ISSN:0003-2654    

DOI:10.1039/AN98409FX041

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALAO 109( 1 1 ) 13651 51 6 (1 984) November 198413651375138313891393139714011405TheThe Analytical Journal ofAnalystThe Royal Society of ChemistryCONTENTSFluorigenic Reagents for Primary and Secondary Amines and Thiols in High-performance Liquid Chromatography.Instability of Analytical ligands in Solution. Part 1. Hydrolysis Reactions and Interchange Reactions of C=N Groups. AInstability of Analytical Ligands in Solution. Part II. Redox Reactions, Molecular Aggregate Formation Reactions andSpectrophotometric Study of the Complexation Equilibria of Yttrium(ll1) With Quinizarin Green-Kamal Abdel-Extraction Spectrophotometric Determinathm of Iron(ll1) With 2-Hydroxy-1-naphthaldehyde Oxime-ShigerokuHigh-sensitivity Extraction - Spectrophotometric Determination of Iron With 3-(2-Pyridyl)-5,6-diphenyl-1,2,4-triazinePhoto-oxidation of Acridine and Acridine Yellow in the Presence of Iron(ll1): Determination of Micro-amounts of Iron,Spectrophotometric Determination of Platinum With Iodine and Pyronine G-Sambamoorthy Jaya, Talasila PrasadaA Review- Kazuhiro Imai, Toshimasa Toyo'oka and Hiroshi MiyanoReview-Maria Dolores Luque de Castro, Manuel Silva and Miguel ValcarcelPhotochemical Reactions. A Review-Maria Dolores Luque de Castro, Manuel Silva and Miguel ValcarcelRahman Idriss, Moustafa Kamal Hassan, Mohamed Said Abu-Bakr and Hassan SedairaYamaguchi and Katsuya Uesugiand Tetrabromophenolphthalein Ethyl Ester-Shigekazu Tsurubou and Tadao SakaiFluoride and Phosphate-Tomas Perez-Ruiz, Carmen Martinez-Lozano and Virginia TomasRao and Tiruvesaloor Venkatrama Ramakrishna1409 Spectrophotometric Determination of 1-Naphthylamine in Aqueous Solution by Coupling With Diazotised 4-1413 Determination of Thebaine in Crude Thebaine Samples by Infrared and Ultraviolet Spectrophotometric Methods-1417 Spectrophotometric Determination of Some Corticosteroid Drugs Through Charge-transfer Complexation-Magda M.1423 Spectrophotometric Determination of Chlordiazepoxide and Diazepam Using Orthogonal Polynomials-Mona Bedair,Aminoacetophenone-Bushra Sulaiman and Wadala A.BashirArun Agnihotri, Satish Chandra Tewari, Pavan Khatod, Sadhana Banerjee and M. BalasubramanianAyad, Saied Belal, Sobhi M. El Ad1 and Afaf A. Al KheirMohamed A. Korany and Mohamed E.Abdel-Hamid1427143114351439144314491451145514611465146914751483Reagent System for the Spectrophotometric Determination of Methanol in Environmental and Biological Samples-Miss Sweta Upadhyay and V. K. GuptaSpectrofluorimetric Micro-determination of lmidazoline Derivatives Using 1 -Dimethylaminonaphthalene-5-sulphonylChloride-Magda M. Ayad and M. H. Abd El-HaySelective Determination of Trace Amounts of Iron by a Kinetic Fluorimetric Method-Aurora Navas Diaz and FuensantaSanchez RojasDevelopment of an Assay Method for Cyanide, a-Aminonitriles and a-Hydroxynitriles for the Study of the BiologicalHydrolysis of these Compounds-Jean-Claude Jallageas, Hugues Fradet, Kien Bui, Marc Maestracci, Alain Thiery,Alain Arnaud and Pierre GalzyImpulse Response Photoacoustic Spectroscopy of Biological Samples-(The late) Gordon F.Kirkbrig ht, Richard M.Miller, Dominic E. M. Spillane and Ian P. VickeryTerbium Chelate for Use as a Label in Fluorescent Immunoassays-Michael P. Bailey, Bernard F. Rocks and CliffordRileyAtomic-absorption Spectrometric, Neutron-activation and Radioanalytical Techniques for the Determination of TraceMetals in Environmental, Biochemical and Toxicological Research. Part I. Vanadium-Francis Mousty, NicoloOmenetto, Romano Pietra and Enrico SabbioniDetermination of Copper and Zinc in Serum and Urine by Use of a Slotted Quartz Tube and Flame Atomic-absorptionSpectrometry-A. A. Brown and Andrew TaylorElimination of Metal Interferences in the Hydride Generation Atomic-absorption Spectrometry of Arsenic UsingSodium Tetrahydroborate(ll1) Solution-Manabu Yamamoto, Yuroku Yamamoto and Takashi YamashigeContinuous Internal Standardisation With a Sequential Inductively Coupled Argon Plasma System-Tim CatterickComparison of Methods for the Determination of Sodium in Alumina-Henry A.FonerDetermination of Titanium in Titanium Dioxide Pigments, Paints and Other Materials by Chromium(l1) ChlorideReduction and Automatic Potentiometric Titration-J. D. NorrisDifferential-pulse Voltammetric Study of Selected Inorganic and Organic Arsenic Compounds at a HangingMercury-drop Electrode and Its Analytical Applications-Mohammad Rasul Jan and William Franklin Smythcontinued inside back coverElectronically typeset and printed by Heffers Printers Ltd, Cambridge, EnglanCONTENTS-confinued1487149314971503150515071509151 1151315151516New Approach t o the Simultaneous Determination of Pollutants in Waste Waters by Flow Injection Analysis.Part 1.Reversed-phase Extraction Chromatographic Separation of Tin with Trioctylphosphine OxideRajendra B. HeddurScheme for the Identification of Sperm Whale Oil and Its Products in Commercial Formulations and in LeatherAnionic Pollutants-Angel Rios, M. Dolores Luque de Castro and Miguel Valcarceland Shripad M. KhopkarArticles-Stephen Crisp, Ray F. Eaton and Hugh M. TinsleySHORT PAPERSSpecific Enzymatic Procedure for the Determination of Starch in Soya-based Animal Feed Pre-mixes-M. S. HuiDemonstration of Collagen in Meat Products by an Improved Picro-Sirius Red Polarisation Method-F.Olga Flint andElectrochemical Reduction of 7-Aminodesacetoxy-[5-thio-( 1 -N-methyltetrazoly)]cephalosporanic Acid and Its Deter-Extraction - Photometric Determination of Microgram Amounts of Niobium(VtY. K. Agrawal and K. T. JohnSpectrophotometric Determination of Copper With 2-(2-Benzothiazolylazo)-5-dimethylaminobenzoic Acid-TakeoSpectrophotometric Determination of Piperazine With Chloranil-AbdeI-Aziz M. Wahbi, Mohammad Abounassif andKathleen Pickeringmination by Differential-pulse Polarography-L. Camacho, J. L. Avila, A. M. Heras and F. Garcia-BlancoKatami, Tomokuni Hayakawa, Masamichi Furukawa and Shozo ShibataEl-Rasheed A. Gad KariemBOOK REVIEWSERRATUMHigh-performance Liquid Chromatographic Assay of Temocillin and Epimerisation of its Diastereoisomers-Al bert E.Bird, Chieh-Hua Charsley, Keith R.Jennings and Anthony C. MarshallThe Periodic Tableof the ElementsThe Royal Society of Chemistry has produced acolourful wall chart measuring 125cm x 75cmcovering the first 105 elements as they exist today.Each group is pictured against the same tintedbackground and each element, where possiblephotographed in colour and discussed with regardt o its position in the hierarchy of matter. Additionalinformation for each element includes chemicalsymbol, atomic number, atomic weight and orbitsof electrons.The chart is particularly useful for both teachersand students and would make a worthwhileaddition t o any establishment.Price f2.35 ($4.50) RSC Members f 1.18Teacher Members f5.90 for 10Prices subject t o VAT in the UKRSC members should send their orders to: TheRoyal Society of Chemistry, The MembershipOfficer, 30 Russell Square, London WClB 5DT.Non-RSC members should send their orders to:The Royal Society of Chemistry, DistributionCentre, Blackhorse Road, Letchworth, HertsSG6 IHN.BUREAU OF ANALYSEDSAMPLES LTDannounce the availability shortly ofnewEURONORM CERTIFIEDREFERENCE MATERIALSECRM 096-1" Low S, Low Ca Node SteelECRM 097-1" High Purity IronECRM 585-1 Ferro-Chromium (ChargeChrome)For full details of these, and for copies of BAScatalogue , write, telephone or telex to:BAS Ltd., Newham Hall, Newby,Middlesbrough, Cleveland, TS8 9EATelephone: Middlesbrough (0642) 317216Telex: 587765 BASRID* These samples available both in finely divided form forchemical analysis and disc form for spectroscopicanalysis.A201 for further information. See page viii

ISSN:0003-2654    

DOI:10.1039/AN98409BX043

出版商:RSC    

年代:1984

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN98409BP085

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST. NOVEMBER 1984 VOL. 109 136.5 Fluorigenic Reagents for Primary and Secondary Amines and Thiols in High-performance Liquid Chromatography A Review Kazuhiro lmai,* Toshimasa Toyo'oka and Hiroshi Miyano Faculty of Pharmaceutical Sciences University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 7 73 Japan Summary of Contents Introduction Fluorigenic reagents for primary and secondary amines 0-P ht h a I a lde h yde FI uorescam i ne Dansyl chloride Ha loge no nitro benzof u razans 4-Fluoro-7-nitrobenzo-2-oxa-I ,3-diazole (NBD-F) 4-Chloro-7-nitrobenzo-2-oxa-I ,3-diazole (N BD-CI) Fluorigenic reagents for thiols N-Su bstituted maleirnide Da nsyl azi rid i ne Bimanes Halogenosulphonylbenzofurazans (SBD-F and SBD-CI) New reagents References Keywords Review; high-performance liquid chromatography; fluorigenic reagents; primary and secondary amines; thiols Introduction High-performance liquid chromatography (HPLC) has been widely used in many fields of science.For the sensitive detection of solutes in the picomole to nanogram range, fluorimetric analysis has often been adopted. Many flu origenic reagents for amines thiols phenols alcohols and carboxylated compounds have been developed and some of them are now being used as pre- and post-column derivatisa-tion reagents in HPLC. In this paper fluorigenic reagents for primary and secon dary amines and thiols are reviewed with respect to their reactivity selectivity stability fluorescence characteristics and especially their applicability to HPLC. There are many substances that have amino and/or thiol groups in their structures such as biogenic amines amino acids peptides, proteins and pharmaceuticals in research studies in bioche-mistry and clinical chemistry.Some examples of these reagents and their applications in HPLC are summarised in Tables 1 and 2. References 1-8 may be consulted for information on reagents that are not discussed in this review. Fluorigenic Reagents for Primary and Secondary Arnines OPA (o-phthalaldehyde) ,'+ 19 fluorescamine { 4-phenylspiro-[furan-2(3H) 1 '-phthalane]-3,3'-dione} ,2°-24 DNS-CI (dansyl chloride ; 5 -N N-d i m e t h y 1 amino n a p h t h a 1 en e s u 1 phony 1 chloride) ,25-30 NBD-F (4-fluoro-7-nitrobenzo-2-oxa-1,3-diazoIe),31-33 NBD-Cl (4-chloro-7-nitrobenzo-2-oxa-l13-diazoIe)34.35 and other nitrobenzof~razans-~6.37 have been reported as sensitive reagents for amines; others include f-1 uor e sce in i so t hio c y an ate s j X and p y r i do xi n e derivatives .3') .40 * To whom correspondence should be addressed.o-Phthalaldehyde OPA (m.p. 55-58 "C) reacts only with primary amines at alkaline pH in the presence of certain thiols (2-mercaptoethanol or ethanethiol) to give fluorescent adducts with excitation at 340 nm and emission at 4.55 nm (Fig. 1). 11.12.17.1X. The reaction is performed in borate buffer solution, which is more suitable than phosphate buffer solution19,12 as the latter quenches the fluorescence of the OPA adducts.9 The reagent stock solution [30 ml of 0.1 M borate buffer solution (pH 9.5) 0.5 ml of an ethanolic solution of OPA (10 mg ml-I) and 0.5 ml of 2-mercaptoethanol solution (0.5% in ethanol)] remains stable for 1-4 d.14 41 The reaction is usually complete within about 1 min by the addition of OPA (which is added in 2- to 3-orders of magnitude higher amounts than the amines) in the borate buffer (pH 9.7-10.0 for amino acids and pH &8 for amine~)14~15 to the sample solution at room temperature in the presence of 2-mercaptoethanol (of concentration not less than ~ ) .1 4 The resultant fluorophores 1-alkylthio-2-alkylisoind-oles,1°~13.1~ which have quantum yields of 0.33-0.47,1h fluores-cence lifetimes of 18-20 ns and a constant fluorescence intensity from pH 6.0 to 11.S.Y.11 are unstable. They decom-pose via a spontaneous intramolecular sulphur to oxygen rearrangement to non-fluorescent 2,3-dihydro-1H-isoindoI-l-one.IO li Therefore it is difficult to measure the reaction rates.12.14.16 SR' R N H ~ kex. = 340 nm NR kern. = 455 nm + R'St-i CHO 0 PA Fluorophor Fig. 1. Reaction of OPA with primary amine 1366 ANALYST NOVEMBER 1984. VOL. 109 OPA adducts with cysteine cystine and lysine fluoresce only weakly,g although the fluorescence of lysine is enhanced in the presence of a detergent.1"Q -44 OPA is less efficient in detecting peptides owing to the quenching of the isoindole fluorescence by the carboxamide group. 16 The quenching is released by detergents such as sodium dodecylsulphate and dimethyl sulph0xide.1~~~~ OPA stains proteins intensely.45 OPA - amino acid solutions,4~~~7 for the detection of the amino group in protein hydrolysates43.48-5() and biological materials ,51-66 biogenic amines67 in biological.materialshs-77 and the pharmaceuticals gentamicin78 and phenylpropanol-amine,79 are injected on to reversed-phase columns sepa-rated and detected at sub-nanogram to picomole levels. Factors affecting the retention of OPA adducts of amino acids have been discussed.53 The behaviour of some OPA adducts are as follows the OPA adducts of lysine and ornithine obtained in the presence of ethanethiol give double peak+; the separation of threonine from glycine is difficult on a particular type of CI8 column51."7566.62; cysteine can be derivatised with iodoacetamideS9 or oxidised with performic acid49 prior to the reaction with OPA and then sensitively detected; some of the OPA adducts such as glycine and lysine are very unstable and have to be injected on to a column within 1 min of the derivatisation reactionQ.53 (the same instability is observed for the adducts of polyaminesh7) (Table 1) ; therefore an on-line pre-column derivatisation technique has recently been introduced.50.60.67 Amino a~ids6,44,,8()-*~ in biological materials 790-97 (Table 2) in other material~Y8.~~ and from gels,l(K) D,r2-amino acids,""l peptides in biological m a t e r i a l ~ ~ ~ " * ~ 2 - ~ ~ ) ~ biogenic arninesl09.110 in biological materials111-'2() and drugs, kanamycin,l2' carbamates,41 glyphosate herbicide122 and p-lactam antibiotics,l23 separated by €{PIX are reacted post-column with OPA and sensitively detected.Various post-column reaction systems have been described.18.829124 Amino acids lacking an a-hydrogen atom react slowly with OPA at a low temperature (25 "C) but react sufficiently rapidly at high temperature (100 "C).84 For secondary amines. such as proline and h ydroxyproline a their oxidation to primary amines with an oxidising agent (sodium hypochlorite or chloramine-T) post-column prior to the reaction with OPA is required."-89 96797799,100 The pres-cence of the oxidising agent in the final medium sometimes obstructs the highly sensitive detection of the fluorescent adducts.83.99 A split-stream device has been used in peptide analysis103 and an on-line hydrolysis technique has also been introduced.41 Sometimes a high base-line level on the chromatogram is obtained because of fluorescent impurities in the OPA product or polymerised OPA itself.Interferences by the co-existing fluorophores in biological materials are often encountered with the lower wavelengths of excitation and emission employed (340 and 455 nm respectively). A comparison was made between OPA and fluorescamine with respect to sensitivities characteristics and practical use.6 OPA is suitable for low relative molecular mass amines such as amino acids44 and fluorescamine for peptides. 104,106 Fluorescarnine Fluorescamine (m.p. 154-156 "C) reacts with primary amines to give fluorescent adducts that fluoresce at 475 nm with excitation at 390 nm (Fig. 2). Thiols and alcohols affect the reaction.24 Fluorescamine also reacts with secondary amines to give non-fluorescent unstable amines.125 Fluorescarnine is generally dissolved in a water-miscible non-hydroxylic sol-vent such as acetone acetonitrile or dioxane and added to the aqueous sample solution (pH 8.0-9.5) with vigorous shaking. The reaction is complete within a few seconds (t? = 1-5 s)~O and the yield of the fluorophore is about 80-90%.22 The reagent hydrolyses in 5-10 s (t+) and the hydrolysis RNHZ 0 Fluorescarnine Fluorophor = 390 nm = 475 nm Fig. 2. Reaction of fluorescamine with primary amines product does not fluoresce.20,23 However fluorescence quenching is observed when amounts of fluorescamine above 1 mM are used.22 The fluorescamine adducts have a fluorescence quantum yield of 0.09-0.34") and a fluorescence lifetime of 11.7 ns in acetonitrile.22 Their fluorescence intensities are the same from pH 4.5 to 10.5 and low in the sufficiently acidic conditions owing to lactone formation between the hydroxy and carboxy groups of the adducts.24 However the intensity decreased as the amount of organic solvent in the final assay sample increased.The adducts are stable for several hours at low temperatures in the dark.Z"J26 The fluorescarnine adducts of 3-methylhistidine ,127 pep-tides vasopressin and oxytocinl28 (Table 1) catecholam-ines,l29J30 polyamines,131- 133 aminocaproic acid,' 34 antide-pressants,'?S tocainide and other drugs12h can be separated on reversed-phase columns and detected at the picomole level. When the reaction mixture of amino acids with fluorescamine was injected on to a column double peaks were observed, probably owing to intramolecular cyclisation136.Amino acidslf7- 179 of protein hydrolysates*4()-14* (Table 2) from polyacrylamide gels,143 peptides and proteins ,106.144 148 polyamine~'4h.1~~ and drugs.121 amoxicil-lin ,150 cefatrizinel51 and sulphapyridine ,152 separated on columns were reacted post-column with fluorescamine and detected at the picomole level. Thioglycollic acid interferes with the detection of cystine.l42,'4? With secondary amines. an oxidant (N-chlorosuccinimide) is also required. as with OPA for their conversion into primary amines prior to the fluorescamine reaction. 137.- 13', Care should be taken to avoid precipitation of buffer salt in the flow line when fluorescamine - acetone solution mixes with the flow of buffer.An automatic monitoring device has been described for the preparative-scale analysis of peptides and pr0teins.1~~~1~8 Efficient reaction conditions have also been repor-Proteins can be stained with fluorescamine in a gel electropherogram.155 However a combination of HPLC of proteins with fluorigenic reaction and detection has not been achieved probably because of the lower column efficiency in size exclusion chromatography. ted. 145.147.153.1S4 Dansyl Chloride DNS-CI (m.p. 69-71 "C) reacts with both primary and secondary amines to give fluorescent adducts with excitation at 350 nm and emission at 530 nrn (Fig. 3). The reaction conditions have been thoroughly studied with the use of amino acids as all the amino acids including proline and hydroxy-proline can be derivatised and sensitively detected (except cysteine).For cysteine dansyl cysteine is unstable in the presence of amines and undergoes S+N migration (N,S-diDNS-cysteine-N-DNS-cysteine + DNS-amine).28 For the complete derivatisation of amino acids with DNS-CI the following reaction conditions have been recom-mended 0.5% DNS-C1 in dioxane and an equal volume of sample solution (0.1 M triethylamine) for 16 h with cooling, then addition of 90% formic acid and a further 1-2 h reactio ANALYS'T. NOVEMBER 1984 VOIL. 109 F I I 1367 R' L N / R 2 DNS-Cf Fluorophor Fig. 3. Reaction of DNS-CI with primary and secondary amines at room temperature to cleave the DNS moiety from DNS-imidazole of di-DNS-histidine.29 A smaller amount of DNS-Cl (0.25%) is insufficient for dansylation of the a-amino group of lysine.29 possibly owing to the rapid hydrolysis of DNS-Cl.A recent report156 recommends other conditions for suppressing the side-reaction that occurs with mixed anhy-dride formation by DNS-amino acids with DNS-Cl and the subsequent degradation of the adduct to give DNSamine3[): 0.15% DNS-C1 in acetonitrile - 0.04 M lithium carbonate solution (pH 9.5) (1 + 2 ) for 35 min at room temperature (22-23 "C) in the dark then addition of 2% methylammonium chloride to destroy the excess of reagent and suppress the side -reac tion. DNS-Cl also reacts with the phenolic hydroxy group of tyrosine and the imidazole group of histidine to give fluores-cence (excitation at 360 nm emission at 470 nm).The former phenomenon has been used successfully for the detection of phenols,157 drugs,ls+160 estrogens,161.16* vanillylmandelic acid163 and thyroxinel64 in reversed-phasel"-164 or normal-phase30J62J63 HPLC. 0,O-Di-DNS-catechol is reported to degrade easily on exposure to LJV light to yield O-mono-DNS-catecholamine. 154.165 Quantum fluorescence yields of DNS-tryptophan range from 0.068 in water to 0.70 in dioxane.166 The DNS adducts are stable in the dark at 4 OC.161 The hydrolysis product of DNS-C1 DNS-OW (dansylsul-phonic acid) produced during the reaction shows strong fluorescence (excitation at 330 nm emission at 470 nm) in the pH range from acidic to alkaline and interferes in the fluorescence analysis of DNS-amines. For this reason only pre-column derivatisation of amines with DNS-Cl has been adopted in HPLC and only one report on the reaction with DNS-Cl and its subsequent extraction by an organic solvent in flow injection analysis has appeared.167 DNS-amino acidslj66.1"7.168-188 (Table 1) of peptides and protein hydrolysates,l7".17'.173.'8"."r6 of N-termini of pep-D,L-amino a~idsl89-1~~ (Table I) DNS-catecholamines 198,199 DNS-polyamines200-206 (Table 1) in tissue extracts201 and in urine,203-()5 DNS-histamine in tissue ,207 DNS-phosphoserine,208 DNS-phospholipids20" and DNS-have been separated and detected sensitively by HPLC. For amino acids the separation frorn DNS-hydrophilic amino acids such as aspartic acid glutamic acid and asparagine and of large amounts of DNS-OH or DNS-methylamine derived from the excess of reagent is not easy but has been Recent progress enables us to use the cheniiluminescence reaction of bis(2,4,6-trichlorophenyl) oxalate (TCPO) and a hydrogen peroxide for the more sensitive detection of fluorophores in HPLC.For example DNS-amino acids can be detected at the 10 fmol level by this technique.174 Proteins can be stained effectively with a cycloheptaamy-lose - DNS-CI complex.^^^ tides,176.178,180 in biological materials,'81,18'.1"- 186,188 DNS-&~gsl5%16O.210-221 in biological fl~ids158,159,212,213,215-21Y achieved. 176,180.181.~83.186.18?,19~ Halogenonitrobenzofurazans 4-Fluoro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-F) has been proposed as a replacement for the chloro analogue 4-chloro-7-nitrobenzo-2-oxa-l,3-diazole (NBD-Cl) as the former is a NO2 NBD-F No2 Fluorophor Fig.4. Reaction of NBD-F with primary and secondary amines 50-100 times more reactive fluorigenic reagent for amines.32 The alternatives are 4-alkoxy-7-nitrobenzofurazan (benzo-2-oxa-l,3-diazole) derivatives reported recently.36737 However, these alkoxy analogues showing fluorescence themselves are not as reactive as NBD-F.223 Halogeno- and alkoxybenzofurazans also react with phenolic hydroxy groups but the resultant adducts do not fluoresce.34 The reagents also react with thiols at acidic pH (3-5) but their fluorescence intensities are only about 2% of those of NBD-arnine~.?~ For cysteine the NBD moiety of S-NBD transfers to an amino group and N-NBD-cysteine or N-NBD-cystine appears.35 4-Fluoro-7-nitrobenzo-2-oxa-l,3-diazole (NB D-F) NBD-F (m.p.53.5 "C) reacts with primary and secondary amines to give fluorescent adducts that fluoresce at 530 nm with excitation at 470 nm (Fig. 4). The reaction is thought to proceed via a Meisenheimer complex.224 The reaction condi-tions with NBD-F have been thoroughly studied with proline as a representative secondary amine. Increases in the pH, temperature and proportion of organic solvent in the reaction medium increase the reaction rate. Various organic solvents and buffers affect the reaction rate. Ethanol and acetonitrile are better solvents for NBD-F and borate buffer is the best for the reaction. One tninute is sufficient for the complete reaction of amino and imino acids in 50% ethanol - 0.1 M borate buffer (pH 8.0) at 60 "C in the dark and the addition of hydrochloric acid for termination of the reaction and suppression of the blank value.The quantum efficiencies of NBD-hydroxyproline range from 0.01 in water (pH 9) to 0.80 in isobutyl methyl ketone.36 Tryptophan does not fluoresce with NBD-F under these experimental conditions.32 The resultant fluorophores in the reaction medium are stable for about 1 week under refrigeration in the dark. However with tyrosine the adduct is stable for only 1 d on account of the lower stability of the 0-NBD moiety of N 0-bis-NBD-tyrosine. The fluorescence of the hydrolysis product of NBD-F, namely 4-hydroxy-7-nitrobenzo-2-oxa-l,3-diazole (NBD-OH) is quenched by decreasing the pH of the reaction medium to less than 1 which results in a shift of its absorption maximum from 480 to 440 nm.The fluorescence characteris-tics of the NBD adducts remain constant with variation in pH. Thus the final reaction medium should be at a pW of about 1. Reaction mixtures of amino acids including proline ,225,226 of protein hydrolysates226 (Table 1) and of biogenic amines'2 with NBD-F were injected on to reversed-phase columns, separated and detected at sub-picornole levels. Amino and imino acids in blood platelets have been separated on an ion-exchange column reacted with NBD-F post-column and after addition of hydrochloric acid the resultant fluorophores detected at the picomole leve1.227 The fluorescence characteristics at longer wavelengths (excitation at 470 nm emission at 530 nm) seem to be favourable for the avoidance of the interferences frorn contami nants in biological materials.4-Chloro-7-nitrobenzo-2-oxu-l,3-diazole (NBD-Cl) NBD-C1 (m.p. 97.0 "C) reacts well with secondary amines and less well with primary amines.36 The reaction of hydroxyprol 1368 ANALYST NOVEMBER 1984 VOL. 109 ine is performed at pH 9.5 and 60 "C for 3 min.36 The reaction mechanism with amines is the same as that with NBD-F. Reaction mixtures of hydroxyproline in collagen hydroly-sate ,36 amines derived from nitrosoamines228.229 or drugs*"-232 in biological fluids231J32 were injected and separated on reversed-phase columns and detected at the picomole level. The post-column reaction of hydroxyproline with NBD-C1 has also been reported.233 Fluorigenic Reagents for Thiols N-Substituted maleimide derivatives,234 dansylaziridine ,235 bimanes,236.237 N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulphonic acid,238 SBD-F (ammonium 7-fluorobenzo-2-oxa-1.3 ,diazole-4-sulphonate)*39 and SBD-C1 (ammonium 7-chlorobenzo-2-oxa-1,3-diazole-4-sulphonate)2~~~ have been reported as fluorigenic reagents for thiols.These reagents are mainly used in studies on the active sites of enzymes or in the environmental analysis of proteins. N-Substituted Maleimide Fluorescent probes are obtained by substitution of benziniid-azolylphenyl (BIPM m.p. 243-245 "C) ,241-243 7-dimethyl-amino-4-methylcoumarinyl (DACM m.p. 204-306 "C) ,244724s 1-anilinonaphthyl-4- (ANM m.p. 207-208.5 "C),246 3-fluor-anthyl (FAM m.p. 175-176 0C)247 or 9-acridinyl "AM m.p.248 "C (decomp.)]248J49 in the N-position of maleimide to afford fluorigenic characteristics (Fig. 5 ) . They are soluble in acetone ethanol dimethoxyethane and dimethyl sulphoxide. The reaction proceeds for a few minutes at pH 5-8 and room temperature or 37 "C. The quantum yield of the DACM adduct of 2-mercaptoethanol is 0.12 in water.245 The longest fluorescence lifetime is obtained with FAM adducts.247 The fluorescent adducts are unstable and are converted into two ring-cleaved fluorophores at the N-C=O position of maleimide .245.250-251 The site of scission depends on the steric hindrance of the N-substituted moiety of the reagents and difficulties are sometimes encountered in obtaining a single peak on the chromatograni.N-Acetylcysteine was subjected to reaction with N-( 1-pyrene)maleimide249J50 (Table 1) and with DACM249.2Si) and the resultant fluorophores were separated on reversed-phase columns (Table 1) and detected at sub-picomole to picomole levels. The pre-column labelling and HPLC determination of cysteine and glutathione with NAM252 and D-penicillamine with BOPM [N-(y-2-benzoxazolyl)phenylmaleimide]2"- have also been reported. One trial of the post-column derivatisation of N-acetylcy-steine with NAM254 has been performed but the detection limit was 50 pmol owing to the high background level. SR Maleimide Fluorophor Reaction of N-substituted maleimides with thiols Fig. 5. h = 338 nm he = 540 nm Da nsylazi r idi ne Fluorophor Fig. 6. Reaction of dansylaziridine with thiols Dansy laziridine An excess of about 3 mol of dansylaziridine (rn.p.88-90 "C, 1 mM) was reacted with cysteine and glutathione at pH 8.2 and 60 "C for 1 h (Fig. 6 ) . 2 5 5 The resultant fluorophore with cysteine was separated on a reversed-phase column and detected at the 10 pmol level with excitation at 338 nm and emission at 540 nm. Bimanes Bimanes [monobromobimane (mBBr) . dibromobimane (bBBr) and monobroniotrimethylaminobimane (qBBr)] have been reacted with thiols at pH 8.0 and room temperature for 3 min (Fig. 7)256.257 (Table 1). The resultant fluorophores were separated on reversed-phase columns and detected at the picomole level with excitation at 375 nm and emission at 480 nm. The quantum yield of the adduct of glutathione was 0.07-0.09 in ~ a t e r .2 ~ ' However care should be taken not to use excess amounts of the reagents which are fluorigenic, otherwise they have to be removed by the addition of thiol agarose after the reaction.256 Halogenosulphonylbenzofurazans (SBD-F and SBD-CI) SBD-F [ammonium 7-fluorobenzo-2-oxa- 1,3-diazole-4-sulphonate. m.p. 280 "C (decomp.)] reacts with thiols 30-100 times faster than does SBD-Cl [ammonium 7-chlorobenzo-2-oxa-l,3-diazole-4-sulphonate m.p. 330 "C (sublimes)] .239 A more electron-withdrawing group at the para position of the fluorine moiety might afford a more reactive reagent than SBD-F.258 These reagents have no fluorescence themselves and are stable at pH 9.5 and room temperature for about 1 week. The reaction of SBD-F with thiols is complete within 1 h at pH 9.5 and 60 "C to give fluorophores (excitation at 380 nm, emission at 515 nm) (Fig.8). The resultant fluorophores are stable at pH 9.5 in a refrigerator for 1 week. The fluorophores of cysteine glutathione and other thiols have been separated on a reversed-phase column and detected at 0.1-1 pmol levels.259 An antihypertensive drug captopril has also been derivatised with SBD-F and determined by HPLC.260 SBD-C1 reacts with thiols but its application in HPLC has not been reported. New Reagents As illustrated above many fluorigenic reagents for amines and thiols are now being used although they have various disadvantages as described. New fluorigenic reagents should preferably have fluorescence characteristics at longer Bimane Fluorophor Fig.7. Reaction of bimanes with thiols F SR S03-N",+ SO3-SBD-F Fluorophor Fig. 8. Reaction of SBD-F with thiol ANALYST NOVEMBER 1984 VOL. 109 1369 ~ ~~ Table 1. Use of fluorigenic reagents for pre-column derivatisation Substances (detection limit) Amino acids (50 fmol) Oxytocin, vasopressin (10 pmol) Amino acids (ca. 10-50 PmOl) D,L- Amino acids (sub-pmol level) Putrescine, spermidine, spermine, (1 pmol, signal to noise ratio = 3) Amino acids (ca. 10fmol) Mercapto-acetate, acetyl-cysteine (400 fmol) Mercapto-acetate , acetyl-cysteine (40 fmol) Cysteine N- ace t yl-cysteine (100pg). (200 Pg) HPLC conditions Eluent Gradient elution A tetra-hydrofuran - MeOH - 0.5 M sodium acetate (pH 5.9) (1 + 19 + 80) and B MeOH -0.05 M sodium acetate (8 + 2).For gradient programme and flow-rate, see ref. 42 Detection Application Ref. Ex. 330 nm Hydrolysate of 42 418-nm cut- peptides off filter Column Altex Ultra-sphere ODS (250 x 4.6 mm i.d. 5 pm) Reaction conditions Amino acids in 0.4 M sodium borate (pH 9.5) containing 2% sodium dodecylsulphate and OPA solution (50 mg OPA in 1.25 ml MeOH 50 p1 2mercaptoethanol and 11.2ml0.4~sodium borate) (1 + 1 + l ) reaction for 1 min Peptides in borate buffer (pH 11 .0) 0.5 M KH,PO in 0.02 M disodium EDTA and 20 mg per 100 ml fluorescamine in acetone (ca. 8 + 1 + 5) Aliquots of extracted samples added to equal volumes of 0.5 M sodium hydrogen carbonate (pH 8.5) and 6 mg ml- DNS-Cl in acetone (1 + l ) reaction at room temperature for 3-4 h Partisil ODS Linear gradient elution from 15% acetone in water contain-ing 0.03% ammonium formate and 0.01% thiodiglycol to 50% acetone over 55 min; flow-rate 0.25 ml min-1 Gradient elution A 10 mM sodium acetate buffer (pH 4.18) - tetrahydrofuran (95 + 5) and B, acetonitrile - tetrahydrofuran (90 + 10).For gradient programme see ref. 181; flow-rate 1 ml min-1 4 mM L-prolyloctylamide -Ni(II) 8.75 mM ammonium acetate (pH 9.0) MeOH -water (50 + 50,60 + 40, 70 + 30); flow-rate, 2.0 ml min-1 Cut-off filter (not described in detail) Rat tissues 128 Ultrasphere-ODS (250 x 4.6 mm i.d., 5 CLm) Fluorimeter (Gilson Spectral Glo); excitation filter 7-51X; emission filter 3-72M Schoeffel Model FS 970 spectro-fluoro-monitor (Westwood, NJ USA) Ex.365 nm, em. 510 nm Rat liver, brain and serum 181 Amino acids in 40 mM Li2C03 buffer (pH 9.5) and 1.5 mg ml-1 DNS-Cl in acetonitrile (2 + l), reaction at room temperature for 35 min C8 Hypersil (150 x 4.6 mm i.d. 5 pm) (60 x 4.6mm i.d. 5 pm), 25 "C 195 Gradient elution (not linear): acetonitrile - l-heptane-sulphonic acid (50 + 50) to acetonitrile - l-heptane-sulphonic acid (80 + 20) within 20 min; flow-rate, 2 ml min- 1 Gradient elution A MeOH -tetrahydrofuran - 0.1 M phosphate buffer (pH 6.0) (3.75 + 1.6 +94.65) and B MeOH - tetrahydrofuran -0.1 M phosphate buffer (pH 6.0) (25 + 15 + 60).Also isocratic elution C MeOH -water (40 + 60). For gradient prcgramme see ref. 226; flow-rate 2 ml min-1 2 mM sodium phosphate buffer (pH 7.4) - MeOH (7 + 3) containing 10 mM tetra-methylammonium hydroxide (TMA); flow-rate 0.75 ml min-1 2 mM sodium phosphate buffer (pH 7.4) - MeOH (85 + 15) containing 10 mM TMA; flow-rate 0.75 ml min-1 204 Polyamine in 0.5 M carbonate buffer (pH 9.2) and 10 mg ml-1 DNS-Cl in acetone (1 + 1) reaction at 54 "C for 60 min pBondapak C18 (300 x 3.9 mm i. d . , ambient temp. 10 pm), Urine Amino acid (500 pmol each) in 0.1 M phosphate buffer (pH 8.0) and 50 mM NBD-F in EtOH (1 + l ) reaction at 60 "C for 1 min pBondapak C18 (300 x 3.9 mm i.d., ambient temp. 10 pm) 5 Ex. 470 nm, em.530 nm Protein 226 h ydrol ysate 1 VM thiol in carbonate buffer (pH 9.0) and N-( 1-pyrene)maleimide in acetone EtOH (5.05 + 0.5), instantaneous reaction LiChrosorb 4 mm i.d., RP-8 (250 X 5 vm) Ex. 342 nm, em. 396 nm Urine 249 249 Ex. 400 nm, em. 480 nm 1 p~ thiol in carbonate buffer (pH 9.0) and 20 p~ N-(7-dimethylamino-4-methyl-3-coumariny1)maleimide (DACM) in acetone - EtOH (5.05 + 0.5) instantaneous reaction Sample solution of 0.5 M Na,C03 - H3B03 - KCI (pH 8.8) 5 N NaOH and N-( 9-acridiny1)maleimide (0.5-2 pmol ml-1) in acetone (3 + 0.05 + l ) , reaction at room temperature for 2 h Ex. 360 nm, em. 435 nm 250 SC-02 (Jasco) for cysteine, SN-01 (Jasco) for N-acetyl-cyste i ne (250 x 4.6 mm i.d.) Acetonitrile - 0.05 M NH,OAc (18 + 82), acetonitrile - NaOAc (55 + 45); flow-rate, 1.5-2.0 ml min-ANALYST NOVEMBER 1984 VOL.109 1370 Table 1. Continued Substances (detection N-Acetyl-cysteine monobromotrimethyl-CoA CoM ammoniumbimane or mono-cysteine bromobimane in 10 mM homocysteine NH4HC03 (pH 8.0), mercapto- reaction at room ethanol temperature for 3 min met hanet hiol, pantetheine, pantetheine, etc. (ca. 1 pmol) limit) Reaction conditions 1 mM thiol and 2 mM 4’-phosph0-HPLC conditions Column Eluent Beckman Stepwise elution A, AA-10 Beckman buffer (pH 3.25, (150 x 4 mm i.d.) buffer (pH4.25,0.2 Y); 0.2 N) B C D Beckman D‘ 0.95 M NaCl(+0.05 N sodium borate);-E 0.8 M NaCl(+O.2 N trisodium citrate); and F 0.1 M NaCl(+O.l N NaOH); flow-rate 0.2 ml min-1.For other conditions see ref. 256 De.tection ADDlication Ref. Ex. 340 nm Human red 256 and cut-off blood cells filter Table 2. Use of fluorigenic reagents for post-column derivatisation Substances HPLC conditions (detection limit) Reaction conditions Column Eluent Detection Application Ref. Amino acids [0.2 pmol (Leu11 0.8 g of OPA in 10 ml of EtOH and 1 ml of 2-mercaptoethanol to 1 1 of borate buffer (pH 10.5) containing 1.7 ml Aminco J5-7409 resin (35 cm x 2.38 mm i.d., 7.5 pm), first at 37.5 “C and at 62 “C 50 min after sample injection of 30% Brij 35 Stepwise elution 0.067 M Aminco Guinea pig 93 peril ymph citrate buffer A pH 3.20 (0.2 M Li) B pH 4.26 (0.2 M Li) and C pH 7.70 (1 .0 M Li); A 0-97 min, B 97-177 min and C 177-262 min; flow-rate 3.9 ml h-1.For other conditions see ref. 93 HPLC anal yser (Aminalyzer) Amino acids 0.16 M borate buffer (pH Durrum DC Long column stepwise elution; Primary filter BSA hydrolysate 142 (50prnol 9.6); flow-rate 13 ml h-1. 4A resin A 0.2 N sodium citrate (pH Corning No. (1 pg) limit) in acetone; flow-rate 10 i.d. 8 pm citrate (pH 4.25); A 0-45 secondary determination 15 mg per 100 ml fluorescamine (30 x 0.28 cm 3.28) and B 0.2 N sodium 7-51; ml h-1. Reaction time 20 s and7.5 x min and B 45 min to end; 0.28 cm i.d. flow-rate 7.0 ml h-1. Wratten 8 pm) 53 “C Short column 0.35 N sodium citrate (pH 5.26); flow-rate, 12.4 mi h-1 filter, No. 4 wavelengths similar to those of nitrobenzofurazan (excitation at 470 nm emission at 530 nm) as there are many substances that fluoresce at 300-400 nm in biological samples and interfere in the type of analyses being discussed.Also for more sensitive detection chemiluminescence reactions such as those described above or a time-resolved laser tech-nique261,26* might be considered. For these techniques suit-able candidates for fluorophore skeltons for each technique are required. For example polycyclic aromatic hydrocarbons such as perylene rubrene and rhodamine will be effectively excited by the former technique,263 and pyrene 2-phenyl-naphthalene and benzopyrene having longer fluorescence lifetimes are advantageous for the latter technique. 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Takahashi H., and Meguro 14 Yakugaku Zasshi 1981 101 1002. Yamamoto K. Sekine T. and Kanaoka. Y.,Anal. Biochem., 1977 79 83. Takahashi H. Nara Y. Meguro H . and Tuzimura K . , Agric. Biol. Chem.1979,43 1439. Miners J. J. Fearnley I. Smith K. J. Birkett D. J . Brooks, P. M. and Whitehouse M. W. J . Chrornatogr. 1983,275,89. Takahashi H. Yoshida T. and Meguro H . Bunseki Kagaku 1981 30 339. Lankmayr E. P. Bunda K. W. Muller K. and Nachtman, F . Fresenius 2. Anal. Chem. 1979 295 371. Fahey R. C. Newton G. L. Dorian R. and Kosower, E. M. Anal. Biochem. 1981 111 357. Newton G . L. Dorian R. andFahey R. C. Anal. Biochem., 1981 114 383. Toyo’oka T . Miyano H. and Imai K. 104th Annual Meeting of the Pharmaceutical Society of Japan Sendai. March 1984 Abstracts,” p. 558. Toyo’oka T. and Imai K. J . Chromatogr. 1983 282 495. Toyo’oka T. Imai K. and Kawahara Y. J . Pharrn. Biomed. Anal. in the press. Richardson J . H. Larson K. M Haugen G. R . Johnson, D.C. and Clarkson J. E. Anal. Chim. Acta 1980 116 407. Imasaka T. Ishibashi K. and Ishibashi N. Anal. Chim. Acta 1982 142 1. Imai K. Miyaguchi K. and Honda K. in Knox van Dyke. Editor “Luminescence Detection-Applications and Instrumentation,” CRC Press Boca Raton FL 1984. in the press. Paper A41122 Received March 26th 1984 Accepted April 26th 198

ISSN:0003-2654    

DOI:10.1039/AN9840901365

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST NOVEMBER 1984 VOL. 109 1375 Instability of Analytical Ligands in Solution Part 1. Hydrolysis Reactions and Interchange Reactions of C=N Groups A Review Maria Dolores Luque de Castro Manuel Silva and Miguel Valcarcel Department of Analytical Chemistry Faculty of Sciences University of Cordoba Cordoba Spain Summary of Contents Introduction Hydro I ysi s reactions Partial hydrolysis Hydrolysis followed by recondensation Complete hydrolysis Erroneous determinations of acid - base constants Determination of metal ions acting as catalysts in hydrolysis reactions Improper use of amines as prior reducers Diacetyl monoxime azomethinic derivatives - hydroxylamine systems 6-Methylpicolinaldehyde azine - amine systems in the presence of metal ions 2-Hydroxybenzaldehyde azine - amine systems Interchange reactions of C=N groups Keywords Review; instability of analytical ligands; hydrolysis reactions; interchange reactions of G N groups Introduction When new analytical methods are established the possibility of the ligand experiencing irreversible changes (total or partial chemical transformations which hinder its action as such) under the working conditions is frequently ignored-we have not found any systematic studies concerning the lability of analytical ligands in solution.In recent monographs devoted to the use of organic compounds in analytical ~hemistryl-~ there is no clear reference made to the instability of ligands in solution even though the behaviour of the ligand with respect to its stability in solution can be of great importance in determining its suitability as an analytical reagent.It has frequently been observed that when the reaction conditions are empirically optimised to favour the formation and/or the stability of a complex serving as the basis of a determinative method conditions favouring the stability of the ligand (as far as possible) and avoiding side-reactions are actually being created. Thus there are many methods in the literature involving the use of a large excess of reagent (up to 100-200-fold over the stoicheiometric amount) which cannot be explained purely on the basis of a low stability constant. Firstly we should like to make it clear that we are not referring to the well known reversible changes in the behaviour of the ligand such as acid - base reactions and prototropic or keto - enolic equilibria but those side-reactions of the ligand in which it may undergo transformations that prevent it from acting as such.This behaviour can be regarded as a negative factor in the general behaviour of unstable ligands although in some instances this instability is a positive factor for their use. The following reactions are the most important arising from the lability of analytical ligands: 1. Hydrolysis reactions. 2. Interchange reactions of C=N groups. 3. Redox reactions. 4. Molecular aggregate formation reactions. 5. Photochemical reactions. This paper discusses the first two types whereas the other three will be discussed in the following paper (p. 1383). In neither of the papers have we attempted to present a complete compilation of all the work presented in the literature but in showing the most significant examples of each type of reaction we have aimed at bringing this common but at the same time so little studied subject to the attention of analytical chemists.Hydrolysis Reactions This type of reaction is especially important for those Iigands resulting from the condensation of carbonyl compounds with amines such as Schiff bases and oximes. Hydrolysis an inverse reaction to condensation is catalysed by H+ and OH-ions: H’ (OH-) RR’CNR’’ + HOH * RR’CO + HZNR” Ligand Carbonyl compound Amine The greater or lesser tendency of the C-N bonds to hydrolyse depends on the nature of the R R’ and R” groups. In spite of being a reaction that takes place in a solution of the majority of Schiff bases (at a pH below 1-2 and above 10-11), on reviewing the literature of these compounds,S no specific references to their lability have been found.Some examples in which hydrolysis conditions favour or hinder the development of analytical methods are described below. Partial Hydrolysis The Fe(I1) - methyl 2-pyridyl ketone azine system is an example undergoing this type of hydrolysis. When the cation and ligand solutions are mixed a soluble and very unstable red ferroin-type (1 3 metal to ligand ratio) chelate is formed. The terminal C=N bond which does not take part in the chelation 1376 ANALYST NOVEMBER 1984 VOL. 109 is quickly hydrolysed giving rise to the stable orange ferroin-type (1 3 metal to ligand ratio) Fe(I1) - hydrazone chelate which is suitable for photometric purposes.6 A molecule of the corresponding ketone results from this reaction as shown below: 2+ I $C-CH3 6 A,,, = 520 nm -2-t + QL0 I CH3 It should be noted that (i) the C=N bonds in the chelate rings are not hydrolysed as this bond type is stabilised by the formation of these rings.(ii) The hydrolysis of the Fe(I1) -hydrazone chelate is very slow and negligible. When this chelate boils for a long time at a pH below 1.5 it is destroyed, forming hydrazine and ketone as the orange colour disappears from the solution. This behaviour is also observed without heating in a concentrated hydrochloric acid medium. (iii) If the original azine ligand employed is dissolved in nitrobenzene and the complex is formed by extraction from an aqueous solution of Fe(II) the red organic solutions of the Fe(I1) -azine are perfectly stable (Amax = 525 nm) because their hydrolytic degradation does not take place in this organic solution.Perchlorate is used as a forming agent for the ion pair making the extraction of the charged chelate possible. One example that differs from the above owing to the complexity of the reactions resulting from hydrolysis is the Pd(I1) - picolinaldehyde azine system. The reason for this different behaviour could be the greater ease with which the Pd(I1) ion forms complexes. Picolinaldehyde azine (PAA) is very easily hydrolysed between pH 0 and 5 yielding the corresponding hydrazone. In the presence of Pd(I1) and at pH 1.7-2.5 the formation of the following complexes takes place: NH2 A,,, = 660 and 730 nm (El A binuclear 2 1 (metal ligand) complex (Amax = 420 nm) (A) is attributable to the azine ligand which is very unstable and is transformed in less than 1 h into a very stable 1 1 complex (Amax = 400 nm) (B) attributable to the hydrazone a 2 2 complex (kmax = 545 nm) (C) attributable to the azine a 2 1 2 Pd - azine - hydrazone mixed ligand complex that corresponds to the 2 3 Pd(I1) to azine ratio initially added (Amax = 520 nm) (D) and shows lower chromaticity than the previous one because of its lower degree of conjugation and a 1 3 Pd(I1) to hydrazone complex (E) which has an intense blue colour with two characteristic maxima at 660 and 730 nm attributable to the hydrazone.The occurrence of this wide variety of complexes has been shown by different spectroscopic and chromatographic tech-niques.7 Other azines such as those of 2-benzoylpyridine8 and that of di-2-pyridyl ketone9 show similar behaviour. This type of hydrolysis is fairly common in compounds bearing the azine group. 10 Hydrolysis Followed by Recondensation When diluted solutions of Fe(1I) and picolinaldehyde azine (PAA) are mixed a red ferroin-type (1 3 metal to ligand ratio) chelate (Amax. = 475-480 nm) is formed [as shown in equation (l)] that without heating is rapidly transformed into the ferroin-type 1 3 Fe(I1) - hydrazone chelate (Amax = 435 nm). This behaviour is similar to that of the first example described under Partial Hydrolysis.The peculiarity of this system is that if an excess of picolinaldehyde is added to the solution of the hydrazone chelate the azine is again formed (by condensation with the terminal amine group) but in this instance a chelate with an intense blue colour and 1 2 metal to ligand stoicheiometry is formed the azine acting as a terdentate ligand bound to two pyridinic nitrogens and to one azinic nitrogen. This behaviour can be accounted for on the basis of the existence of three isomers of the azine according to the position of the pyridinic rings with respect to the two C=N bonds. The trans - trans form (which can have two rotational isomers) is stable both in the solid state and in solution and responsible for the formation of the initial red complex.When 2+ A,,, = 420 nm pH 1-3 Azine + Pd2+ A,,,. = 400 nm (€3) 14+ A,,, = 545 nm (C) -1 A,,, = 520 nm (D ANALYST NOVEMBER 1984 VOL. 109 0- Am i ne p he n o I a te NH2 /DH-\\ // c-c I I 1377 1 .N \c \ I H 2+ r Fe/3 I L L h,,,. = 475-480 nm Amax. 435 nrn . + O C H O the azine is formed again by recondensation the Fe(I1) bound to the hydrazone facilitates the azine formation as a terdentate ligand yielding the blue chelate which is much more stable than the red one. This blue chelate has excellent analytical photometric properties which have allowed the development of a selective method for the determination of trace amounts of Fe(I1) in the 1-8 p.p.m. range." Complete Hydrolysis As an example the well known Ca(I1) - glyoxal bis(2-hydroxyanil) system is used and the hydrolysis mechanism and absorbance profile are shown in Fig.1. This is widely accepted for the photometric determination of trace amounts of calcium in many samples. The difficulty involved in this photometry due to the instability of the coloured solutions is well known; Linstrom and Milligan12 have demonstrated that the loss of absorbance with time can be explained 2s follows. (i) The 1 1 I I H H (GBHA)Ca It H H GBHA G lycolate Ca(C2H303h 1 HO-CH2 -COO Calcium glycolate BSHB(A = 370 nm) 1 2 3 4 Tirne/h Fig. 1. Complete hydrolysis mechanism for the Ca(I1) - glyoxal bis(2-hydroxyanil) system and the corresponding absorption spectra 2+ Excess ____, +o H u A,,, = 660 nrn .chelate has a low stability constant and it dissociates even if an excess of ligand is used. (ii) The C=N bonds hydrolyse very easily yielding 2-aminophenol and glyoxal. This reaction is catalysed by OH- ions and it is necessary to take into account that the reaction only occurs in an alkaline medium. (iii) Glyoxal undergoes an internal regrouping mechanism (one aldehyde group is oxidised and the other is reduced) in a basic medium the glycolate anion being formed as a result. The glycolate anion reacts with the calcium liberated in (i) to form calcium glycolate Ca(C2H303)2 whose solubility depends on the percentage of organic solvent present in the medium. Therefore the hydrolysis of the ligand (not only that resulting from the chelate dissociation but also that in excess) is favoured by the conversion of glyoxal into another ligand, which is bonded to the calcium from the complex.From a comparative point of view it is interesting to mention the different behaviour of another imine ligand, diphenylglyoxal bis(2-hydroxybenzoyl hydrazone) (BSHB) ,I3 which we have suggested as a photometric reagent for the determination of calcium with which it forms an intense yellow chelate of 2 3 metal to ligand stoicheiometry. Both the BSHB (Amax = 370 nm) and the calcium chelate = 435 nm) are perfectly stable for long periods of time. There are two probable reasons for this higher stability in general the complexes of BSHB14-16 are much more stable than those of glyoxal bis(2-hydroxyanil) (GBHA) and the C=N bonds in the hydrazone tend to be hydrolysed to a lesser extent.Erroneous Determinations of Acid - Base Constants Incorrect data on acid - base constants (pK,) concerning organic ligands17-19 are sometimes found in the literature because the hydrolytic degradation of the compound under study at the end of the pH scale has not been taken into account. In these situations one must ensure that the measurements of the analytical signal are free from this disturbing effect. Therefore the stability of the values of the analytical signal must be tested with time for the moment when the samples are prepared if these samples show extreme pH values; if these samples are unstable the value of the analytical signal must be tested with time from the moment started ( t = 0) must be calculated and it is only the ligand that generates this signal that has to be taken into account (this calculation can be carried out by extrapolation of the analytical signal versus time graphs).Fig. 2 shows the absorbance versus pH graph for 6-methyl-picolinaldehyde azine. 19 This compound apparently shows three pK values but two of them are calculated for pHs at which the absorbance is unstable. Therefore each point must be calculated in these zones for t = 0 prior to its measurement. This study is shown in Fig. 2(b) and (c) in which an exponential decrease in absorbance with time corresponding to the extreme zones of pH can be observed. This decrease is more important in the acidic zone owing to the higher rate at which the hydrolytic degradation of this azine occurs.Once these corrections have been made the absorbance versu 1378 ANALYST NOVEMBER 1984 VOL. 109 0.60 b’ 8 p 0.58 -0.56 -n Q 0.54 0.52 m 0, --I I I I 0.096 8 0.094 e 0.092 n C m Z J a 0.090 \ pH = 12.2 0.088 I I I I 1 2 2 4 6 8 Timeimi n Fig. 2. (a) Absorbance - pH curve for 6-methylpicolinaldehyde azine and ( h ) and (c) influence of the hydrolytic cleavage of the C=N group on the determination of acid - base constants of 6-methylpico-linaldehyde azine. ( b ) Acidic hydrolysis; and (c) alkaline hydrolysis pH graph shows a single pK due to the single acid - base equilibrium: H L e L - + H+ It proves to be more advisable to carry out the calculation of the pK of unstable ligands in solution by the flow injection analysis (FIA) technique which is very much faster.20 FIA permits measurements to be taken immediately after reagent -acid (or base) mixing in such a manner that in most situations the hydrolysis process is not developed to any appreciable extent.Determination of Metals Ions Acting as Catalysts in Hydrolysis Reactions This is an example in which the hydrolytic degradation of the ligand proves useful as it is the basis for the determination of metal ions acting as catalysts in the reaction. It is a special catalytic effect because the catalyst does not change its oxidation state during the catalytic cycle,21 but its action involves the weakening of the hydrolysable bonds in the molecule by the formation of complexes or chelates. There is some literature available concerning this type of reaction the most studied examples being those concerning the hydrolysis reaction of amino acids or esters of phosphoric acid deriva-tives.22-24 Amongst the metal ions that exhibit a catalytic effect on these compounds Cu(II) Zn(I1).Mn(I1) and Cd(I1) are the most important. Other species involved in these hydrolysis degradation reactions catalysed by metals are for example thioesters and Schiff bases.ls For instance the hydrolysis of 2-hydroxybenz-aldehyde azine is discussed. This reaction takes place slowly at pH 12 (basic hydrolysis) in which the corresponding hydraz-one and 2-hydroxybenzaldehyde are formed and the fluores-cent properties of the solution change from A, = 420 nm and A, = 520 nm to A, = 355 nm and A,, = 465 nm with a remarkable increase in the fluorescence intensity.If trace amounts of copper(I1) (i.e. [copper] [azine] 2 1 1000) are added to alkaline solutions of 2-hydroxybenz-aldehyde azine the hydrolysis rate is greatly increased because this metal ion forms a chelate with the ligand. As copper(I1) is a charge inductor the nitrogen of the chelate ring bears a residual positive charge which is displaced to the carbon adjoining the C=N group. Because of this effect the hydrolysis reaction cannot be carried out in an acidic medium as the positive polarisation of the C=N bond prevents the electrophilic attack of the hydrogen ion. This polarising effect of the catalyst produces an electrophilic site in the molecule, which is easily attacked by the hydroxide ion.Therefore the hydrolytic reaction rate is increased with respect to the reaction in the absence of the metal ion which permits the development of catalytic - kinetic method for the determina-tion of trace amounts of copper.26 The reaction mechanism is shown in equation (2) on the opposite page. This reaction proceeds to the extent that the concentration of 2-hydroxybenzaldehyde hydrazone formed in the catalysed reaction is higher than the remaining concentration of 2-hydroxybenzaldehyde azine. In this example the chelate between copper(I1) and hydrazone prevents the reaction of this metal ion with the azine and therefore the catalytic cycle is prevented. The catalytic action of copper in this hydrolytic reaction is in disagreement with the study carried out by Bozhevol’nov et al.,*7 who pointed out that the reaction between copper(I1) and 2-hydroxybenzaldehyde azine corresponds to the forma-tion of a fluorescent chelate rather than to a catalytic reaction. From our point of view the fluorescence measurements at 490 nm that have been reported by Bozhevol’nov et al. correspond to a reaction stage in which 2- hydroxybenzaldehyde azine is being partially hydrolysed to 2-hydroxybenzaldehyde hydra-zone. It is interesting to note that when the pH was adjusted with amine bases the reaction rate sharply increased and the catalytic effect of copper(I1) was not detected. The enhance-ment of the reaction rate in the presence of amine bases could be assumed to be due to interchange reactions of C=N groups, according to the following reaction: The analytical scope of these reactions for the kinetic determination of amine bases and for those of the metal ions, due to their effects on these reactions is expanded in the following section.Interchange Reactions of C=N Groups ‘There are some types of reactions that have already been described28 and applied to the synthesis of metal chelates,29 but which we have shown to be a cause of ligand instability, i.e. the transformations that some organic reagents ligands or chelates can undergo in the presence of several different amines. In the interchange reactions of C=N groups an azomethinic ligand [ligand (l)]. with one or several groups of thi5 type (Schiff bases for example) undergoes a change in the presence of an excess of amine which is added to the solution to transform it into another azomethinic ligand [ligand (2)], but with a net change of the group R3 by another group R4 as follows”: RlR2C=NRj + RjNHz -+ RIRzC=NR4 + RiNH2 Ligand 1 Amine 2 Ligand 2 Amine ANALYST NOVEMBER 1984 VOL.109 1379 Lex = 420 nm kern = 520 nm r OH- [Azinel << [Hydrazone] Aex. = 355 nrn kern. = 465 nm I Table I Transformations due to interchange reactions of C=N groups with four different amine 2 compounds (ammonia hydroxylamine, hydrazine and thiosemicarbazide) Ligand 2 Ligand 1 Ammonia Hydroxylamine Hydrazine Thiosemicarbazide Azine . . . . . . Hydrazone Oxime Hydrazone Thiosemicarbazone Hydrazone . . . . Hydrazone Oxime Other hydrazone Thiosemicarbazone Oxime .. . . . Hydrazone - Hydrazone Thiosemicarbazone Thiosemicarbazone . . Hydrazone Oxime Hydrazone -These reactions take place at a moderately high rate in an aqueous medium at a suitable pH provided an excess of amine 2 is added. The transformations that we have verified are given in Table 1. These transformations are very interesting from an ana-lytical point of view in the presence of transition metal ions, which form chelates that have different properties with ligands 1 and 2. The following behaviour must be taken into account when considering these reactions. (i) The metal ion also reacts with amines 1 and 2. Undoubtedly this can complicate the system as these amines can also form complexes (soluble or not) with the cation competing with the main ligands or form mixed-ligand complexes or reduce the cation to an oxidation state which may or not be suitable for chelate formation.(ii) R3 does not take part in the formation of the chelate with the initial azomethinic ligand. Its replacement by R4 can give rise, for exampIe to a change in the chelate solubility a change in the absorption spectra of the chelate-batho- or hypso-chromic shifts depending on whether the conjugation of the bond system increases or decreases and a change in the selectivity as the steric effect may undergo a change either making possible or hindering the tris-chelate formation on transposing R3 by R4. (iii) R3 has some active “sites” in the formation of the first chelate so that its replacement by R4 may involve a cleavage of the chelate ring and therefore a fundamental change.R4 can have or not have acidic or basic groups with differences in activity or position which can either favour or hinder the transformation. Some of our experiments in this area are discussed below. Improper Use of Amines as Prior Reducers Hydroxylamine and hydrazine are frequently used as prior reducers in the photometric determination of some metal ions such as iron(I1) and copper(I) which has allowed us to describe the interchange reactions of C=N groups in the presence of metal ions. Suggi et al.32 reported the photometric determination of iron(I1) with PAA using hydroxylamine as a prior reductant. However we have demonstrated” that they did not work with the original azine ligand which forms an unstable reddish (Amax = 485 nm) ferroin-type [Fe(PAA)3] chelate with iron(II) but that the real ligand was picolinaldehyde oxime, which also produces a yellow 1 3 metal to ligand chelate (Amax.= 420 nm). This is the suggested wavelength for the photometric method. Suggi et al.32 indicated that to achieve the fast stabilisation of the absorbance values it is necessary to heat for 20 min at 40-50 OC with addition of azine in a very large excess above the stoicheiometric amount. All of these experimental data indicate the occurrence of the following interchange reactions of C=N groups: Reducer 3L + Fe2+ - Fe3+ - FeL32+ Red chelate Hvdroxvlamine i 3L + Fez+ - Fe3+ - 3L’ + Fez+ -+ FeL’32+ (or hydrazine) Schiff base 1 Schiff Red base 2 chelate Diacetyl Monoxime Azomethinic Derivatives - Hydroxylamine Systems Diacetyl monoxime hydrazone (DMH) semicarbazone (DMS) and thiosemicarbazone (DMT) undergo respective interchange reactions of their C=N groups upon treatment with an excess of hydroxylamine in an acidic medium, dimethyl glyoxime (DMG) being formed in situ as a result.If palladium(I1) is present in the reaction medium these reac-tions serve as a basis for the homogeneous precipitation of palladium dimethylglyoximate as well as for the subsequent gravimetric determination of micro-amounts of this metal DMT is an exception and although it undergoes inter-change reactions of the C=N groups with an excess of hydroxylamine in acidic medium the formation of very stable soluble complexes between thiosemicarbazide DMT and palladium(I1) hinders the formation of Pd(DMG)*.The kinetic study of these systems has permitted the establishment of reactivity sequences related to the ease of formation of dimethyl glyoxime in solution from the i0n.3 1380 ANALYST NOVEMBER 1984 VOL. 109 Table 2. Influence of some metal ions on the 6-MePAA - amine systems Effect of metal ion Type of transformation* Metal ion pH E,/kJ mol- on reaction rate 6-MePAA into 6-MePAO . . Cu(1) 4.5 33.56 Slight enhancement 6-MePAA into 6-MePAH . . Cu(1) 4.5 52.50 Moderate delay 8.6 31.60 Slight delay 6-MePAA into 6-MePAT . . Cu(1) 4.5 45.39 High delay Ni(I1) 4.5 36.70 Moderate delay Co(I1) 4.5 12.58 Moderate enhancement * 6-MePAA = 6-methylpicolinaldehyde azine; 6-MePAO = 6-methylpicolinaldehyde oxime; 6-MePAH = 6-methylpicolinaldehyde hydrazone; and 6-MePAT = 6methylpicolinaldehyde thiosernicarbazone.aforementioned azomethinic compounds. In addition this study allows a definite mechanism for these reactions to be hypothesised which is similar to that of hydrolysis reactions or Schiff base formation.31 6-Methylpicolinaldehyde Azine - Amine Systems in the Presence of Metal Ions 6-Methylpicolinaldehyde azine (6-MePAA) undergoes inter-change reactions of its C=N groups in the presence of amines such as hydrazine hydroxylamine and thiosemicarbazide , yielding the corresponding azomethinic derivative. The influ-ence of several metal ions on these systems is shown in Table 2. From these observations some interesting conclusions can be drawn the maximum reaction rate is obtained for moderately acidic pHs (about pH 4.5); copper(1) is the most important metal ion because of the presence of the cuproin group in the azomethines involved; the azine - thiosemicarba-zone transformation is special as the azomethine obtained, although bearing the cuproin group does not show selectivity towards copper(1).In the mechanism by which the transformation takes place three steps can be established (1) protonation of the azomethinic compound; (2) nucleophilic attack of the amine molecule on the protonated azomethinic compound followed by an internal rearrangement of a proton; and (3) formation of the second amine followed by deprotonation. The role of copper(1) (the only cation forming complexes with the azine molecule) in this system is specifically to facilitate the formation of the initial carbocation which most readily reacts with the C=N group that participates in the coordination.As can be observed this effect is similar to that indicated for the hydrolytic degradation of the 2-hydroxy-benzaldehyde azine catalysed by copper(I1). In contrast, nickel(I1) and cobalt(I1) ions do not form complexes with the azine but they do form them with the thiosemicarbazone, which accounts for the great rapidity of the azine - thiosemi-carbazone interchange in the presence of these metal ions a behaviour that is more marked in the presence of cobalt(I1) as the pH at which the interchange reaction occurs is the optimum for the formation of the Co(I1) - 6-MePAT com-plex.3435 The different reaction rates with which these chelates are formed by their respective interchange reactions of C=N groups permits the application of differential kinetic analysis methods to the resolution of mixtures of these cations. The interference of EDTA in these systems permits their determi-nation as well as the indirect determination of zinc(I1) and bismuth(II1) on the basis of the different stability of the NiYZ- ZnY2- and BiY - complexes and on the displacement effected by zinc(I1) and bismuth(II1) cations on nickel(I1) complexed with EDTA. 2-Hydroxybenzaldehyde Azine - Amine Systems The use of interchange reactions of C=N groups in the 2-hydroxybenzaldehyde azine (2-OHBAA) - amine systems Table 3. Features of the kinetic - fluorimetric determination of amines based on interchange reactions of C=N groups EJkJ System pH mol-1 Determination rangeh 2-OHBAA - NH3 .. 10.5-10.9 46.98 5 X 10p3-3 X 2-OHBAA - NHZNHZ 10.5-10.8 30.01 2.5 X 10-5-6 X 10-3 2-OHBAA-NHZOH . . 10.6-11.0 27.75 1 X 10-3-1 X 10 - 2 2-OHBAA -NH2NHCSNH2 . . 10.8-11.1 23.41 5 X 10-‘-1 X lo-’ has permitted the direct kinetic - fluorimetric determination of amines.35 As we have indicated above these reactions can be used for the determination of copper(I1) by its catalytic effect on the hydrolysis of 2-hydroxybenzaldehyde azine.26 The action of various amines such as ammonia hydrazine, hydroxylamine and thiosemicarbazide has been studied. Table 3 summarises the most important features of these determi-nations. The different kinetic behaviour of each of these C=N interchanges has permitted the simultaneous determination of hydrazine - hydroxylamine ammonia - hydroxylamine and ammonia - hydrazine mixtures.In this section it is worth mentioning the behaviour of 2-hydroxybenzaldehyde hydraz-one in solution a common product resulting from the interchange reactions of C=N groups in acidic medium. This behaviour can be used for the determination of the acidity constants of this compound as below pH 4.5 fluctuations in the measurement made (fluorescence intensity or absorb-ance36) are observed. The process corresponds to an auto-transformation of the hydrazone resulting from an inter-change reaction of the C=N groups into the corresponding azine as is shown in the following scheme: pH < 4.5 I The mechanism by which this reaction and other similar reactions take place has been reported by Szmaut and McGinnis.37 References Flaschka H.A. and Barnard A. J . “Chelates in Analytical Chemistry,” Volume 2 Marcel Dekker New York 1969. Holzbecher Z . Divis. L . Kral M. Sucha L. and Vlacil F., “Organic Reagents in Inorganic Analysis,” Wiley New York, 1976. Shilt A. A. “Analytical Applications of 1 ,lo-Phenanthroline and Related Compounds,” Pergamon Press Oxford 1969 ANALYST NOVEMBER 1984 VOL. 109 1381 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15, 16. 17. 18. 19. 20. 21. 22. Burger K. “Organic Reagents in Metal Analysis,” Pergamon Press Oxford 1973. Jungreis E . and Thabet S . “Chelates in Analytical Chern-istry.” Volume 2 Marcel Dekker New York 1976 chapter IV.Luque de Castro M. D. and Valcarcel M. Afinidad 1977, 348. 405. Garcia-Vargas M. and Valcarcel M. An. Quim. 1980 76, 471. Luque de Castro M. D. Valcarcel M. and Pino F. An. Quim. 1976 72 382. Martinez M. P. Valcarcel M. and Pino F. Analyst 1975, 100 33. Luque de Castro M. D. Garcia-Vargas M. and Valcarcel, M. Quim. Anal. 1982 1 1. Luque de Castro M. D. and Valcarcel M. Anal. Lett. 1978, 1 1. Linstrom F. and Milligan C. W. Anal. Chem. 1967,39,132. Silva M. and Valcarcel M. Analyst 1980 105 193. Silva M. and Valcarcel M. An. Quim. 1980 76 129. Silva M. and Valcarcel M. Microchem. J. 1980 25 289. Silva M. and Valcarcel M. Microchem. J. 1980 25 117. Green R. W. Hallman P. S . and Lions F.Znorg. Chem., 1964,3 376. Green R. W. Hallman P. S . and Lions F. Znorg. Chem., 1964 3 1541. Valcarcel M. Perez-Bendito D. and Pino F. inf. Quim. Anal. 1971 25 1. RGiiCka J and Hansen E. H. ”Flow Injection Analysis,” Wiley New York 1981. Bontchev P. R. Talanta 1970 17 449. Kroll H. J. Am. Chem. Soc. 1952 74 2036. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. Tikhonova L. P. and Yatsimirskii K. B. Zh. Neorg. Khim., 1966 11 2259. Yatsimirskii K. B. and Tikhonova L. P. Zh. Neorg. Khim., 1965 10 2070. Fernando Q. Ad. Inorg. Chem. Radiochem. 1965,7,234. Alarcon R. Silva M. and ValcBrcel M. Anal. Lett. 1982, 15 891. Bozhevol’nov E. A. Kreongol’d S. U. and Sovenkova L. I., Tr. Vses. Nauchno Zssled. Znst. Khim. Reakt. Osobo Chist. Khim. Veshch. 1967 30 176;Anal. Abstr. 1968 15 3806. Zymalkowski F. Editor “Methodicum Chimicum. C-N Compounds,” Volume 6 Academic Press New York 1975. Martin D. F. “Metal Complexes of Ketimine and Aldimine Compounds,” in Jolly W. L. Editor “Preparative Inorganic Reactions,” Volume 1 Wiley-Interscience New York 1964. Valcarcel M. and Pino F. Talanta 1973 20 224. Patai S. “The Chemistry of the Carbon-Nitrogen Double Bond,” Interscience London 1970 p. 81. Suggi A. Dan M. Inone Y. and Nakamura H. Bunseki Kagaku 1965 16 1133. Rios A. and Valcarcel M. Analyst 1982 107 737. Rios A. PhD Thesis University of Cordoba 1983. Rios A. and Valcarcel M. Quim. Anal. 1983 1 227. Alarcon R. Thesis University of Cordoba 1982. Szmaut H. H. and McGinnis C. J. Am. Chem. SOC. 1950, 72,2890. Paper A41100 Received March 15th 1984 Accepted April 16th 198

ISSN:0003-2654    

DOI:10.1039/AN9840901375

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1984, VOL. 109 1383 Instability of Analytical Ligands in Solution Part 11.* Redox Reactions, Molecular Aggregate Formation Reactions and Photochemical Reactions A Review Maria Dolores Luque de Castro, Manuel Silva and Miguel Valcarcel Department of Analytical Chemistry Faculty of Sciences, University of Cordoba, Cordoba, Spain Summary of Contents Introduction Redox reactions instability of conventional ligands Catalytic oxidation Ligand as an internal reductant Formation of molecular aggregates Dyes with an o,o'-dihydroxyazo group Triphenylmethane derivative dyes Photochemical reactions Photoredox reactions Syn - anti photoisomerisation Keywords: Review; instability of analytical ligands; redox reactions; formation of molecular aggregates; photochemical reactions Introduction In Part I1 we explained the causes of the instability of analytical ligands in solution and emphasised why this behaviour has not been studied in depth in the literature, but instead has been avoided by using an excess of the unstable ligand in the experimental procedure for the determination of a metal ion.In that paper, hydrolysis and C=N group interchange reactions were discussed with typical examples, taking into account the advantages and/or disadvantages of these reactions in analytical chemistry. In this paper, redox and photochemical reactions, as well as the self-association of dyes in aqueous solution, are discussed. This behaviour can be very advantageous in some situations as instability of the ligand may result in a change in the solution species closely related to an enhancement of the selectivity and sensitivity of the analytical method.The effect of temperature is another well known cause of ligand instability in solution and, therefore, will not be discussed in this paper. However, the effect of light, although also well known, is dealt with in this paper only in those instances in which it is the basis of or is advantageous to a particular analytical technique. Redox Reactions Redox reactions in which organic ligands are involved have been frequently studied. Their importance is due to the reducing character of these compounds and, therefore, it is common to find studies of their behaviour described in the literature; however, we have chosen to present less studied reactions in this paper. These reactions have been studied from the two following aspects, which we consider to be of interest to the analytical chemist: the study of the sources of their instability and therefore methods of incorporating simple modifications to the procedure that will remove the source; and the use of the side reactions as the basis of an analytical method.Some characteristic examples are discussed. * For Part I o f this series, see p. 1375 The instability of some well known ligands in analytical chemistry, such as dithiocarbamates, dithizone, cupferron and their derivatives, has already been studied and, therefore, their half-lives have been reported, either as a function of pH or as a function of initial concentration in solution. Instability of Conventional Ligands The change with time of solutions of dithizone (a ligand with a thiocarbonyl group that is easily oxidised) from green to yellow, accompanied by a decrease in its ability to form chelates with metal ions, is widely known.This decomposition increases with increasing pH and temperature and is acceler- ated by aeration or by exposure to light.2 Further, several metal ions act as catalysts in this decomposition and, therefore, the addition of masking agents such as EDTA or reducing agents such a5 hydroxylamine and sulphurous acid avoid the instability of carbon tetrachloride and chloroform solutions of dithizone, as does storage in the dark at S "C. This process is accompanied by a number of decomposition products, depending on the oxidising agent, and the experimental conditions used.These products have been confirmed by several experimental methods and are produced under the following conditions. (i) With mild oxidants such as dissolved oxygen, dehydrodithizone (mesoionic compound) is obtained. Its absorption spectrum changes with the solvent, from A,,, = 480 nm in ethyl acetate to A,,, = 380 nm in water or 1 N hydrochloric acid. (ii) With iodine, a disulphide [bis-( 1 ,S-diphenylformazan-3-y1) disulphide] is formed. This yellow compound (h,,, = 392 nm) undergoes spontaneous thermal fission by a first-order reaction to yield an equimole- cular mixture of dehydrodithizone and the parent dithizone. Therefore, the chelating ligand is partially recovered. (iii) With stronger oxidants such as alkaline solutions of concen- trated hydrogen peroxide, a sulphonic derivative is formed that gives yellow solutions in water (A, = 440 nm) and red - violet solutions in concentrated perchloric acid (h,,,, = 540 nm).( i v ) With concentrated mineral acids or heated glacial acetic acid a different oxidation product is obtained. This is a bicyclic compound, 3-phenylazobenzo-l,3,4-(4H)-1384 ANALYST, NOVEMBER 1984, VOL. 109 thiadiazole, whose structure has been confirme4 by X-ray crystallography. These decompositions are accelerated by light and temper- ature and, in general, a mixture of these compounds is obtained as a result. Dithiocarbamates such as sodium diethyl dithiocarbamate (DDTC) or ammonium tetramethylene dithiocarbamate (ammonium pyrrolidine dithiocarbamate; APDC) are widely used in analytical chemistry,3 mainly for the complexation - extraction of trace amounts of metal ions from aqueous solutions.However, the instability of these solutions is known to cause many problems in analyses. There are two reasons for this decomposition. Dithiocarbamates are easily oxidised by dissolved oxygen or by oxidants such as iodine and hydrogen peroxide yielding thiuram disulphide: R=N_C/S Oxidant b R \ ,N-c-S-S-C-N / R R ‘ S - R II II ‘R S S These species can undergo an irreversible decomposition in which the corresponding thiuram monosulphide and elemen- tal sulphur are obtained.4 This behaviour is also observed for several metal dit hiocarbamates.5.6 Another cause of the instability of these compounds in solution is closely related to the pH.Thus, two different reactions take place when acid is added to dithiocarbamate solutions: R\N-C@S + H + d R, ,N-C Hs R’ ‘ S - R ‘SH Fast R \ ,N-CHs + H’ __+ R R>AH~ + CSZ Slow R ‘SH The instability of metal dithiocarbamates is due to the second reaction, because even after extraction into organic solvents, if trace volumes of the aqueous phase are still present , decomposition occurs.7~8 Cupferron (ammonium N-nitroso-N-phenylhydroxy- aminate) and its derivatives are used as ligands for the separation and determination of metal ions in chemical analyses.9 Their acidic solutions are unstable with time and, according to Grigorovich et al. ,lo their decomposition corre- sponds to an autocatalytic process yielding nitrosobenzene. This reaction has an induction period, closely related to the pH, from 8 to 40 min with a pH change from 1.2 to 2.0.Further, nitrosobenzene is unstable in acidic media and undergoes some changes, as indicated by the change in colour of the solution, which becomes dark after 1-2 d, and by the change in its spectrum. This process can be attributed to an aldol - crotonic condensation.11 Because trace amounts of metal ions catalyse these decompositions, the purity of the cupferron solutions is fundamental in order to avoid degrada- tion. Catalytic Oxidation Redox reactions have also been studied as a basis for analytical determinations. Thus, the oxidation of photometric ligands allows the development of selective and sensitive kinetic methods for metal ions when they act as catalysts in redox reactions.Some typical examples are decribed below. Kojic acid [5-hydroxy-(2-hydroxymethyl)-4Zf-pyran-4-one] forms stable chelates with different metal ions12J3 and has been used for the photometric determination of iron.14 Although its different forms in solution do not show fluores- cence, Murata and Ujiharals reported the fluorimetric deter- mination of gold(II1) with this reagent in a weakly acidic medium. They assumed that the kojic acid - Au(II1) reaction corresponded to a chelation reaction. However, later studies have shown that the reaction is an autoxidation process of kojic acid catalysed by gold(III).l6 This behaviour has been confirmed by comparing the spectral identity of a solution of kojic acid in the presence of gold(II1) with the same solution after its oxidation with potassium peroxodisulphate.The 2,2-dipyridyl ketone hydrazone is oxidised by the dissolved oxygen in an acidic medium in the presence of trace amounts of copper(I1) or mercury(II), which act as catalysts. This reaction, shown in equation (l), yields a product with an intense blue fluorescence (hex, = 349 nm, hem. = 435 nm) that enables the reaction to be monitored. Fluorimetric reaction- rate methods can then be established for the determination of these cations. 17 N I NHZ N=N kex. = 349 nm, kern, = 435 nm Similar reactions such as the kinetic - fluorimetric determi- nation of gold(III), cobalt(II), platinum(1V) or titanium(IV), which catalyse the self-oxidation of substituted azines and hydrazones, can be included in this field.18 Phthalimide dithiosemicarbazone forms an orange complex with osmium(VII1) (Amax. = 450 nm), used for the photometric determination of trace amounts of osmium.1’ However, if this reagent is oxidised with cerium(1V) an oxidation product (Amax.= 400 nm) is produced with a greater molar absorp- tivity. In addition, this reaction is also catalysed by osmium- (VIII), which has enabled this metal ion to be determined at a level 20-fold smaller than the photometric method.19 This behaviour is noteworthy because a single metal ion forms a complex and catalyses the oxidation of the same organic ligand. In this example, the side reaction is the basis of a new analytical method and, therefore, the lability of the ligand is not a negative factor in the analytical technique. The reducing character of ligands can be also used in order to improve the conditions of the photometric analytical method.Thus, when a metal ion in an unstable oxidation state forms chelates with an organic ligand, this ligand can be used as an internal reductant in these reactions. Ligand as an Internal Reductant Solutions of iron(I1) (partially oxidised) or copper(I1) are used in the Fe(I1) - ferroin or Cu(1) - cuproin systems, respectively. Thus, it is necessary to add a prior reductant such as hydroxylamine, hydrazine or ascorbic acid in order to reduce iron(II1) to iron(I1) or copper(I1)) to copper(1). However, several ligands can act as prior reductants of trace amounts of these metals ions and, therefore, the addition of an external reductant becomes unnecessary.It should be noted that hydroxylamine and hydrazine cannot be used as reductants in these reactions because these species give rise to the corre- sponding interchange reactions of C=N groups already re- ported in Part 1.1 An example of these reactions is exhibited by the Cu(I1) - 6-methylpicolinaldehyde azine system shown in equation (2), with which the data obtained for the photometric determi- nation of copper are the same as when ascorbic acid or a suitable azomethine compound is used as the reductant.20 This behaviour can be displayed by Job plots, which are shown in Fig. 1. In the presence of the reductant, the stoicheiometric metal to ligand ratio is 1 : 2, in agreement with other cuproin complexes. However, when the reductant is not added to copper( 11) - azine solutions, the stoicheiometric metal to ligand ratio is 1 :2.5, although the spectral properties areANALYST, NOVEMBER 1984, VOL.109 138: 0.6 0.5 a, CII 0.4 ? 2 2 0.3 0.2 0.1 0 0.2 0.4 0.6 0.8 [Cu+li(~Cu+l + [Ll) Fig. 1. complex in (A) the presence and (B) the absence of ascorbk acid Composition of the Cu(1) - 6-methylpicolinealdehvde azine identical in both instances. Hence, we can assume that 0.5 mol of ligand effects the reduction of copper(I1) to copper(1). Because the ligand can exist in several resonance forms (including the azo form) in solution, its transformation into an azoxy compound can be assumed because of its extensive conjugate bond structure: -N=N-+H20 =-N-N- +2H+ + 2e- 1 0 The instability of ligands due to their reduction in solution has been less studied than that due to their oxidation, being a less important instability factor when new analytical methods are established.In general, these reactions have been deve- loped with stronger chemical reductants such as titanium(II1) or chromium(I1) as well as by electrochemical methods. Formation of Molecular Aggregates Several bulky organic compounds, frequently termed dyes, are used in analytical chemistry as metallochromic indicators or as photometric ligands.21-23 Their well known instability in solution necessitates the use of freshly prepared solutions, to which inert salts or additives in solvent mixtures are added in order to extend their usable time. \ ' ' ,' CUI 2 + . . . . (2) The cause of this instability is probably the self-associatior of these dyes by formation of charge-transfer complexes, a these compounds simultaneously contain both activating electron-releasing groups (NH2, OH, OR and NR2) an( deactivating, electron-withdrawing groups (NO2, COOH COOR, S03H, CN and CONH2).These groups confer on thi molecule a residual negative (ti-) or a positive (a+) charge respectively. Thus, charge-transfer complexes are formec between two or more molecules. This reaction, labelled as I self-association, aggregation or polymerisation reaction results in the following behaviour of the dyes, which great1 changes their properties as analytical reagents: changes ii acid - base constants; full or partial hindrance to form meta chelates; formation of colloidal solutions; and precipitatio- from their solutions.Two typical examples of these reactions are discussel below. Dyes with an opDihydroxyazo Group These compounds are frequently used as metallochromi indicators in complexometry and as ligands in photometri determinations (e.g., for the determination of magnesiur with Mordant Black 11, also known as Eriochrome Black T or photometric titrations [e.g., for the determination o zinc(I1) and magnesium(I1) with EDTA with Mordant Blac 11 as indicator]. Na03S \ Mordant Violet 5 (C.I. 15.679) Mordant Black 3 (C.I. 15.705) Mordant Black 11 (C. I. 14.645) 51386 ANALYST, NOVEMBER 1984, VOL. 109 The Solochrome mordant dyes readily form mole- cular aggregates in aqueous solutions and mainly in acidic media.2426 However, only the monomeric form is found in semi-organic solutions (e.g., containing less than lS0/o of dioxane).However, not all dyes show an identical tendency to self-associate. Thus, at the same pH and concentration, Mordant Violet 5 and Mordant Black 3 (Calcon) do not self-associate whereas Mordant Black 11 does. The presence of a nitro group in the molecule of Mordant Black 11 is decisive as it confers a residual positive charge on the aromatic ring, which is necessary for the formation of a charge-transfer complex with another molecule of this com- pound bearing a residual negative charge on its aromatic ring owing to the electron-releasing effect of the hydroxy group. The presence of OH and S03H groups attached to the same aromatic ring yields opposite effects; the distribution of charge is shown below.The formation of the charge-transfer complex is helped by the formation of an intramolecular hydrogen bond, which strengthens the planarity of the molecule. Therefore, self- association is higher in an acidic medium. A dimer species of Mordant Black 11 might have the following structure: Na03S The occurrence of intermolecular hydrogen bonds has been demonstrated to occur between both planes in these polymers and this strengthens the formation of the molecular aggreg- ates. Self-association can be defined in terms of the aggregation number, N , which is the ratio between the relative molecular masses of the aggregate, M , and monomeric, M,, states; N = M/M,. The aggregation number can be calculated from spectrometric27328 or polarographic29 data. Generally, for a given series of dyes, self-association increases with increasing relative molecular mass of the dye and its initial concentration.Recently, a new method for the determination of the aggregation number has been developed in our Department. This method is based on the polarographic data obtained from the diffusion intensity versus time graphs, from which the diffusion coefficient of the dye, a parameter closely related to self-association, is obtained.30 Triphenylmethane Derivative Dyes These dyes are bulky organic compounds, intensely coloured and fluorescent. At a suitable pH value, these species are present as cations as they have a quaternary nitrogen bearing a positive charge delocalised into a quinonoid structure. These compounds have been extensively used in the photometric and fluorimetric determination of both anions, such as perchlor- ate, iodide or nitrate, and cations as anionic complexes (e.g., Hg142- and CdBr42-) as these can be extracted as ion pairs in organic solvents. A typical representative of these dyes is Brilliant Green, although Rhodamine (B, 3G, 6G, etc.)31 and Crystal Violet are also worth mentioning.These compounds show a greater tendency to dimerise in the aqueous phase under the experimental conditions invol- ved in the extraction - photometric technique. Therefore, an excess of the dye must be added to the aqueous phase in order to ensure the formation of the ion pair with the monomeric form and its subsequent extraction. Thus, only about one fifth of the total Brilliant Green is available for extraction at the 10-3 M leve1.32 Photochemical Reactions Amongst the numerous changes, either reversible or not, direct or indirect, that light can bring about in organic ligands (photochromism, syn - anti photoisomerisation, photoreduc- tion, photoalkylation, photoelimination, photocyclisation, photocycloaddition, photofragmentation and photore- arrangement) only a few examples related to their influence on the development of analytical methods, such as photoredox reactions and syn - anti photoisomerisation, are discussed in this paper.Although other forms of interconversion of syn - anti isomers [such as those caused by acids, iodine, sulphur dioxide, hydrogen sulphide, mercury(I1) oxide and elemental sulphur] can be considered, only those based on irradiation, on the grounds of its interest in analytical chemistry, are dealt with here. Photoredox Reactions Light can affect the induction of a redox reaction, and the changes that occurs in one or more components of the reaction can be used as a means of monitoring the reaction.The most important instances of the oxidation of the ligand by a species obtained by radiation are the electroanalytical titrations of metal ions with EDTA - 12/1- systems. For both methods, the determination is based on the use of the 12121- redox pair as the indicator in the titration of metal ions with these aminopolycarboxylic ligands. A small excess of the ligand reduces the iodine added to the titration vessel. Thus, the potential is decreased (potentiometric titrations) or the anodic current is increased (amperometric titrations) owing to the oxidation of iodide.Light only affects iodine (absorption of a photon, h = 470 nm), according to the following reaction: 12 z I* +I* in which iodine atoms are formed, reacting with the ligand via a chain reacti0n.33~34 The end products are carbon dioxide and amine oxides. This reaction has been used as a basis for the determination of metal ions by potentiometric35 or ampero- m e t r i ~ ~ ~ - ~ * techniques. These reactions have also been studied by Woodruff et al. from kinetic39 and thermodynamic40 view points. The systems involved are represented by the following equation: x2 M2+L2- --+ M3+ + X- + r.p. where M is the iron, cobalt or manganese, X is iodine or bromine, L is EDTA or CyDTA and r.p. are the reaction products of the ligands.These systems have been used for the photometric determinaton of cobalt with an excess of ligand and halogen.41 The oxidation of cobalt(I1) to cobalt(II1) is inhibited by nitrite, probably because this anion reacts with activated iodine atoms, according to the reaction which can be used for the indirect determination of this anion. I* + NO2- I- + NO2ANALYST, NOVEMBER 1984, VOL. 109 1387 Syn - Anti Photoisomerisation The syn - anti photoisomerisation of azomethine compounds such as oximes and hydrazones has been widely used, as is shown in Padwa’s review on the photochemistry of the C=N bond.42 The most important reference to these reactions is the synthesis of the active pharmacological isomer of trans- isonicotinaldehyde oxime.43 From an analytical point of view, these photoisomerisation reactions are important because some ligand types (e.g., l-N-heterocyclic hydrazones) show different ratios of these isomers in solution and/or in their ~ y n t h e s i s .~ ~ The “anti” isomer forms an intramolecular hydrogen bond and therefore cannot act as a terdentate ligand, its complexes showing a smaller molar absorptivity as a result. The “syn” isomer can act as a terdentate ligand and its chelates show a greater molar absorptivity [e.g., the iron(I1) - pyrazinyl hydrazone of the dipyridyl ketone system] .45 For this reason, the determination of the syn to anti isomer ratio, which can be obtained by spectroscopic techniques46 (NMR or ESR) or by preparative chromatography.47 becomes especially important.The photoisomerisation of hydrazones such as pyridyl hydrazones of 2-thiophenaldehyde (TAPH) and 2-pyral- aldehyde (FHPH) can be used for the determination of metal ions. Thus, cobalt(I1) and nickel(I1) can be photometrically determined in the ranges 0.05-1.3 and 0.05-0.9 pg ml-1, respectively, if irradiated solutions of FAPH and TAPH (anti form) are used. The non-irradiated syn form of FAPH is used for the determination of palladium(I1). In the Cu(I1) - TAPH system, the anti isomer produces chelates with a stoicheiome- tric metal to ligand ratio of 3 : 1, whereas the complexes with the syn isomer show stoicheiometric ratios ranging from 2 : 1 to 3 : 1. A warp in the ligand molecule (smaller for the anti than for the syn complex) is developed in the formation of the chelate.The irradiation of the mixture accelerates the formation of this warp and the anti complex is thus enhanced. The fluorimetric determination of zinc(I1) by the syn isomer of FAPH has also been developed. In all instances, the stoi- cheiometry of the chelates has been determined after taking into account the syn to anti ratio of these isomers in solution.48 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Luque de Castro, M. D . , Silva, M.. and Valcircel, M., Analyst, 1984, 109, 1375. Irving, H. M. N. H . , “Dithizone.” Chemical Society, London, 1977. Thorn, G . D., and Ludwig, R . A . , “The Dithiocarbamates and Related Compounds,” Elsevier. Amsterdam, 1962. Brand, J . C. D., and Davidson, J . R . , J . Chem. Soc., 1956, 15. Hendrickson, A.R . , Martin. R . L., and Rhode, N. M., Znorg. Chem., 1975, 14, 2980. Tung, K. S . , and Karweik, D. H . , Anal. Chem.. 1980,52,1387. Jenne, E . A . , and Ball, J . W., At. Absorpl. Newsl., 1972, 11, 90. Subramanian K. S . , and Meranger, J. C . , Analyst, 1980, 105, 620. Majundar, A . K., “N-Benzoylphenylhydroxylamine and its Analogues,” Pergamon Press, Oxford, 1972. Grigorovich. A. Yu.. Lobanov, F. I . , and Savostina, V. M., Zh. Anal. Khim., 1971, 26, 265. Ninetsecu, K., “Organic Chemistry.” Volume 1, Izd-vo Inostr. Lit, Moscow. 1963. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42, 43. 44. 45. 46. 47. 48. Wiley, J. W., Tyson, G. N., Jr., and Stillner, G . S . . J . Am. Chem. Soc., 1942, 64, 963.Stampfli, R., and Choppin, G . R . , J . Coord. Chem., 1971, 1 , 173. McBryde, W. A . E . , and Atkinson, G . F., Can. J. Chem., 1961, 39, 510. Murata, A., and Ujihara. T., Bunseki Kagaku, 1961, 10, 497. Naik, D. V., Anal. Chim. Acta, 1979, 106, 147. Grases, F., Garcia-Sanchez, F . , and Valcarcel, M., Anal. Chim. Acta, 1980, 119, 359. Valcarcel, M., and Grases, F . , Talanta, 1983, 30, 139. Guzman, M., Perez-Bendito, D., and Pino, F., Anal. Chim. Acta, 1976, 83, 259. Valcarcel, M., PhD Thesis. University of Seville, Spain, 1972. Bishop, E . , “Indicators,” Pergamon Press, Oxford, 1972. Marczenko, Z.. “Spectrophotometric Determination o f Ele- ments,” Ellis Horwood, Chichester, 1976. Snell, F. D., “Photometric and Fluorimetric Methods of Analysis.Metals,” Parts 1 and 2, Wiley, New York, 1978. Coates, E . , and Rigg, B., Trans. Faraday Soc., 1961,57, 1637. Coates, E., Rigg, B., and Smith, D. L., Trans. Faraday Soc., 1969, 65, 3255. Malik, W. U., and Gupta, P. N., Electroanal. Chem., 1975,62, 441. Rabinowitch, E . , and Epstein, L. F . , J . Am. Chem. Soc., 1941, 63, 69. Lemin, D. R., and Vickerstaff, T., Trans. Faraday SOC.. 1947, 43, 491. Hillson, P. J . , and McKay, K. B., Trans. Faraday Soc., 1965, 61, 374. Luque de Castro, M. D., Silva, M., and Valcarcel, M., unpublished results. Haddad, P. K., Talanta, 1977, 24, 1. Fogg, A. G . , Willcox, A., and Burns, D. T., Analysr, 1976, 101, 67. Faure. J . , and Dubien, J. J . , Bull. Soc. Chim. Fr., 1967, 8, 3064. Violet, F. de, and Faure, J . , J . Chim. Phys. Physicochim. B i d . . 1972, 69, 996. Sierra, M. T., Garcia, M. S . , Sierra, M. I . , and Sierra, F.. An. Quim., 1979, 75. 517. Sanchez-Pedreno, C., Garcia, M. S., Sierra, M. T., and Sierra, M. I., An. Quim., 1980, 76, 281. Sanchez-Pedreno C., Sierra, M. T., and Garcia, M. S . , An. Quim., 1981, 77, 107. Sierra, M. T., Sanchez-Pedreno, C., Garcia, M. S . , and Martin, J . M., An. Quim., 1982, 78. 108. Woodruff, W. H . , Burke, B. A., and Margerum. D. W., Znorg. Chern., 1974, 13, 2573. Woodruff, W. H., and Margerum, D. W., Inorg. C‘hem. 1974, 13, 2578. Sierra, M. T., Garcia, M. S . , and Sanchez-Pedreno. C . , An. Quim., 1983, 79, 264. Padwa, A., Chem. Rev., 1977, 1, 39. Poziomek, E. J.. J . Pharm. Sci., 1965, 54, 333. Going, J . E . , and Pflamm, R. T., Anal. Chem., 1970,42, 1098. Schilt. A. A . , Ouinn, P. C., and Johnson, C. L., Talanta, 1979, 26, 373. Rao, C. N., “Ultra-violet and Visible Spectroscopy,” Butter- worths, London, 1967. Randerath, K., “Dunnschicht Chromatographie,” Verlag Che- mie, Berlin, 1965. Hernandez Lopez, J . M., PhD Thesis, University of Malaga, Spain, 1983. Paper A411 01 Received March 15th, 1984 Accepted April 16th, 1984

ISSN:0003-2654    

DOI:10.1039/AN9840901383

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST. NOVEMBER 1984, VOL. 109 1389 Spectrophotometric Study of the Complexation Equilibria of Yttrium(ll1) With Quinizarin Green Kamal Abdel-Rahman Idriss, Moustafa Kamal Hassan, Mohamed Said Abu-Bakr and Hassan Sedaira Department of Chemistry, Faculty of Science, University of Assiut, Assiut, Egypt The complexation equilibria of yttrium(ll1) with quinizarin green [1,4-bis(4'-methylanilino)anthraquinone] were studied spectrophotometrically in the presence of 40% dimethylformamide at 20 "C and an ionic strength of 0.1 M (NaC104). The composition, molar absorptivities, equilibrium constants and stability constants of the complexes formed were determined using graphical analysis of the absorbance curves within the pH range studied. The optimum conditions for the spectrophotometric determination of Y(III) with this reagent were established.Keywords: Yttrium(111) complexes; quinizarin green; complexation equilibria; spectrophotometry Among aminoanthraquinone derivatives, the acid - base and complexing properties of which we have studied,1-12 1,4- bis(4'-methylanilino)anthraquinone (quinazarin green, QG) has several advantages for its application in analytical che- mistry. Because of the high acidity of QG reagent compared with 1,4-dihydroxyanthraquinone,Y~13 it can be expected that the stability of the complexes of the arylamino derivative will be lower than that of the complexes of the analogous hydroxy compound (quinizarin) and also the formation of its com- plexes will be affected less by the pH of the solution. Both of these properties are favourable attributes in analytical appli- cations of QG reagent.However, no studies have yet been reported involving the complex equilibria of arylaminoan- thraquinones with metal ions. In this work, detailed studies on the complexation equilibria of QG with Y(II1) in 40% dimethylformamide (DMF) were carried out, the aim being to establish the equilibria existing in solution and to determine the basic characteristic of the complexes formed. The optimum conditions favouring the direct spectrophotometric determination of Y(1II) using QG were investigated. Experimental Reagents A stock solution of QG of concentration 2 x 10-3 M was prepared by dissolving the accurately weighed amount of the purified reagent in DMF. More dilute solutions were obtained by appropriate dilution.A 5 x 10-3 M solution of yttrium nitrate was prepared by dissolving the required amount of the AnalaR product in re-distilled water. The metal content of the solution was determined as recommended. 14 Solutions of lower concentra- tions were obtained by accurate dilution. Thiel buffer solutions consisting of boric acid, disodium tetraborate(III), succinic acid and sodium sulphate (pH 3-9) and tris(hydroxymethy1)aminomethane buffers (pH 7-9) were used for pH adjustment and were prepared according to recommended procedures.15~16 The ioiiic strength, I , of the solution was kept constant at 0.1 (NaC104). Apparatus Measurements of pH values were carried out using an Orion pH meter (M601A). The pH values in the partially aqueous solutions were corrected by making use of the equation of Douheretl7: where pH* is the corrected reading and pH(R) is the meter reading obtained in partially aqueous buffer.The absorption spectra of the solutions were recorded on a Pye Unicam SP 8000 spectrophotometer in the wavelength range 350-750 nm using 1 TI matched quartz cells. All measurements were carried out at a constant temperature of 20 "C. pH* = pH(R) - 6 Results and Discussion Acid - Base Equilibria of QG in 40% DMF The dissociation constants of QG in 40% DMF have already been determined 18 graphically from the absorbance versus pH graphs using the methods reported elsewhere.8 The absor- bance versus pH graphs for QG suggest the occurrence of different acid - base equilibria in solution. The predominant form of QG in acid solution is the cationic species, which undergoes stepwise ionisation on increasing the pH of solution.The different acid - base equilibria that may occur in solutions of QG can be represented by the scheme shown in Fig. 1. The pK, values and the corresponding acid - base equilibria are given in Table 1, together with the A,,,, values of the individual forms. The visible spectra of QG within the pH range 4-11.5 in the presence of 40% DMF are shown in Fig. 2. Complex Equilibria of Y(II1) with QG in 40% DMF Complex formation of Y(II1) with QG was examined at different pH values in equimolar solutions and solutions containing an excess of one component (cf., Fig. 3). The absorption curves reflect the formation of a complex with Amdx at 535 and 560 nm at about pH 6.2 and another complex with A,,,.at 550 and 602 nm at pH 7.6. The absorption curves of equimolar solutions (C, = CM = 3.5 X 10-1 M) and of solutions with an excess of ligand (CL2 = 4.5 x 10-4 M, CM = 1.5 x 10-4 M) are analogous. Above pH 9.5, the absorbance decreases rapidly owing to hydrolysis of the complexed ligand. In the presence of excess of metal, the hydrolysis begins at about pH 8.8. The absorbance versus pH graphs at 535, 550, 560 and 602 nm (Fig. 4) show the various ranges of formation and existence of the equilibria in solution. The ascending or descending portions of the graphs were analysed graphic- ally.19 The dependence of the absorbance of QG - Y(II1) solutions on the pH of the medium in 40% DMF at I = 2.0,l.O or 0.1 was investigated, The graphs obtained at selected wavelengths indicated the existence of two basic complexation equilibria within the pH range 5.5-8.25 that are sufficiently separated.The first complexation equilibrium, which begins at pH 6-6.5 in equimolar solutions or in solutions containing an excess of one component, probably involves complexation through interaction of Y(II1) with H,L+ or H2L forms of the ligand according to the general equation The second complexation equilibrium is attained in the pH region 7.25-8, probably as a complex transformation accord- ing to the equation where Pi and p2 are the over-ail absolute stability constants for the particular reactions. MY,+ + uLH, Y,L,H,,, - q)(3m - 4 ) + + qH+ (B1) Y,L,H, + pLHx = YrnL,, + px - q ) + qH+ (I3211390 ANALYST, NOVEMBER 1984, VOL,.109 Monoprotonated (pH 3.5-6) Orange - yellow Diprotonated (below pH 3.5) Pale yellow Non-ionic (pH 6-8.5) Orange - red Monovalent anions (pH 9-10.5) Divalent anions (above PH 10.5) Red Pink - violet Fig. 1. Acid - base equilibria occurring in solutions of QG 0.8 0.7 0.6 ar 0.5 2 a 2 0.4 0.3 0.2 0.1 17 I I I I I I 400 450 500 550 600 650 Wavelengthinm Fig. 2. Absorption spectra of 1.12 X 5 , 6.5; 6, 7.1; 7, 8.6; 8, 9.0; 9, 9.4; 10, 9.7; 11, 9.9; 12, 10.1; I!?, 10.3; 14, 10.5; 15, 10.8; 16, 11.1; and 17, 11.5 M QG at different H values in the presence of 40% VIV DMF. pH: 1, 4.0; 2, 4.5; 3 , 5.0; 4, 5.9; The number of protons (4) released during complexation and the equilibrium constant( Keq:) were determined graphic- ally from the graphs obtained with three different metal to ligand molar ratios, as follows.(a) For equimolar solutions the following equation was deduced: absorbance maximum and C, is the total metal concentration. The logarithmic dependence of this equation is a straight line with a slope q and an intercept including Keq.: A AA,2[H+]q Keq. = . . . . . . 4CM'(A,, - A)3 L J (b) In the presence of a slight excess of metal ion the (l) following equation is valid: AAo2 [H+]q Keq. = . * ( 3 ) where A is the absorbance at a given pH value, A, is the mCM'(2A, - mA) ( A , - A)'ANALYST, NOVEMBER 1984, VOL. 109 1391 where m = CL/CM <1, CL being the total ligand concentra- tion. The logarithmic transformation of this equation also gives a straight line. (c) For solutions with an excess of the ligand, the logarithmic transformation of the equation AA[H+]q .. . . . . (AA, - AA)CL2 Keq. = (4) was used. The absorbance of solutions containing an excess of reagent was corrected for the absorbance of the surplus of reagent at the same wavelength, the amount complexed being taken into account. Various pH values were employed, depending on the shape of the absorbance versus pH graph, in the range 5.5-9.8. The stoicheiometric ratios of the complexes formed were found by the method of continuous variations in equimolar solutions20 and by the molar ratio method.2’ It follows from the shape of the dependences obtained that Y(II1) does not form higher complexes even in the presence of an excess of 0.6 1 7 n 0.5 a, 5 0.4 2 0.3 e a 0.2 0.1 500 550 600 650 Wavelengthinm Fig.3. Absorption spectra of Y(II1) - QG complexes at different pH values. pH: 1, 5.55; 2,6.05; 3,6.60; 4,7.32; 5,7.74; 6,8.55; 7.8.89; 8, 9.23 ; 9,9.45; 10,9.85; and 1 1,10.05. CL = CM = 3.5 x lop4 M , I = 0.1 and in the presence of 40% DMF Table 1. pKa values and A,,,,,. of the individual forms of QG in 40% DMF PKa Lax./nm 465 (H,L+) 480 (H2L) 510 (HL-) 550 (Lz-) 5.15 (H3L+/H2L) 9.46 (H,L/HL-) 10.85 (HL-/L2-) ligand. The continuous variations graphs for C, = CM + CL = 5 X 10-4 M and I = 0.1 at pH 6.5 and 550 and 600 nm unambiguously confirm the formation of a complex with an M to L ratio of 1: 1. At pH 7.15 the position of the maxima indicates the presence of a mixture of 1 : 1 and 1 : 2 complexes, whereas the graphs obtained at pH 8.2 confirm the assumption that the sole complex present has the composition 1 : 2. According to the results of this study, the reaction of Y(II1) with QG can be represented by the following scheme: pH 5.5-7.1: Y3+ + H’L+ eYHL2+ + 2H+ K * 1 ( 2 H ) (A) Y’+ + H2L eYHL2+ + H+ K*l(H) (B) pH 7.25-8.0: YHL2+ + H2L YHL.L + 2H+ K*q2H) (C) pH 8.1-8.8: YHL.L e YL2- + H+ YL2- + H I 0 C YL*(OH)’- + H+ (D) (E) pH 3 9: By considering the values of the dissociation constants of the reagent, it can be concluded that reactions (A) and (C) or (B) and (C) represent the two basic equilibria that may exist in solutions of Y(II1) - QG within the pH range 5.5-8.2.0.5 0.4 a, V (I: (0 ? 0.3 P 2 0.2 0.1 0 / . I I I I 6 7 8 9 PH Fig. 4. Absorption versus pH graphs for the QG - Y(II1) system for different concentrations of ligand and metal.A, CL = CM = 3.5 x loP4 M; B, CL = 4.5 x 10-4 M, CM = 1.5 x 10-4 M; and C, CL = 2.0 x M, CM = 6.0 X 10 - 4 M. h = 550 nm, I = 0.1 and in the presence of 40% DMF Table 2. Data obtained from logarithmic analysis of the absorbance versus pH curves. I = 0.1 Slope G y H ) 550 565 600 550 565 600 pHrange M:Lratio nm nm nm nm nm nm 5.5-7.1 CL=CM 1.15 1.20 1.21 0.190 0.151 0.158 cL/cM=3 1.15 1.12 1.15 0.144 0.204 0.281 CM/CL = 3 2.05 2.05 -* 7.76 x 10-8 1.09 x 10-7 - * 7.25-8.0 CL=CM 1.90 1.95 1.85 1 . 3 0 ~ 10 1.38X 10 1.86X 10 c1/CMz3 1.85 1.85 1.90 1.44 X 7.41 x 10 4.16 X lo-* CM/CL= 3 1.95 1.88 1.85 1.00 X lop7 3.80 X 1 0 ~ ’ 5.01 X 1 0 ~ ’ * Values could not be determined.1392 ANALYST, NOVEMBER 1984, VOL. 109 Table 3.Stability constants (mean values) and spectral characteristics of Y(II1) complexes of QG in 40% V/VDMF, 20 “C, I = 0.1. A1 is the difference in the wavelengths of the maximum of the Y(II1) complex and that of the given acid - base form of the reagent. Values of E~~~ and Ah are valid for the 1 : 2 complex at 600 nm L a x 1 ~ m a x 1 Log Kz(yH) Log 6, Log p2 nm 1 mol-1 cm-1 AMnm -7.03* 7.57* l l . l l $ 560 4.6 x lo3 137(LH3+) -6.86$ 92(LH-) -0.731. 8.721 600 122( LHJ * According to reaction (A). -t According to reaction (B). j According to reaction (C). The results obtained indicate that reaction (A) is valid in solutions containing an excess of metal at pH <7, whereas reaction (B) is the prevailing equilibrium in equimolar solutions or in the presence of an excess of ligand at pH 6 7 .2 . The number of protons liberated in reactions (D) and (E) is determined from the interpretation of the descending bran- ches of the absorbance versus pH graphs in the pH range 8-9.8. The equilibrium constants, K;(qH), are related to the stability constants, Pn, by the expressions22 = K*1(2H) Kal-’ Ka2-’ = K* 1(H) Ka2-i P2 = PIK*2(2H) Ka2 The calculated values of the constants on and K,*, calculated from the average values determined at various metal to ligand ratios, are given in Tables 2 and 3. Effect of Buffers Thiel buffer [boric acid - disodium tetraborate(II1) - succinic acid - sodium sulphate] gave the best results. Phosphate and citrate buffers strongly interfere. At pH 7.0-8.5 a tris- (hydroxymethy1)aminomethane buffer can be employed.Effect of Ionic Strength The absorbance of the solution increases with increasing salt concentration. However, this effect is negligible in the range 1 = 0-0.2 (NaC10,); above I = 0.5 the absorbance increases sharply. Spectrophotometric Determination of Yttrium(II1) at pH 7.2-8.0 The spectrophotometric determination of Y(1II) with QG employs the complex with a molar ratio of M to L of 1 : 2 , which is formed in solution at pH 7.2-8. Optimum conditions for determining Y(I1I) are CL = 3.5 x M and pH 7.7 in 40% V/V DMF at I = 0.1. Optimum Y(1II) concentrations lie in the range 7.12-28.5 pg ml-1. The calibration graphs are linear down to 1.8 v g ml-1 at 550-600 nm. Procedure An aliquot of a standard solution of Y(TI1) containing 0.13-0.71 mg of yttrium was introduced into a 25-ml calibrated flask, then 5 ml of 1.5 X 10--? M QG solution in DMF were added.The pH was adjusted to pH 7.7, 1 ml of 0.5 M NaC104 was added and the solution was diluted to volume with doubly distilled water while keeping the concentration of DMF at 40% V/V. After thorough mixing, the absorbance was measured at 600 nm against a reagent blank similarly prepared but containing no yttrium. The system obeyed Beer’s law over the range 2 x 10-5-3 X 10-4 M of yttrium(II1). The molar absorptivity was 4.6 X 103 1 mol-1 cm-1. Ten identical samples, each with a final yttrium(II1) concentration of 1.6 x 10-4 M, were treated according to the recommended procedure and their absor- bances were measured. The mean absorbance was 0.54.5, with a standard deviation of 0.005 absorbance unit.1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22, References Idriss, K. A . , Issa, I. M., and Seleim, M. M., J . Appl. Chern. Biotechnol., 1977, 27, 549. Issa, I. M., Idriss, K. A , , and Seleim, M. M., Monarsh. Chrrn., 1977, 108, 1461. Idriss, K. A , , Seleim, M. M., and Khalil, M. M., Monatsh. Chern., 1978, 109, 1883. Idriss, K. A., Awad, A. M., and Seleim, M. M., J . Indian Chern. SOC., 1979, S O , 464. Idriss, K. A.. Issa, I. M.. and Seleim, M. M., Rev. Rourn. Chirn., 1979, 24, 555. Idriss, K. A., Seleim, M. M., and Khalil, M. M., Curr. Sci., 1979, 48, 343. Idriss, K.A., Seleim, M. M., and Abu-Zuhri. A . Z., Indian J . Chern., 1979. 17, 532. Idriss, K. A . , and Seleim, M. M., J . Chern. Technol. Biotechnol., 1980, 30, 136. Idriss, K. A., and Seleim, M. M., Indian J . Chern., 1980, 19, 771. Idriss, K. A , , Awad, A . , Seleim, M. M., and Abu-Bakr, M. S . , Bull. SOC. Chirn. Fr., 1981, 180. Idriss, K. A., Seleim, M. M., Abu-Bakr, M. S . . and Saleh, M. M . , Analyst, 1982, 107, 12. Idriss, K. A , , Seleim, M. M., Abu-Bakr, M. S., and Saleh, M. M., Indian J . Chern. , 1982, 21A, 395. Issa, I. M., Issa, R. M., Idriss, K. A., and Hammam, A . M., Indian J . Chern., 1976, 14, 117. Scott, W., and Furman, H., “Standard Methods of Chemical Analysis,” Sixth Edition, Van Nostrand, New York, 1962. Britton, H. T. S . , “Hydrogen Ions.” Fourth Edition, Chapman and Hall, London, 1952. Perrin, D. D., and Dempsey, B . , “Buffers for pH and Metal Ion Control,” Chapman and Hall, London, 1974. Douheret, G., Bull. Soc. Chirn. Fr.. 1968, 3122. Idriss, K. A., and Seleim, M. M., in preparation. Nonova, D . , and Evtimova, B., J . Inorg. Nucl. Chern., 1973, 35, 3581. Job, P . , Ann. Chirn. (Rome), 1928, 9, 113. Yoe, J. H., and Jones, H. L., Ind. Eng. Chern., Anal. Ed., 1944, 16, 111. Suchanek, M., and Sucha, L., Collect. Czech. Chem. Com- mun., 1978, 43, 1393. Paper A4180 Received February 27th, 1984 Accepted May 21st, 1984

ISSN:0003-2654    

DOI:10.1039/AN9840901389

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1984, VOL. 109 1393 Extraction Spectrophotometric Determination of Iron(ll1) With 2- H yd roxy- 1 -naphtha Ide h yde Oxi me Shigeroku Yamaguchi" and Katsuya Uesugi Laboratory of Analytical Chemistry, Himeji Institute of Technology 2167, Shosha, Himeji-shi, Hyogo, Japan A selective extraction - spectrophotometric method is proposed for the determination of microgram amounts of iron. The method is based on the formation of an insoluble iron(ll1) - 2-hydroxy-1-naphthaldehyde oxime complex, which is extractable into chloroform from an aqueous solution at pH 3.5. The iron(ll1) - 2-hydroxy-1 -naphthaldehyde oxime complex in chloroform exhibits an absorption maximum a t 580 nm with a molar absorptivity of 6.4 x 103 I mo1-l cm-l. The complex system conforms to Beer's law for up to 8 p.p.m.of iron(ll1). The method is simple in that a single extraction suffices; common ions, except molybdenum(V1) and titanium(lV), do not interfere in the determination. The method has been applied successfully to the analysis of non-ferrous alloys. Keywords: Spectrophotometry; iron(ll1) determination; 2-h ydroxy- 7-naphthaldeh yde oxime Salicylaldehyde oxime and its derivatives have attracted much attention as analytical reagents, because they react with several metal ions to give complexes that are insoluble in water. Their properties have been described by Burger and Egyed.1 Some of them have been used in gravimetric solvent extraction - spectrophotometric3-~ and flame spectropho- tometrich procedures. Nine compounds have been synthesised and used for the gravimetric determination of palladium7 and nickel8 and the extraction - spectrophotometric determination of palladium,g nickel,") copper" and cobalt.l2 This paper describes the extraction - spectrophotometric determination of iron(1II) with 2-hydroxy-1-napthaldehyde oxime (HNA). HNA reacts with iron(II1) to form an insoluble complex that can be extracted quantitatively into organic solvents, such as benzene, chloroform and 1,2- dichloroethane. The method can be successfully applied to the determination of iron in non-ferrous alloys. Experimental Apparatus Absorption spectra and absorbances were measured with a Hitachi Model 624 automatic recording digital spectro- photometer using a quartz cell of 10-mm path length. A Hitachi-Horiba Model F-7LC pH meter equipped with a combined glass electrode was used for the pH measurements.Reagents All chemicals used were of analytical-reagent grade unless stated otherwise. HNA solution. The HNA was obtained by oximation of 2-hydroxy-1-naphthaldehyde in ethanol at 0 "C with hydroxyl- ammonium chloride. The compound was recrystallised twice from a chloroform - petroleum mixture, giving a melting-point of 159-160 "C (found: C 70.44, H 4.88, N 7.31; CllH9N02 requires C 70.58, H 4.85, N 7.48%). The compound was slightly soluble in water and very soluble in virtually all organic solvents. A solution of 2.0 x 10-2 mol 1-1 in chloroform was prepared and stored in the dark. The solution was stable for several weeks. * Present address: Himeji Junior College, Shinzaike, Himeji, Hyogo 670, Japan.Standard iron(ll1) solution. A stock solution containing 1 mg ml-1 of iron(II1) was prepared by dissolving 1.000 g of pure iron by heating in 30 ml of dilute hydrochloric acid (1 + l ) , oxdising the solution with 3 ml of nitric acid, heating and boiling for 1 min and then diluting with distilled water to 1 1. This solution was further diluted as required. Buffer solution ( p H 3.5). An acetate buffer solution of pH 3.5 was prepared by mixing 0.2 M sodium acetate and 0.2 M acetic acid solutions. Procedure Transfer the sample solution containing up to 80 pg of iron(II1) into a 50-ml separating funnel. Add 1 ml of 3% hydrogen peroxide solution and adjust the pH to 3.5 with 10 ml of 0.2 M acetate buffer solution. Dilute to 30 ml with distilled water, add 10 ml of the HNA - chloroform solution and shake the mixture for 5 min.Filter the organic phase through a dry filter-paper. Measure the absorbance of the organic phase at 580 nm against a reagent blank. Results and Discussion Absorption Spectra The absorption spectrum of the blue complex formed between iron(II1) and HNA in a chloroform medium is shown in Fig. 1. I !1 350 400 450 500 550 600 650 Wavelengthhm I0 Fig. 1. Absorption spectra of HNA complexes in chloroform. Conditions as follows: (1) Fe, 50 yg,pH 3.5; (2) CU, 35 pg, pH 1.5; (3) Co, 20 yg, pH 8.8; (4) Ni, 50 yg, pH 5.8; ( 5 ) reagent blank, 0.02 M HNA in 10 ml of chloroform1394 ANALYST, NOVEMBER 1984, VOL. 109 I : 6 0.3 . 2 0.2 . 0.4 . m al LD - -e v) 0.1 . 0 2 3 4 5 PH Fig. 2. Effect of pH on absorbance.Conditions as follows: Fe, 50 pg; [HNA], 2 x 10-2 M ; 3% hydrogen peroxide, 1 ml; absorbance measured against a reagent blank Table 1. Absorption characteristics of iron(II1) - salicylaldehyde - oxime complexes. Solvent, chloroform E x 10-31 Reagent A,,, lnm 1 mol 1 cm-l Salicylaldehyde oxime (SA) . . 523 4.7 3-Methoxy-SA . . . . . . 555 5.1 2-Hydroxypropiophenone oxime 508 2.5 5-Bromo-SA . . . . . . . . 535 6.0 5-Chloro-SA . . . . . . . . 532 5.5 o-Hydroxyacetophenone oxime 5 14 3.2 2-Hydroxy-1-naphthaldehyde oxime(HNA) . . . . . . 580 6.4 PH 4.1-4.5 4.5 4.0-4.6 4.0-4.5 4.0-4.5 4.5 3 .5-5 .0 Table 2. Effect of diverse ions. Amount of Fe(II1) taken, 50 pg Amount Fe added/ found/ Ion mg Yg Al(II1) . . 5.0 50.6 10.0 50.7 Cd(I1) . . 1.0 49.4 1.0 52.7 Cr(II1) .. 0.5 50.5 1.0 52.3 1.0 50.2 Hg(I1) . . 1.0 49.4 Co(I1) . . 0.5 49.7 CU(I1) . . 0.5 51.0 Amount Fe Error. added1 found/ o/o Ion mg pg +1.2 Mg(I1) . . 1.0 +1.4 . . . . 10.0 -1.2 Mn(I1) . . 1.0 -0.6 Mo(V1) . . 0.1 +5.4 . . . . 0.2 +1.0 . . . . 1.0 +4.6 Ni(I1) . . 5.0 +2.0 . . . . 10.0 +0.4 Ti(IV) . . 0.02 -1.2 0.05 50.4 51.2 49.4 49.2 48.6 43.2 50.5 50.3 48.3 43.2 Error, Yo +0.8 +2.4 -1.2 -1.6 -3.0 - 13.6 +1.0 +0.6 -3.4 - 13.5 The iron(II1) complex has two maxima at 380 and 580 nm, whereas the other complexes have only one maximum each near 390 nm: cobalt(I1) 387 nm, copper(I1) 385 nm and nickel(I1) 410 nm. We could not find any other metal - HNA complex that showed an absorption maximum over 500 nm. Hence the maximum at 580 nm is thought to be a characteristic absorption of iron(II1).As the HNA blank shows no absorption above 480 nm, enhancement of the accuracy for the determination of iron(II1) might be expected. Effect of pH The influence of the pH of the aqueous phase on the extraction of the iron(TI1) complex was examined by measur- ing the absorbance of the organic phase at 580 nm. The final pH of each aqueous solution was measured after extraction. The results are shown in Fig. 2, from which it can be seen that a maximum and constant absorbance can be obtained over the pH range 3.3-5.5. In more acidic or more alkaline solutions, the absorbance decreased, because of the incomplete complex formation and hydrolysis of the complex, respectively. An acetate buffer solution was finally chosen and used as described under Procedure.Effect of HNA Concentration The absorbances of a series of solutions containing 50 pg of iron(II1) and various amounts of HNA in chloroform were measured. It was found that 1.5 x 10-2 M HNA sufficed for less than 80 pg of iron(II1). Hence, 10 ml of 0.02 M HNA chloroform solution were adopted in further studies. Shaking Time and Stability The shaking time for the extraction was varied from 0.5 to 20 min. The minimum shaking time for complete extraction of the complex with chloroform was found to be 2-3 min at room temperature. The absorbance at 580 nm was then stable for at least 2 h. Therefore, a 5-min shaking time was adopted in further studies. Effect of Oxidising and Reducing Agents In order to check that the reagent does not react with iron(II), 0.1-5 ml of 3% V/V hydroxylammonium chloride solution were added as a reducing agent.On addition of 1 ml of the solution we did not find any absorbance and it could therefore be deduced that HNA reacts with iron(II1) to give the blue complex. In order to ensure that iron is present as iron(III), 1 ml of 3% V/V hydrogen peroxide solution was added to the solution as an oxdising agent. Various volumes (0.1-5 ml) of 3% V/V hydrogen peroxide solution were added while the other variables were kept constant. There was no significant difference. Therefore the total iron content was determined by adding hydrogen peroxide solution. Calibration, Sensitivity and Precision The colour system obeys Beer’s law over the range 0-8.0 p.p.m, of iron(II1). The molar absorptivity and Sandell’s sensitivity for log IdI = 0.001 are 6.4 X l o 3 1 mol-1 cm-1 and 8.73 X 10-3 pg cm-2, respectively.The coefficient of variation of the absorbance for 5.0 p.p.m. of iron(1II) was 0.84%, which was determined from six measurements. The 2-hydroxy-l- naphthaldehyde oxime reagent was compared with a method using salicylaldehyde oxime and five other derivatives. From the absorption characteristics of their iron(II1) complexes presented in Table 1 it can be seen that the proposed reagent is the most sensitive for the determination of iron(II1). Effect of Diverse Ions The effect of diverse ions on the determination of iron(II1) was examined. The results are summarised in Table 2. The method is remarkably free from interferences because most of the metallic chelates of HNA in chloroform have their absorption peaks between 370 and 410 nm and their precipi- tates, which are caused by their high concentrations, are removed simply by filtering through dry filter-paper.Iron(II1) can be determined in the presence of 10 mg of aluminium(III), magnesium(I1) and nickel(T1) each without the use of masking agent, but molybdenum(V1) and titanium(1V) interfere seri- ously. Determination of Iron in Non-ferrous Alloys The proposed method has been successfully applied to the determination of iron in some synthetic solutions containing foreign ions, which were treated as Cu - A1 and A1 base alloysANALYST, NOVEMBER 1984, VOL. 109 1395 Table 3. Determination of iron(II1) in synthetic solutions Contents.* Yo Synthetic SampleNo.solution Cu Al Mn Ni 1 CU-AI 85.89 7.98 1.53 1.53 2 80.07 9.34 1.25 4.89 3 72.58 8.06 12.10 3.23 4 Al base 0.04 99.58 0.03 5 4.05 93.25 0.57 6 0.27 97.58 0.15 7 3.24 92.98 0.54 * Other metals present in samples 4-7: Zn(I1). Cr(III), Ti(1V) and Mg(I1). Fe(II1). o/o Fe 3.07 4.45 4.03 0.25 0.47 0.69 1 .OH Found Error 2.98 -2.9 4.41 -0.9 3.97 -1.5 0.26 +4.0 0.46 -2.2 0.70 +1.4 1.04 -3.7 Table 4. Determination of iron(II1) in alloys Sample Fe J IS Main No. Alloy found, YO CV, Yo method.*% constituents, YO I t Al 0.24 0.82 (n = 5) 0.24 Al. 93 2 cu 5.00 1.20 ( n = 5) 5.08 Cu, 80; Ni. 12 3 Mg 0.023 0.63 (n = 6) 0.024 Mg, 95 4 Ni-Cu 2.26 0.43 ( n = 4) 2.24 Ni. 63: Cu. 34 5 Zn 0.10 0.98 ( n = 4) 0.098 Zn, 95 * Reagents: 2, thiocyanate1-3; 3. o-phenanthrolinelj; 4, sulphosalicylic acidI5; and 5 , o-phenanthroline.’(1 t NBS standard sample 8Sb, certified iron content = 0.24%. (Table 3). The proposed method was compared with JIS (Japanese Industrial Standards) methods1-i-16 for the determi- nation of iron in real samples and in a standard sample for which the iron content was certified. The procedure for the preparation of the sample solution was as follows. A 0.5-g amount of alloy was accurately weighed and then placed in a 100-ml beaker, to which were added 20-30 ml of 6 M hydrochloric acid and 1 ml of 30% hydrogen peroxide solution for aluminium, magnesium and zinc alloys, and 2&30 ml of 6 M nitric acid for copper and nickel - copper alloys. On heating on a hot-plate, the mixture dissolved completely and the excess of hydrogen peroxide decomposed or the nitrogen oxides were removed.After cooling, the sample was diluted to 100 ml with water in a calibrated flask. An aliquot of this sample solution was taken and the proposed procedure was followed. The results shown in Table 4 are in good agreement with the certified values or results obtained by the JIS methods. References 1. Burger. K., and Egyed. l . , J . lnorg. Nucl. Chem.. 1965, 27. 2361. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Burger. K., “Organic Reagents in Metal Analysis,” Pergamon Press. New York, 1973, p. 62. Dahl, I., Anal. Chim. Acta, 1968, 41, 9. Simonsen. S . H., and Burnett, H. M.. Anal. Chem., 1955. 27, 1336. Yamamoto, Y . , Ueda, K . , and Ueda, S . , Nippon Kagaku Zasshi, 1968. 89. 288. Eshelman, H. C., and Dean. J . A , Anal. Chern.. 1961. 33, 1339. Kumagai. T., and Uesugi, K . , Bunseki Kagaku, 1980.29, 791 Kumagai. T., and Uesugi, K.. BunJeki Kagaku. 1982,31,271. Uesugi, K., and Yamaguchi, S., Bunseki Kagaku, 1972, 28. 268. Uesugi, K . , and Yamaguchi, S . . Microchem. J . , 1982. 27. 71. Yamaguchi, S.. and Ucsugi, K., Bunseki Kuguku, 1982. 31, 338. Yamaguchi, S . , and Uesugi, K . , Bunseki Kuguku, 1984, 33. 112. Japanese Industrial Standard, H 1201, 1977. Japanese Industrial Standard, H 1338, 1976. Japanesc Industrial Standard. H 1271 1962. Japanae Industrial Standard. H 11 11, 1975. Puper A411 77 Received Muy loth, 1984 Accepted Jirrie 6th, 1984

ISSN:0003-2654    

DOI:10.1039/AN9840901393

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1984, VOL. 109 1397 High-sensitivity Extraction - Spectrophotometric Determination of Iron With 34 2-Pyridyl)-5,6-diphenyl-l,2,4-triazine and Tetrabromophenolphthalein Ethyl Ester Shigekazu Tsurubou and Tadao Sakai" Department of Chemistry, Gifu College of Dentistry, 1857- 1 Hozumi, Hozumi-cho, Gifu 501-02, Japan A sensitive extraction - spectrophotometric method for the determination of iron has been developed. Iron(l1) forms a complex cation with 3-(2-pyridyl)-5,6-diphenyl-l,2,4-triazine (PDT) in aqueous solution and may be extracted into 1,2-dichloroethane (DCE) with tetrabromophenolphthalein ethyl ester (TBPE) as an ion pair at pH 5-7.5. The maximum absorbance of the extracted species occurs at 610 nm. The calibration graph is rectilinear over the range 0-0.25 p.p.m.of iron(ll) and the apparent molar absorptivity of the ion-association complex is 1.9 x l o 5 I mol-1 cm-1. The extracted species has a molar ratio of Fe(ll) : PDT : TBPE = 1 : 3 : 2. The method has been applied to the determination of iron in various sera and also to river and well waters. Keywords : Iron determination; spectrop h otom etry; 3-(2-pyridyl)-5,6-diph en yl- 1,2, 4-triazine; tetra brom o- phenolphthalein ethyl ester; serum iron Numerous reagents have been proposed for the spectro- photometric determination of iron and of these, some repre- sentative ferroin-type chromogens were selected for their high sensitivity to iron, such as l,lO-phenanthroline, 4,7-diphenyl- 1,lO-phenanthroline (bathophenanthroline),' 2,4,6-tris(2- pyridyl)-l,3,5-triazine (TPTZ) ,2 3-(2-pyridyl)-5,6-diphenyl- 1,2,4-triazine (PDT)3 and 3-(2-pyridyl)-5,6-bis(4- phenylsulphonic acid)-l,2,4-triazine (ferrozine, PDTS).4 However, the molar absorptivities of these iron complexes are only 22-28 X 103 1 moi-1 cm-1, so in order to determine a trace amount of iron it is desirable to increase the molar absorptivity.It is common to extract the ion complex into an organic solvent as an ion-association complex with some suitable counter ion in order to increase the sensitivity. If the counter ion is intensely absorbing, the extraction procedure leads to improved spectrophotometric sensitivity.5-8 In this work, an extraction - spectrophotometric method has been developed for the determination of trace amounts of iron using an ion-association complex of the Fe(I1) - PDT cation with tetrabromophenolphthalein ethyl ester (TBPE) as the counter ion.This method was applied to the determination of trace amounts of iron in sera, river waters and well waters. Extraction of the Fe(I1) - PDT cation with thiocyanate9 and perchlorate3 under various conditions has been reported. However, when using a weakly absorbing ion, one cannot expect an increase in molar absorptivity. Experimental Apparatus Spectrophotometric measurements were carried out using a Hitachi Model 556 double-beam spectrophotometer with 10-mm quartz cells. Extraction was carried out by shaking with an Iwaki Model KM shaker. A Hitachi-Horiba Model F-7 I1 pH meter with a glass electrode was used to measure the pH of aqueous phases after extraction.Centrifugation was performed with a Kubota Model KS-4000 centrifuge. Reagents All reagents were of analytical-reagent grade. Standard iron(II) solution, 1.0 g 1-1 of iron(II). A 7.0215-g mass of ammonium iron(1T) sulphate hexahydrate was dis- solved in 10 ml of 1 + 1 hydiachloric acid and diluted to 1000 ml with distilled water in a c )librated flask. * To whom correspondence should be addl*-.;sed. PDTsoEution, 5 X 10-3 M. A 0.3880-g mass of 3-(2-pyridyl)- 5,6-diphenyl-l,2,4-triazine (Dojindo Laboratories) was dis- solved in 250 ml of ethanol. TBPE solution, 3 x 10-3 M. A 0.5251-g mass of tetrabromo- phenolphthalein ethyl ester potassium salt (Nakarai Chem- icals) was dissolved in 250 ml of ethanol by heating on an electrical heater. Buffer solution, p H 6.0.A mixture of 0.5 M sodium acetate and 0.1 M acetic acid was adjusted to pH 6.0 with 1 N sulphuric acid or 1 N sodium hydroxide solution. Ascorbic acid solution, 1% mlV. This solution was prepared fresh daily. Standard Procedure Place 1 ml of sample solution containing up to 2.5 pg of iron, 1 ml of 1% mlV ascorbic acid and 10 ml of buffer solution (pH 6.0) in a 50-ml calibrated flask. After standing for 5 min, add 1 ml of 5 x 10-4 M PDT solution, 1 ml of 1.5 x 10-3 M TBPE solution and dilute with distilled water to 50 ml. Transfer the solution into a 100-ml separating funnel and shake the solution with 10 ml of 1,2-dichloroethane €or 5 min. After separation of the two layers, centrifuge the organic layer to remove droplets of water. Measure the absorbance of the extracts at 610 nm against a reagent blank or water as a reference.Results and Discussion Absorption Spectra The Fe(I1) - PDT - TBPE ion-association complex in 1,2-dichloroethane had a maximum absorption at 610 nm. The absorbance of the reagent blank at 610 nm (less than 0.03) was small enough to allow the determination of iron at this wavelength. Effect of Variables Effect of p H The effect of pH on the formation of the Fe(I1) - PDT complex in aqueous solution has been reported3 to be constant at pH 3.5-6.0. The effect of pH on the formation and extraction of the Fe(I1) - PDT - TBPE ion-association complex in 1,2- dichloroethane was examined. The optimum pH was in the range 5.0-7.5. In more acidic media (below pH 4) the formation of the ion-pair was incomplete owing to the reduction in the concentration of the TBPE anion, which has a1398 ANALYST, NOVEMBER 1984, VOL.109 pK, of about 4. In subsequent work, extraction was carried out at pH 6.0. Selection of counter ions Anionic dyes such as 2,6-dichlorophenolindophenol (DCIP), 2,6-dibromophenolindophenol (DBIP), picric acid (PCA) and resazurine(RZ) as counter ions were examined for the extraction of the Fe(I1) - PDT complex. The redox reagents DCIP and DBIP were not suitable anions in such a reducing medium. The ion associate of PCA (pK, = 1) had a lower molar absorptivity than TBPE under these experimental conditions. Also, RZ was not a suitable anion for the formation of an ion pair, as its formation requires a more alkaline medium. 10 Phthaleins such as bromophenol blue, bromocresol green, bromothymol blue and tetrabromophenol blue as counter ions were also examined for the extraction of the Fe(I1) - PDT complex under these experimental condi- tions. However, none of these phthaleins could be extracted into 1.2-dichloroethane. Reagent concentration The effect of the concentration of PDT and TBPE on the extraction of the ion-association complex was examined.It was found that the concentrations of both PDT and TBPE should be maintained at more than a 10-fold molar excess over iron(I1) in order to obtain a constant and maximum absor- bance. It was found that 0.5 ml of 1% m/V ascorbic acid gave a constant and maximum absorbance within 5 min. Shaking time and stability The minimum shaking time for complete extraction of the ion pair into 1,2-dichloroethane was found to be 1-3 min at room temperature.The absorbance at 610 nm was then stable for at least 5 h. The selection of extraction solvents for complexes with TBPE has already been reported." Calibration Graph and Sensitivity A calibration graph for the determination of iron(I1) was prepared. A good linear relationship, passing through the origin, was obtained in the iron(I1) concentration range 0-0.25 p.p.m. From this straight line, the average apparent molar absorptivity was calculated to be 1.9 X 105 1 mol-1 cm-1. The reproducibility of this method was examined for 0.25 p.p.m. of iron(I1) and the coefficient of variation was 1.3% for ten determinations. Composition of the Ion-association Complex The composition of the ion-association complex was examined by the continuous variations method.The molar ratio of PDT to iron(I1) was found to be 3 : 1. On the other hand, the molar ratio of the Fe(I1) - PDT complex cation to TBPE was found to be 1 : 2. From these results, the composition of the complex is assumed to be [Fe(PDT)3]'+[(TBPE)2]2-. Effect of Foreign Ions The effect of various amounts of foreign ions on the determination of 2.5 pg of iron(I1) per 50 ml of solution was examined under the experimental conditions used. The tolerance limit was taken as the amount that caused an error of +2% in the absorbance. The results are summarised in Table 1. Ti(IV), Ru(II), Pd(II), Co(II), Cr(VI), Cu(I1) and Ni(II), especially the last two, formed intensely coloured complexes with PDT.If necessary, these interferences can be decreased by the addition of various masking agents, as shown in Table 2. Ni(I1) and Cu(1I) can be removed by extraction with dimethyl glyoxime12 and bathocuproine,13 respectively. In these methods, 1,2-dichloroethane was used as the extraction solvent. Other masking agents such as thiosulphate, SCN- and P043- also examined but were not as effective as the ions listed in Table 2. Applications The method developed here has been applied satisfactorily to the determination of iron in various materials. Synthetic samples In order to test the accuracy of the method, recovery tests were performed on artificial mixtures and the results are summarised in Table 3. The procedure for the analysis of synthetic sample solution No. 3 is as follows.Place an aliquot of sample solution, 1 ml of 1% mlV ascorbic acid and 10 ml of buffer solution (pH 6.0) in a 50-ml calibrated flask. After standing for 5 min, add 1 rnl of 1% miV dimethyl glyoxime solution and dilute to 50 ml with distilled water. Transfer the solution into a 100-ml separating funnel and shake it with 10 ml of 1,2-dichloroethane for 5 min. After separation of the two layers, discard the organic phase, add 1 ml of 5 x 10-4 M PDT and 1 ml of 1.5 X 10-3 M TBPE solution to the aqueous phase and shake the solution with 10 ml of 1,2-dichloroethane for 5 min. Continue the determination according to the above standard procedure. Serum samples Several types of sera were analysed for iron by the proposed method and the results are shown together with those obtained by atomic-absorption spectrometry in Table 4.The serum samples were prepared as follows. Place 1 ml of serum and 4 ml of 1 N hydrochloric acid containing 10% rn/Vof trichloroacetic acid in a test-tube and shake the mixture for 20 min. After standing for 5 min, transfer the supernatant into a centrifuge tube and centrifuge for 20 min at 3000 rev min-1. Place 2.5 ml of the supernatant in a beaker, adjust the pH to about 6 with 6 N sodium hydroxide or 1 M ammonia solution and dilute to 5 ml with distilled water. River and well waters Several river and well waters were analysed directly for iron by the proposed method using standard additions and the results are compared with those obtained by the 1,10- phenanthroline14 and atomic-absorption methods14 in Table 5.The sample solution for the 1 ,lo-phenanthroline method was prepared as follows. Place 100 ml of river or well water in a 200 ml beaker, add 3 ml of concentrated hydrochloric acid, Table 1. Tolerance limits for the determination of iron. Iron(I1) concentration, 0.05 pg ml Ion or species added Amount toleratedl pg ml- Ag(I), As(III), Ba(II), Cd(II), Hg(I1). Li(I), Mg(II), Mn(II), Mo(VI), Pb(II), Se(IV), Si(IV), Sr(I1). V(V), F-, I-, Br-, sodium citrate, sodium tartrate, sodium thiogiycollate, thiourea . . . . . . . . 20 Ca(II), SCN- . . . . . . Bi(III), Pt(I1). Sb(II1) . . . . . . . . . . 5 AI(III), Sn(II), Zn(II), Zr(IV), P043- . . . . 3 15 Au(II1). W(VI), s&km'thiosuIphate . . . . 10 Cl04- . . . . . . . . . . . . . Ti (IV) . . . . . .. . . . . . . Ru(II), Pd(1I) . . . . . . . . . . . . 0. I Co(II), Cr(V1) . . . . . . . . . . . . 0.0s Ni(I1) . , . . . . . . . . . . . . . . 0.02 Cu(I1) . . . . . . . . . . . . . . . . 0.01ANALYSl', NOVEMBER 1984, VOL. 109 1399 Table 2. Tolerance limits on addition of masking reagents. Iron(I1) concentration, 0.05 pg ml-* Amount toleratedipg ml- With masking reagent (20 pg ml-1) Ion Ti(1V) Ru(I1) Pd(I1) Cr(V1) Ni(I1) Co(I1) Cu(I1) Without Thiogly- masking agent collate Thiourea Citrate . . 0.5 1 .0 3.0 3.0 . . 0.1 3.0 0.5 . . 0.1 1 .0 0.3 . . 0.05 0.1 . . 0.05 0.5 . . 0.02 . . 0.01 *A, Extraction with dimethyl glyoxime; €3, extraction with bathocuproine. ~ Tartrate F- I- Br A* B* 0.5 0.5 0.3 0.5 0.5 0.1 0.1 0.1 0.1 0.1 0.1 3.0 3.0 40.0 5 .0 -~ Table 3. Determination of iron in synthetic samples With masking reagent Without masking reagent Ions added and Sample concentration/ Found/ Recovery, 'YO * Found/ Recovery, YO" 1 Fe(2.5), Ti( lSO), Thiourca (20 yg ml-1) 2.47 98.7 2.17 87.1 2 Fe(2.5), Ru(50), Sodium thioglycollate 3 Fe(2.5), Ni(1000), Extraction with solution No.yg per 50 ml Masking reagent added yg per 50 ml yg per 50 mi Pb(500), Bi(250) Pd(25), Pt(250) (20 pg ml 1) 2.48 99.4 3.97 158.7 Cr(2.5), Co(2.5) dimethyl glyoxime 2.47 98.9 -t -1- * Mean values of three determinations. t Scale out of range. Table 4. Determination of iron in sera Iron contentipg ml-1* Serum Proposed method AASt Human . . . . 1.72 1.70 Goat . . . . 1.70 1.65 Horse . . . . 3.00 3.06 Chicken . . . . 1.51 1.55 Calf . . . . 1.28 1.30 * Mean values of three determinations. t Atomic-absorption spectrometry.Table 5. Determination of iron in river and well waters Iron contentiyg ml- I * Sample Proposed l,l0-Phenanthroline Sample No. method method AAST Riverwater . . 1 0.033 0.030 0.031 2 0.042 0.042 0.041 3 0.070 0.071 0.070 Wellwater . . 1 0.024 0.023 0.022 2 0.009 0.01 1 0.008 3 0.064 0.065 0.064 * Mean values of three determinations. t Atomic-absorption spectrometry. boil the solution on a hot-plate until the volume is reduced to 30-40 ml, then cool it to room temperature. Transfer the solution into a 50-ml calibrated flask and dilute to 50 ml with distilled water. Take suitable aliquots of this solution and continue the determination according to the method. Conclusion The complex of iron(I1) with 3-(2-pyridyl)-5,6-diphenyl-l,2,4- triazine can be extracted into 1,2-dichloroethane as an ion-association complex with tetrabromophenolphthalein ethyl ester.The ion-association complex formed is very sensitive for the spectrophotometric determination of trace amounts of iron(I1). The calibration graph is linear over the range 0-0.25 p.p.m. of iron(1I) and the apparent molar absorptivity is 1.9 x l o 5 1 mol-1 cm-1 at 610 nm. The stoicheiometric ratio is 1 : 3 : 2 (Fe : PDT : TBPE). Although the method is relatively free from interferences, if necessary interferences can be decreased by adding a masking agent, and the interference from Ni(I1) and Cu(I1) can be eliminated by extraction with dimethyl glyoxime and bathocuproine. Satis- factory results were obtained when the method was applied to synthetic samples, serum samples and river and well waters. The authors are grateful to Dr. Shozo Shibata of the Government Industrial Research Institute, Nagoya, for help- ful discussions. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Smith, G. F . , McCurdy, W. H., and Diehl. H., Analyst, 1952. 77, 418 and 524. Collins, P. F., Diehl, H . , and Smith, G. F., Anal. Chern., 1959. 31, 1862. Schilt, A. A., and Taylor, P. J . , Anal. Chern., 1970, 42. 220. Stookey, L. L., Anal. Chern., 1970, 42. 779. Hulanicki, A , , and Nieniewska, J . , Talanta, 1974, 21, 896. Sekine, K., and Onishi, H., Anal. Lett., 1974. 7 , 187. Nishida, H., and Nishida, T., Bunseki Kagaku, 1977, 26, 645. Tsurubou, S . , and Sakai. T., Bunseki Kagaku, 1984, 33, 139. Chriswell, D. D . , and Schilt, A. A., Anal. Chern., 1974, 46, 992. Takagi, M., Nakamura, H., Sanui, Y., and Ueno, K.. Anal. Chim. Acta, 1981, 126, 185. Sakai, T., Hara, I.. and Tsubouchi, M.. Chern. Pharrn. Bull.. 1976, 24, 1254. Kitagawa, H., and Shibata, N . , Bunseki Kagaku, 1958, 7, 284. Matanb, N . , and Kawase, A , , Bunseki Kagaku, 1962, 11, 346. Japanese Industrial Standard. JIS K 0102, Japanese Industrial Standards Committee, Tokyo, 1971. Paper A4195 Received March 12th, 1984 Accepted June 12th, 1984

ISSN:0003-2654    

DOI:10.1039/AN9840901397

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1984, VOL. 109 1401 Photo-oxidation of Acridine and Acridine Yellow in the Presence of Iron(ll1): Determination of Micro-amounts of Iron, Fluoride and Phosphate Tomas Perez-Ruiz, Carmen Martinez-Lozano and Virginia Tomas Department of Analytical Chemistry, University of Murcia, Murcia, Spain Acridine (A) and acridine yellow (AY) are decolorised, in the presence of iron(lll), by illumination with light of wavelength shorter than 360 nm. The decolorisation mechanism involves HO radicals, which are formed during the photo-excitation of hydrolysed iron(ll1) species. In the presence of oxygen, iron(1ll) acts as a catalyst in the photochemical process. The photo-oxidation of A and AY is followed by measuring the decrease in absorbance or fluorescence intensity of the dyes and linear calibration graphs in the range 0.05-7 p.p.m.of iron are obtained. Fluoride and phosphate ions strongly inhibit the iron(ll1)-catalysed photodecolorisation of A and AY and sensitive methods are proposed for their determination. Keywords: Iron, fluoride and phosphate determination; photocatalytic method; acridine; acridine yellow There are two main analytical methods involving applications of photocatalytic reactions in use. In one method, a reaction that proceeds slowly in the dark is made to occur at a rate suitable for analytical measurements by adding a photocata- lyst to the solution and irradiating the system. By selection of the appropriate experimental conditions, chromate can be titrated with methyl orange if an iron(II1) oxalate photocarrier is added.1 The other method employs an iron(II1) catalysed photo-oxidation of the dyes methyl orange,' Erioglaucin-A2 and Safranine T3 for the determination of iron(II1).This paper describes studies on the photo-oxidation of acridine (A) and acridine yellow (AY) by oxygen. It has been found that this reaction is strongly accelerated by even small amounts of iron(II1). We have used this method for the determination of trace amounts of iron and fluoride and phosphate anions. Experimental Apparatus A Pye Unicam SP8-200 spectrophotometer with 1-cm silica cells was used for recording and absorbance measurements. Fluorescence spectra and spectrofluorimetric measurements were obtained with a Perkin-Elmer Model 3000 spectro- fluorimeter, equipped with a quantum counter. Excitation spectra were corrected, but emission spectra were not.In the photolysis device, the light from the lamp (Osram mercury discharge lamp) was passed through a normal quartz cell placed in a thermostatic cell holder. Irradiation intensities were adjusted by two metal screens. The emission spectrum of the lamp was obtained with a Beckman DK2A spectrophotometer . Reagents Analytical-reagent grade chemicals and doubly distilled water were used throughout. Zron(ZZZ) standard solution, 0.01 M. Prepared by dissolving iron(II1) perchlorate in 0.01 M perchloric acid and standard- king by titration with EDTA solution.4 Working standards were prepared from this solution as required. Phosphate standard solution, 0.01 M. prepared from dried potassium dihydrogen phosphate and kept in a polythene bottle.Working standards were prepared by dilution as required. Fluoride standard solution, 0.01 M. Prepared from dried sodium fluoride and stored in a polyethylene bottle. Aqueous acridine and acridine yellow solutions. Prepared from Aldrich products and purified by recrystallising twice from a water - ethanol mixture.5.6 Procedure for the Determination of Iron(II1) Absorbance method In a 25-ml calibrated flask place 2 ml of 10-3 M acridine or acridine yellow, 2 ml of 0.1 M perchloric acid and enough standard iron(II1) solution to give a final iron concentration of between 0.5 and 7 p.p.m. and dilute to volume with doubly distilled water. Transfer part of this solution into a 1-cm silica cell, then switch on the photolysis device for 10 min.Measure the absorbance at 355 nm for acridine and 435 nm for acridine yellow. Construct calibration graphs by plotting the iron concentration versus change of absorbance of the dye. Fluorescence method Prepare the sample solution in the same way as described above but using 2 ml of 2.5 x 10-5 M acridine and 3 ml of 2.5 x 10-5 M acridine yellow. Measure the fluorescence at 472 nm with excitation at 350 nm for acridine and at 505 nm with excitation at 435 nm for acridine yellow, again using a photolysis time of 10 min. Construct calibration graphs by plotting the iron concentration versus fluorescence intensity change of the dyes. 9 Procedure for the determination of fluoride and phosphate In a 25-ml calibrated flask place 2 ml of 10-3 M acridine or acridine yellow, 2 ml of 10-3 M iron(II1) perchlorate, enough fluoride or phosphate standard solution to give a range of final fluoride and phosphate concentrations of 0.41-3.40 p.p.m. and 0.33-8.64 p.p.m., respectively, and 1-1.5 ml of 0.1 M perchloric acid in order to obtain a pH of 3.Dilute to volume with doubly distilled water and proceed in the same way as described for the determination of iron by the absorbance method. Results Acridine and acridine yellow are food colouring matters, which are noted for their resistance to reduction or oxidation in the dark."." When solutions of these two dyes are irradiated, a decolori- sation of about 1% can be observed but only after a long period of irradiation (>40 min). However, in the presence ofANALYST, NOVEMBER 1984.VOL. 109 A 1402 a, C m n n $ 1 a 0 AY 1 I I 1 I 250 400 600 200 400 600 Wavelengthhm 0.6 0.4 0.2 Fig. 1. Absorption spectra after different irradiation times. Curves 1-4: 0, 5 , 10 and 15 min, respectively. Reaction conditions: [Fe(III)], 8 x lop5 M: [A] or [AY]. 8 X lopi M ; and pH, 2.7 . - - I I 1 I 1 250 400 550 400 500 600 Wavelengthhm Fig. 2. Fluorescence spectra after different irradiation times. Curves 1-4: 0. 5. 10 and 15 min. resoectivelv. Reaction conditions: [ Fe ( 111) pH, 2.7 a, C m n n 0.8 m C a, 0 7 k 0.4 r 0 .- 4 x 10-6 M ; [A], 2 x 10-k M or [AY], 3 x 10F M; and A I 2.0 3.0 J , 1 .o 0.6 0.4 0.2 AY 2.5 3.0 3.5 PH Fig. 3. Dependence of pH on iron(II1) catalysed hotodecolorisation. Conditions: [dye], 8 X 10-5 M ; [Fe(C104y3], 8 X lo-' M; and photolysis time, 10 min iron(II1) a decolorisation can be observed if light with a wavelength shorter than 360 nm is used; photons with lower energy are completely ineffective.Similar results can be observed by measuring the fluorescence intensity of both dyes (Figs. 1 and 2). The dyes A and AY, in the presence of iron(II1) and in an inert atmosphere, also undergo photo-oxidation. In this situation, the decolorisation of the dye is accompanied by the reduction of iron(III), in a 4 : 1 dye to metal molar ratio. However, in the presence of oxygen, iron(I1) ions are not formed, as the decolorisation occurs at the expense of dissolved oxygen and the decolorisation of A and AY is several times greater than in its absence. 40C 'u c a, v) 2 5 300 - Y- C a, Is) C m r .- * 200 \ I I 1 I I I 1 .o 2.0 3.0 2.5 3.0 PH Fig.4. tion. Conditions: [A], 2 X 4 X lo-" M; and photolysis time, 10 min Dependence of pN on iron 111) catalysed photodecolorisa- M ortAY], 3 x M: [Fe(ClO,),], a, C m 0 m C a, + 0.8 n .- 0.4 m r 0 I I 1 I I 1 , Dye concentration!M x 10 4 0.2 0.6 1.0 1.4 0.2 0.6 1.0 1.4 Fig. 5. Dependence of dye concentration on iron(I1I)-catalysed photodecolorisation. Conditions: [Fe(ClO,),], 8 X lop5 M ; pH. 2.7: and photolysis time, 10 rnin a, C % 400 ? 3 t - .I- .- g zoo C m r 0 * I 300 200 100 1 I I J 0 2 4 A l I I I 0 2 4 Dye concentrationh x 10-6 Fig. 6. Dependence of dye concentration on iron(II1)-catalysed photodecolorisation. Conditions: [Fe(CIO,),]. 4 x 10-6 M; pH. 2.7: and photolysis time, 10 min The effects of foreign ions on the iron(II1) catalysed photo-oxidation of A and AY are shown in Table 1.Cations were added as perchlorates and anions in the form of sodium or potassium salts. An appreciable decrease in the bleaching can be observed in the presence of As(III), fluoride, bromide, iodide and phosphate ions. Oxidants such as bromate, chlorate and nitrate slightly affect the photochemical process. For the nitrate ion, decolorisation can also be observed in the absence of iron(II1). In the absence of oxygen, the hydrogen peroxide can promote the bleaching of A and AY, but the photochemical process is more complex because a chemical reaction occurs simultaneously in the dark.AN/\I_YS'I. NOVEMBER 19x3. VOL. 109 1403 Figs. 3 and 4 show that the photo-oxidation of A and AY, in the presence of iron( 111) ion, is predominantly dependent on the pH.It is worth noting, however, that no change in pH can be observed during the photo-oxidation of the two dyes. The photodecolorisation of A and Ak' at constant pH and iron(II1) concentration depends on the dye concentration (Figs. 5 and 6). The form of the graph of absorbance change versus dye concentration is determined by the cell thickness at which the irradiation is performed. The photo-oxidation process depends strongly on the iron(II1) concentration. Under the experimental conditions applied, the decrease in absorbance or fluorescence intensity is proportional to the iron(II1) concentration in the range 4 x 10-'-1.6 x 10-4 M , but at a higher catalyst concentration the decolorisation reaches a maximum.Based on thesz observations, suitable methods for the determination of the catalyst and the inhibitors have been devised. Determination of Iron A hsorhuncr method The optimised conditions are a p€I of 2.7 and a dye concentration of 8 X 10-i M. There is a linear relationship between the decrease in absorbance and iron(II1) concentra- tion in the range 0.5-7 p.p.m. When the recommended procedure was applied to two series of ten samples of 1.5 and 3.0 p.p.m. of iron, the relative standard deviations were found to be 1.2 and 0.9%. respectively. Fluorescence method Under the recommended conditions given under Experimen- tal a linear relationship between the decrease in the fluores- cence intensity of both dyes and iron(II1) concentration was obtained.For the photo-oxidation of A, the iron(1II) concen- tration range was 0.02-0.44 p.p.m. and for ten samples of 0.10 p.p.m. of iron the relative standard deviation was 0.5%. For the photo-oxidation of AY, the iron(I1I) concentration range was 0.06-0.70 p.p.m. and for ten samples of 0.30 p.p.m. of iron the relathe deviation standard was 0.2'%). Determination of fluoride and phosphate The inhibiting effects of fluoride and phosphate on the iron(II1)-catalysed decolorisation of A and AY have been applied to the determination of these ions. As can be seen in Fig. 7, under optimum conditions a very low concentration of each inhibitor can be determined. At the 4 x lo-' M level, the relative standard deviations for ten samples were 0.62"/0 for fluoride and 0.9% for phosphate.Practical Applications Acridine gives better results in the determination, because the molar absorptivity (A,,, = 355 nm) and fluorescence yield for acridine are higher than for acridine yellow. The method has been applied satisfactorily to the determi- nation of iron in different reagents. Table 2 shows the results obtained for each salt, which are compared with results from an o-phenanthroline photometric method. The method was also applied to the determination of fluoride in waters (Table 3) and phosphorus in wines (Table 3 ) . Discussion Under the excitation conditions employed (A > 250 nm), the direct photo-activation of the oxygen molecule cannot be considered. In principle, oxygen can be activated as a result of A or AY acting a5 an energy transmitter; however.only a 1% photo-oxidation was observed, Further, the extent of decol- orisation did not change even when the photo-oxidation was carried out urder aqueous and non-aqueous conditions in the Table 1. Influence of diverse ions on the iron(II1) catalysed photo-oxidation of acridine and acridine yellow. Results are molar ratios at which a 2% variation i n decrease in absorbance (or fluorescence intensity) was first detected Ion added As(II1) . . AI(II1) . . Ba(l1) . . Cd(1I) . . Ca(I1) . . Co(I1) . . CU(I1) . . MP(II> ' . Cr(II1) . . Pb(I1) . . Ni(I1) . . Na(1) . . . . Zn(l1) . . Molar ratio of added ion to Fe(I1I) Ion added . . 0.02 I . 10 . . 500 . I 10 . . 500 . . 1 . . 5 . . 0.2 . . 10 . . 500 . . 20 . . 5000 . . 20 Acetate . . Bromate .. Bromide . . Chlorate . . Chloride . . Iodide . . Nitrate . . Phosphate . . Sulphate . . Fluoride . . Molar ratio of added ion to Fe(II1) . . 5 . . 10 . . 0.01 . . 10 . . 0.5 . . 0.01 . . 20 . . 0.005 . . 5 . . 0.05 Table 2. Determination of iron in analytical-reagent grade chemicals Iron found,* (Yo o-Phenanthroline Proposed \pectrophotometric Sample method met hod Sodium oxalatei . . . . . . 0.00103 0.00 1 Sodium hydrogen carbonate , . 0.00098 0.001 * Average of five separdte determinations. + Sample prepared by evaporating the mixture twice until perchloric acid tumes are evolved and then following the described procedure. Table 3. Results for the determination of fluoride in water samples Fluoride, p.p.m. Water sample Certified Found* Mineral water (Malavella) .. . . 7.50 7.57 Mineral water (Vichy Catalrin) . . 7.51 7.45 * Average of five separate determinations Table 4. Results for the determination of phosphorus in wine samples that have been submitted to the mineralisation process with nitric acid and t h e n w i t h pe rc h 1 or i c aci d Phosphorus Method of found'i Murphy and Wine sample* P ' ' Riley'ig I ~~ I Red wine, Jumilla (San Simcin) . . 0.090 0.085 Red wine. Jumilla (Oro Viejo) . . 0.104 0.101 Red wine, Yecla (Infantado) . . 0.140 0,142 Sherry wine, Montilla (Montulia) 0.123 0.125 * Average of five separate determinations. 0.4 K m L 0 0.4 0.2 I I 1 I I 0 5 1 0 1 5 0 5 1 0 1 5 Fig. 7. Dependence of the variation of the absorbance ot A or AY with inhibitor concentration. I , Phosphate. 11, fluoride Conditions.[A] or (AY] 8 x 10 ' M. (Fe(CIO,),], 8 Y 10 ' M. and pH, 3 0 Inhibitor concentration M x 10 41404 ANALYST, NOVEMBER 1984. VOI-. 109 presence of fluorescein or methylene blue. These two dyes are effective sensitisers for the production of singlet oxygen. particularly in a non-aqueous medium, where the lifetime of singlet oxygen is long enough8 to give rise to a chemical reaction. As even these sensitisers did not enhance the decolorisation of A and AY, it may be concluded that singlet oxygen does not participate or plays only a subordinate role in the photo-oxidation. The oxidative decolorisation of A and AY was observed only at wavelengths shorter than 360 nm. Based on this observation and taking into account the strong influence of pI1 on the reaction rate (Figs.3 and 4), as happens with other dyes,’--? the mechanism can be explained by assuming that only hydrolysed iron(I1I) species are responsible for the photo-oxidation. On the basis of the quantum yield of iron(I1I) and their distribution with pI-l,‘.9--’2 it can be assumed that the ion pair complex Fe(OH)’+,, plays an essential role in the photo- oxidation of A and AY. Further, as the decolorisation processes of A and AY are in good agreement with the earlier studies on iron(II1)-catalysed photo-oxidations, we can also deduce that this process is initiated by the photo-activation of Fe(OH)2+: Fe(OH)2+ + hv+ Fe2f + OH The hydroxyl radical will react with the dyes A and AY forming a dye radical, which can be further oxidised, leading to extended conjugation compared with the original structure of the molecule.In the absence of oxygen the decolorisation of 1 niol of A or AY is accompanied by the formation of 4 niol of iron(I1). According to this stoicheiometric relationship, four HO radicals are necessary for each oxidised dye molecule. Because in the presence of an excess of oxygen, iron(1T) ions are not formed during the photochemical process, it must be assumed that the oxygen reacts with the dye radical to form a dye peroxide radical that rapidly oxides iron(1I) to iron(II1) and for this reason iron(II1) behaves as a catalyst in the photochemical oxidation of A and AY. The shape of the decolorisation versus dye concentration graph can be explained by considering that in concentrated acridine dye solution, polymeric species are always present.6 These colloidal particles scatter the light and this apparent absorbance may compensate the decrease in absorbance accompanying photo-oxidation.If the thickness of the layer is greater, the scattering effect may compensate for the greater extent of the photo-oxidation as the dye concentration is increased, and then a maximum in the curve is obtained. From the data given in Table 1, it can be deduced that in the photochemical process the oxygen molecule is not replaced by other oxidants. Although hydrogen peroxide acts as the source of oxygen, the system becomes too complicated because decolorisation of the two dyes is also produced by a radical formed in a reaction that takes place in the dark between hydrogen peroxide and iron(I1) or iron(II1). The inhibiting effect of fluoride, bromide, iodide and phosphate can be explained by the different stabilities and photochemical activities of the complexes formed between iron(II1) and those ions. Further, the potential reactions between the discussed ions and the radicals must be con- sidered. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. References Kharlamov. I. P., Dodin, E. I . , and Mantsevich. A. D., Zh. Anal. Khim., 1967, 22, 371. Peter, A.. and Csanyi. L. J . , Actu Chim. Acud. Sci. Hung., 1979, 100, 163. Peter, A , , and Csanyi, L. J . , Actu Chim. Acad. Sci. Hung., 1979, 101, 379. Schwarzenbach, G., and Flaachka, H., “Complexometric Titrations,” Second Edition. Methuen, London, 1969. Albert, A., “The Acridines,” Second Edition, Edward Arnold. London, 1966. Acheson, R. M., “Acridines,” Wiley, New York. 1973. Murphy, J.. and Riley, J . P., Anal. Chim. Acta, 1962, 27. 31. Kearns, D. R., and Khan, A . V., J . Am. Chem. Soc., 1967,89, 5455. Evans, M.G., Santappi, M., and Uri, N., 1. Polym. Scz., 1951, 7, 243. Woods, R., Kolthoff, I. hl., and Meehan, E. J . , J . Chem. Soc., 1963, 85, 2385. Hedstrom, B. 0. A., Ark. Kemi, 1953, 5 , 457. Charlot, G., “Les Reactions Chimiques en Solutions,” Sixth Edition, Masson, Paris, 1969. Pup er A4143 Received January 27th, 1984 Accepted June lath, I984

ISSN:0003-2654    

DOI:10.1039/AN9840901401

出版商:RSC    

年代:1984

数据来源: RSC