1、BRITISH STANDARD BS 6986-4: 1990 ISO 7514:1990 Analysis of instant tea Part 4: Method for determination of total ashBS6986-4:1990 This British Standard, having been prepared under the directionof the Agriculture andFood Standards Policy Committee, was published underthe authority of the BoardofBSI a
2、nd comes intoeffecton 30 November 1990 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference AFC/8 Draft for comment 89/52868 DC ISBN 0 580 19213 X Committees responsible for this British Standard The preparation of this British Standard was entrusted by t
3、he Agriculture and Food Standards Policy Committee (AFC/-) to Technical Committee AFC/8, upon which the following bodies were represented: Campden Food and Drink Research Association Department of Trade and Industry (Laboratory of the Government Chemist) Ministry of Agriculture, Fisheries and Food N
4、atural Resources Institute Tea Producers Association United Kingdom Tea Association Amendments issued since publication Amd. No. Date CommentsBS6986-4:1990 BSI 12-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references 1 3 Definition 1 4 P
5、rinciple 1 5 Reagent 1 6 Apparatus 1 7 Sampling 1 8 Preparation of the test sample 1 9 Procedure 1 10 Expression of results 2 11 Precision 2 12 Test report 2 Publication(s) referred to Inside back coverBS6986-4:1990 ii BSI 12-1999 National foreword This Part of BS 6986 has been prepared under the di
6、rection of the Agriculture and Food Standards Policy Committee. It implements an agreement, to which the UK was a party, reached in Subcommittee 8, Tea, of Technical Committee TC 34, Agricultural food products, of the International Organization for Standardization (ISO). The UK also provides the sec
7、retariat for the Subcommittee. This Part of BS 6986 is identical with ISO 7514:1990 “Instant tea in solid form Determination of total ash”. This standard describes a method of test only and should not be referred to as a specification defining limits of purity. Reference to the standard should indic
8、ate that the method of test used is in accordance with BS 6986-4. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity
9、 from legal obligations. Cross-references International Standard Corresponding British Standard ISO 7513:1990 BS 6986 Analysis of instant tea Part 3:1990 Method for determination of moisture content (loss in mass at 103 C) (Identical) ISO 7516:1984 Part 1:1988 Methods of sampling (Identical) Summary
10、 of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 and 2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside fron
11、t cover.BS6986-4:1990 BSI 12-1999 1 1 Scope This International Standard specifies a method for the determination of the total ash of instant tea in solid form. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Inter
12、national Standard. At the time of publication, the editions 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.
13、 Members of IEC and ISO maintain registers of currently valid International Standards. ISO 7513:1990, Instant tea in solid form Determination of moisture content (loss in mass at103 C). ISO 7516:1984, Instant tea in solid form Sampling. 3 Definition For the purposes of this International Standard, t
14、he following definition applies. total ash the residue obtained after treatment with hydrochloric acid and incineration at550 C 25 C under the conditions specified in this International Standard 4 Principle Destruction of organic matter by treatment with concentrated hydrochloric acid solution and h
15、eating at 550 C. Weighing of the residue. 5 Reagent 5.1 Hydrochloric acid, concentrated solution ( 20= 1,16 g/ml to 1,18 g/ml), of recognized analytical grade. WARNINGConcentrated hydrochloric acid solution is corrosive, has an irritant vapour and causes burns; it shall be handled in accordance with
16、 good laboratory practice. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Dish, of approximately 50 ml capacity, made of platinum, porcelain or any other material unaffected by the conditions of the test. 6.2 Furnace, capable of being controlled at550 C 25 C. 6.3 Hot-p
17、late, thermostatically controlled. 6.4 Desiccator, containing an efficient desiccant. 7 Sampling Sampling shall have been carried out in accordance with ISO 7516. 8 Preparation of the test sample Thoroughly mix the instant tea sample as received by shaking or inverting the sealed sample container. 9
18、 Procedure 9.1 Preparation of the dish Ensure that the dish (6.1) is completely clean, and then heat it in the furnace (6.2) at 550 C 25 C for at least 30 min. Cool in the desiccator (6.4). After cooling to room temperature, weigh to the nearest0,001 g. 9.2 Test portion Open the sample container and
19、 immediately weigh, to the nearest 0,001 g, about 2 g of the prepared test sample (clause 8) into the prepared dish (9.1). Spread the sample evenly over the base of the dish. 9.3 Determination Add, drop by drop, to the test portion contained in the dish (9.2), sufficient (approximately 1 ml) of the
20、concentrated hydrochloric acid solution (clause 5) to wet it completely. Place the dish on the cool hot-plate (6.3), set the control to medium and heat for 30 min. Raise the hot-plate temperature to the highest setting in three successive steps, allowing the test portion to heat at each stage for 30
21、 min. Keep the test portion at the highest setting until no fuming has occurred for at least 5 min. Place the dish containing the test portion in the furnace (6.2) at 550 C 25 C for 16 h. Remove, leave to cool and add a few drops of water to moisten and disperse the ash. Evaporate to dryness on the
22、hot-plate (6.3) as before, and then return to the furnace (6.2) for a further 30 min. Remove, cool to room temperature in the desiccator (6.4) and weigh to the nearest 0,001 g. Determine the mass of the total ash to the nearest 0,001 g. NOTE 1Instant tea ashed under these conditions should give a gr
23、ey/white ash. 9.4 Number of determinations Carry out two determinations on the same test sample.BS6986-4:1990 2 BSI 12-1999 10 Expression of results The total ash, expressed as a percentage by mass of the sample on a dry basis, is given by the formula where Take as the result the arithmetic mean of
24、the two determinations, provided that the requirement for repeatability (see 11.1) is satisfied. 11 Precision 11.1 Repeatability For a total ash content within the range of 10% (m/m) to 22% (m/m), the difference between the values of two determinations, carried out in rapid succession (or simultaneo
25、usly) by the same operator using the same apparatus on the same test sample, shall not exceed 0,4% (absolute value). 11.2 Reproducibility For a total ash content within the range of 10% (m/m) to 22% (m/m), the difference between the values of the final result obtained by two laboratories using this
26、method for the analysis of the same laboratory sample, shall not exceed 1,2% (absolute value). 12 Test report The test report shall specify the method used and the result obtained. It shall also mention all operating details not specified in this International Standard, or regarded as optional, toge
27、ther with details of any incidents which may have influenced the result. The test report shall include all information necessary for the complete identification of the sample. m 0 is the mass, in grams, of the test portion; m 1 is the mass, in grams, of the total ash; RS is the dry matter content, e
28、xpressed as a percentage by mass, of the test sample. It is equal to 100 minus the moisture content determined using the method specified in ISO 7513. m 1 m 0 -100 100 RS - BS6986-4:1990 BSI 12-1999 Publication(s) referred to See national foreword.BS 6986-4: 1990 ISO 7514:1990 BSI 389 Chiswick High
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