
9、ly valid International Standards. IS0 2 12: 1973, Essential oils - Sampling. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted w
10、ithout license from IHS -,-,- IS0 1279:1996(E) 0 IS0 IS0 356:1996, Essential oils - Preparation of test sample. IS0 127 1: 1983, Essential oils - Determination of carbon yl value - Free h ydroxylamine method. 3 DEFINITION For the purposes of this International Standard, the following definition appl
11、ies. 3.1 carbonyl value (of an essential oil): Number of milligrams of potassium hydroxide, per gram of essential oil, required to neutralize the hydrochloric acid liberated in the oximation reaction with hydroxylammonium chloride. 4 SAMPLING Sampling shall be carried out in accordance with IS0 212.
12、 5 METHOD I: METHOD OF COLD OXIMATION OF ALDEHYDES WITH HYDROXYL- AMMONIUM CHLORIDE 5.1 Principle Conversion of the carbonyl compounds to oximes by reaction with hydroxylammonium chloride. Potentiometric determination with standard potassium hydroxide solution of the hydrochloric acid liberated by t
13、his reaction. 5.2 Reagents 5.2.1 Potassium hydroxide, standard solution, c(KOH) = 0,5 mol/l in 95 % (V/V) ethanol. 5.2.2 Potassium hydroxide, standard solution c(KOH) = 0,l mol/l in 95 % (V/v) ethanol. 5.2.3 Ethanol, 95 % (V/v). 5.2.4 Bromophenol blue, 2 g/l solution. Heat 0,2 g of Bromophenol blue
14、in 3 ml of ethanolic potassium hydroxide solution (5.2.2) and 10 ml of ethanol (5.2.3). After cooling, dilute to 100 ml with ethanol. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2
15、007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 1279:1996(E) 5.2.5 Hydroxylammonium chloride, 50 g/l solution. Dissolve 50 g of hydroxylammonium chloride in 100 ml of water and add about 800 ml of ethanol (5.2.3). Neutralize with the ethanolic potassi
16、um hydroxide solution(5.2.1) in the presence of 10 ml of the Bromophenol blue solution (5.2.4) to the mid-green endpoint of the indicator (equivalence point of pH 3,4) and dilute to 1000 ml with ethanol. NOTE: The neutralized solution is stable for 1 week at least. 5.3 Apparatus Usual laboratory equ
17、ipment and, in particular, the following. 5.3.1 Beaker, of capacity 100 ml, tall form. 5.3.2 Automatic burette 5.3.3 Recorder 5.3.4 pH-meter 5.3.5 Glass electrode 5.3.6 Printer 5.4 Procedure 5.4.1 Preparation of test sample See IS0 356. 5.4.2 Test portion Weigh, to the nearest 0,001 g, between 1 g a
18、nd I,5 g of the essential oil. NOTE: If the test sample should be larger, this will be stated in the appropriate International Standard for the oil concerned. 5.4.3 Determination Add to the test portion (5.4.2) 25 ml of the hydroxylammonium chloride solution (5.2.5) and mix well. Add 3 drops of Brom
19、ophenol blue (5.2.4) and mix well. Dip the glass electrode (5.3.5) into the solution. Titrate with the potassium hydroxide solution (5.2.1) and mix the contents until the pH is lower than 4,20. It is important that the pH value does not exceed 4,20 during the determination. 3 Copyright International
20、 Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 1279:1996(E) 0 IS0 Allow to stand for 15 min. Titrate with potassi
21、um hydroxide solution (5.2.1) to the equivalence point the green to blue colour change of the Bromophenol blue (5.2.411. The equivalence point on pH is around a value of 3,4. 5.4.4 Expression of results 5.4.4.1 The content of carbonyl compounds, expressed as a percentage by mass, of the reference al
22、dehyde specified is given by the formula: M,xVxc IOm where n/l, is the relative molecular mass of the aldehyde specified in the standard specific to the essential oil concerned; V is the volume, in millilitres, of potassium hydroxide solution (5.2.1) used in the titration; C is the exact concentrati
23、on, in moles per litre, of the potassium hydroxide solution; m is the mass, in grams, of the test portion. 5.4.4.2 The carbonyl value, expressed in milligrams of potassium hydroxide per gram of essential oil, is given by the formula: 56 1 Xc I m where the symbols are as given in 5.4.4.1. 6 METHOD II
24、: METHOD OF HOT OXIMATION OF KETONES WITH HYDROXYL-AMMONIUM CHLORIDE 6.1 Principle Conversion of the carbonyl compounds to oximes by reaction with hydroxylammonium chloride. Determination with potassium hydroxide solution of the hydrochloric acid liberated by the reaction. 4 Copyright International
25、Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 1279:1996(E) 6.2 Reagents Use the reagents given in 5.2. 6.3
26、Apparatus Usual laboratory equipment and, in particular, the following. 6.3.1 Automatic burette, 50/0,1/B. 6.3.2 Beakers, of capacity 100 ml, tall form. 6.3.3 Flask, of capacity 100 ml, with reflux tube. 6.3.4 pH-meter 6.3.5 Glass electrode 6.3.6 Heater with magnetic stirrer 6.4 Procedure 6.4.1 Prep
27、aration of test sample See IS0 356. 6.4.2 Test portion Weigh, to the nearest 0,001 g, between 2 g and 2,5 g of the essential oil in the flask (6.3.3). See note to 5.4.2. 6.4.3 Determination Add to the test portion (6.4.2) 25 ml of the hydroxylammonium chloride solution (5.2.5). Insert the glass elec
28、trode (6.3.5). Titrate with potassium hydroxide (5.2.1) until the pH is lower than 4,2. Add the reflux tube to the flask. Place the flask on the heater (6.3.6)and heat with stirring to a temperature sufficient to keep a constant reflux. After 10 min, cool, add 3 drops of Bromophenol blue (5.2.4) and
29、 slowly titrate with the potassium hydroxide solution (5.2.1) to a pH lower than 4,22. It is important that the pH value does not reach or exceed 4,22 during the determination. Stop when the colour begins to change. Put the flask back on the heater. Repeat this operation every 10 min, as many times
30、as necessary, until the addition of a supplementary drop of solution is enough to pass the equivalence point. 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo rep
31、roduction or networking permitted without license from IHS -,-,- IS0 1279:1996(E) 0 IS0 NOTE: The determination time is usually 2 h, but for certain fragrances this is not enough. In this case, go on until the inflexion curve. 6.4.4 Expression of results Trace the pH curve as a function of the volum
32、e V of potassium hydroxide (5.2.1) used in the titration: pH = f(V) Note the equivalence point. Calculate the content of carbonyl compounds using the formula given in 5.4.4.1. Calculate the carbonyl value using the formula given in 5.4.4.2. 7 TEST REPORT The test report shall include the method used
33、 and the results obtained. It shall also mention any operating details not specified in this International Standard or regarded as optional, together with details of any incidents which might have influenced the results. The test report shall include all details necessary for the complete identifica
34、tion of the sample. 6 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 1279:1996(E) 0 IS0 IC
35、S 71.100.60 Descriptors: fruit and vegetable products, essential oils, chemical analysis, determination of content, carbonyl compounds, potentiometric methods. Price based on 5 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:20:14 MDTNo reproduction or networking permitted without license from IHS -,-,-
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