1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58benzoic acid content Spectrophotometric methodICS 67.080.01Fruits, vegetables and derived products
2、Determination of BRITISH STANDARDBS ISO 5518:2007BS ISO 5518:2007This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 February 2007 BSI 2007ISBN 978 0 580 50209 5Amendments issued since publicationAmd. No. Date Commentscontract. Users are respo
3、nsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations. National forewordThis British Standard was published by BSI. It is the UK implementation of ISO 5518:2007.The UK participation in its preparation was entrusted to Technical Committee
4、AW/21, Fruit and vegetables juices.A list of organizations represented on AW/21 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a INTERNATIONALSTANDARDISO5518Second edition2007-02-01Reference numberISO 5518:2007(E)Fruits, veget
5、ables and derived products Determination of benzoic acid content Spectrophotometric methodFruits, lgumes et produits drivs Dtermination de la teneur en acide benzoque Mthode spectrophotomtriqueBS ISO 5518:2007iiiiiForewordISO (the International Organization for Standardization) is a worldwide federa
6、tion of national standards bodies(ISO member bodies). The work of preparing International Standards is normally carried out through ISOtechnical committees. Each member body interested in a subject for which a technical committee has beenestablished has the right to be represented on that committee.
7、 International organizations, governmental andnon-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the InternationalElectrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with
8、the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International Standardsadopted by the technical committees are circulated to the member bodies for voting. Publication as anInternational Standard requires approval by
9、 at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patentrights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 5518 was prepared by Technical Committee ISO/TC
10、34, Food products, Subcommittee SC 3, Fruit andvegetable products.This second edition cancels and replaces the first edition (ISO 5518:1978), which has been technically revised.BS ISO 5518:2007ivIntroductionA method for determining the benzoic acid content of fruits, vegetable and derivatives, descr
11、ibed in 1959, wasbased on the technique of peak emergence. The advantage of this method was that it was specifically intendedfor benzoic acid, with one exception: p-chlorobenzoic acid.However, it was necessary to make a modification, consisting of purifying the ethereal extract by chromic acidoxidat
12、ion. This results in the elimination of the effects of colouring substances in certain vegetable productscontaining anthocyanins, and also all the oxybenzoic acids and sorbic acid which may be present if severalantiseptics have been used. Moreover, purification increases the sensitivity of the metho
13、d. This improvedtechnique was also more rapid.BS ISO 5518:20071Fruits, vegetables and derived products Determination of benzoic acid content Spectrophotometric method1ScopeThis International Standard specifies a method for determining the benzoic acid content of fruits, vegetablesand derived product
14、s.As chlorobenzoic acids are resistant to oxidation, the method cannot be applied in the presence ofp-chlorobenzoic acid, as the absorption spectrum of this acid is close to that of benzoic acid. Neither can it beused in the presence of cinnamic acid, which is transformed into benzoic acid by chromi
15、c acid oxidation.NOTE The cinnamic acid determined as benzoic acid in this method exists generally only in the form of traces invegetables, and therefore has no effect on the result obtained, except in the case of cinnamon bark, which contains higherquantities.2 PrincipleThe test sample is homogeniz
16、ed, followed by dilution and acidification of a test portion. The benzoic acid isextracted by diethyl ether, then this acid undergoes alkaline re-extraction and purification by oxidation usingacidified potassium dichromate. The purified benzoic acid dissolved in diethyl ether is determined byspectro
17、photometry.3ReagentsUse only reagents of recognized analytical quality and distilled water or water of at least equivalent purity.3.1 Tartaric acid COOH(CHOH)2COOH, crystalline.3.2 Sodium hydroxide (NaOH), approximately solution.3.3 Potassium dichromate (K2Cr2O7), solution containing to .3.4 Dilute
18、sulfuric acid (H2SO4), obtained by diluting 2 volumes of concentrated sulfuric acid( ) with 1 volume of water.3.5 Diethyl ether (CH3CH2)2O, recently distilled.3.6 Benzoic acid (C6H5COOH), standard solution in diethyl ether containing .3.7 Sodium hydrogen carbonate (NaHCO3), crystalline.4 ApparatusUs
19、ual laboratory apparatus and, in particular, the following.4.1 Volumetric flasks, of capacities and .4.2 Beakers, of capacities and .1 mol/l33 g/l 34 g/l20= 1,84 g/ml0,100 g/l50 ml 1 000 ml50 ml 100 mlBS ISO 5518:200724.3 Graduated pipettes, of capacities , and .4.4 Flasks, of capacity , having grou
20、nd-glass stoppers and made of borosilicate glass.4.5 Separating funnels, of capacities and .4.6 Evaporating dish, of diameter about .4.7 Water bath, capable of being controlled at a temperature of to .4.8 Homogenizer or mortar, as appropriate.4.9 Spectrophotometer for determination in the ultraviole
21、t range, equipped with a monochromator allowingmeasurement to the nearest , with silica cells of optical path length or (preferably so as to increase sensitivity), equipped with ground glass covers.4.10 Analytical balance.5 SamplingA representative sample should have been sent to the laboratory. It
22、should not have been damaged or changedduring transport or storage.6 Procedure6.1 Preparation of test sample6.1.1 Liquid products (e.g. juices, pulpy fluid products, syrups)Thoroughly mix the laboratory sample.6.1.2 Thick products (e.g. marmalades, jams)Homogenize the laboratory sample after having
23、carefully mixed it.6.1.3 Solid products (e.g. fruits, vegetables)Cut a part of the laboratory sample into small pieces and remove seeds, stalks and carpellary cells, ifnecessary. Carefully homogenize approximately of the sample.6.1.4 Frozen or deep-frozen productsAfter thawing the sample in a closed
24、 container and removing, if necessary, seeds, stalks and carpellary cells,mix the product with the liquid formed during the thawing process and proceed as described in 6.2.1, 6.2.2 or6.2.3 as appropriate.6.2 Preparation of test portion6.2.1 Liquid productsUsing a pipette (4.3), take of the test samp
25、le (6.1), free from substances in suspension, dilute it withapproximately of water and transfer it to a separating funnel (4.5) (separating funnel A).10 ml 20 ml 50 ml250 ml100 ml 500 ml10 cm70C 80C0,5 nm 10 mm 20 mm 20 mm40 g20 ml50 ml 500 mlBS ISO 5518:20073The test portion may also be taken by ma
26、ss by weighing, to the nearest , approximately of the testsample.6.2.2 Pulpy and fluid productsTake of the test sample (6.1). Place in a mortar (4.8) and dilute with of water. After decanting, filterthe liquid.Twice successively, take up the residue in of water and filter after decanting.Collect all
27、 the filtrates directly in a separating funnel (4.5) (separating funnel A).The test portion may also be taken by mass by weighing, to the nearest , approximately of the testsample.6.2.3 Thick or solid productsWeigh, to the nearest , approximately of the test sample (6.1) and, using to of water,trans
28、fer it to a flask (4.4).Add approximately of sodium hydrogen carbonate (3.7) (see Note). Shake, then place the flask on thewater bath (4.7), controlled at to , and leave for to . Filter the contents of the flask andrinse twice using to of water each time.Collect all the filtrates in a separating fun
29、nel (4.5) (separating funnel A). Allow to cool.NOTE The addition of sodium hydrogen carbonate is intended to neutralize the benzoic acid, traces of which could be lostby volatilization.6.3 Extraction of the benzoic acidWARNING Attention is drawn to the hazard derived from the use of diethyl ether, w
30、hich is a highlyflammable, explosive and harmful substance.6.3.1 Introduce of the tartaric acid (3.1) into the separating funnel A (4.5) containing the diluted test portion(6.2), add of the diethyl ether (3.5) and shake carefully.Allow to separate, then collect the ethereal layer in a second separat
31、ing funnel (4.5) (separatingfunnel B).Wash the aqueous phase in the first separating funnel (A) with of the diethyl ether.Allow to separate, then collect the ethereal layer in the separating funnel (B) containing the first layer collected.Proceed similarly with a third extraction with of the diethyl
32、 ether and combine the ethereal layer with thefirst two in the separating funnel (B).6.3.2 Extract the benzoic acid from the ethereal solution by adding successively and then of thesodium hydroxide solution (3.2), and then twice of water. After each addition, shake, then allow toseparate and collect
33、 the aqueous phase.Collect the aqueous phases in an evaporating dish (4.6). Place the dish on the water bath (4.7), controlled atto , and leave until the volume of the alkaline solution is reduced by approximately half, to removethe residual dissolved diethyl ether.0,01 g 20 g20 ml 20 ml20 ml500 ml0
34、01 g 20 g0,01 g 10 g 30 ml 40 ml250 ml50 mg70C 80C 15 min 30 min15 ml 20 ml500 ml1g60 ml500 ml60 ml30 ml10 ml 5ml10 ml70C 80CBS ISO 5518:200746.4 Purification of the benzoic acidAfter cooling, pour the contents of the dish into a flask (4.4) containing a mixture of of the dilutesulfuric acid (3.4)
35、and of the potassium dichromate solution (3.3). Stopper the flask and leave for at least.Other preservatives derived from benzoic acid may be present. In this case, leave the flask for at least tooxidize completely the three hydroxybenzoic acids and prevent any interference in the determination. The
36、extension of the reaction time creates no problem as the benzoic acid resists this oxidizing mixture.When the initial product also contains sorbic acid, it is necessary to prolong oxidation for so as to ensurethe complete destruction of this acid.6.5 Extraction of the purified benzoic acidExtract th
37、e benzoic acid by treating the above solution (6.4) twice with to of the diethyl ether (3.5),collecting the ethereal solutions. Wash the ethereal solutions twice with several millilitres of water. Afterdecanting very carefully, filter through a dry filter paper and collect the filtrate in a volumetr
38、ic flask (4.1).Then wash the filter with several millilitres of the diethyl ether, adding sufficient washing solvent to dilute to themark.6.6 DeterminationUsing the spectrophotometer (4.9), measure the absorbance of the ethereal solution (6.5) in relation to theabsorbance of the pure diethyl ether a
39、t , and (see Note).The absorbance due to benzoic acid is given by the formula for the differential measure of emergence at:whereis the absorbance at ;is the absorbance at ;is the absorbance at .NOTE Examination of the absorption spectrum of the ethereal solution of purified benzoic acid allows chara
40、cterization ofthis product by the presence of two peaks at and .The benzoic acid extracted by the diethyl ether is determined by the measurement of the relative height of the peak atwith respect to the straight line which joins the points on the abscissa between and .6.7 Number of determinationsCarr
41、y out two determinations on the same test sample (6.1).6.8 Plotting the calibration curveInto a series of six volumetric flasks (4.1), introduce respectively , , , , andof the standard benzoic acid solution (3.6). Dilute to the mark with the diethyl ether (3.5).The solutions obtained contain respect
42、ively , , , , and of benzoic acid perlitre.250 ml 20 ml20 ml1h3h24 h20 ml 25 ml50 ml267,5 nm 272 nm 276,5 nm272 nmA2A1+ A32A1267,5 nmA2272 nmA3276,5 nm272 nm 279 nm272 nm 267,5 nm 276,5 nm50 ml 5ml 7,5 ml 10 ml 12,5 ml 15 ml20 ml10 mg 15 mg 20 mg 25 mg 30 mg 40 mgBS ISO 5518:20075Plot the curve show
43、ing the different measurements according to the content of benzoic acid, in milligrams perlitre, indicated above.7 Calculation and expression of results7.1 Test portion taken by pipettingThe benzoic acid content, expressed in milligrams per litre of product, is given bywhere is the mass, in milligra
44、ms, of benzoic acid read on the calibration curve (6.8).7.2 Test portion taken by weighingThe benzoic acid content, expressed in milligrams per kilogram of product, is given bywhereis the mass, in grams, of the test portion (6.2);is the mass, in milligrams of benzoic acid, read on the calibration cu
45、rve (6.8).8 RepeatabilityThe absolute difference between two independent single test results, obtained using the same method onidentical test material in the same laboratory by the same operator using the same equipment within a shortinterval of time, will in not more than of cases exceed of benzoic
46、 acid per litre or per kilogram,depending on the individual circumstances.NOTE The method allows determination of the quantity of benzoic acid to the nearest when the product contains lessthan per litre or per kilogram.9 Test reportThe test report shall specify:a) all information necessary for the c
47、omplete identification of the sample;b) the sampling method used, if known;c) the test method used, with reference to this International Standard;d) all operating details not specified in this International Standard, or regarded as optional, together withdetails of any incidents which may have influ
48、enced the test result(s);e) the test result(s) obtained or, if the repeatability has been checked, the final quoted result obtained.m25020= 2,5m2m2m250m1m1m25% 10 mg2mg50 mgBS ISO 5518:2007BS ISO BSI389 Chiswick High RoadLondonW4 4AL5518:2007 BSI British Standards InstitutionBSI is the independent n
49、ational body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter.RevisionsBritish Standards are updated by amendment or revision. Users of British Standards should make sure that they possess the latest amendments or editions.It is the constant aim of BSI to improve the quality of our products and services. We would be grateful if anyone finding an inaccuracy or am
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