ISSN:0003-2654    

DOI:10.1039/AN95883FX047

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX049

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP207

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

December, 19581 THE ANALYST...XI11CLASSIFIED ADVERTISEMENTSThe rate f o r classified aduertisenicnls i s 5s. a lin4 (or spaceequivalent of a line], with an extra charge of Is. for theme of a Box Number. Semi-displayed classifiedNALYST back volumes and sets wanted to buy for cash.Write to A. Ashley, AAlso other scientific journals.27, East 21 Street, Xew York, 10, N.Y., U.S.A.SMALL CHEMICAL LABORATORY, London, N.W.10for sale, freehold, owing to rmioval to new premises.Details apply Box No. 3 ! ) i 3 , The Analyst, 47, Gr?shamStreet, London, E.C.4.ALE ANALYSTS arc required for work on vitaminssynthetic drugs in a new well-equipped laboratoryin Welwyn Garden City. Some previous experience ofindustrial analysis is essential. Commencing salary accordingto qualifications, agc and experience.Please write with f u l ldetails to the Secretary, Roche Products Limited, 15, Man-Chester Square, London, W.l.BRITISH INDUSTRIAL PLASTICS LIMITEDI.P. CHEMICALS LTD., Oldbury, have the followingB;acancy for an Analytical Chemist:-Analytical licsearch Chemist to take charge of a laboratoryengaged on the investigation of analytical problems associatedwith the Plastics Industry with particular reference tothermosetting resins. The work will involve the use ofmodern techniques, including spectroscopy and gas-chromatography, together with the investigation of newmethods of analysis. A.R.I.C. or equivalent qualificationis essential and previous industrial experience is desirablc.Preferred age 30-35 years.The company offers goodconditions of employment and a generous pension and lifeinsurance scheme.Applications, which will be treated in strict confidence,giving full details, should be made in writing to: PersonnelManager, B.I.P. Chemicals Ltd., Oldbury, Birmingham.BRITISH INDUSTRIAL PLASTICS LIMITEDI.P. CHEMICALS LTD., Oldbury, have the followingB;acancy for an Analytical Chemist:-Analyst to take charge of a works control laboratory.Minimum qualification A.R.I.C. Previous experience oforganic and inorganic analysis and works control is desirable,together with ability to control staff. The position offersscope for initiative as early expansion of the work of thelaboratory is planned. The company offers good conditionsof employment and a generous pension and life insurancescheme.Applications, which will be treated in strict confidence,giving full details, should be made in writing to: PersonnelManager, B.I.P.Chemicals Ltd., Oldbury, Birmingham.ULLARD SOUTHAMPTON WORKS will shoitlyM h a v e TWO VACANCIES in their Works Laboratoryas follows:-.4 SENIOR ANALYST who must be a qualified Analyst,B.Sc. and/or A.R.I.C., who should have industrial analyticalexperience. The work will include the developnient 01methods and techniques for the analysis of materials usedin the Semi-conductor field.PHYSICAL CHEMIST-A Graduate Chcmist is required foiinvestigational work on materials used in the Semi-Conductoifield.The Comnanv's eeneral conditions of emnlovment will befound t o de aitragive and interested candidat& are requcstect o apply in writing to the Pcrsonnel Officer, Mullard Southampton Works, Millbrook Industrial Estate, Southampt orHE MULLARD RADIO VALVE CO.LTD. requinTfor their materials Kesearch Laboratory a CHEMISIof graduate level for work on special analysis and the dcvelopment of analytical methods. This vacancy is in imodem laboratory about 12 miles south of London. Salaqwill be commensiirate with age, ability and expericnccPost is pensionable and permanent. Applications, in writingshould be sent to Mr. J. C. Ross. Plant Personnel OfficerThe Mullard Radio Valve Co. Ltd., New Road, MitchanJunction, Surrey, quoting reference MR.180.(jEXIOI< ASSISTANT required in Public Analvsts Labora-tory in Northern Ireland.F.R.I.C. (Branch I;). Fnllp,irticulars from Hawthorne 8; Lawton, 16, Donegall SquareSouth, Bdfast.ASPRO-NICHOLAS LIMITED invite applications forthe position of Analytical Chemist for their newly-equippedControl Laboratory situated at Slough, Buckinghainshire.I n addition to routine analysis the person appointed will brriqriired to carry oiit work on the application of niodemanalrtical chrniiitrv to pharinaceutical problrnis. Salaryarrording to qiialifications and rxperiencr. An exccllvntpension schrmr in opvration and escellrnt staff facilities.Apply in writing stating agr, qualifications and rxpericncetr, Personnrl Managw, Aspro-Sicholas Limited, Bath Road,Slough, Biicks.LBRIGHT & WIISON (MFG.) LIMITEII, h a w two&'acancies for qualified Chemists in the Rcst%rch Dept.A .4 Chcniist is rcquirrd as Assistant to tht, Chrmist inrhargc of routine analysis in the Analytical Srction of theI-:rsrarch Dcpt. Srvrral years expericnrr of AnalyticalChemistry is ?ssential. Gent,ral B.Sc. levrl prrfrrrrd, butthose possessing H.N.C. would ba con5idcred. (Krf. ZOi.)I?. A Chemist with G.R.I.C. or an Honours Drgrce incicrnistry is nt,eded for research and drvelopnicnt of nicthodof analysis. Sonie analytical rxprrirncr would bc anadvantago. (Ref. ;lK.)Applicants should be aged 26-33.Son-contributory pension and housing schrmc.; arr inApply, stating age oiialifirations and <%xnrrirnrr tooprration.\Ir. F. R. Hiint S t rGood conditions of service and salary.RITISH ACHESON ELECTRODES LIMITED invite13apylic r1 t' ions from Spectroscopists for a position in theiranalytical laboratories.Applicants should be undcr 41)yrars with at least two years expcrirnce of emission spectro-scopy and preferably they should hold H.N.C. or its equiva-lmt. A competitive salary will be paid, normal welfaref icilities, contributory superannuation and Frer Life Assnr-ance available. Apply in writing giving details of experirnceand salary expected to:-Chirf Industrial Relations Officer,Grange Mill Lanr, Wincobank, Sheffield, 9.1HEMIST with 1st or 2nd class honours required for'Jrescarch work on coal minerals and slaqs. Startingsalary &ROO -&l,OOO p a . according to qualifications andexperience.&day week. Superannuation and GradingC,chemes. Apply in writing to thr Assistant Sccrrtarv,Icef. I3.16, The British Coal Utilisation Research Association,Itandalls Road, Leatherhead, Surrey.CHEMISTSSMITH & NEPHEW ASSOCIATED COMP.iNIES' r O meet the drmands of an expanding programme, theResearch Organisation for the above Group invitr applica-tions from qualified chemists for positions in the followingfields of Research and Development. Minimum qualifica-lions are Second Class Honours or Associatcship of theInstitute of Cheniistry. but for some of the vacancirs post-(:raduate research experience would be an advantage.PHYSICAL CHEMISTS. Vacancies exist for work onfundamental studies in the rheology of rubber and highpolymers. A new position also exists for a man with experi-mce in physical test methods to develop tests for the assess-ment of plastics and pressure-sensitive adhesive products.A chemist is required to,n.ork on the analysis of pressure-sensitive adhesive productsand their componcnts, including the development of specifica-:ions and test methods.DEVELOPMENT. Technological experience in textiles,vlastics or adhesives IS desirable. A Pass or General Degree#:overing Physics, Mathematics and Chemistry provided it is:supported by adequate practical experience will be acccptablcfor this position.The salaries offered are in line with the more generous!scales in industry and chosen candidates will be paid accordingto qualifications and experience. Holidays and workinghours art: also in conformity with modern practicc in industryand a generous contributory pension scheme is in operation.'The Laboratories are sited in a country district 25 miles fromLondon.Write to:-Technical Secretary, Smith & Nephrw ResearchLtd., Hunsdon Laboratories, Ware, Herts.ANALYTICAL CHEMISTRY

ISSN:0003-2654    

DOI:10.1039/AN95883BP217

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

DECEMBER, 1958 THE ANALYST Vol. 83, No. 993 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY JOINT MEETING A JOINT Meeting of the Society and the Association of Public Analysts was held at 3 p.m. on Wednesday, December 3rd, 1958, in the Wellcome Building, Euston Road, London, N.W.I. The meeting took the form of a Symposium on “Food Analysis.” During the afternoon session, the Chair was taken by the President of the Society, Dr. J. H. Hamence, MSc., F.R.I.C., and the following papers were presented and discussed: “The Determination of Chemical Antioxidants in Fats after Separation by Partition Chromato- graphy,” by K. G. Berger, M.A., N. D. Sylvester, M.Sc., F.R.I.C., and Miss D. Ril. Haines, B.Sc. ; The Estimation of Egg in Certain Foods by Enzymic Hydrolysis of the Phospholipids,” by C.B. Casson, BSc., F.R.I.C., and F. J. Griffin, BSc., A.R.I.C. Mr. H. E. Monk, B.Sc., F.R.I.C., P.A.I.W.E., President of the Association of Public Analysts, took the Chair at the evening session, which was opened by J. R. Nicholls, C.B.E., D.Sc., F.R.I.C. Under the general heading “The Identification of Coal Tar Colouring Matters in Foodstuffs,” two papers were presented by P. S. Hall, BSc., F.R.I.C., and R. C. Spalding, M.A., F.R.I.C., and were discussed. DEATHS WE record with regret the deaths of Alexander Hutcheon Bennett William Lincolne Sutton. SCOTTISH SECTION AN Ordinary Meeting of the Section was held at 7.15 p.m. on Wednesday, October 15th, 1958, at the Kenilworth Hotel, 5 Queen Street, Glasgow, C.1. The Chair was taken by the Vice-chairman of the Section, Mr.A. N. Harrow, A.H.-W.C., F.R.I.C. The following papers were presented and discussed: “The Determination of Acidity in Dark Lubricating Oils,” by W. Gibb, BSc., Ph.D., A.R.I.C., A.R.C.S.T., A.M.Inst.F., and H. Gibson, BSc. (see summary below); “Volumetric Analysis of Stannous and Total Tin in Acid-soluble Tin Compounds,” by J. D. Donaldson, B.Sc., and W. Moser, BSc., A.R.I.C. THE DETERMINATION OF ACIDITY IN DARK LUBRICATIXG OILS DR. W. GIBB said that the deterioration of mineral lubricating oils under conditions found in internal combustion engines was primarily the result of the reaction of oxygen with the oil at elevated temperatures. Acidic bodies, inter alia, were formed, and the oil became dark coloured. The determination of acid number was complicated by this dark colour, the weak acidity and the small amounts present.The direct determination of the oxygen content of the deteriorated oil by the Unterzaucher method (Analyst, 1952, 77, 584) now made possible an oxygen balance and the separate determination of the various groups of acidic constituents of major importance. Two-phase colour indicator methods of acid-number determination were unreliable (H. P. Ferguson, Anal. Chem., 1950,22, 289) owing to the absorption of carbon dioxide, saponification and emulsion formation. With heavily oxidised oils of high acid number, 653654 PROCEEDINGS [Vol. 83 even I.P. 1/55 method A (“Standard Methods for Testing Petroleum and Its Products,” The Institute of Petroleum, London, 1957, p. 13) could give a two-phase system. The newer method I.P.139/57T was only suited to lightly oxidised material, as the solvent (isopropanol - benzene - water) had difficulty in dissolving heavily oxidised sludges, and the p-naphtholbenzein end-point was difficult to see in black solutions. Determination of the end-point was improved by observing the colour change in froth (Ibid., p. 4), in narrow-bore glass tubing (Ibid., p. lo), in special titration flasks with narrow necks or narrow side-limbs (Ibid., p. 13; I. Kukin, Anal. Chem., 1957, 29, 461) or by means of fluorescent lamps (“Standard Methods for Testing Petroleum and Its Products,” p. 4), or a photoelectric colorirneter (R. H. Osborne, J. H. Elliott and A. F. Martin, Ind. Eng. Chem., Anal. Ed., 1943, 15, 642). The A.S.T.M.potentiometric method D664 (“A.S.T.M. Standards,” American Society for Testing Materials, Philadelphia, Pa., U.S.A., 1955, part 5 , p. 285) made use of the same solvent as I.P. 139/57T. The technique was time-consuming, and the electrodes had to be scrupulously clean and carefully shielded from electrical inter- ference. Since most oxidised samples gave no points of inflexion on the titration curve, end-points had to be taken at meter readings corresponding to suitable standard buffer solutions. Potentiometric titration of oxidised oils in a strongly basic solvent had attractive possibilities, since in such a medium weak acids showed a much greater acid strength than in water or alcohols (M. L. Moss, J. H. Elliott and R. T. Hall, Anal. Chem., 1948,20, 784; V.2. Deal and G. E. A. Wyldl, Ibid., 1955,27,47). Accordingly, potentio- metric curves that did not show points of inflexion in alcohol solvents should show them in a suitably basic solvent, so permil ting differentiation between carboxylic acids and phenols. With basic solvents, such as ethylenediamine, a totally enclosed anhydrous titration system was necessary. Anomalous titration curves had been reported for in- sufficiently basic solvents (H. B. van der Heijde, Anal. Chim. Acta, 1957, 16, 378). For the rapid determination of the acid number of very dark oils, Fenske’s fluorescein - methyl red indicator (Ind. Eng. Chem., 1941, 13, 51) had been used successfully. The red form of methyl red masks the fluorescence, which can be made to show up clearly on the alkaline side.Observation of the end-point is aided by illuminating the titration vessel strongly from the side and using a dark background to reduce transmitted light. No difficulty had been experienced in dissolving the sludges of heavily oxidised oils in the n-butanol - toluene solvent. Improved accuracy could be obtained with insufficiently dark samples by the addition of a neutral black dye to the oil solution. A complete oxygen balance also required the determination of carbonyl compounds. The oil was treated with hydroxylamine hydrochloride and the liberated acid was determined potentiometrically (J. Knotnerus, J . Inst. Petrol, 1956, 42, 355). A.S.T.M. method D664 was applicable. For rapid determination of liberated acid, the Fenske method in its original form was useless, as sodium butylate and methyl orange react with hydroxylamine hydrochloride.I.P. 139/57T solvent and titrant in conjunction with fluorescein - methyl orange indicator had been used successfully. The titrant was sodium butylate. AN Ordinary Meeting of the Section was held at 7.15 p.m. on Friday, October 31st, 1958, in the Lecture Room cf the Royal Society of Edinburgh, 22 George Street, Edinburgh 2. The Chair was taken by the Chairman of the Section, Dr. Magnus Pyke, F.R.I.C., F.R.S.E. The following paper was presented and dscussed: “The Analytical Chemistry of Phos- phorus,” by N. T. Wilkinson, F.R.I.C. AN Ordinary Meeting of the Section was held at 7.15 p.m. on Wednesday, November 19th, 1958, in the Upper Hall of the Royal Philosophical Society of Glasgow, 207 Bath Street, Glasgow, C.2. The Chair was taken by the Chairman of the Section, Dr. Magnus Pyke, F.R.I.C., F.R.S.E. The subject of “Developments in Gas Chromatography” was introduced by A. F. Williams, BSc., F.R.I.C., and the following papers were presented and discussed: “Quanti- tative Analysis Using Thermal Conductivity Detection,” by G. R. Jamieson, B.Sc., F.R.I.C. ; “The Application of Gas Chromatography tcl Reaction Kinetics,” by J. H. Knox, B.Sc., Ph.D. ; “Chromatographic Examination of a Low-temperature Tar,” by L. Irvine, BSc., Ph.D., A.R.C.S.T., A.R.I.C.Dec., 19581 PROCEEDINGS 655 MIDLANDS SECTION A JOINT Meeting of the Midlands Section and the Birmingham and Midlands Section of the Royal Institute of Chemistry was held at 7 p.m. on Thursday, November 13th, 1958, in the Main Chemistry Theatre, The University, Edgbaston, Birmingham, 1.5. The Chair was taken by the Chairman of the Midlands Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. The following paper was presented and discussed : “The Infra-red Analysis of Solid Sub- stances,” by Professor G. Duyckaerts (Li&ge University).

ISSN:0003-2654    

DOI:10.1039/AN9588300653

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Dec., 19581 PROCEEDINGS 655 Determination of Zinc and Other Elements in Plants by Atomic-absorption Spectroscopy BY D. J. DAVID (Division of Plant Industry, C.S.I.R.O., Canberra, A.C.T., Australia) Results of investigations into the application of atomic-absorption spectroscopy to the analysis of plant material for zinc, magnesium, copper and iron are given. For zinc and magnesium, the method is a t least as accurate and sensitive as other methods currently available, and is con- siderably better in both rapidity and freedom from interference by extraneous elements. For copper and iron, the method is insufficiently sensitive for general application in its present form. THE aim of the work described was to test the application of atomic-absorption spectroscopy, developed by Walshl and Russell, Shelton and Walsh,2 to the analysis of plant material for certain inorganic elements, particularly zinc.Most methods currently available for determining zinc in plant material involve pre- liminary chemical concentration with a solution of dithizone or another complexing reagent in chloroform or carbon tetrachloride. The dithizone extract can be subjected to arc-emission spectrographic analysis,s to further extraction to remove interfering elements and then photometric measurement of the zinc - dithizone complex4 or to evaporation, digestion and polarographic analy~is.~ Atomic-absorption spectroscopy has advantages over these methods in that the diluted plant digest is used directly and special precautions to avoid interference from other ions of plant origin are not necessary.Verdier, Steyn and Eve’s polarographic method6 and a method in which zinc is separated with Dowex 1 ion-exchange resin and then colorimetrically determined with Zincon7 both avoid the use of complexing reagents in organic solvents. When compared with the proposed method, however, they have the disadvantage that some chemical preparation of the solution is necessary before the zinc can be determined, and the polarographic method, at least, is inferior in sensitivity and accuracy. Calculations based on the data reported for the polarographic method6 suggest that the lower limit of determination of zinc in solution is about 1 p.p.m., but no estimate of accuracy is given at this level. At 31.5 p.p.m. of zinc in solution, a standard deviation of k1.26 p.p.m.is claimed. Six operations are necessary to prepare a solution for polarographic analysis by this method. DESCRIPTION OF APPARATUS A Lundegdrdh air - acetylene flame of the type described by Mitchel1,g into the base of which a fog of the sample solution is introduced, was placed on the optical axis between the slit of a flat-field Hilger medium-quartz spectrograph and a hollow-cathode discharge tube, which emitted intermittent light of the element to be determined at a frequency of 50 cycles per second. The plate holder of the spectrograph was replaced by a horizontal platform carrying a slit and photomultiplier assembly, which could be moved along guide grooves so that the slit remained in the focal plane of the spectrograph. During determina- tions, this exit slit was placed on the resonance line of the element to be determined and the transmitted light was picked up by an RCA 1P28 photomultiplier tube. The signal from the photomultiplier tube was fed to an a.c.amplifier tuned at 50 cycles per second, and the rectified output was measured with a millivoltmeter.656 DAVID : DETERMINATION OF ZIXC AND OTHER ELEMENTS [Vol. 83 Earlier apparatus described by Russell, Shelton and Walsh2 was similar in principle to that used in this investigation, but differed slightly in that a mechanical chopper was used to modulate the hollow-cathode beam and the signal from the ax. amplifier was rectified and fed into a pen recorder. The use of an intermittent hollow-cathode discharge and an a x . amplifier precludes all interference by flame-emitted light.As the apparatus described operates on the single-beam principle and the intensity of light emitted from the hollow-cathode discharge tubes is sensitive to slight fluctuations in mains voltage, an electronic a.c. voltage-stabiliser that delivered 240 & 1 volts was used to supply the hollow-cathode tubes. When the apparatus was used for analysis, the amplifier was adjusted to zero with the spectrograph-slit shutter closed and to full-scale deflection with the shutter open and a fog of pure water entering the base of the flame. The percentage reduction in reading when the water fog was replaced by a fog of sample solution was a measure of the absorption by the flame of the resonance line of the element to be determined.Adjustment to full-scale deflection was e-ffected by varying either the gain of the amplifier or the voltage applied to the photomultiplier stages. The air and acetylene pressures applied to the Lundegirdh flame assembly, which were kept constant by means of reducing valves during determinations, were 36 lb per sq. inch and 40 cm of water, respectively. Other equi-pment settings used are shown in Table I. TABLE: I INSTRUMENT SETTINGS FOR THE DETERMINATION OF ZINC, MAGNESIUM, COPPER AKD IRON Width of Width of Hollow-cathode Wavelength of Element entrance slit, exit slit, tube current, spectral line, mm mm mA A Zinc .. . . 0.10 0.2 10 2139 hfagnesium . . 0.15 0.!1 10 2852 Copper .. .. 0.20 0 4 20 3247 Iron .. .. 0.05 0.:2 50 3758 EXPERIMENTAL REPRODUCIBILITY OF THE METHOD- Atomic-absorption readings on thirty-nine portions of each of two zinc solutions in thirty-nine Lundegirdh spray bulbs gave results of 58.56 1.07 per cent.absorption at a zinc level of 10 p.p.m. and 7.26 +_ 0.94 per cent. absorption at a zinc level of 1 p.p.m. These variations, which are standard deviations of single determinations, may originate from variations in the dimensions of the spray Elulbs, from electrical variation, from variations in acetylene and air pressures or from inaccuracies when readings are made. A similar test for magnesium gave results of 10.37 & 0-33 per cent. absorption at a magnesium level of 0.5 p.p.m. and 43.15 i 1 4 1 per cent. absorption at a magnesium level of 5 p.p.m. The variation at the latter level includes a slight drift similar to that in the magnesium results shown in Table 11.TESTS FOR INTERFERENCES- A solution containing all the water-so1ubl.e major elements likely to be encountered in plant material was prepared by dissolving 10 g of potassium chloride, 2 g of sodium chloride, 4 g of calcium carbonate, 1 g of magnesium ox.ide, 3 g each of ammonium dihydrogen ortho- phosphate and ammonium sulphate and 0.4 g (of aluminium ammonium sulphate in sufficient hydrochloric acid to convert the calcium carbonate and magnesium oxide to chlorides. This solution was diluted to 1 litre with water, which gave a solution approximately equivalent to that obtained when 0.2 g of the ash from about 2 g of dry plant material (from an “average” pasture samples) is dissolved in a volume of 10 ml.Atomic-absorption measurements at 2139 A were made for zinc at six concentration levels in this solution and in water; the results were as follows- Amount of zinc present, p.p.m. . . . . . . 1 2 4 8 16 32 Absorption in water, % . . . . .. .. 10 18.5 34 69 86 100 Absorption in synthetic plant-ash solution, yo . . 11 21 35 60 88 100Dec., 1958; IN PLANTS BY ATOMIC-ABSORPTION SPECTROSCOPY 657 To study the interference of individual inorganic plant-elements on the absorptionat four levels of zinc, copper and iron, each of the ions Kf, Na+, Ca2+, hfg2+, AP+, SO,2- and PO:- was varied individually between zero and from two to ten times its concentration in the solution mentioned in the previous paragraph, the concentrations of the other ions remaining TABLE I1 EFFECT OF MAJOR ELEMENTS IN PLANT MATERIAL ON THE ATOMIC ABSORPTION All concentrations, except those for magnesium, must be divided by 100 for application to magnesium OF ZINC, IRON, COPPER AND MAGNESIUM Absorption of- Absorption of- Amount Possible of interfering element element present, % Sodium .. -!-:&8 10.78 r 0.0 Potassium . . ‘1 0.52 1.04 0.0 Calcium . . { 0.16 0.80 0.0 0.403 r 0.0 10,012 Amount Possible of interfering element element present, % 0.0 0.80 Calcium . . { 0.16 r 0.0 Magnesium { ::4: 0.403 0.0 0.115 Sulphur . . (,.023 0.012 0 p.p.m. of zinc, % 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4 p.p.m. ? f zinc, % 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0 18.0 18.0 18.0 18.0 18.0 16.0 16.0 16.0 14.0 12.0 12.0 12.0 0 p.p.m.0 p.p.m. of of iron, copper, % % 0.2 0.4 0.0 0.0 0.0 0.4 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 Absorption of- A 80 p.p.m. 8 p.p.m. of of iron, copper, % % 4.0 5.8 4.0 6.0 4.0 5.4 4.2 5.8 4.0 3.8 4.0 5.8 3.6 5.6 4.0 5.8 4.2 5.6 2.0 6.0 1.4 6.2 1.6 6.0 1.8 6.0 1.8 6.0 1.8 6.2 1.8 6.0 1.4 5.8 1.4 4.6 3.6 4.6 2.8 4.4 3.6 4.2 6 p.p.m. of mag- nesium, 50.0 52.0 50.0 48.0 50.0 48.0 44.0 48.0 48.0 % - - - 46.0 44.0 44.0 42.0 44.0 42.0 44.0 42.0 44.0 1 p.p.m. of zinc, 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 6.0 6.0 6.0 6.0 4.0 4.0 4.0 4.0 4.0 4.0 % 20 p.p.m. 2 p.p.m. of of iron, copper, % % 0.8 1.6 0.8 1.6 0.6 1.8 0.8 1.8 1.0 1.8 1.0 1.8 1.4 1.8 1.2 1.8 1.2 1.8 0.6 1.8 0.4 2.0 0.4 1.8 0.6 1.6 0.6 1.6 0.4 1.6 0.4 2.0 0.4 2.0 0.6 1.4 1.2 1.2 1.2 1.2 0.8 1.2 Absorption of- 6 p.p.m. of mag- nesium, % 50.0 50.0 50.0 48.0 50.0 48.0 46.0 48.0 48.0 - - - 46.0 46.0 44.0 44.0 48.0 44.0 44.0 42.0 42.0 8p.p.m.160p.p.m. 16p.p.m. of of of zinc, iron, copper, % % Yo 30.0 7.0 10.6 30.0 7.0 10.6 30.0 7.0 10.6 30.0 7.0 10.4 30.0 7.0 10.4 30.0 7.0 10.6 30.0 7.4 10.6 30.0 6.4 10.4 30.0 6.6 10.0 40.0 3.2 12.0 36.0 3.4 12.0 40.0 3.2 11.6 44.0 3.8 12.2 46.0 4.0 13.7 48.0 3.6 14.0 44.0 4.0 12.0 43.0 4.0 12.0 45.0 3.6 11.7 24.0 6.0 8.2 24.0 6.0 8.2 24.0 6.6 8.6 -7 6 p.p.m. of mag- nesium, 60.0 50.0 50.0 50.0 50.0 50.0 46.0 46.0 46.0 % - - - 46.0 46.0 44.0 42.0 44.0 44.0 44.0 44.0 42.0 -7 6 p.p.m. of mag- nesium, 50.0 50.0 50.0 48.0 48.0 46.0 46.0 48.0 48.0 % - - - 46.0 44.0 44.0 44.0 44.0 42.0 44.0 42.0 42.0658 DAVID: DETERMIEATION OF ZINC AND OTHER ELEMENTS [Vol.83 unchanged. The details of zinc, copper and iron levels and the results of the experiment are shown in Table 11. A similar study of the interference of K+, Naf, Ca2+, A13+, SO,2- and PO,3- on magnesium absorption was made by measuring the magnesium absorption after hundredfold dilution of the solutions from the previous test. These results are also shown in Table 11, but it must be borne in mind that all solution concentrations, except those heading the magnesium columns, should be divided by 100 for application to the magnesium results. As a residual amount of sulphuric acid is present in a solution prepared by digesting plant material with a mixture of sulphuric, perchloric and nitric acids, the effect of high concentrations of sulphuric acid on the absorption of zinc, copper, iron and magnesium was investigated; the results are shown in Table 111.TABLE I11 EFFECT OF SULPHURIC ACID ON THE ATOMIC ABSORPTION OF COPPER AND MAGNESIUM Absorption Amount Absorption in presence of of element in absence of 2.5 per cent. v/v Element present, sulphuric acid, of sulphuric acid, p.p.m. % % r o 0.0 0.0 Zinc . . . . Iron . . . . Copper . . . . Magnesium . . 1 4 8 0 20 80 160 { ,i r o 4.0 9.0 18.0 0.0 0.6 3.0 6.2 0.0 1.0 4.0 8.2 0.0 2.0 9.0 16.0 0.0 0.6 2.6 5.6 0.0 0.8 4.0 7.4 0.0 72.0 96.0 98.0 ZINC, IRON, Absorption in presence of 10 per cent. v/v of sulphuric acid, % 0.0 2.0 8.0 14.0 0.0 0.4 2.0 4.2 0.0 0.8 3.0 5.6 0.0 60.0 94.0 97.6 ANALYSIS OF PLAST MATERIAL- In view of the fact that the only definite interference would be that of residual sulphuric acid from the digestion of plant material, the following procedure for preparation of the sample was investigated.Between 1 and 2 g of oven-dried plant material were digested in 8-inch x I-inch Quickfit test-tubes with 4 ml, accurately measured, of sulphuric acid - perchloric acid mixture (1 + 7 ) and about 15 ml of nitric acid. More nitric acid was added if the destruction of organic matter was incomplete after the mixture had been evaporated to a small volume. When the organic matter had been completely destroyed, the digest was heated strongly to the stage at which all the nitric and perchloric acids had been driven off and the 0.5 ml of sulphuric acid remained.The digest was cooled, and 9.7 ml of water were added to make the final volume to 10 ml. Ground-glass stoppers were placed in the test-tubes, which were then heated in a water bath for 30 minutes with intermittent shaking. After cooling and chilling to below room temperature with an ice -water mixture to prevent possible crystallisation after filtration, the solution was filtered through a Whatman No. 42 filter-paper, and 7-ml portions of the filtrate were transferred to Lundegkrdh spray bulbs for direct atomic-absorption analysis. Standards containing 0, 1, 2 , 4, 8, 16 and 32 p.p.m. of zinc in 5 per cent. v/v sulphuric acid were prepared, and 7 ml of each were placed in Lundegkrdh spray bulbs for absorption measurement and subsequent preparation of a calibration curve.The sample solutions were analysed first, and then the standards, after which the analysis of several of the earlier samples was repeated to ensure that no drift in sensitivity had occurred during the series of tests. A calibration curve, plotted from the measurements on the standards, was used to determine the concentrations of the sample solutions. A typical calibration curve for zinc is shown in Fig. 1.Dec., 19581 I N PLANTS BY ATOMIC-ABSORPTIOX SPECTROSCOPY 659 COMPARISOS WITH POLAROGRAPHIC AXALYSES- petiole samples from clover. met h0d.j Table IV shows polarographic and atomic-absorption results for zinc in stem, leaf and The polarographic analyses were carried out by Walkley's 4 1 A / L 2 E 15- L 0 " Absorption, % Fig.1. Atomic-absorption calibration curves for the analysis of plant material for zinc and magnesium. The lines used are Zn 2 1 3 9 ~ and Mg 2852.4: curve A, zinc; curve 13, magnesium TABLE IV Z I S C DETERMINATION BY ATONJC-ABSORPTION AND POLAROGRAPHIC METHODS Amount of zinc found in clover stem bv- atomic absorption, polarographp, p.p.m. p.p.m. 27.5 28.2 27.5 28.8 25.5 28.8 21.5 22.8 Amount of zinc found in clover leaf by- r - - u atomic absorption, polarography, p.p.m. p.p.m. 49.5 47.3 48.5 47.7 51.5 55.1 - - ;\mount of zinc found in clover petiole by- atomic absorption, polarography, p.p.m. p.p.m. 29.5 30.5 49.0 54.4 7 - - Mean of atomic-absorption results = 36.7 p.p,m, Alean of polarographic results = 38.2 p.p.m.TABLE V RECOVERY O F ZINC FROM MATERIAL OF PLANT ORIGIN BY ATOMIC ABSORPTION .Approximate weight of dry Sample sample, g Phalaris tops . . . . 0.8 Wheat heads . . . . 2.0 White clover leaf . . 0.8 White clover straw . . 1.8 Oat straw . . . . 1.3 Sheep faeces . . .. 0.9 Amount of zinc originally present, r g 127 44 82 90 30 123 Amount of zinc added, r g 118 118 118 118 118 118 Amount of zinc found, Recovery, Pg % 255 108 164 102 198 98 202 95 152 103 340 99660 DAVID: DETERMIXATION OF ZINC ASD OTHER ELEMENTS [Vol. 83 ~ C O V E R Y EXPERIMEKTS FOR ZINC- The results of a series of recovery tests for zinc on a variety of materials of plant origin are shown in Table V. These tests were carried out by coning and quartering samples of dry material, combining opposite quarters and digesting the two portions so obtained after an appropriate amount of zinc had been added to one of them.The digests were analysed by the proposed method. DISCUSSION OF IWSULTS Although the differences between zinc absorption in water and in synthetic plant-ash solutions are within those that could be expected from experimental error, it can be seen that the discrepancy is in the same direction at all zinc levels except the highest (see p. 656). This is probably due to slight contamination by zinc in the analytical-reagent grade salts used in preparation of the synthetic plant-ash solution. I t can be seen from Table I1 that the concentrations of iron and copper are approximately in the range that would be found in normal plant material that had been prepared for analysis by the procedure described.As the atomic-absorption measurements on these solutions were generally too low to be reliable, it is considered that both the proposed method and the apparatus, in their present forms, are unsatisfactory for determining copper and iron in plant material. The results shown in Table I1 for magnesium, although only applicable to one level of magnesium (6 p.p.m. in solution), suggest that no interferences of plant origin will occur during analysis. As plant digests prepared for zinc determination must be diluted one hundred times before magnesium is determined, 110 interference by residual sulphuric acid from the digestion reagents on magnesium absorption would be expected (see Table 111).Standards for plant analysis for magnesium can therefore be prepared by dissolving a mag- nesium salt in water only. A typical calibration curve for magnesium is shown in Fig. 1. Atomic-absorption readings for magnesium were found to be much more steady than those for zinc, owing, probably, to the effect of variation in supply voltage being less for magnesium emission than for zinc emission from the respective hollow-cathode tubes. Table I1 shows that a change in level of some of the absorption results occurs between the figures for calcium and magnesium interferences and also between those for sulphur and aluminium interferences. A shortage of Lundeggrdh spray bulbs made it necessary to analyse the solutions in batches of thirty-six, zinc, copper and iron being determined in one batch before analysis of the next batch.The change in level of results was caused by an alteration in the sensitivity of the apparatus when it was changed from analysis for one element to another and then re-set on the first element. The results for magnesium in Table I1 indicate that a discernible, but insignificant, drift occurred over the whole series of determinations. This is not surprising when it is considered that the series took more than 2 hours to complete. If the number of analyses in a batch of samples were kept to twenty or less, such a drift would not affect the results. As the results of polarographic and atomic-absorption analysis are in agreement, choice between the two methods must be based on rapidity and freedom from possible sources of contamination.Analysis by atomic-absorption spectroscopy is superior in both these respects. The recovery experiments indicate that the proposed procedure for digestion of plant material and subsequent dissolution of the zinc is satisfactory; they also give an additional check on accuracy. It can be seen from Fig. 1 that the curves for zinc and magnesium are approximately linear up to 18 and 8 p.p.m., respectively. Experience has so far shown that these upper limits of accurate analysis for zinc and magnesium are adequate for the analysis of plant material that has been prepared in the manner described. The lower limits of reasonably accurate analysis for zinc and magnesium in solution were found to be about 0.5 and 0.2 p.p.m., respectively . I thank Mr. C. H. Williams for the polarographic analyses quoted, Mr. A. Walsh for supplying the electronic equipment8 used and both for valuable discussion during the work.Dee., 19581 Ih’ PLANTS BY ATOMIC-ABSORPTION SPECTROSCOPY 661 1. 3. 4. 5 . 6. 7. 8. 9. > -. REFERENCES Walsh, .1., Spectrockim. Acta, 1966, 7, 108. Russell, B. J . , Shelton, J . P., and Walsh, A , , Ibid., 1987, 8, 317. Massey, H. F., Soil Sci., 1957, 83, 123. Cowling, H., and Miller, E. J . , I n d . EYg. Chem., Anal. Ed., 1941, 13, 148. \\‘alkley, A,, Australian J . E.zpt1. Biol. Med. Sci., 1942, 20, 139. Trerdier, E. T., Steyn, W. J . .L, and Eve, D. J . , J . Agric. Food Chem., 1957, 5, 354. Jackson, R. H., and Brown, J. G., Proc. Amer. SOC. Hort. Sci., 1986, 68, 1 . Mitchell, R. L., “The Spectrographic Analysis of Soils, Plants and Related Materials,” Tech. Comm. N o . 44, Commonwealth Bureau of Soil Science, 1948. Box, G. F. H., Russell, B. J., and TI7alsh, A , , to be published. Received June 5th, 1968

ISSN:0003-2654    

DOI:10.1039/AN9588300655

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Dec., 19581 Ih’ PLANTS BY ATOMIC-ABSORPTION SPECTROSCOPY 661 4: 4’- Substituted 2: 2’-Dipyridyls in Chelation Reactions With Ferrous Iron BY G. FREDERICK SMITH AND WM. M. BANICK (,Voyes Chemical Laboratories, University of Illinois, Urbana, Illinois, U.S.A .) The molecular extinction coefficients and wavelengths of maximum absorption in the visible and near ultra-violet part of the spectrum have been determined for the ferrous complexes of eleven new 4 : 4’- derivatives of 2 : 2’-dipyridyl, viz., those with -CH,, -C,H,, -Rr, -C1, -OCH,, -OC,H,, -OC,H,, -COOC,H,, -CONH,, -COOH and -KO, as substituent. Division of these complexes into three groups according to the shape of their absorption spectra is suggested. In general, spectrophotometric absorption by the uncomplexed ligands is negligible a t the wavelengths of maximum absorption in the ultra-violet region for the ferrous complexes; this is in contrast with the substituted 1 : 10- phenanthrolines as a class.Possible applications to analysis are discussed. THIS paper continues the study of the iron11 complexes formed by chelating agents containing the grouping =N-C-C-N= and their use in analysis. Substitution in the 3-, 4-, 5- and 6- positions in both rings of the 2:2’-dipyridyls changes the properties of the chelate formed with ironII. These changes are not the same as those brought about by similar substitu- tions in the 3-, 4-, 5-, 6- and 7- positions in the 1:lO-phenanthrolines, The results of substitutions in the 6 : 6’- positions in dipyridyls and the 2 : 9- positions in 1 : 10-phenanthro- lines are comparable; chelation with iron11 to form a colour is inhibited in both cases.The most consistent modifications in properties for the whole series of dipyridyls, diquinolyls, tripyridyls and 1 : 10-phenanthrolines are brought about by substitutions in the 4- and 4 : 7 - positions (para to ring nitrogens). The ferroine and cuproine reactions (chelation with ironII and copper1) differ markedly and in a predictable manner. II I / NEW 4 : 4‘- DISUBSTITUTED 2 : 2’-DIPYRIDYLS STUDIED The formation of the iron11 complex cations and the way their physical constants vary -CH,, --C,H, -Br, -C1, -OCH,, -OC,H,, -OC,H,, -COOC,H,, -CONH,, -COOH and -NO, I, 11, 111, IV, v, VI, VII, VIII, IX, X and XI have been investigated for dipyridyls substituted in the 4 : 4’- positions with- PREVIOUS STUDIES OF SUBSTITUTED DIPYRIDYLS The ferroine reaction of 3-methyl-2 : 2’-dipyridyl yields a complex of lower stability than the unsubstituted 2 : 2’-dipyridyl, and 3 : 3’-dimethyl-2 : 2’-dipyridyl forms a complex stable only in a narrow range of pH.I 3 : 3’-Dicarboxyl substitutions completely inhibit the formation of a coloured chelate with ir0nII.29~ Single substituent groups in the 6- position diminish, and in the 6 : 6’- positions completely inhibit, the ferroine reaction, but permit the cuproine reaction.19496 Dipyridyls substituted in the 5 : 5’- positions with -NO,, -Br or -C1 groups do not give a ferroine reactiom6662 SMITH AND BANICK: 4 : 4’-SUBSTITGTED 2 : 8‘-DIPTRIDYLS [Vol.83 Substituent groups such as -C,H, in the 4 : 4’- positions of 2 : 2’-dipyridyls (para sub- stitutions to nitrogen atoms) produce marked changes in property,‘ and this is also true for the three other types of organic ligand, 1 : 10-phenanthrolines, 2 : 2’-diquinolyl and 2 : 2‘ : 2”-tripyridyl.l97,8 Further 4 : 4‘- substitutsed 2 : 2’-dipyridyls with a variety of sub- stituent groups have been studied in an endeavour to provide data for the selection of the groupings most likely to produce improved reagents when substituted into other types of ligand containing the cuproine or ferroine functional group, such as the tripyridyls.Such compounds might then be synthesised. REAGENTS- of solution. copper by treatment with bathophenanthroline and extraction with isoamyl alcohol. EXPERIMENTAL Standard iron solzttiolz-A solution of ferric chloride containing 0.1108 mg of iron per g Hydroxylamine hydrocizloride--A 10 per cent.aqueous solution freed from iron and Ethanol, 95 per cent.-Analytical-reagent grade, for preparing solutions. isoAmyl alcohol-Analytical-reagent grade, for extractions. Buffer solutions-Solutions 1.0 M in the first named of the following pairs of substances- Potassium chloride - hydrochloric acid Potassium chlorilcle - hydrochloric acid Acetic acid - sodium acetate Acetic acid - sodium acetate Sodium acetate - acetic acid Ammonium chloride - ammonium hydroxide Ammonium chloride - ammonium hydroxide Ammonium chloride - ammonium hydroxide Ammonium chloride - sodium hydroxide PH 1 pH 1.9 pH 3.1 pH 4.0 pH 5.7 pH 7.1 Ammonium acet,ate pH 8.3 pH 8.8 pH 9.4 pH 9.4 to pH 12 DIPYRIDYL SOLGTIONS- 0.01 M Solutions in ethanol of unsubstituted 2 : 2’-dipyridyl and of 2 : 2‘-dipyridyls substituted in the 4:4‘- positions by -CH, (I), -C,H, (11), -Br (111), -C1 (IV), -OCH, (V), -OC,H, (VI) and -OC,H, (VII).This last was least soluble in ethanol and had to be treated with sufficient hydrochloric acid to form the hydrochloride. 0.01 M Solutions in 50 per cent. ethanol made 1.5 M in hydrochloric acid of the -COOC,H, and -CONH, derivatives (VIII and IX). A 0.005 M solution of the -COOH derivative (X) in water to which sufficient ammonium hydroxide was added to complete dissolution. -4 0.0025 M solution of the -NO, derivative (XI) in distinctly acidified water. OPTIMUM pH FOR FORMATION OF CHELA.TE COMPLEX AND ITS EXTRACTION Before the spectrophotometric constants of the iron11 complexes could be evaluated, it was necessary to find the pH for maximum colour development.To each of a series of test-tubes containing 5 0 ml of buffer solution, 1.0 ml of hydroxyl- amine hydrochloride solution and 0.25 ml of iron111 solution was added 0.5 ml of a 0.01 M solution of the ligand. (The ligand solutions that were 0.005 M were added in 1.0-ml portions.) Those ligands prepared in 1.5 M hydrochloric acid were treated by addition of 0.10 M sodium hydroxide in sufficient amount to neutralise the acid. If the complex or the excess of ligand was precipitated, enough 95 per cent. ethanol was added to re-dissolve it. The colours produced at the various pH values were noted. The solution of the complex in each tube was extracted, if possible, by adding 2.0 ml of isoamyl alcohol and then shaking the tube (one or two extractions only were applied).Because only a limited amount of ligand XI, the -NO, derivative, was available, it was not included in these tests. No reducing agent other than hydroxylamine was tested. In the buffer solutions of pH 8.8 to 9.4, for three of the ligands studied, there was interference by ammonium hydroxide; when sodium hydroxide was used instead, there was no interference and the maximum colour intensity was attained. In the course of obtaining the results in Table I, it was noted that the narrow range of maximum colour formation with the dibromo and dichloro derivatives was due to their low instability constants. This same effect The results are shown in Table I.Dilution with ethanol augmented this effect.Dec., 19581 IN CHELATION REACTIONS WITH FERROUS IRON 663 has previously been noted for some chloro derivatives of 1 : lO-phenanthr~line.~ The -COOC,H, derivative, which also gave a complex whose colour was stable only over a narrow range of pH, was affected by atmospheric oxidation when extracted into isoamyl alcohol. Although the -C2.H5 derivative gives its maximum colour over a wider range of pH than does the -CH, derivative, it is noteworthy that for the -OCH, and -OC,H, deriva- tives this effect is reversed. Only the -OC,H, derivative gave a ferrous complex that was insoluble in aqueous solution. TABLE I INFLUENCE OF pH ON FORMATION AND COLOUR INTENSITY OF IROKII COMPLEXES ~SOAMYL ALCOHOL OF 4 : 4'- DISUBSTITUTED 2 : 2'-DIPYRIDYLS AND THEIR EXTRACTABILITY INTO Disubstituted pH range for pH range for Ligand with complex formation maximum colour Unsubstituted ___ 1.0 to 12 3.1 t o 7.1 I -CH.1.9 to 12 3.1 to 8.3 I1 -C& 111 -Br IV -C1 1.9 to 12 1.0 to 12 1.0 to 12 3.1 to 12 1.9 to 3.1 1.0 to 3.1 V -OCH8 1.9 to 12 3.1 to 8.3 VI -OC,H, 3.1 to 12 4.0 to 8.3 VII -OC,H5 1.0 to 12 3.1 to 8.3 VIII -COOC2H5 1.0 to 12 3.1 to 4.0 4.0 t o 12 X -COOH 1.0 to 13 3.1 to 12 IX -CONH, 1.0 to 13 * Extractability: = extracted; 0 = not extracted Extractability* 0 0 0 0 + + + + 0 0 T DETERMINATION OF SPECTROPHOTOMETRIC CONSTAKTS Ligands I, 11, V and VI and the unsubstituted dipyridyl were prepared for spectro- photometric examination as follows.Five millilitres of a buffer solution having a pH within the range that gave maximum colour intensity (pH 3.1 to 5.0; see Table I), 2 ml of hydroxyl- amine hydrochloride solution and 2.0ml of 0.01 M ligand solution were placed in 25-ml calibrated flasks with transfer pipettes. A weighed amount of standard iron solution was added, and the contents of the flasks were made up to volume with water. The same procedure was followed for ligand VII, except that the dilution to volume was with 95 per cent. ethanol. For ligand VIII, the procedure was the same as for ligand VII, except that 3.0 ml of the 0.005 M ligand solution were taken and a few drops of ammonium hydroxide were added to neutralise the excess of hydrochloric acid. For ligand X, the procedure used for ligand VII was followed, except that 3.0ml of 0.005 M solution of ligand were taken.For ligand IX, the procedure used was that for ligand VIII, except that the dilution was with water and the excess of reagent that was precipitated was filtered off. The slight tendency for the colour of this complex to diminish on dilution with ethanol made this mandatory. For ligands I11 and IV, 5.0 ml of buffer solution (pH 3.1), 2.0 ml of hydroxylamine hydrochloride solution and 5.0 ml of 0.01 M ligand solution were transferred by pipette to 10-ml calibrated flasks. Weighed amounts of iron solution were then added, the complexes were allowed to form, and the contents of the flasks were diluted to volume with 95 per cent. ethanol. The excess of ligand that was precipitated was filtered off before spectro- photometric observations were made.The iron" complex of ligand XI was prepared by taking 5 ml of the 0.0025 M solution of the derivative and adding 2.0 ml of hydroxylamine hydrochloride solution and weighed amounts of iron, in a 50-ml calibrated flask. Dilute ammonium hydroxide solution was added until the colour developed, and the flask contents were then diluted to volume with water. As soon as they had been prepared, the solutions were examined spectrophotometrically with a Cary recording instrument, model 14M. Matched 10-mm silica cells were used for all measurements. A wavelength range of 340 to 650mp was covered, and appropriately prepared blank solutions were used for all measurements.664 [Vol. 83 Calculations of the molecular extinction coefficient were based upon the amount of iron added, and each value is the average of a series with increasing amounts of iron.(That for ligand XI is based upon a single observation.) All complexes gave colours that conformed to Beer's law over the range 1 to 6 p.p.m. of iron. SMITH AND BANICK : 4 : 4'-SUBSTITUTED 2 : 2'-DIPYRIDYLS The spectrophotometric results are shown in Table 11. TABLE I1 SPECTROPHOTOMETRIC Disubstituted Ligand with Unsubstituted _- I -CH, I1 -C,H, I11 -Br VI -c1 V -0CH. VI -oc,€f, VIII -OC&I, VIII -COOC,H6 IX -CONH, X -COOH- XI -NO, DATA FOR THE 4 : 4'- DISUBSTITUTED 2 : 2I-DIPYRIDYLS AS FERROUS COMPLEXES Wave1e:ngth Average Wavelength Average No. of of maximum molecular of maximum molecular deter- absorpt.ion, extinction absorption, extinction minations mP coefficient mP coefficient 4 3491 6430 522 8710 4 354. 7860 528 9340 4 356, 8410 529 9880 2 357 4960 534 5550 2 3561 7500 532 8300 3 35" 7750 525 6680 4 35Gl 9100 525 7660 5 3631 10,180 540 8060 5 384.10,380 541 14,150 4 384. 11,120 540 14,940 5 378 10,990 540 14,760 1 - - 525 9190 No diminution in colour intensity on storage for 30 days in glass-stoppered containers was noted for these solutions, except for ligands I11 and XI. The colours of these solutions, which had lost much of their original intensity, were not restored by the addition of another portion of reducing agent. From Table I1 it will be seen that the absorption peak in the near ultra-violet region (349 to 384mp) is common to all these complex cations. This peak was also found by Schilt and Smith' for 4 : 4'-diamino- and 4 : 4'-diphenyl-2 : 2'-dipyridyls.There is no comparable absorption peak for 1 : 10-phenanthrolines, and this serves as a differentiating characteristic. All the 4 : 4'- disubstitutions led to increase:; in the wavelength of maximum absorption as compared with the unsubstituted ligand at both absorption maxima (Tables I1 and 111). TABLE I11 CHANGE IN WAVELENGTH OF MAXIMUM ABSORPTION (Ah,,,) AND MOLECULAR EXTINCTION COEFFICIENT (A€) FOR THE 4 : 4'- DISUBSTITUTED 2 : 2'-DIPYRIDYL - IRONII COMPLEXES Relative to Am=. = 6430 at 349 mp and E =- 8710 at 522 mp for the unsubstituted 2 : 2'-dipyridyl- iron11 complex Ultra-violet absorption maximum Disubstituted (---, Ligand with AX,,,., A€, mP % I -CH, +5 + 22 I1 -C2H6 + 5 +31 I11 -Br $8 - 23 IV -c1 + 6 -C 17 V -0CH.1 8 , - VI -oczz, -10 VII -0CaHS + I 1 VIII -COOC,H. 35 IX -C0NHo " + 35 + 21 + 41 + 58 + 61 + 73 Visible region absorption maximum t 3 + 3 + 18 + 19 + 18 - 23 - 12 - 7 + 62 i 72 X -COOH" + 29 + 7 1 + 18 + 70 4 : 4'-diamino* + 30 + 112 + 47 -5 4 : 4'-diphenyl* +37 +216 + 30 + 144 * Taken from the values reported for these ligands by Schilt and Smith.' Ligands V, VI and VII differ from the remainder in that their iron11 complex cations have higher molecular extinction coefficients in the near ultra-violet than they possess inDec., 19581 IN CHELATION REACTIONS WITH FERROUS IRON 665 the visible portion of the spectrum. To this group should be added 4:4'-diamino-2:2'- dipyridyl. The molecular extinction coefficients for the iron11 chelate of unsubstituted 2 : 2'-dipyridyl (8710 at 522 mp and 6430 at 349 mp) found in this work are in good agreement with values reported by Busch and Bailar,lo who gave values of 8700 at 522 mp and 6500 at 348 mp.The re-determination of the molecular extinction coefficient of ligand I gave a value 10 per cent. higher than that reported at 528 mp by Cagle and Smith.2 In Table I11 are shown the changes in wavelength of maximum absorption and in molecular extinction coefficient brought about by the substitutions in the various ligands. It can be seen that- (a) the spectra for all the complex cations exhibit bathochromic shifts in the maximum absorption in both the ultra-violet and visible regions ; ( b ) diphenyl substitutions produce the greatest alteration of A,,,.and E values (compare Table 11), an effect that also occurs for similarly positioned phenyl-group substi- tutions in diquinolyls, tripyridyls and phenanthrolines ; (c) in general, increase in A,,,, values is accompanied by an increase in E values, and this trend is most consistent for the near ultra-violet absorption; and (d) the last five groups listed in Table 111, when substituted with dipyridyl, have the greatest influence on the spectrophotometric constants, a finding that is in agreement with similar experimental results for the corresponding 1 : 10-phenanthrolines, diquinolyls and tripyridyls.' To these five substituent groups (-COOC,H,, -CONH,, -COOH, -NH, and -C,H,) the hydroxyl group should be added, as exem- plified by Synder's reagent (4 : 7-dihydroxy- 1 : 10-phenanthroline), as shown by Schilt, Smith and Heimbuch.ll GROUPING OF REAGENTS BY SPECTROPHOTOMETRIC DATA Spectrophotometricaly, unsubstituted 2 : 2'-dipyridyl and ligands I, 11, I11 and IV are similar.Absorption peaks, both in the ultra-violet and visible (349 to 357 mp and 522 to 534 mp) regions, are pronounced, and are sharper than those of the similarly substituted 1 : 10-phenanthrolines, although less sharp than those of the similarly substituted tripyridyls.8 U .- 5 0 ' 6 p - J $ 0.4 ; 0 ' 6 R 5 0.4 - ,; 0.2 8 '5 0.2 0 0" '350 450 550 650 Wavelength, mp Wavelength, rnp Fig. 1. Absorption spectrum Fig. 2. Absorption spectrum of the 4: 4'-dimethyl-2: 2'-dipy- of the 4 : 4'-diethoxy-2: 2'-dipy- ridyl - iron11 complex 350 450 550 650 ridyl - iron11 complex Wavelength, mp Fig.3. Absorption spectrum of the 4: 4'-dicarboxy-2: 2'-dipy- ridyl - iron11 complex All four ligands have a peak absorption in the ultra-violet region that is 10 t o 15 per cent. Fig. 1 shows an example of this type of absorption lower than that in the visible region. spectrum.666 [Vol. 83 The ultra-violet absorption peak is sharp, while that in the visible region is broad. For this group the ultra- violet absorption is the more intense by 17 to :26 per cent. Fig. 2 shows an example of this type. Ligands VIII, IX and X (see Fig. 3) have similar absorption characteristics to those shown in Fig. 1. They are distinguished by the absence of a shoulder on the short-wavelength peak and by having only a slight indication of a shoulder on the long-wavelength peak, THE POSSIBLE DETERMINATION OF IRON B Y ULTRA-VIOLET SPECTROPHOTOMETRY Attempts to use the 1 : 10-phenanthrolines - iron11 complexes for the determination of iron by ultra-violet absorption, with possibly increased sensitivity, have failed owing to interference by absorption at practically the sa:me wavelength from the necessary excess of ligand present.Similar difficulties occur with the substituted dipyridyls, although in certain circum- stances it might be possible to use ligands 11, VI, VII and VIII (and 4:4'-diphenyl-2:2'- dipyridyl), which absorb negligibly at 340, 330, 340 and 350 (and 356) mp, respectively, whereas their respective iron11 complexes absorb at 355, 359, 363 and 384 (and 386) mp. This makes the proposed scheme of analysis less attractive, except when special conditions owing to other colour interferences are met with. The syntheses of the newly prepared 2 : 2'-dipyridyls herein described were carried out by Professor F. H. Case and G. Maerker of Temple University in Philadelphia and will be described elsewhere. Only through this valued assistance in a series of difficult and carefully developed synthetic reaction techniques has thir; study been made possible. FEIGL AND JUNGREIS: SPOT TESTS FOR PHENOLS AND Ligands V, VI and VII are again similar in a.bsorption characteristics. All the ferrous complexes as well as the excesses of ligand are extractable. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Smith, G. Frederick, Anal. Chem., 1954, 26, 1534:. Cagle, F. W., and Smith, G. Frederick, J. Amer. Chem. SOC., 1947, 69, 1860. Richter, F. P., Doctorate Dissertation, University of Illinois, 1941. Burstall, F. H., J . Chem. SOC., 1938, 1664. Gaines, X., jun., Hammett, L. P., and Walden, C;. H., jun., J. Amer. Chem. SOC., 1936, 58, 1668. Case, F. H., I b i d . , 1946, 68, 2574. Schilt, A. A,, and Smith, G. Frederick, Anal. Ch;:m. Acta, 1957, 16, 401. -,- , Ibid., 1956, 15, 567. Schilt, A. A,, Doctorate Dissertation, University of Illinois, 1956. Busch, D. H., and Bailar, J . C., jun., J . Amer. Chem. SOC., 1956, 78, 1137. Schilt, A. X., Smith, G. Frederick, and Heimbucli, X., Anal. Chem., 1956, 28, 809. First received November 26th, 1957 Amended, July 16th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300661

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

666 FEIGL AND JUNGREIS: SPOT TESTS FOR PHENOLS AND [Vol. 83 Spot Tests for Phenols and Alkylated Anilines Based on the Duff Formylation BY F. FEIGL AXD ES. JUNGREIS TRANSLATED BY R. E. OESPER (Laboratdrio da Produgdo Mzneral, Mznzstdrzo da Agrzcultura, Rzo de Janezro, B$ azzl) (Unzuerszty of Cznciizizatz, Czncznnatz, Ohzo) The formylation of phenols and dialkylanilines, as developed by Duff, has been extended to monoalkylanilines, and is accomplished by brief heating a t 150" to 160' C with a mixture of crystalline oxalic acid and hexamethylene- tetramine. The resulting o-hydroxyaldehydes and p-dialkylaminobenzalde- hydes or 9-monoalkylaminobenzaldehydes can be detected readily by either production of fluorescent aldazines with .hydrazine or formation of orange Schiff's bases with benzidine.These test:: for phenols or alkylated anilines come within the scope of spot-test analysis and have microanalytical sensitivity. DUFF^ has reported that satisfactory yields of o-hydroxyaldehydes and P-dialkylamino- benzaldehydes can be obtained by formylation of phenols and dialkylanilines withDec., 19581 ALKYLATED ANILINES BASED ON THE DUFF FORMYLATION 667 hexamethylenetetramine (hexamine). The procedures involve two partial reactions. In- itially, hexamine reacts in its trialkyl form,, and, when heated, participates in the following condensations- OH I OH I CH,--N=CH, + NH, . , 3 * (1) \=/- In fact, if hexamine is dry-heated with phenols or dialkylanilines, the evolution of ammonia from the reacting mass can be readily demonstrated by means of appropriate indicator-papers.In the second stage, the condensation products (I) are hydrolysed in their isomeric form (11) by dilute mineral acids to give the respective aldehydes according to reaction (3). + R I I)N<$I=N-CH3 + H,O + H+ -+ /-L-/- \ /-\ CHO+NH,-CH, (3) For the condensation reactions, Duff recommends conditions in which hydrolysis of the hexamine is kept a t a minimum or even avoided. This is achieved in reaction (1) by heating phenol and hexamine to 150" C for 15 minutes with a mixture of glycerol and boric acid that has previously been kept at 170" C for 30 minutes to remove water. Reaction (2) was accomplished by heating dialkylanilines and hexamine under reflux in a boiling-water bath for 5 hours with a mixture of glacial acetic acid and 90 per cent.formic acid. I t has been found that the formylations, i.e., reactions (l), ( 2 ) and (3), occur easily and readily when phenols or dialkylanilines are melted with a mixture of hexamine and oxalic acid dihydrate, although the latter, by virtue of its water of crystallisation, is known3 to bring about numerous hydrolyses, including the cleavage of hexamine by the following react ion- (CH,),N4 + 6H,O -+ 6CH,O + 4NH, I t appears, therefore, that reactions (1) and (2), as well as this hydrolysis, occur rapidly. I t should likewise be noted that equilibrium reactions are involved (which lead to extensive transformations of phenols and dialkylanilines) and that the reaction products are removed from the equilibrium mixture by the hydrated oxalic acid; ammonia by formation of am- monium oxalate, and condensation products by hydrolysis, as shown in reaction (3).This assumption is supported by the fact that microgram amounts yield the respective aldehydes after heating for 5 minutes at 150" C with oxalic acid and hexamine. Possibly the oxalic acid melt leads to improved yields of aldehydes, but this was not investigated, as our objective was to ascertain whether or not the Duff formylation can be used to detect phenols and alkylated anilines. Satisfactory results were achieved by fusing with oxalic acid, dissolving the reaction mixture in water and testing for aldehyde. The necessary operations are easily conducted by spot-test techniques. The tests described are additional examples to demonstrate one important point, namely, that suitably modified syntheses and methods of formation can be used as a basis for the detection of organic compounds and functional groups that take part in these changes4668 FEIGL AND JUNGREIS: SPOT TESTS FOR PHENOLS AND [Vol.83 DETECTION OF PHENOLS WITH FREE ortho-POsITIONs To detect o-hydroxyaldehydes formed in the Duff formylation, use is made of the im- mediate condensation of these compounds with hydrazine5 according to the following reaction- OH 013 OH I ,- I /-\ ' :-CH=N-N=CH--// +2H,O 2 Y-N-CHO + 2NH,-NH, -+ \=/ \=/ \=/ The aldazines formed in this reaction are resistant to dilute acids and show a yellow-green (or sometimes orange) fluorescence in ultra-violet light. When phenol and cresols undergo formylation, the resulting o-hydroxyaldehydes vaporise at the reaction temperature.Such aldehydes can be detected by holding a piece of filter- paper moistened with hydrazine sulphate solution over the melt. -4 stain, which exhibits yellow-green fluorescence, can be easily discerned even when no more than a trace of volatile aldehyde is produced. REAGEXTS- methylenetetramine. sodium acetate in 100ml of water. PROCEDCRE- add 1 drop of a solution of the sample in ethanol or diethyl ether. test-tube, and warm gently to remove the solvent. can be used, instead of its solution.) previously heated to 150" C. temperature for 1 to 2 minutes, and then remove the test-tube. hydrazine sulphate reagent solution to the reaction mass. shake the suspension, place it on a filter-paper, and dry for a short time, filter-paper in ultra-violet light. exhibit a blue-green, or sometimes orange, fluorescence.RESULTS- Use of the proposed procedure resulted in the detection of 0.25pg each of phmol, &-naphthol and resorcinol, 1 pg of 9-hydroxydiphenyl, 2 pg of salicylic acid, 5 pg of o-hydroxy- diphenyl and 15 pg of 2 : 7-dihydroxynaphthalene. No aldazine-fluorescence reaction was given by di-P-naphthol, naphthoresorcinol, 2 : 4-dinitroresorcinol or 1 : 8-dihydroxynaphtha- lene-1 : 3 : 6-trisulphonic acid. The fact that certain phenols, contrary to expectation, cannot be detected by the proposed procedure shows that no formylation occurred in the ortho-position, but this still leaves open the question of the possible introduction of a -CHO group meta or pava to the phenolic -OH group.To test this point, di-P-naphthol, naphthoresorcinol, 2 : 4-dinitro- resorcinol and 1 : 8-dihydroxynaphthalene-1 : 3 : 6-trisulphonic acid were heated to 150" C with hexamine. Ammonia was evolved, which indicates a condensation analogous to reaction (1). When phenols that show no aldazine-fluorescence reaction are melted with oxalic acid - hexamine mixture and the reaction mass is dissolved in water, the addition of benzidine produces a brown-yellow precipitate, which indicates the formation of a Schiff's base of the resulting aldehyde. These experiments show that a formylation has occurred, but, as yet, no information is at hand regarding its position and extent. It is remarkable that loss of ammonia can still be detected when 150 to 200 pg of these phenols are heated to 160°C with hexamine.Phenetole and acetylsalicylic acid were tested as representative of phenolic derivatives with free ortho-positions. The former gave no aldazine-fluorescence reaction, but the latter responded strongly (0.5 pg was detected). The response of acetylsalicylic acid is obviously due to the fact that, when heated with oxalic acid, hydrolytic splitting-off of acetic acid Oxalic acid - hexamine mixtw,e-Xx equal weights of crystalline oxalic acid and hexa- Hydrazzne sulphate reagent solution-Dissolve 10 g each of h ydrazine sulphate and The mixture should be freshly prepared before use. Place several centigrams of oxalic acid - hexamine mixture in a micro test-tube, and Nix the contents of the (If desired, a trace of the solid sample Place the test-tube in a glycerol bath that has been Raise the temperature of the bath to 160" C, maintain this When cool, add 1 drop of Add 1 drop of water, if necessary, Examine the If the sample contained phenols, the stains on the filter-paperDec., 19581 ALKYLATED ANILINES BASED ON THE DUFF FORMYLATION 669 occurs with production of salicylic acid.Other phenolic esters may be expected to behave analogously. The formylation test for phenols is impaired by the presence of aromatic amines and their N-alkyl derivatives, since, as shown by the positive aldazine-fluorescence response, o-hydroxyaldehydes may also be formed. A preliminary separation is therefore required. In many instances, this can be successfully accomplished by adding mineral acid or alkali hydroxide solution to the test solution and then extracting with diethyl ether; the aqueous layer will contain the salts of the amines or phenols.DETECTION OF MONO AXD DIALKYLANILINES The 9-dialkylaminobenzaldehydes produced by the Duff formylation can be detected by formation of orange Schiff’s bases with benzidine6 according to the following reaction- As in the test for phenols, there is no need to isolate the aldehyde after the fusion reaction; the test can be conducted on the aqueous solution of the oxalic acid melt. I t is noteworthy that monoalkylanilines (and even aniline itself) can be formylated by heating with oxalic acid - hexamine mixture. It appears that, during formylations, not only are -C,HO groups introduced in para-positions, but reactions also occur by which amines are converted to phenols.This is shown by the fact that addition of hydrazine salts to an aqueous solution of the oxalic acid melt produces the aldazine-fluorescence reaction of o-hydroxylaldehydes. PROCEDURE- The procedure is similar to that described for phenols, except that the cooled reaction mixture is treated with 1 to 2 drops of water, and the solution (or suspension) is placed on filter-paper impregnated with a solution of benzidine in diethyl ether. If the test is positive, an orange stain appears, the intensity of which depends on the amount of aromatic aldehyde formed. RESULTS- Use of the proposed procedure resulted in the detection of 2 pg each of dimethylaniline, diethylaniline and monomethylaniline and 3 pg of monoethylaniline. The test cannot be applied directly in the presence of either aldehydes that form coloured Schiff’s bases with benzidine or phenols that are formylated by hexamine.If such substances are present, the bases must be separated beforehand; this can be readily accomplished by ,dissolving the sample in acid and treating the solution with molybdophosphoric acid. The bases can then be recovered from the precipitate by adding alkali and extracting with diethyl ether. If mono and dialkylanilines are to be detected in the presence of aniline, the aniline should be converted to phenol by warming with nitrous acid (alkali nitrite plus hydrochloric acid). If the solution is then treated with alkali hydroxide solution and shaken with diethyl ether, the ethereal solution can be tested for mono and dialkylanilines by the proposed procedure. 1. 2. 3. 4. 5 . 6. REFERENCES Duff, J . C . , J . Chem. Soc., 1941, 547; 1945, 276. Losekann, G., Chem. Ztg., 1890, 14, 1409. Feigl, F., Jungreis, E., and Stark-Slayer, C., Anal. Chim. Acta, in the press. Feigl, F., “Spot Tests in Organic Analysis,” Fifth Edition, Elsevier Publishing Co., Amsterdam and Kew York, 1956, Chapter 1 . -, 09. cit., p. 185. Chakravarti, S. N., and Roy, M. B., Amzlyst, 1937, 62, 603. Received March 215t, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300666

出版商:RSC    

年代:1958

数据来源: RSC

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670 SAVILLE : A SCHEME FOR THE COLORIMETRIC DETERMINATION [Vol. 83 A Scheme for the Colorimetric Determination of Microgram Amounts of Thiols BY B. SAVILLE* (Chemical Defence Experimental Establishment, Porton Down, Salisbuvy, Wdts.) A method has been found of converting thiols, and other molecules possessing -SH groups, to their S-nitroso derivatives, which yield an equiva- lent of nitrous acid on mercuric ion-assisted hydrolysis. This nitrous acid is finally used in the formation of a brilliant azo dye from sulphanilamide and N-1-naphthylethylenediamine. The correspondence between dye produced and thiol used has been utilised in the development of a general analytical method. Sensitivity is extremely high, for as little as 2 x lo-* g-equivalents of a thiol in 1 ml of solution can be determined.The accuracy is to within &1 to 2 per cent. for determinations on about 2 x 10-7 g-equivalents of thiol. ALTHOUGH early work112 has shown that thiols can be converted to the corresponding S-nitroso derivatives by means of nitrosyl chloride, etc., little systematic investigation of the more simple chemical properties of these compounds has been reported. It has now been found that the S-nitroso derivatives of some of the more familiar thiols, such as ethanethiol, phenyl- methanethiol, cysteine, thiophenol and thioglycollic acid, undergo facile hydrolysis to nitrous acid in the presence of mercuric, silver or cupric salts. Hence, a solution of S-nitrosocysteine, which can be readily prepared by adding cysteine to excess of sodium nitrite in 0.1 to 1.0 N sulphuric acid, is relatively stable (ti N 50 hours) in the presence of ammonium sulphamate, which is added to remove the excess of free nitrous acid; the reactions are as follows- RSH + HONO =?- RSNO + H,O I Fast NH4S03NH2 NH4+ HS0,- + N, + H,O This indicates that the hydrolysis of the S-nitrosothiol (shown by the broken arrow) is slow in acid solution, in contrast to the corresponding behaviour of alkyl nitrites.On the other hand, if a slight excess of mercuric chloride, mercuric acetate or silver nitrate is added to the solution of the S-nitrosothiol prepared in the way described, there is an immediate liberation of nitrogen and the red colour of the nitroso compound is rapidly destroyed. This extremely rapid hydrolysis can be explained by assuming that those metal cations known to possess high affinities for sulphur can engage in rapid reversible co-ordination with the S-nitrosothiol to form a complex (I), which, owing to the weakened N-S bond, is then highly susceptible to nucleophilic attack by water molecules.The reactions are as follows- ' Hg+ 0 N-S + Hg2+ + N-S+/ I1 I1 I (1) R I R H 0 H 0 \+ I/ /Hg+ \o -N I1 __ :/Hg+ - + 0 - N + S R / H ' 11 \R H H+ + HONO * Present address : The British Rubber Producers' Research Association, 48 Tewin Road, IVelwyn Garden City, Herts.Dec., 19581 OF MICROGRAM AMOUNTS OF THIOLS 67 1 In the experiments described, the liberated nitrous acid immediately reacts with the excess of ammonium sulphamate to form recognisable gaseous nitrogen. However, if sulphanil- amide or some other reactive aromatic amine is mixed with the mercuric salt before addition to the S-nitrosothiol solution, the amine competes favourably with the sulphamate for the nitrous acid equivalent to the S-nitrosothiol and gives a high yield of the corresponding diazonium salt.For sulphanilamide, conditions have been found in which diazonium salt formation is almost exclusive, i.e., reaction ( 2 ) in the following equation is much more rapid than reaction (1)- pNH,IHSO, + rCT2 + HZO NH,SO,NH,/ H+ Hg2+ - - /(I) RSH -+ HONO - RSNO - HONO \(a) Excess of A vNH,,HX\ 4 nitrous acid removed 11[4rN=Nj+X- + 2H,O As the diazonium salt (which is formed in amounts equivalent to the thiol taken) can be made to couple with an amine to yield an intensely coloured azo dye, a potential colorimetric method for the determination of thiols was at once realised.METHOD REAGENTS- of 0.2 to 1.0 N sulphuric acid. Solution A-Mix 1 volume of a 0.01 M aqueous solution of sodium nitrite with 9 volumes Solution B-Prepare a 0.5 per cent. solution of ammonium sulphamate in water. Solution C-Mix 1 volume of a 1.0 per cent. aqueous solution of mercuric chloride with Solution D-Prepare a 0.1 per cent. solution of N-1-naphthylethylenediamine dihydro- This solution can be prepared as required. 4 volumes of a 3.4 per cent. solution of sulphanilamide in 0.4 N hydrochloric acid. chloride in 0.4N hydrochloric acid. PROCEDURE- To 5 ml of solution A in a 25-ml calibrated flask, add 1 ml of a solution of the thiol (0*00002 to 0.0005 M ) in water or aqueous ethanol.Set aside for & to 5 minutes, according to the nature of the thiol, and then add 1 ml of solution B. Insert the stopper, and shake well for a few seconds to ensure complete removal of excess of nitrous acid. After 1 to 2 minutes, rapidly add 10ml of solution C (to hydrolyse the S-nitrosothiol and form the diazonium salt), and then make up to the mark with solution D. Colour development is rapid and is usually complete in 3 to 5 minutes with no further change in intensity over a prolonged period. After 10 minutes, measure the coloured solution against an appropriate blank solution with a Spekker absorptiometer and Ilford No. 605 yellow-green filters. (It is advisable to cover the cell containing the blank solution with a cover-glass to prevent access of atmos- pheric nitrogen oxides.) Calibration graphs relating absorptiometer reading to thiol concentration can be plotted.These graphs are linear over a wide range of readings and are extremely reproducible. This solution must be freshly prepared each day. DISCUSSION OF THE METHOD ACCURACY- The accuracy of the method depends on the concentration of thiol being analysed. For 1 ml of 0.00002 M thiol, the accuracy is to within + l o per cent., whereas, for 0*0001 and 0.0004M solutions, the respective accuracies are to within i 2 to 3 per cent. and + 1 to 2 per cent. INTERFERENCES, SPECIFICATION AND SCOPE- As far as I am aware, the method is of general applicability to all thiols and has been shown to be specific for thiols in the presence of substances that might be thought, on a rational basis, to interfere. Hence, small amounts of dialkylamines, which could form nitros- amines as a potential source of nitrous acid, do not interfere.This may be because the rate of nitrosation of secondary aliphatic amines is low in acid solution3 and the rate of hydrolysis672 GAGE: THE DETERMINATION OF TRACES OF LEAD [Vol. 83 of secondary nitrosamines is high. In general, modifications will need to be introduced to compensate for interfering substances that either rapidly destroy nitrous acid or form coloured nitroso derivatives. As the rate of S-nitrosation of cysteine is several orders greater than the rate of de-amination of simple amino acids, cysteine can be determined without inter- ference from extremely large excesses of amino acids in protein hydrolysates. The method may therefore be of immediate importance to 'biochemists. A convenient standard thiol solution can be prepared by allowing the corresponding isothiuronium salt to undergo quantitative hydrolysis in dilute sodium hydroxide solution containing about 0.05 per cent. of alkali cyanide to prevent oxidation of the thiol. The reaction is as follows- NH \ // HO- + C-S-R- H'O-C + RSH (urea) I thank R. Bond (vacation student from the University of Glasgow, 1956), H. F. Liddell and Miss P. M. Smyth for assistance and advice during this work. REFERENCES 1. 2. 3. Tasker, H. S., and Jones, H. O., J . Chem. SOC., 1909, 95, 1917. Rheinboldt, H., Ber., 1926, 59, 1311; 1927, 60, 184. Taylor, T. W. J., J . Chem. SOL, 1928, 1897. Received May 29th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300670

出版商:RSC    

年代:1958

数据来源: RSC

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672 GAGE: THE DETERMINATION OF TRACES OF LEAD [Vol. 83 The Determination of Traces of Lead and Bismuth in Organic Material BY J. C. GAGE (Imfierial Chemical Industries Ltd., Industrial Hygiene Research Laboratories, The Frythe, Welwyn, Herts.) It has been shown that the method previously described for the deter- mination of lead in organic material ma.y be subject to interference from bismuth, but this can be avoided by reducing to 0.1 N the concentration of hydrochloric acid used to extract lead from its diethyldithiocarbamate complex in organic solution. The determination of both lead and bismuth can be made on the same solution by a second extraction of the organic layer with 1.75 N hydrochloric acid. IN two previous papers112 a method has been described for determining traces of lead in organic material.It was claimed that the dieth yldithiocarbamate separation of lead used in this method holds back any bismuth that may b'e present and that relatively large amounts of this metal do not interfere in the determination of lead. Experience in other laboratories has not entirely supported this claim, and a further investigation has indicated that the conditions of separating the lead must be more clearly defined in order to remove interference from bismuth. The possibility of adapting the rnethod so that both lead and bismuth can be determined when present together in trace a.mounts has been investigated. EXPERIMENTAL DETERMINATION OF LEAD IN THE PRESENCE OF BISMUTH- In the original method, lead was extracted, after destruction of organic matter by dry ashing, as its diethyldithiocarbamate complex into a mixture of equal volumes of pentanol and toluene.The lead was extracted from the olrganic layer with dilute hydrochloric acid, which was then added to an alkaline solution of dlithizone, and the lead dithizonate complex was extracted with carbon tetrachloride for the colorimetric determination of lead. The dilute hydrochloric acid used to extract lead from its diethyldithiocarbamate complex solutionDec., 19581 AND BISMUTH IN ORGANIC MATERIAL 673 in pentanol - toluene mixture was prepared by diluting constant-boiling acid (1 + 9) with distilled water; this dilute acid is approximately 0.6 N, but different batches show considerable variation. When the concentration of this acid is varied, all other conditions in the method remaining unchanged, there is no effect on the extraction of lead; this is shown by the results in Table I over a range of acid concentrations from 0.05 t o 0.65 N.The extraction of bismuth from the diethyldithiocarbamate complex solution has, however, been found to be greatly influenced by the concentration of acid used. The results in Table I1 show that, when 1 mg of bismuth, added as a standard solution of bismuth nitrate in diluted nitric acid (1 + 9), is subjected to the analytical procedure, negligible amounts of bismuth are extracted with acids below 0.5 N, but, above this concentration, the amount extracted rises sharply. It can also be seen from Table I1 that sub-maximum extraction of bismuth is also influenced by the composition of the solvent; the higher the proportion of pentanol in the mixture the greater the extraction.TABLE I EFFECT OF ACID CONCENTRATION ON THE EXTRACTION OF LEAD FROM A SOLUTION The optical densities of the lead dithizonate complex from 20 yg of lead in carbon tetrachloride were measured at 515 mp in a 1-cm cell OF ITS DIETHYLDITHIOCARBAMATE COMPLEX IN PENTANOL - TOLUENE MIXTURE Concentration of hydrochloric acid, N . . 0.05 0.1 0.25 0.5 0.65 Optical density . . . . . . . . 0.362 0.341 0.384 0.370 0.361 TABLE I1 EFFECT OF ACID CONCENTRATION AND COMPOSITION OF SOLVENT MIXTURE ON THE The optical densities of the bismuth dithizonate complex from 1 mg of bismuth in carbon tetrachloride were measured at 495 mp in a 1-cm cell EXTRACTION OF BISMUTH FROM A SOLUTION OF ITS DIETHYLDITHIOCARBAMATE COMPLEX Composition of solvent Optical density a t different concentrations of mixture hydrochloric acid P r h > Pentanol, Toluene, % v/v % v/v 0.1 N 0.25 0.5 N 0.65 N 0.8 N - - 0.062 - 40 60 0 50 50 0 0.006 0-025 0.124 0.5 13 60 40 0.005 - - 0.20 - The results in Tables I and I1 indicate that, when 0.1 N hydrochloric acid is used to extract the organic layer, extraction of lead will be complete, but no bismuth will be removed, even when present in large excess.DETERMINATION OF BISMUTH- A series of solutions containing 20 pg of bismuth has been submitted to the complete procedure, hydrochloric acid solutions ranging from 0.1 to 2.0 AT being used to extract the diethyldithiocarbamate complex. The optical density reached a maximum value with 1.5 N acid, and no increase was observed at higher acid concentrations.This maximum optical density has been found to be unaffected by minor variations in the proportions of the solvent mixture. In all subsequent experiments, 1.75 N hydrochloric acid was used to extract the bismuth from the first stage of the method. A calibration graph prepared by plotting the optical densities of a series of standard bismuth solutions, measured at 495 mp in 1-cm cells, against their bismuth contents, gave a straight line with a slope of 0.018 units per pg. The slope of this line is almost identical with that of a calibration graph for lead prepared in a similar manner at 515 mp. The results are shown in Table 111. TABLE I11 EFFECT OF ACID COSCENTRATIOK ON THE EXTRACTION OF BISMUTH The optical densities of the bismuth dithizonate complex from 20 yg of bismuth in carbon tetrachloride were measured at 495 my in a 1-cm cell Concentration of hydrochloric acid, N .. 0.1 0.5 1.0 1.6 1.55 2.0 Optical density . . .. . . . . 0.031 0.073 0,188 0.329 0.330 0.333674 GAGE [Vol. 83 DETERMINATION OF LEAD AND BISMUTH TOGETHER- To determine traces of lead and bismuth in organic material without including the error due to destruction of organic matter, a sample of tinned spinach was ashed in a silica basin at 450" C, a little magnesium nitrate solution being used to remove final traces of carbon. The ash was dissolved in constant-boiling hydrochloric acid, the solution was evaporated to dryness and the residue was dissolved in the constant-boiling acid diluted (1 + 9) with distilled water to make a solution equivalent to 40 per cent.w/v of spinach. Ten millilitres of this solution were subjected to the analytical procedure, two 10-ml portions of 0.1 N hydrochloric acid being used to extract the lead, and then two 10-ml portions of 1.75 N hydrochloric acid to extract the bismuth. Each of these extracts was submitted to the final colour-development stage, and the optical density of the dithizone complex in carbon tetrachloride was measured in 4-cm cells. The sample solution was found to contain 1.3 pg of lead in 10 ml, after the reagent blank equivalent to 1.5 to 2 pg of lead had been subtracted; no bismuth was found in the sample or in the reagent blank solution. To 10-ml portions of the sample solution were added known amounts of lead and bismuth, and then the analytical procedure was carried out; with a sample containing 400 pg of lead, it was found necessary to extract three times with 0.1 N hydrochloric acid to remove final traces before proceeding to the determination of bismuth.To confirm that iron does not interfere in this deter- mination, an experiment was made in which an excess of iron was present; the results are shown in Table IV. TABLE IV RECOVERY OF ADDED LEAD AND BISMUTH FROM SPINACH Determinations were carried out on 10-ml portions of the spinach extract (equivalent to 4 g of spinach), and each result is the mean of two determinations Lead added, r g 4 4 400 4 0 4 Bismuth added, Pg 0 400 4 4 0 4 Iron added, PLg 0 0 0 0 400 400 Lead found, Bismuth found, Pg CLg 3.6 - 4.4 - 3.6 4.0 1.2 0 4.4 4.0 3.25 - DISCGSSIOK OF RESULTS The investigation has shown that the concentration of hydrochloric acid used to extract lead from its solution as diethyldithiocarbamate in pentanol - toluene mixture is not critical, but that it must be controlled for the determin,xtion of lead in the presence of bismuth and for the subsequent separation of bismuth for colorimetric determination as its dithizone complex.The experiments with ashed spinach extract, fortified with known amounts of lead and bismuth, have shown that both metals a t concentrations equivalent to 1 p.p.m. in the fresh spinach can be determined with adequate accuracy in the presence of 100 p.p.m. of the other metal. Lead and bismuth together, both at a concentration of 1 p.p.m., can be deter- mined on the same solution by successive extraction with 0.1 N and 1-75 N hydrochloric acid, recoveries being within 10 per cent. of the expected values. The presence of 100 p.p.m. of iron causes no interference in the determination of bismuth, but a slight reduction has been found in the recovery of lead. Technical assistance in this investigation was provided by Miss Sylvia Morrissey and RIr. T. V. H. Chalker. REFERENCES 1. 2. Gage, J. C., A?talyst, 1955, 80, 789. __ , Ibid., 1957, 82, 453. Received July 8th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300672

出版商:RSC    

年代:1958

数据来源: RSC