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1、 Reference number ISO 6488:2004(E) ISO 2004 INTERNATIONAL STANDARD ISO 6488 Second edition 2004-02-15 Tobacco and tobacco products Determination of water content Karl Fischer method Tabac et produits du tabac Dtermination de la teneur en eau Mthode de Karl Fischer Copyright International Organizatio
2、n for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6488:2004(E) PDF disclaimer This PDF file may contain embedded typefaces. In a
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5、rinting. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. ISO 2004 All rights reserved. Unless otherwise specified, no part of th
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7、11 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2004 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 No
8、t for Resale, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6488:2004(E) ISO 2004 All rights reserved iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies).
9、The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-g
10、overnmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2
11、. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a
12、vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6488 was prepared by Technical Committee ISO/TC 126, Tobacco and tobacco products. This sec
13、ond edition of ISO 6488 cancels and replaces ISO 6488-1:1997, which has been technically revised. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 07:45:44 MDTNo reproduction or n
14、etworking permitted without license from IHS -,-,- ISO 6488:2004(E) iv ISO 2004 All rights reserved Introduction During the development of International Standards, inter-laboratory tests were carried out using two different principles for the determination of water content of raw tobacco and tobacco
15、 taken from finished products. These were this Karl Fischer procedure, and the gas chromatographic procedure. These studies show that no differences occur between the results obtained by the two different methods. The gas chromatographic method is described in ISO 16632. Copyright International Orga
16、nization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 6488:2004(E) ISO 2004 All rights reserved 1 Toba
17、cco and tobacco products Determination of water content Karl Fischer method 1 Scope This International Standard specifies a method for the determination of water content by the Karl Fischer method. It is applicable to raw tobacco as well as tobacco taken from finished products. The method is suitabl
18、e for water contents ranging from a mass fraction of at least 2 % to 55 %. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referen
19、ced document (including any amendments) applies. ISO 648, Laboratory glassware One-mark pipettes ISO 3696, Water for analytical laboratory use Specification and test methods ISO 4874, Tobacco Sampling of batches of raw material General principles ISO 8243, Cigarettes Sampling ISO 10362-2, Cigarettes
20、 Determination of water in smoke condensates Part 2: Karl Fischer method ISO 15592-1, Fine-cut tobacco and smoking articles made from it Methods of sampling, conditioning and analysis Part 1: Sampling 3 Terms and definitions For the purposes of this document, the following terms and definitions appl
21、y. 3.1 high-moisture tobacco any tobacco sample containing volatile matter over 20 % as determined by drying at between 100 C and 105 C 4 Principle The water content of a sample of tobacco or a tobacco product is determined by extraction of water by shaking the sample with dry methanol, followed by
22、injection of an aliquot portion into the titration vessel, titration with pyridine-free Karl Fischer reagent and calculation of the water content. The method is applicable to any type of tobacco sample provided that the particle size reduction is less than 4 mm. NOTE If a size reduction (grinding or
23、 cutting) is applied, it can create a decrease in the original water content. Cryogenic techniques may be used to prevent such moisture losses. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resal
24、e, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6488:2004(E) 2 ISO 2004 All rights reserved 5 Reagents Use only reagents of recognized analytical grade. 5.1 Karl Fischer reagent, free from pyridine, having a water equivalent per millilitre of reag
25、ent of approximately 2 mg to 5 mg. 5.2 Methanol, with a water content of less than 0,05 g per 100 g. This is hygroscopic so it is recommended to cap the bottle with an automatic delivery pipette equipped with drying tube. WARNING Methanol is hazardous to human subjects and to the environment. Handle
26、 it with care. 5.3 Desiccant, silica gel, freshly activated. 5.4 Water, complying with grade 2 of ISO 3696, or better. 6 Apparatus Usual laboratory apparatus and, in particular, the following items. All glassware used in the preparation and in the water determination shall be heated at (105 5) C for
27、 at least 1 h after visible water has evaporated. The glassware shall then be cooled and stored in a desiccator over desiccant (5.3) until used. 6.1 Karl Fischer apparatus for automatic titration, consisting of items 6.1.1 to 6.1.5. 6.1.1 Apparatus for the detection of the titration endpoint, accord
28、ing to the biamperiometrical method. 6.1.2 Double electrode, made of platinum. 6.1.3 Magnetic stirrer. 6.1.4 Titration vessel. 6.1.5 Automatic burettes, for methanol and Karl Fischer reagent. 6.2 Mechanical shaker, rotary platform, adjustable to a shaking frequency of 155 min1. 6.3 Microsyringe, for
29、 the determination of the water equivalent, of capacity 50 l. 6.4 One-mark pipettes, of capacities 10 ml and 20 ml, complying with Class A of ISO 648. 6.5 Conical flasks, of capacities 250 ml and 500 ml, with a conical ground glass joint. 6.6 Hot-air oven, capable of maintaining a temperature of (10
30、5 5) C. 7 Standardization of the Karl Fischer reagent Add sufficient methanol (5.2) to the titration vessel (6.1.4) to immerse the tips of the electrodes. Titrate any residual solution (see Note) in the titration vessel to its endpoint by addition of Karl Fischer reagent (5.1). Copyright Internation
31、al Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6488:2004(E) ISO 2004 All rights reserved 3 Add 50 l of water to
32、 the titration vessel using the microsyringe (6.3). To ensure that the syringe does not contain air bubbles, fill it to above the 50 l mark, invert it and tap the air bubbles to the top. Then depress the plunger to the 50 l mark and remove excess water quickly from the needle tip with a tissue. As a
33、n alternative, fill the syringe with 50 l of water and weigh the syringe. After dosage, weigh the syringe again and note the exact mass of water. Transfer the 50 l of water to the titration vessel, taking care to inject the water directly into the solution, not allowing any to fall onto the neck or
34、walls of the vessel. Where the vessel can be fitted with a rubber membrane cap, this shall be used and the needle inserted through the cap. If a water droplet remains on the needle tip, remove it by touching the surface of the solution in the vessel. Titrate with Karl Fischer reagent (5.1) and recor
35、d the titration value. Repeat the process. If the difference between the values of two determinations is not greater than 0,05 ml, take the mean of two determinations. Otherwise repeat the whole determination. Standardize the Karl Fischer reagent every working day. For best results with the Karl Fis
36、cher technique, it is important to ensure that all stages of the analysis are carried out in a uniform manner, extract to extract, sample to sample, day to day. NOTE It is common practice with the direct titration technique to carry out a titration “on top” of residual solution in the titration vess
37、el, i. e. without removing the residual solution. When the volume in the vessel reaches a certain level, the liquid is run to waste, retaining just enough for the electrode tips to be immersed. In time, however, the methanol concentration in the vessel falls to a level such that the reaction cannot
38、proceed satisfactorily. A precipitate may form and false titration values may be obtained. Only experience will tell when titration “on top of” residual solution has reached this point and then the titration vessel has to be completely emptied to waste, rinsed, and recharged with methanol. Calculate
39、 the water equivalent of the Karl Fischer reagent according to the following equation: w w m E V = (1) where E is the water equivalent, in milligrams of water per millilitre of reagent; mw is the mass, in milligrams, of the water used for the standardization of the Karl Fischer reagent; Vw is the me
40、an volume, in millilitres, of the Karl Fischer reagent used for the titration. Repeat the determination of the water equivalent daily and on each new batch of Karl Fischer reagent. 8 Sampling Sample raw tobacco in accordance with ISO 4874 and cigarettes in accordance with ISO 8243. Sample fine- cut
41、tobacco in accordance with ISO 15592-1. Each time a sample is collected and stored, it should be placed in an airtight container having a size just sufficient to contain the sample. If samples are stored at 4 C, allow the closed container to equilibrate at room temperature before opening. Copyright
42、International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 07:45:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6488:2004(E) 4 ISO 2004 All rights reserved 9 Procedu
43、re 9.1 Sample handling Combine and mix enough retail units to constitute at least 100 g for each test subsample. If size reduction is employed, the sample should be cut sufficiently to pass through a 4 mm screen. The sample may be frozen with liquid nitrogen before cutting if the absolute moisture l
44、evel is of interest. Cut filler from cigarettes need not be reduced further in size. If high-moisture samples (see 3.1) cannot be analysed immediately, they should be stored below 4 C for no longer than 10 days. 9.2 Test portion 9.2.1 Take a test portion of about 5 g from the sample that has been pr
45、epared according to 9.1. Weigh to the nearest 0,001 g and transfer this test portion to a 500 ml conical flask (6.5). Add (250 1) ml of methanol to the flask and close the flask immediately. Shake on the mechanical shaker (6.2) for 30 min, with a shaking frequency of 155 min1. 9.2.2 If a sufficientl
46、y sized sample is not available, the determination may also be carried out with a reduced test portion. The minimum test portion is 0,5 g. In this case use a 250 ml conical flask and add at least 50 ml of methanol. 9.2.3 For the determination of the water content of tobacco stems and tobacco leaves,
47、 an extraction time of 30 min is not sufficient. In this case extract the sample in a 500 ml conical flask with 250 ml of methanol, shake for 30 min and let stand for at least 24 h. The test portions should be gently swirled or mixed mechanically prior to removal of the analysis aliquot. In special
48、cases a longer extraction time may be necessary. In this case extract the sample until constant results are obtained, i.e. the difference between the two calculations at different times is equal to or less than 0,5 g per 100 g. 9.2.4 If the extract is not analysed on the same day, store in a refrigerator. After conditioning to room temperature, the extract should be analysed. 9.3 Preparation of titration apparatus Prepare the titration apparatus in accordance with the instructions for use.