ISSN:0003-2654    

DOI:10.1039/AN96691FX013

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BX015

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

iv SUMMARIES 01; I’AI’EKS I N THIS ISSUE [April, 1966Summaries of Papers in this IssueAn Automatic Apparatus for the Determination of TitaniumA method is described for the determination of titanium in solution.The titanium is reduced with cadmium in a column-type reductor and titratedwith ferric alum solution to a potentiometric end-point. The determinationis carried out automatically once the sample solution has been placed inthe instrument, and the result is obtained in approximately 7 minutes.Results are given demonstrating the excellent precision obtainable withthe instrument.C. L. DENTON and J. WHITEHEADBritish Titan Products Company, Ltd., Billingham, Co. Durham.Analyst, 1966, 91, 224-236.The Polarographic Determination of Lead afterCation-exchange SeparationFrom M hydrofluoric acid solution, lead, cobalt, copper(II), nianganese(II),nickel and a small part of chromium(II1) are strongly adsorbed on a column ofstrongly acidic cation-exchange resin in the hydrogen form, while otherelements present in steel are either not adsorbed or only weakly adsorbed, andare removed from the column on washing it with M hydrofluoric acid.On elution with 2 M hydrochloric acid, the lead is removed from thecolumn and determined by d.c.polarography. This method is applied to thedetermination of lead (>0.01 per cent.) in steels.A. G. HAMZA and J. B. HEADRIDGEDepartment of Chemistry, The University, Shcfield 10.Analyst, 1966, 91, 237-240.The Determination of Sodium in Aluminium Alloys by FlameSpectrophotometry with Fuel-rich Flames to Reduce InterferenceThe determination of trace quantities of sodium in aluminium alloysby flame spectrophotometry offers a rapid and accurate control procedure.When conventional flames with a balanced fuel - air mixture are used,molecular oxide band spectra of iron and manganese are strongly excited,and interfere with the measurement of the sodium emission.The interferenceis much less in fuel-rich flames while the sensitivity to sodium is slightlyincreased. The use of fuel-rich flames therefore provides a more versatileand accurate method than those hitherto used. As in most methods forthe determination of sodium it is advantageous to add lithium as an internalstandard to compensate for minor variations in conditions. The results areof general application to the analysis of other materials which may containiron and manganese, and possibly nickel and chromium.R. A.HINE, R. CRAWFORD, J. E. DEUTSCHMAN and P. J. TIPTONAluminium Company of Canada, Ltd., Arvida, Quebec, Canada.Analyst, 1966, 91, 241-246.The Determination of Water in Lubricating Oils by aNear-infrared Spectrophotometric MethodThe water content of clear mineral oils can be quickly and accuratelydetermined by dissolving the wet oil in ethyl acetate and measuring thenear-infrared absorbance of the solution, relative to a similar referencesolution previously dried by molecular sieves. In discoloured or cloudy, wetoils the water can be removed by azeotropic distillation with ethyl acetate,and the water content of the distillate determined spectroscopically.Withthe latter procedure, errors that arise a t low water concentrations may bedue to the absorption of atmospheric moisture by the solvent.B. D. PEARSONDerby and District College of Technology, Derby.Analyst, 1966, 91, 247-260Vi SUMMARIES OF PAPERS I N THIS ISSUE [April, 1966The Determination of Residual Anionic Surface- active Reagentsin Mineral Flotation LiquorsA method is described for the determination of residual amounts ofanionic surface-active reagents, used as flotation promoters, in mineralflotation liquors. The method is equally effective for the long carbon chaincarboxylates and the anionic non-soapy surface-active agents. The reagentused is the cationic copper(I1) triethylenetetramine complex, which reacts inalkaline solution with anionic surface-active agents to give an adduct thatcan be extracted into an isobutanol - cyclohexane mixture.The copper asso-ciated with the surface-active anion in the extract is determined photo-metrically as the coloured complex using diethylammonium diethyldithio-carbamate. Long chain carboxylates with carbon numbers from C,, to C221 aswell as anionic non-soapy surface-active reagents, can be determined in therange 0.2 to 10 p.p.m. The effect of a number of likely interferences hasbeen investigated.G. R. E. C. GREGORYWarren Spring Laboratory, Stevenage, Herts.Analyst, 1966, 91, 251-257.Polarographic Determination of Arsenic in SteelA method for the polarographic determination of arsenic in steel isdescribed.It consists of the reduction of arsenic(v) to arsenic(II1) in 9 . 5 ~hydrochloric acid solution by means of potassium iodide in the presence ofascorbic acid, and of the extraction of arsenic(II1) with chloroform. Arsenicis then re-extracted from chloroform with 0.2 M ascorbic acid and determinedpolarographically with the same ascorbic acid solution as supporting electrolyte.The method was checked on NBS steel standards and synthetic mixtures.Arsenic contents greater than 0.01 per cent. can thus be determined easilywithout concentrating in the re-extraction step.MILENKO V. sU8IC and MILJAN G. PJESCICDepartment of Physical Chemistry, Faculty of Science, University of Belgrade]Yugoslavia.Analyst, 1966, 91, 258-260.A Simple Chromatographic Method for Determining the BasicAmino- acids in Protein HydrolysatesA new micro method utilising charcoal chromatography has been de-veloped for the determination of the individual basic amino-acids in proteinhydrolysates.It is based on the fact that both the aromatic amino-acidsand basic amino-acid picrates are strongly adsorbed by active-charcoalcolumns, and that the latter can be freed from the aromatic amino-acids bytreatment of the adsorbent with aqueous ethyl acetate solution. The separa-tion of the individual basic amino-acids depends on differential decompositionof their picrates on the columns by various eluents. The method can beused for the determination of histidine in the presence of other imidazolederivatives.AHMED S .M. SELIM and NAG1 N. MESSIHADepartment of Biochemistry, Abbassia Faculty of Medicine, Abbassia, Cairo, U.A.R.Analyst, 1966, 91, 261-267...Vlll SUMMARIES OF PAPERS I N THIS ISSUEThe Micro Determination of Cyanide: Its Application to theAnalysis of Whole BloodAn introduction to the existing methods for the analysis of cyanide isgiven and some of the limitations to the methods are pointed out.A modification of the Epstein method is described, in which Cavett blood-alcohol flasks are used. This method can be applied to small samples of 2 mlvolume containing 0.2,ug of cyanide. By strict control of the conditions itis shown that a high degree of accuracy can be achieved. Interference byheavy metal ions is avoided by using 2 mg of the disodium salt of EDTAper ml of blood.It is therefore suggested that this anti-coagulant shouldbe used when the blood is collected. Experiments on the partition of cyanidein whole blood showed that 5 minutes’ exposure resulted in more than70 per cent. of cyanide being bound to haemoglobin. This value remainedunchanged in the presence of a transport inhibitor.S. BAARM.R.C. Industrial Injuries and Burns Research Unit, Birmingham Accident Hospital,I h t h Row, Birmingham, 15.Analyst, 19G6, 91, 268-272.[April, 1966Determination of Particulate Matter in Intravenous FluidsMethods for the examination of intravenous solutions for suspendedparticles have been investigated. A visual inspection method has beendevised, which enables samples to be graded by comparison with referencematerials.For quantitative work, techniques for particle-size analysis witha Coulter Counter have been developed. ,4 survey of all the solutions com-mercially available in Australia has been made, and limits for the acceptanceof such solutions have been proposed.I. VESSEY and C. E. KENDALLNational Biological Standards Laboratory, Canberra, A.C.T., Australia.Analyst, 1966, 91, 273-279.The Amperometric Titration of Submillinormal Concentrationsof Iodine with Mercury(1) PerchlorateShort PaperJOHN T. STOCKDepartment of Chemistry, The University of Connecticut, Storrs, Connecticut,U.S.A.Analyst, 1966, 91, 280-282.Replacement of Benzidine by Copper Ethylacetoacetate and TetraRase as Spot-test Reagent for Hydrogen Cyanide and CyanogenShovt PaperF.FEIGLLaboratorio da ProduEBo Mineral, Ministerio das Minas e Energia, Rio de Janeiro.and V. ANGERResearch Laboratory, Lobachemie, Vienna.Analyst, 1966, 91, 282-284.A Projection Method for Inspection of AmpoulesShort PaperC. E. KENDALLNational Biological Standards Laboratory, Canberra, A.C.T., Australia.Analyst, 1966, 91, 284-285x SUMMARIES OF PAPERS IN THIS ISSUE [April, 1966The Determination of Water in Beryllium OxideShort PaperL. E. SMYTHE and T. L. WHATELEYAustralian Atomic Energy Commission Research Establishment, Sydney, N.S. W.,Australia.Analyst, 1966, 91, 285-287.The Determination of Quinizarin in Hydrocarbon OilShort PaperK.IFIELD and E. W. GODLYMinistry of Technology, Laboratory of the Government Chemist, Cornwall House,Stamford Street, London, S.E. 1.Analyst, 1966, 91, 287-289.The Effect of Particle Size on Back-scattered X-ray CorrectionMethods in On-stream X-ray Fluorescence AnalysisShort PaperK. G. CARR-BRIONWarren Spring Laboratory, Stevenage, Herts.Analyst, 1966, 91, 289-290.Interference from Silica in Phosphate AnalysisShort PaperA. HENRIKSENThe Norwegian Institute for Water Research, Oslo 3, Norway.Analyst, 1966, 91, 290-291.The Collection of Fractions Separated by Gas - LiquidChromatographyShort PaperM. D. D. HOWLETT and D. WELT1Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford.Analyst, 1966, 91, 291-293

ISSN:0003-2654    

DOI:10.1039/AN96691FP069

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BP083

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

APRIL, 1966 THE ANALYST Society for Analytical Chemistry Gold Medal Vol. 91, No. 1081 COUNCIL, on the recommendation of its Honours Committee, has decided to award the first Society for Analytical Chemistry Gold Medal to HERBERT NEWTOK WILSON formerly Analytical Group Manager, Imperial Chemical Industries Ltd. (Billingham Division and, later, Agricultural Division). H. N. Wilson has spent the major part of his career in the Research Department’s analytical laboratories at I.C.I., Billingham, where he helped to build up and later took complete charge of, an analytical department well equipped and of outstanding quality, covering an extremely wide field. Sections included were sampling, standards, raw materials and finished products (from argon to cement, and numerous organic chemicals as the Division’s research and manufacturing programme expanded). The Billingham laboratories have always been early users of new techniques, and were among the first British industrial labora- tories to establish a microchemical section, to use spectrophotometry, polarography, gas chromatography and X-ray fluorescence analysis.The extent and quality of the training available and the personal influence of “H.N.” is seen in the list of men, now in senior positions elsewhere, who were under him in all or part of the formative stages of their careers, including- J. Borrowdale, Chief Chemist, Richard Thomas & Baldwins Ltd., Scunthorpe. W. T. Elwell, Chief Analyst, Imperial Metals Industries Ltd., Birmingham. M. Gibson, Technical Manager, J. C. Gregory gi Son Ltd., Stoke-on-Trent.H. Hollis, Director of Chemical Inspection, Ministry of Defence, Woolwich. J. R. Hudson, Research Manager, Brewing Industry Research Foundation, Caterham. J. Norris, Director, J. H. Marks & Co. Ltd., Cleckheaton. G. E. Penketh, Chief Analyst, I.C.I. Ltd. (Heavy Organic Chemicals Division). P. ,4. Raine, Chief Chemist, Crown Cork Co. Ltd. A. Robertson, Personnel Director, I.C.I. Ltd. (Mond Division). A. Wilson’s published work covers a wide range of analytical problems dating back to the 1930’s when papers on such diverse topics as selenium in sulphur and the determination of OH groups by the pyridine - acetic anhydride method were published; through the 1940’s on amines, trace elements in phenol, uranium in urine, arsenic in glass, nitromethane in air; to a very productive period in the ’50’s and ’60’s including some outstanding work on the deter- mination of silicate and phosphate.He was also joint editor of both editions of “Chemical Analysis-The Working Tools.” His latest book, just published, “An Approach to Chemical Analysis-Its Development and Practice” can be recommended to all analytical chemists and their “customers” for its wide scope and penetrating observations. H. N. Wilson was the first Royal Institute of Chemistry examiner for the Fellowship in General Analytical Chemistry from 1941 to 1949, and served on the Council of that body in 194546 and 1949-52. Within the Society for Analytical Chemistry, of which he has been a member for over 30 years, he served on Council in 1947-48 and is perhaps best known for his chairmanship of the joint S.A.C. - A.B.C.M. Committee on Trade Effluent Analysis and for the resultant monograph of approved methods. For some years before 1962 he was also a member of the Fertiliser Manufacturers’ Association analytical committee and served on the scientific sub-committee of the Fertilisers and Feeding Stuffs Act, 1926, Standing Advisory Committee of the Ministry of Agriculture, Fisheries and Food. For his contributions to chemical analysis the Society is proud to award its first Society for Analytical Chemistry Gold Medal to HERBERT NEWTON WILSON. 223 Smales, Head of Analytical Chemistry Branch, A.E.R.E., Harwell.

ISSN:0003-2654    

DOI:10.1039/AN9669100223

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

224 DENTON AND WHITEHEAD : AN AUTOMATIC APPARATUS [AndySt, VOl. 91 An Automatic Apparatus for the Determination of Titanium BY C. L. DENTON AND J. WHITEHEAD (British Titan Products Company Ltd., Billingham, Co. Durham) A method is described for the determination of titanium in solution. The titanium is reduced with cadmium in a column-type reductor and titrated with ferric alum solution to a potentiometric end-point. The determination is carried out automatically once the sample solution has been placed in the instrument, and the result is obtained in approximately 7 minutes. Results are given demonstrating the excellent precision obtainable with the instrument. IN the titanium pigment industry it is necessary to analyse a large number of samples, mostly liquid, for titanium content.The method most frequently used for this determination is to reduce the titanium to the tervalent state and oxidise with a standard oxidising agent.ls2 -4gents which have been used for reducing titanium include the following : aluminium, fusible alloys, cadmium, iron, zinc, bismuth, lead, slightly amalgamated zinc and liquid amalgams of zinc, bismuth, lead, tin or cadmium. Solid reducing agents are generally used in a column or Jones-type reductor, and liquid reducing agents in the separating-funnel type of reductor of which the Nakazono is a typical developed form? Solid reducing agents may also be added directly to the solution, a typical example of this being aluminium. After reduction is complete, excess aluminium dissolves in the solution and does not interfere in the subsequent t i t r a t i ~ n .~ Cathodic reduction has also been used, particularly in the coulometric generation of tervalent titanium.5 Reduced titanium solutions can be titrated with a variety of standard titrimetric reagents. Among the commonest of these are solutions of potassium dichromate, perman- ganate or bromate, ceric sulphate and ferric solutions. The end-point may be determined using indicators such as methylene blue, diphenylamine, indigo carmine or sodium or potassium thiocyanate. Solutions containing titanous salts are unstable and easily oxidised by the atmosphere, but this may be avoided by the use of an inert atmosphere or by adding the titanous solution to an excess of oxidising agent. Alternatively, the solution may be run into an excess of ferric sulphate solution and the ferrous equivalent titrated with standard oxidising agent.Even in the most rapid of the above methods, the manipulative time is still considerable, and it is evident that an automatic instrument would achieve a large saving in man-hours. It was envisaged that such an instrument would carry out automatically a determination of titanium in a solution which had been manually inserted into the instrument. At the end of the determination the result would be displayed in digital form and the instrument would be ready for another determination. The above methods were critically examined in order to select the most suitable for further consideration. Initially, attempts were made to use liquid amalgams since they are rapid and efficient in action.The titanium solution was agitated with the amalgam in a glass cylinder, by means of a mechanically operated perforated glass piston, until all the titanium was reduced to the tervalent form. The reduced solution was then run off into a titration vessel via a side arm, situated at the amalgam level. The reduction appeared to be complete, but slight oxidation took place during transference to the titration vessel despite the presence of an inert atmosphere of carbon dioxide and the presence of potassium thio- cyanate which stabilises tervalent titanium. In view of this and mechanical difficulties, no further work was done on this method. Electrolytic reduction is potentially very attractive, but it was shown that the current densities required to reduce the quantity of titanium in the average sample in a reasonable time were too high. The titration may also be completed potentiometrically.April, 19661 FOR THE DETERMINATION OF TITANIUM 225 The column-type of reductor was next investigated. Experience has shown that cadmium metal granules (1 to 2 mm) are superior to amalgamated zinc as reducing agent in a column- type reductor.A column-type reductor, packed with cadmium, was therefore fitted with a solenoid-operated outlet valve and platinum level probes in the top of the column. The cadmium was supported on a sintered-glass disc protected by a plug of glass-wool. With this system, the complete reduction and washing of a sample solution took about 15 to 20 minutes, but this time progressively increased as the granules decreased in size and packed into the base of the column.This was clearly unsuitable for an automatic method and consequently the upward flow of liquid was investigated. A simple apparatus was assembled to investigate this technique. The sample was pumped from a beaker into the bottom of the column using a mechanically operated nylon syringe and two glass non-return valves. Level probes were used to control the reduction and washing processes, and the solution was finally titrated manually. Consistent reduction efficiencies and constant reduction times were obtained over many determinations, indicating that the upward flow was fluidising the column and preventing it from packing. This reduc- tion procedure was accordingly adopted and incorporated into the final apparatus. Ferric alum solution was chosen as titrant in view of the fact that many of the sample solutions contained ferrous iron which would react with such oxidising agents as potassium dichromate and ceric sulphate.The nature of the samples, which varied appreciably in colour, precluded the use of photpmetric methods for end-point detection, and a potentiometric method was therefore selected for use. The change in potential at the end-point was enhanced by the presence of potassium thiocyanate, and this was added in all titrations. It has the further advantage of stabilising the tervalent titanium to atmospheric oxidation and the colour change at the end-point provides a visual check on the accuracy of the instrument. Several methods of adding titrant were examined. The standard burette with location of meniscus by light source and photoelectric cell was rejected because it is too complex.Preliminary work with an early form of peristaltic pump indicated that it was not sufficiently accurate and it would be difficult to incorporate in an automatic system. Frequent calibration would also be necessary. A glass syringe pipette, operated by a precision calibrated leadscrew driven by a syn- chronous motor, was next investigated. A cam on the top of the leadscrew operates a mechanical counter, which is adjusted so that the full traverse of the syringe, i.e., 50m1, is equivalent to 1000 revolutions. This method, which was proved to be completely satisfactory for dispensing accurate volumes of liquid, was incorporated into the automatic titrator. Very careful lining up of the syringe and leadscrew was found to be necessary to prevent breakage of the syringe.This was avoided by using a shorter piston made from Teflon with an O-ring seal fitted to the end. These have proved to be extremely satisfactory in use, and breakages have been almost eliminated. GENERAL DESCRIPTION OF THE JNSTRC‘MENT END-POIKT DETECTOR- The end-point detector is essentially the same as that described by Brown and Weir,6 which is incorporated in the Model 34 Titromatic Analyser made by Electronic Instruments Ltd. It has, however, been modified to give a direct reading in pH units. The modified circuit is given in Fig. 1, and a list of components can be found in Appendix I.The modifications are as follows: A 100-0-100 microammeter with series resistor R,, (5600 ohms) is connected across the cathodes of V4. R, is omitted, and the value of R,, is changed to 22,000 ohms. R4oA and RdOB form part of a twin-ganged potentiometer, connected so that as one increases the other decreases. R41 is a potentiometer to give the required pH scale length, and R,, is a 25,000-ohm helical potentiometer that gives a direct indication of the pH of the solution. The manual-check auto switch is converted to a two-position rotary switch giving manual and auto positions only. The neon lamps, V1, and V,,,!normally in the Brown - Weir unit) that are used to indicate “Titrate on” and “Titrate off, are omitted, and have been replaced by the meter connected across the cathodes of V,.This is the set buffer control.226 DENTON AND WHITEHEAD 1 AN AUTOMATIC APPARATUS [AutalySt, VOl. 91 2 0 7 - > m i - - A d - N d + d r 0 Z M M al r L I 0-April, 19661 FOR THE UETERMINATION OF TITANIUM 227 The value of R,,, the anticipation control, is change.d to 25,000 ohm, with R45, 180,000 ohm, connected from the top end of R,, to R21. The E l contact is now made normally closed to operate the sequence unit, The end-point detector is capable of being used for pH or potentiometric titrations. C I I_ O F I .6 cm - A = 5-cm diameter ring with several holes to run wash liquor into beaker B = Platinum probe fused through glass C = 610 socket D = PVC tubing E = Outlet to glass filter F = Air hole G = QVF 614 socket H = PTFE cone to fit 614 socket J = I x 25-s.w.~.platinum wire fused through end of glass tubing and soldered to tinned-copper wire Fig. 2. Sample beaker and probes SAMPLE BEAKER- This is a modified 250-ml squat-type beaker, and a diagram of it is shown in Fig. 2. The top of the beaker is widened to take the wash liquor manifold. This consists of a 7 to 8-mm diameter tube, with holes at 1-cm intervals through which wash liquor is passed to rinse the sides of the beaker. The tube is recessed to prevent solution spraying straight into the beaker and not washing the sides. The beaker has a sloping base so that a minimum volume of solution is retained in the beaker when a change is made to the next sequence in the operations. The volume o f wash solution is determined by three probes which are placed in a side arm to avoid accidental wetting by the wash solution. As a further precaution against spurious contact, the connecting wires are encased for most of their length in glass- tubing.SAMPLE TRANSFER PUMP- The syringe is driven by a 250-volt, a.c,, 50 c/s geared induction motor, running at 4-75 r.p.m., connected to the syringe by means of a crankshaft. The arrangement can be seen in Fig. 3. REDUCTOR- A 20-ml nylon syringe is used for this purpose. A diagram of the apparatus is shown in Fig. 4. The solution is pumped from the sample beaker to the reductor through a non-return valve system, consisting of hollow, ground-glass valves weighted with mercury, fitted to the base of the reductor column so that the solution can only pass from the beaker to the column.Since small particles of solid material interfere with the operation of the glass valves, all228 DENTON AND WHITEHEAD: AN AUTOMATIC APPARATUS [Ana&d, VOl. 91 solutions used must be free from suspended matter, and a KO. 1 porosity sintered-glass filter is fitted in the sample line as an additional precaution. The column has a series of indentations to improve distribution, and is fitted with a 75-mm No. 0 porosity sintered-glass filter a t the base to support the cadmium reducing agent. A similar filter is fitted at the upper end to prevent cadmium passing into the titration beaker. Two clip-on joints are fitted to the column to facilitate re-packing. The space between the top joint and the sintered-glass filter is also packed with glass-wool as an additional precaution.To the upper end is attached an outlet tube leading into the titration beaker. The glass reductor column is 20 mm in diameter and 35 cm long. A To motorised syringe To titration beaker C E D A = QVF ball joint, m.s. 12/2 BS B = 75 x 0 sintered disc C = Glass valves weighted with mercury D = BIO cone and socket E = BIO cone F = Constrictions ground t o form valve seat G = 7 x I sintered disc H = I-inch clip-on joint J = 20-mm bore with indentations K = I-inch clip-on joint Fig. 4. Keductor column and valvc assembly From reductor To beaker drain valve A = Calomel electrode B = Platinum earth electrode C = Titrant delivery D = Carbon dioxide inlet E = Carbon dioxide ring F = Stirrer G = Thiocyanate delivery H = Platinum indicating electrode K = Perspex beaker top Fig.5. Titration beaker and electrodes TITRATION BEAKER AND ELECTRODE SYSTEM- I t is made from a 1-litre beaker, the top of which is cut off to the dimensions shown, and a drain outlet fitted. The lid of the beaker is machined from solid Perspex, and is drilled to take the calomel reference and two platinum electrodes, which are held in position by clips attached to the centre bridge-piece. The lid also contains holes through which pass the stirrer, the sample solution, the inert purge gas, the potassium thiocyanate inlet and the titrant. The inert gas and drain outlet are both controlled by standard solenoid valves that are obtainable from Baird and Tatlock Ltd., Chadwell Heath, Essex. All the valves used in the instrument are of the energise - to - open type.The stirrer This is shown in Fig. 5.Fig. 3. General view of titrator [To face page 228April, 19661 FOR THE DETERMINATION OF TITANIUM 229 has a shaft of diameter 5 to 6 mm, and is fitted with four blades. The bearing is machined from PTFE, and the drive is by a flexible shaft from a'456 r.p.m., 250-volt ax., 50 c/s geared induction motor. kmj ,Ground toform I -- d7%Lva've Floating Seat I IzI I Fig. 6. Potassium thiocyanate vessel Fig. 6 shows the vessel from which 10 ml of potassium thiocyanate solution are trans- ferred to the beaker. Solenoid valves are used to control the filling and emptying of the vessel, the seal being effected by a floating glass valve which is simpler and more reliable than a system of level electrodes.The inert-gas supply is also controlled by a solenoid valve. A standard calomel electrode with a porous plug base is used. The platinum indicating and earth electrodes consist of 25 s.w.g.-platinum wire fused into a glass tube so that a length of 1 cm is exposed. TITRANT SYRINGE- This consists of a glass syringe of 20-mm i.d. barrel, and a piston made of PTFE with a rubber sealing ring. The piston is attached to a leadscrew driven by a 250-volt a.c., 50 c/s, 19-r.p.m. reversible geared induction motor. The leadscrew also drives a mechanical counter which indicates the amount of titrant added. The early form of syringe consisted of a glass piston and barrel, and considerable care had to be taken in the assembly of the drive mechanism to prevent fracture of the syringe.Replacement of the piston by one machined from Teflon, fitted with a rubber O-ring seal eliminated this trouble, and at the same time increased the accuracy of the delivery. The filling and emptying of the syringe is controlled by a parallel pair of solenoid valves mounted in a Perspex block. When the syringe is full, a micro-switch, Sw,, is operated which automatically closes the fill valve. The empty valve is opened when the drive motor starts to operate. If, in the preliminary experiments, a speed of delivery was selected such that over- shooting of the fill position or the end-point did not occur, the rate of filling of the syringe was very slow and the duration of determination was lengthened appreciably. Accordingly, a two-speed gearbox was designed and fitted to the drive, so that a fast rate could be used for most of the filling and emptying, and a slow rate when the end-point or the fill positions were being approached.A diagram of the gearbox system is shown in Fig. 7 . The change- over is operated by a micro-switch, Sw,, when the syringe is being filled, and by an anticipation control when the end-point is approached. CONTROLS- The titrator consists of three basic units, all of which are readily detachable and replace- able. The end-point indicator, set-buff er control, scale-length control, manual - auto switch and anticipation control are contained in the end-point unit which is housed in the upper part of the instrument. A switch is also incorporated to allow for change in the direction of the titration.230 DENTON AND WHITEHEAD : AN AUTOMATIC APPARATUS [AutdySt, VOl.91 I Sliding spindle ‘ ~ o g coupling Fig. 7. Two-speed gearbox The centre unit, which controls the sequence of operations, contains the mains on - off switch, the start button, the manual advance control and indicating lights. A fill-deliver control is also installed for use in priming the syringe when a new one is being fitted. The manual advance control enables wash stages to be by-passed if required. The lower section houses the titration assembly. SEQUENCE OF OPERATIONS The instrument has been designed so that many of the operations take place simul- taneously, resulting in a considerably reduced cycle time; this is summarised in Table I. Before starting a determination, the ferric alum, potassium thiocyanate and wash solution reservoirs should all be filled, and the ferric alum syringe should be primed by manual operation of the fill-deliver control.The instrument should be switched on for approximately 1 hour before use to allow the end-point system to become stabilised. The “stand-by” light, L,, should be illuminated to indicate that the Uniselector is in the first or “stand-by” position. Reference should be made to the sequence unit circuit shown in Fig. 8, for details of the circuit, and to the appendix for component details. The sample solution is transferred to the sample beaker and the start button pressed. This closes Swla and Swlb which energises relay RLS. Closure of Sla maintains relay RLS in an energised state when the “start” button is released.Energising relay RLS moves the Uniselector to position 2, indicated by the lighting of L,. UNISELECTOR POSITION 2- Contact Slb is closed, thereby opening the potassium thiocyanate delivery valve, and potassium thiocyanate is added to the beaker. Slc is closed and the circuit through RLB to earth is completed via electrode probes. The wash syringe motor is started when S2 is closed and S3a opens causing the beaker drain valve to close. Relay RMF is then energised by change over of S3b. Closure of MF1 energises the “fill titrant” valve, causing it to open.Uni- selector position 1 2 3 4 Potassium thiocyanate deliver Closed Open. Solution added to titration beaker Open TABLE I SUMMARY OF OPERATIONS CARRIED OUT AT EACH UNISELECTOR POSITION > 3.L + W 45 45 U Inert-gas valve Closed Open Open Beaker drain valve Open Closed Closed Ferric alum feed valve Closed Open Closed Closed Open Open Closed Closed Open Closed. Vessel fills Open Open Closed Closed Closed Closed Titration syringe Stopped Syringe fills with ferric alum a t fast rate until the last 50 revs., which are added a t the slow rate. When the zero end stop is reached, the ferric alum feed valve is closed Titration starts a t slow rate for first 50 revs., then a t fast rate until the anticipation is reached. At the end of the titration, i.e., when the end-point potential is maintained for 20 seconds, the Uniselector moves to position 1 Wash solution valve Closed Closed Open. Solution added to top level probe, then valve closes (first wash) Open.Solution added as above (second wash) Open. Solution added as above (third wash) Closed Wash syringe motor Pumps sample solution from beaker, through the reduction column to the titration beaker. When the liquid level falls to the lower level probe, the Uni- selector moves to position 3 Solution pumped as above, and when the liquid level falls to the lower probe the Uniselector moves to position 4 As above. When the lower probe is reached, the Uniselector moves to position 5 As above. When the lower probe is to reached, position the 6 Uniselector moves Stopped232 DENTON AND WHITEHEAD: AN AUTOMATIC APPARATUS [Ana&St, VOl. 91 h I aApril, 19661 FOR THE DETERMINATION OF TITANIUM 233 The titrant motor is started when MF2 changes over and MF3 opens. The phase difference ensures that the titrant motor starts rotating in the correct direction and titrant is pumped to the syringe.The rate of filling the syringe is increased by changing the gear drive. This is accomplished when MF4 is closed and relay RLG is energised. GI is closed which energises the gearbox solenoid and the gear is changed to the fast rate. Immediately before the syringe is full, the rate of filling is decreased to avoid over- shooting the end-point. This is achieved by the opening of Sw, when the leadscrew reaches a pre-set position. The gearbox solenoid is de-energised and the gear is changed back to the slow rate. When the titrant syringe is full, Sw, is opened; this de-energises RMF. Contact MF2 reverts to the normal position and the titrant motor stops, the braking components ensuring that the motor stops instantaneously. The above operations are all carried out on position 2 of the Uniselector. The sample is gradually pumped from the sample beaker to the reductor column and the beaker is washed out with three lots of wash solution.The detail of how this is done is as follows: When the liquid level falls below probe 2, relay RLB is de-energised and closing of B2 energises the Uniselector coil. B1 closes which energises relay RLC. This relay remains energised because C2 is closed. C1 closes, thus causing wash solution to pass into the beaker. UNISELECTOR POSITIONS 3 TO 5- When the liquid makes contact with probe 2, relay RLB is energised which opens B2. This advances the Uniselector to stage 3, lamp 2 is switched off and lamp 3 switched on.Kote that B1 is opened, but owing to C2 being closed relay RLC remains energised. When the liquid level makes contact with probe 1, relay RLA is energised which opens Al. This de-energises relay RLC which opens C1 and the flow of wash solution stops. This wash procedure is repeated until three washes have been completed and the uni- selector is on position 5. UNISELECTOR POSITION 6- T1 is opened which ( a ) , closes the potassium thiocyanate deliver valve, ( b ) , keeps the drain valve closed and (c), de-energises relays RLS and RLC. This stops the wash syringe motor. T2 is closed, so starting the stirrer motor. T3 opens to maintain the Uniselector in position 6. T4 changes over and relay RMD is energised which ( a ) , opens the titrant delivery valve and ( b ) , starts the titrant motor in the delivery direction. Note that D4 is always closed at the beginning of a titration.Titrant is then delivered to the beaker a t the slow rate. During the titration the potassium thiocyanate vessel is filled, since the fill valve is directly in contact with position 6 on the Uniselector. When the relay RLY is energised owing to Sw, being closed by the lead screw, the contact Y1 maintaining the circuit through RLY when the Sw, circuit is broken, Y2 closes, energising relay RLG and so causing the gear to change so that titrant is delivered at a fast rate. At the anticipation setting, D4 opens, relay RLY is de-energised and Y1 and Y2 open. Relay RLG and hence the gearbox solenoid are de-energised and the titrant addition reverts to the slow rate.Closure of D4 causes addition of titrant to occur. Titrant is added in short bursts until the potential difference between the electrodes is the same as the end-point potential and has remained unchanged for a pre-set period. El opens and de-energises relay RLT so that T3 closes and the Uniselector operates on its motoring contacts and returns to position 1 indicated by lamp L,. In this position T1 closes and the beaker drain valve opens. Since position 1 of bank 1 on the Uniselector is not earthed, the carbon dioxide valve closes. When the Uniselector is moved to position 6, relay RLT is energised. Relay RMD is de-energised and the titration stops. The titration is controlled by the signal from the end-point detector.METHOD CALIBRATION AND STANDARDISATION- millivolts is required. millivolt supply and proceed as follows : To standardise the end-point detector a high-impedance potential source of 0 to 500 Disconnect the electrodes from the end-point detector, connect the234 DENTON AND WHITEHEAD: AN AUTOMATIC APPARATUS [Analyst, VOl. 91 Set the end-point pH control to 400 and the potential supply to 100 millivolts. Adjust the set-buffer control until the meter reads zero, Change the potential supply to 300 milli- volts and rotate the end-point pH control until the meter reads zero. The end-point pH control should read 800. If the reading is not 800, adjust the scale length control and repeat the previous operations until the correct scale length is obtained.Disconnect the potential source and connect the electrodes to the end-point detector. Transfer to the titration vessel a titanium solution which has been titrated to the end-point. Set the end-point pH control to 250 and adjust the set-buffer control until the meter reads zero. Set the “anticipation” control to a value which will cause the first anticipation to occur about 5 ml from the end-point. This value can only be found by trial and error. Weigh accurately to 0.1 mg a catch weight of approximately 0.9 g of titanium dioxide (99.9 per cent, purity) which has been previously dried in an air-oven at 105” C. Transfer to a 250-ml beaker, and dissolve by heating with 40 ml of concentrated sulphuric acid and 30 g of ammonium sulphate. Cool and dilute to 500 ml in a calibrated flask with distilled water.Pipette a 50-ml aliquot into the sample beaker, set the manual - auto switch to the manual position and press the “start” button. When the titanium solution has been reduced and transferred to the titration beaker, continue the titration manually and construct a curve of titrant versus potential difference. Select the setting for the end-point by inspection of the graph and use this value for all subsequent titrations. Set the manual - auto switch to auto and repeat the titration using a 50-ml aliquot each time. The calibration should be carried out in triplicate, and the volume of ferric alum used in each case noted in revolutions. The scatter between replicate titrations should be within k0.1 per cent. The weight of titanium dioxide per revolution can then be calculated.N.B.-This procedure eliminates the need to standardise the ferric alum before use on the titrator. REAGENTS- The instrument is now set approximately to the required end-point. Cadmium granules-1 to 2 mm in size. Potassium thiocyanate solution, 20 per cent. w/v. Wash solution-Prepare 10 per cent. w/v ammonium sulphate in sulphuric acid (1 + 50). Ferric alum solution, approximately 0.0625 N-Dissolve 1200 g of ferric alum, A.R., in 400 ml of concentrated sulphuric acid and 7 litres of water. Dilute to 36 litres and mix well. Oxidise any ferrous iron by adding 0.1 N potassium permanganate solution until one more drop will just colour 50 ml of the solution. PROCEDURE- Any substance which is reduced by cadmium metal and re-oxidised by ferric alum will interfere in the determination. Interfering agents include chromium, vanadium, niobium, tungsten, uranium, platinum, molybdenum, arsenic and antimony, as well as nitric acid and certain organic compounds.Those which occur in titaniferous materials are chromium, vanadium, niobium and molybdenum. Chromium, vanadium and molybdenum reduce to a definite valence and may be allowed for in the determination if their concentration is known. To determine the titanium content of a solution, a suitable aliquot is transferred to the sample beaker, the manual - auto control is set to auto and the start button pressed. At the end of the determination the weight of titanium dioxide present in the solution is calcu- lated from the reading on the counter and the conversion factor for the ferric alum titrant.Note that there is no need to rinse the titration beaker between determinations because the residual solution is at the end-point condition and will not interfere in the titration of the next sample. RESULTS Then add 20 ml in excess. The accuracy of the instrument was assessed by making 30 determinations on the same sample. The following results were obtained- TiO,, per cent. w/v . . 15.35 15-36 15.37 15-38 15.39 Number of results . . .. 1 9 4 3 5 TiO,, per cent. w/v . . . . 15.40 15.41 15.42 15.44 Number of results .. . . 3 3 1 1 Average determination-15.38 per cent. Standard deviation-0.023 per cent. Coefficient of variation--0.145 per cent.April, 19661 FOR THE DETERMINATION OF TITANIUM 235 PERFORMANCE A complete determination takes 7 minutes, during which time the operator is available to carry out other work such as the preparation of the next sample.The instrument has resulted in a substantial saving of time and has also increased the accuracy of the deter- mination by the use of a potentiometric instead of a colorimetric end-point. It is natural that such an instrument requires careful maintenance, and a scheme of routine preventative maintenance has been drawn up which has greatly contributed to reducing the down-time of the instrument. It has been found that particular attention should be paid to the elec- trodes and to ensuring that the solutions are iree from insoluble particles. The cadmium granules should be sifted to remove any fine particles before use.The instrument has been in use in the laboratories of this Company for longer than a year and has given satisfactory service during this period. The total cost of the instrument, including labour, materials and commissioning, is approximately L550. We thank Mr. R. Hutton and Mr. D. L. Suttill for technical assistance, and the Directors of British Titan Products Company Ltd., for permission to publish this paper. Appendix I COMPONENTS LIST FOK END-POINT DETECTOR (FIG. 1) Unless otherwise stated, the resistors have a tolerance of k2 per cent. and are made R1, R2, R,6 R,i, = l.8-megohm, 0.25-watt resistors R3 = 27,000-ohm, 0.25-watt resistor R4, R,, R,, R,,, R,,, R3, = 1-megohm, 0-25-watt resistors R61 R 7 = 10-ohm, 0.25-watt resistors R t 7 p R19, R28, R36 = 22,000-ohm, 0.25-watt resistors R,,, R,,, R,,, R,,, R,,, R,, = 2.2-megohm, 0.25-u-att, resistors R151 Rl13 = 39,000-ohm, 0.25-watt resistors Rl, = 1800-ohm, 0.25-watt resistor R21 = 2-megohm, 0.26-watt resistor R24 = 10-megohm, 0-25-watt resistor R25 = 560,000-ohm, 0.25-watt resistor R29, R3; = 33,000-ohm, 0.25-watt resistors R30 = 560@-ohm, 0.25-watt resistor R33 = 33-megohm, 2-watt resistor R341 R44 = 1000-ohm, O.25-watt resistors R35 = 470,000-ohm, 0.25-watt resistor R42 = 22-megohm, 0.25-watt resistor R45 = 180,000-ohm, 0.25-watt resistor %n = 25,000-ohm, 4-watt, 10-turn helically-wound Potentiometer, with a resis- tance tolerance of 5 per cent.and linearity tolerance of &0.5 per cent. R,, = 25,000-ohm, I-watt, wirc-wound potentiometer with a tolerance of h20 per cent.R3 1 = 3300-ohm, 5-watt, wire-wound resistor with a tolerance of 5 per cent. R32 = 22,000-ohm, 5-\vatt, wire-wound resistor with a tolerance of 5 per cent. R40.4, R40~ = 100,000-ohm, O-.Fi-watt, twin-gang potentiometer with a tolerance of R4 1 : 100,000-ohm, l-watt, wirc-wound potentiometer with a tolerance of Cll c, = 0.005-pF tubular paper capacitors, 500-volt, d.c., working ‘3, ‘4 = 0.001-pF tubular paper capacitors, 500-volt, d.c., working C5 = 0.25-pF tubular paper capacitors, 500-\dt, d.c., working C6 = 1-pF tubular paper capacitor, 500-volt, d.c., working of high stability carbon. 1 2 0 per cent. *20 per cent. R4,,* increases as R4,,~, decreases. = 0.05-pF tubular paper capacitor, 500-volt, d.c., working = 32-pF electrolytic capacitor, 450-volt, d.c., working = 2-pF paper capacitor, 600-volt, cl.c., working = 8-pF electrolytic capacitor, 500-volt, d.c., working = 0.02-pF tubular paper capacitor, 500-volt, d.c., working c, C8 C , ClO Cll Cl, = 20-pF metallised paper capacitor, 150-volt, d.c., working MR1, MR, = 250-volt, r.m.s., silicon metal rectifiers = Round, double-pole, double-throw toggle switch - $pole, %way wafer switch = ME 1400 valve = EF 37A valve = ECC 83 valve Sl sz v, v2 v3 v4, v,, v6, vll = 6060 valves236 DENTON AND WHITEHEAD [Artalyst, VOl.91 = E Z 80 valve = 108 C1 valves = Constant voltage transformer, input : 240 volts, 50 c/s; output: 6-0 volts = Main transformer, input: 200-250 volts; output: 250-0-250 volts, 60 mA; = 20,000-ohm coil, 4-pole change-over, Post Office type 3000 plug-in relay = 20,000-ohm coil, 2-pole change-over, Post Office type 3000 plug-in relay = Centre-zero microammeter, 2.5 inch diameter, 100-0-100 pA full-scale = Painton Multicon 12-pole socket 6.3 volts, 3 amps and 6.3 volts, 1 amp deflection RLD/4 RLE/1 M P Appendix I1 COMPONENTS LIST FOR THE SEQUENCE UNIT (FIG.8) MR,, MR,, MR,, MR, RLA. RLB. RLC MR3, MR, RLG; RLS,.RLT, RLY RMD, KMF 1. 2. 3. 4. 5. 6. 7. 8. = BjO-ohrn, l-watt, high-stability carbon resistors = 600-ohm, &watt, wire-mound resistors = 100-ohm, B-watt, high-stability carbon resistor = 1-pF, 500-volt d.c. working paper capacitors = 64-pF, each composing 2 32-pF, 450-volt d.c. working, electrolytic = 0-l-pF, 500-volt d.c. working, tubular paper capacitor = REC 23a metal bridge rectifier, 54 volts r.m.s., 1 amp input, 50 volts = REC 51A silicon rectifier, 250 volts r.m.s., 500 mA capacitors d.c. output = Miniature plug-in relays, 24-volt d.c., 650-ohm coil, 4-pole change-over = Miniature flag-in relays, 48-volt d.c., 1850-ohm coil, 4-pole change-over = Push to make, release to break, double-pole double-throw switch = Push to break, release to make, double-pole double-throw switch = Centre-off, double-pole double-throw toggle switch = Round double-pole double-throw toggle switches = Micro-switches = Micro-switch = $-inch 2-amp fuse = Transformer: primary, 250 volts; secondary, 50 volts, 2 amps = Standard filament transformer: primary, 250 volts; secondary, 6.3 volts = 3-bank, 12-position, plug-in type Uniselector unit, 250-ohm coil = 6-3 volts, l-watt, panel lamps contacts rated a t 3 amps a.c. contacts rated a t 250 volt, 3 amp a x . REFERENCES Wilson, C. L., and Wilson, D. W., Editors, “Comprehensive Analytical Chemistry,” Elsevier Kolthoff, I. M., and Elving, P. J ., Editors, “Treatise on Analytical Chemistry,” Interscience Nakazono, T., J . Chem. SOC. Japan, 1921, 42, 526, 761. Kahm, J. A., A n a l y t . Chem., 1962, 24, 1832. Malmstadt, H. V., and Roberts, C. B., Ibid., 1956, 28, 1884. Brown, J. F., and Weir, K. J., Analyst, 1958, 83, 491. Labovatory Equipment Digest, Volume 2, KO. 3, p. 11. British Patent 39,786, 1962. Publishing Company, Amsterdam, London, New York, 1962, Volume lC, p. 501. Publishers, New York and London, 1961, Part IT, Volume 5, p. 30. Received A p r i l 14t12, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100224

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

April, 19661 HAMZA AND HEADRIDGE 237 The Polarographic Determination of Lead after Cation-exchange Separation BY A. G. HAMZA AND J. B. HEADRIDGE (Department of Chemistry, The University, Shefield 10) From ni hydrofluoric acid solution, lead, cobalt, copper(u), manganese(II), nickel and a small part of chromium(II1) are strongly adsorbed on a column of strongly acidic cation-exchange resin in the hydrogen form, while other elements present in steel are either not adsorbed or only weakly adsorbed, and are removed from the column on washing it with M hydrofluoric acid. On elution with 2 M hydrochloric acid, the lead is removed from the column and determined by d.c. polarography. This method is applied to the determination of lead (>0.01 per cent.) in steels. THE direct polarographic determination of lead in the presence of aluminium, chromium(m), cobalt, copper, iron(II), manganese, nickel, tin( 1v) and zinc is straightforward, and alloys containing these elements have been satisfactorily analysed for 1ead.l 9 2 9 3 However, the polaro- graphic determination of lead is more difficult in the presence of titanium(1v) and molyb- denum(vI), elements often present in high-alloy steels, because these species often produce reduction waves that interfere with the lead wave.Hamza and Headridge,* using M ammonium fluoride adjusted to pH 7 as the base electrolyte, obtained a reversible reduction wave for lead, E+ = -0.453 volt against a S.C.E., with which there is no interference from molybdenum(vI), titanium(1v) and vanadium(1v). However, if that base electrolyte was used for the direct determination of lead in steel, there would be interference from iron( HI), which produces an irreversible reduction wave, E, = -0-77 volt against a S.C.E., that interferes with the lead wave when the molar ratio of iron(II1) to lead exceeds 4 to 1.Although attempts were made to remove interference from iron(rI1) by reducing it quantitatively to iron(II), these were unsuccessful because iron(I1) is a powerful reducing agent in M ammonium fluoride. It was, therefore, decided to examine the possibility of separating lead from iron(m), molybdenum(v1) , titanium ( ~ v ) and vanadium(v) using a cation-exchange resin. Headridge and Dixon5 have reported that aluminium, iron(Ir1) and vanadium(v) are scarcely adsorbed on the cation-exchange resin, ZeoKarb 225, in the hydrogen form, from M hydrofluoric acid.On the other hand, cobalt, copper (11), nickel and manganese(I1) are strongly adsorbed. The behaviour of chromium( 111) was unusual. From boiled solutions, the chromium(II1) was obviously present in two complexes not in rapid equilibrium. The complex present in major amount was not adsorbed by the cation-exchange resin from M hydrofluoric acid, but the minor complex, possibly Cr(H,O) 4F,+, was strongly adsorbed. Nikitin6 has reported that lead is adsorbed by a cation-exchange resin from M hydro- fluoric acid. This is to be expected since lead, like copper(II), complexes only weakly with fluoride,' and copper(I1) is strongly adsorbed by ZeoKarb 225 from M hydrofluoric acid. arsenic(II1) and (v), antimony(II1) and (v), tin(Iv), titanium(Iv), zirconium, niobium(v), tantalum, molybdenum(v1) and tungsten(v1) are either not adsorbed or only weakly adsorbed by a cation-exchange resin from M hydrofluoric acid.6 8 9 9 A simple method is therefore available for separating lead from elements that interfere with its polarographic determination.The alloy is dissolved in a mixture of hydrofluoric and nitric acids, the excess of nitric acid is removed by evaporation, and a M hydrofluoric acid solution of the metallic ions is passed down a column of ZeoKarb 225 in the hydrogen form. Lead, cobalt, copper(rI), manganese(II), nickel and a small fraction of the chromium(II1) are adsorbed. On washing with 16 column volumes of M hydrofluoric acid, arsenic(v), antimony(v), aluminium, iron(m), tin(Iv), titanium(Iv), zirconium, vanadium(v) , niobium(v), tantalum, molybdenum(vI), tungsten(v1) and most of the chromium(II1) are removed from the column.Most, or all, of the copper(II), cobalt, chromium(m), manganese(I1) and nickel accompany the lead, but cobalt, manganese and nickel do not interfere with the polarographic determination of lead in a base electrolyte of M hydrochloric acid. Copper in amounts considerably in excess of the lead causes difficulties with the d.c. polarographic determination of lead in M hydrochloric Hydrochloric acid (2 M) was considered to be a suitable eluant for lead.238 HAMZA AND HEADRIDGE : POLAROGRAPHIC DETERMINATION [Analyst, Vol. 91 acid, but not with a differential cathode-ray or pulse polarographic determination. Chro- mium( 111) interferes with the polarographic determination of lead in M hydrochloric acid, and, if more than a trace of chromium(II1) is present, a base electrolyte of 0-5 hi acetic acid - 0.5 M sodium acetate - 0.5 M sodium chloride may be used.There is no interference from chro- mium(II1) in this base electrolyte. A polarographic method based on this scheme is now described for the determination of lead in steels. EXPERIMEKTAL APPARATUS- Polarograph-A Sargent model XV polarograph was used. Polarographic cell-This was a Meites-type H-cell with a saturated calomel electrode in the electrode compartment and an agar-saturated potassium chloride bridge. The volume of solution used in the solution compartment was 40 ml.The cell was immersed in a water tank thermostatically controlled at 25.0" C,. Oxygen-free nitrogen was used to free the solution from dissolved oxygen. Polythene column-This was constructed as follows. The bottom of part of a polythene specimen tube, of length 2.0 cm and internal diameter 1.3 cm, was drilled with eight holes of diameter 0.05 cm, and half-filled with polythene drillings. A polythene disc, of diameter 1-35 cm, was also drilled with eight holes of diameter 0.05 cm, and was forced into the specimen tube until it came into contact with the drillings. A piece of polythene tubing, 34 cm long with an internal diameter of 1.0 cm and external diameter of 1.3 cm, was then inserted into, and welded to, the specimen tube. A short piece of flexible plastic tubing was pushed over the lower end of the specimen tube and fitted with a screw clamp.An aqueous slurry of ZeoKarb 225 (SRC14), of mesh size 52 to 100, was added to the column to produce a resin bed 3.8 cm high and 3-0 ml in volume. The top 30 cm of the column acted as a reservoir. The resin was washed with 5 M hydrochloric acid to convert it entirely to the hydrogen form, and then by water until free from chloride ions. It was then ready for use. REAGENTS- Hydrochloric, hydrojluoric and nitric acids-These were of analytical-reagent grade. High-pzzrity iron-This was Specpure iron obtained from Johnson, Matthey and Company Limited. Standard lead solution-Prepare an exactly M solution from the appropriate weight of analytical-reagent grade lead nitrate crystals, the lead content of which has been previously determined by a complexometric titration with standard EDTA solution.The lead solutions used in obtaining the calibration graph are prepared from this standard lead solution by diluting with 2 M hydrochloric acid and water. METHOD- Dissolve 1 g of steel in 15 ml of 40 per cent. w/w hydrofluoric acid plus 1 ml of nitric acid, sp.gr. 1.42. Evaporate the solution just to dryness and dissolve the residue in 5ml of 40 per cent. w/w hydrofluoric acid. Re-evaporate just to dryness. Dissolve the residue in 25 ml of 10 M hydrofluoric acid and dilute the solution to 260 ml in a graduated flask. Immediately transfer the solution to a dry polythene bottle. Add a suitable aliquot of the M hydrofluoric acid solution to the column of ZeoKarb 225 resin at a flow-rate of approximately 2 ml minute-l, such that the quantity of lead, copper, cobalt, manganese, nickel and chromium(II1) does not exceed 0.8 millimoles (Notes 1 and 2).Then pass 50 ml of M hydrofluoric acid through the column at a flow-rate of approximately 2 ml minute-l, followed by 10 ml of water. NOTE 1. Only 2 per cent. of the total chromium(II1) is retained by the cation-exchange resin. Make allowance for this when calculating the quantity of adsorbable cations. NOTE 2. The column of cation-exchange resin has a total capacity of 3.2 millimoles for doubly charged ions. By restricting the total quantity of strongly adsorbed ions t o 0.8 millimoles, only the top 25 per cent. of thc column will be occupied by these ions. This is considered to be an adequate safety factor t o ensure that no lead is removed when 50 ml of M hydrofluoric acid are subsequently passed through the column.April, 19661 OF LEAD AFTER CATION-EXCHANGE SEPARATION 239 Elute all of the lead from the column with 50 ml of 2 M hydrochloric acid at a flow-rate of 2 ml minute-l, collecting the effluent in a 100-ml graduated flask.Dilute the solution to the mark with water. Place 40ml of this solution in the solution compartment of the polarographic cell and record a polarogram over the potential range of 0 to -1.0 volt against a S.C.E. When more than a trace of chromium(II1) is present in the alloy, transfer 50 ml of the M hydrochloric acid solution by pipette into a 100-ml graduated flask, make up to the mark with 2 M sodium acetate solution, and record a polarogram with this solution.Measure the lead diffusion current at -0.55 volt against a S.C.E. and determine the concentration of lead in the solution from a suitable calibration graph. Hence calculate the amount of lead in the alloy. The authors used a lead calibration graph prepared from six solutions in the concentration range of to M. The standard deviation of the error in diffusion current was 0.010 pA corresponding to a relative standard deviation of 1.4 per cent. at a lead concentration of M. The error in diffusion current is expressed by id (measured) - id (calculated), where the values of i d (calculated) are points exactly on the straight-line calibration graph of diffusion current versus concentration. RE su LTS ANALYSIS OF SYNTHETIC SOLUTIONS- Four synthetic solutions of iron(m) plus lead in M hydrofluoric acid were prepared and carried through the cation-exchange and polarographic procedures.Each synthetic solution contained 1 g of Specpure iron. The volume of each solution passed through the column was such that the lead concentrations of the solutions being polarographed were in the range of 4 x to 1 0 - 4 ~ . The recoveries of lead are shown in Table I. TABLE I THE RECOVERIES OF LEAD AFTER A CATION-EXCHANGE SEPARATION FROM IRON(III) Lead taken, mg . . . . 1.00 4.11 8-19 20.3 Lead found, mg . . . . 1-00 4.08 8.22 20.3 ANALYSIS OF STEELS- mentioned previously. Two steels were analysed by the recommended method using the calibration graph The results are shown in Table 11.TABLE I1 RESULTS FOR THE DETERMINATION OF LEAD IN STEELS Lead found Lead content, polarographically, Alloy per cent. per cent. Mild steel, BCS 329 . . . . 0.050 0.050, 0.050 Lead steel, BCS 212jl . . 0.22 0.21, 0.22 DISCUSSION ,4 cation-exchange separation of lead prior to its polarographic determination is not actually necessary with the two steels analysed above, but the results, in conjunction with those for the synthetic solutions, are proof of the reliability of the separation scheme. Although the above results are satisfactory, the metallurgist is primarily interested in amounts of lead less than 100 p.p.m. Because the d.c. polarograph is incapable of producing precise results for lead determinations at concentrations below 100 p,p.m. in the alloy by the above method, we were unable to examine the full potentialities of the method.However, we see no reason why the lower limit of determination should not be lowered to 1 p.p.m. by using a more sensitive polarograph such as a differential cathode-ray or pulse polarograph. Parts per million of trace metals in alloys have already been determined using a square-wave polarograph. The method should be particularly suitable for the determination of lead in alloy steels containing titanium, vanadium, niobium, tantalum, molybdenum and tungsten, all of which are soluble in a mixture of hydrofluoric and nitric acids. The method could also be applied240 HAMZA AND HEADRIDGE [Analyst, Vol. 91 to the determination of lead in niobium- and tungsten-base alloys, etc. With all alloys precautions must, of course, be taken to ensure that the column is not overloaded with cobalt, copper, nickel and manganese, which are adsorbed with the lead. We are indebted to Riyadh University, Saudi Arabia, for providing one of us (A.G.H.) with a maintenance grant. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Ferrett, D. J., and Milner, G. W. C., Analyst, 1956, 81, 193. Scholes, P. H., Ibid., 1961, 86, 116. Meites, L., Editor, “Handbook of Analytical Chemistry,” McGraw-Hill Book Company Tnc., New Hamza, A. G., and Headridge, J. B., Talanta, 1965, 12, 1043. Headridge, J. B., and Dixon, E. J., Analyst, 1962, 87, 32. Nikitin, M. K., Dokl. Akad. Nauk SSSR, 1963, 148, 595. “Stability Constants,” The Chemical Society, London, 1964, pp. 263 and 266. Fritz, J. S., Garralda, B. B., and Karraker, S. K., Analyf. Chew., 1961, 33, 882. Faris, J. P., Ibid., 1960, 32, 520. York, 1963, pp. 5-127. Received September 3rd, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100237

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

April, 19661 HINE, CRAWFORD, DEUTSCHMAN AND TIPTON 241 The Determination of Sodium in Aluminium Alloys Flame Spectrophotometry with Fuel-rich Flames to Reduce Interference BY R. A. HINE,* R. CRAWFORD,? J. E. DEUTSCHMAN AND P. J. TIPTON: (Aluminium Company of Canada, Limited, A rvida, Quebec, Canada) The determination of trace quantities of sodium in aluminium alloys by flame spectrophotometry offers a rapid and accurate control procedure. When conventional flames with a balanced fuel - air mixture are used, molecular oxide band spectra of iron and manganese are strongly excited, and interfere with the measurement of the sodium emission. The interference is much less in fuel-rich flames while the sensitivity to sodium is slightly increased. The use of fuel-rich flames therefore provides a more versatile and accurate method than those hitherto used. As in most methods for the determination of sodium it is advantageous to add lithium as an internal standard to compensate for minor variations in conditions. The results are of general application to the analysis of other materials which may contain iron and manganese, and possibly nickel and chromium.THE deleterious effects of small amounts of sodium in aluminium - magnesium alloys were first described by Ransley,l who showed that as little as 10 p.p.m. of sodium could cause embrittlement leading to cracking on hot-rolling of the ingots. With large ingots even smaller sodium contents have adverse effects, and it is therefore necessary to be able to carry out accurate analysis before fabrication of the ingot.Spectrographic determination of sodium is used in routine control but requires chemically- analysed metal standards for calibration. Careful attention to the sampling procedure is also necessary because of the tendency for sodium to segregate. Flame spectrophotometry offers a highly sensitive means of determining sodium,2 and has been used to establish the calibration values of spectrographic standards. Moreover, samples can also be taken by drilling the solid ingot, thus avoiding segregation difficulties. Matelli3 described a method using a Beckman DU spectrophotometer with flame attachment capable of determining down to 10 p.p.m. of sodium in aluminium alloys. By using the more sensitive Unicam SP900 flame spectrophotometer, Hine and Rates4 extended the range to 1 p.p.m.without using methanol to intensify the emission. However, in applying the latter method to the analysis of a variety of aluminium alloys it has been found that errors can result from interference unless the metal used for calibration is identical in composition (other than sodium content) with the sample being analysed. In particular, differences in iron and manganese contents between the sample and calibration metal give rise to serious errors. In this paper it is shown that the extent of interference is governed by the type of flame used and that with cool, fuel-rich flames the interference is slight. EXPERIMENTAL APPARATUS- Flame spectrophotomeler-~nicam SP900 with acetylene - air flame. All other apparatus should be made of quartz, translucent silica or polythene, as appropriate.REAGENTS- Sodium-free alloy for calibration-Place a clean piece (10 to 50 g) of alloy, of the same type as that to be analysed, in a graphite crucible in a vacuum distillation apparatus capable of maintaining a vacuum of at least 10-5 mm of mercury. A suitable apparatus is described * Present address : Aluminium Laboratories Limited, Banbury, Oxon. t Present address : International Alloys Limited, hylesbury, Bucks. Present address: Canada Colors & Chemicals Dominion Ltd., Toronto 3, Ontario.242 HINE, CRAWFORD, DEUTSCHMAN AXD TIPTON: DETERMINATION [Analyst, Vol. 91 on p. 24 of “Analysis of Aluminium and its Alloys.”2 Heat to 900” C for 1; hours. Cool, remove the specimen, pickle the surface in dilute hydrochloric acid, rinse and dry.Repeat the vacuum treatment, Reduce by milling or drilling with scrupulously clean tools. Take 1-g portions of the metal for calibration. Pure water-Pass water (preferably distilled) through a mixed-bed resin, e.g., Amberlite MB3, using all-plastic apparatus. Hydrochloric acid, 6 N-Prepare from the purest obtainable reagent ; if necessary, distil in quartz. Sodium chloride stock solution-Dry pure sodium chloride at 105” C ; dissolve 2.5418 g in water and make up to 1000 ml in a volumetric flask. Transfer immediately to a polythene bottle. Sodium chloride working solutions-Prepare dilutions of the stock solution such that 1 ml = 10 pg of sodium and 1 ml = 1 pg of sodium, respectively. Lithium chloride stock solution-Dissolve 5-32 g of lithium carbonate in a minimum of dilute hydrochloric acid in a platinum dish.Heat gently to expel carbon dioxide, cool and make up to 1000 ml in a volumetric flask. Transfer immediately to a polythene bottle. 1 ml = 1 mg of lithium. Lithium chZoride working solutions-Prepare dilutions of the stock solution such that 1 ml = 100 pg of lithium and 1 ml = 10 pg of lithium, respectively. Other metals used were of Johnson and Matthey “Specpure” grade. 1 ml = 1 mg of sodium. PROCEDURE (FOR RANGE 0 TO 10 P.P.M. O F SODIUM)- Weigh 1 g of sample into a 250-ml silica beaker; at the same time weigh six 1-g samples of sodium-free alloy for calibration into other beakers. Wash beakers and contents by decantation three times with de-ionised water, carefully draining off the water each time.Add 30ml of 6~ hydrochloric acid, cover with a silica watch-glass and warm to start the reaction, finally heating to complete solution. Evaporate to incipient crystallisation of salts and allow to cool. Re-dissolve the salts in 25 ml of water and transfer (filtering if necessary) into 100-ml quartz volumetric flasks. Add to each 5 ml of lithium solution (1 ml = 10 pg of lithium) and to five of the calibration solutions add 2, 4, 6, 8 and 10 ml of standard sodium solution (1 ml = 1 pg of sodium) retaining the remaining one as a blank. Adjust to volume with de-ionised water, mix and transfer to clean polythene bottles. Set up the flame photometer using suitable slit and gain control settings and adjust the flame as indicated below. Aspirate the highest standard and arrange to give 90 to 95 per cent.galvanometer deflection when set on the sodium line at 589 mp. Aspirate all the standards and samples, clearing between each by passing de-ionised water, and record the sodium emission readings. Re-set the instrument to the wavelength of the lithium peak at 670-7 mp to give a galvanometer deflection of 40 to 60 per cent. and again aspirate standards and samples, recording the lithium emissions. Subtract the blank sodium reading from the readings for the standards and samples. Plot the sodium-to-lithium emission ratios against sodium content and read the contents of the samples from the graph. For sodium contents above 10 p.p.m. use the stronger sodium and lithium solutions for calibration, with appropriately lower gain settings on the instrument.NOTE-In the case of alloys containing Inore than 1 per cent. of silicon, ignite the filtered silicon Dissolve residue in a platinum crucible, treat with hydrofluoric and nitric acids and evaporate to dryness. the residue in a little hydrochloric acid and add to the main solution. FLAME BACKGROUND- The air was set at 23 p.s.i. throughout, as lower pressures are insufficient to give good atomisation of the solution. Variation of flame conditions was obtained by adjusting the gas pressures. For the examina- tion of traces of sodium it is obviously necessary to keep contamination and over-all back- ground down to a minimum. The background at 589 mp was therefore measured at a series of acetylene pressures using a solution of sodium-free N8* alloy (1 g per 100 ml).The instrument settings were arranged to give full deflection of the galvanometer with a solution containing 0.1 pg of sodium per ml using pure water as the reference solution. An acetylene - air flame was used in these experiments. * The alloy designations used throughout are those of B.S. 1470.April, 19661 OF SODIUM IN ALUMINIUM ALLOYS BY FLAME SPECTROPHOTOMETRY 243 The results are shown in Fig. 1, from which it is seen that minimum background is obtained at positions A or B. At position B the flame is fuel-rich and just verging on luminosity. At position A it is air-rich and unstable. Position C represents the balanced flame usually used and recommended by the manufacturers; it is achieved by starting with a gas pressure of about 10 cm and turning down the gas until the blue burner cones just verge on instability.Surprisingly, this conventional flame gave high background, and the gas-rich flame type I3 appeared to be preferable. However, this experiment alone was not conclusive since background is composed of several factors, including sodium impurity in the reagents, effects of reagents on the flame and, possibly, effects of alloying elements in the metal. Conceivably, the higher emission with flame C could be reflecting a greater sensitivity to the sodium impurity unavoidably present. 24 $22 rn co In % 20 c .- v) .- E I* w 16 26 I - - - - - I I I 141 I I I 1 1 - 2 4 6 8 10 12 14 Acetylene pressure, cm O' I ; ; 1 ; Q ; pg of sodium per 100 ml Fig. 1. Effect of flame condition on back- Fig.2. Calibration graphs for different flame conditions. Acetylene pressure: (A) 8 cm; (B) 14 cm; (C) 4 cm ground emission a t 589 mp. A: Air-rich and un- stable flame; B: Fuel-rich flame and C: Balanced flame Calibration curves were therefore constructed for the three types of flame, again using N8 alloy as the calibration metal. The results are shown in Fig. 2. This figure demonstrates again the higher background with the conventional balanced flame, but also shows that the sensitivity to sodium is actually better in the other types of flame. To determine the reason for the higher background intercept with the conventional balanced flame, other experiments were carried out. No effect was found by adding magnesium up to the equivalent of 10 per cent.to calibration solutions, hence the magnesium content of S8 alloy was not the cause. This alloy also contains about 0-8 per cent. of manganese, 0-3 per cent. of iron and 0.2 per cent. of silicon (the silicon is removed in processing so this could not be the cause of the background). Similar behaviour in different flame types was found with commercially pure aluminium (0-4 per cent. of iron, 0.3 per cent. of silicon) but not with super-purity metal (99.89 per cent. of aluminium). Thus attention was given to the effects of iron and manganese on background emission. EFFECT OF IRON AND MANGANESE Both iron and manganese are shown by Dean5 to exhibit pronounced molecular oxide bands in the region of sodium emission. The exact situation at 589 mp is difficult to assess because of sodium impurity in the solutions used, but it seems possible that excitation of oxides could vary considerably in different flame types and hence give rise to the anomalous effects observed.Solutions were prepared containing 1 mg and 5 mg of iron per 100 ml, and also 5 and 10 mg of manganese per 100 ml. The spectra recorded showed much higher emission from iron and manganese in balanced and air-rich flames than in the fuel-rich flame. However, the presence of sodium impurity in these solutions complicates the interpretation, and a more convincing experiment was carried out. Duplicate samples of aluminium were dissolved in hydrochloric acid and 10 mg of iron added to the solution. Iron was extracted from one solution with di-isopropyl ether and the spectra of the solutions then recorded in244 HINE, CRAWFORD, DEUTSCHMAN AND TIPTON: DETERMINATION [Analyst, Vol.91 three types of flame. The results are shown in Fig. 3. In each case the broken line shows the emission from sodium only (after iron extraction) while the full line shows the spectrum with superimposed emission from molecular iron oxide. These results show conclusively that iron oxide band spectra interfere seriously in the determination of sodium when conventional balanced or air-rich flames are used for excitation, but that interference is slight in a fuel- rich flame. Wave I ength, mp Wavelength, rnp L I 580 600 t Wavelength, rnp Fig. 3. Spectra of solutions before and after extraction of iron (10 mg per 100 ml). Broken lines, iron-free spectrum; continous line, iron with sodium impurity.( a ) air pressure, 23 p.s.1. ; acetylene pressure, 14 cm; (b) air pressurc, 23 p.s.i., acetylene pressure, 8 cm; (c) air pressure, 23 p.s.i., acetylene pressure, 4 cm The effect of increasing iron contents on the emission from 5 pg of sodium per 100 ml, in the presence of aluminium, is shown in Fig. 4 for the three flame types. Similar results were obtained for manganese additions except that the magnitude was lower with manganese. Again it is obvious that the fuel-rich flame is least sensitive to interference and gives an almost horizontal line, whereas the most air-rich flame has the steepest slope. MAGNITUDE OF ERRORS The magnitude of errors caused by iron or manganese interference depends on the relative contents of these elements in the calibration metal and the sample.The errors will be positive if the sample contains more of these elements than the calibration metal and negative if it contains less. Thc crror is always at a minimum with a fuel-rich flame. Some examples are given in Table I. In this table the figure given as the established value is the best estimate of sodium content obtained by a radioactivation method. The calibration metal was commercially pure aluminium containing about 0-25 per cent. of iron. TABLE I RESULTS OBTAINED ON ALUMINIUM ALLOYS IN FUEL-RICH AND AIR-RICH FLAMES Composition, per cent. Established 7- sodium, iron manganese p.p.m. 1.2 0.04 2 0-22 0.3 7 0-3 0.8 1.1 0.16 0.17 3.2 0.01 0.0 1 < 0.5 I Fuel-rich flame sodium found, p.y .m. 3.3 6.3 1.5 3.8 0 11 Air-rich flame sodium found, 8-5 Serious iron effects in I1 10 Manganese effect in I1 4.0 Manganese effect in I1 5.0 - 2-2 Negative errors in I1 clue to lower iron content of sample p.p.m. Remarks -April, 19661 OF SODIUM IN ALUMINIUM ALLOYS BY FLAME SPECTROPHOTOMETRY 245 Iron, mg per 100 ml Fig. 4. Effect of increasing iron on emission of 5 pg of sodium per 100 ml. Acetylene pressure: Graph A (A), 8 cm; graph B (e), 14 cm; graph C (O), 4 cm FLAME REPRODUCIBILITY AND PRECISION USING FUEL-RICH FLAME The fuel-rich flame shown to be preferable from the point of view of interferences is less familiar than the conventional balanced flame, and possibly less convenient to work with. However, after some experience it is possible to reproduce the flame and obtain consistently good results.The general stability of the instrument under these conditions is excellent, as shown by the following experiment. A solution of an aluminium - magnesium alloy con- taining 3.5 p.p.m. of sodjum was prepared, the instrument set up and a calibration carried out; 6 readings were taken on the sample solution and the sodium content determined. The flame was then turned out, re-lit, re-adjusted and the procedure repeated to a total of 6 times. The “within-run” standard deviation found was equivalent to t-0-15 p.p.m. of sodium and the “between-run” value was also &0-15 p.p.m. The over-all precision of the method, established by processing separate weighed samples of several alloys was found to be about &O-5 p.p.m.for a content of 3 p.p.m. of sodium. DEFINITIOK OF FLAME TYPES The figures for fuel pressure given in the text, and illustrations as representing the flame types used, only provide a general indication of the value. The exact pressure to use depends upon the age and condition of the burner jet and other variables. Final adjustment of the flame is therefore carried out visually according- to the following instructions. (For the Unicam SP900 instrument, with air pressure at 23 p.s.i., the approximate acetylene pressures are shown in brackets.) Bnlmzcecl pame-This is the conventional flame in which there is sufficient air to give steady and complete combustion of the fuel. I t is obtained by starting with a slightly fuel-rich flame and then turning down the gas pressure until the inner blue burner cones just become unstable, then increasing the pressure slightly until the cones regain stability (8 to 10 cm of acetylene pressure).Air-richflame-The fuel pressure is turned down to the point where the flame will only just remain alight. The flame is weak, short and barely visible (4 to 5 cm of acetylene pressure). Fuel-richjame-The fuel pressure is turned up until the flame becomes luminous and then turned back until the luminosity just disappears (11 to 14 cm of acetylene pressure). DISCLJSSION AKD CONCLUSIONS The interference caused by excitation of molecular oxide bands of iron and manganese was the most important aspect of a larger investigation into the determination of trace amounts of sodium in aluminium alloys. Other work showed that the acidity of the solution246 HINE, CRAWFORD, DEUTSCHMAN AND TIPTON [Analyst, Vol.91 affected the emission from sodium and that there were complex interactions between various factors. However, by close standardisation of the procedure, and the use of lithium as an internal standard to compensate for small variations in conditions, accurate results could be obtained. The errors caused by iron or manganese, or both, when a conventional flame is used, are of sufficient magnitude that the calibration metal must be of almost identical composition with the sample to obtain correct results. In practice this would mean subjecting a portion of each sample to vacuum distillation to serve as its own calibration metal. On the other hand, although some interference still occurs in fuel-rich flames, it is so small that calibration metal of similar alloy type to the sample can be used without incurring appreciable error.In fact, several groups of alloys, such as the aluminium - magnesium series, are sufficiently similar in iron and manganese contents to allow common standards of sodium-free calibration metal to be used. Of other common alloying elements, it has been found that copper, zinc and magnesium have no appreciable effect, but a few less common elements such as nickel and chromium (which are known to give oxide bands) may have similar effects to iron and manganese. However, the use of calibration metal of the same alloy type in conjunction with a fuel-rich flame would be likely to give accurate results in these cases also.It is not clear whether the lower emission from iron and manganese oxides in fuel-rich flames is a result of the lower temperature of such flames, or whether the reducing character of the flame suppresses the formation of oxides. Fasse16y7 and his co-workers have carried out extensive investigations into the flame spectra of rare-earth elements and of vanadium, niobium, etc. They have shown that, whereas in conventional (stoicheiometric) flames monoxide band spectra of these elements predominate, in fuel-rich flames distinctive line spectra appear which allow quantitative determination of the elements. Fassel considers that though the fuel-rich flames are cooler, the main reason for the predominance of line spectra is that the conditions for monoxide formation are unfavourable (reducing species present) and lead to a high atom population in the flame.A similar explanation fits all of the observations made in the present work. Analogous effects were also found in the deter- mination of lithium in aluminium alloys, and the wider investigation of unconventional fuel-rich flames may result in improvements in flame spectrophotometry procedures for many elements. Although the work was concerned with the analysis of aluminium alloys, the results are of general application, and could be of significance in the determination of sodium in biological samples, plant materials and minerals. For all analyses where iron or manganese, or both, may be present, the use of a fuel-rich flame, just verging on luminosity will give the greatest freedom from interference coupled with high sensitivity. REFERENCES 1. 2. 3. 4. 5. 6. 7. Ransley, C. E., and Talbot, D. E. J., J . Inst. Metals, 1959-60, 88 (4), 150. “Analysis of Aluminium and its Alloys,” The British Aluminium Company, Limited, Publication No. 405. Mattelli, G., and Attini, E., “Determination of Sodium in Aluminium by Flame Spectrophoto- metry,” Instituto Sperimentale dei Metalli T.eggcri, Publication No. X-243, 1960. Hine, R. A., and Bates, J. F., “Applied Materials Research,” October, 1963, 216. Dean, J . .4., “Flame Photometry,” McGraw-Hill Book Company Inc., Sew Yorli, 1960. Fassel, V. A,, Curry, R. H., and Kniseley, R. N., Spectrochzm. A d a , 1962, 18, 1127. Fassel, V. A., RiZyerP, R. B., and Kniseley, R. N., Ibzd., 1963, 19, 1187. Received August lGtJz, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100241

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

April, 19661 PEARSON 247 The Determination of Water in Lubricating Oils by a Near-inf rared Spectrophotometric Method BY B. D. PEARSON (Dmby and District College of Technology, Derby) The water content of clear mineral oils can be quickly and accurately determined by dissolving the wet oil in ethyl acetate and measuring the near-infrared absorbance of the soh tion, relative to a similar reference solution previously dried by molecular sieves. In discoloured or cloudy, wet oils the water can be removed by azeotropic distillation with ethyl acetate, and the water content of the distillate determined spectroscopically. With the latter procedure, errors that arise at low water concentrations may be due to the absorption of atmospheric moisture by the solvent. MANY workers have shown that water can be simply, rapidly and accurately determined in such liquids as glycerol, ethylene and propylene glycols, methanol, isopropanol, butanol and fuming nitric acid, by near-infrared spectroph~tometry.~ v 2 9 3 9 4 9 5 In general, the method has been considered to be applicable to the determination of water in alcohols, aldehydes, amines, esters and ketones.6 Because spectrophotometric measurements can be rapidly made over a single sharp absorption peak with a high degree of accuracy, it would be useful if the technique could be extended to hydrocarbons, particularly lubricating oils.Undiluted oils are difficult to manipulate into absorption cells ; measurements would be greatly simplified by the use of a solvent, not particularly hygroscopic and yet easily dried, for the oil and a reasonable amount of water.Ethyl acetate is a solvent which fulfils these conditions. Water in water - oil emulsions could also be determined using this procedure. Neither typical lubricating-oil additives nor lubricating oils interfere with the near-infrared water absorption band at 5290cm-l. Difficulties arise in the spectroscopic determination of water in used oils. These contain finely divided particles that are suspended in the oil and scatter much of the incident radiation, so introducing intolerably large errors. No simple method of removing the suspended material is available, and so this difficulty is overcome by the rapid azeotropic distillation of the water from the oil with ethyl acetate. The water content of the ester distillate is then determined spectroscopically.A similar procedure has been used to determine the water content of powders.' METHOD AND RESULTS REAGENTS- for at least 48 hours over molecular sieves (with approximately 25 g per 24 litres). sieves, regenerate them in a stream of argon at 250" to 300" C for 10 hours. Ethyl acetate-Dry ethyl acetate (Hopkin and Williams AnalaR grade) was further dried LWolecular sieves, Linde Air Products 4A grade (supplied by B.D. H.)-After using the CALIBRATION-BEER'S LAW MEASUREMENTS- Near-infrared spectrophotometric measurements were made on a Unicam SP700 instru- ment, with 10-mm stoppered cells. Standard solutions of water in ethyl acetate (or in ethyl acetate and oil) were prepared by the weight-fraction method, from solvents (or solutions) previously dried over molecular sieves.The absorbance of these wet solutions relative to the dry solvent (or solution) was measured. The results obtained are shown in Fig. 1. REMOVAL OF WATER FROM ETHYL ACETATE BY MOLECULAR SIEVES- To 57 g of ethyl acetate containing 0424 per cent, of water, w/w were added 5.9 g of molecular sieves. Samples of the solution were withdrawn at intervals ; their absorbance was measured and then the samples were returned to the bulk of the solution.248 PEARSON : DETERMINATION OF WATER IN LUBRICATING OILS [AndySt, VOl. 91 Resdts- Time, in minutes . . .. 10 20 35 55 86 125 230 3G0 480 Percentage of water (w/w) in solution . . . . . . 0.290 0.210 0.155 0.105 0.070 0.040 0.020 0.015 0.007 The above results were obtained when the samples were withdrawn at the times indicated.Identical results for the same water content were obtained for solutions of 40g of ethyl acetate and 17 g of oil, regardless of whether the oil was of the straight or detergent type, In each instance the time required to remove half the water from the solutions was 20 minutes. Water, per cent. (w/w) Fig. 1. Beer’s Law relationships for water in lubricating oil samples. Graph A, in ethyl acetate; graph B, in ethyl acetate and straight oil, 2 to 1, v/v; graph C, in ethyl acetate and detergent oil, 2 t o 1, viv UPTAKE OF ATMOSPHERIC MOISTURE BY ETHYL ACETATE- Ten-ml samples of ethyl acetate were measured into eight similar specimen-tubes, 7-5 cm in length and 1.7 cm in diameter. These tubes were placed in a tank saturated with water vapour, at 24” C.One tube was immediately withdrawn to determine the small “handling correction,” and the other tubes were withdrawn at intervals. RCSW~~S- Time, in minutes . . . . . . . . 30 63 90 110 195 255 305 Percentage of water (w/w) dissolved (corrected) 0.034 0.081 0-102 0.124 0.215 0.278 0.374 The above results were obtained when the samples were withdrawn at the times indicated. AZEOTROPIC DISTILLATION APPARATUS- Attach a round-bottomed, side-arm flask of 500 nil capacity to a lagged column 50 cm long and 3 cm in diameter, which has been loosely packed with glass rings. Connect this, via a distillation head and a 35-cm long condenser, to a calibrated receiver protected by a drying tube. Support the flask-heating mantle by means of a laboratory jack so that it can be lowered for fast cooling.Before use, dry the apparatus by distilling at least 80 ml of dry ethyl acetate. REMOVAL OF WATER BY AZEOTROPIC DISTILLATION- 1.360 per cent. of water, w/w. intervals from the distillation flask was determined. The apparatus described above was used to distil 345 ml of ethyl acetate containing The near-infrared absorbance of 5-ml samples withdrawn at Volume of ethyl acetate distilled, in ml . . 50 100 150 200 250 Percentage of water (w/w) remaining . . 0.565 0.337 0.150 0.072 G.018 Percentage of water removed . . . . 58.5 75.2 89.0 94.7 ’38.7April, 19661 BY A NEAR-INFRARED SPECTROPHOTOMETRIC METHOD 249 DETERMINATION OF WATER IN OIL SAMPLES BY USING AZEOTROPIC DISTILLATION- Wash a 50-ml wet-oil sample into the distillation flask with 100 ml of ethyl acetate.Add two dry anti-bumping granules and distil the mixture until 80 ml of distillate have been collected. Measure the absorbance of the distillate in the region 5450 to 5150cm-l, and determine the percentage of water in the distillate by reference to the calibration graph (Fig. 1 ) . It was found that the results for twelve 50-ml samples, containing between 0.0440 and 0-2550 g of water, determined by this method showed an average error of 0.04 per cent. The maximum error was +2.6 per cent. DIRECT DETERMINATION OF WATER IN NEW OR CLEAR OILS- Dissolve 33 ml of wet oil in ethyl acetate and make the volume up to 100 ml. Measure the near-infrared absorbance of this solution relative to a similar solution that has been dried over molecular sieves. Find the water content of the solution from the ethyl acetate and oil calibration graph.DISCUSSION Meeker, Critchfield and Bishop6 have shown that dry reference solutions for near- infrared spectrophotometry can be quickly obtained by using molecular sieves, type 4A. Their results by this method, for the water determination in ethyl acetate and a number of other organic liquids, were in close agreement with those obtained by the Karl Fischer method. This investigation has shown that this drying technique is as equally effective for ethyl acetate - oil mixtures as for ethyl acetate alone. Water can be accurately determined in new or clear oil samples by measuring the absorbance of such systems as water - ethyl acetate - oil or water - diethyl ether - acetone - oil, in the region 5450 to 5100 cm-l.The former system is the simpler of the two for practical use. It is not particularly hygroscopic, absorbing approximately 0.001 per cent. of its own weight of atmospheric moisture per minute, under the experimental conditions used. The ethyl acetate can be readily recovered, and in the proportion of two parts of ethyl acetate to one part of oil (by volume), approximately 0-5 per cent. of water (i.e., 1-5 per cent. of water with respect to the oil), readily dissolves. A disadvantage of this system is that ethyl acetate precipitates some oil additives, but this factor does not lead to errors in the determination of the water content of the oil. The system, diethyl ether - acetone - oil (5.5 to 2.5 to 2.0, by volume) is less convenient ; solvent recovery is more difficult, and cell-window cleaning before measurement is troublesome due to solvent creepage.This system does, however, take up rather more water (2.6 per cent. with respect to the oil). The experimental procedure indicated has the advantage that a dry-oil solution, for reference purposes, can be readily obtained from a wet-oil sample. The wet oil is dissolved in ethyl acetate, and the solution is divided into two parts, one of which is dried with molecular sieves for about 24 hours. This forms the reference solution from which calibration solutions containing, say, 0.1, 0.2, 0.3 and 0.4 per cent. of water may be prepared. A calibration graph is then constructed and the absorbance of the retained wet-oil solution determined.Such a procedure would be tedious if it had to be carried out for every oil sample, but where the same type of oil is dealt with many times only a few minutes are required for each deter- mination, as the same refercnce solution and calibration graph can be used in each case. Calibration graphs are very similar for straight or detergent oils (Fig. l), and if some accuracy can be sacrificed, an “average” calibration graph can be used. However, if the maximum degree of accuracy is required, solutions should be made up by weight rather than volume, and the base-line accuracy of the spectrophotometer periodically checked against solutions of known water content. Under such conditions the limit of accuracy previously suggested6 for the near-infrared determination of water at 5290 cm-l, i.e., k0-02 per cent.absolute, in the range 0-02 to 1.00 per cent. of water, can probably be improved to +0.004 per cent. absolute above the 0-075 per cent. water level. The absorbance of ethyl acetate solutions of many used and all cloudy oils cannot be measured spectroscopically as the solutions scatter much light. In these instances the water in the oil may be removed by azeotropic distillation with ethyl acetate and the amount of water in the distillate determined spectrophotometrically. The efficiency of water-removal by this type of distillation was illustrated by distilling 250 ml of ethyl acetate from 345 ml250 PEARSON [Analyst, VOl. 91 of the ester containing 1.360 per cent.of water. Examination of the distillation residue at this stage showed that 98.8 per cent. of the water had been removed. So, for an ethyl acetate and oil solution containing only up to about 0-5 per cent. water, all the water will have been removed if the volume is reduced to one-fifth by distillation. This is the procedure that was adopted. To determine the accuracy of this method, known amounts of water were added to mixtures of ethyl acetate and oil which had previously been dried over molecular sieves. The ester was distilled and the water content of the distillate determined. For twelve such samples containing 0.1 to 0-6 per cent. of water with respect to the oil, the average error was 0.04 per cent., with a maximum error of +2.6 per cent. The accuracy of the method is highest for oil samples containing more than 0.3 per cent, of water.At lower water con- centration levels the accuracy decreases, possibly due to the now important effect of atmos- pheric moisture during the transference of solutions. For new or clear oil samples good agreement was obtained between the direct spectrophotometric and azeotropic distillation methods. It is interesting that Beer’s law, for solutions of water in ethyl acetate, is only obeyed up to a concentration of 0-42 per cent. w/w of water. Deviations that occur above this value are possibly due to the association of water molecules. A similar deviation was observed for solutions of water in the esters, ethyl propionate and methyl acetate. I thank Mr. J. Duncalf for help with the preliminary experimental work. REFERENCES 1. 2. 3. 4. 5. 6. 7 . Keyworth, D. A., Talanta, 1961, 8, 461. Cordes, H. F., and Tait, C. W., Analyt. Chem., 1957, 29, 485. Chapman, D., and Nacey, J. F., Analyst, 1958, 83, 377. White, L., and Barrett, W. J., Analyt. Chem., 1956, 28, 1538. Sakai, K. et aZ., J . Chern. SOC. Japan, Ind. Chem. Sect., 1959, 62, 632; AnaZyt. Abstr., 1961, 8, 1832. Meeker, R. L., Critchfield, F. E., and Bishop, E. T., Analyt. Chem., 1962, 34, 1510. Brandenberger, H., and Bader, H., Ibid., 1961, 33, 1947. Received June 2nd, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100247

出版商:RSC    

年代:1966

数据来源: RSC

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April, 19661 GREGORY 25 1 The Determination of Residual Reagents in Mineral Flotation Liquors Anionic Surface-active BY G. R. E. C. GREGORY ( JVarren Spritzg Laboratory, Stevenage, Herts.) A method is described for the determination of residual amounts of anionic surface-active reagents, used as flotation promoters, in mineral flotation liquors. The method is equally effective for the long carbon chain carboxylates and the anionic non-soapy surface-active agents. The reagent used is the cationic copper(1r) triethylenctetramine complex, which reacts in alkaline solution with anionic surface-active agents to give an adduct that can be extracted into an isobutanol - cyclohexane mixture. The copper asso- ciated with the surface-active anion in the extract is determined photo- metrically as the coloured complex using diethylammonium diethyldithio- carbamate. Long chain carboxylates with carbon numbers from C,, to C,,, as well as anionic non-soapy surface-active reagents, can be determined in the range 0-2 to 10 p.p.m.The effect of a number of likely interferences has been investigated. ANIONIC surface-active agents, particularly the carboxylate soaps, are extensively used in the mining industry as promoters for the separation of minerals by flotation. A simple and rapid method of determining residual amounts of these reagents is required for plant control, and also for investigating their adsorption on to mineral surfaces. The usual method of analysis for traces of anionic surface-active agents is that of Jones,l modified by Longwell and Maniece,2 in which a cationic dye, methylene blue, is added and the coloured adduct extracted into chloroform solution for photometric measurement.Many similar dye-adduct extraction systems have been reported3 but these generally fail when applied to the carboxylic acid soaps. The quaternary dye pinacyanol has been suggested as a reagent for the determination of laurates in weakly alkaline solution using bromobenzene as extractant for the a d d ~ c t , ~ but the reagent is too unstable for routine use. Tomlinson and Sebba5 determined traces of soaps in neutral solution with the cationic dye crystal violet. The adduct formed was removed by a process described as “ion flotation” and the optical density of the residual dye solution measured. The reaction is non-stoicheiometric, requires precise control of conditions and is very susceptible to interference from dissolved inorganic ions.Milligram amounts of long chain fatty acids in aqueous solution were determined photo- metrically by Aye& and by Iwayama7 by extracting the coloured cobalt or copper(I1) soaps into chloroform. Metal cations are more attractive as reagents than organic dyes that are difficult to obtain in an adequate state of purity, may not be completely stable and frequently tend to adsorb on to the surfaces of vessels used in the analysis. On the other hand, the extinction coefficients of the cobalt or coppcr(r1) soaps in organic solution, as in the methods of Ayers and of Twayama, are too low to be used for the present purpose. However, it has been found that the sensitivity can be considerably increased by adding a sensitive colorimetric reagent for the metal concerned to the metal-soap extract.This procedure has the advantage that slight differences in the extinction coefficients of the metal soaps of the various fatty acids used do not affect the optical density of the extract. A suitable reagent for copper(I1) soaps is dimethylammonium diethyldithiocarbamate. The extinction coefficient of the copper(1r) complex is about 11,000, and both the reagent and the complex are soluble in organic solvents. Attempts to extract microgram amounts of fatty acids from neutral or near neutral aqueous solution into organic solvents have not been successful. At this concentration level no extraction occurs when cupric nitrate is added, as in the method of Ayers, but some extraction does take place when an acetate buffered triethanolamine solution is used as described by Iwayama.Here, however, the reagent blank is very high. A better extraction occurs when alkaline solutions of complex copper ammines are used in place of the simpler copper(I1) salts. Thus, for example, traces of soaps extract into chloroform with copper(I1)252 GREGORY: DETERMINATION OF RESIDUAL ANIONIC [Analyst, Vol. 91 ions in the presence of alkali hydroxide and an excess of ammonia. Recoveries using this method tend to be low and erratic, but can be improved by replacing the cuprammonium ion by the complex triethylenetetramine copper(I1) cation. The necessary alkaline pH can conveniently be achieved by incorporating the required base in the copper reagent solution.EXPERIMENTAL PREPARATION OF THE REAGENT- The reagent is prepared with a slight excess of triethylenetetramine in addition to that necessary to complex the copper, thus avoiding precipitation of copper as the hydroxide on adding alkali. There is a tendency for copper(1) oxide to precipitate slowly from the reagent when either sodium or potassium hydroxide is used, but a completely stable reagent can be prepared by using monoethanolamine as the base. This forms a complex with copper(I1) ions which does not react with soaps to give extractable products, and is much less stables (log K = 16-48) than that of trieth~lenetetramine~ (log K = 20.6). The separation of the organic phase is also much cleaner when monoethanolamine is used as the base. CHOICE OF EXTRACTANT- Of a wide range of organic liquids tried, only chloroform and the immiscible aliphatic alcohols give anything approaching complete extraction of the soap adducts.Chloroform gives a lower extraction than the alcohols and this is obtained only at very high pH values. The alcohols, however, tend to give cloudy extracts containing aqueous entrained phase ; also the reagent blanks are high and increase as the ionic strength of the aqueous phase is increased. The entrainment effect is least with isobutanol, although particularly high reagent blanks are obtained. The addition to the isobutanol of either benzene or cyclohexane, which do not themselves extract the soap adducts, not only reduces the reagent blanks but also prevents entrainment of the aqueous phase without affecting the recovery.Because it has a much lower toxicity, the use of cyclohexane is preferred to that of benzene. REAGENTS- Copper - triethylenetetramine reagent-Dissolve 25 g of copper( 11) nitrate trihydrate in 125 ml of water and stir slowly into a solution containing 16.25 g of triethylenetetramine in 125 ml of water. Add 250 ml of monoethanolamine in 250 ml of water and dilute with water to 1 litre. Isobutanol - cyclohexane extractant-Mix 200 ml of isobutanol with 800 ml of cyclohexane. Diethylammonium diethyldithiocarbamate solution-Dissolve 2 g of diethylammonium diethyldithiocarbamate in 100 ml of isobutanol. Standard soap solution-Dissolve 0.250 g of the required pure fatty acid in 200 ml of methylated spirit, add 1 ml of 0.88 sp.gr.ammonia solution and dilute with water to 1 litre. Standard solutions of non-soapy surface-active agents may be prepared in water or alcohol - water mixture. Prepare freshly every 2 days. PROCEDURE- Perform the extractions in 75-ml boiling tubes fitted with size B24 interchangeable ground-glass stoppers. Centrifuge samples which are cloudy, or which contain particulate matter, until clear. Transfer a 25-ml sample by pipette to an extraction tube and add 5 ml of the copper - triethylenetetramine reagent, followed by exactly 10 ml of the isobutanol - cyclohexane extractant. Stopper the tubes and invert rapidly 100 times. After the phases have separated, transfer the organic layer to a dry test-tube by means of a dropping pipette fitted with a rubber bulb.Mix the extract with two drops of the diethylammonium diethyl- dithiocarbamate solution and allow to stand in a dark place for 15 minutes. Measure the optical density relative to the extractant in 2-cm cells at a wavelength of 435 mp. A blank determination must be made. For calibration purposes, take aliquots of a standard solution in a series of extraction tubes and dilute each to 25ml with water to give a range of concentrations from zero to 10 p.p.m. Complete the determinations as described above.April, 19661 SURFACE-ACTIVE REAGENTS IN MINERAL FLOTATION LIQUORS 253 DISCUSSION The presence of traces of surface-active material in reagents or on glassware must be avoided. One batch of triethylenetetramine, which is only readily available in technical quality, gave a 0.3 p.p.m.intercept on the calibration graph. This can be overcome by adding an equivalent amount of sodium lauryl sulphate to the reagent, but at the cost of a slightly higher blank. Distilled water from an all-glass still has been found satisfactory for the determination. Glassware should be treated with chromic acid, rinsed with water, alcohol and chloroform and allowed to drain dry. COMPOSITION OF THE EXTRACTANT- The addition of cyclohexane to the isobutanol extractant has two effects. These are the reduction of the reagent blank and the prevention of entrainment of aqueous copper solution when soaps are present. With too much cyclohexane the recovery is reduced and cloudy extracts are obtained. These effects are shown in Fig.1. The best extractant contains 80 per cent, by volume of cyclohexane, and it can be seen that the recovery is not critically dependent upon its exact composition. Identical results are obtained when the cyclohexane is replaced by benzene, but hexane almost completely suppresses extraction. EFFICIENCY OF EXTKACTION- No further improvement in extraction occurs after shaking the tubes 40 times, but vigorous agitation sometimes produces a fairly stable emulsion when more than 5 p.p.m. of a soap is present. By rapidly inverting the tubes 100 times, in place of shaking, maximum extraction is obtained and the phases usually separate completely within 10 minutes. The volume of the organic phase after extraction is 8.5 ml, that of the aqueous phase having increased by 1-5 ml.Successive extractions of the aqueous phase with more of the same extractant result in an increasing isobutanol concentration in the aqueous phase, thus giving increased blanks and entrainment of aqueous copper solution. By performing second and subsequent extractions with 8-5 ml of (5 + 80) isobutanol - cyclohexane mixture, the original extraction conditions are maintained. Under these conditions no further recovery can be detected in a second extraction. A = Ll r-l Y Ll Cyclohexane, per cent. I I I 70 80 90 0 I Fig. 1 . Effect of addition of cyclo- Fig. 2. Effect of pI-1 on the determina- hexane to the isobutanol extractant: curve A, blank; curve B, sample corrected for blank tion of 4.74 p.p.m. of oleic acid EFFECT OF pH- From Fig. 2 it can be seen that a large increase in extraction occurs as the pH is raised above a value of 9, and that it reaches a maximum between pH 11 and pH 12.6.When the pH is raised above 13 there is a noticeable lightening in the blue colour of the aqueous phase, and the extraction falls to a low value. With the recommended reagent, the aqueous phase after extraction has a pH of 11.6.254 GREGORY: DETERMINATION OF RESIDUAL ANIONIC [Analyst, Vol. 91 DEVELOPMENT OF COPPER(II) DITHIOCARBAMATE COLOUR- JanssenlO has determined the stability constant for the copper(I1) diethyldithiocarbamate system and gives log K = 28.8. This is sufficiently high for the coloured complex to be expected to form readily in the presence of triethylenetetramine. Whereas, in practice, the addition of a considerable excess of triethylenetetramine has no effect on colour development, the reaction is slow under the conditions used.This can be seen from Fig. 3, which also shows that the dithiocarbamate complex is not stable to light. After addition of the reagent the extract should be allowed to stand in the dark for 15 minutes. Fig. 3. Development of copper(I1) dithiocarbamate colour : 0, protected from light; X, exposed to light I I 1 500 I000 I500 Mole r a t i o of copper to f a t t y acid Fig. 4. Effect of rcagent concentration on the extractior REAGENT CONCENTRATION- The relationship between the optical density of the extract and the mole ratio of copper(I1) triethylenetetramine complex to oleic acid is shown in Fig. 4. The very large excess of copper reagent required for the reaction to approach completion suggests that the adduct formed between the fatty acid anion and the complexed copper cation must be highly dissociated. For a high recovery, the mole ratio of copper to fatty acid must be at least of the order of 1000.COMPOSITION OF THE EXTRACTED SPECIES- Chaberek and hlartellll state that triethylenetetramine forms with divalent copper a square planar tetraco-ordinated (1 + 1) ion, and Schwar~enbach~ has determined the stability constant log K = 20.6. It is very likely that it is this stable chelate which reacts with fatty acid anions to give a neutral adduct which can be extracted into organic solvents. Because of the high dissociation of the adduct, the Job method of continuous variation12 and the mole ratio method13 are not suitable for determining its composition.The Harvey and Manning slope-ratio method14 is usually effective in such cases, but cannot be applied here as very stable emulsions are formed when the necessary very large excess of surface-active reactant is present. However, on making the assumption that extraction is sensibly complete, a comparison of the measured molar extinction coefficients for copper(I1) diethyldithiocarbamate in the equilibrated extractant, and for oleic acid taken through the full procedure provides an approximate figure for the combining ratio of oleic acid with the copper complex. The measured molar extinction coefficient for copper( 11) diethyldithiocarbarnate, prepared from copper(I1) oleate in (5 + 80) isobutanol - cyclohexane mixture, is 10,700. For oleic acid taken through the procedure the value found is 5280, after correction for the reduction in volume of the extractant.The ratio between these figures is 2.03, which is close to the expected ratio of 2 molecules of oleic acid for each molecule of copper, supporting the view that the extracted compound is probably a neutral ion-association system.April, 19661 SURFACE-ACTIVE REAGENTS IN MINERAL FLOTATION LIQUORS 255 APPLICATION TO OTHER SURFACE-ACTIVE ANIONS- A calibration for oleic acid is given in Fig. 5 and shows a close adherence to the Beer - Lambert law. Similar calibrations are obtained with other fatty acids from myristic (C,,H,,COOH) to behenic (C,,H,,COOH) . Lauric acid (C,,H,,COOH) gives low recoveries and no extraction occurs with capric acid (C,H,,COOH).Very low and erratic recoveries are obtained with the almost insoluble montanic acid (C,,H,,COOH). The method is also effective for non-soapy anionic surface-active agents of the alkyl sulphate, alkyl phosphate and alkyl - aryl sulphonate types. Fig. 5. Calibration for oleic acid When plotted on a molar basis, the calibrations for various anionic surface-active agents all lie fairly close to one another. Comparative optical densities for a number of these materials are given in Table I. The optical density figures quoted are those given by a molar solution of the surface-active agent, under the conditions of the determination. TABLE I RELATIVE MOLAR SENSITIVITY OF THE METHOD FOR A NUMBER OF ANIONIC SURFACE-ACTIVE AGENTS Surface-active agent Lauric acid .. . . . . . . . . . . .. *Palmitic acid .. . . . . . . . . .. *Stearic acid . . . . . . . . . . . . . . *Oleic acid . . . . . . . . . . . . . . Behenic acid . . . . . . . . .. . . *Myristic acid. . . . . . . . . . . . .. *Sodium lauryl sulphate . . . . . . . . . . Sodium cetpl sulphate . . . . . . . . . . Sodium dodecylbenzene sulphonate . . . . . . Sodium di-2-ethylhexyl sulphosuccinate . . . . . . Di-n-nonyl phosphoric acid . . . . . . . . Optical density for a 10-5 molar solution 0.016 0.305 0.316 0.314 0.3 12 0.287 0.333 0-278 0.266 0.328 0.3 34 * Purity of materials checked by analysis, other substances are of reagent chemical grade. REPRODUCIBILITY OF THE METHOD- The mean was 4.76 p.p.m. and the standard deviation 0.05.INTERFEHENCES- Flotation systems with soaps are frequently adversely affected by the presence of dissolved cations that precipitate insoluble metal soaps. The soap remaining in solution is determined in this procedure after spinning the sample liquor in a centrifuge to remove allinsoluble material. If it is required to determine the total amount of soap present, both in soluble and insoluble form, the effect of some of the precipitating cations can be overcome by the addition Sixteen determinations were made of the oleic acid concentration in a 4.74 p.p.m. solution.256 GREGORY: DETERMINATION OF RESIDUAL ANIONIC [Ana&St, VOl. 91 of EDTA. This liberates carboxylate ions from many soaps, while forming a copper(r1) complex of lower stability 15(10g K = 18-86) than that of triethylenetetramine.However, a new calibration must be made with EDTA added as the extraction is slightly reduced in its presence. The addition of 1 ml of a 6-25 per cent. solution of disodium ethylenediamine tetra- acetate dihydrate before the copper - triethylenetetramine reagent, is sufficient to complex the dissolved cations present in most hard waters in Great Britain. The effect on the determination of oleic acid, of the presence of a number of common cations, and also of some anions which might be present in flotation liquors, is shown in Table 11. TABLE I1 EFFECT OF VARIOUS IONS ON THE DETERMINATION OF 4-74 PARTS PER MILLION OF OLEIC ACID Ion . . K+ . . NH,+ . . Mg2+ . . Ca2+ . . .4P+ . . Mn2+ , . Fe3+ . . Co2+ . . Ni2+ .. Zn2+ . . F- . . c1- . . SO,2- . . PO,,- . . CO,Z- . . B,0,2-. . CN- . . CH,COO- CrO,2- Silicate . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . Concen- t ra tion present, p.p.m. 240 240 48 120 240 240 . . 120 240 240 . . 120 240 120 240 120 240 240 240 240 240 240 240 100 240 240 240 Added as : KNO, NH,NO, Ni(NO,), ZnSO, NaF NaCl Na,SO, Na,H PO, Na,C03 KCN CH,COONa K,CrO, Water glass N a,B@ 7 No EDTA present 7.- Oleic acid found, Error, p.p.m. per cent. 4.60 - 2.9 3.84 - 19.0 4.60 - 2.9 3.35 - 29.3 2-02 - 57.4 2.58 - 45.5 3.38 - 28.7 0*59* - 87.5 3*02* - 36.3 3.63* - 23.4 2.67* - 43.8 4-05 - 14.5 3.35 - 29.3 3.98 - 16.0 3.7 1 - 21.7 4.86 -+ 2.5 4.74 0 4.54 - 4.3 4.49 - 5.3 4.41 - 7.0 4-60 - 2.9 4-60 - 2.9 4-60 - 2.9 4.57 - 3.5 4.6 1 - 2.7 EDTA added , Oleic acid found, p.p.m.- - 4.58 4.83 2.92 3.87 3*72* 3.84* 3.97* 4-58 4-78 4.63 4.95 4-76 - - - - - - - - - - 5 Error, per cent. - - - 3.3 + 2.0 - 38.4 - 18.4 - 21.6 - 18.9 - 16.2 - 3.3 + 0.9 - 2.2 + 4.4 + 0-4 - - - - - - - - - - * Some precipitation of metal compounds occurred in these cases, Non-soapy surface-active agents, which do not generally form insoluble metal salts, are less affected by cationic interference. Thus for a 5 p.p.m. solution of sodium lauryl sulphate in the presence of 240 p.p.m. of calcium as calcium chloride, the concentration found was 4.86 p.p.m., an error of -2.8 per cent., whereas the error caused for oleic acid is over 50 per cent., although this difference was not apparent in the presence of EDTA. Traces of long chain alkyl amines do not interfere seriously with the determination of fatty acids, but the surface-active quaternary amines completcly inactivate an equivalent amount of soap.APPLICATION TO FLOTATION SYSTEMS- In practice flotation liquors may contain considerable amounts of residual solids and slimes. Although these generally remain in the aqueous phase after the extraction, the adsorbed surface-active agent tends to be stripped by the reagent and is determined. Most filter materials adsorb anionic surface-active agents to a considerable extent, even from pure solutions. Nylon filter- cloth is free from this defect but has a relatively high porosity. Particulate matter can readily be removed, however, by centrifuging the sample before analysis. Much of the preceding part of this paper has dealt with ideal systems.April, 19661 SURFACE-ACTIVE REAGENTS IN MINERAL FLOTATION LIQUORS 257 A number of anionic surface-active agents have been successfully recovered from laboratory test flotations.Continuous analysis records of anionic surface-active agents are being obtained by the use of the Technicon AutoAnalyzer. The application of the method to this system, and the results obtained in flotation experiments will be the subject of a future publication. CONCLUSION The determination of anionic surface-active agents, including the fatty-acid soaps, in mineral flotation liquors can be done by extraction of the adduct with the copper - triethylene- tetramine complex, followed by photometric determination of the coloured copper - diethyl- dithiocarbamate complex in the organic phase. The method should also find application in fields other than in the mineral flotation industry. 1. 2. 3. 4. 5. 6. 7 . 8. 9. 10. 11. 12. 13. 14. 15. REFERENCES Jones, J. H., J . Ass. Off. Agric. Chem., 1945, 28, 398. Longwell, J., and Maniece, W. D., Analyst, 1955, 80, 167. Rosen, J . M., and Goldsmith, H. A., “Systematic Analysis of Surface-active Agents,” Interscience - _ _ _ , op. cit., p. 54. Tomiinson, H. S., and Sebba, F., Analytica Chim. Acta, 1962, 27, 596. Ayers, C. W., Ibid., 1956, 15, 7 7 . Iwayama, Y., J . Pharm. SOG. Japan, 1959, 79, 552; Analyt. Abstr., 1960, 7, 3519. Flannery, J., Ke, B., Grieb, M. W., and Trivich, D., J . Amer. Chem. SOL, 1955, 77, 2996. Schwarzenbach, G., Helv. Chim. Acta, 1950, 33, 974. Janssen, M. J . , R e d . Trav. Chim. Pays-Bas Belg., 1956, 75, 1411. Chaberek, S., and Martell, A. E., “Organic Sequestering Agents,” John Wiley & Sons, Inc., New Job, P., Annls Chim., 1928, 9, 133. Kolthoff, I . M., and Elving, P. J ., “Treatise on Analytical Chemistry,” Interscience Publishers Harvey, A. E., jun., and Manning, D. L., J . Amer. Chem. Soc., 1951, 70, 4488. Schwarzenbach, G., and Freitag, E., Helv. Chim. Acta, 1951, 34, 1503. Publishers Inc., New York, p. 16. York, 1959, p. 149. Inc., New York, Part 1, Volume 5, p. 2981. Received June 18t?z, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100251

出版商:RSC    

年代:1966

数据来源: RSC