ISSN:0003-2654    

DOI:10.1039/AN98106FX041

出版商:RSC    

年代:1981

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98106BX043

出版商:RSC    

年代:1981

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98106BX047

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

iV SUMMARIES OF PAPERS IN THIS ISSUE November, 1981Summaries of Papers in this IssueSpectrophotometric Determination of Aluminium in Alloysand Ores. Part 1. Removal of Interfering Metals as Their2- Isopropylq~olin-8-01 Chelates by Precipitation and ExtractionA simple and rapid method for determining aluminium in permanent magnetalloy, iron and manganese ores and nimonic 90 alloy is described. Thesample is dissolved in acid and the aluminium is separated from the interferingmetals such as iron, cobalt, nickel, chromium, copper, manganese and titaniumby extracting these into chloroform as their 2-isopropylquinolin-8-01 chelates.The aluminium is left behind and is extracted into chloroform as its quinolin-8-01 chelate and determined spectrophotometrically. For aluminium contentsranging from about 7 to 1.4% the method uses a sample mass of between500 and 2000 pg present in the aliquot taken and can therefore be consideredas a useful microchemical technique.Keywords : A luminium determination ; spectrophotonzetry ; 2-isopropyl-quinolin-8-01 separationA. NARAYANAN and D.A. PANTONYDepartment of Metallurgy and Materials Science, Royal School of Mines, ImperialCollege of Science and Technology, Prince Consort Road, London, SW7 2BP.Analyst, 1981, 106, 1137-1144.Spectrophotometric Determination of Aluminium in Alloys andOres. Part 2. Stripping Aluminium after Chelation of OtherMetals with 2-Isopropylquinolin-8-01 in Butan- 1 - 01In Part 1, aluminium was separated after extracting the other metals present,as their 2-isopropylquinolin-8-01 chelates, from aqueous solutions. In thispaper a simpler and more efficient method of separation of aluminium isdescribed.Instead of precipitating the interfering metals as their 2-iso-propylquinolin-8-01 chelates and then extracting them into chloroform, theyare prepared directly in butan-1-01. Chelation of aluminium with the 2-iso-propyl compound does not occur in butan-1-01 medium. The butanolicsolution containing unchelated aluminium and the chelates of other metalsis mixed with chloroform and then extracted with alkaline tartrate-bufferedsolution. In this way the uncomplexed aluminium is transferred to theaqueous phase, from which it is extracted as its quinolin-8-01 complex anddetermined spectrophotometrically. The technique has been applied to thedetermination of aluminium in complex matrices such as permanent magnetand nimonic 90 alloys.Keywords : Chelation of metals ; 2-iso~ropylquinolin-8-ol; butan-1-01 ; solventextractionA. NARAYANAN and D.A. PANTONYDepartment of Metallurgy and Materials Science, Royal School of Mines, ImperialCollege of Science and Technology, Price Consort Road, London, SW7 2BP.Analyst, 1981, 106, 1145-1149November, 1981 SUMMARIES OF PAPERS I N THIS ISSUESolvent Extraction of the Thiocyanate Mixed-ligand Complexes ofIron(II1) with Various Hydroxyamidines and SpectrophotometricDetermination of Iron(II1) in Various Biochemical and BiologicalSamplesThe reaction in benzene of 1 1 newly synthesised N-hydroxy-NN’-diarylbenz-amidines (HOA) with iron(II1) in the presence of thiocyanate has been inves-tigated spectrophotometrically.The study revealed the formation of a 1 : 2 : 1iron(II1) - thiocyanate - HOA mixed complex in acidic media (0.2-0.8 Mhydrochloric acid). On the basis of this sensitive colour reaction, a simple,rapid, selective and highly reproducible method for the extractive - spectro-photometric determination of microgram amounts of iron( 111) in various bio-chemical and biological samples has been developed. The molar absorptivitiesof the systems are found to be between 1.1 and 1.35 x lo4 1 mol-1 cm-l in thewavelength range 460-470 nm. The method is free of interference from mostof the common metal ions and commonly used sequestering agents.Theeffects of experimental variables on the procedure are discussed.Keywords : Solvent extraction ; spectrophotometry ; iron (111) - thiocyanatecomplex ; hydroxyamidinesMISS A. R. JHA and R. K. MISHRADepartment of Chemistry, Ravishankar University, Raipur-492 010, M.P., India.Analyst, 1981, 106, 1150-1156.VUtility of r- Acceptors in Charge- transfer Complexation of Alkaloids :Chloranilic Acid as a Spectrophotometric Titrant inNon-aqueous MediaA spectrophotometric titration method is described for the determination ofsome alkaloids and their dosage forms using 0.005 M chloranilic acid solution in1,4-dioxan as the titrant. The end-point is determined by measuring thechange in absorbance of the sample a t 535 nm. Quantitative recoveries withgood reproducibility are reported for atropine, emetine, reserpine, strychnine,yohimbine and four dosage forms.The least-squares method for the end-point location in the syectrophotometric titration is also proposed.Spectrophotometric titration ; alkaloid determination ; chloranilic Keywordsacid ; charge-transfer complexationSURAJ P. AGARWAL and M. ABDEL-HADY ELSAYEDFaculty of Pharmaceutical Sciences, University of Nigeria, Nsukka, Nigeria.Analyst, 1981, 106, 1157-1162.Spectrophotometric Determination of Piperazinevia Charge - transfer ComplexesIodine - piperazine or chloranil - piperazine charge-transfer complexes havebeen used for the sensitive assay of piperazine or its salts; these complexesexhibit intense absorption bands in the electronic spectrum.The molecularratios of the reactants in the complexes have been established and the experi-mental conditions leading to maximum charge-transfer bands were alsostudied. The proposed procedures have been applied successfully to puresamples and drug formulations with good accuracy. The average recoverywas 100.26-100.84~0 with piperazine - iodine and 99.33-100.33y0 withpiperazine - chloranil charge-transfer complexes, with an average standarddeviation for each method of 0.8-3.90,0.Keywords : Piperazine and piperazine salt determination ; spectrophotometry ;charge-transfer complexes ; drug formulationsMOHAMED S. RIZK, MOHAMED I. WALASH and FAWZIA A. IBRAHIMDepartment of Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura,Egypt.Analyst, 1981, 106, 1163-1167Vi SUMMARIES OF PAPERS IN THIS ISSUESimultaneous Determination of Eight Trace Elements in HumanSkin by Instrumental Neutron-activation AnalysisNovember, I981Eight trace elements (scandium, chromium, iron, cobalt, zinc, selenium,rubidium and caesium) were determined simultaneously in human skin byinstrumental neutron-activation analysis.The concentrations of all traceelements studied were higher in the abdominal epidermis than the dermis.Site specification was found to be essential.Application of cluster analysis revealed that iron and zinc were the mostsimilar trace elements in their distribution in the dermis relative to the othersstudied, and chromium in the epidermis was the most dissimilar.Keywords : Trace element determination ; epidermis ; dermis ; cluster analysisANAT MOLOKHIA and ALAN DYERDepartmentM5 4WT.of Chemistry and Applied Chemistry, University of Salford, Salford,and BENJAMIN PORTNOYThe Skin Hospital, University of Manchester School of Medicine, Quay Street,Manchester, M3 3HL.Analyst, 1981, 106, 1168-1173.Method for the Simultaneous Determination of Arsenic, Aluminium,Iron, Zinc, Chromium and Copper in Plant TissueWithout the Use of Perchloric AcidA 0.5-g sample of plant tissue was digested with a mixture of concentratednitric and sulphuric acids (2 + 1 V / V ) and hydrogen peroxide.Arsenic wasdetermined by the hydride generation method. Aluminium, iron, zinc,chromium and copper were determined by direct flame atomic-absorptionspectrometry.The detection limits in dry plant material using 50 ml ofaqueous solutions for analysis were 0.5 ng g-I for arsenic and 0.1 pg g-I foraluminium, iron, zinc, chromium and copper. The relative standard deviationswere 4, 6, 1, 11, 6 and 7y0, respectively. All six metals were determined fromthe same aliquot with recoveries ranging from 93 to 118y0. A study was madeof the composition of the precipitate that settled out from the extracts. X-raydiffraction revealed the presence of ct-aluminium oxide (corundum) and somequartz in the anti-bumping granules. a-Aluminium oxide was a source ofcontamination for the aluminium analysis.Keywords : Metal determination ; plant tissue ; atomic-absorption spectrometry ;X-ray diffraction; acid digestionNABIL M.ARAFAT and WALTER A. GLOOSCHENKONational Water Research Institute, Canada Centre for Inland Waters, P.O. Box5050, Burlington, Ontario, Canada L7R 4A6.Analyst, 1981, 106, 1174-1 178November, 1981 SUMMARIES OF PAPERS I N THIS ISSUESome Observations on the Capabilities of Photoacoustic FourierTransform Infrared Spectroscopy (PAFTIR)viiThe interfacing of a photoacoustic cell to a Fourier transform infraredspectrometer is described. The performance of the system with some powderand film samples has been evaluated and the differences between the photo-acoustic spectra and corresponding transmission spectra are discussed. Dataare presented that indicate the possibility of quantitative analysis employingthe PAFTIR system.Keywords 1 Photoacoustic spectroscopy ; infrared spectroscopy ; Fourier trans-form infrared spectroscopy ; interferometry ; polymer characterasationJ.M. CHALMERS and B. J. STAYImperial Chemical Industries Limited, Petrochemicals and Plastics Division, WelwynGarden City, Hertfordshire.G. F. KIRKBRIGHT and D. E. M. SPILLANEDepartment of Instrumentation and Analytical Science, University of ManchesterInstitute of Science and Technology, P.O. Box 88. Manchester, M60 1QD.and B. C. BEADLEEDT Research, 14 Trading Estate Road, London, NWlO 7LU.Analyst, 1981, 106, 1179-1186.Pattern Display for Characterisation of Trace Amounts of OdorantsDischarged from Nine Odour SourcesThe odorants discharged from nine odour sources were classified into eightcompound groups and were analysed by a systematic gas-chromatographictechnique.The characterisation of trace amounts of the odorants was carriedout by using the values for new proposed units (pOU,, pOUa, IogOU, OUt andOU ; all terms are dimensionless) based on the ratio of the detected concentra-tion to the odour recognition threshold concentration. The graphical repre-sentation of these data is effective for rapid recognition of the whole state. Apolar co-ordinate pattern display was also proposed for the explanation of therelationship between odour characteristics (odour quality and intensity) andchemical analysis data of the odorants responsible for each odour dischargedfrom nine odour sources. The calculated pOU, and POUa values of eightodorant groups were plotted on polar co-ordinate circular odour charts.Thesecharts illustrated a characteristic pattern and it was found that the shapes andsizes of each odour chart could characterise the quality and intensity ofeach odour from the nine odour sources. This was confirmed by investigatingexamples of processes or factories belonging to the nine odour sources.Keywords ; Odorant Gharacterisation ; air analysis ; gas chromatography ; cold-and adsorption-trapping ; pre-column concentrationYASUYUKI HOSHIKAAichi Environmental Research Centre, 7-6, Tsuji-machi, Kita-ku, Nagoya-shi, Aichi,462, Japan.YOSHIMASA NIHEIInstitute of Industrial Science, University of Tokyo, 7-22- 1, Roppongi, Minato-ku,Tokyo, 106, Japan.and GIICHI MUTOSaitama Institute of Technology, 1690, Fusaigi, Okabe-machi, Osato-gun, Saitama,369-02, Japan.Analyst, 1981, 106, 1187-1202viii SUMMARIES OF PAPERS IN THIS ISSUESeparation and Identification of Aminocarboxylic AcidSequestrants by High-performance Liquid ChromatographyNovember, 1981A simple method has been developed for the separation by high-performanceliquid chromatography of some common aminocarboxylic acid sequestrants astheir copper complexes.The copper complex is formed in situ by using acopper salt solution as the eluate. Detection using visible light at 760 nmeliminates interference from ultraviolet absorbing compounds often presentin mixtures containing sequestrants.Keywords : High-performance liquid chromatography ; aminocarboxylic acids ;sequestrants ; copper complexesC.C. T. CHINNICKApplied Chemicals Limited, P. 0. Box No. 43, Salisbury Road, Uxbridge, Middlesex,UB8 2SW.Analyst, 1981, 106, 1203-1207.Determination of Pyrimethamine in Animal FeedsReport prepared by the Medicinal Additives in Animal FeedsSub-committee (A)Keywords : Pyrimethamine determination ; animal feeds ; gas - liquidchromatographyANALYTICAL METHODS COMMITTEEThe Royal Society of Chemistry, Burlington House, Piccadilly, London, W1V OBN.Analyst, 1981, 106, 1208-1209.Determination of Tungsten in its Ores and Concentrates byAtomic-absorption SpectrometryShort PaperKeywords : Tungsten detervnination ; ores ; atomic-absorption spectrometryEDWARD C. SPRENZ and MANFRED J. PRAGERUnited States Customs Laboratory, 6 World Trade Centre, New York, N.Y. 10048,USA.Analyst, 1981, 106, 121 0-1213.Differential-pulse Polarographic Determination of DegradationProducts of Cephalosporins : Comparison of the Degradation ofCephaloglycin in Neutral Solution with that of CephalexinShort PaperKeywords : Differential-pulse polarography ; cephaloglycin ; degradationA. G. FOGG and M. J. MARTINChemistry Department, Loughborough University of Technology, Loughborough,Leicestershire, LEll 3TU.Analyst, 1981, 106, 1213-1217

ISSN:0003-2654    

DOI:10.1039/AN98106FP133

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

November, 1981 SUMMARIES OF PAPERS IN THIS ISSUEIndirect Amplification Method for Determining Peroxydisulphate byAlternating-current PolarographyixShort PaperKeywords : Peroxydisulphate determination ; amplification ; polarographyD. AMINDepartment of Chemistry, College of Science, University of Mosul, Mosul, Iraq.Analyst, 1981, 106, 1217-1221.Titrimetric Micro- determination of Peroxydisulphate byAmplification ReactionsShort PaperKeywords : Peroxydisulphate determination ; amplification ; iodimetryD. AMIN and A. K. HAREEZDepartment of Chemistry, College of Science, University of Mosul, Mosul, Iraq.Analyst, 1981, 106, 1221-1224.Indirect Spectrophotometric Determination of Iodide in TableSalts and Pharmaceutical ProductsShort PaperKeywords : Iodide determination ; 3-(2’-thiazolylazo)-2,6-diaminotolueneV.GONZALEZ DiAZ, C. R. TALL0 GONZALEZ and F. GARCfAMONTELONGODepartment of Analytical Chemistry, University of La Laguna, Tenerife, CanaryIslands.Analyst, 1981, 106, 1224-1227.reagent ; palladium complex ; spectrophotometryInterference Due to Crystal Formation in the SpectrophotometricDetermination of Iron(I1) Using 2,4,6-Tri(2’-pyridyl)- 1,3,5-triazineShort PaperKeywords : Iron(1I) determination ; spectrophotometry ; 2,4,6-tri(2’-pyridyl)-1,3,5-triazineJ. D. BOXMacleay Building, School of Biological Sciences, University of Sydney, N.S. W. 2006,Australia.Analyst, 1981, 106, 1227-1229X SUMMARIES OF PAPERS I N THIS ISSUESpectrophotometric Determination of Trace Amounts of Iron(II1) with2-(5-Chloro-2-pyridylazo)-5-diethylaminophenolNovember, 1981Short PaperKeywords : Iron determination ; spectrophotometry ; 2-( 5-chloro-2-pyridylazo) -5-diethy lamino phenolSHEN NAI-KUI and CHU WEN-TIENDepartment of Chemistry, Bengbu Medical College, Bengbu, Anhui Province, China.WE1 FU-SHENG and SHEN SHAN-SHANDepartment of Modern Chemistry, University of Science and Technology of China,Hefei, Anhui Province, China.Analyst, 1981, 106, 1229-1233.Spectrophotometric Determination of Micro-amounts ofChromate in the Presence of Iron(III), Chromium(II1) and Other IonsShort PaperKeywords : Chromium( V I ) determination ; spectrophotometry ; iron(II) -FerroZine complexFREDERICK BET-PERA and BRUNO JASELSKISDepartment of Chemistry, Loyola University of Chicago, Chicago, Ill.60626, USA.Analyst, 1981, 106, 1234-1237.Dithiooxamide as a Reagent for the Detection andSpectrophotometric Determination of Chloral Hydrate inAlcoholic BeveragesShort PaperKeywords : Chloral hydrate determination ; dithiooxamide ; spectrophotometry ;alcoholic beveragesK. A. AMBADE and S . K. MEGHALRegional Forensic Science Laboratory, State of Maharashtra, Dhantoli, Nagpur-440012, India.Analyst, 1981, 106, 1237-1239.Sample Re-radiation Effects in the Quantitative Analysis ofCrystalline Silica in Foundry Samples by InfraredSpectrophotometryCommunicationKeywords : Crystalline silica ; quartz ; cristobalite ; tridylnite ; infrared spectro-photometryROBERT D. FOSTER and RONALD F. WALKERHealth and Safety Executive, Research and Laboratory Services Division,403 Edgware Road, London, NW2 6LN.Ana/-vst, 1981, 106, 1240-1242November, 1981 SUMMARIES OF PAPERS IN THIS ISSUEA Toluidine Blue Stain Mountant for the Microscopyof Comminuted Meat ProductsCommunicationKeywords : Microscopy ; single-stage staining ; meat tissues ; wheat gluten ;soya protein determinationF. 0. FLINT and B. M. FIRTHProcter Department of Food Science, University of Leeds, Leeds, LS2 9 JT.Analyst, 1981, 106, 1242-1243.x

ISSN:0003-2654    

DOI:10.1039/AN98106BP139

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

NOVEMBER 1981 The Analyst Vol. 106 No. 1268 Spectrophotometric Determination of Aluminium in Alloys and Ores Part 1 .+ 2-lsopropylquinolin-8-01 Chelates by Precipitation and Extraction Removal of Interfering Metals as Their A. Narayanan and D. A. Pantony Department of Metallurgy and Materials Science, Royal School of Mines, Imperial College of Science and Technology, Prince Consort Road, London, S W7 2BP A simple and rapid method for determining aluminium in permanent magnet alloy, iron and manganese ores and nimonic 90 alloy is described. The sample is dissolved in acid and the aluminium is separated from the interfering metals such as iron, cobalt, nickel, chromium, copper, manganese and titanium by extracting these into chloroform as their 2-isopropylquinolin-8-01 chelates. The aluminium is left behind and is extracted into chloroform as its quinolin- 8-01 chelate and determined spectrophotometrically.For aluminium contents ranging from about 7 to 1.4% the method uses a sample mass of between 500 and 2000 pg present in the aliquot taken and can therefore be considered as a useful microchemical technique. Keywords : A luminium determination ; spectrophotornetry ; 2-isopropyl- quinolin-8-01 separation Ever since Merrit and Walker1 showed that 2-methylquinolin-8-01 chelates with many metals but not with aluminium, methods have been developed with a view to separating aluminium from other metals associated with it by the use of this reagent. However, the results obtained have not been satisfactory, especially when aluminium was a minor constituent.Pantony and Selfe (unpublished work) found that quantitative separation of aluminium using 2-methyl- quinolin-8-01 was possible only for binary alloys of aluminium with magnesium , nickel, copper or beryllium. They also found that despite varying extraction conditions the results obtained for aluminium in complex alloys and iron ore using 2-methylquinolin-8-01 separation were high. Their observations were supported by the method described by Hynek and Wrangell,2 who used mercury cathode electrolysis in conjunction with 2-methylquinolin-8-01 to separate the interfering elements from aluminium in complex alloys. Although they obtained accurate results by this method, it appears to have no great advantage over existing methods. According to Dagnall et u Z . , ~ aluminium is in fact extracted by 2-methylquinolin-8-01 into chloroform to a certain extent.They showed that the recovery of aluminium after prelimi- nary extraction with 2-methylquinolin-8-01 was low. Hence there is a degree of uncertainty about the quantitative results obtained for aluminium using 2-methylquinolin-8-01 for the removal of interfering elements. The use of 2-isopropylquinolin-8-01 for the separation of aluminium from interfering elements might be of advantage in two ways: 1. substitution of the 2-isopropyl group in place of 2-methyl will cause increased steric hindrance and therefore prevent the extraction of aluminium ; and 2. the higher solubility ratios of the chelates of this alkyl homologue compared with those below it should ensure more complete removal of the interfering metals.With this objective, previous investigators4r5 synthesised 2-ethyl-, 2-isopropyl- and 2-tert- butylquinolin-8-01s. Although the synthesis of the reagents and their physico-chemical properties were studied, their analytical usefulness was not firmly established. Haba4 used the 2-ethyl and 2-isopropyl homologues for separating aluminium in a complex alloy and * For Part 2 of this series, see p. 1145. 11371138 NARAYANAN AND PANTONY : SPECTROPHOTOMETRIC DETERMINATION Analyst, YoZ. 106 found that the 2-isopropyl homologue gave satisfactory results for aluminium. Kazi,5 how- ever, found that the method described by Haba produced high aluminium figures. This indicated that Haba’s method was not effective in removing the metals that interfere in the spectrophotometric determination of aluminium by quinolin-8-01. I t was therefore decided to investigate the best experimental conditions for the removal of interfering elements by 2-isopropylquinolin-8-01 prior to the determination of aluminium in different matrices.Experimental 2-Isopropylquinolin-8-01 was synthesised by the direct alkylation of quinolin-8-01 by the appropriate lithium alkyl according to methods described p r e v i o ~ s l y . ~ ~ ~ Preliminary Investigations The wide pH range over which metal ions such as iron, copper, nickel, cobalt, manganese and zinc are reported4y6 to be extracted into chloroform by 2-isopropylquinolin-8-01, and the failure of this reagent to react with aluminium under any conditions, indicated the feasibility of separating aluminium from the other metals, when present.However, extraction of metals chelated by the 2-isopropyl compound was not rapid when the aqueous solution of the metal ion at a suitable pH was shaken with a solution of the reagent in an organic solvent such as chloroform. This has been explained elsewhere6 in terms of kinetic factors involved in the extraction process. This difficulty was overcome by precipitating the metal chelates from the aqueous solution at a suitable pH and then extracting them into chloroform. In this method of extraction the number of precipitations and extractions required to remove the interfering metal ions depended on the total amount of metals present, the valence states of the metal ions, the concentration of the reagent and the time allowed for the precipitation of the metal chelates at the chosen pH.Investigations on various metal ions either independently or in combinations were carried out to find the maximum amount of metals that could be efficiently separated so that the limitation of the technique to the determination of aluminium could be ascertained. Efficiency of Removal of Interfering Metal Ions by 2-Isopropylquinolin-8-01 Synthetic alloy solutions containing various amounts of iron, copper, nickel, cobalt and manganese were prepared from Specpure metals. A 5-ml fraction containing a total amount of the metal ions between about 4 and 6 mg was pipetted out into a 100-ml separating funnel. To this were added 10 ml of 1% m/V tartaric acid followed by 10 ml of Z-isopropylquinolin- 8-01 (1% m/V in 0.2 M hydrochloric acid).The pH was adjusted to 9.5-10 with 1 M sodium hydroxide solution and the mixture was allowed to stand for 5min. The precipitated chelates were extracted into 15ml of chloroform and the organic phase was discarded. These operations were repeated on the aqueous phase but using only half the amount (5 ml) of the reagent for precipitation and 10 ml of chloroform for extraction each time, until the chloroform extract was colourless. The aqueous phase was washed with 5 ml of chloroform and the washings were discarded. After adjusting the pH of the aqueous phase to 5 with glacial acetic acid, it was extracted with 5-rnl portions of 1% m/V quinolin-8-01 in chloroform. The extracts were made up to 10 ml, dried with anhydrous sodium sulphate and the absorbance was measured at 400 nm, the wavelength suitable for the aluminium - quinolin-8-01 complex.A blank determination using all of the reagents (except the synthetic alloy solutidn) was conducted using the same procedure. The absorbance measured for the quinolin-8-01 extract obtained from the synthetic alloy (after 2-isopropylquinolin-8-01 extraction) was not significantly different from the reagent blank. This indicated the efficiency of removal of metals that would interfere in the determination of aluminium by quinolin-8-01. Separation and determination of aluminium were attempted by adding known amounts of aluminium to synthetic alloy mixtures. Although the results in general were slightly low, they were considered reasonable for routine purposes.In synthetic alloy solution B the total mass of metals separated was more than in A and therefore required an increase in the number of extractions. Also in the synthetic alloy solution B the higher concentration of nickel and copper compared with A was considered to cause the inefficient extraction of iron(III), which chelates less readily The results are presented in Table I.November, 1981 OF ALUMINIUM IN ALLOYS AND ORES. PART 1 1139 than the bivalent metals, accounting for an increase in the number of extractions required. This possibly could have incurred some loss of aluminium, resulting in a slightly low recovery. However, there was sufficient indication that by an appropriate choice of sample mass the method can be used advantageously for determining aluminium above 1% m/m levels in fairly complex alloys.TABLE I ALUMINIUM RECOVERED AT DIFFERENT LEVELS AFTER 2-ISOPROPYLQUINOLIN-8-OL SEPARATION OF IRON, COPPER, NICKEL, COBALT AND MANGANESE Aluminium Total mass of Composition of matrix equivalent matrix metals metals to the in 5-ml r-A--, amount Aluminium, Sample aliquotlpg Metal Amountlpg added, % found, % Synthetic alloy A . . . . 4176.4 Iron 2 792.5 0.239 0.226 Copper 317.9 Nickel 291.0 Cobalt 500.0 Manganese 275.0 Synthetic alloy B . . . . 5734 Iron 2 234 0.105 0.093 Copper 635 0.157 0.144 Nickel 2 355 0.209 0.187 Cobalt 400 0.244 0.217 Manganese 110 Interferences Due to Chromium and Titanium The fact that chromium is not extracted at room temperature by quinolin-8-01 and its 2-methyl, 2-ethyl and 2-isopropyl homologues was considered favourable for the separation of aluminium from chromium.However, in alloys rich in chromium (about 20% m/m), nickel (about 59%) and cobalt (about 15%) and low in titanium, iron and aluminium, the recovery of aluminium varied widely when separation of metals other than chromium and aluminium was carried out as described previously. It was noticed in these instances that a precipitate developed as a “veil” a t the interface, resulting in unsatisfactory extraction conditions, especially during the extraction of aluminium by quinolin-8-01, When chromium was expelled as chromyl chloride prior to the extraction of other matrix metals with the 2-isopropyl compound, hardly any “veil” was noticeable.As there was a possibility of losing aluminium by volatilisation when chromium was expelled as chromyl chloride, this method was not preferred. I t was therefore decided to precipitate chromium together with other metals by 2-isopropylquinolin-8-01 from hot solution. Interference due to chromium in aluminium extraction could therefore be eliminated. Although it would seem attractive to precipitate chromium together with other metal chelates of the 2-isopropyl compound from a hot tartrate-buffered solution in a single step, it was found that tartrate made the precipitation of chromium incomplete. This is in agreement with published information. ** However, the use of an acetate-buffered medium and a pH of 5 precipitated most of the chromium, which was then extracted into chloroform.A second precipitation was conducted in a hot tartrate-buffered medium a t pH 10. At this pH, which was suitable for the precipita- tion of nickel, cobalt and manganese chelates of the 2-isopropyl compound, any residual chromium remaining in the solution was also precipitated. Experiments conducted on synthetic alloy solutions containing chromium, nickel, cobalt, iron and titanium to examine the efficiency of removal of these metals showed that the blank was, on average, 0.02 absorbance unit higher than the blanks from the reagents. The aluminium equivalent to this absorbance was 0.08 pg ml-l in the final quinolin-8-01- cliloro- form extract. As the metal solutions were prepared from Specpure materials with an aluminium content of between 1 and 10 p.p.m.they could not be expected to make significant contributions to the higher absorbance noted for the synthetic alloy blank. Investigations showed that incomplete removal of titanium contributed to the higher absorbance noted for the synthetic alloy.1 140 NARAYANAN AND PANTONY : SPECTROPHOTOMETRIC DETERMINATION Analyst, V d . 106 Influence of Titanium In the presence of chromium, titanium at the 50-pg level (equivalent to 2.5y0 m/m of the total metals) in the solution analysed was removed only up to 90%. However, if the quinolin-8-01 extraction of aluminium in the final solution was carried out at pH 11 trace amounts of titanium present were not extracted as indicated by the synthetic alloy blank not being significantly different from the blank obtained from the reagents.Experiments on the synthetic alloy with known amounts of added aluminium showed the method to be suitable for similar alloys containing l--2y0 m/m of aluminium using a sample mass of 2 mg. In the absence of chromium, titanium at the 1% m/m level does not interfere. Determination of Aluminium in Alloys and Ores Apparatus Spectrophotometer, Silica or glass cuvettes, path length 10 mm. Separating fiLnnels, 100 ml, with P T F E keys. PTFE beakers, 50ml. Reagents Doubly distilled water and analytical-reagent grade acids were used throughout. Hydrochloric acid, sp. gr. 1.18. Nitric acid, sp. gr. 1.42. Perchloric acid, sp. gr. 1.54. Sulphu~ic acid, sp. gr. 1.84. Acetic acid, glacial. Tartaric acid. 2-Isopropylquinolin-8-01. Sodiztm hydroxide solution, 1 M.Qztimolin-8-ol. Chloroform. p H indicator paper strips. 0.5 or 1% m/V as required. 2 or 4% m/V in 0.4 M hydrochloric acid, or solid reagent, as required. from hexane and a 1% m/V solution in chloroform was prepared. Prepared from Ultrar grade reagent. The commercially available reagent was steam distilled and crystallised Analytical-reagent grade ; freshly distilled if necessary. Strips of good quality were used. Sample mass aluminium in the final volume of the quinolin-8-01 chloroform extract. centration of aluminium should preferably be not more than 2.4 pg ml-1. The sample mass was so chosen that an aliquot taken resulted in at least 1 pg ml-1 of The maximum con- Aluminium in Permanent Magnet Alloy Permanent magnet alloy [British Chemical Standard (BCS) 2331, chosen as a typical alloy for the study, has the following Composition: iron 51.15, nickel 11.22, cobalt 23.72, copper 5.09, titanium 0.79, aluminium 6.99 and nianganese 0.235y0.Preparation of sample solution A 0.1-g amount of carefully sampled alloy was dissolved in 10 ml of hydrochloric acid (sp. gr. 1.18). A 2-ml volume of nitric acid (sp. gr. 1.42) was added to complete the dissolution and the solution was taken to fumes with 10 ml of perchloric acid (sp. gr. 1.54). The solution was cooled and diluted with 100ml of water and gently warmed to dissolve the salts. It was then treated with a further 5 ml of percliloric acid and made up to 1 1 with water. Extraction procedure An aliquot representing about 500pg of sample was pipetted into a 100-ml separating fl~nnel and treated with 5 ml of 0.5% m/V tartaric acid solution.This was followed by the addition of 5 ml of a 2% m/l/ solution of 2-isopropylquinolin-8-01 in 0.4 M hydrochloric acid. The pH was adjusted to 10 (with the help of appropriate pH indicator paper strip) withNovember, 1981 OF ALUMINIUM IN ALLOYS AND ORES. PART 1 1141 1 M sodium hydroxide solution and the mixture was shaken for 2 min. The precipitate was allowed to stand for 10,min and extracted into 15 ml of chloroform, the chloroform phase being discarded. The aqueous phase was treated with 5 ml of 2-isopropylquinolin-8-01 and mixed well. Precipitation and extraction were repeated as before using only 1Oml of chloroform for extraction. A third precipitation and extraction step was conducted under similar conditions using only half the amount of the 2-isopropyl reagent.The aqueous phase was washed with 5ml of chloroform and the washings were rejected. The solution was adjusted to pH 5 with glacial acetic acid and extracted successively with 10- and 5-ml portions of 1% quinolin-8-01 in chloroform. The chloroform extracts were made up to 25 ml with chloroform and dried with anhydrous sodium sulphate. The absorbance of the extract was measured at 400 nm on a Hilger and Watts Uvispek spectrophotometer against chloro- form. A blank run was conducted under the same conditions used for the sample. A stock solution containing 1 g 1-1 of aluminium was prepared by dissolving Specpure aluminium in hydrochloric acid, and from this a range of aluminium standards were prepared by extraction.The best straight line fit for the graph plotted of absorbance veysus aluminium concentration was obtained with the help of a computer. Using the slope of the line the aluminium content in the sample was calculated after deducting the blank. The results are presented in Table 11. Alumina in Iron. Ore following procedure. BCS 301 Lincolnshire iron ore was taken for this analysis and treated according to the Preparation of sample solution Method 1. About 0.1 g of dried sample (dried at 105 "Cj was accurately weighed into a platinum basin and covered with 2 ml of water. I t was then treated with 5 ml of hydro- chloric acid (sp. gr. l.l8), keeping the basin covered with a glass cover to prevent losses due to effervescence.When dissolution was complete the glass cover was removed and rinsed into the basin with the minimum possible amount of water. The solution was treated with 1 ml of hydrofluoric acid (40% m/m) and 5 ml of perchloric acid (sp. gr. 1.54) and evaporated to fumes. After fuming for 10 min it was cooled and treated with 2 ml of water and evaporated to fumes again. I t was then cooled, diluted with 10 ml of water and gently heated to dissolve the salts. As there was 110 noticeable residue left at this stage the solution was made up to 100 ml with water after adding a further 2 ml of perchloric acid. In this method about 0.2 g of sample was weighed and dissolved in a mixture of 4 ml of wate-nd 10 ml of hydrochloric acid (sp. gr. 1.18). After complete dissolution it was evaporated almost to dryness.The residue was covered with 5 ml of hydrochloric acid (sp. gr. 1.18) and 15 ml of water and gently boiled. After diluting with water to 50 ml, the solution was filtered through a 9-cm filter-paper (No. 40) into a 250-ml calibrated flask. The insoluble material was transferred and washed with 3% V/V hydrochloric acid. The washing was finally completed with water. The filter-paper was ashed in a platinum basin at 900 "C, the ash was covered with 1 ml of water and 0.5 ml of sulphuric acid (1 + l), then treated with 5 ml of hydrofluoric acid and evaporated until fumes of sulphur trioxide began to be evolved vigorously. After fuming to dryness the residue was fused with 0.2g of anhydrous sodium carbonate. The fused mass was leached with dilute hydrochloric acid ( I + 9) and transferred to the main bulk of the filtrate collected in the 250-ml flask.The solution was diluted to volume with water. Method 2. NoTE-For ores rich in iron, dissolution of sample directly in concentrated hydrochloric acid is to be preferred. Extraction procedure A suitable volume of sample containing about 30pg of aluminium was pipetted into a separating funnel and 5ml of 1% m/V tartaric acid were added, followed by 10ml of 2% 2-isopropylquinolin-8-01 in 0.4 M hydrochloric acid. The pH was adjusted to 10 with 1 M sodium hydroxide solution, the mixture was shaken vigorously for 10 min and the precipitate was extracted into 10 ml of chloroform. After discarding the chloroform, precipitation and1142 NARAYANAN AND PANTONY : SPECTROPHOTOMETRIC DETERMINATION Analyst, Vol.106 extraction were repeated twice with half the amount of reagent. The aqueous phase was washed with 5ml of chloroform and the washings were rejected. The pH of the aqueous solution was adjusted to 5 with glacial acetic acid and the aluminium was determined by quinolin-8-01 extraction as described for permanent magnet alloy. Alumina in Manganese Ore Manganese(I1) has been found to be extracted with 2-isopropylquinolin-8-01 at pH 9.8-10.7. At this pH iron, which is normally the other matrix element present in appreciable amounts in manganese ore, is also extracted. This indicates the possibility of separation and deter- mination of alumina in manganese ore. The manganese ore (BCS 17611) selected for this investigation had the following compo- sition: manganese 49.00, iron 5.2, silica 5.6, alumina 4.1 and phosphorus 0.140/,.Preparation of sample solution A 0.1-g amount of dried sample (dried at 110 “C) was dissolved in a mixture of 2 ml of water and 10 rnl of hydrochloric acid (sp. gr. 1.18). Subsequent treatments in the prepara- tion of the sample solution for analysis were carried out as described under Method 2 for iron ore (see above). Procedure An aliquot representing about 2mg of sample was pipetted into a separating funnel and treated with 5 ml of tartaric acid (1% m/V), then 10 ml of 2-isopropylquinolin-8-01 (2% m/V in 0.4 M hydrochloric acid) were added. The pH was adjusted to 10 with 1 M sodium hydroxide solution and the mixture was gently agitated to assist precipitation and allowed to stand for 10min.The mixture was extracted with 15ml of chloroform, the organic phase was discarded, the aqueous solution was washed with 51x1 of chloroform and the washings were rejected. Another precipitation and extraction step was carried out as before but using only 5 ml of the reagent for precipitation and 10 ml of chloroform for extraction. After rejecting the chloroform phase the aqueous phase was washed with 10 ml of chloroform and the washings were discarded. From the aqueous solution aluminium was extracted and determined as described for permanent magnet alloy. Aluminium in Nimonic 90 Alloy The nimonic 90 alloy (BCS 310) had the following composition: nickel 58.75, chromium 19.22, cobalt 15.6, titanium 2.46, aluminium 1.43, iron 1.35, manganese 0.04, carbon 0.098 and silicon 0.84y0.Preparation of sample solution About 0.1 g of the alloy was dissolved in 10 ml of concentrated hydrochloric acid in a PTFE beaker. The dissolution was completed by adding 1 ml of nitric acid (sp. gr. 1.48). The solution was diluted to 25 ml with water and gently boiled. After cooling it was trans- ferred into a 100-ml polypropylene flask and made up to the mark with water. Procedure A 0.1-g amount of 2-isopropylquinolin-8-01 was weighed into a 50-ml PTFE beaker and 2 rnl of the alloy solution (about 2 mg of sample) were added from a pipette. The acid in the alloy solution was sufficient to dissolve the reagent. The solution was treated with 1 ml of 35% V/V acetic acid and diluted to 15 ml with water, then heated to 60-70 “C and the pH was adjusted to 5 with 1 M sodium hydroxide solution.The precipitate was digested for 10 min, then the precipitate and the solution were transferred into a separating funnel. Quantitative transfer of the complexes was accomplished by washing with two 5-ml portions of chloroform followed by the minimum possible amount of water. The complexes were extracted into chloroform and the organic extract was discarded. Occasionally a small amount of “veil” may be formed at the interface under the conditions employed, in which event it would be necessary to retain the “veil” with the aqueous phase. The aqueous phase was transferred into the original beaker in which the first precipitation was made.November, 1981 OF ALUMINIUM I N ALLOYS AND ORES.PART 1 1143 The separating funnel was washed with 5 ml of tartaric acid solution (1% m/V) followed by a small amount of water and the washings were collected in a beaker containing the aqueous extract. The solution was evaporated to 20 ml and treated with 5 ml of a 4% m/V solution of 2-isopropylquinolin-8-01 in 0.4 M hydrochloric acid. The pH was adjusted to 10 with 1 M sodium hydroxide solution and the precipitate was digested for 10 min at 70" C. The mixture was transferred quantitatively and extracted into 15ml of chloroform. After discarding the organic phase a third precipitation and extraction step was carried at room temperature using only half the amount of reagent used in the second precipitation and extraction. The aqueous phase was adjusted to pH 5 and washed with 5 ml of chloroform. After discarding ,the chloroform layer, the pH of the aqueous solution was adjusted to 11 with 1 M sodium hydroxide solution and aluminium was extracted and determined as described for permanent magnet alloy.The aluminium extraction for the preparation of the calibration graph was carried out at pH 11. Results and Discussion The results obtained by the proposed method for aluminium in various British Chemical Standards samples are shown in Table 11. TABLE I1 DETERMINATION OF ALUMINIUM IN BRITISH CHEMICAL STANDARDS Aluminium found 1 Mean Standard Certificate value concentration, No. of deviation, for aluminium, Sample % determinations % Yo Permanent magnet alloy, BCS 233 . . 6.98 16 0.07 6.98 (&0.08)* Iron ore,? BCS 301 .. .. .. 4.14 8 0.06 4.26 (fO.l2)* Manganese ore,$ BCS 176/l . . . . 4.02 22 0.09 4.07 (&0.15)* Nimonic 90 alloy, BCS 310 . . - . 1.43 15 0.08 1.43 (+0.05)* * Values in parentheses are standard deviations estimated from available information. t Aluminium reported as alumina. In general the agreement is good. It should be pointed out that the certified values for aluminium or alumina content represent the average results obtained independently by various procedures by different analysts. As there is no indication of the precision of the method used by different analysts, it is difficult to compare the precision of the proposed method with those of the other methods. In this situation, by using the standard deviation of the reported values for each of the test samples, an estimate of the precision for the umpire methods was obtained.By statistical tests of significance it has been shown elsewhere6 that the estimated precision is comparable to the precision obtained by the proposed method. The proposed method does not suffer from the complicated, time-consuming separation procedures required by methods such as mercury cathode electrolysis. Some of the methods of solvent extractions described in the literature9-l2 for the separation and determination of aluminium in samples similar in nature to those considered in this work involve the use of various masking agents and preliminary extraction agents. Preliminary extraction agents such as cupferron have been reported3 to be unsatisfactory. In the proposed method the extraction reagents used are limited to two.The time required to complete a triplicate determination is about 3 h. One of the distinct advantages of the method is that the extrac- tion procedure for samples such as permanent magnet alloy, manganese ore and iron ore are similar, and this allows the handling of three different kinds of samples. In this situation, with a single calibration graph three different samples can be analysed. In all of the experi- ments fresh calibration graphs were prepared for each batch of replicates. However, investi- gations showed that the slope did not alter significantly for at least 2 d if the standards were stored in the dark. In a laboratory analysing regularly these kinds of samples, this would be an additional advantage in saving time spent on the preparation of a fresh calibration graph for each batch of sample.1144 NARAYANAN AND PANTONY One of the authors (A.N.) is grateful to the Science Research Council of Great Britain and the Imperial College authorities for providing him with a research grant to carry out this work. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References Memt, L. L., and Walker, J . IS., Ind. Eng. Ckem., Anal. Ed., 1944, 16, 387. Hynek, J. R., and Wrangell, J . L., Anal. Ckem., 1956, 28, 1520. Dagnall, R. M., West, T. S., and Young, P., Analyst, 1965, 90, 13. Haba, F. R., PkD Thesis, University of London, 1966. Kazi, G. H., PhD Thesis, University of London, 1971. Narayanan, A., PhD Thesis, University of London, 1979. Blair, A. J., and Pantony, D. A., Anal. Chim. Acta, 1956, 14, 545. Puri, B. K., and Gautam, M., TaEanfa, 1978, 28, 484. Kassner, J. L., and Ozier, M. A., Anal. Chem., 1951, 23, 453. Wiberly, S. E., and Basset, L. G., Anal. Chem., 1949, 21, 609. Gentry, C. H. R., and Sherrington, L. G., Analyst, 1946, 71, 432. Scholes, P. H., and Smith, D. V., Analyst, 1958, 83, 615. Received March 23rd, 1981 Accepted May 19th, 1981

ISSN:0003-2654    

DOI:10.1039/AN9810601137

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

Analyst, November, 1931, Vol. 106, $9. 1145-1149 1145 Spectrophotometric Determination of Aluminium in Alloys and Ores Part 2." with 2-lsopropylquinolin-8-01 in Butan-I -01 Stripping Aluminium after Chelation of Other Metals A. Narayanan and D. A. Pantony Department of Metallurgy and Materials Science, Royal School of Mines, Impevial College of Science and Technology, Prince Consort Road, London, S W7 2BP In Part 1, aluminium was separated after extracting the other metals present, as their 2-isopropylquinolin-8-01 chelates, from aqueous solutions. In this paper a simpler and more efficient method of separation of aluminium is described. Instead of precipitating the interfering metals as their 2-iso- propylquinolin-8-01 chelates and then extracting them into chloroform, they are prepared directly in butan-1-01.Chelation of aluminium with the 24.50- propyl compound does not occur in butan-1-01 medium. The butanolic solution containing unchelated aluminium and the chelates of other metals is mixed with chloroform and then extracted with alkaline tartrate-buffered solution. In this way the uncomplexed aluminium is transferred to the aqueous phase, from which it is extracted as its quinolin-8-01 complex and determined spectrophotometrically. The technique has been applied to the determination of aluminium in complex matrices such as permanent magnet and nimonic 90 alloys. Keywords : Chelation of metals ; 2-isopropylquinolin-8-01; butan- 1-01 ; solvent extraction Development of the Method It was pointed out in Part l1 that prolonged equilibration of the phases was necessary to achieve extraction when the aqueous solution of metal ions was shaken with a solution of 2-isopropylquinolin-8-01 in an organic solvent.The extraction rate is controlled by the rate of transfer of the reagent from the organic to the aqueous phase. From kinetic considerations it has been shown2 how the low aqueous solubility of the 2-isopropyl compound can affect the rate of extraction of metal ions. Although this problem was overcome by precipitation of metal chelates from a homogeneous aqueous medium prior to their extraction, it was found that complete extraction of metal ions could be achieved only by repeated precipita- tions and extractions, as precipitation of the reagent decreased the concentration of the reagent available. The limitation thus imposed by the aqueous solubility of the reagent suggested that it was desirable to consider solvents other than water in which both the metal ion and the reagent could be kept at a suitable concentration to achieve rapid and efficient chelation.Continuous variation experiments performed to study the composition of metal chelates of 2-isopropyl- and 2-tert-butylquinolin-8-01s in butan-1-01 have shown that fully chelated species are present in solutions containing a sufficient concentration of chelating reagent. This indicated the possibility of preparing the metal chelates of these reagents in butan-1-01. The advantages of using this alcohol in preference to others have been discussed elsewhere.2 As aluminium is not chelated under the conditions used, it can be stripped from the butan-1-01 by extraction with an aqueous buffer solution.Experimental Conditions The chelating reagent can be added as a solid to the butanolic solution of metal salts or as a solution in butan-1-01. If a butanolic solution is to be used, the metal residue can be dissolved directly so that the solvent could be used economically. As chelation of the 2- isopropyl homologue with some metals, such as nickel, cobalt and manganese, requires a basic medium it is necessary to use a suitable base. In practical situations the butanolic * For Part 1 of this series, see p. 1137.1146 NARAYANAN AND PANTONY : SPECTROPHOTOMETRIC DETERMINATION A%U&St, V d . 206 solution of metal ions would be strongly acidic so that the base will neutralise the acid and bring the pH to a value suitable for chelation to occur.Aromatic amines such as aniline or aliphatic amines such as triethylamine are soluble in butan-1-01 and can be used advantage- ously. Of these two bases triethylamine was chosen as it is available in a sufficiently pure state. The amount of amine that would be necessary to keep the butan-1-01 sufficiently basic was determined from blank runs conducted under the same experimental conditions as for the sample. Stripping of Aluminium from Butan- 1-01 Containing Chelates of Other Metals The fact that butan-1-01 is only slightly soluble in water is advantageous in stripping aluminium with an aqueous buffer, but its viscous nature and low specific gravity (0.8) lead to unsatisfactory phase separation under experimental conditions.Also, as further work is to be carried out with the aqueous phase the low specific gravity of butan-1-01 creates practical difficulties. In view of these factors, it would be desirable to mix butan-1-01 containing the metal chelates with a suitable volume of chloroform, which would give a solvent of low viscosity and a higher specific gravity than water. The aqueous buffer used to strip aluminium and the unchelated metal ions, if any, should be maintained at an optimum pH, which would prevent the extraction of chelated metal ions in favour of the aqueous phase. As 2-isopropyl chelates of many metals have been shown2v3 to be extracted after precipitation from a basic tartrate solution between pH 9 and 12, it was decided to use a tartrate-buffered aqueous solution maintained at pH 11 to extract aluminium from the organic phase. In order to ensure that complete removal of metals interfering in the quinolin-8-01 method for aluminium was accomplished, a precipitation and extraction step was carried out on the aqueous phase according to the procedure described for the samples chosen for this investigation.Limitation of the Method The limitation of the method is set by the amounts of the metal ions that can be kept in solution in butan-1-01. This limits the determination of aluminium to concentration levels of 0.5% m/m and above, as otherwise it would mean the use of large sample size to give a sufficient concentration of aluminium for the quinolin-8-01 method to be applicable.Experimental and Results Preliminary Investigations Qualitative tests with metal perchlorates of iron, copper, nickel, cobalt, zinc and lead showed that their solution in butan-1-01, when treated with 2-isopropylquinolin-8-01, pro- duced the same colour as the solution of their precipitated chelates in this solvent. With nickel and cobalt a small amount of triethylamine was added to keep the solution sufficiently basic for efficient chelation to occur. The metal chelates prepared in butan-1-01 when mixed with chloroform and extracted with water maintained a t pH 10-11 were retained in the butan-1-01 - chloroform phase as indicated by the colour of the mixed solvent phase. From this it was inferred that the coloured product produced by the addition of the reagent to the butanolic solution of a metal ion was due to the formation of uncharged metal chelates of 2-isopropylquinolin-8-01.Efficiency of Chelation in Butan-1-01 Medium Solutions of iron, cobalt, nickel, copper, chromium and zinc ions, each containing 250 pg of metal in perchloric or hydrochloric acid (see Note l), were evaporated nearly to dryness. To the residue were added three drops of water and the solution was treated with 5 ml of butan-1-01 containing 50 mg of 2-isopropylquinolin-8-01. A reference solution containing no metal ions but only the appropriate acid at a concentration matching that of that present in the metal solution was also treated in the same way as the metal solutions. After the addition of the butanolic reagent, the solutions were heated (60 "C) to homogenise them.They were then treated with triethylamine. The amount of amine to be added was deter- mined from the reference solution (see Note 2). In this solution, when all of the acid present had been neutralised the butan-1-01 turned colourless. To the solution containing metal ions two drops of amine in excess (to ensure sufficient basicity) of the amount needed for the reference solution were added. When chromium is present , the solution should be heated Spectroscopic studies2 also confirm this view. -November, 1981 OF ALUMINIUM IN ALLOYS AND ORES. PART 2 1147 on a steam-bath for 2min after addition of the amine. The solutions were mixed with 15 ml of chloroform and extracted with 25 ml of water adjusted to between pH 10.5 and 11 and containing 5 ml of 5% tartaric acid for every 100 ml.The pH of the aqueous phase was maintained at 10.5-11 and the concentration of alkali that must be added to tartrate-buffered aqueous solution to attain this pH range was deter- mined from the extractidn of the reference solution. The butan-l-ol- chloroform phase was discarded. The aqueous phase was washed with 10 ml of chloroform and the washings were rejected. The aqueous phase was then tested for the metal ion concerned by quinolin-8-01 extraction under suitable conditions. The chloroform extracts of quinolin-8-01 were virtually colourless and the absorbances measured at appropriate wavelengths were not significantly different from that of the blank. This indicated that chelation of these metal ions occurred quantitatively in butan-1-01 and that the chelates were retained efficiently in butan-l-ol- chloroform even after extraction with the aqueous buffer. NOTES- 1.When a solution of chromium(II1) in perchloric acid is fumed the chromium is oxidised to chromium(V1). The chromium(V1) in the presence of trace amounts of perchloric acid in the evapora- ted residue oxidises butan-1-01 under the conditions employed. The oxidation products of butan- 1-01 are reported2 to interfere in various ways in the extraction of chelates, particularly in presence of nickel, cobalt and other metals. For this reason, a solution of chromium(II1) prepared in hydrochloric acid medium should be used. Addition of amine neutralises the acid and renders the solution colourless. Thus the reagent served as an indicator in controlling the amount of amine added.2 . In acidic butan-1-01 the reagent produces a yellow coloration. Efficiency of Aluminium Recovery Tests with pure aluminium solutions showed that under any conditions it remained un- chelated by the 2-isopropyl compound in butan-1-01 medium also. The unchelated aluminium was quantitatively extracted from the butan-l-ol- chloroform phase into the aqueous phase. This was ascertained by carrying out separations using only aluminium standards ranging from 10 to 50 pg under conditions similar to those described for other metals. The aluminium extracted into the aqueous phase was extracted as its quinolin-8-01 chelate into chloroform. The extracts were made up to 25 ml, dried with anhydrous sodium sulphate and their absorh- ances were measured at 400 nm.Another set of standards of the same range were prepared by directly extracting aluminium from aqueous solution, using 1 yo m/V quinolin-8-01 in chloroform. The slopes of the best straight-line fit for the graphs of absorbance versus concentration are presented in Table I. TABLE I SLOPES OF CALIBRATION GRAPHS FOR ALUMINIUM Slope in absorbance units per pg of aluminium in 25 ml &lethod of preparation of standards Butan-1-01 method . . . . .. .. . . (96.86 f- 0.36) x 10-4 Direct extraction from aqueous solution without using butan-1-01 . . .. .. . . (97.29 f. 1.1) x 10-4 The difference in the slopes is due mainly to errors imposed by instrumental limitations in measuring absorbance and not to differences in the recoveries of aluminium.Such a differ- ence is expected in spectrophotometric work even if the graphs are plotted for standards prepared under similar conditions. The efficiency of removal of metals other than aluminium by chelating them in butan-1-01 medium and the quantitative recovery of aluminium provided a rapid and simple method for determining aluminium in commercial alloys. Determination of Aluminium in Alloys and Ores Apparatus Spectrophotometer. Silica or glass cuvettes, path length 10 mm. Separating funnels, l@O ml, with PTFE keys.1148 NARAYANAN AND PANTONY : SPECTROPHOTOMETRIC DETERMINATION Analyst, VOl, 106 Reagents Doubly distilled water and analytical-reagent grade acids were used throughout. 2-Isopropylquinolin-8-oZ (synthesised material).Acidic 2-iso~ro~yZqzcinoZin-8-ol. Triethylamine. Analyt ical-reagent grade. Sodizcm hydroxide solution, 1 M. Tartrate bufer. Quinolin-8-ol. ChZoroform. pH indicator paper strips. Aluminium in Permanent Magnet Alloy [British Chemical Standard (BCS) 2331 The sample solution was prepared as described in Part 1.l Step 1 A suitable aliquot ( ~ 5 0 0 pg of sample) was pipetted into a 50-ml beaker and evaporated nearly to dryness. An equal volume of a blank solution, prepared in the same way as the sample, was also pipetted and evaporated to the same extent as the sample. To each of them was added 0.2 rnl of 0.5 M perchloric acid, which was allowed to spread uniformly, followed by 5 ml of butan-1-01. The mixture was homogenised by warming, then 5 ml of 1 yo 2-isopropylquinolin-8-01 in butan-1-01 was added to each beaker.The blank solution turned yellow and the sample solution dark green. The blank solution was treated with triethylamine until the yellow colour was discharged. Two drops of amine in excess were added beyond this point to ensure sufficient basicity of the solution. The same amount of amine as that used in the blank was added to the sample solution. The butanolic solution of metal chelates was mixed with 15 ml of chloroform and transferred into a separating funnel, then 5 ml of chloroform were used to wash the beaker and the washings were also transferred into the funnel and mixed. The beaker was washed with 25ml of tartrate buffer solution (pH 11) and the washings were transferred into the separating funnel.The organic and aqueous phases were shaken together to extract the uncomplexed aluminium into the aqueous phase. The pH of the aqueous phase was maintained at 10-10.5. The organic phase was separated and discarded. Step 2 The aqueous phase was treated with 1Oml of chloroform and the chloroform layer was allowed to separate, then 5 ml of 1% m/V 2-isopropyl compound in 0.2 M hydrochloric acid were added and allowed to mix with the aqueous layer. The pH of the aqueous layer was adjusted to 10-10.5 with sodium hydroxide by gentle mixing without disturbing the chloro- form layer. Then the solution was allowed to stand for 2 min and the pH was again ascer- tained. The solution was shaken vigorously to extract into chloroform any residual iron, cobalt, nickel and copper.The removal of these interfering metals was probably complete in the first step itself, but the second extraction served to ensure complete removal. After rejecting the chloroform layer the aqueous phase was washed with 5 ml of chloroform and the washings were discarded. Step 3 portions of 1% m/V quinolin-8-01 in chloroform. the same as described previously. sample. prepared under the same conditions as the sample. calibration graph of absorbance zleysus concentration. Aluminium in Nimonic 90 Alloy (BCS 310) senting 2 mg of sample was used. 1 or 2% m/ V (as required) in analytical- reagent grade butan-1-01. 1 or 2% m/V in 0.2 and 0.4 M hydrochloric acid. Prepared from Ultrar grade reagent, Every 25 ml of the buffer contained 1 ml of 5% m/V tartaric acid, the The commercially available reagent was steam distilled and cryst allised pH being adjusted to 11 with sodium hydroxide solution. from hexane and a 1% m/V solution in analytical-reagent grade chloroform was prepared.Analytical-reagent grade ; freshly distilled if necessary. From the aqueous solution aluminium was extracted successively with 10- and 5-ml Further treatment of the extracts was The blank was taken through the same procedure as the Standards with aluminium contents ranging from 10 to 50pg per 25 ml were Aluminium was determined from a The solution of the alloy was prepared as described in PaIt 1.l A suitable aliquot repre- Separation and determination of aluminium were accom-November, 1981 OF ALUMINIUM I N ALLOYS AND ORES. PART 2 1149 plished by the same procedure as that for the permanent magnet alloy, except for the following slight modifications.In view of the increase in the sample mass the concentration of the 2-isopropyl corppound used in steps 1 and 2 was 2% m/V in butan-1-01 and 0 . 4 ~ hydrochloric acid, respectively. Also, after the addition of amine in step 1 the solution was heated on a steam-bath for 2 min. This was necessary as the sample contained chromium, which chelates only when heated. The aluminium results for the samples analysed by the proposed method are presented in Table I1 together with the results obtained by the precipitation and extraction technique described in Part 1.l Table I1 also gives the certified values for aluminium in these samples. TABLE I1 DETERMINATION OF ALUMINIUM IN BRITISH CHEMICAL STANDARDS Butan-1-01 method Precipitation method P i r \ A Mean Standard Mean Standard Certified concentration, No. of deviation, concentration, No.of deviation, aluminium Sample yo determinations yo % determinations % content, % Permanent magnet alloy Nimonic 90 alloy (BCS (BCS 233) . . 7.00 310) .. .. .. 1.43 * Estimates based on available information. 11 0.1 6 6.98 10 0.08 1 .P3 16 0.07 6.98 15 0.08 1.43 Standard deviation, % 0.08* 0.05* Discussion and Conclusion The results are in excellent agreement with certified values for aluminium in both alloys. The precisions of the results for the British Chemical Standards samples are only estimates based on available information. For nimonic 90 alloy the butan-1-01 method produces results with a precision indistinguish- able from that obtained using precipitation followed by extraction from aqueous solutions.Statistical analysis based on the estimated precision for the standard methods shows that the precision obtained by the butan-1-01 method is not significantly different from that of the standard methods. For the permanent magnet alloy the results of the butan-1-01 method have a precision that is inferior to that obtained by the precipitation - extraction method. The precision is also inferior to that of the British Chemical Standards method. However, for routine purposes the precision in this instance can be considered adequate at the level of aluminium determined. A distinct advantage the butanol method had over the precipitation extraction method is its simplicits rapidity and that it requires only a third of the amount of chelating reagent used in the precipitation - extraction method. With these merits the method has sufficient scope for separating aluminium in iron and manganese ores and in zinc-based alloys at levels down to 0.5% rnlm using only a few milligrams of sample. One of the authors (A.N.) is grateful to the Science Research Council of Great Britain and the Imperial College authorities for providing him with a research grant to carry out this work. References 1. 2. 3. Narayanan, A., and Pantony, I>. A., Analyst, 1981, 106, 1137. Narayanan, A., PhD Thesis, University of London, 1979. Haba, F. R., PhD Thesis, University of London, 1966. NOTE-Reference 1 is to Part 1 of this series. Received March 23rd, 1981 Accepted May 19th, 1981

ISSN:0003-2654    

DOI:10.1039/AN9810601145

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

1150 Analyst, November, 1981, Vol. 106, $$. 1150-1156 Solvent Extraction of the Thiocyanato Mixed-ligand Complexes of Iron(ll1) with Various Hydroxyamidines and Spectrophotometric Determination of Iron( Ill) in Various Biochemical and Biological Samples Miss A. R. Jha and R. K. Mishra Department of Chemistry, Ravishankar University, Raipztr-492 010, M.P., India The reaction in benzene of 11 newly synthesised N-hydroxy-NN’-diarylbenz- amidines (HOA) with iron(II1) in the presence of thiocyanate has been inves- tigated spectrophotometrically. The study revealed the formation of a 1 : 2: 1 iron(II1) - thiocyanate - HOA mixed complex in acidic media (0.2-0.8 M hydrochloric acid). On the basis of this sensitive colour reaction, a simple, rapid, selective and highly reproducible method for the extractive - spectro- photometric determination of microgram amounts of iron(II1) in various bio- chemical and biological samples has been developed.The molar absorptivities of the systems are found to be between 1.1 and 1.35 x lo4 1 mol-1 cm-’ in the wavelength range 460-470 nm. The method is free of interference from most of the common metal ions and commonly used sequestering agents. The effects of experimental variables on the procedure are discussed. Keywords : Solvent extraction ; spectrophotometry ; iron(II1) - thiocyanate complex ; hydroxyamidines Numerous methods have been reported for the spectrophotometric determination of iron in various complex materials,1-20 and of these, the iron(II1) - thiocyanate and 1 ,lo-phenan- throline methods have been used over a long period.The iron(II1) - thiocyanate method has a number of limitations, e g . , variation of colour intensity with respect to the concentration of thiocyanate in addition to that of the metal, standing time, deviation from Beer’s law and reaction of the thiocyanate with other elements to give coloured products. The iron(I1) - 1,lO- phenanthroline method is widely applicable to routine determinations of iron but it suffers from serious interference from many common ions such as nickel(II), cobalt(II), copper(I1) and bismuth(II1) .l The iron(I1) - 4,7-diphenyl-1 ,lo-phenanthroline method is highly sensitive and selective but it also suffers from serious interference from copper(II), cobalt(I1) and nickel(I1) .5 Other m e t h ~ d s ~ ~ , ~ - l l that are based on the colour reaction of iron with phenols, dyes, nitroso- R salts or phenol - Rhodamine B are highly sensitive, but also suffer from serious interference from various common d-group elements.In addition, the complete extraction of the metal takes a long time and a narrow pH range is required. For these reasons, a simple, rapid and highly selective method, based on the extraction of iron(II1) thiocyanate with N-hydroxy-NN’- diarylbenzamidines (HOA) in benzene, has been developed. The proposed method offers several advantages over other well known methQds.1-20 I t is highly selective and can be used over a wide acidity range; it is applicable to all complex materials because most common ions do not interfere seriously; the reagent is easy to prepare and, if kept in amber-glass bottles, solutions can be stored for at least 15 d without any deterioration; and the solutions are unaffected by light, air and temperature. The additional advantages of this method over the original thiocyanate method are that the sensitivity is increased markedly and that all of the practical drawbacks have been overcome, as mentioned above.N-Hydroxy-NN’-diarylbenzamidines, which are monovalent, bidentate chelating agents, have been used recently for the determination of various element~.~l-~@ This work investigates the colour reaction of 11 newly synthesised N-hydroxy-NN’-diarylbenzamidines (I) with iron(II1) in the presence of thiocyanate, in order to study the effect of substituents on the complexing properties of the -N = C-N(0H)- group.The spectral data for the metal chelates extracted into benzene showed that the reactions with N-hydroxy-N-(p-toly1)-Nf-(2,3- dimethy1)phenylbenzamidinium chloride is the most sensitive reagent, so this was used for theJHA AND MISHRA 1151 solvent extraction and subsequent spectrophotometric determination of iron(1II). The general structural formula for compounds I [where X = H, m-C1, $-Cl or P-CH, and Y = H, 0-CH,, m-CH,, P-CH,, 2,3-(CH3),, 2,5-(CH3)2, 2,6-(CH3), or $-OCH,] is shown below. CI- L i Experimental Apparatus A Carl-Zeiss Specord ultraviolet - visible spectrophotometer and Carl-Zeiss Jena spectro- colorimeter (Spekol) with 1-cm silica cells were employed for recording the spectra and measuring the absorbance values, respectively.The pH values were determined using a Systronic pH meter, Type 322. Chemicals and Reagents Standard iron(III) solution nitric acid. diluted to 1 1 with doubly distilled water. Preparation of hydroxyamidines Hydroxyamidines were prepared by the condensation of equimolar amounts of N-aryl- benzimidoyl chloride and N-arylhydroxylamine in diethyl ether.21 The resulting hydro- chloride was recrystallised from absolute ethanol containing a few drops of concentrated hydrochloric acid. Extraction solutions A 5% m/V solution of potassium thiocyanate in water and a 0.2% m/V solution of the hydroxyamidine in benzene were used for all extraction work. As the solubility of the free base in benzene is higher than that of the corresponding hydrochloride, a few drops of ammonia solution were added to the solution of the hydroxyamidine in benzene, the excess of ammonia being removed by boiling.All of the chemicals used were of analytical-reagent grade. A stock solution of iron(II1) was prepared by dissolving pure iron wire (Merck) in dilute The oxides of nitrogen were expelled by boiling and the solution was finally Satisfactory results were obtained for the elemental analyses. Caution-Benzene is highly toxic and appropriate precautions should be taken. Procedure To this, add 2 ml of potassium thiocyanate solution and 3 ml of 5 M hydrochloric acid and then adjust the total volume of the aqueous phase to 25 ml. Equilibrate the aqueous phase with 15 ml of the solution of the hydroxyamidine in benzene for 1 min. Transfer the organic layer into a 50-ml beaker containing anhydrous sodium sulphate (2 g).Wash the aqueous phase with two 4-ml portions of fresh benzene. Transfer the combined extract into a 25-ml cali- brated flask and dilute to volume with benzene. Measure the absorbance of the complex a t the absorption maximum against a reagent blank as a reference. Place an aliquot of solution containing 50 pg of iron(II1) in a 100-ml separating funnel. Results and Discussion Absorption Spectra The red - orange complexes of iron(II1) with thiocyanate and hydroxyamidines showed a sharp The absorption spectra of complexes and reagent in benzene are illustrated in Fig. 1.1152 JHA AND MISHRA: EXTRACTION OF FE(III) COMPLEXES AND Analyst, VoZ. 106 0.5 (D 0.4 n L 0.3 n 0 Q f3, a 0.2 0.1 I A 420 460 500 540 580 620 Wavelength/nm Fig.1. Absorption spectra of the reagent and metal complexes. [SCN-1, 0.05 M ; [HOA], 0.003 M ; [HCI], 0.4 M. A, N-Hydroxy-N-(p-chlorophenyl)-N’-(2,3-di- methy1)phenylbenzamidine hydrochloride ; [Fe], 4.29 x 10-5 M. B, N-Hydroxy-N-(m-chlorophenyl)-N‘-(2,3-di- methy1)phenylbenzamidine hydrochloride; [Fe], 3.22 x M. C, N-Hydroxy-N-phenyl-N’-(2,3-dimethylf- phenylbenzamidine hydrochloride ; [Fe], 3.94 x M. D, N-Hydroxy-N-(p-tolyl) -N’- (2,3-dimethyl)phenyl- benzamidine hydrochloride; [Fe], 3.58 x LO-5 M. E, N-Hydroxy-N- (m-chlorophenyl) -N’-phenylbenzamidine hydrochloride; [Fe], 2.86 x M. F, N-Hydroxy-N- (p-tolyl)-N’-(2,3-dimethyl)phenylbenzamidine hydro- chloride. absorption maximum around 465 nm, showing that the position of the absorption maximum is not much affected by substituents.The molar absorptivity values are evidently affected by the type of substituent and the position or degree of substitution in the three phenyl rings of the hydroxyamidine . Choice of Solvents Various solvents, such as chloroform, carbon tetrachloride, esters, ethers, alcohols and aro- matic hydrocarbons, were investigated. Of these, benzene was found to be the most suitable solvent as the extractability of the complex was very high. Toluene can also be used as a diluent but the distribution coefficient of the reagent in it is about half of that in benzene. The other solvents were found to be unsuitable for the extraction work owing to either low absorbance values or instability of the metal complexes in them.Effect of Acidity The acidity of the aqueous phase was maintained with 5 M hydrochloric acid (Fig. 2). Sulphuric acid was unsuitable owing to the low absorbance of the complex in it. The optimum acidity range for accurate determination of the metal was found to be 0.2-0.8 M hydrochloric acid. Therefore, in all later experimental work the acidity of the aqueous phase was adjusted to 0.6 M in hydrochloric acid in order to ensure lOOyo extraction of the metal. Effect of Reagents At least 100- and 120-fold molar excesses of hydroxyamidine and thiocyanate, respectively, are necessary for complete extraction of the metal. Addition of more hydroxyamidine (up to 0.01 M) caused no adverse effect on the position of A,,,. or on the absorbance of the coloured system. However, the extraction is incomplete when the thiocyanate concentration is aboveNovember, 2981 DETERMINATION OF BIOCHEMICAL AND BIOLOGICAL FE(III) 1153 100 8 2 E .- CI CI u1 90 I I I 1 I 0.2 0.4 0.6 0.8 1.0 1.2 Concentration of hydrochloric acid/ M Fig.2. Graphical representation of the effect of concentration of hydrochloric acid on extraction of Fe(lI1) as an Fe(II1) - SCN- - HOA complex. [Fe], 3.58 x M ; [SCN-1, 0.05 M ; and [HOA], 0.003 M, 0.25 M, which may be a result of the high affinity of thiocyanate towards iron(II1). The optimum concentration range of thiocyanate for 100~o extraction of the metal is 0.007-0.25 M. Effect of Substituents In order to study the influence of substituents on the complexing properties of the ligand, 1 1 analogues of AT-hydroxy-NN’-diarylbenzamidines were synthesised and their behaviour in the extractive separation a i d spectrophotometric determination of iron(II1) was examined. The absorption spectra of the ternary complexes of these reagents were measured and the molar absorptivities of the coloured complexes were evaluated on the basis of iron content at their respective values of A,,,.(Table I). It is observed that the presence of substituents in the AT-phenyl or N’-phenyl rings has little effect on the position of Amax.. However, the presence of substituents in both rings affects the molar absorptivity of the complex. The apparent trends observed are as follows: firstly, the introduction of a methyl group into the N’-phenyl ring had a large effect on the absorptivity of the complex and the introduction of other substituents into this ring resulted in a hyperchromic shift in the absorbance, the effect of the substituents decreasing in the order @CH, > 2,3-(CH,), > o-CH,.> m-CH, ,> 2,6- (CH,), m 2,5-(CH,), > p-(OCH,) (compounds 1-8) ; secondly, introduction of substituents TABLE I SPECTRAL DATA FOR IRON (111) - THIOCYANATE COMPLEXES WITH HYDROXYAMIDINES IN BENZENE Sample No. 1* 2 3 4* 5* G 7 8 9 10 11 X m-C1 m-C1 m-C1 m-C1 m-C1 m-C1 m-C1 m-C1 H P-CH3 p-Cl hnax.ln1n 460-470 460-470 460-470 460 460 460-470 460-470 460 460 460 460-470 Molar absorptivity/ 1 mol-f em-‘ 1.10 1.19 1.17 1.23 1.12 1.16 1.16 1.20 1.15 1.35 1.30 x 104 Sandell’s sensitivity1 5.07 4.69 4.77 4.54 4.98 4.81 4.69 4.65 4.85 4.13 4.29 p g cm-2 of iron x 10-3 * Compounds 1, 4 and 5 are free bases.1154 JHA AND MISHRA: EXTRACTION OF FE(III) COMPLEXES AND Analyst, vd.106 into the N-phenyl ring also causes a hyperchromic shift, the effect being in the order p-CH, m $-Cl > m-C1 (compounds 8-11). It is obvious that the introduction of methyl substituents into both of the phenyl rings attached to nitrogen atoms greatly enhanced the molar absorptivity of the complex. Conse- quently, the mixed complex of iron(II1) - thiocyanate with N-hydroxy-N-(p-tolyl)-N'-(2,3- dimethy1)phenylbenzamidinium chloride is found to be the most sensitive. Effect of Other Variables Complete extraction of the metal could be achieved in 1 min and further extraction for a period of up to 30 min had no adverse effect. The extracted species was very stable and its absorbance at A,,,.in benzene was constant for at least 4011 at room temperature. A variation in temperature from 20 to 40 "C and volume of aqueous phase from 15 to 60 ml had no effect on the nature of the extracted species. Beer's Law, Sensitivity and Precision of the Method The Sandell's sensitivities of the colour reactions lie between 0.0041 and 0.0050 pg cm-2 of iron with respective molar absorbances in the range 1.10-1.35 x lo4 1 mol-1 cm-" (Table I). Beer's law is obeyed in the range 0.44.8 p.p.m. of iron. The optimum range for accurate determinations, as evaluated from a Ringbom plot,30 is 0.8-3.4 p.p.m. of the metal. The pre- cision of the method was determined for ten samples, each containing 50 pg of iron per 25 ml of solution, giving a mean value for the absorbance of 0.48 with a relative standard deviation of 0.69%.Composition Therefore, a curve-fitting method31 only was used for the determination of the ratio of metal to reagents in the complex. The slope of the graph obtained by plotting logD venus log[SCN-]/log[HOA] (where D is the distribution coefficient of the metal), keeping other variables constant, showed the number of moles of hydroxyamidine or thiocyanate per mole of metal chelate. The iron(II1) - thiocyanate - HOA ratio was found to be 1 : 2: 1 (Fig. 3). Therefore, the compo- sition of the neutral complex in benzene should be Fe(SCN),OA. The reaction of iron(II1) with reagents in benzene is non-stoicheiometric. 5 -5 Log [SCN-]/log [HOA] Fig. 3. Curve-fitting method for the determination of the ratio of iron(II1) to HOA or SCN-.[Fe], 3.58 x M ; [HCI], 0.4 M ; [KCI], 0.1 M. A, Log D versus log[SCN-1; [HOA], 0.003 M. B, Log D veYsus log [HOA] ; [SCN-1, 0.05 M.November, 2982 DETERMINATION OF BIOCHEMICAL AND BIOLOGICAL FE(III) 1155 Effect of Diverse Ions The effect of diverse ions on the determination of iron(II1) was studied, as described under Procedure. A t least 2500 p.p.m. of chloride, bromide, nitrate, sulphate and alkali and alkaline earth elements did not interfere in the determination of iron(II1) a t concentration levels of 2 p.p.m. A small amount of copper(I1) is tolerated by controlling the concentration of the reagents and using thiourea as a masking agent. Silver(1) is precipitated out as a simple complex and does not interfere in the determination of the metal.The amounts of other ions tolerated are shown in Table 11. TABLE I1 AMOUNTS OF DIVERSE IONS TOLERATED IN THE DETERMINATION OF IRON(II1) (50 pg PER 25 ml) Amount Amount tolerated,* tolerated,* Ion added Added as p.p.m. Ion added Added as p.p.m. Fe(I1) . . . . FeSO,(NH,),SO,.- V(V) . . .. NH,VO, 50 CU(I1) . . . . CuS0,.5H2O 50 W(V1) .. . . Na2W0,.2H20 40 Co(I1) . . .. Co(NO,), 400 U(V1) . . . . UO2(NO,),.6H,O 300 Mn(I1) .. . . MnC1,.7H,O 600 F- . . .. .. NaF 600 Zn(I1) . . . . ZnS04.7H,0 2 000 I- . I .. .. KI 300 Be(I1) . . . . BeSO, 1500 Po4,- .. .. Na,PO, 1600 Pb(I1) . . .. Pb(NO,), 2 000 . . .. Na,HAsO, 1600 Al(II1) . . . . AI(NO,), 1000 Oxalate . . . . Na,C,O, 800 Cr(II1) . . . . (NH4),S0,Cr2- Citrate . .. . Na&H,0,.2H2O 1000 (S04),.24H,O 800 Tartrate . . . . NaKC4H40,.4H,0 800 Se(1V) . . . . Na2Se0, 300 Triethanolamine . . N(CH,CH,OH), 400 6H,O 800 Mo(V1) .. . . (NH,),MoO, 10 Ni(I1) . . . . NiC12.6H,0 500 La(II1) .. . . La(NO,), 1000 Cd(I1) . . . . CdC1,.5H20 2 000 S,O,*- * . . . Na,S,O,.SH,O 100 BifIII) . . . , Bi(NO,), 1500 Acetate . . .. NaC,H,O, 200 Th(1V) .. . . Th(NO,), 200 EDTA .. * (CH,),N,(CH,- Zr(1V) . . . . ZrOC1, 300 COONa),.2H20 100 Ti(1V) . . . . TiOC,O, 100 COOH),(CH,- Phthalate . . . . KHC,H,O, 400 * Causing an error of less than 2%. Application of Method biochemical and biological samples, as shown in Table 111. The proposed method was found to be applicable to the determination of iron in various TABLE I11 DETERMINATION OF IRON IN BIOCHEMICAL AND BIOLOGICAL SAMPLES Calculated iron content* f A 3 1,lO- Sample Phenanthroline Hydroxyamidine No.Sample Reported iron content method method 1 Folitrin (Biochem Pharmaceuteticals) Iron(I1) fumarate, 0.35 g 0.349 g 0.349 g 2 Foliplex (Kopran Chemicals) Iron(I1) fumarate, 0.050 g 0.050 g 0.049 g 3 Globintone (Searle) Iron(I1) fumarate, 0.200 g 0.196 g 0.195 g 4 Redieyte (Merck, Sharp & Dohme) Iron(I1) sulphate, 0.3 g 0.28 g 0.28 g 5 Calglufer (Sandoz) Iron(I1) gluconate, 0.075 g 0.071 g 0.070 g 6 Ferronicum (Sandoz) Iron(I1) gluconate, 0.325 g 0.324 g 0.324 g 7 Blood 0.057 yo o.057y0 9 Brassica oleracia var. 8 Spinacia oleracia (leaves) 0.0109%t 0.01 12% 0.011 1% botrytis (leaves) 0.04y0t o.04170 0.040 9% 10 Solanum tuberosum 0.007% t 0.006 5% 0.006 5% * Average of six determinations.t Values obtained from reference 32, pp. 71, 65 and 75, respectively.1156 JHA AND MISHRA A weighed amount of the sample was transferred into a Kjeldahl flask and heated gently with a mixture of concentrated nitric and sulphuric acids (LO + 1 V / V ) until charring com- menced. Dropwise addition of concentrated nitric acid and boiling were continued until either a colourless or a pale yellow solution was obtained. This was cooled, a few millilitres of water were added and then the solution was evaporated until white fumes were evolved. The procedure was repeated two or three times. A few millilitres of dilute hydrochloric acid were added and heating was continued until fumes of nitric acid had been removed. The solution was then diluted to an appropriate volume.An aliquot of the solution was taken and iron(II1) was determined by the procedure recom- mended earlier. The results were compared with those obtained by the spectrophotometric method using 1,lO-phenanthroline (Table 111). 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. References Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience, New Oka, Y., and Miyamoto, M., Nippon Kagaku Zasshi, 1954, 75, 864. Shibata, S., Anal. Chim. Ada, 1960, 23, 367. Twamoto, T., Bull. Chem. Soc. Jpn., 1961, 34, 605. Gahler, A. R., Hamner, R. M., and Shubert, R. C., Anal. Chem., 1961, 33, 1937. Takeuchi, T., and Shijo, Y., Bunseki Kagaku, 1965, 14, 930.Otomo, M., Bunseki Kagaku, 1965, 14, 677. Nishida, H., Bunseki Kagaku, 1970, 19, 221. Horiuchi, Y., and Nishida, H., Bunseki Kagaku, 1970, 19, 930. Ishito, T., and Ichinohe, S., Bunseki Kagaku, 1972, 21, 1207. Korenaga, T., Motomiju, S., and Tbei, K., Anal. Chim. Acta, 1973, 65, 335. Dominguez, R. J., and Irgolic, K. J., Anal. Chim. Acta, 1976, 83, 169. Corigliano, F., and Pasquale, D. S., Talanta, 1976, 23, 545. Yamamoto, K., and Ohashi, K., Anal. Chim. Acta, 1977, 88, 141. Desai, B. M., and Parghi, J. V., J . Indian Chem. Soc., 1977, 54, 1102. Desai, B. J., and Shinde, V. M., Analyst, 1979, 104, 160. Gallego, M., Garcia-Vargas, M., and Valcarcel, M., Analyst, 1979, 104, 613. Begheijn, L. Th., Analyst, 1979, 104, 1055. Thorburn Burns, D., and Abdel Aziz, M. E. M., Analyst, 1980, 105, 333. Pandell, A. J., Montgomery, R. A., and Meissner, R. A., L4nalyst, 1980, 105, 181. Satyanaryana, K., and Mishra, R. K., Anal. Chem., 1974, 46, 1609. Deb, K. K., and Mishra, R. K., Curr. Sci., 1976, 45, 134 and 341. Patel, K. S., Deb, K. K., and Mishra, R. K., Ann. Chim. (Rome), 1978, 68, 803. Patel, I<. S., and Mishra, R. K., J . Indian Chem. Soc., 1979, 55, 462 and 773. Patel, K. S., and Mishra, R. K., Bull. Chem. SOC. Jpn., 1979, 52, 592. Patel, K. S., Deb, K. K., and Mishra, R, K., Sep. Sci., 1979, 14, 333 and 815. Kharsan, R. S., Patel, K. S., and Mishra, R. K., Mikrochim. Acta, 1979, I, 353. Kharsan, R. S., Patel, K. S., and Mishra, R. K., Talanta, 1979, 26, 50 and 254. Patel, K. S., Deb, K. K., and Mishra, R. K., Bull. Chem. SOC. Jpn., 1979, 52, 595. Ringbom, A., 2. Anal. Chem., 1939, 115, 332. Sillen, L. G., Ada Chem. Scand., 1956, 10, 185. Gopalan, C., Ram Sastri, B. V., and Balasubramanian, S. C., “Nutritive Value of Indian Foods,” National Institute of Nutrition, Indian Council of Medical Research, Hyderabad, 1978, pp. 65, 71 and 75. Received October loth, 1980 Accepted May 21st, 1981 York, 1959, p. 97.

ISSN:0003-2654    

DOI:10.1039/AN9810601150

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

Analyst, Noziember, 1981, Vol. 106, $9. 1157-1162 1157 Utility of -rr-Acceptors in Charge-transfer Complexation of Alkaloids: Chloranilic Acid as a Spectrophotometric Titrant in Non-aqueous Media Suraj P. Agarwal and M. Abdel-Hady Elsayed Faculty of Pharmaceutical Sciences, University of Nigeria, Nsukka, Nigeria A spectrophotometric titration method is described for the determination of some alkaloids and their dosage forms using 0.005 M chloranilic acid solution in 1,4-dioxan as the titrant. The end-point is determined by measuring the change in absorbance of the sample at 535 nm. Quantitative recoveries with good reproducibility are reported for atropine, emetine, reserpine, strychnine, yohimbine and four dosage forms. The least-squares method for the end- point location in the spectrophotometric titration is also proposed.Keywords : Spectrophotometric titration ; alkaloid determination ; chtoranitic acid ; charge-transfer complexation The use of chloranilic acid { 2,5-dichloro-3,6-dihydroxy-p-benzoquinone) in the determination of metal ions has been described.lS2 Slifkin et aL3 studied the nature of complexes of chloranilic acid and amino acids and showed that a 1 : 1 complex is formed in solution and a 1 : 2 complex is formed in the solid state. On the basis of the infrared spectra of amino acids and chloranilic acid complexes, it was shown that hydrogen-bonded ionic species are formed. The spectro- photometric determination of certain alkaloids such as atropine, pilocarpine and strychnine via charge-transfer complexation with chloranilic acid has recently been reported by Elsayed and A g a r ~ a l .~ The instantaneous formation of a stable purple 1 : 1 complex between chloranilic acid and the alkaloid prompted us to study further the use of chloranilic acid as a possible titrant, in order to devise a simple, rapid and accurate method for the determination of alkaloids as pure substances as well as in their representative pharmaceutical dosage forms. Hitherto, the use of chloranilic acid as a titrant has not been reported. Experimental Reagents and Materials The following reagents were obtained from commercial sources and used as supplied: chloranilic acid (Riedel-de Haen) ; atropine, emetine hydrochloride and yohimbine hydro- chloride (BDH) ; atropine sulphate, reserpine and strychnine (Merck) ; and strychnine hydro- chloride (Sigma).Dosage forms such as atropine sulphate eye drops [ l yo solution containing 0.002y0 of phenylmercury(I1) nitrate, Evans Medical J , atropine sulphate injections BP (0.1%, E.G.Y .T.), atropine sulphate injection BP (0.060/,, Evans Medical), reserpine tablets (0.25 mg per tablet, Ciba) and emetine hydro- chloride injection BP (65 mg ml+, Burroughs Wellcome) were obtained. Chloraizilic acid s o l d o n , 0.005 M. Dissolve 0.1045 g of 9-chloranilic acid in 1,Cdioxan and make up to 1 1. The solution, when stored in an amber-glass bottle, was found to be stable for at least 6 weeks. Alkaloid base solution. Dissolve 0.1 g of alkaloid (atropine, strychnine or reserpine) in chloroform and make up to 50 ml. Use 4-6 ml of this solution for assay as described below under general procedure.Alkaloid saEt solution. Dissolve 0.1 g of the alkaloid salt (atropine sulphate, strychnine hydrochloride, emetine hydrochloride or yohimbine hydrochloride) in about 15 ml of water in a 100-ml separating funnel. Add a few drops of dilute ammonia solution to make the solution alkaline to litmus. Extract the liberated alkaloid with 1 5 , lo-, 10- and 10-ml portions of chloroform. Wash each extract with the same 15 ml of water in another separating funnel. Pass each of the chloroform extracts through anhydrous sodium sulphate supported on filter- Other solvents and reagents used were of analytical-reagent grade.1158 AGARWAL AND ELSAYED : T-ACCEPTORS I N Analyst, Vol. 106 paper in a funnel and collect the extract in a 50-ml calibrated flask and make up to the mark with chloroform.Use 4-6ml of the extract for assay as described below under General Procedure. Transfer 10.0 ml of the solution into a 100-ml separat- ing funnel containing 10 ml of water. Make it alkaline to litmus with dilute ammonia solution and extract the alkaloid as described above. Use 4-6 ml of the extract as described below under General Procedure. Transfer 50.0 ml of the pooled ampoule contents into a 100-ml separating funnel and make alkaline to litmus with few drops of dilute ammonia solution. Extract the liberated alkaloid in the manner described above. Use 6-8 ml of the 0.1% atropine sulphate ampoule extract or 8-10 ml of 0.06% atropine sulphate ampoule extract for assay as described below under General Procedure. Transfer 2.0 ml of the solution into a 100-ml separating funnel containing 10ml of water.Add a few drops of dilute ammonia solution to make the solution alkaline to litmus and extract the liberated alkaloid as described under Alkaloidal salt solution. Use 3.04.0 ml of the extract for assay as mentioned under General Procedure. Reserpine tablet solution. Pulverise 30 tablets to a fine powder in a glass pestle and mortar; transfer into a dry 25-ml beaker and extract with 10 ml of chloroform. Decant through filter- paper into the titration flask. Complete the extraction of the alkaloid with three further 10-ml portions of 1,4-dioxan, decanting each portion through the same filter-paper into the titration flask. Deliver the titrant in 0.5-ml increments as described under General Procedure.Atropine suZPhate eye drops solution. Atropine sulphate ampoules (0.1 and 0.0670). Emetine hydrochloride ampozdes (65 mg ml-l solution). Apparatus Absorbance measurements were made with a Bausch and Lomb Spectronic-20 spectro- photometer. The spectrophotometeric titration unit was that described by Rehm et aZ.5 and consists of a 125-ml titration flask having inlet and outlet tubes connected by short lengths of polystyrene tubing to the inlet and outlet tubes inserted into a rubber stopper, The rubber stopper was fixed on to the absorption tube contained in the cell compartment. Homogeneity was achieved by using a magnetic stirrer. The titrant was delivered from a 10-ml burette, graduated to 0.02 ml.General Procedure Transfer 35 ml of 1,4-dioxan into the titration flask followed by an aliquot of the sample solution as described under Reagents and Materials. Deliver the titrant in 0.5-ml increments, stir and read the absorbance of the solution at 535 nm after each addition of titrant. The end- point is determined from a graph of absorbance veysus volume of titrant as being the inter- section of the two straight line segments, or mathematically using the equation derived by the least-squares method. Results and Discussion The alkaloids atropine, strychnine, reserpine, emetine and yohimbine have different struc- tures and exhibit different absorption maxima in the ultraviolet region.6 However, with chloranilic acid in a non-aqueous medium these alkaloids give a purple chromogen with almost similar maxima in the vicinity of 535nm.The identical nature of the absorption spectra (Fig. 1) is probably due to the common origin of the charge-transfer complexation between the alkaloid acting as n-donor and chloranilic acid (CA) acting as a n-acceptor with the subsequent formation of a coloured anion radical of chloranilic acid (CA-), according to the following equation : R3N + CA 2 [R,N -+ CAI -+ R3& + CA- 1,4-Dioxan was used as the solvent owing to its low dielectric constant and it appears not to compete or shield the charge-transfer process from donor to acceptor that is necessary for instant and stable colour formation at room temperature (about 25 "C). Chloroform was used in the extraction of alkaloid dosage forms and the small proportion (usually less than ZOyo) that was present in the titration process did not exhibit any interference.Intermediate Radical anionNovember, 1981 CHARGE-TRANSFER COMPLEXATION O F ALKALOIDS 1159 360 400 440 480 520 560 600 640 680 Waveiengthhm Fig. 1. Absorbance spectra of chloranilic acid, 0.35 mg ml-l (A), and its complexes with: atropine, 0.15 mg ml-l (B); emetine, 0.2 mg ml-l (C) ; reserpine, 0.28 mg ml-l (D) ; strychnine, 0.16 mg ml-l (E); and yohimbine. 0.24 mg ml-1 (F). All in l,.l-dioxan. The operating wavelength of 535 nm was selected as it was the wavelength of maximum absorbance for the complex and owing to the fact that there was no interference by other absorbing substances at this wavelength. The absorbance of the solution was corrected for dilution by multiplying the observed absorbance by the factor (V, + v)[V, where V , is the volume prior to the titrant addition and z1 is the volume of titrant added.Failure to make volume corrections may introduce unsuspected errors as extrapolation of a line of incorrect slope will give an incorrect end-point. Fig. 2 illustrates a typical titration graph obtained with reserpine and is also representative of those obtained with atropine, strychnine and yohimbine. Initially, there is an increase in absorbance owing to complex formation but after the equivalence point is reached there is very little further increase in absorption. Fig. 3 gives the titration graph obtained with emetine. As emetine contains two basic moieties in its structure, these appear to be successively titrated as there are two breaks in the graph. The second inflection in the graph was used to determine the end-point as it gave more accurate and reproducible results compared with the calculation based on the first inflection.0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 0.005M chloranilic acidhi Fig. 2. Photometric titration curve for reserpine with 0.005 M chloranilic acid at 535 nm.1160 AGARWAL AND ELSAYED T-ACCEPTORS IN Analyst, Vol. 106 I .2 1 .O 8 0.8 .f! 0.6 n C $ a 0.4 0.2 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 0.005 M chloranilic acid/ml Fig. 3. Photometric titration curve for emetine with 0.005 M chloranilic acid at 535 nm. Use of the Least-squares Method to Determine the End-point in Spectrophotometric Titrations In spectrophotometric titration graphs, where the graphical location of the end-point may not be easy and subject to individual variation, we propose the following mathematical pro- cedure based on the least-squares method for location of the end-point.The absorbance readings are measured not in the vicinity of the end-point but before and after the end-point and the absorbances should give a least-squares straight line. Under such conditions at least four absorbances are measured on each side of the end-point. Using the least-squares method,' the regression line for the points located before the equivalence point can be described as '. * * (1) 0 . - * (2) A , = a, + b, V , . . .. .. A , = a,+ b2V2 .. .. .. and after the equivalence point, the regression equation for a given line is where A , and V , are the variable absorbances and volumes, respectively, before the end-point and A , and V , the corresponding variables after the equivalence point.The constants a, and b, are the intercept and the slope before the end-point, respectively, and a, and b, the constants after the end-point. Therefore, equating the right-hand side of equations (1) and (2) : At the equivalence point, these two lines intersect, k., A , = A , and V , = V,. a, + b, V = a, + b, V .. .. .. * (3) Rearrangement gives .. .. v = - b2 - bl where V is the volume of titrant at the equivalence point. In equation (4) - - a, = A , - b, V , a, = A , - b, V , - - n, CV,A, - CV, CA, n,I: V12 - (CVJ2 n,I:V,A, - ZV,ZA, nCV22 - (CV,), b, = b, =November, 1981 CHARGE-TRANSFER COMPLEXATION OF ALKALOIDS 1161 A,, A2, 8, and v2 are the corresponding mean values and n1 and n, denote the number of absorbance measurements before and after the end-point.Graphical and mathematical location of the end-point was applied to the data obtained in the spectrophotometric titration of atropine, strychnine and reserpine bases (Table I). The percentage recovery was calculated using the following equation : V x molarity of chloranilic acid x F x 100 Mass of sample (g) Recovery (yo) = The factor F for emetine is equal to half of the relative molecular mass as the second inflec- tion was used for the calculation and as 1 mol of emetinereacted with 2 mol of chloranilic acid. For the other alkaloids F equals the relative molecular mass of atropine, reserpine, strychnine or yohimbine.Statistical comparison for graphical and mathematical location of the end-point (Table I) reveals that both methods are of equal accuracy, as none of the values for tcalculated exceed itheoretic al. TABLE I ASSAY RESULTS FOR ATROPINE, RESERPINE AND STRYCHNINE BASES USING GRAPHICAL AND LEAST-SQUARES METHODS FOR THE LOCATION OF END-POINT The figures in parentheses are the mean percentage recovery f the standard deviation Graphical method Least-squares method A Amount -7 taken/ Volume I Recoverv, Volume/ Alkaloid base Atropine . . .. Reserpine . . .. Strychnine . . .. mg 8.0 8.0 10.0 8.5 8.0 16.0 16.0 15.0 12.0 14.0 8.0 9.0 12.0 8.0 8.0 10.0 ml 5.50 5.52 7.05 6.00 5.48 5.20 5.32 4.65 3.96 3.94 4.78 5.44 7.32 4.72 4.76 6.10 d - % 99.48 99.84 102.20 102.14 99.12 (100.56 f 1.50) 98.91 101.20 100.37 100.44 99.93 0.83* (100.17 & 0.84) 99.91 100.33 102.00 98.65 99.49 102.00 0.45* (100.40 f 1.4) 0.86f.ml 5.585 9 5.692 4 6.971 2 5.906 5 5.504 2 5.2145 5.2920 4.947 3 4.161 2 4.547 0 4.704 5 5.388 7 7.1054 4.750 5 4.869 8 6.061 2 Recovery, 101.04 101.52 100.87 100.55 99.49 % (100.69 f 0.76) 2.03* 99.19 100.66 100.38 100.54 98.85 (99.92 f 0.84) 98.33 100.11 99.01 99.29 101.78 101.35 (99.98 f 1.36) 0.211 0.04t Subjecting assay results of pharmaceutical preparations to Student's t-test, the percentage recoveries found in the dosage forms of atropine eyedrops, atropine injections (0.1%) and emetine injections were not significantly different from the label claims as tcaleulated does not exceed ttheoretical.However, in other preparations, atropine injection (0.06y0) and reser- pine tablets, the percentage found, although it is within the pharmacopoeia1 limits,* is signifi- cantly different from the label claim. In these instances, the values for tcalculated exceed /theoretical at 95% confidence limits. Therefore, an acceptable assessment for the accuracy of the proposed method is to find the percentage recovery from a known amount (Table I, alkaloid bases and Table IT, alkaloid salts) and not from the label claim. In all these instances, /calculated is within the limits of &heoretical, which indicates the high accuracy of the method.1162 AGARWAL AND ELSAYED TABLE I1 ASSAY RESULTS FOR SOME ALKALOID SALTS AND THEIR PHARMACEUTICAL PREPARATIONS Preparation Atropine sulphate eye drops Atropine sulphate injection (1 mg ml-l) Atropine sulphate injection Emetine hydroehloride injection Reserpine tablets (0.25 mg per tablet).. Strychnine hydrochloride . . . . Atrophine sulphate . . 0 . .. (10 mg ml-l) . . .. ,. .. (0.6 mg ml-l) . . .. .. .. Emetrne hydrochloride . . . * .. (65 mg ml-l) . . .. .. .. Yohimbine hydrochloride . . .. Amount taken/ n* mg 5 8-10 5 8-9 4 7-8 4 5-6 6 6-10 5 7-10 4 8-10 6 8-10 5 8.5-1 0.5 Mean recovery1 f standard deviation, yo 100.59 f 0.79 100.06 j= 1.35 101.69 f 1.84 108.82 f 1.67 100.56 f 1.33 100.73 f 0.64 96.35 f 0.36 100.69 f 0.97 100.69 f 1.42 tcalculated: 1.67 0.20 1.84 10.56 1.03 2.55 20.28 1.74 1.09 * n = Number of determinations. t Percentage recovery in alkaloid salts and percentage of label claim in pharmaceutical preparation. Values forttheoretlcal a t cc = 0.05 are 3.182,2.776 and 2.571 for 3 , 4 and 5 degrees of freedom, respectively.Auxiliary substances that are likely to be present as the preparation base, e.g., starch, lactose, talc and magnesium stearate in tablets and preservatives, antioxidants or buffering agents in other pharmaceutical preparations, exhibited no interference during the assay procedure, as in the proposed method the free base is extracted prior to the instant complexa- tion of the alkaloid with chloranilic acid. The use of the least-squares method in the location of the equivalence point is better than the graphical method as the certainty with which the end-point is determined is increased. As indicated above, the graphical method is subjective, as in some instances different lines can be drawn through the points on the graph giving different end-point, whereas only one end- point is obtained by the least-squares method.Our preliminary trials using chloranilic acid in potentiometric titrations of the investigated alkaloids were unsuccessful. However, attempts to find an appropriate solvent system and electrode combination are still continuing. The authors are grateful to Professor P. Iwe Akubue, Dean, Faculty of Pharmaceutical Sciences, University of Nigeria, Nsukka, Nigeria, for providing facilities, to Mr. S. 0. Ejikeme, Chief Pharmacist, University of Nigeria Teaching Hospital, Enugu, Nigeria, for providing the dosage forms used in the analysis and to Senate Research Grants Committee, University of Nigeria, Nsukka, for funds (Grant No. 00354/79). References 1. 2. 3. 4. 5. 6. 7. 8. Perrin, D. I)., “Organic Complexing Reagents,” Interscience, New York, 1964, p. 189. Verchere, J . F., J. Chem. Res. ( S ) , 1978, 178. Slifkin, M. A., Smith, B. M., and Walmsley, R. H., Spectrochim. Acta, 1969, 25A, 1479. Elsayed, M. A., and Aganval, S. P., Tulunta, to be published. Rehm, C., Bodin, J. I., Connors, K. A., and Higuchi, T. I., Anal. Chem., 1959, 31, 483. Clarke, E. G. C., Editor, “Isolation and Identification of Drugs,” Volume I, Pharmaceutical Press, Spiegel, M. R., “Theory and Problems of Probability and Statistics,” McGraw-Hill, New York, 1975, “British Pharmacopoeia 1973,” HM Stationery Office, London, 1973, pp. 40, 183 and 411. London, 1974, pp. 203, 536, 545, 325 and 598. pp. 215 and 250. Received April 9th, 1981 Accepted May 8th, 1981

ISSN:0003-2654    

DOI:10.1039/AN9810601157

出版商:RSC    

年代:1981

数据来源: RSC

摘要:

Analyst, November, 1981, VoL. 106, $p. 1163-1167 1163 Spectrophotometric Determination of Piperazine via C harge-transfer Com plexes Mohamed S. Rizk, Mohamed I. Walash and Fawzia A. lbrahim Department of Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt Iodine - piperazine or chloranil - piperazine charge-transfer complexes have been used for the sensitive assay of piperazine or its salts; these complexes exhibit intense absorption bands in the electronic spectrum. The molecular ratios of the reactants in the complexes have been established and the experi- mental conditions leading to maximum charge-transfer bands were also studied. The proposed procedures have been applied successfully to pure samples and drug formulations with good accuracy. The average recovery was 100.26-100.84% with piperazine - iodine and 99.33-100.33% with piperazine - chloranil charge-transfer complexes, with an average standard deviation for each method of 0.8-3.9y0.Keywords : Piperazine and piperazine salt determination ; spectrophotometry ; charge-transfer complexes ; drug formulations Amines are excellent electron donors, and charge-transfer complexes of these compounds with halogens and pseudohalogens have been rep~rted.l-~ Iodine acceptor charge-transfer com- plexes have been recommended in pharmaceutical analysis , e.g., the complexes formed with alkaloids* and with ethambuto15 have been utilised for their sensitive determination in dosage forms. Similarly, chloranil, a v-acceptor , is known to form charge-transfer complexes and radical ions with a variety of electron donors, including a r n i n e ~ .l ~ ~ ~ ~ Feigl et aL7 reported that chlor- anil forms coloured condensation products with primary and secondary arylamines, amino acids, phenols and naphthalene. The utility of chloronil as a reagent for the spectrophoto- metric analysis of various amino acids has been studied by many workers8-10; these investiga- tions revealed that the spectra produced were due to n - 7~ ,charge-transfer complexes. Al- Ghabasha et aZ.ll investigated the reaction of chloranil with a wide range of amines and described a method for their determination. Korany and Wahbi12 used chloranil for the spectrophotometric determination of primary and secondary amines. The secondary amine piperazine and its salts have therapeutic importance, and are in- corporated in many pharmaceutical formulations.Gravimetric,13-17 near-infrared spectro- photometric,l* complexometricls and colorimetric20-24 methods were reported for the determina- tion of piperazine. This paper describes the use of charge-transfer complexes for the sepectrophotometric determinaten of piperazine and its salts. The investigation involved the determination of the molecular ratios and the experimental conditions to give a maximum absorption band either in the ultraviolet region for the iodine - piperazine complex or in the visible region for the chlora- nil - piperazine complex. Experiment a1 Reagents and Materials The reagents used were of analytical-reagent grade and the solvents were of spectroscopic grade.Standard solution of piperazine hexahydrate. Weigh accurately 50 mg of piperazine hexa- hydrate ( l O O ~ o purity calculated on a dry basis), dissolve it in anhydrous chloroform and dilute to 100 ml with chloroform in a calibrated flask. Standard solutions of piperazine phosphate, adipate and citrate. Weigh accurately 50 mg of the salt (100% purity calculated on a dry basis), transfer into a 60-ml separating funnel, dis- solve the powder in 3ml of 10% sodium hydroxide solution and extract with five 15-rnl portions of chloroform. Combine the chloroform extracts, dry with anhydrous sodium sul- phate (5 min) and filter through dry filter-paper into a 100-ml calibrated flask. Rinse the1164 RIZK et aE. : SPECTROPHOTOMETRIC DETERMINATION OF Analyst, VOl. 106 sodium sulphate and filter with chloroform, add the washings to the filtrate and dilute to 100 ml with chloroform. Working solution.A working solution (for determination of piperazine using iodine) was prepared containing 0.1 mg ml-l of piperazine and its salts. Iodine solution, 4 x M. Chloranil sohtion, 0.1 yo. Dissolve chloranil (purified by recrystallisation from acetone) in Dissolve the required amount of iodine in chloroform. chloroform. Instrument Pye Unicam SP 1800 spectrophotometer. Procedures ( A ) Piperazine - iodine Transfer a volume of the sample solution (containing 0.1-0.15 mg) from a microburette into a 10-ml calibrated flasks, add 4 ml of 4 x lov4 M iodine solution and dilute to volume with chloroform. Measure the absorbance at 264 nm after 5 min against a reagent blank in a 1-cm cell.(B) Piperazine - chloranil Transfer a volume of the sample stock solution (containing 0.1-0.8 mg) into a 10-ml Cali- brated flask, add 2 ml of 0.1% chloranil solution and dilute to volume with propan-2-01. Measure the absorbance at 545 nm after 1 h against a reagent blank in a 1-cm cell. Assay of pharmaceutical preparations Transfer an amount of the powdered tablet or granules or measure a volume of syrup equivalent to 50 mg of piperazine or its salts into a 60-ml separating funnel, dissolve in 3 ml of 10% sodium hydroxide solution and extract with chloroform as for the preparation of standard solutions. Dilute the chloroform extract further with chloroform to give a concentration of about 0.1 mg ml-l Transfer a volume containing 0.1 mg (i.e., about 1.0 ml) into a 10-ml calibrated flask and proceed as under A , or transfer a volume containing 0.4 mg (i.e., about 4.0 ml) into a 10-ml calibrated flask and proceed as under B.Calculate the concentration of piperazine or its salts by reference to a calibration graph. Results and Discussion Determination of Piperazine - Iodine Charge-transfer Complex The immediate change of the violet colour of iodine in chloroform to lemon yellow or yellow- ish purple upon reaction with piperazine suggested charge-transfer complex formation, and the ultraviolet region was scanned for the new band. Fig. 1 shows a hypsochromic shift of the iodine band from 520 to 264 nm with piperazine hexahydrate as a model. The Job method of continuous variation25 indicated a molar ratio of donor to acceptor of 1 : 1 for the piperazine - iodine complex (Fig.2). In order to make use of this complex formation for the determination of piperazine, the con- centration of iodine must be suitable for quantitative reaction, and should not be much higher than the piperazine concentration in order to avoid the formation of termolecular complexes with a consequent positive deviation from Beek’s law, so 4 m1 of 4 x M iodine solution were adequate. Also, the absorbance should be measured 5 min after the addition of the reactants in order to minimise changes in the absorbance with time owing to conversion of the outer complex into the inner complex, the latter form being common for electron donor corn- plexes with i0dine.l Different solvents were tried, e.g., chloroform, carbon tetrachloride, hexane and cyclohexane.The spectrum of the complex in hexane showed a low absorbance, and with cyclohexane Beer’s law was not obeyed. With chloroform or carbon tetrachloride Beer’s law was obeyed with a significant absorbance; chloroform was selected as the solvent. The optimum temperature was 25 O C , as heating the complex solution decreased the absorb- ance. Beer’s law (Fig. 3) was obeyed in the range 0.01-0.15 mg. Log E (E = molar absorptiv- ity) for piperazine hexahydrate, adipate and phosphate was 3.87 and for piperazine citrate 4.19.November, 1981 PIPERAZINE VIA CHARGE-TRANSFER COMPLEXES 1165 0.6 A 0.5 0.4 $ 0.3 n 0.2 0.1 m 0.0 200 240 280 320 360 B I .- ,' '\ I ) / I 1 / \ 400 440 480 520 560 600 Wavelength/nrn Fig.1. Absorption spectra of A, piperazine hexa- hydrate (15 pg ml-l) - iodine charge-transfer complex in chloroform and €3, iodine - chloroform (4 x M). 0.5 $ 0.4 f! 0.3 c m s a 0.2 n 0.1 2 4 6 8 10 12 14 Concentration/pg mi-' Fig. 3. Verification of Beer's law for the charge-transfer complex formed between iodine and piperazine and its salts: 0, piperazine hexahydrate ; 0, piperazine phosphate; 0, piperazine adipate; and A, piperazine citrate. 0.0 0.2 0.4 0.6 0.8 1.0 lPl/([Pl + [/*I) Fig. 2. Continuous variation plot of piper- azine hexahydrate - iodine in chloroform (2.15 X 10-4 M). 0.4 0.3 a c m f! 0.2 s n Q 0.1 360 400 440 480 520 560 600 640 680 Wavelengthtnm Fig. 4. Absorption spectrum of piper- azine hexahydrate (50 pg ml-*) - chloranil complex.Determination of Piperazine - Chloranil Charge-transfer Complex Chloranil in propan-2-01 - chloroform medium reacts with piperazine and its salts to form n - T charge-transfer complexes. The spectra of the complexes exhibit maximum absorption at 545 nm (Fig. 4). Because the reaction with chloranil at room temperature is slow,l0 the absorbance was measured after 1 h. Trials were made in order to accelerate the reaction by heating in a water-bath at different temperatures, but decay of the absorbance was observed. The molar ratio determined according to Job's method of continuous ~ a r i a r i o n ~ ~ indicated a donor to acceptor ratio of 3 : 2 for piperazine and chloranil (Fig. 5 ) . 0.3 a 2 0.2 f! a 2 0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Continuous variation plot of piperazine hexa- [Pl/([Pl + [CII Fig.5. hydrate - chloranil in propan-2-01 - chloroform medium.1166 Analyst, VoZ. 106 Different solvents were tried, e.g., acetonitrile, ethanol, methanol and propan-2-01- chloro- form. Acetonitrile afforded a higher sensitivity than the other solvents, but it is a poor sol- vent for piperazine phosphate, adipate and citrate. To overcome this difficulty, the base was extracted in chloroform from alkaline medium, the chloroform evaporated under nitrogen and the residue was dissolved in acetonitrile, but unsatisfactory results were obtained. With ethanol, the reaction was examined in alkaline media using alcoholic potassium hydroxide, sodium acetate or pyridine, and the reaction failed to give a stable product. With methanol, the reaction was examined at pH 7.5 and 8.4, but a high blank reading of the same order as that of the sample was obtained.Propan-2-01- chloroform was the solvent of choice with respect to the reaction and the stability of the complex. It was not possible to state positively that the outer complex actually takes part in the reaction but the inner complex is certainly present.26 It is suggested that propan-2-01- chloroform may stabilise the inner complex formed. Beer’s law (Fig. 6) was obeyed in the range 0.1-0.8 mg and 2 ml of 0.1% chloranil solution were sufficient for quantitative reaction. Log E for piperazine hexahydrate, phosphate and adipate was 3.14 and for piperazine citrate 3.43. The average recovery was 99.33-100.33%. RIZK et a,?.: SPECTROPHOTOMETRIC DETERMINATION OF 0.0 10 20 30 40 50 60 70 80 Concentration/pg mi-’ Fig. 6. Verification of Beer’s law for the charge- transfer complex formed between chloranil and piperazine and its salts : 0, piperazine hexahydrate ; , piperazine phosphate ; 0, piperazine adipate ; and A, piperazine citrate. TABLE I COMPARISON OF THE RECOMMENDED PROCEDURES WITH THE OFFICIAL BP (1973) METHOD13 Recovery* f standard deviation, yo Sample Piperazine hexahydrate Urolithine eff .-granules Urosolvine eff .-granules Piperazine adipate . . Piperazine phosphate Parazine tablet . . Piperazine citrate . . Piperazine citrate syrup Vermizine syrup . . .. .. .. .. .. .. .. .. * . Official rnethodl3 100.00 85.6 3. 0.7 119.3 + 0.6 99.2 99.9 88.43 + 0.4 99.5 103.90 + 2.0 112.46 + 1.8 Charge-transfer complex with iodine method 100.3 f 3.1 83.5 -& 4.2 83.5 f 4.2 100.3 f 2.7 99.7 f 3.3 99.1 f 3.9 100.9 & 3.2 98.5 f 1.6 103.3 f 1.1 Charge-transfer complex with chloranil method 100.3 f 0.9 -t -t 100.1 f 1.7 100.0 & 2.1 100.0 f 0.00 99.3 f 2.00 109.0 f 2.0 106.0 f 0.8 * Results are the averages of at least six experiments.t No reaction occurs.November, 1981 PIPERAZINE VIA CHARGE-TRANSFER COMPLEXES 1167 Comparison of Methods Table I gives the results obtained by application of both methods and an official methodf3 to the determination of piperazine and its salts in pure form and in pharmaceutical preparations. The longer time and variable results are disadvantages of the official assay.13 The results showed a standard deviation of about 0.&3.9y0 for the recommended procedures, and 0.01- 0.1 mg could be determined with good accuracy.Statistical parameters for the two methods are given in Table 11. When a t-test at the 95% confidence level was applied, the calculated value of t did not exceed the theoretical value, which indicates that there is no significant difference between the two mean recoveries, thereby confirming the high accuracy of the two methods. The variance ratio, F, also reveals that there is no significant difference between the precision of the two methods. TABLE I1 STATISTICAL ANALYSIS OF IODINE AND CHLORAPJIL METHODS Piperazine hexahydrate Parameter method method No. of experiments . . 8 6 Mean recovery, yo . . 100.3 100.3 Coefficient of variation, yo 9.5 0.7 Calculated value of t* 0.05 Calculated value of Ft 2.86 Piperazine phosphate method method 8 6 99.7 100.0 11.3 4.3 0.38 2.61 Piperazine Piperazine adipate citrate method method method method 8 6 8 6 100.3 100.1 100.8 99.3 7.3 3.0 10.4 4.1 0.23 1.00 2.39 2.57 -- * Theoretical value 1.78 ( p = 0.05).t Theoretical value 5.1 ( p = 0.05). 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. References Rao, C. N. R., Bhat, S. N., aiid Dwivedi, P. C., in Brame, E. G., Editor, “Applied Spectroscopy Reviews,” Vol. 5, Marcel Dekker, New York, 1972, pp. 1-170. Popov, A. I., and Rugg, R. H., J . Am. Chem. Soc., 1957, 79, 4622. Foster, R., “Organic Charge-transfer Complexes,” Academic Press, London, 1969. Taha, A. M., Ahmed, A.K. S., Gomaa, C. S., and El-Fatatry, H., J . Pharm. Sci., 1974, 63, 1853. Henry, S. I. T., Eric, D. G., and Anthony, S. D., J . Pharm. Sci., 1977, 66, 767. Melby, L. R., in Patai, S., Editor, “The Chemistry of the Cyano Group,’’ John Wiley, Chichester, Feigl, F., Gentil, V., and Stark-Meyer, C., Mikrochim. Acta, 1957, 350. Birks, J. B., and Slifkin, M. A., Nature (London), 1963, 197, 42. Al-Sulimany, F., and Townshend, A., Anal. Chim. Acta, 1973, 66, 195. Lin, B. Y., and Cheng, K. L., Anal. Chim. Acta, 1980, 11, 386. Al-Ghabasha, T. S., Rahim, S. A., and Townshend, A., Anal. Chim. Acta, 1976, 85, 189. Korany, M. A., and Wahbi, A.-A. M., Analyst, 1979, 104, 146. “British Pharmacopoeia 1973,” HM Stationery Office, London, 1973, pp. 371-372. Bandel, H., Dtsch. Apoth-Ztg., 1958, 98 (3), 61; Chem. Abstr., 1959, 53, 18733f. Grecu, l., Farmacia (Bucharest), 1960, 8, 261; Chem. Abstr., 1960, 54, 23186a. “US Pharmacopeia,” Nineteenth Revision, US Pharmacopeial Convention, Mack Publishing “Official Methods of Analysis of the Association of Official Analytical Chemists,” Twelfth Edition, “Official Methods of Analysis of the Association of Official Analytical Chemists.’’ Twelfth Edition, Erben, J., Cesk. Farm., 1959, 8, IS; Chem. Abstr., 1960, 54, 173i. Dessouky, Y. M., and Ismaiel, S. A., Analyst, 1974, 99, 482. Baggi, T. R., Mahajan, S. N., and Ras. G. R., J . Assoc. Off. Anal. Chem., 1974, 57, 1144. Beckman, H. F., and Feldman, L., J . Agric. Food Chem., 1960, 8, 227. Pankratz, R. E., J . Pharm. Sci., 1961, 50, 175. Abou-Ouf, A. A., Taha, A. M., and Saidhom, M. B., J . Pharm. Sci., 1973, 62, 1700. Rose, J ., “Advanced Physico-chemical Experiments,” Pitman, London, 1964, p. 54. Finley, K. T., in Patai, S., Editor, “The Chemistry of Quinonoid Compounds, Part 2,” John Wiley, Received December 8th, 1980 Accepted May 1st’ 1981 1970, pp. 639-670. Company, Easton, Pa., USA, 1975, pp. 386-388. AOAC, Arlington, Va., 1975, Sec. 38.204. AOAC, Arlington, Va., 1975, Sec. 38.206. Chichester, 1974, p. 1076.

ISSN:0003-2654    

DOI:10.1039/AN9810601163

出版商:RSC    

年代:1981

数据来源: RSC