ISO INTERNATIONAL STANDARD 1802 Third edition 1992-03-15 Natural rubber latex concentrate Determination of boric acid content Latex concentre de caoutchouc naturel -Dosage de I'acide borique Reference number ISO 1802:1992(E) IS01802:1992(E) Foreword Iso (the international Organization for Standardization) is a woridwide federation of national standards bodies (isO member bodies). 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, govern- mental and non-governmental, 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. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an Inter- national Standard requires approval by at least 75 % of the member bodies casting a vote. international Standard Iso 1802 was prepared by Technical Committee Iso/Tc 45,Rubberand rubberproducts,Sub-Committee SC 3,Raw ma- terials (including latex) for use in the rubber industry. Thisthird edition cancelsand replaces the second edition (isO 1802:1985), of which it constitutes a minor revision. OSI 1992 or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. Internatlonal Organizationfor Standardization Case Postale 56 . CH-1211 Geneve 20 : Switzeriand Printed In Switzerland i 1S01802:1992(E) NTERNATIONALSTANDARD Natural rubber latex concentrate --- Determination of boric acid content 1 Scope 4 Reagents This International Standard specifies a procedure for During the analysis, use only reagents of recognized the determination of boric acid in natural rubber la- tex concentrate. of equivalent purity. The procedure is not necessarily suitable for latices from natural sources other than Hevea brasiliensis 4.1 Hydrochloric acid, 2 % solution (m/m). or for latices of synthetic rubber, compounded latex, vulcanized latex or artificial dispersions of rubber. 4.2 Stabilizer solution,containing5%(m/m)of a suitable non-ionic stabilizer of the ethylene oxide condensate type. 2 Normative reference 4.3 Mannitol. The following standard contains provisions which, through reference in this text, constitute provisions 4.4 Boric acid solution. of this International Standard. At the time of publi- cation, the edition indicated was valid. All standards Weigh, to the.nearest .1 mg, about 5 g of boric acid are subject to revision, and parties to agreements (H,BOs), dissolve in water and.dilute to. 1 000 cm3 in based on this International Standard are encour- a volumetricflask. aged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISoO maintain registers of cur- 4.5 Sodium hydroxide, standard solution, rentiy valid International Standards. c(NaOH) ~.0,05 mol/dm3. Iso123:1985,Rubberlatex-Sampling. 4.5.1 Standardization of the solution Using a pipette (5.2), introduce, 5 cm' of the boric acid solution (4.4) into a 250 cmbeaker,Add 2 cm of the stabilizer solution (4.2) and 50 cm of water. If 3 Principle the pH of the solution, measured using the pH-meter (5.1), exceeds 5,5, add hydrochloric acid solution The pH of a test portion containing about 0,02 g of (4.1), drop by drop, with constant stirring,to reduce boric acid is adjusted to 7,50, at which value boric the pH to a value between 5,5 and 2,5. Allow the acid exists substantially in the undissociated form. solution to stand for 15 min.Add sodium hydroxide Mannitof is then added in excess to form the solution (4.5) from a burette (5.3), with constant stir- strongly acidic boric-acid/mannitol complex. Hydro- ring, until the pH is 7,50. Add 4 g of the mannitol gen