A Reference number ISO 6293 2 1 998(E) INTERNATIONAL STANDARD ISO 6293 2 First edition 1 998 05 01 Petroleum products — Determination of saponification number — Part 2 Potentiometric ti tration method[.]
I SO I N TE RN ATI ON AL STAN D ARD 6293-2 Fi rst ed i ti on 998-05-01 Petrol eu m prod u cts — Determi n ati on of saponi fi cati on n u m ber — Part 2: Poten ti om etri c ti trati on m eth od Produ i ts pétrol i ers — Déterm i n ati on de l ’ i n di ce de sapon i fi cati on — Parti e 2: M éth ode par ti trag e poten ti om étri qu e A Referen ce n u m be r I SO 6293-2: 998 ( E ) I SO 6293-2: 998(E) Foreword ISO (the International Organization for Standardization) is a worldwide 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, governmental 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 International Standard requires approval by at least 75 % of the member bodies casting a vote International Standard ISO 6293-2 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants This first edition, together with ISO 6293-1 , cancels and replaces ISO 6293:1 983, which has been technically revised ISO 6293 consists of the following parts, under the general title Petroleum products — Determination of saponification number : — Part : Colour-indicator titration method — Part 2: Potentiometric titration method Annex A forms an integral part of this part of ISO 6293 © ISO 998 All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher International Organization for Standardization Case postale 56 • CH-1 21 Genève 20 • Switzerland Internet central@iso.ch X.400 c=ch; a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii I NTERN ATI ON AL STAN DARD © I SO 6293-2: 998(E) I SO Petrol eu m produ cts — Determi n ati on of saponi fi cati on n u mber — Part 2: P o te n ti o m e tri c ti trati o n m e th o d WARNI NG — Th e u se of th i s part of I SO 6293 m ay i n vol ve h azardou s m ateri al s, operations and eq u i pment Th i s part of I SO 6293 d oes n ot pu rport to ad dress al l of th e safety problems associated wi th i ts u se I t i s th e responsi bi l i ty of th e u ser of th i s part of I SO 6293 to establi sh appropriate safety and h eal th practices and d etermi n e th e appl i cabi l i ty of reg u l atory l i m i tati ons pri or to u se Scope Th i s part of I SO 6293 co n s ti tu en ts in s peci fi e s petro l e u m a m eth o d pro d u cts th at fo r wi l l th e d ete rm i n ati o n , s apo n i fy u n d er th e by po ten ti o m etri c co n d i ti o n s of th e ti trati o n , tes t of th e I SO 6293-1 am o u n t of s pe ci fi e s a d e te rm i n ati o n by co l o u r i n d i cato r ti trati o n Th e m e th o d i s appl i cabl e to m ate ri al s h avi n g s apo n i fi cati o n n u m be rs i n th e ran g e m g KOH /g to 0 m g KOH /g C o m po u n d s o f s u l fu r, ph o s ph o ru s , h al o g en s an d some o th e r co m po u n d s re act wi th th e al kal i an d aci d s u n d e r th e te s t co n d i ti o n s N OTE S Th e re s u l ts on u sed cran kcas e an d tu rbi n e oi l s, an d on oi l s co n tai n i n g th e co m po u n d s abo ve as ad d i ti ve co n s ti tu e n ts , s h o u l d be i n te rpre te d wi th care , be ari n g i n m i n d th e po s s i bl e h i g h e r val u e s o btai n abl e d u e to th e s e ad d i ti o n al re acti o n s Th e s e e xtran e o u s m ate ri al s i n cl u d e th e e n d o f th e back- ti trati o n s te p i s an co m po u n d s , as we l l ce rtai n o rg an i c aci d s an d m ost n o n - al kal i s o aps Th e odou r of i n d i cati o n o f th e pre s e n ce o f ce rtai n re acti ve s u l fu r co m po u n d s , as th o s e o f ch l o ri n e , ph o s ph o ru s an d o th e r i n te rfe ri n g m ate ri al s , g i ve n o h yd ro g e n s u l fi d e n e ar bu t o th e r re acti ve s u l fu r s i m pl e i n d i cati o n d u ri n g th e te s t A g ravi m e tri c d e te rm i n ati o n o f fatty aci d co n te n t i s an al te rn ati ve pro ce d u re fo r th e e s ti m ati o n o f s u ch co m po u n d s N orm ati ve referen ces Th e fo l l o wi n g s tan d ard s co n tai n pro vi s i o n s wh i ch , I SO 6293 parti es to At th e ti m e ag ree m en ts of pu bl i cati o n , bas e d on th i s th e ed i ti o n s th ro u g h re fe re n ce i n i n d i cated part o f I S O are we re th i s te xt, val i d en co u rag ed Al l to co n s ti tu te pro vi s i o n s o f th i s part o f s tan d ard s i n ves ti g ate are th e s u bj e ct po s s i bi l i ty to re vi s i o n , o f appl yi n g an d th e m o s t re cen t e d i ti o n s o f th e s tan d ard s i n d i cated be l o w M e m be rs o f I E C an d I S O m n tai n re g i s te rs o f cu rre n tl y val i d I n te rn ati o n al S tan d ard s I S O 69 : 7, Wate r fo r an al yti cal l abo rato ry u s e — S pe ci fi cati o n an d te s t m e th o d s I S O 62 - : 9 6, P e tro l e u m pro d u cts — D e te rm i n ati o n o f s apo n i fi cati o n n u m be r — P art : C o l o u r- i n d i cato r ti trati o n m e th o d I SO 6293-2: 998(E) © ISO ISO 6353-2:1 983, Reagents for chemical analysis — Part 2: Specifications — First series ISO 6353-3:1 987, Reagents for chemical analysis — Part 3: Specifications — Second series Defi n i ti on s For the purposes of this part of ISO 6293, the following definitions apply saponi fy saponi fi cati on n u m ber to hydrolyze a fat with alkali to form an alcohol and the salt of a fatty acid the number of milligrams of potassium hydroxide that is consumed by g of a sample under the specified conditions of this test Pri n ci pl e A test portion of known mass, dissolved in butan-2-one, is heated with a known amount of alcoholic potassium hydroxide solution The excess alkali is potentiometrically titrated with standard volumetric hydrochloric acid solution and the saponification number is calculated Reag en ts an d m ateri al s During the analysis, use only reagents specified in ISO 6353-2 and ISO 6353-3, if listed there, or if not, of recognized analytical grade Use only distilled water or water according to grade of ISO 3696 95 % (V/V ) ethanol, or parts of 95 % (V/V ) ethanol to which has been added part of methanol or absolute alcohol Eth anol , NOTES For the purposes of this part of ISO 6293, the expressions “% ( m/m )” and “% (V/V )” are used to represent the mass and volume fractions of a material respectively For routine analysis, 99 % (V/V ) propan-2-ol can be substituted for ethanol without compromising the sensitivity or precision of the method Ethanol should always be used for referee tests c (KOH) = 0,5 mol/l, standard volumetric alcoholic solution Prepare in accordance with 5.2.1 or use a commercially available solution Standardize in accordance with 5.2.2 5.2.1 Potassiu m h yd roxi d e, Preparation Add approximately 29 g of solid KOH to litre of ethanol (5.1 ) in a litre conical flask Boil gently while stirring for to Add at least g of barium hydroxide [Ba(OH) 2] and boil gently for a further to CAUTI ON — Bari u m h yd roxi d e i s strong l y al kal i n e and toxi c i f i n g ested U se protective cl oth i n g to avoi d severe i rri tati on cau sed by contact wi th th e ski n Allow to cool and stand at room temperature for at least 24 h in the dark Transfer to the storage container by filtration or pressure displacement under inert gas conditions (carbon dioxide-free) Store the solution in a chemically resistant dispensing bottle out of contact with cork, rubber, or saponifiable stopcock lubricant, and protected by a guard tube containing soda lime or non-fibrous soda silicate absorbent Glass bottles are not recommended for storage © ISO I SO 6293-2: 998(E) 5.2.2 Stand ardi zati on Standardize frequently enough to detect changes of 0,000 mol/l, preferably against 2,0 g to 2,1 g of pure potassium acid phthalate (5.7), which has been dried for h at 1 °C, weighed with an accuracy of ± 0,000 g and dissolved in 00 ml ± 0,01 ml of carbon dioxide-free water, using phenolphthalein (5.6) to detect the end-point c (HCl) = 0,5 mol/l, standard volumetric aqueous solution Prepare in accordance with 5.3.1 or use a commercially available solution Standardize in accordance with 5.3.2 5.3.1 H yd roch l ori c aci d , Preparation Mix 45 ml of concentrated hydrochloric acid [35,4 % (m/m )] with litre of water 5.3.2 Stand ardi zati on Standardize frequently enough to detect changes of 0,000 mol/l, preferably by electrometric titration of approximately ml (accurately measured) of the 0,5 mol/l alcoholic potassium hydroxide solution (5.2) diluted with 25 ml of carbon dioxide-free water NOTES Because of the relatively large coefficient of cubic expansion of organic liquids such as ethanol or propan-2-ol, the standard alcoholic solutions should be standardized at temperatures close to those employed in the titrations of sample, and close to 20 °C Where saponification numbers below are expected, better precision may be obtained by substituting 0,1 mol/l potassium hydroxide and hydrochloric acid solutions for the 0,5 mol/l reagents in 5.2 and 5.3, and those in clauses and No exact precision values are yet available for this technique Bu tan -2-one (meth yl eth yl ketone), reagent grade NOTE — Store the butan-2-one in a dark or brown glass bottle 5 Petroleu m spi ri t, 60 °C to 80 °C boiling range neutralized indicator solution Dissolve ,0 g of phenolphthalein in 00 ml of ethanol (5.1 ) and neutralize to a faint pink colour with 0,1 mol/l ethanolic potassium hydroxide solution Ph en ol ph th al ei n , Potassiu m aci d ph th al ate 3,0 mol/l aqueous solution Dissolve 225 g of solid potassium chloride (KCl) in ,0 litre of water Potassiu m ch l ori d e, Xyl ene Ch l orobenzene CAUTI ON — Ch l orobenzene i s h armfu l to th e envi ronm ent Al ternati ve sol vents are u n d er i n vesti g ati on I SO 6293-2: 998(E) © I SO Apparatu s Ordi n ary l aboratory apparatus an d g l assware, i n cl u d i n g : Con i cal fl ask an d d en ser A i cal fl ask, 250 m l or 300 m l capacity, al kal i -resi stan t (see th e fol l owi n g n ote) , to wh i ch i s attach ed a strai g h t or m u sh room -type refl u x d en ser Th e strai g h t-type d en ser sh al l be fi tted to th e fl ask by m ean s of a g rou n d g l ass j oi n t; th e m u sh room-type d en ser sh al l fi t l oosel y to perm i t ven ti n g of th e fl ask Al l g l assware sh al l be ch em i cal l y cl ean N OTE — Th e fl asks sh ou l d be cl ean ed by n on -al kal i n e cl ean i n g ag en ts to m atch th e cl ean l i n ess obtai n ed by th e u se of ch rom osu l fu ri c aci d (see warn i n g ) For th e com pari son of cl ean i n g effi ci en cy, th e vi su al appearan ce an d l oss i n m ass on h eati n g m ay be u sed Deterg en t cl ean i n g , or th e u se of oth er stron g oxi d i zi n g ag en ts, avoi d s th e speci fi c h azard s rel ated to ch rom osu l fu ri c aci d , an d i s preferred for rou ti n e an al ysi s Fl asks of borosi l i cate g l ass are preferred N ew fl asks m ay g i ve h i g h val u es, an d ol d fl asks th at h ave becom e etch ed by l on g u se sh ou l d n ot be u sed Bl an k tests sh ou l d be ru n cu rren tl y on both u sed an d n ew fl asks WARNI NG — Ch romosu l fu ri c aci d i s a h eal th h azard I t i s toxi c, a recogn i zed carci n og en as i t contai ns Cr(VI ) compou n d s, h i g h l y corrosive and potenti al l y h azardou s i n tact wi th org ani c m ateri al s Wh en u si n g ch romosu l fu ri c aci d cl eani n g sol u ti on, eye protection and protective cl oth i n g are essenti al Never pi pette th e cl eani n g sol u ti on by m ou th After u se, d o n ot pou r cl eani n g sol u ti on d own th e d rai n , bu t n eu tral i ze it wi th g reat care, owi n g to th e concentrated su l fu ri c aci d present, and d i spose of it in accordance wi th stand ard procedu res for toxi c l aboratory waste (ch romi u m i s h i g h l y d ang erou s to th e en vi ron m ent) Non-ch romi u m contai n i n g , strong l y oxi d i zi n g aci d cl ean i n g sol u ti ons are al so highly corrosive and potenti al l y h azardou s i n contact wi th org ani c m ateri al s, bu t d o n ot tai n ch romi u m wh i ch h as special d i sposal probl ems H otpl ate, h eated by ei th er el ectri ci ty or steam Potenti ometri c ti trator, of h i g h preci si on , capabl e of di sti n g u i sh i n g th e carbonate i on from th e h ydroxi d e i on i n th e ti trati on of reag en t g rade potassiu m h ydroxi de (KOH ) by h ydroch l ori c aci d Au tom ati c, recordi n g or m an u al apparatus are su i tabl e 6.4.1 El ectrodes, of h i g h q u al i ty Th e cl eani n g an d m n tenan ce of th e el ectrodes are d escri bed i n an n ex A Combi n ati on g l ass el ectrode, or a su i tabl e g l ass el ectrode an d a su i tabl e reference el ectrode N OTE — E i th er si l ver ch l ori d e (Ag Cl ) , satu rated l i th i u m ch l ori d e (Li Cl ) or satu rated potassi u m ch l ori d e (KCl ) /cal om el el ectrod es are su i tabl e referen ce el ectrod es Sti rrer, ei th er m ag n eti c sti rri n g bars or a propel l er sti rrer, capabl e of provi d i n g very vi g orou s ag i tati on N OTE — Th e opti m u m m ag n eti c sti rri n g bar h as been fou n d to be a 25 m m ¥5 m m pl n pol ytetrafl u oroeth yl en e (PTFE ) coated cyl i n d er 6 Beakers, of capaci ty 250 m l or 300 m l , tal l form, wi th or wi th ou t spou t Ti trati on assembl y, typi cal l y as i l l u strated i n fi g u re 6.7.1 Sti rrer, of vari abl e speed, ei th er m ech an i cal or el ectri cal , wi th propell er or paddl e of i n ert m ateri al , or a m ag n eti c sti rrer wi th sti rri n g bars (6 5) Al l el ectri cal d evi ces sh al l be g rou n d ed (earth ed) so th at n o perman en t ch an g e to th e m eter readi n g occu rs d u ri n g th e cou rse of th e ti trati on © I SO I SO 6293-2: 998(E) Key Lead for referen ce el ectrod e E l on g ated bu rette ti p (i n fron t of sti rrer) Referen ce el ectrod e, B Sl eeve wi th g rou n d -g l ass tact j oi n t Sh i el d ed l ead for g l ass el ectrod e Bakel i te su pport G l ass el ectrod e, C (i n tern al l y sh i el d ed ) Beaker, A Propel l er sti rrer, D (beh i n d bu rette ti p) Fi g u re — Typi cal ti trati on cel l assembl y 6.7.2 Bu rette, m an u al or au tom ati c, of capacity m l or 25 m l , g radu ated i n 0, 05 m l d i vi si on s, an d cal i brated wi th an accu racy of ± 0, 02 m l 6.7 Ti trati on stand , capabl e of su pporti n g th e beaker, el ectrodes, sti rrer an d bu rette N OTES An arran g em en t th at al l ows for th e rem oval of th e beaker wi th ou t d i stu rbi n g th e el ectrod es, bu rette an d sti rrer i s d esi rabl e Som e apparatu s i s sen si ti ve to i n terferen ce by stati c el ectri ci ty, sh own by errati c m ovem en ts of th e record er pen or m eter i n d i cator, wh en th e ti trati on assem bl y i s approach ed by th e operator I f th i s occu rs, su rrou n d th e beaker cl osel y wi th a cyl i n der of copper g au ze th at i s el ectri cal l y g rou n d ed (earth ed ) Bal ance, capable of wei g h i n g to th e n earest 0, m g Bl an k test Carry ou t on e or m ore bl an k determ i n ati on s concu rren tl y wi th each set of sam pl es i n th e m an n er descri bed i n an d N OTE — Bl an k d eterm i n ati on s sh ou l d be ru n i n d u pl i cate on sam pl es req u i ri n g th e h i g h est accu racy Th e preci si on d ata are based on d u pl i cate bl an k d eterm i n ati on s A si n g l e bl an k i s su ffi ci en t for rou ti n e work Du pl i cate bl an k d eterm i n ati on s sh ou l d ag ree wi th i n 0, m l Take th e averag e for cal cu l ati on s (see cl au se 9) M easu re, from a bu rette or pi pette (see n ote i n th i s su bcl au se) i n to th e coni cal fl ask (6 ) , 25 m l th e al coh ol i c potassiu m h ydroxi d e sol u ti on (5 2) an d 25 m l ±1 ± 0, 03 m l of m l of th e bu tan -2-on e (5 4) Con n ect th e den ser to th e fl ask an d h eat for 30 m i n after refl u xi n g begi n s (see n ote i n th i s su bcl au se) Tu rn off th e h eat sou rce an d i m m edi atel y add 50 m l of th e petrol eu m spi ri t (5 5) (see n otes an d i n th i s su bcl au se) by cau ti ou sl y pou ri n g i t d own th e d en ser (di scon n ect th e d en ser i f a m u sh room -type i s u sed) N OTES I f a vol u m etri c pi pette i s u sed , wai t 30 s after d el i very for com pl ete d rai n ag e Stan d ard proced u re req u i res th at th e m i xtu re i s refl u xed for m i n H owever, i t i s kn own th at som e fats are read i l y sapon i fi ed an d com pl ete sapon i fi cati on takes pl ace wi th i n m i n On th e oth er h an d , som e m ateri al s are sapon i fi abl e on l y wi th © ISO I SO 6293-2: 998(E) difficulty and are known to require more than h in some cases Neither the shortened period nor the longer period should be used except by mutual consent of the interested parties The reflux time of the blank should be the same as that of the sample in all cases Pouring 50 ml of petroleum spirit down the condenser at the end of the saponification not only rinses the condenser, but also cools the reaction mixture In the case of insulating oils, the addition of petroleum spirit is not necessary Titrate the blank potentiometrically while hot, without reheating, with the hydrochloric acid solution (5.3) Transfer the solution to a beaker (6.6) Wash the flask with two ml portions of petroleum spirit, and add these washings to the beaker Place the beaker, with a magnetic stirring bar if used, on the titration stand (fitted with a magnetic stirplate if stirring bars are included) Immerse the electrodes as far as possible, without interfering with the stirrer or stirring bars Stir to the maximum agitation without causing excessive aeration or splattering of the solution Titrate the blank solution with aqueous hydrochloric acid (5.3), added at the rate of ml/min, using the potentiometric titrator 7 7 NOTE — Two inflections with corresponding equivalence points are expected The first one corresponds to the free potassium hydroxide (KOH), and the second to the small amount of potassium carbonate (K2CO3) generally present in commercial KOH Record the first inflection point 7 NOTE — A pre-addition of hydrochloric acid titrant can be used in the blank to expedite the titration Proced u re Test porti on Estimate the saponification number and select a test portion mass from table NOTE — The mass is based on an anticipated back-titration of between 40 % and 80 % of the blank, with a maximum test portion of 20 g Tabl e — Mass of test porti on Esti m ated sapon i fi cati on n u m ber Mass of test porti on mg KOH/g g 81 111 71 31 16 to to to to to to 400 80 110 70 30 15 10 20 Determ i n ati on Weigh the test portion, to the nearest 0,01 g, into the conical flask (6.1 ) Add 25 ml ± ml of the butan-2-one (5.4), followed by 25 ml ± 0,03 ml of the alcoholic potassium hydroxide solution (5.2) measured from a burette or 8.2.1 © I SO I SO 6293-2: 998(E) pi pette (see n ote i n 2) Di ssol ve th e d i ffi cu l t to d i ssol ve sam pl es fi rst i n m l to 25 m l of xyl en e (5 9) , before add i n g th e bu tan -2-on e 8.2.2 Con n ect th e d en ser to th e fl ask an d h eat for 30 m i n after refl u xi n g beg i n s (see n ote i n 2) Tu rn off th e h eat sou rce an d i m m edi atel y add 50 m l of th e petroleu m spi ri t (5 5) (see n otes an d i n 2) by cau ti ou sl y pou ri n g i t d own th e d en ser (di scon n ect th e d en ser i f a m u sh room -type i s u sed) 8.2.3 Ti trate wh i l e h ot, wi th n o pre-add i ti on of ti tran t, wi th th e h ydroch l ori c aci d sol u ti on (5 3) as speci fi ed i n an d 7 A com pl ete ti trati on cu rve i s i l l u strated i n fi g u re N OTE — Th e poten ti al read i n g s are fai rl y stan t Th e read i n g before ad d i ti on of ti tran t i s – 520 m V Th e fi rst i n fl ecti on poi n t i s m od eratel y sh arp an d takes pl ace arou n d – 300 m V Th e secon d i n fl ecti on i s extrem el y sh arp an d takes pl ace arou n d 50 m V A Sam pl e B Bl an k C Sam pl e D Bl an k a) U si n g carbonate-contai n i n g al coh ol i c KOH b) U si n g carbonate-free al coh ol i c KOH Fi g u re — Typi cal ti trati on cu rves Cal cu l ati on Cal cu l ate th e saponi fi cati on n u m ber, SN , i n m i l l i g ram s of KOH per g ram , from th e fol l owi n g equ ati on : SN = (V0 − V1 ) c H Cl × 56,1 (1 ) m wh ere V1 i s th e vol u m e, i n m i l l i l i tres, of h ydroch l ori c aci d sol u ti on requ i red for ti trati on of th e test porti on ; V0 i s th e vol u m e, i n m i l l i l i tres, of h ydroch l ori c aci d sol u ti on requ i red for ti trati on of th e bl an k sol u ti on ; c H Cl i s th e cen trati on , i n m ol es per l i tre, of th e stan d ard vol u m etri c h ydroch l ori c aci d sol u ti on ; m i s th e m ass, i n g ram s, of th e test porti on I SO 6293-2: 998(E) 10 © I SO Expressi on of resu l ts Report the results, calcu lated in clause 9, as saponification nu mber (mi ll igrams KOH per gram of sample) , as follows: a) for el ectri cal i n su l ati n g oi l s: to th e n earest 0, ; b) for saponi fi cati on n u m bers bel ow 50: to th e n earest 0, 5; c) for saponi fi cati on n u m bers of 50 an d above: to th e n earest 11 Preci si on Th e precisi on of th e m eth od, as obtai n ed by stati sti cal exam i n ati on of i n terl aboratory test resu l ts, i s g i ven i n 1 an d 1 1 Repeatabi l i ty l i m i t Th e di fferen ce between su ccessive test resu l ts obtai n ed by th e sam e operator wi th th e sam e apparatus u n der stan t operatin g cond i ti on s on i den ti cal test m ateri al wou l d , i n th e n orm al an d correct operation of th e test m eth od, exceed 2, 76 m g KOH /g i n on l y on e case i n 20 1 Reprod u ci bi l i ty l i m i t Th e di fferen ce between two si n g l e an d i n depen d en t resu l ts, obtain ed by d i fferen t operators workin g i n d i fferen t l aboratories on n om i n al l y i den ti cal test m ateri al wou l d, i n th e n orm al an d correct operati on of th e test m eth od, exceed 0, m g KOH /g i n on l y on e case i n 20 12 Test report Th e test report sh al l tai n at l east th e fol l owi n g i n form ati on : a) a referen ce to th i s part of I SO 6293; b) th e type an d com pl ete i d en ti fi cati on of th e produ ct tested; c) th e resu l ts of th e test (see cl au se 0) ; d) an y d evi ati on , by ag reem en t or oth erwi se, from th e stan d ard procedu res speci fi ed; e) th e d ate of th e test © I SO I SO 6293-2: 998(E) An n ex A (n orm ati ve) Preparati on , testi n g an d m n ten an ce of el ectrod e system A Preparati on of el ectrod es A I f th e cal om el el ectrode i s to be ch an g ed from n on -aqu eou s to aqu eou s bri dg e, d rai n ou t th e n on -aqu eou s sol u ti on , wash wi th water an d m eth an ol , th en ri n se th e ou ter j acket (salt bri dg e) several ti m es wi th potassiu m ch l ori d e sol u ti on (5 8) an d , fi n al l y, fi l l th e ou ter j acket wi th th i s sol u ti on A When u si n g th e sl eeve-type el ectrode, careful l y rem ove th e g rou n d-g l ass sleeve an d th orou g h l y wi pe both g rou n d su rfaces Repl ace th e sl eeve l oosely an d al l ow a few d rops of el ectrolyte to d rai n th rou g h to fl u sh th e g rou n d-g l ass j oi n t an d to wet th e g rou n d su rfaces th orou g h l y wi th el ectrolyte Set th e sl eeve fi rm l y i n pl ace, refi l l th e ou ter j acket wi th potassi u m ch l ori d e sol u ti on (5 8) , an d ri n se th e el ectrode wi th ch l orobenzen e (5 0) A When i n u se, th e el ectrolyte l evel i n th e cal om el el ectrode sh al l be kept above th at of th e l i qu i d i n th e ti trati on beaker to prevent en try of contam i n an ts i n to th e sal t bri d g e When n ot i n u se, fi l l th e cal om el el ectrode wi th potassiu m ch l ori de sol u ti on (5 8) , l eave th e bu n g i n th e fi l l i n g ori fi ce, an d i m m erse both el ectrodes i n water, keepi n g th e l evel of th e el ectrol yte above th at of th e water A Testi n g of el ectrod es Test wh en n ew el ectrodes are i n stal l ed an d retest on ce a m on th th ereafter by stan dardi zi n g m l of potassi u m h ydroxi d e sol u ti on (5 2) u si n g h ydroch l ori c aci d sol u ti on (5 3) A M n ten an ce of el ectrod es A C l ean th e g l ass el ectrode at l east on ce every week d u ri n g ti n u al u se, by i m m ersi on in col d ch rom osu l fu ri c aci d (see warn i n g to ) or an al tern ati ve stron g oxi d i zi n g cl ean er A Drai n th e cal om el el ectrode at l east on ce each week an d refi l l wi th fresh potassiu m ch l orid e sol u ti on (5 8) as far as th e fi l l i n g h ol e Ascertain th at crystall i n e KCl i s present M n tai n th e el ectrolyte l evel i n th e cal om el el ectrode above th at of th e l i q u i d i n th e ti trati on beaker at al l ti m es A 3 When n ot i n u se, i m m erse th e l ower h al ves of th e el ectrodes i n water Do n ot al l ow th em to rem n i m m ersed i n ti trati on sol ven t for an y appreci abl e peri od of ti m e between ti trati on s Al th ou g h th e el ectrodes are n ot extremel y frag i l e, h an d l e th em wi th care at al l ti m es N OTE — Th orou g h cl ean i n g of th e el ectrod es, keepi n g th e g rou n d -g l ass j oi n t free of forei g n m ateri al s, an d reg u l ar testi n g of th e el ectrod es are very i m portan t i n obtai n i n g repeatabl e poten ti al s, si n ce tam i n ati on can i n trod u ce u n certai n an d errati c l i q u i d tact poten ti al s, resu l ti n g i n n on -repeatabl e resu l ts A At th e en d of th e bl an k ti trati on , an d between su ccessive ti trati on s, a th i n fi l m of potassiu m ch l ori d e (KCl ) crystals coats th e el ectrode an d ti trant del i very ti p U se a j et of water from a pl asti c squ eeze bottl e to rem ove i t Th en ri nse th e el ectrode by i m m ersi on i n a beaker fu l l of water for a few second s Dry th e el ectrode by bl otti n g wi th a paper towel ; d o n ot ru b th e el ectrode A At th e en d of a set of sampl e ti trati on s, a m i xtu re of potassiu m ch l ori de (KCl) an d of sam pl e fracti on s coats th e el ectrode an d ti tran t d el i very ti p Cl ean th ese by i m m ersi on i n a sol u ti on of 50 m l of xyl en e; 38 m l of propan-2-ol ; 38 m l of water I SO 6293-2: 998(E) S ti r th e s o l u ti o n fo r a © ti m e l on g en o u g h to d i s s o l ve th e co ati n g , typi cal l y l ess th an R e m o ve th e I SO trace s of was h i n g s o l u ti o n fro m th e e l ectro d e wi th a j et o f wate r fro m a pl as ti c s q u e e z e bo ttl e Th e n ri n s e th e e l e ctro d e fu rth e r by i m m e rs i o n i n a be aker fu l l o f water s ti rre d fo r a few s e co n d s n ot D ry th e e l e ctro d e by bl o tti n g wi th a pape r to we l ; d o ru b th e e l ectro d e A Th e e l e ctro d es s h al l be h el d fi rm l y i n a s te ad y h o l d e r s o th at th ey d o n o t wo bbl e wh en th e l i q u i d i s vi g o ro u s l y s ti rre d N OTE — E l e ctro d e wo bbl i n g n o n - re pe atabl e re s u l ts 10 cre ate s e l e ctri cal n oi se wh i ch i n te rfe re s wi th th e d e te rm i n ati o n of e n d - po i n ts , re s u l ti n g in I SO 6293-2: 998(E) © I SO I CS 75 080 Descri ptors: pe tro l e u m pro d u cts , P ri ce bas e d o n pag e s ch e m i cal an al ys i s , d e te rm i n ati o n , s apo n i fi cati o n n u m be r, vo l u m e tri c an al ys i s , po te n ti o m e tri c m e th o d s