1、BRITISH STANDARD BS4317-11: 1976 ISO2164:1975 Methods of test Cereals and pulses Part11: Determination of glycosidic hydrocyanic acid in pulses UDC 633.1/.3:664.7:543.8:546.267BS4317-11:1976 This British Standard, having been prepared under the directionof the Farming, Food andAgriculture Industry S
2、tandards Committee, was published under the authority ofthe Executive Board on 31March1976 BSI08-1999 The following BSI references relate to the work on this standard: Committee reference FAC/4 Draft for approval74/51852 ISBN 0 580 09112 0 Co-operating organizations The Farming, Food and Agriculture
3、 Standards Committee, under whose supervision this British Standard has been prepared consists of representatives of the following Government departments and other organizations: Agricultural Co-operation and Marketing Services British Food Manufacturing Industries Research Association British Indus
4、trial Biological Research Association Campden Food Preservation Research Association Central Council for Agricultural and Horticultural Co-operation Consumer Standards Advisory Committee of BSI Department of Agriculture and Fisheries for Scotland* Department of Industry, Laboratory of the Government
5、 Chemist* Flour Milling and Baking Research Association* Food Manufacturers Federation Inc.* Institute of Brewing Local Authority Joint Advisory Committee on Food Standards Ministry of Agriculture, Fisheries and Food* Ministry of Agriculture, Northern Ireland National Farmers Union* National Farmers
6、 Union (Scotland) Tobacco Advisory Committee The Government departments and other organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this BritishStandard: Association of Public Analysts Br
7、ewing Industry Research Foundation British Association of Grain, Seed, Feed and Agricultural Merchants British Maize Starch and Glucose Manufacturers Association Home-Grown Cereals Authority Incorporated National Association of British and Irish Millers Incorporated Oil Seed Association Seed, Oil, C
8、ake and General Produce Association Society of Chemical Industry Ulster Farmers Union Amendments issued since publication Amd. No. Date of issue CommentsBS4317-11:1976 BSI 08-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope and field of application 1 2 Reference
9、s 1 3 Definition 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Procedure 2 9 Expression of results 3 10 Note on procedure 3 11 Test report 3 Annex Determination of glycosidic hydrocyanic acid by themercurimetricmethod 4BS4317-11:1976 ii BSI 08-1999 Foreword This Part of this British Stan
10、dard is one of a series of methods of test for cereals and pulses and is published under the authority of the Farming, Food and Agriculture Industry Standards Committee. It is identical with ISO2164 “Pulses Determination of glycosidic hydrocyanic acid”. Other Parts of this British Standard are: Part
11、1: Determination of the mass of1000 grains; Part2: Determination of moisture content of cereals and cereal products (basic reference method); Part3: Determination of moisture content (routine methods) (inpreparation). Part4: Determination of impurities in pulses; Part5: Determination of size of puls
12、es; Part6: Tests for foreign odours in pulses; Part7: Tests for infestation of pulses by insects; Part8: Tests for species and variety of pulses; Part9: Determination of falling number of cereals; Part10: Determination of ash in cereals, pulses and their derived products (inpreparation). For the pur
13、poses of this British Standard the text of ISO2164 should be modified as follows. Terminology. The words “British Standard” should replace the words “International Standard” wherever they appear. Decimal point. The decimal point should replace the decimal comma wherever it appears. Cross references.
14、 The references to other International Standards listed in clause2 should be replaced by references to British Standards as follows. Distilled water. Wherever reference is made to distilled water, water complying with the requirements of BS3978 “Water for laboratory use” will be suitable. Text chang
15、es. The following text changes should be made. Sieves. In6.2 add “complying with the requirements of BS410 “Test sieves”. Volumetric flasks. In6.7 add “complying with the requirements of BS1792 “One-mark volumetric flasks”, Class A”. Pipette. In6.8 add “complying with the requirements of BS1583 “One
16、-mark pipettes”, Class A”. 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 from legal obligations. Reference to I
17、nternational Standard Appropriate British Standard ISO/R951 Pulses Sampling BS4511 Methods for sampling pulses ISO2170 Cereals and pulses Sampling of milled products a BS5333 Methods for sampling cereals and pulses (as milled products) (inpreparation) a Published15October,1972 Summary of pages This
18、document comprises a front cover, an inside front cover, pagesi andii, pages1 to4 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 front cover.BS4317-11:1976 BSI 08-1999 1 1 Sco
19、pe and field of application This International Standard specifies a method for the determination of glycosidic hydrocyanic acid in pulses. The method is generally applicable but may require modification if sulphides or certain other sulphur compounds are present. Conversely, if no such compounds are
20、 present, a mercurimetric titration procedure may be used, details of which are given in the Annex. 2 References ISO/R951, Pulses Sampling. ISO2170, Cereals and pulses Sampling of milled products. 3 Definition glycosidic hydrocyanic acid in pulses hydrocyanic acid, determined according to the method
21、 described the content of glycosidic hydrocyanic acid is expressed as milligrams of hydrocyanic acid (HCN) per kilogram of product 4 Principle After enzymic or acid hydrolysis of the glycosides, steam distillation of the hydrocyanic acid liberated. Determination of the quantity of acid obtained: eit
22、her by direct titration of the acid in the distillate with silver nitrate solution in an ammoniacal medium and in the presence of potassium iodide, the hydrocyanic acid forming the soluble complex Ag(CN) 2 and the end point of the titration being characterized by the appearance of permanent turbidit
23、y due to precipitation of silver iodide; or by back titration of an excess of silver nitrate solution with ammonium thiocyanate solution, in a sufficiently dilute nitric acid medium and in the presence of iron(III) ions, the hydrocyanic acid being precipitated as silver cyanide (AgCN). 5 Reagents Al
24、l reagents shall be of analytical quality; the water used shall be distilled water or water of at least equivalent purity. 5.1 Potassium dihydrogen phosphate (KH 2 PO 4 ),20g/l solution. 5.2 Sodium acetate, 20g/l solution brought to pH5,0 0,5 with a few millilitres of acetic acid. 5.3 Sodium hydroxi
25、de, in pellets. 5.4 Ammonia solution, about6N ( 20 0,96g/ml), obtained by diluting concentrated ammonia solution, 20 0,92g/ml, with an equal volume of water. For direct titration: 5.5 Silver nitrate, 0,01N standard volumetric solution. 5.6 Potassium iodide (KI),50g/l solution. For back titration: 5.
26、7 Nitric acid, 20 1,38g/ml. 5.8 Silver nitrate, 0,02N standard volumetric solution. 5.9 Ammonium thiocyanate, 0,02N standard volumetric solution. 5.10 Indicator, prepared by mixing one part by volume of the nitric acid(5.7) and one part by volume of saturated ammonium iron(III) sulphate solution. 6
27、Apparatus Usual laboratory apparatus not otherwise specified, and the following: 6.1 Mechanical grinding mill, easy to clean, enabling samples to be ground without becoming heated and without appreciable change in moisture content. 6.2 Sieves, with1mm apertures. 6.3 Balance 6.4 Incubator, adjusted t
28、o operate at38 2 C. 6.5 Steam distillation apparatus, provided with a1lflask with ground neck. It should be possible to stopper this removable flask hermetically with a ground stopper. The end of the condenser shall be provided with an extension drawn out to a point. 6.6 Ice-water bath For direct ti
29、tration: 6.7 Volumetric flask, 250ml. 6.8 Pipette, 100ml. For back titration: 6.9 Volumetric flasks, 250ml and500ml. 7 Sampling Prepare a final lot sample of appropriate size in accordance with ISO/R951 or ISO2170.BS4317-11:1976 2 BSI 08-1999 8 Procedure 8.1 Preparation of test sample Grind about on
30、e-twentieth of the laboratory sample in the previously well-cleaned mechanical grinding mill(6.1), in order to complete the cleaning of the mill, and reject these grindings. Then grind the rest to particles which will pass through the sieve(6.2) completely, collect the grindings, mix thoroughly and
31、carry out the determination without delay. In the case of ground pulses, use the final lot sample. 8.2 Test portion Weigh, to the nearest0,1g, approximately20g of the test sample(8.1). 8.3 Determination 8.3.1 Methods of hydrolysis Either of the two alternative procedures which follow(8.3.1.1 or8.3.1
32、.2) may be used. If the enzymic power of the sample seems insufficient, enzymic hydrolysis should be the preferred method. 8.3.1.1 ENZYMIC HYDROLYSIS Transfer the test portion(8.2) to the1lflask(6.5). Add50ml of water containing2 crushed sweet almonds (total mass1,5 to2,0g). Stopper the flask hermet
33、ically and leave it for2h in the incubator(6.4) at38 C. NOTEVerify that the almonds used do not contain any hydrocyanic acid that can be liberated under the conditions of the test. Cool the flask and its contents in the ice-water bath(6.6). Add80ml of water,10ml of the sodium acetate solution(5.2) a
34、nd a drop of anti-foaming agent. Fitthe flask immediately to the distillation apparatus(6.5). 8.3.1.2 ALTERNATIVE HYDROLYSIS PROCEDURE Transfer the test portion(8.2) to the1l flask(6.5) and add50ml of distilled water and10ml of the sodium acetate solution(5.2) or potassium dihydrogen phosphate solut
35、ion(5.1). Stopper hermetically, mix well and leave the flask for12h in the incubator(6.4) at38 C. Cool the flask and its contents by immersion in the ice-water bath(6.6) and add80ml of water and a drop of anti-foaming agent; fit the flask to the distillation apparatus(6.5) immediately. 8.3.2 Distill
36、ation Distil, collecting approximately100ml of distillate. If the direct method of titration(8.3.3.1) in the presence of potassium iodide(5.6) is to be used, collect the distillate in20ml of distilled water containing1g of sodium hydroxide(5.3). (SolutionA.) If the back titration method(8.3.3.2) wit
37、h the ammonium thiocyanate solution(5.9) is to be used, collect the distillate in a volume(20 to50ml) of the0,02N silver nitrate solution(5.8), to which has been added1ml of the nitric acid(5.7). (Solution B.) The volume of silver nitrate solution used depends on the presumed content of hydrocyanic
38、acid. 8.3.3 Titration 8.3.3.1 DIRECT TITRATION Transfer solution A to a250ml volumetric flask(6.7), dilute to the mark with distilled water and mix thoroughly. Pipette100ml into a beaker. Add2ml of the potassium iodide solution(5.6) and1ml of the ammonia solution(5.4). Titrate with the0,01N silver n
39、itrate solution(5.5) until permanent turbidity appears. For the easy recognition of the end point of the titration, it is recommended that a black background be used. Make a second titration with another100ml portion of distillate and take the mean of the two titrations. 8.3.3.2 BACK TITRATION Trans
40、fer solution B to a500ml volumetric flask(6.9) and dilute to the mark with water. Mix thoroughly and filter through a dry filter, collecting the filtrate in a dry vessel. Add2 to3ml of the indicator(5.10) to250ml of filtrate measured in a volumetric flask(6.9), and titrate with the ammonium thiocyan
41、ate solution(5.9), while shaking, until a permanent brown-red coloration appears. 8.3.4 Carry out two determinations on the same test sample. 8.4 Test for sulphides A nearly black precipitate denotes the presence of a significant quantity of sulphides, whereas a brownish precipitate denotes only a v
42、ery slight sulphide content (see clause10). 8.5 Blank test Carry out a blank test under the same conditions as in the determination proper but replacing the distillate by distilled water.BS4317-11:1976 BSI 08-1999 3 9 Expression of results 9.1 Direct titration The content of glycosidic hydrocyanic a
43、cid, expressed in milligrams of hydrocyanic acid (HCN) per kilogram of sample, is equal to where m is the mass, in grams, of the test portion; V 0is the volume, in millilitres, of the silver nitrate solution(5.5) used for the determination proper; V 1is the volume, in millilitres, of the silver nitr
44、ate solution(5.5) used for the blank test. 9.2 Back titration The content of glycosidic hydrocyanic acid, expressed in milligrams of hydrocyanic acid (HCN) per kilogram of sample, is equal to where m is the mass, in grams, of the test portion; V 2is the volume, in millilitres, of the ammonium thiocy
45、anate solution(5.9) used for the determination proper; V 3is the volume, in millilitres, of the ammonium thiocyanate solution(5.9) used for the blank test. NOTE (to9.1 and9.2)If the standard volumetric solutions used are not of exactly the strength indicated in the list of reagents, a suitable corre
46、ction factor should be used in calculating the results. 9.3 Take as the result the arithmetic mean of the two determinations. Express the result to one decimal place. NOTEIf the result obtained is less than10mg of hydrocyanic acid per kilogram of sample, consider the sample practically free from gly
47、cosidic hydrocyanic acid. 10 Note on procedure If the distillate contains sulphides or sulphur compounds, a more or less abundant black precipitate appears through action on silver ions. In this case it is advisable to repeat the procedure using only the direct titration method(8.3.3.1), modified by
48、 replacing the first paragraph by the following: Transfer the distillate to a250ml volumetric flask(6.7), dilute to the mark and mix thoroughly. Pipette100ml into a beaker. Add5ml of lead nitrate solution(5 g/l) and mix. After allowing to stand for15min, filter and wash the beaker, the precipitate a
49、nd the filter three times, using10ml of water each time. Add to the filtrate and washings2ml of the potassium iodide solution(5.6) and1ml of the ammonia solution(5.4). 11 Test report The test report shall show the method used, the mode of hydrolysis and the mode of titration followed and the result obtained. It shall also mention any operating conditions not specified in this International Standard, or regarded as optional, as well as any circumstances that may have influenced the result. The report shall include all details for
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