ISSN:0003-2654    

DOI:10.1039/AN95883FX033

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX035

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP149

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

THE AThe rule for classified advcrfiscmcnls is 6s. a linc (or sgaceeguivaknl of a line), with an extra charge of Is. for theuse of a Box Number. Scmi-dis$hyui classifiedANALYST back voluiiics and sets wantrd to hiiy for cash.Also othrr srientific journals. Write to A. Ashley,O i , East 21 St., Srw York, 10, S.Y., lJ.S..4.H E hlONI1 XICKEL COMPANY LIMITED, BIR-T M l i i ( , H A M 1WSli.AliCH LABORATORY, ivvitvsapplications from suitably qualified ASALYTICALCHEhllSIS tor a post as Investigator in tlic Spccial Methodstram of the Analytical Section.Thc Spccial >lethods team is priiiiarily concerned withthc drvclo~~incnt of new malytical ti'chniqucs and theirapplicatinn to the prrcisr analysis of calibration standardsfur optical, X-rav fluorcscciicc and mass sprctronirtrrs..Applicants.under :I0 years of agt', male or fcniale, shoiililpossrsa a good honours dcgrcc or cquivalmt qualifications.Every rcasonablc~ opportunity will Iic afforded for thf:ixcmisc of prsonal initiativv and riitrrprisc: publication oforiginal rnrarch is rncoui-agdSalary will Irr in accordmce with cxprriencc and quali-fications. I'ension and assurance schcincs arc, in operationand, in apprnpriatc cas('s, assistance can bc givrn for horisiiig.Applicatiori5, wliich w ~ i l l l x lr<.atcd i n contidcnce, shoiildgivr drtnils of a g ~ , qualifications aiid t~xprricmcc, and beaddresrd to Thf. Manager, Divhprncnt and Kt,srarchDcpartmerit, The Monil Sickcl Conipany I.iiintd, ThanirsHrnisr, Millbank, London, S.\V.l.I'lt,asr, iiiark fwvclopt:"Confidential 1..6F."UALIFIED CHEMIST rrquircd with vxpi.rir~nct' 111 Q gi.rii~al organic analysis. 1);irticularly of oils ;in11 greasrs.Soiiic krioulcdgc of plastics an advantag?. Age up to 23,with National Service coinplrted. Progrrssive post in plca5.intmcll-cquippcd 1abor;itory. Supcraiinutation sch?i?ir. S<,iidiull &-tails including age, qualifications, rxperitmx: andpresent salary in confidcnce to Box No. :\!Ji2. The, Analyst,4;. Crcshani Street, I.ondon, E.C.2.ASSISTANT CHEMIST of H.S.C. standard, prrfrrablywith experience in the yharniaccutical industry, requirrdfor ( ; i ~ i v r a l Analytical I.:iboratory. Apply in writing.giving details of agr, qualifications and ??rprriencr to 'l'hcCrookis 1,aboratorics Limited, Gorst Road, Park Royal,London, X.W.10.RESEARCH CHEMISSSPI'1.ICATIONS are invited ior tlir fullowing appointiiirntstlir Llrcinistry Ucpartnient of the Central RiwarchLaboratorivs of Richard Thoinas & Ualdwins Liniitnd,Whitchurch, Aylesbury, Bucks.:--(1) PHYSICAL CHEMISS for corrosion research andgcncral chemical investigations on c o a t d products,including tin, zinc and other metallic coatings, andnon-metallic coatings of the plastic arid ccrainic types.(2) ANALYTICAL CHEMIST for advanced analysis ;indrrsearclr on analytical incthods and modcrn physicaltechniques.Applicants should be preferably of Uriivinity drgrrr orequivalent standard, with rxpc~irncr in research or industry,but consideration will be given to recently qualified graduatcsand to applicants of lower acadeniic attainment with adequateindustrial or rcsearclr experience.Gmimencing salarics u d l norinally be in tlie range t730-LR50 accorduig to age, qualifications and experimce, butsalaries up to tl000 per iinnuiii may be offered to exccytionallyqual5c.d applicants.Tho ~ m s t s will he progressive andpensiouablc.Address enquiries, in corifidmcc, to the Director 01 Rrsearch,Tht: Fin. Whitchurch, Aylrsbury, Bucks.SSISTANT required b y consultants and public analysts.AA,R.I,C, or equivalent prrferahle, hut H.S.C. riiight beaccrptable. Some cxprrimcc in food or dnig 1abor;rtoryhelpful h i t not i,ssential. \Vork covvrs a wide field. Salary&600 to €900 according to qualifications antl rxprriciicc..Full details of both required by 1.incolrw Sutton and W'ood,Clarcnce House, Clarcncc Road, Nonvich.INEKALOGIST, preferably with chrniical or physicalMbackgroiind, rcqoircd for research work into coal rnincralsand the utilisation of coal ash slags.1st or 2nd class €lonoiirsin the ceramic industry, isstarting salary LiOO -[lflOOp.a. according to qualifications and cxpcrience. I'ivt-dayweek. Superannuation and grading schenirs. Apply inwriting to the Assistant Sccrctary, Ref. E.16, British CoalUtilisation Rescarch Association, Randalls Road, Leather-head, Surrey.Staff canteen and transport av:rilable._ _ ~ --._A LY ST xiiiSPECTROSCOPISTCaiididates should pmschs a good degreein cithrr Chtwiistry or Physics, or posscss anquivalcnt qualification.Some knowltxlgt.of tlie tlirory and practict' of miissioii and/orinfra-red althorption sprclroscopy is vsseiitial.Thr lrrrrk is larprly nori~routine and isconcmicd with the di~v~lopiurnt of analyticalnictliorls for the (:ompany's proa'ssrs andproducts.Thr siiccvssful candidate will br rqiiiredto take chargr of thr Spectroscopic Lahora-tory amd will be rfsponsililv to t h c ChiriAnalyst for i t 5 oprration. ALility to controlassistant staff is desirable.The coiniiwncing salary will depend on age,qualifications and t'xperirnct', which will beconiirimsurate with the rr*sponsihdit)- of llirposition.Conditions of cmplqwcnt arc ~ o n d andinciuile a I'cnsion Schriiir, Social anil SportsCliiII and all usual aiiwnitiri.I<eplic.s, givingdvtds of agc, qualilicationsand cxpi.riencr aiid quoting Ref. IS'I./.41/2tslroiild be addri~ssc~rl to the 1-aportr (;roiipPrrwnnrl hlaiiag<.r, Hanover House, 1 4 ,Hanuvcr Sqiiarr.I.ondon, W.1. ___ ~ - MPC LEASS LI .IIITIID, C;rrat M'rst h a d , l\rm tford ,tnvites appliretiuiis lruiii 1iit.n with R.Sc. or 4.R.I.C.for a position in thr Control I.aburatory. Applicants shonldbr aljout 4.5 2s ?.cars of ax':, prt~k~ralily with son~e rxprrirnci:in analytical chwiiibtry : i r i d bc ~'rcparcd to ha trained totdw rcq~onaibility in an rxrciitivr capacity. 'Hie dutieswill include suprrvisiw of Laboratory Staff, dev~~lopnicnt of~ilrysicul and chviniral ni?thorls for proilumon control andanalyscs associ.itvd with nictliods for production control andaiialysrs associatrd with cxpcriincntal work.The post isprogrvssivc. conditions of miploymrnt art-. good antl thyre arePfmion and Profit I'articipation Schcmrs in opcration.Applicants should givr full drtails of vxprriimc<,qualifications m d salary rtyurrcd to the Pcrsonncl >lanager.SFXIOR ClIl3lIST (prrfcrablv with analytical back-A g ~ r n d ) for r i . .%-arch arid drvrlopnient wark :Issociatedwith thc dcsign and manulacturf, of indiistrial and lalioratoryanalytical ant1 control equipment. Exptri~:nci: of GasVlrro~iiatograyhy and quality control would br a coiisidf~ahleadvan t agr.-applic;itioii invcstigations'NIOK 1'1 ECTRICAL I~ii(;INEl<KS for instrumentJkpplicatioil.' \Vork consists of ;idaptation of standardc.lcctroriic instnniicnts for 5pvcial nses, (lrsigii vf t ~ b t Rearand installatiou of cquiprntirt in iustruiricntation scherni%Applications to: I'rrsonncl Managcr, \V. G. Pye 8: Co. Ltd.,"Cranh" Works, Krwnlarkct Road, Cdiiilnidgc.l~ALIF113D CHE?vIlS;T is rrquircd by an rxyandingQCrouT, handling arid procvasing ;ininin1 liy-products.Diitirs coinprisc~ analysis and the control of the quality ofproducls, as wi~ll as tlie :icqiiiring uf i i cummt knowlcdgeuf twhnicsl d<~wlopnirnts in the nninial by-products proccsscs.The aucct.ssfu1 carididatt will have an Honours dqrce inChernistry arid hill have n soiind q a s p of hactt.riology. Inaddition he shoulil havr sanie yeals' iudustrial c'xpmencewit11 a coinnimcidl orjiariisatiori. Salarv according toqualifications. l'his is d&iitely a procressive position withgood prosprcts. Apply Uo4 i Grvsh:ini Strcct, J.ondon,A S ANALYST for Laboratory in which classical niethods G o , gas anall. 'sis arc: uicd on a wide variety of fuel and fluegascs. Prwious expmencr and an interrst in physicalmethods is drsiral,lv, Age 25-30, the minimum qualifmition1Jt!llig H.S.C. or cquivalent. licsrarch facilitirs are available.Starting salary within thc range (650-LS00 p.a. according tocxperiencc and qualifications. Fivrday week. Super-annuation and grading schrmcs. Apply in writing to theAssistant Sccrctary, Ref. L l i , British Coal UtilisationRcscarch Association, Randalls Road, Leatherhead, Surrey

ISSN:0003-2654    

DOI:10.1039/AN95883BP159

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

SEPTEMBER. 1958 THE ANALYST Vol. 83, No. 990 EDITORIAL International Symposium on Microchemistry, Birmingham, August 20th to nth, 1958 OVER two years ago the Midlands Section and the Nicrochemistry Group set up an Executive Committee, under the Chairmanship of Mr. J. R. Leech, and with Mr. W. T. Elwell as Honorary Secretary, to plan this Symposium. Since then the Committee has met almost monthly, directing and co-ordinating the eight sub-committees that were charged with the work of getting together in Birmingham some 60 lecturers and 450 delegates (about a quarter of them from overseas), housing and feeding them, and attending to their scientific and social wants for a week. Each sub-committee would claim that its was the hardest task of all; in the event, the organisation that they created together stood up well to the occasion.The milling crowd of delegates around the registration desks was dealt with rapidly and efficiently and, with the aid of a really excellent handbook, delegates quickly settled down to the daily round of scientific and not-so-scientific pursuits. This breadth of interpretation of “microchemistry” might have caused raised eyebrows among the Biological and Physical Methods Groups. In fact, as always, overlapping of interests was not only condoned but encouraged by much able assistance from their officers and members. There were four Plenary Lectures, given by Professors Feigl, Benedetti-Pichler and Lieb, and Dr. Belcher, representing the founding of microchemistry and its progress in South America, North America, Europe and Great Britain, respectively.Apart from these, the lectures with their discussions occupied a total of over 45 hours, and covered the fields of radiochemistry, emission and absorption spectroscopy, chromatography, polarography and biochemical methods, as well as the more recognisably chemical organic elemental and group analysis and gravimetric and titrimetric methods. Another section appropriately marked the interest and devotion that the founders of microchemistry showed in the teaching of their subject. The endurance called upon from delegates was fortunately limited by the lectures being held in three concurrent streams. There was some dashing from lecture theatre to lecture theatre, but with the best will in the world no delegate could attend much more than a third of the programme.With the varying lengths of papers and the proper insistence that social functions should not be unduly curtailed, the task of arranging the papers so that no delegate should ever wish to be in two (or even three) places at once was an impossible one. But there were few overt clashes, and only those with abnormal interests could feel seriously aggrieved. A feature of the lecture programme was the opportunity during extended discussion time for delegates to advance their own smaller contributions. Many of these were of great interest : their full value will only be appreciated when the published discussions are available. Steady interest was shown in the backward look over books and apparatus of early scientific interest.The forward view was provided by the leading scientific houses, which, in their trade exhibition, catered for every likely interest of the microchemist. In addition, 489 The common feature of the scientific content was small quantity of material.490 PROCEEDINGS [Vol. 83 four periods were set aside for demonstrations of micro techniques and apparatus. The firms, institutions and individuals who took part in these satisfied the lovers of everything from the fully automatic black box to the humble but ingenious gadget. All the delegates were invited to receptions by the President of the Symposium, Professor M. Stacey, F.R.S., and by the Lord Mayor of Birmingham, and to the Symposium Dinner, which was necessarily divided into two, each vying with the other in excellence of fare and wit.In addition each delegate had a share in the large number of lunches, receptions and dinners provided by various committees and through the generosity of the directors of local industry. There was evidence here, as well as in the number of firms who received, instructed and entertained delegates during works visits, of the excellence of the co-operation between the industries and the academic life of Birmingham. About a third of the delegates were fortunate in securing seats for the heavily over- subscribed performances of Hamlet or Pericles al the Memorial Theatre, Stratford-upon-Avon. Then there was the ladies’ programme, and the coach tours-but the list grows too nostalgic. Shall we say that there was entertainment, organised and spontaneous, which will a t least compete with the scientific programme in the memories of delegates. The thanks of the organisers must be expressed to Professor Stacey and to the authorities of the University of Birmingham, its Halls of Residence and the Guild of Undergraduates Union for the willingness with which they put their considerable facilities a t the disposal of the Symposium. There is by now probably ncl trace of the Symposium left in Birmingham, but the delegates will remember the welcome and comfort they enjoyed. During the week, discussions were being recorded, verified and edited by a willing but overworked band. When it is finished, all the lectures and discussions will be published by Pergamon Press Ltd. as the Proceedings of the Symposium: a reminder of two years’ of preparation and one crowded week of enjoy- ment as well as scientific accomplishment. The programme of social functions was an impressive one. This was an enormous task. and it is still going on.

ISSN:0003-2654    

DOI:10.1039/AN9588300489

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

490 PROCEEDINGS [Vol. 83 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY NEW MElMBERS ORDINARY MEMBERS Michael Burton, B.A. (Cantab.) ; Thomas Roy Crompton, BSc. (Lond.), A.R.I.C. ; Ian Joseph Draper, BSc. (Dunelm.) ; Philip Juliber Elving, A.B., Ph.D. (Princeton) ; George Fredrick Parker, Dip.Sugar Chem., Dip.Ind.Chem. ; Frederick Henry Pollard, BSc., Ph.D. (Bristol) ; Herbert Kenneth Reatty Rout, F.R.I.C. ; Silvjo J. Tassinari, M.S. (St. Michael’s, Vermont). JUNIOR MEMBER Anthony Francis Morris. DEATH WE record with regret the death of John Hawthorne.

ISSN:0003-2654    

DOI:10.1039/AN9588300490

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Sept., 19581 BROWN AND WEIR 491 A Completely Automatic Titration Unit for Process Use BY J. F. BROWN AND R. J. WEIR (Inaperial Chemical Industries Ltd., Billingham Division, Research Department, Billinglzam, Co. Durham) A completely automatic titration unit for continuous operation on a chemical plant is described. The unit performs all operations of the titration, Le., it takes the sample, delivers a measured volume into the beaker, adds a measured volume of diluent, fills the burette, titrates the sample to a pre-set pH end-point, reads the burette, records the reading on a strip-chart recorder, drains the beaker and repeats the sequence after a set time interval. The flow of liquids into the various vessels is controlled by solenoid- operated glass valves, and volumes of liquid are measured by using level electrodes.The sequence of operations is controlled by a Uniselector, the completion of any operation being used to move the Uniselector to its next position. The pH end-point unit stops the titration a t a pre-set end- point. A special circuit causes the reagent to be added in small increments as the end-point is approached. The level in the burette after the titration is measured by means of a photocell and lamp unit, which is driven up the burette until the meniscus is detected. The distance the unit has travelled, i.e., the level of reagent in the burette, is indicated on a strip-chart recorder. Laboratory tests on the unit give a standard deviation of k0.04 ml in a titre of 10 ml with N acid and N alkali. The unit has been successfully operated on the plant for periods of several months.A standard model has been designed and its commercial manufacture undertaken by Electronic Instruments Limited, Richmond, Surrey, under the name “Titromatic Analyser.” FROM a survey made in 1955 of process analytical instrumentation requirements, it was apparent that many problems could be solved satisfactorily by using a completely automatic titrator. Although several semi-automatic titrators had been developed for laboratory use,1~2J~4 no completely automatic unit of high accuracy suitable for plant use was available. The instrument described was developed to fill this gap ; it operates completely automatically, and records the results of titrations on a strip-chart recorder. It was tested in a prototype form under plant conditions, running for 24 hours each day for several months on the following duty- To sample a 14 to 20 per cent.solution of ammonia in water. Sample volume 1.30 ml, diluted with 100 ml of water before titration. To titrate with N sulphuric acid to an end-point of pH 4. Titre 10 to 15 ml. Titration frequency 7 or 8 per hour. It was found that results were accurate to kO.1 per cent. for the range of ammonia concentrations encountered. Details in the description refer to the prototype model, but the commercial version, the Titromatic Analyser (see Fig. 1) marketed by Electronic Instruments Limited of Rich- mond, Surrey, is very similar. GENERAL DESCRIPTION A successful automatic titrator must be able t o replace the whole routine analytical procedure and produce as accurate an answer.Hence, the unit must perform all the operations of the titration, i.e., take the sample, deliver a measured volume into a beaker, dilute the sample as required, titrate, stop the titration at the desired end-point, read the burette, record the reading, drain the beaker and repeat the sequence after a set time interval. The accuracy and reproducibility of the results must be at least equal to those of the normal process-laboratory method, i.e., better than 1 per cent. of the amount present. The instru- ment must be capable of operating continuously and reliably under plant conditions with the minimum of maintenance. It is also desirable that the unit should operate as far as possible on principles that are readily understood and followed by the plant personnel in charge.Hence, all-glass burettes, pipettes and valves are used and the level in the burette is “observed” by a photocell. Volumes are measured between two liquid levels in a vessel, these levels492 BROWN AND WEIR : A COMPLETELY AUTOMATIC [Vol. 83 being defined either by a suitable overflow or, more usually, by two electrodes. The sequence of operations follows the normal laboratory practice, and a series of indicator lights permits the course of the titration to be followed. The unit consists of three parts (see Fig. IZ), as follows- (a) Titrator unit. ( b ) Control unit. (c) Recorder. The titrator unit houses the various parts with which the titration is carried out, i.e., the It includes an The control burette, pipette, beaker, electrodes and associated electrical equipment.electrical distribution unit, which links the titration unit to the control unit. b Sample h c Valve t Sample Burette- n ( i i= 1 Valve 5 1 3 c =J Diluent pipette \ galve 3” Valve ’ b 3 Valve Valve 3ii””’ Valve Fig. 3. Diagram of the automatic titrator unit comprises two parts, the sequencing unit, which controls all the operations in the titration, and the end-point detector. Finally, the result of the titration is presented on a strip-chart recorder. The titrator is shown diagrammatically in Fig. 3.492 BROWN AND WEIR : A COMPLETELY AUTOMATIC [Vol. 83 being defined either by a suitable overflow or, more usually, by two electrodes. The sequence of operations follows the normal laboratory practice, and a series of indicator lights permits the course of the titration to be followed.The unit consists of three parts (see Fig. IZ), as follows- (a) Titrator unit. ( b ) Control unit. (c) Recorder. The titrator unit houses the various parts with which the titration is carried out, i.e., the It includes an The control burette, pipette, beaker, electrodes and associated electrical equipment. electrical distribution unit, which links the titration unit to the control unit. b Sample h c Valve t Sample Burette- n ( i i= 1 Valve 5 1 3 c =J Diluent pipette \ galve 3” Valve ’ b 3 Valve Valve 3ii””’ Valve Fig. 3. Diagram of the automatic titrator unit comprises two parts, the sequencing unit, which controls all the operations in the titration, and the end-point detector.Finally, the result of the titration is presented on a strip-chart recorder. The titrator is shown diagrammatically in Fig. 3.492 BROWN AND WEIR : A COMPLETELY AUTOMATIC [Vol. 83 being defined either by a suitable overflow or, more usually, by two electrodes. The sequence of operations follows the normal laboratory practice, and a series of indicator lights permits the course of the titration to be followed. The unit consists of three parts (see Fig. IZ), as follows- (a) Titrator unit. ( b ) Control unit. (c) Recorder. The titrator unit houses the various parts with which the titration is carried out, i.e., the It includes an The control burette, pipette, beaker, electrodes and associated electrical equipment. electrical distribution unit, which links the titration unit to the control unit.b Sample h c Valve t Sample Burette- n ( i i= 1 Valve 5 1 3 c =J Diluent pipette \ galve 3” Valve ’ b 3 Valve Valve 3ii””’ Valve Fig. 3. Diagram of the automatic titrator unit comprises two parts, the sequencing unit, which controls all the operations in the titration, and the end-point detector. Finally, the result of the titration is presented on a strip-chart recorder. The titrator is shown diagrammatically in Fig. 3.Sept., 19581 TITRATIOS UNIT FOR PROCESS USE 493 SOLENOID VALVES- The flow of all liquids in the titrator is controlled by solenoid-operated valves similar to those used on an automatic Fischer titration unit previously de~cribed.~ Two types of valve are used, a straight pattern and a side-arm pattern.One straight valve and one side- arm valve together form a unit, the straight valve performing the filling operation and the side-arm valve the emptying operation. The design is such that, by locating the side-arm near the valve seat, the “dead” volume is reduced to a minimum (see Fig. 4). , . I pliii i n c h e s 4 I I I I j I T’ 5 + inch Fig. 4. Solenoid valve with side-arm Common earth contact ‘1 Sample “make“ Sample I ‘ break *’ contact \I 07 If Fig. 5 . Liquid level contacts Each valve after manufacture is subjected to a life test of several hundred operations to ensure that no leaking or sticking occurs. This design has proved to be most satisfactory, and it has been found that the valves tend to grind themselves in with continued operation to give a very good seat.LEVEL-MEASURING ELECTRODES- The method used to deliver accurate volumes of sample and diluent is by measuring between two levels. The simplest method is to have an overflow at the upper level and com- pletely drain the vessel, but complete draining proved to be unreliable and difficult to incor- porate in the automatic system. The apparatus therefore has an overflow upper level in the sample pipette so that flushing of this pipette is possible, but all other fixed levels are defined by the use of two level electrodes (see Fig. 5 ) . The circuit between these electrodes is either made or broken by the liquid level corre- sponding either to filling or emptying operations. The electrodes are of platinum wire sealed into glass tubes with about f inch of wire exposed.The glass tubes are supported in a detachable polythene cone-shaped plug, which fits into a corresponding glass-cone joint on the measuring vessel. Each pair of electrodes is fed through a variable series resistor from a low-voltage a.c. supply, the resistor being adjusted to allow for the variation in different liquids, etc. When the electrodes are uncovered, there is some leakage current, which, in the Leakage rates of less than 0.5 ml per day are normally achieved.494 BROWN AND WEIR: A COMPLETELY AUTOMATIC [Vol. 83 design described above, is equivalent to a resistance of 10,000 to 100,000 ohms, but, when they are both in contact with liquid, the resistance falls to 100 to 10,000 ohms, depending on the disposition of the electrodes and the composition of the liquid.This resistance change is ample to operate an electrical control circuit actuating the solenoid valves through which the liquid flows. The speed of response of the electrical circuit and the valves is such that, for moderate flows of the order of 3 litres per hour into or out of the measuring vessel, the level can be defined by the electrodes to becter than 0.01 ml. By using slower rates of flow, greater accuracy can be obtained. DILUENT PIPETTE- Owing to the small volume of sample used, it is necessary to dilute it to about 100 ml with water before the titration is carried out. The pipette is shown in Fig. 5. Both upper and lower levels of this pipette are defined with level electrodes, and the pipette delivers 120ml of water from a constant-head tank, but could be used to deliver a second reagent instead of water if a back titration were necessary.SAMPLE PIPETTE- For the titration of approximately 10N ammonia solution, a sample volume of about 1.5 ml was required, which was to be measured with a reproducibility of better than 1 per cent. and to be representative of the sample stream with a minimum of sample lag. In order to reduce sample lag and ensure complete flushing of the pipette and sample lines with fresh sample, an overflow is used instead of electrodes to define the upper liquid level. Its method of operation is as follows. The sample flows through the pipette via the solenoid valve and out at the overflow for a definite time interval. This time interval is set to give the required number of titrations per hour, but it must be at least long enough to ensure adequate flushing of the sampling lines.At the end of this time interval, the solenoid valve shuts and the excess of liquid in the pipette drains off to give a fixed upper level. The lower level is de- fined by two level electrodes. The volume delivered by this pipette was found to be about 1.30 ml; the exact volume could be varied by altering the position of the level electrodes. Tests on this pipette system indicated that the volume delivered had a standard deviation of better than 10.005 ml. Other pipettes of larger volumes have been designed and can easily be fitted to the titrator as required. BURETTE- The burette used is an NPL grade A Pyrex-glass burette of 25-ml capacity fitted with a B7 cone joint, in place of the normal tap, for attaching to the solenoid valve.The upper level to which the burette is filled is determined by two level electrodes of the usual type. The reagent is fed to the burette from a 10-litre vessel fitted with a constant-feed device of the Marriotti type. Burettes of other capacities, or precision-bore tubing, can replace the existing burette to permit other titrations to be carried out. BEAKER AND ELECTRODE SYSTEM- The beaker is made of polythene and has a glass siphon tube let in through the side, the lower end almost touching the bottom of the beaker. The draining of the beaker through the siphon tube and solenoid valve is controlled by two level electrodes of the usual type. By careful positioning of the level electrodes, stirrer and siphon tube, the amount of liquid remaining in the beaker after drainage is small, and, since it has been titrated to a neutral end-point, no further flushing is required.The delivery tips of the sample pipette, the diluent pipette and the burette feed into the beaker and are located so that they are all immersed during the titration. The burette tip is located near the stirrer paddle to ensure good mixing during titration. The stirrer is of the normal glass paddle type and is driven by a modified Plessey motor, type CP88208/1, at approximately 500 r.p.m. These are a calomel electrode (Electronic Instruments Ltd., type R J23), a glass electrode (Electronic Instruments Ltd., type GG23) and a platinum-wire electrode, which earths the solution.This earthing electrode is necessary for the correct operation of the pH end-point detector in the presence of stray a.c. currents from the various level electrodes. Also located in the beaker are the three electrodes needed for pH measurement.Sept., 19583 TITRATION UNIT FOR PROCESS USE 495 pH END-POINT DETECTOR- This unit is essentially a pH meter that produces an electrical signal when the sample being titrated reaches a pre-selected pH value. The unit controls the addition of reagent from the burette via a solenoid valve. A special anticipation circuit is so arranged that, near the end-point, the reagent is added in small increments with a suitable time interval between additions to ensure that adequate mixing has occurred and the solution and electrodes are in equilibrium.This is achieved in the following way. A voltage equivalent to the desired “end-point pH voltage” is set on the instrument by means of a calibrated potentiometer. Superimposed on this “end-point pH voltage” is an “anticipatory voltage,” derived from a resistance - capacity network; the “anticipatory voltage” varies during titration. The total of the “end-point pH voltage” and the “anticipatory voltage” is termed the “trigger voltage” and corresponds to a pH voltage slightly in advance of the desired pH end-point. The “trigger voltage” is compared with the indicated pH voltage from the electrodes, and the difference is fed to an amplifier, which controls, through a relay, the solenoid valve on the burette. Provided that the indicated pH voltage is greater than the trigger voltage for longer than 0.4 second, the relay and burette solenoid valve will be energised and allow reagent to flow into the beaker.When the indicated pH voltage, falls below the trigger voltage, the relay is de-energised and the burette solenoid valve is closed, thus shutting off the flow of reagent to the beaker. A second pair of contacts on the relay now allows the “anticipatory voltage” to decay, hence reducing the total “trigger voltage.” At some point the total trigger voltage will fall below the indicated pH voltage, and after 0.4 second will again energise the relay. The time delay of 0.4 second is introduced to ensure that conditions in the beaker have reached equilibrium before adding further reagent. The “anticipatory voltage” continues to decay during this time delay, but returns towards its original value while the relay is energised.Before the original value is reached, the reagent added to the beaker will have caused the indicated pH voltage to fall once more below the “trigger voltage” and the relay will be de-energised, shutting off the solenoid valve, and the cycle of operations will be repeated (see Fig. 6). This pattern of anticipatory voltage decay, time delay and anticipatory voltage growth will continue until, finally, the solution pH will fall slightly below the set end-point pH voltage, the anticipatory voltage will decay to zero and the titration will be completed. The completion of the titration is indicated by a pulse produced when the solution pH potential has remained below the end-point pH potential for 30 seconds, this pulse being fed into the sequencing unit.The pH end-point detector therefore contains three main parts; a pH amplifier incor- porating valves V,, V,, V, and V,, a trigger circuit incorporating valves V, and V, and a time delay incorporating valve V,, (see Fig. 7 ) .496 BROWX ASD WEIR: A COMPLETELY ACTOXMATIC [Vol. 83 As the burette is filled initially to a constant upper level (defined by the level electrodes), the volume of reagent used in the titration is accurately related to the final meniscus level. For determining this meniscus, a unit incorporating a lamp and a photocell is used. The BURETTE RJ3ADER- > > m E! > -+ 0 4 4 > 2 I t n l I I lamp throws a narrow horizontal beam of light through the liquid in the burette, which focuses the light on the photocell as a narrow vertical beam.A motor driving a lead screw raises the lamp - photocell unit up the burette from a fixed starting position. When it reaches the meniscus, the light beam is interrupted and the resulting change in photocellSept., 19581 TITRATION UNIT FOR PROCESS USE 497 current is made to give a pulse to the control unit and t o stop the motor. The number of revolutions of the lead screw necessary to raise the unit from its fixed starting position to the meniscus is used as a measure of the burette level; the lead screw is geared to a variable resistor, which is connected in circuit with a recorder. The position of the meniscus and hence the titre is indicated on a suitably calibrated recorder chart.Tests with the unit on a normal 50-ml burette indicated that it was capable of reading the level equivalent to a volume of about 0.01 ml. The burette reader consists of a head containing a lamp and a photocell (LP, and PC) with a valve amplifier and trigger circuit (V, and V6) on the sequencing unit chassis (Fig. 8). The head is driven up (or down) the burette by a 6-volt a.c. servo motor and receives its power from relay RLB (up) or RLC (down). SEQUENCING CONTROL UNIT- The approach that has been adopted in this instrument is to use the completion of any individual operation to start the next operation. All the sequencing operations are carried out by a 4-bank 25-position Uniselector, which is stepped forward by pulses from a 50-volt ax.supply and the thyratron, V, (see Fig. 8). Under normal conditions the thyratron is held non-conducting, and, when an operation is completed, the “operation completed” signal is arranged to bring the grid more positive than the cathode. This makes the thyratron conduct and the anode current passed operates the Uniselector electromagnet, thus moving the contact arms to the next position. The Uniselector has 4 banks of 25 contacts: No. 1 bank is used to switch power to an interval timer and to operate relays controlling the burette-reader motor; No. 2 bank switches power to the solenoid valves and Nos. 3 and 4 banks switch the “operation completed” signals from the level electrodes and other sensing devices to the thyratron grid. A typical sequence for a normal acid - alkali titration is described below and can be followed by reference to Fig.3 and Table I. SEQUENCE OF OPERATIONS OF THE AUTOMATIC TITRATOR FOR A NORMAL ACID - ALKALI TITRATION OPERATION 1. UNISELECTOR POSITION 1- Operation 1 represents the beginning of a cycle. The previous cycle will have left the beaker full of neutralised solution, the burette partly empty and the burette reader and recorder showing the result of the titration. During operation 1, the burette reader remains stationary, hence the follower potentio- meter and recorder remain at the position corresponding to the last titration. The active function of position 1 is to open the solenoid valve that allows the sample pipette to be filled. Power goes to this valve from the Uniselector bank Xo.2 and holds it open until the “operation completed” signal appropriate to this position is sent to the thyratron. For this particular filling operation, the signal can be derived from contacts at the top of the pipette or alternatively from an interval timer, a selector switch being provided. With the small volume used, flushing of the long sample line is required and the interval timer is used. The interval-timer circuit consists of valve V,, condenser C, and resistors R,, to R,, (see Fig. S), the resistors being chosen so that the timer can be set for intervals of 1, 2, 5, 10, 15, 20 or 30 minutes. When the pulse from this circuit at the end of the pre-set time interval is received by the Uniselector, it moves to position 2 . An electrode at the top of the pipette can be used instead of the interval timer to produce the “operation completed” signal if maximum speed is required.This consists essentially of a wire that is touched by the earthed solution in the pipette as it rises to the required level. When the wire is earthed by the solution, the thyratron conducts, thus causing the Uniselector to move to position 2. OPERATION 2 . UNISELECTOR POSITION 2- The following operations now occur- (i) Valve 1 closes, stopping the supply of sample to pipette A, which drains to a (ii) The motor of the burette-reading unit, B, is switched on and the unit begins to (iii) Valve 2 opens and the contents of the beaker empty through the siphon until the constant upper level. return to its zero starting position. The recorder pen moves with it.falling liquid level breaks the circuit between level electrodes 8.498 BROWN AND WEIR: A COMPLETELY AUTOhlATIC [Vol. 83 The main essential of these electrodes is a wire, which is uncovered by an earthed solution when the pre-determined level is reached. When the wire is uncovered by the solution, the thyratron conducts and the Uniselector moves to position 3. OPERATION 3. UNISELECTOR POSITION 3- into pipette C. when an “operation complete” signal is derived similar to that described on position 1. causes the Uniselector to move to the next position. UNISELECTOR POSITIONS 4 TO 12- Other solenoid valves controlling flows are operated on positions 4 to 12, the electronic system being identical to that used on the previously described positions 2 and 3.The odd numbers are filling operations terminated by a rising level making contact with an electrode, and the even numbers are emptying operations terminated by a falling level breaking contact with an electrode. Valve 2 shuts and valve 3 opens, allowing the diluent (water) to flow from the reservoir The level rises until it completes the circuit between level electrodes 9, This In the example being considered, the operations continue as follows. Valve 3 shuts and valve 4 opens, allowing the diluent to flow into the beaker until the This actuates This corresponds to a fill The appropriate contacts have been set to give an immediate OPERATION 4. UNISELECTOR POSITION 4- level in the pipette falls, breaking the circuit between level electrodes 10.the sequencing circuit and the Uniselector moves to position 5. operation that is not required. “operation complete” signal, and the Uniselectclr therefore moves a t once to position 6. OPERATION 5 . UNISELECTOR POSITION 6- until the level in the pipette falls, breaking the circuit between level electrodes 11. actuates the sequencing circuit and moves the TJniselector to the next position. OPERATION 6. UNISELECTOR POSITION 7- burette until the liquid completes the circuit between level electrodes 12. the sequencing circuit and moves the Uniselector to position 8. wired so that the Uniselector will move straight through to position 13. design, positions 13 to 22 are not used; the Uniselector therefore moves to position 23. Valve 4 shuts and valve 5 opens, allowing the sample in pipette A to flow into the beaker This Valve 5 shuts and valve 6 opens, allowing reagent to flow from the reservoir into the This actuates No more filling or emptying operations are required and therefore contacts 8 to 12 are However, in the OPERATION 7.UNISELECTOR POSITION 23- Valve 6 has now shut. On position 23 the relay, RLC, is energised unless the burette The Unisdector therefore waits when necessary on The “operation complete” signal reader has reached the lower limit. this position for the burette reader to reach its lower limit. is given by a “break” contact on RLC and the Uniselector moves to position 24. OPERATION 8. UNISELECTOR POSITIOK 24- Valve 7 is now put under the control of the pH end-point detector. Under normal conditions, valve 7 will now open and allow the reagent to flow into the sample. When the pH of the solution reaches the “triggering pH,” valve 7 will be momentarily shut off and then actuated intermittently so that small additions of reagent are made until the pH of the solution remains a t the set end-point for 30 seconds, when a pulse is sent to the sequencing circuit, which moves the Uniselector to position 25.OPERATION 9. UNISELECTOR POSITION 25- The motor of the burette-reading unit is now energised and t he unit rises up the burette until it reaches the meniscus; it then stops, and its position is indicated on the recorder. As it stops, the unit sends a pulse to the sequencing circuit, which moves the Uniselector to position 1 to start the next cycle. This complete cycle takes about 5 minutes j&us the interval set on the timing circuit, during which the sample is flushing through the sample pipette.Valve 7 is now shut and is no longer under the control of the pH meter.Sept., 19.581 TITRATION UNIT FOR PROCESS USE 499 The complete sequence of operations and the corresponding Uniselector positions are shown in Table I. TABLE I SEQUENCE OF OPERATIONS Uniselector position 1 2 3 4 5 6 c 8 9 10 11 12 13 to 22 23 24 25 Operation Fill sample Empty beaker Fill diluent Empty diluent Fill (not used) Empty sample Fill burette Empty (not used) Fill (not used) Empty (not used) Fill (not used) Empty (not used) Motor Uniselector Wait for burette motor down Titrate Read burette Operation No. 1 2 3 4 5 6 - - - 7 8 9 Burette reader Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor down Motor up - - CONSTRUCTION OF THE AUTOMATIC TITRATOR As mentioned on p.492, the complete titrator consists of three units. The titration unit is mounted in a metal cabinet of the type made for electronic equip- ment, but with a Perspex front. Inside the cabinet a framework supports the various units. There are three main units; the sample unit, the diluent unit and the burette unit, each having two solenoid valves with the associated glassware and level electrodes. Inlet and exit lines for the liquids are mounted on a board at the bottom of one side of the unit. There are lines for sample, diluent and reagent and two drain lines, one from the unit and one from a polythene tray in the base of the cabinet in case of overflow.In addition, there is an air inlet so that the cabinet can be purged with air. Sample and diluent pass through ceramic- disc filters before passing to the appropriate valves. The burette-reading unit is mounted behind the burette. At the back of the cabinet is the distribution box, which contains the adjustable resistors associated with the level electrodes and the subsidiary relays for the motor of the burette- reading unit. An indicator panel is mounted at the front, which shows, by means of neon lights, the operation in progress. There is also a switch that can be used to control the solenoid valves manually when setting up and a press button for stepping the Uniselector on one position at a time.The titration unit is connected through 15 yards of multicore cable to the control unit. This consists of the sequencing and pH units, which are mounted in standard 19-inch G.P.O. rack-type chassis. The control unit is connected to the recorder through 150 feet of cable. Both the control unit and the recorder can be purged with air for plant use. OTHER APPLICATIONS OF THE AUTOMATIC TITRATOR The apparatus described carries out a straightforward titration with a measured sample, a measured diluent and a pH end-point. I t is designed so that modification for other duties is a simple matter, and, in order to illustrate this point, the modification necessary for a particular titration is described below. The example chosen is a titration in which the pH of the diluent varies and must, therefore, be neutralised before the normal operations start.The extra operations that must be brought in are “fill burette” and “titrate,” and they must come after the “empty diluent” operation, but before the “fill burette” for the true titration. Table I shows that operation 4 is normally the “empty diluent vessel” operation, and therefore Uniselector position 5 may be used for the extra “fill burette” operation. It was previously unused, so this calls for no other change. The new “titrate” operation then has500 BROWN AND WEIR: A COMPLETELY AUTOMATIC [Vol. 83 to be fitted into position 6, and since this was previously used, some changes must be intro- duced. The changes are quite simple; each subsequent operation is moved up two places, Le., position 6 goes to position 8 and position 7 to position 9. Both these positions were unused in the original arrangement.ADJUSTMENTS OF THE AUTOMATIC TITRATOR Switches are provided so that the apparatus can be changed from automatic to manual operation for testing and fault tracing and also when setting up contacts and adjusting control resistors. The only adjustments needed in the electronic equipment are to the resistors, of which there is one for each level-electrode assembly. Adjustment is necessary to allow for the different conductivities of the liquids being controlled and for variations in leakage resis- tance. The method used is to set the level b,y hand to a point just before the “operation completed” signal should be given and to note the range of adjustment over which a false signal appears.The level is then altered by hand until it reaches the point at which the signal should be produced, and then the range of adjustment is again tested. The part of the range over which the signal fails to appear is also unsuitable. The part of the range not rejected by either test is satisfactory and the adjustment is best set in the middle of it. This part of the range must be marked as unsuitable. REX LTS After preliminary trials, the apparatus was tested continuously on constant samples in the laboratory for more than 1 week. The apparatus performed eight titrations per hour, a total of over 1000 titrations. Since, over long periods of the run, the sample composition was constant, it was possible to measure the relxoducibility of the complete instrument from the recorder chart.Two periods of steady conditions were taken and the titration figures measured on the recorder chart. The recorder had been calibrated in terms of millilitres of reagent added. The results from the two runs can be summarised as follows- Run No. 1: 11.45 a.m. to 5.00 p.m., November 22nd, 1955. 44 __ Number of titrations . . -- Standard deviation . . . . -- -- rt0.20 3 k0.043 ml Coefficient of variation . , == h0.35 per cent. Run No. 2: 12.30 p.m. to 5.15 p.m., November 24th, 1955. Number of titrations . . _- -- Mean recorder reading . . -_ -- 56.0 3 12.03 ml Standard deviation . . . . __ -- 1 0 . 2 2 = f0.040 ml Coefficient of variation . , == 1 0 . 3 8 per cent.Mean recorder reading . . -_ -- 52.7 = 11.32 ml 44 The response time of the instrument was also studied. With no flushing of the sample lines, a change in sample strength was not registered for about 50 titrations. This is because the sample lines have a volume of about 100ml and the sample pipette takes only about 2 ml per sample. When, before taking a sampk, the sample pipette is flushed for 1 minute at a flow rate of about 100 ml per minute, a change in sample strength was recorded in the second following titration and a steady reading at the new value was obtained after four titrations. With a 2-minute flushing period, a 75 per cent. change was recorded in the first following titration and a steady reading was obtained after three titrations. For continuous running on the plant, continuous flushing of the sample lines was incorporated and a further 1 minute’s flushing of the actual sample pipette.Under these conditions, 90 per cent. of the change was indicated in two readings and a steady reading was obtained after the third titration. Use of the instrument on various duties on the plant has shown that, with routine main- tenance of reagent, filters, recorders, etc., periods of several months of reliable operation can be achieved (see Fig. 10). In fact, instrumental runs were in most instances terminated by plant shut-downs rather than instrumental failures. The electronic and mechanical parts have proved to be most satisfactory, and only minor alterations in design and lay-out were necessary to convert the prototype instrument into the model now being marketed by Electronic Instruments Limited.Sept., 19581 TITRATIOX UNIT FOR PROCESS USE Fig. 10.Recorder chart 50 = 14.5 per cent. of ammonia 60 = 17.4 per cent. of ammonia Calibration- APPENDIX LIST OF COMPONENTS FOR pH END-POINT DETECTOR (Fig. 7) 1.8-megohm high-stability resistor. 27,000-ohm resistor. 1-meghom resistor. 10-ohm f-watt resistor. 22,000-ohm resistor. 1-meghom high-stability resistor. 2.2-megohm resistor. 2.2-megohm high-stability resistor. 39,000-ohm wire-wound resistor. 1800-ohm wire-wound resistor. 47,000-ohm wire-wound resistor. 100,000-ohm helical potentiometer (10 turn). 220,000-ohm potentiometer. 10-megohm resistor. 560,000-ohm resistor. 1.8-megohm resistor. 501502 BROWN AND WEIR: A C,OMPLETELY AUTOMATIC = 33,000-ohm &watt.resistor. = 1000-ohm resistor. = 33,000-ohm 7-watt. resistor. = 22,000-ohm 10-watt resistor. = 33-megohm resistor. = 470,000-ohm resistor. = 22-megohm resistor. = 0.005-pF condenser, 3000-volt working. = 0.001-pF condenser, 750-volt working. = 0.25-pF condenser, 350-volt working. = I-pF condenser, 3ljO-volt working. = 0.05-pF condenser, 350-volt working. = 32-pF condenser, 450-volt working. = 2-pF condenser, 3ii0-volt working. = 8-pF condenser, 450-volt working. = 0.02-pF condenser. 400-volt working. = 20-pF condenser, 1.50-volt working. = hfE1400 valve. = EF37A valve. = ECC83 valve. = ECC81 valve. = EZ80 valve. = 108C1 valve. = CC7L valve. = N8/15 metal rectifier. = Plessey CZ49112j6 12-pin fixed plug. = Belling - Lee L764 socket.LIST OF COMPONENTS FOR SEOUENC[NG UNIT AND DISTRIBUTION UNIT (figs. 8 and 9) = 100,000-ohm pre-set potentiometer. = 5600-ohm resistor. = 2.2-megohm pre.-set potentiometer. = 6800-ohm resistor. = 220-ohm resistor. = 1800-ohm resistor. = 470-ohm helical potentiometer (10 turn). = 33-megohm resistor. = 10,000-ohm resistor. = 47,000-ohm resistor. = 47-megohm resistor. = 15-megohm resistor. = 22-megohm resistor. = 33,000-ohm resistor. = 220,000-ohm res:stor. = 1-megohm resistor. = 10-ohm resistor. = 560,000-ohm resistor. = 4700-ohm pre-set potentiometer. = 22,000-ohm resistor. = 120,000-ohm resistor. = 180,000-ohm resistor. = 3.3-megohm resi:jtor. = 27,000-ohm resistor. = 4700-ohm resistcr. = 82,000-ohm resistor. = 100,000-ohm resistor. = 1500-ohm resistor. = 10-megohm resistor.= 330-ohm resistor. = 100-ohm resistor. = 15,000-ohm resistor. = 1000-pF Condenser. = 8-pF condenser, 450-volt working. = 20-pF condenser, 150-volt working. = 0.25-pF condenser. = 32-pF condenser, 450-volt working. = 1-pF condenser, 150-volt working. = 200-pF condenser, 20-volt working. = 2-pF condenser. = 500-pF condenser, 50-volt working. = EN32 valve. [Vol. 83PL5 PL I PL2 P L7 M L K J H G B A D C F E 3 i 1 i I-, ri sw I 2A p-- X U Z V T Y W UVJT Y t t z J A B C D E F G H J K L M P O Q T ; R “ Break ” contacts 0 ake ” contacts I I ! ! I I J 1 I J c8T 2 Fig. 8. Circuit diagram of sequencing unit (for values of components, see Appendix. 1’. 502)LP5- I7 0 * To recorder or controller (1 * Level contacts Note circuit is completed by liquid between contacts Contact resistance when closed: 100-10.000 Q Contact resistance when open: 10-I00 k i2 (depends on liquid) \ 12 \ 3 pH electrodes motor limit switches - calomel t I I I I I I I I I I I I I ;lass I I I I I I I I I I I I I I I I I I I I I I R27 IT t I I I I I I I f I I I I I I 1 , 1 I I $ I I I I I I I I I I I I I I I I I I i II; 4 Set contact I Q manual s u w 7 6 8 M N S R O P S PL8 t X U Z V T Y W A B C D E F C H J K L M N P O Q T V Y Y PL9 ? 4 A B C D E F G H 3 PL6 i I - Fig. 9. Circuit diagram of distribution unit (for values of components, see Appendix, p. 502)Sept., 19581 TITRATION CNIT FOR PROCESS USE PL.% = Z900T valve. = ECC81 valve. = KT2 valve. = 9OC1 valve. = 6.3-volt lamp. = &volt KO. 2 follow lamp. = 24-volt KO. 2 lamp. = 60-volt No. 2 lamp. = QS/5 metal rectifier. = 4 x RMO metal rectifier. = S-440-3-1W metal rectifier. = Plessey C249229j1 25-pin fixed socket. = Plessey CZ49229/0 25-pin fixed socket. = Plessey C249459/5 12-pin fixed socket. = Plessey CZ59498 fixed socket. = Plessey C259496 fixed plug. = Plessey CZ49061/1 25-pin fixed plug. = Plessey CZ49061j5 25-pin fixed plug. = Belling - Lee L764 plug. = Follow motor, Plessey type 2521/4. = Stirrer motor, Plessey type CP89208jl. = Photo-electric cell, type GS47X. REFERENCES 503 1. 2. 3. 4. 5. Haslam, J.. and Squirrell, D. C. JI., Analyst, 1954, 79, 689. Bett, N., lTock, W., and Morris, G., Ibid., 1954, 79, 607. Hawes, R. C., Strickler, A, and Petterson, T. H., Elec. N j g . , 1951, 47, 76 and 212. Malmstadt, H. V., and Fett, E. R., Anal. Chew., 1954, 26, 1348. Brown, J. F., and Volume, W. F., Analyst, 1956, 81, 308. Received March 28th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300491

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Sept., 19581 TITRATION CNIT FOR PROCESS USE 503 A System for the Determination of Certain Trace Metals in Crops* BY W. D. DUFFIELD (26 Pavk Crescent, Povtland Place, Londoia, W.1) The system described has been developed to meet the need for a rapid routine evaluation of trace-element levels in crops and foodstuffs. Copper, cobalt, nickel, molybdenum and boron are determined by paper chromato- graphy. Zinc, manganese, and, in certain contingencies, molybdenum are determined colorimetrically. Is the course of a comprehensire long-term agricultural investigation, I have examined large numbers of assorted crops, fodders and pastures with a view to establishing concentration levels of trace metals and detecting significant fluctuations in these levels. Because of the number of elements of established importance to plant growth that had to be considered and the variety of samples involved, it was obvious that classical methods of separation and determination of these metals would be excessively laborious and time-consuming.A rapid method for routine use must satisfy the following criteria: (a) simplicity and rapidity of technique, ( b ) use of the minimum of apparatus, which should be unspecialised in nature and economical of bench space, and (c) suitability to the examination of large batches of samples in routine series. The methods chosen are either paper chromatographic or colorimetric, and in every instance the final determination is effected by visual comparison against standards. This technique has been found to give accuracies adequate to the scope of the system and within the limits of experimental error of the methods as a whole.DISCUSSION OF METHODS The methods available for determining boron are primarily based on distillation as methyl borate and subsequent titration of boric acid after the addition of glycerol or mannitol. * Presented a t the meeting of the Society on Wednesday, October 2nd, 1957.504 DUFFIELD A SYSTEM FOR THE DETERMINATION [Vol. 83 Alternatively, a colorimetric end-point can be achieved with curcumin. It was thought that this separation would be unsuitable for the routine examinations envisaged and that it should be avoided if possible. The possibility of a paper-chromatographic separation was considered, and the work of Lacourt, Sommereyns, Claret and W’antier was investigated.l? It was found that reproducible results were only obtained under rigidly controlled conditions of temperature and humidity, and frequent unexplained inconsistencies were encountered.The reaction of boron with curcumin was next investigated. Boron, in company with iron, molybdenum, vanadium and titanium, forms a pink colour with curcumin in faintly acid solutions. When the solution is made alkaline, however, only boron produces a blue-green complex. This reaction was utilised in developing the method described later. The term paper chromatography is loosely applied to the technique, which is, in fact, a controlled spot test and then a paper-chromatographic procedure, i.e., separation of excess of reagent from the stationary test spot.The colour produced is fugitive and must be compared with simultaneously prepared standards within 20 minutes. Copper, cobalt and nickel are determined simultaneously by paper-chromatographic separation in an ethyl methyl ketone - hydrochloric acid - water system and then colour development with rubeanic acid. These metals lend themselves readily to paper chromatography and many successful methods with ketone - acid solvents have been d e s ~ r i b e d . ~ 2 ~ 1 ~ 9 ~ The most consistent of those investigated was that of Hunt, North and Wells,6 which was adopted in toto with satisfactory results. During the investigation, it was found that zinc also was separated in this solvent system and that its presence a t R, 0.9 (approximately) could be detected by spraying with a dilute solution of dithizone in chloroform.Unfortunately, the stains produced were not quantita- tively consistent, partly owing to the extraordinary sensitivity of the reaction. The method finally adopted for the determination of zinc was colorimetric, based on the reaction of zinc with dithizone at pH 5.0 after interfering metals had been complexed with sodium thio- sulphate. Visual comparison of the “mixed-colour” zinc dithizonate was found to be satis- factory, and the use of sodium thiosulphate avoided interference, particularly by copper, in the ranges normally encountered in crops.’ In this respect, the almost invariable heavy preponderance of zinc over copper, cobalt and nickel is advantageous, since the method as applied is only valid in the presence of up to a twofold excess of copper or a tenfold excess of cobalt or nickel.Molybdenum is separated by paper chromatography in a a-butyl alcohol - hydrochloric acid - water system. Several solvent mixtures have been recommended4 ~8 and investigation led to the adoption of rt-butyl alcohol saturaled with 10 per cent. v/v hydrochloric acid, which gave the most consistent results with the materials under examination. It was also established that separation, particularly from iron, was improved on pre-conditioning the paper by suspending it in an atmosphere saturated with water vapour at room temperature. Under these conditions, molybdenum was satisfactorily separated from up to one hundred times its concentration of iron. Toluene-3 : 4-dithiol is used for colour development, a strong apple-green band being formed: amounts from 0.5 to 5.0 pg can be compared directly with standards. This is insufficiently sensitive for the amounts of molybdenum normally en- countered in crops.Sensitivity is increased by standing the papers in a-butyl acetate, which diffuses up the strips and collects the dithiol cohur into a thin concentrated line, thus permit- ting the detection of 0.005pg of molybdenum and visual colour comparison in the range When the concentration of iron exceeds that of molybdenum by more than one hundred times, an adaptation of the well known potassium thiocyanate - stannous chloride method is used with solvent extraction of the thiocyanate colour in order to concentrate it for comparison. It has been establishedg that, for optimum colour development, the concentration of hydro- chloric acid should be between 4 and 6 per cent ; the concentration of potassium thiocyanate should be not less than 0.6 per cent.The amount of stannous chloride present is not critical, and no differences have been observed in colour developed at a range between 0.05 and 1.0 per cent. Of necessity, there must be sufficient present to furnish a slight excess over what is needed to decolorise the ferric thiocyanate. Some iron must be present to ensure complete development of the molybdenum c o l x r , particularly if the molybdenum concen- tration is above 4pg. The amount of iron needed at this concentration is 0.5mg.10 If these not particularly stringent conditions are observed, excellent results can be obtained 0.02 to 0.2 pg.Sept., 19583 OF CERTAIN TRACE METALS IIY CROPS 505 in the presence of normally occurring acid radicles, such as sulphate and perchlorate, and of more than thousandfold excesses of such metals as titanium, vanadium, chromium and uranium.The technique adopted specifies extraction of the molybdenum thiocyanate complex in 1 ml of n-butyl acetate. This permits the detection of 0.1 pg of molybdenum and visual colour comparison in the range 0 to 4.0 pg in 0.2-pg stages. Manganese is determined by the familiar potassium periodate oxidation to permanganate. The statement by Koroleffll that silver nitrate enhances colour development with microgram amounts of manganese has been in the main confirmed. It was also confirmed that, at low concentrations, full colour development could only be ensured by heating for 2 hours on a water bath after the initial boiling with periodate.12 METHOD PREPARATION OF THE SAMPLE- At this temperature the alkaline nature of cereal and vegetable ashes is sufficient to prevent serious losses of the more volatile metals, such as zinc, molybdenum and boron.Triturate the ash, in the crucible, with 0.5 ml of water, and set aside for 2 hours. From the resulting solution remove 0.02 ml for the determination of bcron. To the remainder of the aqueous solution add a few millilitres of 50 per cent. hydrochloric acid, evaporate to dryness and heat on a high-temperature electric hot-plate for 30 minutes. Twice repeat this treatment with hydro- chloric acid to ensure precipitation of silica in pure white crystals.Finally, moisten the residue with 50 per cent. hydrochloric acid, and evaporate to dryness on a steam-bath. An alternative procedure consists in transferring the ash solution to a platinum crucible and removing the silica by evaporation to dryness with hydrofluoric acid. To the cooled crucible add accurately 0.5 ml or, if necessary, 1.0 ml of 50 per cent. hydrochloric acid, cover with a watch-glass, gently warm, and set aside for a few hours. CHROMATOGRAPHIC PROCEDURE- In the paper-chromatographic procedures, the papers used are Whatman No. 1 (Chemical Research Laboratory pattern). This is a slotted paper that permits the simultaneous treatment of ten separate specimens. The 0.01 or 0.02-ml aliquots are applied to the paper by means of capillary pipettes prepared in the laboratory and calibrated by weight with distilled water.These pipettes can be made and calibrated rapidly and have a reproducibility of k0.2 mg per delivery. A satisfactory pipette contains 0.01 ml in a length of 3 to 4 cm, fills to the mark by capillary action and delivers steadily and evenly on to the chromatographic strip by absorption of the liquid on to the paper. The test aliquot is applied as an even band across the whole width of the strip, about 1 6 c m from the bottom. DETERMINATION OF COPPER, COBALT AND KICKEL- Ash 10 g of finely ground sample at a temperature not exceeding 550" C. Reagents- Solvent mixture-Mix ethyl methyl ketone, concentrated hydrochloric acid and water, Ammonia solution, sp.gr. 0.880-Analytical-reagent grade.Rubeanic acid reagent solution-Dissolve 0.1 g of rubeanic acid (dithio-oxamide) in 60 ml Pyocedure- Apply 0.01 ml of the hydrochloric acid solution of the sample to the chromatographic strip as previously described. Form the paper into a cylinder by clipping together the two ends with a paper clip at the top so that the separate strips stand in the vertical plane. Dry the paper by standing it for 5 minutes in a 600-ml beaker that is floating in a 2-litre beaker of boiling water. Remove the paper and stand it with the test spot downward in 20 ml of solvent mixture contained in a 600-ml tall beaker. Cover with a watch-glass and set aside until the solvent front has diffused to the top of the strips. This should take about 30 minutes. Remove the paper, allow to dry in air for 5 minutes and stand it in a 600-ml beaker that has a 50-ml beaker of ammonia solution, sp.gr.0.880, in the centre. Cover with a clock-glass and set aside for 5 minutes to neutralise. in the volumetric ratio of 15 : 3 : 2 , respectively. of ethanol. Filter the solution, and dilute the filtrate to 100ml with water.506 DCFFIELD : A SYSTEM FOR THE DETERMINATION [Vol. 83 When the small beaker of ammonia solution is placed inside the 600-ml beaker before the introduction of the paper cylinder, take care to spill no liquid into the larger vessel, as any moisture will diffuse up the paper and distort or completely destroy the separated zones. Remove the paper and spray it on both sides with rubeanic acid reagent solution. Separate colour bands will appear, denoting nickel (purple-blue, RF about O - l ) , cobalt (yellow, RF about 0.4) and copper (olive-green, RF about 0.6).Compare these bands with similarly prepared standards covering the range 0.2 to 2.Opg. The limit of visual detection is of the order of 0.05 to 0.1 pg. In this solvent system, iron travels in the solvent front (RF 1.0) and is visible as a band of brown ferric hydroxide. On counter-spraying with a dilute solution of dithizone in chloroform, zinc is detectable as a pink band a t R, about 0.9. DETERMINATION OF ZINC- Reagents- Hydrochloric acid, 1 per cent. v / v . Bufer solution, pH 5--Mix equal volumes of 2 S sodium acetate solution and 2 AT Sodium thiosulphate solution, 25 per cent. w / v . Dithizone reagent solution-Prepare a saturated solution of dithizone in 0.05 X sodium Carbon tetrachloride-Analytical-reagent grade. Procedure- By pipette, place 0.01 ml of sample solution in 1 ml of 1 per cent. hydrochloric acid con- tained in a 10-ml stoppered test-tube.Add 1.0 ml of buffer solution, 1.0 ml of sodium thiosulphate solution and 0.2 ml of dithizone solution. Mix, add 1 ml of carbon tetrachloride, insert the stopper and shake for 1 minute. Allow to separate, withdraw the carbon tetra- chloride layer by means of a capillary pipette and suction bulb and transfer it to a narrow-bore comparison tube. Compare with similarly prepared standards covering the range 0 to 4.0 pg in 0.2-pg stages. acetic acid. hydroxide. PAPER-CHROi'iL4TOGRAPHIC DETERMISATION OF MOLYBDENUM- Reagents- Solvent mixture-Shake n-butyl alcohol with 10 per cent.v/v hydrochloric acid. Allow Dithiol reagent solution-Prepare a solution in i\' sodium hydroxide containing 0.1 per n-Butyl acetate. Procedure- Apply a 0.02-ml test band of sample solm-ion to a paper strip, and dry as previously described. Suspend the paper cylinder for 30 minutes in a closed tank saturated with water vapour a t room temperature. Place the paper with test band downwards in a 600-ml beaker containing 20 ml of solvent mixture, cover with a watch-glass and set aside until the solvent front approaches the top of the strips (1 to 14 hours). Remove the paper, dry for a few minutes a t 100" C and spray with dithiol reagent solution. Molybdenum will appear as an apple-green band at about RF 0.6. Iron can be seen as the purple thioglycollate complex at about RF 0.4.Dry the paper cylinder a t 100" C for a few minutes, and stand it in a few millimetres depth of n-butyl acetate in a covered beaker. Allow the solvent to diffuse just to the top of the original dithiol band, remove immediately and allow to dry. This con- centrates the band and permits comparison with similarly prepared standards covering the range 0 to 0.2 pg in 0.02-pg stages. COLORIMETRIC DETERMINATION OF MOLYBDEXCM- more than one hundred times. the mixture to separate and use the supernatant layer. cent. w/w of toluene-3 : 4-dithiol and 0.1 per cent. w/v of thioglycollic acid. Use this procedure when the concentration of iron exceeds that of molybdenum by Reagents- Potassium thiocyanate solution, 10 per cent.w/w. Stannous chloride solution-Prepare a solut Lon containing 40 per cent, w/v of stannous n-Butyl acetate. chloride in concentrated hydrochloric acid.Sept., 19581 OF CERTAIN TRACE METALS I N CROPS 507 Procedure- By pipette, place 0.2 ml of sample solution in a 10-ml stoppered test-tube. Add 2 ml of potassium thiocyanate solution and 0.1 ml of stannous chloride solution, and mix. Add 1 ml of n-butyl acetate, insert the stopper and shake vigorously for 1 minute. Allow the layers to separate, and withdraw the n-butyl acetate layer. (Use a capillary pipette and bulb to transfer it to a narrow-bore comparison tube,) Compare with similarly prepared standards covering the range 0 to 4.0 pg in 0.2-pg stages. Note that, in the preparation of standards, 0.5 mg of iron must be incorporated to ensure optimum development of the molybdenum colour.DETERMINATION OF BORON- Reagents- Curcumin reagent solzhon-Dissolve 0.1 g of curcumin and 5-0 g of oxalic acid in 100 ml Ethanol. Sodium hydroxide solution, 0.5 per cent. w/w-Freshly prepare this solution before use. Procedure- Lightly mark a chromatographic paper with a pencil line about 1.5 cm from the bottom of the strips to ensure that all test spots are applied at exactly the same level. Apply 0.02 ml of the aqueous extract of the ash (see “Preparation of the Sample,” p. 505) along the pencilled line, and spray with curcumin reagent solution. Dry at 100” C for 1 minute, and stand the paper immediately, test spots downwards, in a Petri dish containing a few millimetres depth of ethanol.Remove from the ethanol, and dry at 100” C for 1 minute. Place immediately in a few millimetres depth of 0.5 per cent. sodium hydroxide solution, and set aside until the purple colour developed by the excess of curcumin has been carried just clear of the stationary blue-green boron band. Compare the band with simultaneously prepared standards covering the range 0 to 2.0 pg in 0.2-pg stages. The colour is fugitive, and comparison must be made immediately. Fading is appreciable after 20 minutes. DETERMINATION OF MANGANESE- of ethanol. Allow the ethanol to diffuse just to the top of the pink test band. Reagents- All reagents should be of recognised analytical grade. Sulphuric acid, concentrated. Nitric acid, concentrated. Orthophosphoric acid.Silver nitrate. Potassium periodate. Procedure- Take 0.1 ml of sample solution in a 6-inch x 1-inch boiling-tube. Add 0.4 ml of concentrated sulphuric acid, 0.5 ml of concentrated nitric acid and 0.1 ml of orthophosphoric acid. Add 1.0 ml of water, and again heat until fumes are evolved. Cool, and add 7.0 ml of water and 0.1 g each of potassium periodate and silver nitrate. Boil for 5 minutes, and place in a boiling-water bath for 2 hours. Cool, and dilute suitably for comparison with standard potassium permanganate solutions covering the range 0 to 1OOpg of manganese in 10-pg stages. Heat until fumes are evolved. RESULTS AND CONCLUSIONS The proposed procedures were tested by means of a series of recovery experiments in which known amounts of various metallic salts were added to the hydrochloric acid solution of the ash.The results, which are shown in Table I, indicate that consistent recoveries can be obtained within the intended scope of the system. It is suggested that this analytical system serves as a rapid sorting test, whereby significant fluctuations in trace-element levels can be detected. Naturally, more accurate results can be obtained by using larger amounts of samples. The paper-chromatographic techniques for copper, cobalt, nickel, zinc and molybdenum are strongly recommended, as they afford rapid and absolute separations for amounts up508 DUFFIELD [Vol. 83 to 100 pg. At these levels, the developed chroniatograms can be cut into appropriate sections and the individual metal complexes extracted and determined by colorimetric procedures.TABLE I RECOVERY OF VARIOUS METALS FROM WHEAT, BARLEY AND OATS Wheat Barley Oats P Amount found in Total original Amount amount Element material, added, found, CLg CLg CLg Copper . . 2.4 0.4 3.0 1.6 1.0 2.5 1.5 1.5 2.8 Cobalt . . . . 0.1 0.1 0.2 0.1 0.2 0.4 0.1 0.3 0.5 Xickel . . . . 0.2 0.1 0.3 0.3 0.2 0.4 0.2 0.3 0.6 Zinc . . . . 5.0 1.0 5.8 4.5 2.0 6.4 4-0 5.0 9.4 lIolybdenum* 0.10 0.05 0.16 0.05 0.10 0.16 0.04 0.15 0.20 Molybdenumt 1.2 0.5 1.7 0.4 1.0 1.5 0.4 1.5 2.0 Boron . . . , 1.0 0.5 1.5 0.8 1.0 2.0 0.8 1.5 2.5 Amount found in Total original Amount amount material, added, found, CLg: Pg CLg 2.0 0.5 2.5 1.7 1.0 3.0 1.7 1.5 3.3 0.05 0.1 0.2 0.1 0.2 0.3 0.1 0.3 0.5 0.23 0.1 0.3 0.2 0.2 0.5 0. L 0.3 0.4 4.11 1.0 6.0 4.6 2.0 6.5 3.11 5.0 9.0 0.06 0.05 0.10 0.06 0.10 0.15 044 0.15 0.21 0.h 0.5 1.0 O.El 1.0 1-5 O*CI 1.5 2.1 0.8 0.5 1.2 0.tl 1.0 1.5 0.4 1.5 2.0 7 - 7 Amount found in Total original Amount amount material, added, found, PLg CLg Pg 1.5 0.5 1.9 1.5 1.0 2.4 1.8 1.5 3.5 0.1 0.1 0.2 0.1 0.2 0.4 0.05 0.3 0.4 0.3 0.1 0.4 0.2 0.2 0.5 0.2 0.3 0.5 4.8 1.0 6.8 4.0 2.0 6.2 3.2 5.0 8.0 0.12 0.05 0.16 0.08 0.10 0.20 0.08 0.15 0.22 1.1 0.5 1.5 0.75 1.0 1.8 0.75 1.5 2.4 0.8 0.5 1.4 0.8 1.0 1.6 0.6 1.5 2.0 Manganese ..60 10 72 50 10 59 80 10 90 45 20 65 50 20 73 75 20 90 40 30 71 30 30 60 i 0 30 102 * Determined by paper-chromatographic procedure. t Determined by colorimetric procedure. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Lacourt, A,, Sommereyns, Gh., and Claret, M., Mikrochemie, 1951, 38, 444. Lacourt, A., Sommereyns, Gh., and Wantier, G., Analyst, 1952, 77, 943. Burstall, F. H., Davies, G. R., and Wells, R. A,, Disc. Faraday SOC., 1949, 179. Burstall, F. H., Davies, G. R., Linstead, R. P., and Wells, R. A,, J . Chem. Soc., 1950, 516. Arden, T. V., Burstall, F. H., and Linstead, I?. P., Nature, 1948, 162, 691. Hunt, E. C., North, A. A,, and Wells, R. A., /!nalyst, 1955, 80, 172. Fischer, H., and Leopoldi, G., 2. anal. Chem., 1937, 107, 241. Shibata, M., and Uemura, T., J . Chem. SOC. Japan (Pure Chem. Sect.), 1951, 72, 541. Hurd, L. C., and Allen, H. O., Ind. Eng. Chem., Anal. Ed., 1935, 7, 396. Perrin, D. D., N.Z. J . Sci. Tech., 1946, 27A, 396. Koroleff, F., Acta Chem. Scand., 1947, 1, 503. Nydahl, F., Anal. Chim. Ada, 1949, 3, 144. Received January 20th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300503

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Sept., 19581 WOOD AND CLARK 509 Determination of Copper in Titanium, Zirconium and Their Alloys BY D. F. WOOD AND R. T. CLARK (Research Department, Imperial Chemical Industries L t d . , Metals Division, Kynoch Works, Witton, Birmingham, 6 ) A rapid direct absorptiometric method, based on the blue colour produced by the reaction of copper ions with biscyclohexanone oxalyldihydrazone, has been developed for the determination of copper in titanium, zirconium and their alloys. The method is suitable over the range 0.005 to about 3 per cent. of copper. In order to provide a method for determining less than about 0.005 per cent. of copper, a procedure depending on the formation of a copper - diethyl- dithiocarbamate complex has been investigated and shown to be satisfactory over the range 0.0005 to 0.01 per cent.Interference by iron and nickel is overcome by forming complexes of these metals with disodium ethylene- diaminetetra-acetate. THE amount of copper contamination in titanium, zirconium and their alloys is of metal- lurgical interest, particularly in zirconium used in pressurised-water nuclear reactors, in which only small amounts of copper, not more than about 0.005 per cent., can be tolerated because of its effect in reducing corrosion resistance to water a t high temperatures. Interest has also been shown in the effect of alloying amounts of copper in these materials. These considerations have necessitated the development of procedures for the determination of copper in the range 0.002 to about 2 per cent. in titanium, zirconium and their alloys.Absorptiometric procedures based on the use of sodium diethyldithiocarbamate,l 2 : 9-dimethyl-1 : 10-phenanthroline (neocuproine)2 and 2 : 2'-diquinolyP are used in the examination of a variety of materials and are usually applied over the range 0.002 to about 1 per cent. of copper. Both the diethyldithi~carbamate~ and neocuproine5 methods have been recommended for the determination of copper in titanium, but they involve extraction of the copper-organ0 complex with an organic solvent. More recently, details have been published of methods based on the formation of a blue complex when copper ions react with biscyclohexanone oxalyldihydrazone, a reaction first suggested by Nilsson,6 and later applied to the examination of paper,i plant materialspg and steel.1° The complex is formed in a solution controlled at about pH 9 by means of a buffer of either ammonium hydroxide and ammonium citratesJO or sodium hydroxide and sodium b ~ r a t e .~ This procedure does not involve extraction of the complex, and, in this respect, is more rapid than the earlier methods. In order to provide a simple and rapid method for determining copper over the required range in titanium, zirconium and their alloys, the biscyclohexanone oxalyldihydrazone procedure has been investigated. Colour development of the copper complex is inhibited by high salt concentration, which imposes a limitation on the amounts of acid solvent and sample that can be used in the determination; consequently, the procedure is limited to amounts of copper above about 0.005 per cent.Application of the diethyldithiocarbamate method4 to zirconium and its alloys has also been investigated, in order to provide a more accurate procedure for the determination of copper below about 0.005 per cent. EXPERIMENTAL BISC~C~OHEXANONE OXALYLDIHYDRAZONE METHOD FOR COPPER IN TITANIUM PRELIMIXARY EXPERIMENTS- Initial tests with an ammonium hydroxide - ammonium citrate buffer solution permitted conditions to be established for determining copper in the presence of major amounts of titanium only. ~ These tests confirmed that the presence of a high concentration of ammonium ions caused low resultsi; the 0.5-g sample was, therefore, dissolved in a minimum volume of acid (15 ml of diluted hydrochloric acid (2 + 1) and 1 ml of fluoroboric acid) in order to avoid the formation of an excessive amount of ammonium salts when the solution was neutralised.510 WOOD AND CLARK: DETERMINATION OF COPPER [Vol.83 Subsequent tests showed that aluminium, manganese and tin caused both low and erratic results, whereas with the alternative pro~edure,~ in which the complex was formed in a sodium hydroxide - sodium borate buffer solution, no such interferences were observed. The alterna- tive procedure was therefore further investigated; preliminary experiments were made (a) to establish the wavelength at which maximum absorption of the copper - organo complex occurs, and (b) by using this wavelength, to prepare a calibration graph. (a) Absorptiolz curve-A 0.5-g portion of hlgh-purity copper was dissolved in 25 mi of diluted nitric acid (1 + 1) and the solution was boiled for 2 or 3 minutes to expel nitrous fumes; it was then cooled, transferred to a 1-litre calibrated flask and diluted to the mark with water.1 ml = 0.01 mg of copper. To 2.0 ml of this copper nitrate solution in a 50-ml calibrated flask were added 5 ml of 10 per cent. ammonium citrate solution and then 1 drop of 0.05 per cent. neutral red indicator solution. Sodium hydroxide solution (10 per cent.) was added until the colour of the solution changed from red to yellow, and then 5 ml of a sodium borate buffer solution and 0.5 ml of 0.5 per cent. biscyclohexanone oxalyldihydrazone in ethanol - water (1 + 1) were added. The solution was diluted to the mark a,id optical-density measurements were made with a Unicam SP600 spectrophotometer in 4-cm cells at wavelengths between 5000 and 6500 A.It was confirmedlo that the wavelength at which maximum optical density occurs is (b) Calibration gra$Jh-Portions of the copper nitrate solution ranging from 0 to 4.0 ml were transferred t o 50-ml calibrated flasks and Ieagents were added in accordance with the procedure described in (a). These solutions were diluted to the mark and their optical densities were measured at 5950.4 in 4-cm cells; a linear calibration graph was obtained. Tests were then made in the presence of titanium. A 0.5-g sample of copper-free titanium was dissolved in a mixture of 15 ml of diluted hydrochloric acid (2 + 1) and 1 ml of fluoroboric acid. The solution was oxidised with a few drops of nitric acid, sp.gr.1.42, boiled to expel nitrous fumes, cooled, transferred to a 50-ml calibrated flask and diluted to the mark. Five 5-ml portions were transferred to 50-ml calibrated flasks and portions of the copper nitrate solution ranging from 0 to 4.0 ml, am- monium citrate solution and neutral red indicator solution were added as before. On addition of sodium hydroxide solution, however, titanium hydroxide was precipitated, because the amount of ammonium citrate was insufficient t o react with all the titanium. Further tests showed that about 8ml of 20 per cent. ammonium citrate solution were sufficient for this purpose, and, with this modification, a calibration graph was prepared, which was identical with that obtained in the absence of titanium. This graph is suitable for amounts of copper in the range 0.005 to 0.08 per cent.A 10-ml portion of this solution was diluted to 500 ml, so that- 5950 A. EFFECTS OF TEMPERATURE, REAGENT CONCENTRATION AND OTHER FACTORS- No significant variation in optical density OF the complex occurs over the range 18" to 24" C, and strict control of solution temperature during optical-density measurement is therefore not essential. Full colour developmeiit is achieved within about 5 minutes of adding the reagent solution, and the colour is stable for at least 3 hours. The use of different amounts of diluted hydrochloric acid (2 + 1) between 10 and 16 ml has no significant effect, but amounts between 16 and 30 ml of the acid solvent result in a sharp decrease in optical density. Different amounts of fluoroboric acid between 0.5 and 2 ml have no effect on the optical density of the complex.In the range 7.5 to 9.5 ml, the volume of 20 per cent. ammonium citrate solution has a negligible effect on the optical density, but, above this upper limit, optical density decreases with increase in ammonium citrate concentration. Below 7.5 ml, precipitation of titanium hydroxide occurs when the acid solution is neutralised. In subsequent tests 8.0 ml of 20 per cent. ammonium citrate solution were added. Amounts of 10 per cent. sodium hydroxide solution in the range 0.5 to 5 ml, added after neutralisation, have no significant effect on the optical density, but the colour of the complex develops more rapidly in the presence of 1 to 5 ml of this reagent, full colour development being achieved within about 2 minutes.Therefore, in subsequent tests, an excess of 1 ml of 10 per cent. sodium hydroxide solution was added; the pH of the solution at this stage will he nhmit Q4Sept., 19581 IN TITASICM, ZIRCONIUM AND THEIR ALLOYS 51 1 No effect on the optical density was observed when different amounts of sodium borate buffer solution between 3 and 10ml were used, and the pH of the solution remained at 9.0 i 0.05. When 2.5ml of this buffer solution are used, full colour development is not achieved (the pH of the solution was 8.8) ; 5 ml of the buffer solution were added in subsequent tests. Amounts of biscyclohexanone oxalyldihydrazone solution between 0.5 and 3 ml have no effect on the optical density. Experiments were made on solutions containing 50 mg of titanium and the equivalent of 0.005 or 0.08 per cent.of copper to determine the effect of common alloying constituents and likely impurities. It was established that no interference is caused by the presence of at least 20 per cent. of manganese or tin, 10 per cent. of aluminium or 5 per cent. of chromium, iron, nickel or molybdenum. Vanadium above 2.5 per cent. causes a decrease in optical density and the presence of 10 per cent. of vanadium completely inhibits colour development. Interference of vanadium up to about 5 per cent. can be overcome by taking a smaller aliquot of the sample solution, so that the amount of vanadium in the final solution does not exceed 1.25 mg. DETERMISATION OF LARGER AMOUNTS OF COPPER- Tests showed that, by using a smaller sample weight and smaller cells, or smaller cells only, the procedure can be extended to the determination of up to about 3 per cent.of copper. BISCYC~OHEXANONE OXALYLDIHYDRAZONE METHOD FOR COPPER IN ZIRCONIUM Calibration graphs covering the ranges 0.005 to 0.08 per cent., 0.02 to 0.32 per cent. and 0.2 to 3.2 per cent. of copper prepared in the presence of copper-free zirconium are identical with those prepared in the presence of titanium. Effects of temperature, acidity, concentration of reagents and stability of the complex were studied in the presence of zirconium, and results agree with those from similar experiments relating to the determination of copper in titanium. Effects of common alloying constituents and likely impurities were also investigated on solutions containing 50 mg of zirconium and the equivalent of 0.005 or 0.08 per cent.of copper. It was established that up to at least 30 per cent. of tin or 5 per cent. of magnesium, chromium, iron, nickel or molybdenum do not interfere. Vanadium above 2.8 per cent. causes low results, but interference up to 5 per cent. can be overcome by taking a smaller aliquot of the test solution. TABLE I DETERMIXATIOK OF COPPER I N TITASIUM ALLOYS, ZIRCONIUM AND ZIRCALOY 2 Kominal composition Copper Standard added, Coppw found, deviation, % "A % Titanium +- 5 per cent. of aluminium + 2.5 per cent. of tin (317 alloy)* . . .. . , 0.010 0.011 - cent. of tin (371 alloy)* . . . . . . 0.010 0.010 - cent. of manganese (314-1 alloy)* . . . . 0.010 0.010 - 0.080 0.080 Titanium -?; 2.5 per cent.of aluminium + 13 per 0.080 0.080 Titanium $- 4 per cent. of aluminium + 4 per 0.080 0.052 Zirconium + 1.5 per cent. of tin + 0.12 per cent. of iron + 0.1 per cent. of chromium + 0.05 per cent. of nickel (Zircaloy 2)" . . .. 0.010 0.010 - 0.080 0.080 Titanium 317 alloy? .. . . .. , . Nil 0.0178, 0.0180, 0.0182, +0.0002 0.0182, 0.0178, 0,0178 0.0156, 0.0154, 0.0154 Zirconium? . . .. .. .. . . . . Xi1 0.0152, 0.0154, 0.0152, - * Presence of copper compensated for by using an equivalent amount of sample in the t Sample taken from experimental ingot. compensating cell. APPLICATION OF THE BISCYClOHEXANONE OXALYLDIHYDRAZOXE METHOD The results were satisfactory when the recommended method was applied to solutions of titanium alloys and Zircaloy 2 to which the equivalent of 0.01 and 0.08 per cent.of copper512 WOOD AiVD CLARK: DETERMINATION OF COPPER [Vol. 83 had been added. Samples of titanium 317 alloy and zirconium were also examined, and, as shown in Table I, the results were reproducible, the standard deviation at the 0.02 per cent. level being +0.0002 per cent. SODIUM DIETHYLDITHIOCARBAMATE METHOD FOR COPPER I N ZIRCONIUM The diethyldithiocarbamate procedure as applied to the determination of copper in titanium4 was used as a basis for investigation In this procedure, sulphuric acid is used as the solvent, but, as this acid does not readily dissolve zirconium, a mixed sulphuric acid - fluoroboric acid solvent was used in the experiments described. PRELIMINARY EXPERIMENTS- Preliminary experiments were made (a) to establish the wavelength at which maximum absorption of the copper - organo complex occurs and (b) by using this wavelength, to prepare a calibration graph.(a) Absorption curve-A 0.5-g portion of copper-free zirconium was dissolved in a mixture of 25 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; a few drops of nitric acid, sp.gr. 1.42, were added and the solution was boiled to expel nitrous fumes. To the cooled solution, 5 ml of copper nitrate solution (1 ml E 0.01 mg of copper) and 5 ml of 60 per cent. citric acid solution were added. Ammonium hydroxide, spgr. 0.940, was added until the solution was neutral to litmus paper; an excess of 2 ml of ammonium hydroxide was then added. Ten millilitres of 0-1 per cent.sodium diethyldithiocarbamate solution were added, the solution was transferred to a separating funnel and the complex was extracted with two 10-ml portions of chloroform. The combined extracts were diluted to the mark in a 50-ml calibrated flask containing about 1 g of anhydrous sodium sulphate. The optical density of the solution was measured with a Unicam SP600 spectrophotometer in 4-cm cells at wavelengths between 4000 and 4 8 0 0 ~ . The wavelength of maximum absorption was found to be 4 4 0 0 ~ . (b) Calibration graph-Solutions containing 0.5 g of copper-free zirconium and amounts of copper nitrate solution (1 ml = 0.01 mg of copper) ranging from 0 to 5.0 ml were prepared and reagents were added as described in (a). The optical densities were measured at 4400 A in 4-cm cells and a linear calibration graph suitable for determining copper in the range 0.0005 to 0.01 per cent.was obtained. EFFECTS OF TEMPERATURE, REAGEKT CONCENTRATION AXD OTHER FACTORS- Tests with separate 10-ml portions of chloroform showed that about 75 per cent. of the copper - organo complex is extracted in the first 10 ml, about 23 per cent. in the second and about 2 per cent. in the third; the aqueous and organic layers were shaken for 1 minute before each separation. In further experiments, therefore, the complex was extracted with three separate 10-ml portions of chloroform, which were subsequently combined. No significant variation in optical density of the complex occurred over the range 18” to 24” C, and strict control of solution temperature during measurement of optical density is therefore not essential.Sandelll states that “exposure to light, of solutions of copper diethyldithiocarbamate in carbon tetrachloride or isoamyl acetate, causes fading,” but experiments in our laboratories showed that the complex in chloroform is stabk for at least 2 hours in diffused daylight. Increase in the amount of 60 per cent. citric acid solution over the range 2 to 10ml has no significant effect on the optical density of the complex; 1 ml, however, is insufficient to react with all the zirconium, and, on addition of ammonium hydroxide, a faint cloudiness appears owing to precipitation of zirconium hydroxide. Different amounts of ammonium hydroxide, sp.gr. 0.940, in the range 0 to 3 ml, added after neutralisation, have no significant effect on the optical density, but, above 3 ml, optical density decreases with increase in ammonium hydroxide concentration, and this is attributed to incomplete extraction of the complex.More than 0.5 per cent. of iron and 0.005 per cent. of nickel cause high and erratic results. According to Sedivec and Vasak,ll the addition of disodium ethylenediaminetetra-acetate (EDTA) solution overcomes interference by iron tiid nickel, and tests showed that interferencr by nickel up to 0.5 per cent. and iron up to 2.5 per cent. can be overcome by adding 5 ml of 0.75 per cent. EDTA solution before neutralisation. ilddition of this amount of the reagent was therefore made in all subsequent tests, and it was established that up to at leastSept., 19581 I N TITANIUM, ZIRCOSIUM AND THEIR ALLOYS 513 20 per cent.of tin or molybdenum, 10 per cent. of aluminium or 5 per cent. of magnesium, chromium or vanadium do not interfere. Manganese above 0.25 cent. interferes by forming a pink colour in the organic layer. This interference can be overcome,l up to at least 20 per cent. of manganese, by extracting both the copper complex and manganese in chloroform, returning the combined extracts to a separating funnel and shaking for about 10 minutes with dilute ammonium hydroxide solution (1 + 10). Manganese hydroxide is precipitated in the aqueous layer and the copper - organo complex remains unchanged in the chloroform. EFFECT OF EDTA CONCENTRATION- Addition of 0.75 per cent. EDTA solution over the range 2.5 to 10.0ml to solutions containing 0.5 g of zirconium and the equivalent of 0.008 per cent.of copper had no effect on the optical density of the copper complex, but similar tests in the absence of zirconium gave low results, as shown in Table 11. These tests indicate that EDTA solution, in excess of that required to react with interfering elements, inhibits colour development, but this excess of EDTA forms a stable zirconium - EDTA complex and hence does not interfere. TABLE I1 EFFECT OF EDTA CONCENTRATION Zirconium present, EDTA solution added, Copper added, Copper found, g ml % % Xi1 0.5 Nil 0.5 Nil 0.5 Nil 0.5 2.5 2.5 5.0 5.0 7.5 10.0 10.0 c - i ’ D 0.0080 0.0080 0.0080 0.0080 0.0080 0*0080 0.0080 0.0080 0.0075 0.0080 0.0074 0.0080 0.0075 0.0079 0.0076 0.0081 APPLICATION OF THE SODICM DIETHYLDITHIOCARBAMATE METHOD The recommended method was applied to samples of commercially pure zirconium and Zircaloy 2 ; as shown in Table 111, the results were satisfactory, the standard deviation at the 0.005 per cent.level being +O.OOOl per cent. This method differs from that published for the examination of titanium4 in that the sample is dissolved in a mixture of sulphuric and fluoroboric acids and EDTA is added. A calibration graph prepared from solutions containing 0.5 g of copper-free titanium and copper over the range 0.0005 to 0-01 per cent. was identical with that obtained in tests with zirconium solutions. Further tests confirmed that the effects of reagents and other metals were the same as those from similar experiments relating to the determination of copper in zirconium.TABLE I11 QETERMINATION OF COPPER IN COMMERCIALLY PURE ZIRCONI~~M AND ZIRCALOY 2 Sample Xo. Copper found, % 1 0.0052, 0.0052, 0.0054 0.0031, 0.0033, 0.0032 0.0020, 0.0020, 0*0020 0.0055, 0.0057, 0.0056, 0.0056, 0.0057, 0.0058 Zirconium . . ..{ ; 4% 1 0.0041, 0.0041, 0.0040 -{ 2 0.0035, 0.0035, 0.0033 Zircaloy 2 . . * Standard deviation jO*OOOl per cent. METHODS BISCYC~OHEXAXONE OXALYLDIHYDRAZONE METHOD REAGENTS- sp.gr. 1.18, and mix well. Hydrochloric acid, diluted ( 2 + 1)-To 100 ml of water, add 200 ml of hydrochloric acid514 WOOD AND CLARK: DETERMINATIOY OF COPPER TVol. 83 Fluoroboric acid-To 280 ml of hydrofluoric acid maintained a t 10" C add, in small Nitric acid, spgr. 1.42. Ammonium citrate solution, 20 per cent.-Dissolve 50 g of ammonium citrate in about Neutral red indicator solution, 0.05 per cent.---Dissolve 0.5 g of the reagent in about 50 ml Sodium hydroxide solution, 10 per cent.-Dissolve 25 g of sodium hydroxide in 150 ml Sodium borate buffer solution-Dissolve 15.46 g of boric acid in 250ml of water and Dissolve 2.0 g of sodium hydroxide in 75 ml of water and amounts, 130 g of boric acid.Store in a polythene bottle. 100 ml of water and dilute to 250 ml. of water and dilute to 100 ml. of water and dilute to 250ml. dilute to 500 ml (solution A). dilute to 100ml (solution B). in 50 ml of ethanol - water mixture (1 + 1). acid (1 + l), boil for 2 or 3 minutes to expel nitrous fumes, cool, and dilute to 1 litre. 10ml of this solution to 500ml. To 400 ml of solution A , add 60 ml of solution B, and mix well.Biscyclohexanone oxalyldihydrazone solution, 0.5 per cent.-Dissolve 0-25 g of the reagent Standard copper solution-Dissolve 0.5 g of high-purity copper in 25 ml of diluted nitric Dilute 1 ml = 0.01 mg of copper. PREPARATION OF CALIBRATION GRAPHS- Graph 1 : For copper contents between 0.005 and 0.08 per cent.-Add, separately, 0.5, 1.0, 2.0, 3.0 and 4.0ml of the standard copper solution to each of five 50-ml calibrated flasks. Proceed with each solution and a blank as follows Add 8.0 ml of ammonium citrate solution, 1 drop of neutral red indicator solution, and then shake. Continue to shake, add sodium hydroxide solution slowly from a burette until the indicator changes from red to yellow, and then add an excess of 1 ml of sodium hydroxide solution.Add 5 ml of sodium borate buffer solution and 1 ml of biscyclohexanone oxalyldihydrazone solution, and then dilute to the mark. Measure the optical density at 20" C at a wavelength of 5950 A in 4-cm cells. Graph 2: For copper contents between 0.08 and 0.32 per cent., and 0.32 and 3.2 per cent.- Proceed as described for the preparation of graph 1, but make the following modifications- (i) Use 2.0, 4.0, 8.0, 12.0 and 16.0 ml of standard copper solution. (ii) Measure the optical density in 1-cm cells. Take the appropriate weight of sample, as follows- PROCEDVRE- Copper contents, yo . . . . 0.005 to 0.08 0.08 to 0.32 0.32 to 3.2 Sample weight, g . . . . 0.5 0.5 0.1 Dissolve the sample in 15 ml of diluted hydrochloric acid ( 2 + 1) and 1 ml of fluoroboric Oxidise with a slight excess of nitric acid, sp.gr.1.42, Cool, transfer (For copper in the range 0.32 t o 3.2 per Transfer a 5-ml portion (see Note) to a 5o-rfil calibrated flask, add 8.0 ml of ammonium Calculate the copper content of the sample from the appropriate calibration graph, by vanadium (up to the equivalent of 5 per cent ) can be overcome by taking a 2-ml portion. acid; warm gently to assist dissolution. added dropwise, and then boil for 2 or 3 minutes to expel nitrous fumes. t o a 50-ml calibrated flask and dilute to the mark. cent., use a 100-ml calibrated flask.) citrate solution and continue as described for the preparation of graph 1 or 2. SoTE-vanadium above 1% mg (equivalent ';o 2.5 per cent ) causes low results Interference SODIUM DIETHYLDITHIOCARBAMATE METHOD REAGENTS- 1.84, mix well and cool.Sulphuric acid, dilute (1 + 4)-To 400 ml oi water, add 100 ml of sulphuric acid, sp.gr. Fluoroboric acid-Prepare as described previously. Nitric acid, sp.gr. 1-42. Ammonium hydroxide, sp.gr. 0.940.Sept., 19581 I N TITANIUM, ZIRCONIUM AND THEIR ALLOYS 515 Citric acid solution, 60 per cent.-Dissolve 60 g of citric acid in about 80 ml of water and dilute to 100ml. EDTA solution, 0.75 per cent.-Dissolve 3.75 g of crystalline disodium ethylenediamine- tetra-acetate dihydrate in water and dilute to 500 ml. Sodium diethytyldithiocarbamate solution, 0.1 per cent.-Dissolve 0.1 g of the reagent in about 50 ml of water and dilute to 100 ml. Standard copper solution-Prepare as described previously.PREPARATION OF CALIBRATION GRAPH FOR COPPER CONTENTS BETWEEN 0.0005 AND 0.01 PER Transfer 0.5-g portions of zirconium (or titanium) refined by the iodide process to each of six beakers and dissolve in 25-ml portions of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; warm gently to assist dissolution. Oxidise with a slight excess of nitric acid, spgr. 1.42, and boil for 2 or 3 minutes to expel nitrous fumes. Cool, and add, separately, 1.0, 2.0, 3.0, 4.0 and 5.0 ml of the standard copper solution; use the remaining solution as a blank. Add 5 ml of citric acid solution, 5 ml of EDTA solution and ammonium hydroxide, spgr. 0.940, from a burette until the solution is neutral to litmus paper. Cool, add an excess of 2 ml of ammonium hydroxide and 10 ml of sodium diethyldithiocarbamate solution Transfer the solution to a 100-ml separating funnel, add 10 ml of chloroform, shake for about 1 minute and then allow the two layers t o separate.Remove the lower chloroform layer, which contains the copper complex, to a 50-ml calibrated flask containing about 1 g of anhydrous sodium sulphate. Extract with two further 10-ml portions of chloroform, combine the extracts and dilute to the mark with chloroform. Xeasure the optical density at 20” C at a wavelength of 4400 A in 4-cm cells. PROCEDURE- Dissolve 0.5 g of sample in 25 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; warm gently to assist dissolution. Oxidise with a slight excess of nitric acid, sp.gr. 1.42, and boil for 2 or 3 minutes to expel nitrous fumes.Cool, add 5 ml of citric acid solution (see Note) and continue as described for the preparation of the calibration graph. CENT.- Proceed with each solution as follows. Read the copper content of the sample from the calibration graph. XoTE-when manganese is present above 0.25 per cent., return the combined chloroform extracts to a separating funnel, add 50ml of dilute ammonium hydroxide (1 + lo), and shake for about 10 minutes. Remove the lower chloroform layer containing the copper - organo complex and continue as described for the calibration graph. CONCLUSIONS The direct absorptiometric method with biscyclohexanone oxalyldihydrazone is suitable for determining 0.005 to about 3 per cent. of copper in titanium, zirconium and many of their alloys.Vanadium above about 2.5 per cent. causes low results, but this interference (up to about 5 per cent.) can be overcome by taking a smaller aliquot of the sample solution. The procedure is simple, rapid and particularly suitable for control analysis. About 30 deter- minations can be made in 8 hours by one analyst. The standard deviation at the 0.02 per cent. level is about +0.0002 per cent. The sodium diethyldithiocarbamate method is suitable for the determination of copper in the range 0.0005 to 0.01 per cent. in titanium, zirconium and many of their alloys. This procedure can be extended to the determination of larger amounts of copper by using a smaller sample weight, but it is recommended primarily for amounts of copper below about 0-01 per cent. Interference by nickel up to 0.5 per cent. or iron up to 2.5 per cent. is overcome by forming complexes of these metals with EDTA. We thank Mr. W. T. Elwell, Division Chief Analyst, for helpful suggestions and assistance in the preparation of this paper. REFERENCES 1. 2. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience Crawley, R. H. A., Anal. Chim. A d a , 1955, 13, 373. Publishers Inc., New York and London, 1950, Volume 111, p. 304.516 POLLOCK: A PHOTOMETRIC METHOD FOR [Vol. 83 3. 4. 5. 6. 7. 8. 9. 10. 11. Elwell, \V. T., Analyst, 1955, 80, 508. “The Analysis of Titanium and its Alloys,” Imperial Chemical Industries Ltd., First Edition, Frank, A. J., Goulston, A. B., and Deacutis, A. A., Anal. Chem., 1957, 29, 750. Nilsson, G., Acta Chem. Scand., 1950, 4, 205. Wetlesen, C., and Gran, G., Svensk Papperstitlning, 1952, 55, 212. Xf’illiams, T. R.. and Morgan, R. R. T., Chem. 6- I n d . , 1954, 461. Somers, E., and Garroway, J. L., Ibid., 1957, 395. Haywood, L. J. A., and Sutcliffe, P., Analyst, 1956, 81, 651. Sedivec, V., and Vasak, V., Coll. Czech. Chem. Comm., 1950, 15, 260. London, 1956. Received March 7th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300509

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

516 POLLOCK: A PHOTOMETRIC METHOD FOR [Vol. 83 A Photometric Method for the Determination of Tungsten in Low-grade Mine Ore and Mineral-dressing Products BY J. B. PClLLOCK (The Geological Survey of Uganda, P.0. Box No. 9, Entebbe, Uganda) The sample is treated with hydrofluoric acid to remove silica and fused with sodium carbonate, the resulting melt being extracted with water. The solution thus obtained is made up to a known volume and filtered, without washing the precipitate. An appropriate aliquot is acidified to an exact pH, rhodamine B solution is added and the optical density is measured a t 6000 A. THE formation of a coloured complex between rhodamine B and tungsten in dilute acid solution was described by Eegriwel as a qualitative test for tungsten. De Boer,2 and later H e ~ n e , ~ made use of the reaction to determine amounts of tungsten of the order of 0.1 mg, comparison between sample and standard being made visually.The procedure was simple, but the accuracy was low. The photometric method described can be applied directly to samples with a tungsten content in the range 0.2 to 1.0 per cent. of tungstic oxide, and, by adjustment of the initial sample weight and size of aliquot, or both, the range 0.05 to 5 per cent. of tungstic oxide can be covered. The accuracy compares well with that of other methods. No extractions are required, in contrast to other recent applications of rhodamine B,4~6~8 and interference was negligible when low-grade Uganda tungsten ores and the mineral-dressing products derived therefrom were analysed. EXPERIMENTAL OPTIMUM WAVELENGTH FOR MEASURING TUNGSTEN - RHODAMINE B COMPLEX- Curve A, Fig.1, shows that the maximum optical density of the tungsten - rhodamine B complex occurs at 5975 A. Instrument response is, however, rather sluggish at this wave- length and since, in addition, the inevitable presence of aluminium causes a definite smoothing of the peak, as can be seen from curve B, Fig. 1, measurements are made at 6000 A. OPTICAL DENSITY OF TUNGSTEN - RHODAMINE B COMPLEX- factors- The optical density of the tungsten - rhodamme B complex is controlled by the following (i) the pH of the acidified sodium tungstate solution when rhodamine B solution (ii) the time of standing after adding rhodamine B solution, and (iii) the time of standing after adding gum arabic solution and diluting to 100ml.Acidity of the sodium tungstate solution-Fig. 2 shows the influence of the pH of the acidified sodium tungstate solution on the optical density of the tungsten - rhodamine B complex. The optical density is almost constant between pH 1.65 and 1.70, and, as solutions are more easily adjusted to pH 1.65, this value is used in practice. It can be seen that, although aluminium causes interference throughout the entire pH range, it does not alter the optimum pH. is added,Sept., 19581 THE DETERMINATION OF TUNGSTEN 517 Time of standing after addition of rhodamine B solution-The time of standing after rhodamine B solution has been added is critical and must be kept constant to within 3 or 4 minutes in order to ensure reproducible results. One hour has been chosen, after experiment, as this represents a reasonable compromise between incomplete development of the tungsten - rhodamine B complex, resulting from too short a time of standing, and precipitation of the complex after too long standing.If gum arabic solution is not added, precipitation of the tungsten complex will commence about 14 to 2 hours after the rhodamine B solution has been added. t I 0 . 4 L - L u - u A 5925 5975 6025 6075 Wavelength, A Fig. 1. Absorption spectra of tung- sten - rhodamine B complex: curve A, tungsten equivalent to 0.5 per cent. of tungstic oxide in a 0.5-g sample; curve B, as for curve A plus aluminium equivalent to 17 per cent. of aluminium oxide in a 0.5-g sample t o + ~ ~ I I b O I ~o I 1.50 I pH before adding rhodamine B Fig.2. Effect of the pH of the sodium tungstate solution on the optical density of the tungsten - rhodamine B complex: curve A, tungsten equivalent to 0.5 per cent. of tungstic oxide in a 0.5-g sample; curve B, as for curve A plus alu- minium equivalent to 17 per cent. of aluminium oxide in a 0.5-g sample Time of standing after addition of gum arabic solution-Although gum arabic tends to retard further development of the tungsten complex, the optical density increases slowly for some days after make up is complete. For practical purposes, however, solutions can be regarded as stable after standing for 3 hours. Curve B, Fig. 3, shows a typical calibration graph prepared by the procedure described on p. 519, the optical densities being measured after 3 hours; curve A represents the same solutions 24 hours later.It can be seen that hour to hour stability is attained after 3 hours and a delay of 1 or 2 hours when measuring the optical densities will not materially affect the result. The optical densities can even be measured after only 30 minutes' standing, for example, to counteract interference by tin or to obtain results urgently required, but, in such circum- stances, a special calibration graph should be constructed. If time or circumstances do not permit the construction of a special graph, standard solutions in duplicate, containing the equivalent of, say, 0.5 per cent. of tungstic oxide, may be analysed together with the samples, and the results can then be corrected by means of the values found for these standard solutions. U S E OF OTHER ACIDS- Hydrochloric acid may be replaced by sulphuric acid or hydrobromic acid for acidifying the sodium tungstate and blank solutions.Curves B and A, Fig. 4, are calibration graphs for the range 0.1 to 0.5 per cent. of tungstic oxide, obtained by using sulphuric and hydro- bromic acids, respectively. By comparison with curve C, which is a calibration graph for the same range obtained by using hydrochloric acid, it can be seen that sulphuric and hydro- bromic acids give higher optical densities. Measurements at the lower ends of the curves are also more likely to yield accurate results than when hydrochloric acid is used. Unfortunately, when either sulphuric or hydrobromic acid is used to acidify the sample aliquot, traces of tin cause considerable negative interference.More than a trace of tin results in complete suppression of the tungsten - rhodamine B complex. Therefore, unless tin is known to be wholly absent from the sample, only hydrochloric acid can be used for518 POLLOCK: A PHOTOMETRIC METHOD FOR [Vol. 83 acidification, the procedure described under "Volume of aliquot," p. 520, being adopted for samples containing 0.05 to 0.2 per cent. of tungstic oxide. '0 0.4 0.8 1.2 Tungstic oxide in a 0.5-g sample, % Fig. 3. Calibration curves for tungsten: curve A, optical densities measured after 27 hours; curve B, optical den- sities measured after 3 hours - 1.2- - 1.0- - x .- 2 0.8- 0 -0 - - m : O ' T 0.2 OO Tungstic oxide in a 0.5-g sample, yo Fig. 4. Calibration curves for tungstenwithdifferent acids being used for acidifying the sodium tungstate and blank solutions: curve A, hydro- bromic acid ; curve B, sulphuric acid ; curve C, hydrochloric acid O'\ METHOD REAGENTS- Standard sodium tungstate solution-Weigh 0.1778 g of hydrated sodium tungstate, Na2W0,.2H20, into a 600-ml beaker and dissolve in 200 to 300ml of water. Transfer to a 1-litre calibrated flask, wash the beaker three times, add 40 g of sodium carbonate dissolved in about 500 ml of water and dilute to the mark.Standard sodium aluminate solution-Weigh 0.6250 g of aluminium oxide into a 35-ml platinum crucible, add 10 g of anhydrous sodium carbonate and fuse for 3 hours. When cold, place the crucible and lid in a 600-ml beaker, add 200 ml of water and warm on a hot-plate until dissolution of the melt is complete. Transfer to a 250-ml calibrated flask, wash the crucible, lid and beaker three times each, add the washings to the flask, cool, and dilute to the mark.Filter the solution through a dry 15-cm Whatman No. 541 filter-paper into a bottle fitted with a ground-glass stopper. Use the first 10 ml or so of filtrate to rinse the bottle. If after 21 or 3 weeks an insoluble precipitate forms, discard the solution. If alumina purchased from chemical suppliers proves to be refractory, a suitable grade can be prepared by precipitation with ammonia from slightly acidified aluminium chloride solution. Before precipitation is commenced, add a generous amount of filter-paper pulp. This is best prepared by shaking torn-up Whatman No.41 filter-papers with water in a closed jar or bottle, an electric shaking machine being used. Wash the precipitated alu- minium hydroxide thoroughly with boiling 5 per cent. w/v ammonium nitrate solution and ignite cautiously in an electric furnace at a temperature of 700" C. High-temperature ignition will result in a refractory product. Sodium carbonate solution, 4 $er cent. w/v--Prepare from anhydrous sodium carbonate and store the solution in a polythene bottle. Do not wash the precipitate.Sept., 19581 THE DETERMINATION OF TUNGSTEN 519 Hydrochloric acid solution, 20 per cent. v/w. Rhodamine B solution-Weigh 0.2 g of rhodamine B into a 1600-ml beaker. Add 950 ml of water and stir with an electric stirrer for 1 hour. Transfer to a 1-litre calibrated flask, wash the beaker three times, add the washings to the flask and dilute to the mark.Filter the solution through a 9-cm No. 4 sintered-glass Buchner funnel and use the first few millilitres of filtrate to rinse the receiving flask. Prepare several litres a t one time and mix thoroughly together. The solution can be stored for several weeks, for preference in a dark bottle fitted with a ground-glass stopper. Gum arabic solution-Weigh 1 g of gum arabic into a 250-ml beaker, add 100 ml of boiling water, and immerse in a boiling-water bath until dissolution is complete. Filter the solution through a 15-cm Whatman No. 541 filter-paper and store in a covered beaker or stoppered bottle. PROCEDURE FOR PREPARING CALIBRATIOS GRAPH- To each of six 250-ml beakers add, from a 50-ml burette, a volume of sodium aluminate solution that corresponds to the average known or expected alumina content of the samples to be analysed, eg., if the average alumina content is expected to be 10 per cent., add 5 ml of sodium aluminate solution, if 20 per cent.add 10 ml and so on (see “Volume of aliquot,” p. 520). If the alumina content is completely unknown, assume it to be 17 per cent. and add 8 5 m l of sodium aluminate solution. Mark the beakers as containing blank solution, 0.2, 0.4, 0.6, 0.8 and 1.0 per cent. of tungstic oxide, respectively. To the blank solution add, from a 100-ml burette, 16.5ml of 4 per cent. sodium carbonate solution. Into the remaining beakers run 2, 4, 6, 8 and 10-ml portions of standard sodium tungstate solution from a burette of accuracy equivalent to SPL grade A, and then sufficient 4 per cent. sodium carbonate solution to make the total volume in each beaker up to 25 ml.Calibrate the instrument with buffer solution a t pH 4.0. Acidify the blank solution with 20 per cent. v/v hydrochloric acid, using a 3-ml Ostwald - Folin pipette fitted with a rubber bulb, until the aluminium hydroxide, which is a t first precipitated, just re-dissolves and the solution is clear. The sodium aluminate solution added when preparing solutions for the calibration graph, in addition to balancing the alumina in the sample solutions, serves to indicate when an approximate pH of 3 to 4 has been reached and greatly facilitates this stage of the procedure. Immerse the electrodes of the pH meter and, by careful dropwise addition of dilute hydrochloric acid, adjust the pH to 1.65.Remove and wash the electrodes so that the wash water runs into the beaker, and then carefully dry them with filter-paper. Check the calibration of the instrument with pH 4.0 buffer solution and re-set if necessary. Acidify and adjust each of the remaining solutions in turn, completing the whole operation on one solution before proceeding to the next. Check the calibration of the pH meter after the first two solutions and again after the fifth, or otherwise as experience dictates. Exact adjustment of pH is essential to the method, since the pH of the acidified tungsten solution controls the optical density of the complex formed when rhodamine B solution is added, hence the emphasis on careful calibration of the pH meter.Xote that adjustment of the pH of the tungsten solutions must be made only by adding acid; if the correct pH is accidentally passed, it is useless to attempt to restore the status quo by adding sodium carbonate or other alkaline solutions; the state of the tungsten has been fixed unalterably and the standard tungsten solution or sample aliquot must be discarded and the procedure repeated with a fresh solution. When all solutions have been adjusted to pH 1-85, add to each, by pipette, 25ml of rhodamine B solution. Keep the solution in motion while the rhodamine B solution is added, to ensure proper mixing. Set the solutions aside for exactly 1 hour after the last has been treated with rhodamine B solution and then add 5 ml of gum arabic solution to each beaker.Great precision in measuring the volume of gum arabic solution is not critical; a 5-ml Ostwald - Folin pipette fitted with a rubber bulb may conveniently be used. Note, however, that the gum arabic solution must be added before the solutions are diluted in any way; failure to observe this point will result in partial precipitation of the tungsten complex. After adding gum arabic solution, transfer each solution to a 100-ml calibrated flask, rinse each beaker three times, add the washings to the flask, make up to the mark, shake thoroughly and loosen the stopper to allow escape of carbon dioxide. Set the solutions aside for 3 hours and then measure the optical densities in 4-cm cells against the blank solution Do not wash the precipitate.Discard the solution after 4 days. Set up a reliable pH meter of sensitivity not less than 0.05 units of pH. Swirl the beaker to assist evolution of carbon dioxide and wash down the sides.520 POLLOCK: A PHOTOMETRIC METHOD FOR [Vol. 83 at 6 0 0 0 ~ . Construct a calibration graph of optical density against tungsten content, the solutions representing, respectively, 0.2, 0.4, 0.6, 0.8 and 1.0 per cent. of tungstic oxide. PROCEDURE FOR BREAKING DOWN SAMPLES- Weigh exactly 0.5000 g of sample into a 35-ml platinum crucible, add 5 to 10 ml of hydro- fluoric acid and 4 drops of 50 per cent. v/v sulphuric acid and evaporate to dryness on a sand-bath, care being taken not to lose any sample by heating too rapidly. Repeat the addition of hydrofluoric acid and subsequent evaporation twice. Cover the crucible with a platinum lid and ignite, gently at first then more strongly, until red heat is attained, at which stage remove the lid to facilitate expulsion of the last traces of silicon tetrafluoride and sulphur trioxide. Allow to cool and grind up the residue with a smoothly rounded glass rod, a sheet of paper being first placed under the crucible to collect any particles that may jump out during this or the next stage.Add a weighed 4-g portion of anhydrous sodium carbonate, mix thoroughly with the same glass rod, which should finally be dusted with a camel-hair brush. Cover the crucible with the lid used during ignition, and fuse over a Meker burner at full heat for 2 to 3 hours. Allow to cool, place the crucible and lid in a 250-ml beaker and add 50 to 60 ml of water.Heat on a sand-bath or hot-plate at low heat until dissolution is complete, remove and wash the crucible and lid, the former being well scrubbed with a rubber-tipped glass rod. Transfer the solution to a 100-ml calibrated flask, cool, and make up to the mark. Filter through a dry 11-cm Whatman No. 540 filter-paper into a flask or bottle fitted with a ground- glass stopper. Use the first 10ml of filtrate t o rinse the container. PROCEDURE FOR DETERMINING TUNGSTIC OXIDE IN THE RANGE 0.2 TO 1.0 PER CEKT.- Take as many 250-ml beakers as are required for the samples to be analysed, plus one for the blank solution. To the last-named add sodium aluminate solution equivalent to the expected average alumina content of the samples; if this is unknown, add 8.5 ml of sodium aluminate solution, equivalent to 17 per cent.of alumina. Add sufficient 4 per cent. sodium carbonate solution to make the total volume 215 ml. In each of the sample beakers, place, by pipette, 25ml of sample solution. Adjust each solution in turn to pH 1.65, starting with the blank solution, by following the procedure described for preparing the calibration graph. Check the calibration of the pH meter with pH 4.0 buffer solution after adjusting the blank solution, and thereafter as frequently as experience has shown to be necessary. By pipette, place 25 ml of rhodamine B solution in each beaker, set aside for exactly 1 hour, and then add to each 5ml of gum arabic solution. Transfer each solution to a 100-ml calibrated flask, wash the beaker three times, make up to the mark, shake thoroughly, and loosen the stopper to permit escape of carbon dioxide.Set the solutions aside for 3 hours and then measure the optical densities in 4-cm cells against the blank solution at 6000 A ; read the tungstic oxide content from the calibration graph. Volume of aliquot-If the tungstic oxide Icontent is in the range 1.0 to 5.0 per cent., the sample can be analysed by taking an appropriately smaller aliquot. It may be necessary to add sodium aluminate solution to bring the alumina concentration of the sample solution into line with that of the solutions used to prepare the calibration graph, and the total volume before acidification must be made up to 25ml with sodium carbonate solution.If the tungstic oxide content lies in the range 0.05 to 0.2 per cent., either an initial sample of 1.0000 g can be taken or an aliquot of up to 50 ml can be used; both these courses may be followed if necessary. In either event it may be necessary to prepare a separate calibration graph to allow for the higher alumina concentration. INTERFERING ELEMENTS Table I shows the compositions of four typical low-grade Uganda tungsten ores, in which molybdenum and tin were not detected. It can be seen that many of the elements and anions stated by Eegriwel to form com- plexes with rhodamine B are absent. The remainder either separate during break-down of the sample or do not form complexes under the conditions of the analysis. Molybdenum, potentially the most serious interfering element, since it will be found with the tungsten in the final sample solution and will form a complex with rhodamine B, can be disregarded with the others.The molybdenum content of the usual low-grade tungsten ore is zero,Sept., 19881 THE DETERMINATION OF TUNGSTEN 521 so far as interference is concerned, as it amounts at the most to a few parts per million. Even in concentrates containing about 65 per cent. of tungstic oxide, in which molybdenum is often detectable in trace amounts, the maximum molybdenum content on record in Uganda is only 0.27 per cent., as molybdenum trioxide. In low-grade ore containing 1 per cent. of tungstic oxide, this maximum figure would be equivalent to 0.004 per cent. of molybdenum trioxide. The optical density of the molybdenum - rhodamine B complex formed under the conditions of analysis has been found to be approximately one-third that of the tungsten complex, and a maximum content of 0.004 per cent.of molybdenum trioxide would therefore cause negligible interference equivalent to 0.0013 per cent. of tungstic oxide. TABLE I COMPOSITION OF LOW-GRADE UGANDA TUNGSTEK ORES Amount of oxide in ore from Oxide, Bahati mine, 50, 70.65 .41,0, 13.12 FeO 0.69 Fez03 10.23 MnO 0.01 p,o, 0.16 TiO, 0.31 CaO 2.10 MgO 1.12 Na,O 0.09 K2O % Y O 0.74 0.94 0.23 Total 100.37 Amount of oxide in ore from Kirwa mine, 83.50 8.39 0.39 4.07 0.01 0.09 0.51 1.65 0.24 0.01 0.36 0.99 0.30 100.31 % Amount of oxide in ore from Nyamolilo mine, 64.47 25.09 0.30 2.30 0.03 0.09 0.74 0.95 0.83 2.42 0.45 2.06 0.29 100.02 0 1 i 0 Amount of oxide in ore from Ruhiza mine, % 75.01 19.90 0.65 5.40 0.01 0.14 0.45 0.85 0.25 1.05 0.26 1.53 0.22 99.72 Two elements, not stated by Eegriwe to form complexes with rhodamine B, are capable of interference, namely, aluminium and tin.Aluminium passes into solution with tungsten and causes negative interference, as can be seen in Figs. 1 and 2. This is probably due to formation of a complex of low optical density between aluminium and part of the rhodamine B, thus reducing the over-all absorption of the solution. However, compensation for inter- ference from aluminium can be effectively made by adding sodium aluminate to the solutions used to prepare the calibration graph, so that the alumina content of each corresponds to the average known or expected alumina content of the samples to be analysed.In any one mine or deposit there will not be a great variation in alumina content over a large number of samples, and even from mine to mine the difference is sufficiently small to be dealt with by this means. It can be seen from Table I that the preparation of the calibration graph from solutions containing the equivalent of 17 per cent. of alumina will leave a maximum alumina inter- ference of 8.61 per cent. for the sample from Kirwa mine and less with the other three samples. This, of course, represents an extreme variation from the average, for, in the exploration of a single mine or deposit, a calibration graph would be prepared from solutions with an alumina content corresponding to the average alumina content of the particular country rock in that area, and the variation of individual samples from the average alumina content would then be of the order of 2 to 3 per cent.of alumina. The position is the same for mineral-dressing products. In thirty-four samples of slimes, tailings and middlings analysed during the investigation, the variation in alumina content of individual samples from the over-all average was not sufficient t o cause serious error. Maximum deviation from the average alumina content in products from any one mine was of the order of 5 per cent. of alumina when slimes, tailings and middlings were included together, and less when they were assessed separately. Interference by tin in the analysis of low-grade Uganda tungsten ores can be ignored.Examination of tungsten concentrates over many years has shown that tin is often wholly absent or detectable only in trace amounts. In the few instances when more than a trace was present, it did not exceed 0.3 per cent. of tin in a concentrate containing 65 per cent. of tungstic oxide. Scaling down this maximum example to a concentration of 1 per cent.,522 HIGH AND PLACITO : THE SPECTROPHOTOBfETRIC DETERMINATION [Vol. 83 of tungstic oxide (a permissible calculation, since cassiterite in a low-grade ore will be concen- trated with the tungsten) gives 0.0046 per cent. of tin. Experiments have shown, however, that decomposition of cassiterite by the procedure described is incomplete and that only about one-third of the tin present in a sample passes into solution.If, therefore, a sample contains 0.0046 per cent. of tin, approximately 0.0016 per cent. will be found in the final solution. Such an amount will cause no error in the determination of tungsten. For the sake of completeness, experiments were conducted to ascertain the effect of larger amounts of tin, such as would be presen.t in a sample where the cassiterite was equal in quantity to the tungsten ore. It was found that in these circumstances interference could be prevented by measuring the optical density 30 to 40 minutes after making up the solution, instead of 3 hours later. The reason is, apparently, that the optical density of the tin - rhodamine B complex develops more slowly than that of the tungsten complex formed under the same conditions, and indeed interference from tin up to about 30 minutes after adding the rhodamine B solution is negative.From 30 to 40 minutes after preparing the solution there is no interference from tin; thereafter, interference increases progressively for 4 or 5 days and then decreases again. COMPARISON OF RESULTS Synthetic samples, prepared by adding different amounts of sodium tungstate solution The results, as to 0.4-g portions of mica schist, were analyseld by the proposed method. tungstic oxide, were as follows- Tungstic oxide added, yo . . 0.30 0.50 0.54 0.58 0.75 0.95 Tungstic oxide found, yo . . 0.31 0.51 0.58 0.55 0.74 0.96 Samples of mineral-dressing products were also analysed by the proposed method, by The results were a modified version of Jeffery's dithiol method' and gravimetrically. as follows- Tungstic oxide by proposed method, yo . . 0.23 0.18 2.18 1.65 1.09 2.12 2.14 1.88 Tungstic oxide by dithiol method, yo . . 0.24 0.14 - 1.60 1.18 2.26 2.14 1.83 Tungstic oxide by gravimetric method, % - - 2.37 1.54 - 2.19 - - I thank the Director of Geological Survey, IEntebbe, for permission to publish this paper. I also thank Mr. P. G. Jeffery (Geological Survey of Uganda) and Mr. R. Pickup (Mineral Resources Division, Colonial Geological Surveys) for helpful discussion and Dr. A. E. 0. Marzys (World Health Organisation, Teheran) for translating papers by Eegriwe and Heyne from the original German. REFEREKES 1 . 2. 3. 4. 5. 6. 7. Eegriwe. E., 2. anal. Chew., 1927, 70, 400. De Boer, J . H., Rec. Trav. Chim. Pays-Bas, 1929, 48, 979. Heyne, G., 2'. angew. Chenz., 1931, 44, 237. MacSulty, B. J., and Woollard, L. D., Anal. (;him. Acta, 1955, 13, 64. __ __ , Ibid., 1955, 13, 154. Onishi, H., and Sandell, E. B., Ibid., 1955, 13, 159. Jeffery, P. G., Analyst, 1956, 81, 104. Received March 3rd, 19%

ISSN:0003-2654    

DOI:10.1039/AN9588300516

出版商:RSC    

年代:1958

数据来源: RSC