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1、BRITISH STANDARD CONFIRMED NOVEMBER 1992 BS 684-2.42: 1989 ISO 7366:1987 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.42 Determination of 1-monoglycerides and free glycerol contents IMPORTANT NOTE. It is essential that BS 684-0, which is published separately, be read in
2、 conjunction with this Section. UDC 665.1.014:543:547.426.1 + 547.426.21 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.42:1989 This British Standard, having been prepared under the direction of the Food and Agriculture Standards C
3、ommittee, was published under the authority of the Board of BSI and comes into effect on 31 March 1989 BSI 11-1999 First published November 1986 First revision March 1989 The following BSI references relate to the work on this standard: Committee reference FAC/18 Draft announced in BSI News March 19
4、86 ISBN 0 580 17193 0 National foreword This revision of Section 2.42 of BS 684 has been prepared under the direction of the Food and Agriculture Standards Committee. It is identical with ISO 7366:1987 “Animal and vegetable fats and oils Determination of 1-monoglycerides and free glycerol contents”
5、published by the International Organization for Standardization (ISO) and in the preparation of which the UK played a full part. This revision does not differ technically from BS 684-2.42:1986, which it supersedes and which is withdrawn, but the Table in 8.2 has been expanded to give a wider range o
6、f approximate masses of the test portion, and editorial modifications have been made. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical
7、with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its submultip
8、les). In British Standards it is current practice to use the symbol “L”. In British Standards it is current practice to use the spelling “sulphur”, etc. instead of “sulfur”, etc. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS 684
9、”. 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. Summary of pages This document compris
10、es a front cover, an inside front cover, pages i and ii, pages 1 to 4, 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 front cover. Cross-reference Interna
11、tional StandardCorresponding British Standard ISO 5555:1983BS 627:1982 Methods for sampling animal and vegetable fats and oils (Technically equivalent) Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Un
12、controlled Copy, (c) BSI BS 684-2.42:1989 BSI 11-1999i Contents Page National forewordInside front cover 1Scope1 2Field of application1 3Reference1 4Principle1 5Reagents1 6Apparatus1 7Sampling1 8Procedure1 9Expression of results3 10Test report3 Table1 Publication referred toInside back cover License
13、d Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.42:1989 BSI 11-19991 1 Scope This International Standard specifies a method
14、 for the determination of 1-monoglycerides content and of free glycerol content consecutively on the same test portion. 2 Field of application It is applicable to animal and vegetable fats and oils and to interesterified products of oils, fats and fatty acids with glycerol. It is not applicable when
15、 the sample contains a) in addition to 1-monoglycerides: chloroform-soluble polyhydric substances with two or more adjacent hydroxyl groups; b) in addition to free glycerol: water-soluble polyhydric substances with two or more adjacent hydroxyl groups. 3 Reference ISO 5555, Animal and vegetables fat
16、s and oils Sampling. 4 Principle Dissolution of a test portion in chloroform. Extraction of free glycerol from this solution with acetic acid solution. Oxidation of 1-monoglycerides in the chloroform solution by an excess of periodic acid solution. Addition of potassium iodide and titration of the l
17、iberated iodine with a sodium thiosulfate standard volumetric solution. Oxidation of free glycerol in the aqueous solution by an excess of periodic acid solution. Addition of potassium iodide and titration of the liberated iodine with a sodium thiosulfate standard volumetric solution. 5 Reagents All
18、 reagents shall be of recognized analytical grade. The water used shall be distilled water or water of at least equivalent purity. 5.1 Chloroform 5.2 Acetic acid, 5 % (V/V) solution. 5.3 Periodic acid, 2,7 g/l solution. Weigh 2,7 g of periodic acid (H5IO6) in a 1 litre volumetric flask and dissolve
19、in 50 ml of water. Make up to the mark with glacial acetic acid and mix thoroughly. Store in the dark. 5.4 Potassium iodide, 150 g/l solution, not containing free iodine or iodates. 5.5 Sodium thiosulfate, standard volumetric solution, c(Na2S2O3) = 0,1 mol/l. 5.6 Starch, indicator solution, 10 g/l.
20、Dissolve 1 g of soluble starch in 100 ml of water by stirring and heating. Add 0,1 g of salicylic acid to preserve the indicator solution and boil for 3 min. Cool to room temperature. 6 Apparatus Usual laboratory equipment and in particular 6.1 Conical flasks, of capacity 500 ml, with ground-glass s
21、toppers. 6.2 Magnetic stirrer 7 Sampling See ISO 5555. 8 Procedure 8.1 Preparation of the test sample 8.1.1 Solid samples in flake or in powder form Mix the sample thoroughly without melting. 8.1.2 Other solid or semi-solid samples Melt the sample at not more than 10 C above its melting point, mix t
22、horoughly. CAUTION The sample shall not be subjected to excessive temperatures. At temperatures above 80 C the 1-monoglycerides content may decrease as a result of interesterification and/or intraesterification. 8.1.3 Liquid samples Mix the sample thoroughly. 8.2 Test portion Weigh accurately into a
23、 50 ml beaker the appropriate mass of the test portion as indicated in the Table. Table Expected content of 1-monoglycerides or of glycerol Approximate mass of the test portion Weighing accuracy % (m/m)gg 100 75 50 40 30 20 15 10 5 3 or less 0,3 0,4 0,6 0,7 1,0 1,5 2,5 3,0 6,0 10,0 0,000 1 0,000 1 0
24、,000 1 0,000 1 0,001 0,001 0,001 0,001 0,001 0,001 NOTEIf the contents of 1-monoglycerides and glycerol are very different and therefore an intermediate test portion mass is not possible, two test portions are necessary, one for the 1-monoglycerides and the other for the glycerol. Licensed Copy: she
25、ffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.42:1989 2 BSI 11-1999 8.3 Extraction 8.3.1 Take three separating funnels of capacity 250 ml and label them 1, 2 and 3. Use separating funnel 1 to collect aqueous solutions and separating funnels 2 and 3
26、 for washing the solutions. When shaking is required, this is performed vigorously for about 1 min, releasing pressure from time to time through the tap and avoiding the formation of emulsions. Take two volumetric flasks of capacity 100 ml and label them A and B. Use flask A for the chloroform solut
27、ion of 1-monoglycerides and flask B for the aqueous solution of glycerol. 8.3.2 Dissolve the test portion (8.2) in chloroform (5.1), dispersing any free glycerol. Pour quantitatively into separating funnel 1, using successive small quantities of chloroform to aid the transfer until the volume reache
28、s 45 to 50 ml. 8.3.3 Rinse the used 50 ml beaker with about 25 ml of acetic acid solution (5.2) to dissolve any remaining glycerol. Transfer the rinsings to separating funnel 1. Stopper, shake and allow to separate. Run the chloroform (lower) layer into separating funnel 2. Wash the 50 ml beaker wit
29、h 25 ml of acetic acid solution and pour into separating funnel 2. Stopper, shake and allow to separate. Run the chloroform layer into separating funnel 3 and run the aqueous solution into separating funnel 1. 8.3.4 Wash the beaker and separating funnel 2 with a further 25 ml of acetic acid solution
30、 and run this into separating funnel 3. Stopper, shake and allow to separate. Run the chloroform layer into the 100 ml volumetric flask A. Run the aqueous layer into separating funnel 1. Rinse separating funnels 2 and 3 successively with two 20 ml volumes of chloroform and run the chloroform into se
31、parating funnel 1. Stopper, shake and allow to separate. 8.3.5 Run the chloroform layer into the 100 ml volumetric flask A and make up to volume with chloroform. Stopper and mix. 8.3.6 Run the aqueous layer into the 100 ml volumetric flask B. Rinse the separating funnel 1 with acetic acid solution,
32、add the rinsings to flask B and make up to volume with acetic acid solution. Stopper and mix. 8.4 Determination of 1-monoglycerides Using a pipette, transfer 50 ml of the chloroform solution from flask A (8.3.5) into the 500 ml conical flask (6.1), add 50 ml of periodic acid solution (5.3) with a pi
33、pette, mix and stopper. Allow to stand for 30 min in the dark. Carry out a blank test under the same conditions, using 50 ml of chloroform (5.1) and 50 ml of periodic acid solution (5.3). After the 30 min period add 20 ml of potassium iodide solution (5.4) both to the test solution and to the blank.
34、 Stopper the flasks, mix and allow to stand for 1 min longer. Add 100 ml of water to each. Titrate with sodium thiosulfate standard volumetric solution (5.5) whilst stirring continuously using the magnetic stirrer (6.2) in order to ensure thorough mixing. Towards the end of the titration, when the b
35、rown iodine colour has almost disappeared from the aqueous layer, add about 2 ml of starch solution (5.6) as indicator. Continue the titration dropwise until the end-point is reached (disappearance of the blue iodo-starch colour from the aqueous layer). Vigorous agitation is essential for complete r
36、emoval of iodine from the chloroform layer. If the volume used to titrate the test solution is not more than 80 % of the volume used to titrate the blank, repeat the determination using a smaller test portion or taking a smaller aliquot of the chloroform solution (to ensure an adequate excess of per
37、iodic acid). 8.5 Determination of free glycerol Filter the aqueous solution from flask B (8.3.6). Using a pipette, transfer 50 ml of the filtrate into a 500 ml conical flask (6.1), add 50 ml of periodic acid solution (5.3) with a pipette, mix and stopper. Allow to stand for 30 min in the dark. Carry
38、 out a blank test under the same conditions, using 50 ml of acetic acid solution (5.2) and 50 ml of periodic acid solution (5.3). After the 30 min period add 20 ml of potassium iodide solution (5.4) both to the test solution and to the blank. Stopper the flasks, mix and allow to stand for 1 min long
39、er. Add 100 ml of water to each. Titrate with sodium thiosulfate standard volumetric solution (5.5) adding 2 ml of starch solution (5.6) when the brown colour of the iodine has almost disappeared. If the volume used to titrate the test solution is not more than 80 % of the volume used to titrate the
40、 blank, repeat the determination using a smaller test portion or taking a smaller aliquot of the aqueous solution (to ensure an adequate excess of periodic acid). 8.6 Number of determinations Carry out two determinations on the same test sample. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06
41、 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.42:1989 BSI 11-19993 9 Expression of results 9.1 Method of calculation and formulae 9.1.1 Calculation of 1-monoglycerides content The 1-monoglycerides content, expressed as a percentage by mass, is equal to where V0is the volume, in milli
42、litres, of the sodium thiosulfate standard volumetric solution required for the titration of the blank; V1is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution required for the titration of the test solution; cis the concentration, expressed in moles per litre, of the
43、 sodium thiosulfate standard volumetric solution; Mris the relative molecular mass of a particular 1-monoglyceride, the choice depending on the composition of the fatty acids (when the results are expressed as glyceryl monostearate, Mr= 358); mis the mass, in grams, of the test portion; ris the rati
44、o of the volume (100 ml) of the chloroform phase to the volume (50 ml or less) of this phase taken for the determination. Express the result to one decimal place. 9.1.2 Calculation of free glycerol content The free glycerol content, expressed as a percentage by mass, is equal to where V2is the volum
45、e, in millilitres, of the sodium thiosulfate standard volumetric solution required for the titration of the blank; V3is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution required for the titration of the test solution; cis the concentration, expressed in moles per li
46、tre, of the sodium thiosulfate standard volumetric solution; Mris the relative molecular mass of glycerol (Mr= 92,1); mis the mass, in grams, of the test portion; ris the ratio of the volume (100 ml) of the aqueous phase to the volume of this phase (50 ml or less) taken for the determination. Expres
47、s the result to one decimal place. 9.2 Repeatability The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst under the same conditions on the same test sample shall not exceed the values given in 9.2.1 and 9.2.2. 9.2.1 For 1-mono
48、glycerides 0,5 % (m/m) at contents from 15 to 25 % (m/m) 2 % (relative) of the average value at contents from 25 to 50 % (m/m) 1 % (m/m) at contents greater than 50 % (m/m) 9.2.2 For free glycerol 0,1 % (m/m) 10 Test report The test report shall show the method used and the results obtained. It shal
49、l also mention any operating details not specified in this International Standard, or regarded as optional, together with details of any incidents likely to have influenced the results. The test report shall include all the information necessary for the complete identification of the sample. V0V1() crMr 20 m - V2V3() crMr 40 m - Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:37:36 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 blank Licensed Copy: sheffieldun sheffieldun, na, Wed