摘要:

IInternational Conference on Analytical ChemistryJune 15-21, 19WMoscow University, Moscow, RussiaAIMSThe objective of the conference is to highlight the most recent developments in the field of analytical science, specifically in thesubject areas identified below. Presentations will be given in the form of plenary and contributed lectures as well as postersessions. It is hoped that the poster sessions will be used to encourage scientists of different generations to exchange ideas andshare experiences in their respective fields.SCOPEThe following major topics will be discussed at the conference:Analytical chemistry: Philosophical aspectPreconcentration (including solid phase extraction)ChemometricsChromatography (GC, HPLC, TLC, IC etc.)and related techniques (CE)Molecular spectroscopy (IR, Raman)Nuclear methodsKinetic methodsBioanalytical chemistryAnalysis of new materials(including high-purity materials)ORGANISING COMMITTEE llSampling and sample treatmentOrganic analytical reagentsQuality assurance/quality controlAtomic spectroscopy (absorption emission,Mass spectrometryElectroanalytical methodsExpress test methodsAnalysis of raw materialsAnalysis of food and agricultural productsClinical analysisfluorescence, XRF, lasers)Chairperson, Yu A. ZolotovVice-chairmen, B.F.Myasoedova, V.A. Davankov and V.G. KoloshnikovGeneral secretary, L.N. KolomietsYu A. Karpov, I.N. Kiseleva, P.N. Nesterenko, G.I. Ramendik, 0. A. Shpigun, S .I. Sinkov, 1.1. Smirenkina,B.Ya. Spivakov, M.M.ZaletinaINTERNATIONAL SCIENTIFIC COMMITTEEChairman, Yu A. ZolotovF. Adams, BelgiumR. Barnes, USAM. Novotny, USAH. Englehardt, GermanyT. Fujinaga, JapanM. Grasserbauer, AustriaB. Welz, GermanyA. Hulanicki, PolandE. Mentasti, ItalyB. F. Myasoedov, RussiaV .A. Davankov , RussiaH. Frieser, USAE. Pungor, HungaryI. Havesov, BulgariaJ. F. K. Huber , AustriaT Yotsuyanagi, JapanM.I. Karayannis, GreeceCONFERENCE SECRETARIATFor further information please contact :H. Akaiwa, JapanC. Boutron, FranceH. Pardue, USAK. Niemax, GermanyP.G. Zambonin, ItalyI. Kuselman, IsraelS. Tsuge, JapanV . G. Koloshnikov, RussiaG. Werner, GermanyJ.G.H. du Preez, South AfricaJ.A. Perez-Bustamente, SpainL. Sommer, Czech RepublicW. Lindner, AustriaF.Macasek, SlovakiaM. Valiente, SpainH.M. (Skip) Kingston, USAM . W idmer , SwitzerlandYu. A. Karpov, RussiaDr L. N. Kolomiets,Scientific Council on Chromatography RAS, Leninsky Prospect 31, 117915 Moscow, Russia.E-mail : Iarionov@lmm.phyche.msk. suTel: 7 (095) 952 0065; 7 (095) 955 4685 Fax: 7 (095) 952 0065; 7 (095) 952 530From 1 January, all 12 of the RSC’s primary journals will bavailable for subscription via the internet. They will beaccessible through the Catchword system, which is page-based and retains the integrity and clarity of the printedversion in the electronic media. Access to data is either vi;the contents pages, or by searching for key words withinissues (every word in a paper is searchable).Papers canbe displayed, printed and saved for future reference.THE ROYAL Dalton TransactionsSOCIETY OFFar aday Di scu s sionsJournal of Analytical AtomicFaraday TransactionsPerkin Transactions 1Perkin Transactions 2 SpectrometryH Journal of Chemical ResearchJournal of Materials Chemistry An a1 y t ic a1 C ommunic at i on sInformationServices ChemComm Mendeleev CommunicationsI KEY FEATURES & BENEFITS:Access the most recent work, direct from your Pinpoint the information you want easily andefficiently - the journals are fully searchableArticles of interest can be printed or saved to diskThe same high quality research results as in theprinted formIdesktop, as soon as it i s available -while the printed journal may still beon its way to you.in the worldEasy and instant access from anywhereFull technical supportDon’t be left behind!9III IL ~ ~ ~ ~ ~ ~ ml--B-----E---------B-EPlease send me further information about RSC Journals Qnfine 6 1 Name:I Address:Job Title: Organisation:Please return this coupon, or write to: jenny McCluskey, Sales and Promotion Executive, at The Royal Society of Chemistry, 7 homas Graham House,Science Park, Milton Road, Cambridge CB4 4WF.Alternatively, call or fax with your request on (tel) 44-(0)1223-420066 (fax) 44-(0)1223-423429, quoting ref. E13\ ROYAL AUSTRALIAN CHEMICAL INSTITUTE AUSTRALIAN ACADEMY OF SCIENCE vXXX COLLOQUIUM SPECTROSCOPICUM INTERNATIONALEWorld Congress Centre, Melbourne, Australia, September 21st-26th9 1997Participants are invited to submit contributions for presentation on the following topics;Theory, Techniques and Instrumentation of :-Atomic Spectroscopy (Emission, Absorption, Fluorescence)Computer Applications and ChemometricsElectron SpectroscopyGamma SpectroscopyLaser SpectroscopyLuminescence SpectroscopyMass Spectrometry (Inorganic and Organic)Methods of Surface Analysis and Depth ProfilingUVNisible SpectroscopyNIR SpectroscopyIR SpectroscopyMossbauer SpectroscopyNuclear Magnetic Resonance SpectrometryPhotoacoustic and Photothermal SpectroscopyRaman SpectroscopyX-Ray SpectroscopyApplications of Spectroscopy to the Analysis of :-Biological and Environmental SamplesFood and Agricultural ProductsMetals, Alloys and Geological MaterialsIndustrial Processes and ProductsPlenary and Invited SpeakersTo date the following eminent spectroscopists have accepted invitations to present keynote lectures;Freddy AdamsMike AdamsMike BladesJohn ChalmersBruce ChasePeter FredericksManfred GrasserbauerMike GrossMike GuilhausPeter HannafordGary HieftjeKazuhiro ImaiHiroshi MasuharaBelgiumUKCanadaUKUSAAustraliaAustriaUSAAustraliaAustraliaUSAJapanJapanAndrew ZanderRussell McLeanJean-Michel MermetCaroline MountfordNicolo OmenettoMike RamseyAlfredo Sanz MedelBarry SharpMargaret S heilHeinz SieslerRichard SnookYngvar ThomassenBernhard WelzJohn WilliamsUSAAustraliaFranceAustraliaItalyUSASpainUKAustraliaGermanyUKNorwayGermanyUKIn connection with the XXX CSI a number of pre-symposia will be organised, the conference will feature an exhibition ofthe latest spectroscopic instrumentation and associated equipment.Social ProgrammeThe scientific programme will be punctuated with memorable social events and excursions of scientific, cultural and touristinterest.The social programme is open to all participants and accompanying persons.sponsorsAs at August 1995, the following companies have agreed to be major sponsors of XXX CSI 1997;GBC, Hewlett-Packard, Perkin Elmer and VarianFor further information contact -SecretaryMr P.L. LarkinsCSIRO Division of Materials Science & TechnologyPrivate Bag 33, Rosebank MDC, Clayton VIC 3169AUSTRALIATelephone: +61 3 95422003Facsimile: +61 3 95441 128E-mail: larkins@rivett.mst.csiro.auConference SecretariatThe Meeting Planners108 Church Street,Hawthorn VIC 3 122AUSTRALIATelephone: +61 3 98193700Facsimile: +61 3 98195978Updated information may be obtained from the XXX CSI homepage on the World Wide Web at :http://w w w.latrobe.edu. au/CSIconf/XXXCSI. htmlQANTAS has been appointed the sole official carrier to the XXX CSI 1997. When making QANTAS reservations please quote JIF 734.The Analyst and JAAS have been appointed as the official journals for publications resulting from CSI ‘97. Authors are encouragedto bring their manuscripts to the conferenceThe Royal Society of Chemistry Analytical DivisionJune 30 - July 3,1997University of Northumbria at NewcastleAnalytical Science and the EnvironmentAIMS AND SCOPEThe meeting will focus on selected themes to highlight the importance of analytical science inmonitoring the environment.The particular themes to be covered include: sampling/sample preparation;monitoring of pollutants in the environment (off-line versus on-line); data interpretation usingc hemometrics ; and environmental legislation.PLENARY LECTURESSolvent-free Sampling/Sample Preparation Techniques Based on Polymer Technologies and Fibre GeometryProfessor J. Pawliszyn (University of Waterloo, Canada)The Potential of Hyphenated and Coupled-column Techniques in Environmental AnalysisProfessor U. A. Th. Brinkman (Free University, Amsterdam)Automated Interpretation and Analysis of XRF DataProfessor M.J. Adams (University of Wolverhampton, UK)INVITED LECTURESMulti-element Sampling Systems for Gas AnalysisDr C. L. P. Thomas (UMIST, UK)So 1 id Sample Preparation in Environmental AnalysisDr J. R. Dean (University of Northumbria at Newcastle)Monitoring Biogeochernical Processes in the Marine Environment by In Situ Flow Injection TechniquesProfessor P. Worsfold (University of Plymouth, UK)Atmospheric VOC Sampling and Sample PreparationDr N. G. Flesca (INERIS, France)Chemometric Methodologies for Data Interpretation: How to Understand ResultsDr A. D. Walmsley (University of Hull, UK)INVITATION AND CALL FOR PAPERSThe organisers invite contributors, from academia, industry and research students, to present their workon any of the above themes at chaired poster discussion sessions.All delegates presenting papers are encouraged to submit articles for publication as full papers in aspecial issue of The Analyst, subject to the normal review procedure of this journal.The programme will also encompass the 1997 Research and Development Topics in AnalyticalChemistry meeting.For further information please contact:London WlV OBN Tel: +44 (0)171 437 8656; Fax: +44 (0)171 734 1227The Secretary, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly

ISSN:0003-2654    

DOI:10.1039/AN99621BP038

出版商:RSC    

年代:1996

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99621FX049

出版商:RSC    

年代:1996

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99621BX051

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, November 1996, Vol. 121 (IOIR-106R) l0lR Relationship Between Structural Attributes and Observed Electrogenerated Chemiluminescence (ECL) Activity of Tertiary Amines as Potential Analytes for the Tris(2,2=Bipyridine)Ruthenium(ii) ECL Reaction A Review Andrew W. Knight and Gillian M. Greenway* School of Chemistry, University o j Hull, Hull, East Yorkshire, UK HU6 7RX The relationship between the structural attributes of various amine compounds and their observed electrogenerated chemiluminescence (ECL) activity with the tris(2,2-bipyridine)ruthenium(11) ECL reaction was examined, with a view to the determination of these compounds. This was carried out by first examining the reaction mechanism and then predicting the ECL activity of certain classes of compounds by considering the stability of intermediates, and drawing general conclusions by comparing the observations obtained by the authors and other workers.The molecular geometry and alternative anodic reactivity and their effect on ECL activity are discussed and results for the ECL activity of a range of local anaesthetics are presented. Keywords: Electrogenerated c~hemiluminescence; tl-is(2,2-bipyl-icline)ruthenium(u); tertiary amines; review Introduction There are a wide variety of methods that can be used to determine primary and secondary amines, mainly after prior derivatization since many of the compounds do not absorb well in the UV or visible region of the spectrum. Derivatization reagents that have been reported include ninhydrin,' for determination by absorption spectroscopy, and o-phthalal- dehyde2 and 7-chloro-4-nitrobenzo-2-oxa- 1,3-diazole,3 which form fluorescent derivatives.Primary amines have also been determined by chemical excitation of their fluorescent deriva- tives via the peroxyoxalate chemiluminescence (CL) reaction.4 Few methods, however, have been reported for the derivatiza- tion and subsequent determination of tertiary amines. One, involving the reaction of aconitic acid and acetic anhydride with the tertiary amine to produce a green fluorescent product, cannot be carried out in aqueous solution, needs a long incubation time and exhibits a relatively poor limit of detection.5 A CL method has been reported based on the CL emission that occurs on the oxidation of aliphatic secondary and tertiary amines by benzoyl peroxide.6 This reaction must, however, be carried out in a dry, non-aqueous solvent owing to the decomposition of benzoyl peroxide by water.Tertiary aliphatic amines have also been determined via CL emission observed on the oxidation of the amine by hypochlorite in the presence of * To whom corresponence should be addressed. Rhodamine B, and reasonable, but not low limits, of detection were observed.7 Tertiary amine compounds have many varied applications as pharmaceuticals, pesticides and surfactants, and hence the development of sensi tive analytical methods for their determi- nation, especially in aqueous solution, is seen as desirable, Trialkylamines and closely related compounds are problematic to detect since they do not absorb well in the UV/VIS region of the spectrum, exhibiting low molar absorbtivities, and are extremely difficult to derivatize.Tertiary and some secondary amines can, however, be determined by utilizing their electrogenerated chemilumines- cence (ECL) reaction with tris(2,2'-bipyridine)ruthenium(11) [R~(bpy)3~+] without prior derivatization. Such reactions are of particular analytical interest since they are extremely efficient and hence sensitive, and occur in aqueous solution in the presence of dissolved oxygen and other impurities. ECL is a technique whereby a CL emission is produced directly or indirectly as a result of an electrochemical reaction. The occurrence, mechanisms, analytical applications and advan- tages of ECL have been reviewed previously by the authors.8 The mechanism of the reaction of Ru(bpy)32+ with tertiary amines proceeds as follows.A single, appropriate, positive voltage is applied to an electrode to produce the Ru(bpy)33+ active cation by oxidation of the parent complex and at the same time oxidize the amine. Oxidation products of the amine react immediately with the water present to form highly reducing intermediates that can reduce the Ru(bpy)33+ back to Ru(bpy)32+ in an excited state [R~(bpy)~Z+ "I, which emits light with a maximum at a wavelength of 620 nm. ECL reactions of Ru(bpy)32+ have so far been used, for example, in the analysis of pharmaceuticals, amino acids and antibiotics, where the analytes often do not contain a good chromophore. A list of analytical applications of Ru(bpy)32+ ECL for the determination of amines is presented in Table 1.It is not the case, however, that all tertiary amine compounds take part in ECL reactions with Ru(bpy)32+ to produce light. Many tertiary amine compounds produce intense emissions whereas other structurally related similar compounds produce virtually no ECL emission. Although the analytical uses of the ECL reaction of Ru(bpy)32+ with a variety of amines continue to be an active area of research, there has been no detailed study of the relationship between the amine's structural attributes and its ECL activity, e.g., why certain structural features, if present in the molecule, quench the emission whereas others enhance the ECL emission. Most workers have simply opted to test a wide range of compounds, and have only arrived at the limited102R Analyst, November 1996, Vol.121 conclusion that those compounds which produced the most intense emissions invariably contained aliphatic tertiary or secondary amine groups.9 Therefore, there is a need to study the relationship between the structure and apparent ECL activity of amine compounds in order to explain previous observations and effectively target new groups of compounds that could be potential analytes for Ru(bpy)3*+ ECL detection. Such an investigation is, however, difficult from both a theoretical and a practical point of view. The oxidation of amines has been one of the most active areas of research in anodic electrochemistry, because the ease of removal of electrons from the amino functional group makes it possible to study the oxidation using quantitative electroa- nalytical techniques.Several investigations into the anodic oxidation of aliphatic and aromatic amines have been reported, yet the investigators were not always in complete agreement over the mechanisms of all the reactions, and hence some mechanisms are still open to question.24 Without a wholly accurate picture of the mechanism of both the electrochemical and%L reactions, predictions of the effect of substituent groups of the amine on the ECL activity are more difficult. Also, practical difficulties arise if a range or family of compounds are to be compared to determine their relative ECL activity. Relatively small changes in the structure of compounds, e g . , a stepwise increase in alkyl chain length, will often dramatically change its solubility, requiring a change of solvent conditions or a change of optimum pH conditions.Hence comparisons over a range of compounds under the same experimental conditions are often not possible. The aim of this work was to investigate the relationship between the structural attributes of mainly tertiary amine compounds and their apparent Ru(bpy)32+ ECL activity by an examination of the reaction mechanism. This information could then be used to predict the ECL activity of certain classes of compounds by considering the stability of intermediates, and drawing general conclusions by combining and comparing the results of observations obtained by the authors and other workers. Instrumentation There exists very little commercially available instrumentation for the general study of ECL reactions, hence most researchers in the field have constructed their own apparatus.However, most approaches to the construction of an ECL instrument have stemmed from the same basic design as shown in Fig. 1. The most commonly adopted design makes use of a laminar thin- layer flow cell with flat-plate electrodes over which the liquid stream flows. A flow injection manifold is commonly used for the reason that it allows semi-automation of the technique and simplified sample preparation by the reproducible addition and mixing of samples and reagents on-line, leading to a high sample throughput with minimum sample handling and pre- treatment. The sample solutions flow into the cell and over the surface of the working electrode where the ECL reaction is initiated and produces light in direct view of the light transducer before passing to waste.Both a photomultiplier tube25 and a silicon photodiode26 have been successfully used as light transducers in ECL detectors. The electrical signal from the light transducer is then amplified and recorded. Different electrode configurations have been used, but the working electrode at which the ECL reaction occurs must be within the main body of the cell directly in front of the light transducer, with additional counter and reference electrodes positioned either within or downstream of the main body of the flow cell. The Ru(bpy)32+ reagent can also be immobilized at the working electrode and regenerated electrochemically to produce a self-contained sensor without the need for additional reagent^.^ The voltages are generally applied to the working electrode by means of a three-electrode potentiostat. Some of the work reviewed in this paper makes use of alternative methodology, whereby a solution of the R~(bpy)~3+ active cation is produced by bulk electrolysis of an Ru(bpy)32+ solution, and this forms the reagent stream of a conventional CL flow injection manifold.Similar reactions to those produced in the vicinity of the electrode in ECL then occur in solution, and hence observations made by this method are still valid for comparison studies. The ECL results quoted in this paper are generally the ECL intensity recorded after the optimization of the two most important factors, the applied voltage and pH.Reaction Mechanism From previous electrochemical and photochemical studies, the oxidation of tertiary amines is understood to produce a short- lived radical cation. The a-carbon is then deprotonated, forming a strongly reducing intermediate.27-2' This intermediate is the source of the chemical energy to produce, by reduction of R~(bpy)~3+, the excited state of Ru(bpy)32+ in the ECL reaction. In effect, the fact that light emission is observed via a CL reaction is also evidence of the existence of a highly reactive Table 1 Published analytical applications of the Ru(bpy)3*+ ECL reaction in the determination of amines Analyte Alkylamines, NADH, antibiotics Primary arnines (derivatized) Trial kylamines Nicotine, atropine. lindomycin, 1 -ethylpiperazine, diphenidol Tripropy lamine Erythromycin Clindamycin-2-phosphate Valine Serine leucine Amino acids Amino acids Dansylated amino acids Antihistamines Oxaprenolol Codeine, heroin, dextromethorphan * As quoted in the original paper.Reaction medium Acetate buffer Phosphate buffer-MeCN (60 + 40) Acetate buffer-MeCN (90 + 10) MeOH-H20 (50 + 50) Phosphate buffer Acetate buffer-MeCN (73 + 27) Phosphate buffer-MeCN (73 + 27) Borate buffer Borate buffer Acetate buffer Borate-acetate buffer Trifluoroacetic acid-MeCN (85 + 15) Borate buffer-MeCN (60 + 40) Phosphate buffer Acetate and phosphate buffers Limit of detection* Ref. 10 nmol 1-1, 1 pmol 1-I, < 1 pmol 1-1 30-1 pmol 10 Low ng 11 9 0.5-1.8 pmol 0.28 pmol 24 ng ml-' 3 pmol 135, 35 pmol 20 pmol-50 nmol 100 fmol-22 pmol 0.1 pmol 1-1 5-10 pmol 35 nmol 1 - I 10 PPb 12 13 14 15 16 17 18 19 20 21 22 15, 45.44 nmol 1-1 23Analyst, November 1996, V d .121 103R intermediate. Hence the reaction is thought to proceed as outlined in Fig. 2, although the ultimate reducing agent is unknown. Further evidence in support of this mechanism comes from the identification of the reaction products.3" From this proposed mechanism, it is clear that the critical step in the ECL reaction is the oxidation and subsequent deprotona- tion of the amine, to form a reducing radical intermediate, and also important is the reducing ability of the radical once formed. This mechanism is consistent with observations of the effect of pH on the ECL intensity measured by the authors and others for a variety of amines.Fig. 3 shows a typical result obtained for the effect of pH on the ECL intensity from a solution of tripropylamine (TPA) (1 X moll-1) and Ru(bpy)32+ (1 X 10-3 mol 1-1) in phosphate buffer (0.05 mol 1-1). The ECL intensity is seen to increase dramatically above pH 5.75 and a peak at pH 7.50. The ECL intensity is very low when the pH is Amplifier t Recorder I Light I hection Transducer ECL flow cell Sample - - - - - - - - - - - - - _ _ - - - - _ - - - - - - : Reagents CY I l l Towaste I I I Flow-irrjection manifold E = Electrode Fig. 1 Schematic diagram of the instrumentation required for the generation and measurement of electrogenerated chemiluminescence. R2NH + R'CHO + RU(LPY)~~+ * + H30 Fig. 2 amines (based on ref. 27). General mechanism of the ECL reaction of Ru(bpy)32i I I rith tertiary 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 PH Fig.3 with tripropylamine. Effect of pH on the ECL intensity from the reaction of Ru(bpy)32+ not basic enough to deprotonate the TPA radical cation. As the pH range used is more acidic than the pK, of TPA (10.7), it i s likely that the acidity of the TPA radical cation, and not the basisity of TPA, is most important in determining the pH dependence of the ECL reaction.27 Tripropylamine has proved to be perhaps the most efficient amine for this ECL reaction, and is commonly used as a standard by which to compare the ECL activity of other amines. Results and Discussion The first conclusion that is evident from this mechanism is that the amine should have a hydrogen atom attached to the a - carbon, which, after deprotonation, will become the radical centre of the intermediate.This is supported by the fact that nitrogen-containing compounds other than amines, notably amides, only give very weak ECL responses.9 The ability of any a-carbon substituents (i.e., R' in Fig. 2), to stabilize the radical formed, through either electron-donating or conjugation effects, will therefore have an important role to play in determining the compound's ECL efficiency. Similarly, the ability of functional groups attached directly to the nitrogen atom to stabilize the radical first formed in the reaction will affect the ECL activity of the compound. As the final reducing intermediate is likely to contain an electron-deficient carbon atom, generally the stability considerations should be similar to those for carbo- cations, although not as marked.There exists, however, a conflict between the different factors affecting stability. On the one hand the amine should preferably contain substituents which favour the formation of the nitrogen and/or the subsequent carbon radical; however, on the other, the substituents should not stabilize the radical thus formed to the extent that it is unreactive towards the Ru(bpy)33+ ion. On the basis of these considerations, most trends observed in ECL activity across related groups of compounds can be explained, with some significant exceptions as detailed later. In general, electron-withdrawing substituents attached to the nitrogen or a-carbon atom will further destabilize positive or electron-deficient radical ions, and hence tend to reduce the ECL activity of the compound.Most atoms that are attached to the carbon atom are more electronegative than carbon, and hence are electron withdrawing by an inductive effect. For example, this includes compounds where the a-carbon is close (i.e., within two carbon atoms) to a carbonyl, a halogen or, to a lesser extent, a hydroxyl group. This is demonstrated by an example from the results of Brune and Bobbitt,17 as shown in Table 2. They examined the effect of various substituent groups on the ECL intensity measured for ethylamine derivatives with respect to phenethylamine. A correlation could be observed between 01, which is a measure of the electron-withdrawing character of the substituent group, and the measured ECL activity.The greater the electron-withdrawing character of the group, the weaker is the ECL intensity observed. Other examples include the low ECL response observed for the tertiary amines, EDTA and piperidineethanol.27 Conversely, electron-donating substituents attached to the nitrogen or a-carbon will stabilize positive or electron-deficient radical ions, and hence tend to increase the ECL activity of an amine. Hence aliphatic alkyl groups that are electron donating Table 2 Effect of substituent electron-withdrawing groups on the ECL intensity of ethylamine derivatives (taken from ref. 17) Amine Relative ECL signal o1 Phenethylamine 1 .OO 2-Methoxyethylamine 0.402 2-Hydroxyethylamine 0.347 2-Chloroethylamine 0.266 0.1 0.27 0.27 0.46I04R Analyst, Noijemher 1996, Vol.121 by an inductive effect, enhance the ECL of the amine. An increase in the number and length of alkyl chains attached to the nitrogen atom increases the stability of the radical ions and is matched by an increased ECL response. Hence tertiary amines are the most ECL active, followed by secondary and finally primary amines. An example of this is given in Table 3 from the results of Downey and Nieman.9 Primary amines have been analytically determined by the Ru(bpy)32+ ECL reaction, but most sensitively after prior derivatization with divinyl sulfone to form a tertiary amine derivative. 1 0 If substituent groups excessively stabilize the radical inter- mediates, however, they will be less reactive towards the Ru(bpy)3-3+ and hence hinder the ECL reaction.This effect is demonstrated by the fdct that aromatic amines, aromatic substituted amines and amines with a carbon-carbon double bond that can conjugate with the positive charge consistently give a low ECL response, where the radical or positive charge can be effectively delocalized. For example, no ECL is obseived for aniline, diphenylamine or triphenylamine.13 Nicotinamide adenine dinucleotide (NAD+) contains a pyridine ring, and hence this aromatic amine does not yield an ECL emission. In the reduced form (NADH), however, the pyridine ring has been oxidized and its aromaticity destroyed to yield an aliphatic tertiary amine group. NADH has hence been reported to exhibit a strong ECL response, and as a consequence has been determined in Ru(bpy)32+ ECL methods.g,31,32 It should also be noted that aromatic amines have been reported to quench the emission of the Ru(bpy)32+* complex, further reducing the ability of these compounds to give an ECL response.33 A more quantitative approach to predicting ECL activity of the alkylamines was suggested by Noffsinger and Danielson.13 They suggested that since the mechanism of the ECL reaction involves a charge-transfer reaction, then an examination of the energy of the electron from the reducing intermediate may provide a basis for predicting its reactivity and hence ECL activity.In general, the first ionization potential for the alkylamines decreases in the order primary > secondary > tertiary. They demonstrated that a linear correlation could be drawn between the logarithm of the CL signal and the ionization potential of the amine.This is because the ionization potential of the amine is expected to be linearly related to the free energy change of the electron-transfer r e a c t i ~ n , ~ ~ . ~ s and this free energy change is inversely related to the logarithm of the rate constant for the electron tran~fer~366.37 which is essentially directly related to the CL intensity. Hence the magnitude of the first ionization potential of an amine may be a useful indicator in predicting the ECL activity of the compound. However, ionization potential data, usually obtained via photoelectron spectroscopy, are readily available for only a limited number of simple organic compounds, and not complex potential analyte molecules.It has recently been observed by the authors that the molecular geometry of the amine also has a bearing on the stability of intermediates containing an electron-deficient nitrogen atom, and hence affects the ECL activity of the compound. Most simple tertiary amine compounds will have trigonal pyramidal geometry around the nitrogen atom, which has a lone non-bonding pair of electrons. After electrooxidation, an electron is removed from the nitrogen, resulting in a Table 3 Comparison of the ECL activity of the propylamines (taken from ref. 9) Amine ECL intensity (arbitrary units) Monopropy lamine 4 Dipropylamine 48 Tripropylamine 660 positively charged radical ion, with a single non-bonding electron associated with the nitrogen atom (see Fig. 2). Hence the geometry around this nitrogen atom will tend towards a trigonal planar structure such that effective delocalization can occur.Therefore, in order to increase the stability of the positive nitrogen radical formed in the first step of the ECL reaction, the substituent groups attached to the nitrogen will need to be free to move to enable the amine to adopt a more planar geometry. In certain compounds, however, the geometry of the amine is such that the attainment of planarity is inhibited. Hence the instability of the positive nitrogen radical and the consequent difficulty in its formation are increased, and its ECL activity will be diminished. This is demonstrated by the weak ECL response observed for 1,4-diazobicyclo[2.2.2]octane27 and by the authors for quinuclidine and quinine, which gave 700- and 600-fold less intense ECL signals, respectively, than tripropyl- amine under similar conditions.In these compounds the nitrogen is held in a rigid non-linear geometry. On the other hand, the nitrogen atom of codeine, for example, although fixed in a six-membered ring, has a methyl group that is free to move to allow the nitrogen to adopt a more planar configuration on electrooxidation, and hence the formation of the positive radical is not hindered by the molecular geometry and a strong ECL response has been observed.23 The structures of these com- pounds are shown in Fig. 4. It has also been observed by the authors that an important consideration to be taken into account is the possibility of other anodic electrochemical reactions of the compound, e.g., the preferential oxidation of another functional group on the molecule over the one-electron oxidation of the amine function.If other ultimately non-chemiluminescent electrochemical reac- tions can occur involving the analyte molecule at a similar or lower potential than is being used in the ECL experiment, than this may inhibit or otherwise disrupt the ECL reaction. This was strikingly demonstrated in a comparison of the ECL activities of codeine and related pharmaceuticals.23 Codeine was observed to exhibit a strong ECL response (signal-to-blank ratio 2706) compared with that of morphine (signal-to-blank ratio 9.77), despite the close similarity of the compounds (see Fig. 4). A voltammetric investigation demonstrated that a preferential oxidation of the phenolic group of morphine, possibly followed by a coupling reaction, could occur at a much lower potential than that expected for the oxidation of the amine, and this was thought to be inhibiting the ECL reaction.In codeine the phenolic group is absent and this alternative reaction is blocked. A c"4 Quinuclidine H2cx CHOH Quinine y 3 N Codeine Morphine Structures of some of the tertiary amines considered. Fig. 4Analyst, Nm1ernbei- IYY6, Vol. 121 I05R Similarly, the authors have observed that the presence of significant concentrations of other easily oxidized compounds, such as phenol derivatives, added to a sample solution can inhibit the ECL reaction of another amine compound, although it is unclear at present whether these interfere principally with the electrochemical reaction at the electrode or the subsequent CL reactions in the bulk solution.Hence other components or impurities of the sample matrix may adversely affect the apparent ECL activity of the amine, and should also be considered. For example, the Ru(bpy)?2+ ECL determination of codeine in Co-codamol tablets could only be successfully carried out after prior separation of the active ingredients using HPLC. Co-codamol tablets usually contain 8 mg of codeine phosphate and 500 mg of paracetamol. In direct analysis, the high excess of the more readily oxidized phenolic compound, paracetamol, interfered leading to a severe depression of the ECL signal expected for codeine. Co-codaprin tablets, on the other hand, containing 8 mg of codeine phosphate and 400 mg of aspirin, could be readily analysed directly without prior separation, since the aspirin was not observed to be electro- chemically active under the conditions used.The general conclusions drawn here are further supported by considering the ECL activity of a range of local anaesthetics, a class of compounds that have recently been investigated by the authors for possible analytical determination by this Ru(bpy)32+ ECL method.?* The optimum pH conditions producing the most intense ECL emission are given in Table 4, along with the ECL signal-to-blank ratio relative to bupivacaine. The buffer used throughout was 0.05 mol 1- sodium dihydrogenorthophos- phate with the pH adjusted with sodium hydroxide. Most useful local anaesthetics have the same general chemical configuration of an amine portion coupled to an aromatic residue by an ester or an amide link.It is the amine portion that is involved in the ECL reaction with Ru(bpy)?2+. The structures of these compounds are shown in Fig. 5. From Table 4, it can be seen that the most active compound is bupivacaine. This is a relatively simple tertiary amine com- Table 4 Comparison of the optimum conditions and ECL activity of some local anaesthetics Relative signal-to-blank Compound Optimum pH ratio Lignocaine 5.5 63 Procaine 5.5 44 Prilocaine 7.5 18 Amethocaine 6.5 I6 Bupivacaine 5.5 100 G i H C O - cH3 C4H9 -? Amethocaine (Tetracaine) Bupivacaine Lignocaine (Lidocaine) Prilocaine H2N D C O OC HzCH~N(C~H~)~ Procaine - Fig. 5 Structures of the local anaesthetics tested.pound, with effectively two butyl groups attached to the nitrogen. The nitrogen, although captive in a ring, is free to adopt a linear geometry, and the long alkyl groups will effective11 stabilize the electron-deficient intermediate by an inductive effect. Hence this compound exhibits high ECL activity. Lignocaine is a similar tertiary amine compound with shorter ethyl groups attached to the nitrogen, which are less efficient at stabilizing the electron-deficient intermediate, and hence the compound exhibits lower ECL activity than bupiva- caine. Procaine produces an ECL signal that is lower still, probably owing to the presence of the aromatic primary amine. It is likely that this group will be readily oxidized, and the electron-deficient product stabilized by the aromatic ring, and this alternative anodic electrochemical reaction will interfere with the ECL reaction.Prilocaine was expected to give a lower signal since it is a secondary amine, as discussed previously. Finally, amethocaine exhibited the lowest ECL activity, owing to the short methyl groups attached to the nitrogen, which will give the least efficient inductive stabilization of the electron- deficient intermediate, and since it possesses a secondary aromatic amine, which will be readily oxdized in an alternative, interfering, anodic electrochemical reaction. Conclusions A hydrogen atom attached to the a-carbon is usually essential for ECL activity. Electron-withdrawing substituents on the amine close to the radical centre of the molecule, such as a carbonyl, halogen or hydroxy group, will tend to cause a reduction in ECL activity, by destabilization of the radical intermediate.Electron-donating substituents on the amine close to the radical centre of the molecule, such as alkyl chains, will tend to cause an increase in ECL activity, by stabilization of the radical intermediate. Mesomeric or resonance stabilization of the radical inter- mediates, such as occurs in aromatic amines, causes a reduction in the reactivity of the intermediate and hence reduces ECL activity. The ionization potential of the amine may be a useful indicator in predicting its ECL activity. Amines with a structure that inhibits the adoption of a more planar molecular geometry after electrooxidation hinder the formation of the nitrogen radical and, hence, tend to show lower ECL intensities.Other anodic electrochemical reactions of the amine, its impurities or components of the sample matrix should also be taken into consideration, and may interfere with and reduce the ECL intensity observed. It is hoped that by consideration of these general conclusions, the reasons for the often diverse ECL activities observed for seemingly similar compounds can be further explained, and that other classes of amine compounds can be identified and effectively targeted as potential analytes for the Ru(bpy)32+ ECL reaction. References Mell, L. D., Clin. Chern., 1979, 25, 1187. Simons, S . S . , and Johnson, D. F., J . Org. Chem., 1978, 43, 2866. Roth, M., Clin. Chim. Acta, 1978, 83, 273. Mellbin, G., and Smith, I3.6. F., J . Chromutogr , 1984, 312, 203. Pesez, M., and Bartos, J., Colorimetric und Fluorimetric AizulyJis of Organic Compounds and Drugs, Marcel Dekker, New York, 1974, p. 174. Burguera, J. L., and Townshend, A., Tuluntu, 1979, 26, 795. Lancaster, J. S . , Worsfold, P. J., and Lynes, A., Analyst. 1989, 114, 1659. Knight, A. W., and Greenway, G. M., Aizalyst, 1994, 119, 879.106R Analyst, November 1996, Vol. 121 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Downey, T. M., and Nieman, T. A., Anal. Chem., 1992, 64, 261. Uchikura, K., Kirisawa, M., and Sugii, A., Anal. Sci., 1993, 9, 121. Noffsinger, J. B., and Danielson, N. D., J . Chromatogr., 1987, 387, 520. Uchikura, K., and Kirisawa, M., Anal. Sci, 1991, 7, 803. Noffsinger, J. B., and Danielson, N.D., Anal. Chem , 1987, 59, 865. Danielson, N. D., He, L., Noffsinger, J. B., and Trelli, L., ,I. Pharm. Biomed. Anal., 1989, 7, 1281. Targrove, M. A., and Danielson, N. D., J . Chromatogr. Sci., 1990,28, 505. Brune, S. N., and Bobbitt, D. R., Tulanta, 1991, 38, 419. Brune, S. N., and Bobbitt, D. R., Anul. Chrm., 1992, 64, 166. He, L., Cox, K. A., and Danielson, N. D., And. Lett., 1990, 23, 195. Jackson, W. A., and Bobbitt, D. R., Anal Chini. Actu, 1994, 285, 309. Lee, W.-Y., and Nieman, T. A., J . Chromatogr., 1994, 659, 1 11. Holeman, J. A., and Danielson, N. D., J . Chromatogi.., 1994, 679, 277. ,Greenway, G. M., and Knight, P. J., Anal. Proc., 1995, 32, 251. Knight, A. W., Knight, P. J., and Greenway, G. M., Analyst, 1995, 120, 2549. Organic Electrochemistry, ed. Bazier, M. M., and Lund, H., Marcel Dekker, New York, 2nd edn., 1983. Knight, A. W., and Greenway, G. M., Analyst, 1995, 120, 2543. Knight. A. W., Greenway, G. M., and Chesmore, E. D., Anal. Proc., 1995, 32, 125. 27 28 29 30 31 32 33 34 35 36 37 38 Leland, J. K., and Powell, M. J., J . Electrochem. Soc., 1990, 137, 3 127. Chandrasekaran, K., and Whitten, D. G., J . Am. Chem. Soc., 1980, 102, 51 19. DeLaive, P. J., Sullivan, B. P., Meyer, T. J., and Whitten, D. G., J. Am. Chem. Soc., 1979,101,4007. Kirch, M., Lehn, J.-M., and Sauvage, J.-P., Helv. Chim. Actu, 1979, 62, 1345. Martin, A. F., and Nieman, T. A., Anal. Chim. Actu, 1993, 281, 475. Yokoyama, K., Sasaki, S., Ikebukuro, K., Takeuchi, T., Karube, I., Tokitsu, Y., and Masuda, Y., Talanta, 1994, 41, 1035. Bock, C. R., Connor, J. A., Gutiemez, A. R., Meyer, R. J., Whitten, D. G., Sullivan, B. P., and Nagle, J. K., J. Am. Chem. Soc., 1979,101, 4815. Klinger, R. J., and Kochi, J . K., J . Am. Chem. Soc., 1980, 102, 4790. Gassman, P. G., Mullins, M. J., Richtsmeier, S., and Dixon, D. A., J . Am. Chem. Soc., 1979,101,5793. Marcus, R. A., J . Phys. Chem., 1963, 67, 853. Amouyal, E., Zidler, B., Keller, P., and Moradpour, A., Chem. Phys. Lett., 1980, 74, 314. Knight, A. W., and Greenway, G. M., And. Commun., 1996, 33, 171. Paper 610236.56 Received April 4 , 1996 Accepted June 10, 1996

ISSN:0003-2654    

DOI:10.1039/AN996210101R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, Novenzber 1556, Vol. 121 (1 07R-12OR) 107R Tutorial Review Time-resolved Resonance Raman Spectroscopy Steven E. J. Bell School of Chemistry, The Queen's University of Belfust, Beljast, UK BT5 5AG Vibrational Raman spectroscopy is now widely recognized as a useful technique for chemical analysis. It has become increasingly popular for the characterization of stable species since the technology which underpins Raman measurements has matured. Time-resolved Raman spectroscopy has also become established as an excellent method for the characterization of transient chemical species but it is not so widely applied. However, the technical advances which have reduced the cost and increased the reliability of conventional Raman systems can also be exploited in studies of transient species.In some cases it is just as straightforward to record the Raman spectra of a short-lived transient species as it is to monitor a more stable sample. This raises the possibility of routinely adding time-domain Raman measurements to more conventional Raman techniques, increasing the selectivity of the analysis while retaining its ability to provide spectral information which is characteristic of the species under investigation. Keywords: vibrational spectroscopy; Raman spectroscopy; resonance Raman spectroscopy; time-resolved Raman spectroscopy; transient Raman spectroscopy; excited-state spectroscopy; reaction kinetics Introduction Vibrational spectroscopy has long been recognized as a useful and widely applicable method for the characterization of a wide range of chemical species.For many years IR absorption spectroscopy dominated the field but the development of intense monochromatic laser sources in the late 1960s, and latterly multi-channel detectors, has led to a renaissance in Raman spectroscopy. The term ' Raman spectroscopy' is generally used to encompass a whole family of related techniques, each with their own inherent advantages and problems. I Normal, spontaneous Raman scattering is an inherently weak effect but Raman scattering probabilities, and therefore the signals themselves, can be enhanced dramatically through surface enhancement, resonance enhancement or a combination of both.2 The increased sensitivity which these enhanced scattering mechanisms can provide has already led to analytical applications.3--5 Both resonance and surface-en- hanced Raman spectroscopy (SERS) are most widely applied to stable species in the form of pure compounds or in mixtures, solutions, etc.However, it is a relatively straightforward step to expand Raman methods to the study of transient species, i.e., to use time-resolved Raman (TR2) spectroscopy. TR2 spectroscopy can provide information on both the structure and dynamics of transient species so that it allows the time evolution of the composition of a changing sample to be recorded. Up to this point, most time-resolved studies have been aimed at obtaining a detailed understanding of the changes in chemical structure which occur within a sample after a reaction had been initiated. In these types of studies the experiments are very carefully designed around the species of interest so that it is not possible to outline a single set of experimental conditions which constitute a general analytical technique.The approach in this review will be to outline the general principles of the most commonly used time-resolved methods, discussing the experimental protocols which may be imple- mented for different types of sample and/or chemical process (in the interest of brevity, time-resolved coherent anti-Stokes Raman methods have been omitted from this tutorial review; an excellent review of the topic was given by Kamalov et a1.6). Illustrative examples will be used alongside the descriptions of the methods wherever possible. The coverage is biased in favour of techniques based on pulsed lasers (particularly those with nanosecond pulse durations), since this reflects the balance within the literature and because such systems are now based on a mature technology and are both reliable and easy to operate.As such they probably constitute the easiest entry point for new TR2 users, particularly since, in favourable cases, they allow time-resolved (or transient) Raman spectra to be recorded with little more difficulty than those of stable species. Indeed, the experimental complexity of some TR2 methods is not much higher than that of other optical analysis techniques such as time-domain fluorescence measurements. Moreover, the appa- ratus required for such experiments, or at least some of the major components, such as pulsed laser systems and sensitive multi-channel light detectors, has become much more com- monplace so that the cost of adapting existing optical systems to transient Raman techniques is much lower than might be expected.It is hoped that, by demonstrating just how straight- forward some TR2 experiments can be, this review will stimulate new applications of the technique. However, even in favourable cases, careful design of the experiment is needed to obtain spectra of useful quality. The experimental section is intended to provide enough information to allow potential users to judge the feasibility of carrying out such measurements on their own samples and to give some idea of the type of information which they might obtain. The difficulties that may be encountered, as well as the advantages, are discussed.Although time-resolved Raman studies are still not as commonplace as those of stable species, there is still a very extensive literature on the subject? 10 A single review could not possibly cover in detail all the studies which have been carried out since the first reports of time-resolved experiments in 1976." Although the literature cited in this review has been taken primarily from work published since 1989, limiting the coverage to the last 6 years does not reduce this body of material significantly, since much of the work in the area builds on earlier studies which need to be discussed in order to put more recent work in context. Fortunately, much of the research can be divided into groups involving similar broad categories of108R Analyst, November 1996, Vol.121 compounds, such as haem enzymes, and recent comprehensive reviews of the TR2 of many of these broad categories are available. While it is desirable to discuss the types of problems which can be studied alongside descriptions of the experimental protocols, the number and range of experiments carried out with pulsed laser techniques makes it difficult to provide reasonable coverage of even the general classes of transient species which have been studied with this technique alongside the descriptions of the experimental procedures. For this reason, in the discussion of pulsed laser experiments a single class of compounds, the excited states of metalloporphyrins, is used to provide the illustrative examples. A broad overview of the application of pulsed laser Raman techniques to other classes of compounds is provided as a separate section.Raman Spectroscopy-General Considerations In order to keep this brief review as self-contained as possible, it is,useful to summarize some of the general features of Raman scattering experiments before discussing those features which are most important to transient Raman measurements. Con- ceptually, the experiments are very straightforward: a sample is irradiated by intense monochromatic radiation and the scattered photons are then collected, dispersed by a mono- or poly- chromator and detected. The resultant spectrum is plotted as intensity versus wavenumber shift (cm-I) from the excitation wavelength, as shown in Fig. 1. The frequency shift from the excitation line gives the frequency of a vibrational mode within the sample.Scattered photons appear at both higher and lower wavenumbers than the incident radiation; those which appear at lower wavenumber, the Stokes lines, are normally stronger than the anti-Stokes scattering and spectrometers are normally set to collect photons from just the lower wavenumber side.' In modern spectrometers, a laser is used as the light source. It may be any one of a variety of commonly available types, the main requirements being that it is sufficiently powerful to produce detectable signals (typically milliwatt output powers are used) and has a narrow linewidth (typically < 1 cm- 1). The sample may be a solid, liquid or gas and the detector is either a photomultiplier (in which case the spectrum is scanned point by point) or a multichannel silicon detector (a diode array or CCD), in which case the signals from a large spectral region can be detected simultaneously.Multichannel detectors have been used in most transient experiments. The main experimental diziculties arise because of the inherent weakness of the Raman effect, which means that high input laser irradiances (input power per unit area, W cm-2) are 0 2 .- 2 Fig. 1 Stokes Ra 2 3 I!, Anti-Stokes igh -600 -400 -200 0.0 200 400 600 Wavenumber Shift km-' Raman spectrum of CC14, obtained using a single-grating polychromator and a CCD detector. Raman bands to both the high- and low- wavenumber sides of the incident light (anti-Stokes and Stokes scattered photons, respectively) are of comparable magnitude to the small fraction of the elastically scattered light which is not blocked by the filter and appears at 0 cm-1.needed to produce detectable numbers of Raman scattered photons. This can be a serious problem in that the probe light can cause photochemical sample decomposition or the heating it creates can cause thermal decomposition. In addition, the scattered radiation primarily consists of reflected or elastically scattered (Rayleigh) photons, which are at the same frequency as the incident radiation, and a small number of Raman scattered photons, which lie close to them in wavelength. It is necessary to separate the weak Raman scattering from the over- whelmingly intense Rayleigh line. Until recently, this was achieved with large (and expensive) double- or triple-stage polychromators whose throughput was low. These can now be replaced with comparatively low-cost optical filters, such as holographic notch filters, which have very high optical densities (> 6) over a very narrow spectral window and have high transmittance over the rest of the required wavelength range.12 These filters effectively reject the strong Kayleigh line and so can be used with compact and inexpensive single-stage polychromators to transmit the Raman scattered photons without stray light interference, as shown in Fig. 1. Raman experiments on transient species normally involve attempts to record spectra of relatively low-concentration solutions (typically lo-5-10-3 mol dm-3). In such cases, some enhancement mechanism is needed to raise signal levels to detectable values.The most common approach is to use resonance enhancement of the transient signal, i.e., time- resolved resonance Raman (TR3) spectroscopy. Resonance Raman spectroscopy (which can be applied to either stable or transient species) takes advantage of the increase in Raman scattering probability which is observed when the wavelength of the incident radiation is chosen so that it falls within a strong electronic absorption band of the species of interest. Enhance- ment factors are difficult to calculate theoretically but are typically of the order 103-105. The only vibrations which are enhanced are those of the chromophore involved in the particular electronic transition which is in resonance; this gives both increased selectivity and sensitivity.' The selectivity can be used to good effect in studies on complex sample mixtures, eg., biological samples, where small regions of very large molecular assemblies can be selectively probed.'? On a more prosaic level it also allows vibrational spectra of dilute coloured samples within a non-absorbing solvent to be recorded since the solute Raman bands are enhanced over those of the solvent.One disadvantage of tuning the excitation source into an electronic absorption band is that absorption of incident radiation reduces its absolute intensity in regions deeper within the sample. This is compounded by the fact that the Raman scattered photons emanating from the sample will be at wavelengths similar to the incident radiation and can also be absorbed before emerging from the sample and reaching the detector.The result of these self-absorption effects is that although the relative magnitudes of solute versus solvent bands can be dramatically increased by resonance effects, the total Raman signal will actually fall under resonance conditions, as shown in Fig. 2. Experimental Methods for Time-resolved Raman Spectroscopy Time-resolved Raman methods have been used to record the vibrational spectra of a large number of different transient species. This diversity in sample types has led to the development of many different initiation and Raman monitor- ing protocols, some of which are illustrated in Figs. 3 and 4. These experimental techniques can be divided into two broad categories, those which use laser photolysis (or pulse radiolysis) for initiation of the reaction and those in which the process is initiated chemically or electrochemically.The ultimate time resolution of the pulsed methods is extremely fast,'4-'6 but theAnalyst, November 1996, Vol. 121 109R methods are limited to studies of processes which can be initiated by light or pulse radiolysis. For our purposes, it is logical to discuss these broad categories separately, in the order shown below, beginning with the most generally applicable chemical methods before dealing with the various photochemical experiments in increasing order of technical sophistication: (i) Chemically initiated processes. (ii) Photochemically generated transient species. (iii) General considerations for photochemical initiation.( i v ) Single-colour methods. (v) Two-colour experiments. Chemically Initiated Processes The simplest form of time-resolved Raman experiments can involve the monitoring of relatively slow changes in chemical composition with time. If the time-scale for the process is hours then modern spectrometer systems, which can record spectra within a few minutes, can be used to record the spectral changes in much the same way as for stable samples. The general protocol is illustrated in Fig. 3(a). The limiting time-scale for the measurements is the time required to acquire a spectrum of appropriate signal-to-noise ratio [t, in Fig. 3(a)]. This accumula- tion time can be reduced if the signal level can be increased, through either resonance or surface enhancement mechanisms.Many of the studies in this area have used surface enhance- ment,17-24 since this can be particularly effective at increasing signal levels, but there is no fundamental reason why real-time TR3 measurements should not be used instead, provided that the signal levels are adequate.2s Recent reports of real-time or time- resolved SERS (TRSERS) measurements have shown that the total signal accumulation time can be reduced to a few seconds or less, which has allowed the dynamics of species localized on SERS-active substrates to be monitored on the seconds time- scale. Similarly, TR3 measurements have been made on smooth electrode surfaces which are not SERS active.2s The combina- tion of surface and resonance enhancement mechanisms (surface-enhanced resonance Raman spectroscopy, SERRS) should allow even greater enhancement factors with corre- spondingly higher time resolution. Although SERS is normally carried out on Ag or Au surfaces, it has been possible to monitor the formation of surface species created from adsorbed gaseous molecules on other metal surfaces by overcoating an Au surface with ultra-thin layers of transition metals, such as Rh, and then monitoring reaction dynamics on the time-scale of sec- onds.17, 8 The short signal accumulation time required for strongly scattering SERS-active species has prompted the use of time- dependent Raman signals as a chromatographic detection method. Since the eluent, whose composition changes with time, must flow past the detector, the SERS-active medium must either be continuously mixed with the sample upstream from the detector22323 or must be fixed in the detection zone and regularly regenerated, e.g., by electrochemical oxidation- reduction ~ y c l e s .2 ~ A most striking example has been in the use of SERS to detect purine bases eluted from an HPLC column, where the differences between the Raman signatures of the bases has allowed them to be readily identified as they elute from the column.23 Because SERS and resonance Raman measurements can be carried out on electrode surfaces within electrochemical cells, they can be used to monitor processes which are themselves initiated electrochemically, rather than through external chem- ical methods. For example, by applying a step potential and then recording a series of spectra after this initiation step [Fig.3(a)], the intermediates formed on reduction of p-nitrobenzoic acid 1800 16bO 1400 1200 lob0 Wavenumberkm- Fig. 2 Effect of increasing concentration on the resonance Raman spectra (Aex = 457.9 nni) of a metal-polypyridyl complex, C U ( B ~ ~ ) ~ + (Bpy = 2,2'- bipyridyl), in acetone solution. At the lowest concentration the spectrum is almost that of the pure solvent; at the highest concentration the Raman bands due to the complex solute have increased with respect to those of the solvent, but this has been achieved at the cost of a 10-fold decrease in the absolute Raman signal. The decrease in the absolute signal intensity is clearly apparent from the increased apparent noise level at the higher concentrations. All spectra were accumulated for only 10 s to emphasize the effect; superior signals could readily be generated using longer accumula- tion times.Concentrations: (a) acetone only; (b) 3.0 x 10-5; (c) 1.0 x 10-4; (d) 2.5 x 10-4; and (e) 4 x 10-4 mol dm-3. Fig. 3 Schematic diagrams of a range of protocols which have been used to obtain TR3 spectra. (a) Initiation, either chemical or electrochemical, followed by a sequence of spectral acquisitions. (b) Synchronization of an extended series of probe laser pulses with a repetitively cycled electro- chemical potential step. (c) Rapid mixing followed by downstream Raman probing with a CW laser. (d) Continuous photochemical initiation followed by downstream monitoring.110R Analyst, November 1996, Vol. 121 were recorded at 10 ms time intervals.ly,20 Similarly, the formation of surface metal oxides and hydroxides on electro- oxidation of Pt, Au, Rh and Ru overlayers on roughened Au substrates have been recorded at 8 s intervals during the potential sweep.2’ It is possible to increase the time resolution of such experiments if a pulsed laser is used as the monitoring source, but a different protocol is required since the signal obtained from a single laser pulse (or even a short sequence of several laser pulses) will be very weak. The solution to this problem is to take advantage of the fact that the experiment can be repetitively cycled by synchronizing the laser pulse to fall on the sample at the same point in the electrochemical cycle at each repetition, as shown in Fig.3(b). The signal can then be accumulated for as long as is necessary (typically thousands of laser pulses) before the time delay is changed. This strategy has been used to study the first steps in the reduction of heptylviologen films to radical cations with sub-millisecond tirpe resolution, using both TR” and TRSERS measure- ments .25 In the case of chemically generated species, fast mixing techniques, which generate a continuous flow of reacting species downstream from the mixing chamber, have been widely used, particularly for studies of biochemical processes which cannot be initiated photochemically. In these experi- ments [illustrated in Fig. 3(c)], the sample composition at a given point downstream from the mixing chamber remains constant, so that the Raman experiments can be carried out in much the same way as normal Raman experiments on stable species.In such experiments, the time resolution is limited by the sample mixing time. Considerable ingenuity has been expended in reducing these mixing times, with the development High Irradiance - - - _ ---I- Transient Concentration \ ... Time -> Gate pulse ‘on’ . ’ * - - Transient Concentration Pump Probe I-At -1 Time I=> Fig. 4 Schematic diagrams of the processes involved in single-colour transient resonance Raman experiments (upper diagram) and two-colour TR3 experiments (lower diagram). In both cases the transient population rises during the excitation pulse. In the single-colour technique this pulse also acts as the Raman probe and in the two-colour technique a second (time-delayed) laser pulse is used as the Raman probe.of turbulent mixing systems with dead times as low as hundreds of microseconds.26 Even more sophisticated systems, based on collisions between streams of droplets of approximately 100 pm diameter, have been developed. With these systems, mixing times of hundreds of microseconds have been demonstrated for the reaction of Fe” with l,IO-phenanthroline.27~2~ Photochemically Generated Transient Species Generul considerations Photochemical generation of transient species is a clean and convenient method of making large concentrations of a transient of interest within a very short time and in an easily accessible form, typically in the body of the spectrometer itself It is not surprising that the majority of transient species studied have been generated photochemically, rather than chemically.Although the method cannot be completely general, in that it depends exclusively on light initiation, it is not confined exclusively to excited-state studies since the photolysis can be used to generate ground-state species, i.e., photoini tiation can mimic the effects of thermal processes such as deligation or radical formation. For most photochemical TR3 studies, the initiation is by a pulsed laser source but for very photolabile compounds pulsed laser irradiation rapidly leads to decomposition so, as an alternative method, CW irradiation can be coupled with flow systems as shown in Fig. 3(d).2930 In the most straightforward variant of this approach, the same laser is used as the photolysis source and Raman probe.As the sample enters the irradiated volume it is photolysed and for the remainder of the time it remains within the beam and the photoproducts thus generated can Raman scatter. A second variant of this techniques uses two CW lasers, one positioned upstream and used to generate a photoproduct continuously and the other monitoring the photoproduct as it passes downstream. The time resolution is set by the length of the stream which is irradiated and the flow rate. If the photoreaction is reversible, the sample can be recirculated or both lasers can be focused at different points of the circumference of a rotating cell where again the sample passes first through a photolysing and then a monitoring region. This approach has been extensively used in studies of visual pigments (see below).The most popular experimental technique for Raman studies of photochemically generated transient species involves pulsed lasers, which are used to both initiate the chemical reaction and to give the Raman probe radiation. There are two main variants: single-pulse techniques, where the same laser pulse is used for initiation and probing, and two-colour experiments, where pairs of laser pulses are employed. In the latter, one pulse initiates the process and the second is used as the Raman probe, as illustrated in Fig. 4. The same general protocols are used irrespective of whether nanosecond or picosecond pulses are used but, for the purposes of illustration, discussion in this review will assume that nanosecond duration pulses are used.Typically, the transient species are generated at low concentration so that the experiments are carried under resonance conditions, i.e., the wavelength of the probe laser is tuned to fall within a strong electronic absorption band of the transient of interest. The photolysis pulse must, of course, also fall within an electronic absorption band to allow optical pumping to take place. Alternatively, a pulse of high-energy electrons (I 0 ns, 2 MeV) can initiate the reaction.10 The use of pulsed lasers in either single- or two-colour experiments, coupled with absorbing samples, exacerbates the problem of sample decomposition, since very high peak powers and irradiances can be generated. Indeed, it is possible to generate non-linear effects within samples even using the outputAnalyst, November 1996, Vol.121 l l l R of small pulsed lasers. For example, a 10 mJ pulse with a half- width of 10 ns (assumed square) has a peak power of (10 x 10-3 J ) / ( ~ o x 10-9 s) = 106 w If this pulse is focused into a sample with a beam waist of SO pm, the peak irradiance will be 106 W/~c(0.0025)~ cm? = 5 X 10" W cm-2 Under such conditions, it is hardly surprising that two-photon effects and sample decomposition can occur. The obvious solution to these problems is to reduce the input laser pulse energy but, since the Raman signal generated in a given time is directly proportional to the total number of input photons ( i x . , the average incident power), this reduces the signal which can be accumulated within a given time.A second option is to decrease the irradiance at the sample by defocusing the input beam and, since the irradiance is proportional to l/(diameter)2, this readily decreases the irradiance. However, defocusing the beam but retaining the energy per pulse will not give the same detected Raman scattering intensity, since the image of the sample which falls on the spectrometer slit will also grow larger and thus a smaller fraction of the scattered photons will actually pass through the slit and enter the detector. This is the reason for the common practice, when using a back-scattering geometry, of using a cylindrical lens to focus the input laser to a line on the sample, rather than focusing to a point. By defocusing to a line the irradiance is decreased compared with the point focus, but the Raman scattered photons may still be collected efficiently since the line image will still pass through the entrance slit to the monochromator.In practice, experiments are typically carried out near the sample damage threshold to maximize the signal which can be obtained. The best way of maximizing the average power incident on the sample (and therefore the Raman signal) but keeping the peak power generated within the laser pulses low (and so reducing photolysis and sample damage problems) is to use pulsed laser systems with high repetition rates. This approach is well established for picosecond TR3 experiments, where mode- locked lasers can be used to produce either relatively low- energy (nJ) pulses at MHz repetition rates or amplified kHz pulse streams with higher energies (pJ) by a range of different methods.14915.31 In picosecond measurements the short duration of the pulses means that peak powers in the non-linear regime are reached at much lower pulse energies than with nanosecond pulsed systems, so that higher repetition rates are necessary to reduce peak powers to usable levels while maintaining the average power needed to record Raman spectra. With the nanosecond pulse duration, kHz repetition rate Nd : YAG lasers which have recently become available, this high repetition rate approach should become much more common for transient studies using nanosecond pulses? These lasers have the potential to increase dramatically S/N and/or reduce the signal accumulation times compared with more conventional systems operating at < 100 Hz.A major problem with many samples which have been photolysed by pulsed lasers is that they may luminesce strongly in the same spectral region as the Ruman scattered photons. Since this luminescence creates a broad background upon which the Raman bands are superimposed, even moderate lumines- cence can degrade signal quality and at higher levels can completely prevent observation of the bands. The problem is not merely that the Raman bands are concealed by the background. If this were the case then subtraction of a smooth background correction function could eliminate it. Rather, it is that the random photon shot noise associated with the background can be larger than the Raman signals themselves.This noise cannot be digitally subtracted away. Many different approaches have been taken to reduce background luminescence, which is a problem in both normal and transient Raman experiments. Methods which work by quenching the electronically excited states responsible for the luminescence, e.g., by adsorbing the sample on a metal surface (i.e., SERS and SERRS), are inappropriate if it is these states which are the target of the TR? study. In some circumstances it has been shown that photorsac- tions can be induced and monitored on SERS-active surfaces, but these are very much the exception.33 Another approach is to use any differences in the duration of the Raman signal (scattering occurs only within the duration of the probe pulse) and luminescence background.The most widely used strategy is to use a 'gated' multichannel detector in which incident photons are amplified by an intensification stage before falling on the array of light sensitive elements in the diode array or CCD. The accelerating voltage on the intensifier can be turned on and off in less than 10 ns so that the detector can be made active only during the time period when the laser pulse is falling on the sample and the Raman scattering is generated. This means that other background radiation, either luminescence from an electronically excited sample or broad background radiation caused by the photolysis pulse, is rejected. It is useful to separate the discussion of single- and two- colour experiments but to illustrate the points made using examples of experiments made on a single class of compounds.There are several classes of compound for which sufficient literature data are available, such as haem enzymes, but recent reviews of these systems are already available.?4-36 One major class of compounds which has been extensively studied in the past S years and which provides useful illustrative examples is the porphyrins. No extensive review of the TR3 of excited states of porphyrins has yet been published but they do show a remarkable variety in their exci ted-state properties, due to alterations in the nature of their lowest excited states with changing central metal ion, exogenous ligands and porphyrin structure.37 Many of these excited states have now been characterized by transient Raman methods. Some experimental data on these systems are presented in the following section (the nomenclature used is shown in Fig. 5 ) and a fuller discussion is given along with those of other well-characterized systems in a later section.Single-colour experiments The simplest pulsed laser expel-iments are so-called single- colour experiments u2hei.e high in-adiance laser pulses are both used to initiate the photoreaction and then to Raman probe the transient species created. At low irradiance the total number of incident photons per pulse will be lower than the number of K R R = <\ /> TPP TPPS %+- C H 'I'MPyP M = 2H. Zn, c'u Fig. 5 examples herein. Nomenclature used for the meso-substituted porphyrins used as112R Analyst, November 1996, Vol. 121 absorbing molecules present in the sample and the Raman scattering will necessarily be dominated by scattering from the unphotolysed sample. As the irradiance is increased, either by increasing the energy per pulse or focusing the beam more tightly, the leading edge of the pulse will contain sufficient photons to initiate the photoreaction.The trailing edge of the pulse will therefore encounter a photolysed sample and the total Raman signal will contain contributions from both the photo- lysed and unphotolysed sample (see Figs. 4 and 6). At very high irradiance, most of the incident photons will encounter photolysed sample and the signal is dominated by the transient species which are created. The irradiance level at which this occurs will depend on a number of factors: ( i ) the sample concentration; (ii) the absorption coefficient of the unphotolysed sample at (iii) the lifetime of the transient species; and (iv) the relative Raman scattering probabilities (cross-sec- tions) of the starting material and the transient.the laser wavelength; The first two factors are interrelated; a sample with a lower absorption coefficient at the laser wavelength will typically be used at higher concentration to achieve a reasonable ab- sorbance. This will mean that the number of photons required to achieve, for example, a two-fold excess of incident photons over sample molecules will increase proportionately, e.g., the sample will be more difficult to pump optically. The lifetime of the transient species is an important variable only if it is shorter than the laser pulse duration.If it is longer, then the average concentration of the transient species which is encountered by the laser pulse will be the same irrespective of whether its ultimate decay takes place shortly after the pulse has entered the sample or at a time delay hundreds of times that of the laser pulse width. For this reason, the term transient Raman (or resonance Raman) spectroscopy should be preferred over time-resolved resonance Raman (TR3) spectroscopy, since these single-pulse techniques give only limited dynamic information in comparison with the two-colour pulsed tech- nique described below. The final factor that controls the relative contributions of the transient and unphotolysed molecules to the Raman spectrum is their relative Raman scattering cross-sections.The most convenient conditions are those where the Raman scattering cross-sections of ground-state and transitory species are of similar magnitude and so follow the relative concentrations of material present in the sample. These conditions can often be realized relatively easily in practice since the experimental wavelength is chosen so that both ground-state and transient species are strongly absorbing. If the imbalance is too great then it can be difficult to record spectra of both transient and unphotolysed species using laser pulses of the same duration and wavelength. For example, the contribution from a weakly scattering transient species may be drowned by residual unphotolysed material, while a very strongly scattering tran- sient will dominate spectra even under conditions where only a few per cent. of the sample has been photolysed.This second problem is particularly difficult to solve since the only way to reduce the proportion of transient present is either to decrease the incident irradiance or increase the sample concentration. Unfortunately, decreasing the laser irradiance also reduces the Raman signal, whereas increasing sample concentration will also decrease the absolute intensity of the Raman signal, owing to self-absorption, and may be precluded by low solubility. For example, whereas the MLCT state of R~(Bpy)3~+ (whose lifetime is approximately 600 ns) can readily be observed using 10 ns duration laser pulses,3x it is extremely difficult to reduce the input laser irradiance to sufficiently low levels to observe a spectrum of the ground electronic state with the same pulses.Indeed, the transient is sufficiently strongly scattering that it can be observed even using a tightly focused CW laser, whose power is of the order of 100 mW, as opposed to the MW peak powers of nanosecond pulsed lasers.39 The one great advantage of the single-colour technique, apart from its experimental simplicity, is that it can he used to record the Raman spectra of transient species which have V Pulse Energy A 400 450 500 550 Wavelength /nm 1200 1400 1600 W avenumber/cm- Fig. 6 Example of single-colour Raman data showing the effect of increasing laser pulse energy (Aex = 435 nm) on the resonance Raman spectrum of Cu(TMPyP) in aqueous solution with excess 5’-deoxythymidine monophosphate (5’dTMP).Pulse energies: (a) 0. I , (b) 1 .S and (c> 4.0 mJ. The two strongest transient bands (marked with asterisks) increase with respect to those of the unphotolysed complex at higher pulse energies. Inset: (a) UV/VIS absorption spectrum of a similar sample and (b) its transient absorbance difference spectrum. Note that both ground-state and transient species have significant absorbance at 435 nm.Analyst, November 1996, Vol. 121 113R lifetimes significant1.y shorter than the laser pulse duration. This is because, as discussed above, extremely high photon fluxes can be created under what would, at first sight, appear to be relatively mild conditions. For example, a single pulse at 500 nm with an energy of 1 mJ contains 2.5 X 1015 photons, and if this pulse is incident on a sample which is 100 pm in diameter, 1 mm deep and has a concentration of mol dm-3, the number of solute molecules it encounters is (50 X X (6 X 1023) = 4.7 X 10".This is approximately a 5000 : 1 ratio, so that within the duration of a 10 ns laser pulse each molecule would have available 5000 photons, i.e., one photon per 2 ps. Of course, only a fraction of these photons would be absorbed, but clearly even if only 1% are absorbed the pumping rate is sufficiently high that a transient with a lifetime as short as 200 ps will have a significant pseudo-steady-state population throughout the laser pulse. The limiting factor in such experiments is normally not how to generate these high photon densities but whether the sample is sufficiently robust to withstand them without photodecomposi- tion.However, even in cases where lower irradiances are used (to prevent decomposition), the excess can remain so large that the phototransient is observed at all but the very lowest incident power levels. For example, the transient species whose spectrum can be seen to increase with increasing irradiance in Fig. 6 has a lifetime of < 1 ns4" but it is observed (albeit only as shoulders on the main bands) even when the input pulse energy is reduced to one fortieth of its highest value. m)' X 3.14 X m) X (10-4 X lo1 mol m-3) TMTo-colour TR" spectroscopy In two-idour TR-+ spectroscopy, pairs of laser pulses of different wawlength are used to photolyse (optically 'pump') and then to Ranian pi-obe the transient o j interest.The spectral window of the detector is set so that it corresponds to the frequency range of the Raman scattering from the probe laser and the time evolution of the transient signal is monitored by recording a series of spectra at different delays after the photolysis event.f.7-10 The most flexible arrangement is to use two synchronized lasers as the sources of pump and probe light, but both pulses can be taken from the same laser source if it is coupled with a wavelength-shifting device and a means of generating an optical time delay between the shifted and unshifted pulses. With picosecond pulsed lasers this second method is the n0rm,14.~~ optical time delays between pulses up to a few nanoseconds being readily generated by moving optical stages.For experiments on the nanosecond time-scale, it is still feasible to introduce optical delay paths of perhaps 30 m (approximately 100 ns), but generating delays of hundreds of nanoseconds using even longer delay paths becomes im- practical. A schematic diagram of the system used in the author's laboratory, which is a standard configuration for these types of experiments, is shown in Fig. 7. The basic design of these systems has not changed significantly for several years.41 Higher repetition rate lasers, holographic notch filters and CCD detectors can be incorporated into this design and will probably become the norm over the next few years. Much more rapid technological progress has been made in the design of systems used for measurements on the picosecond time-scale.The specific design criteria for such systems and the extraordinary progress which has been made in meeting these criteria have recently been reviewed. l 4 The essential components of a nanosecond TR3 system are shown in Fig. 7. The core of the system is the pulsed lasers, which can be any one of a number of types, the main requirements being: (i) sufficient energy in the photolysis pulses to produce a detectable concentration of transient; (ii) average power in the probe pulse stream high enough to give detectable Raman scattering; (iii) narrow linewidth in the probe pulses, preferably < 1 cm-1; and (iv) pump and probe pulses both at appropriate wavelengths for the sample. In the system shown in Fig. 7, two Nd : YAG lasers produce 1064, 532, 355 and 266 nm pulses with a half-width of approximately 8 ns at a repetition rate of 10 Hz.Firing of both lasers is synchronized via a digital pulse generator, the timing jitter between the pulses being < 2 ns. The intensified diode- array detector is gated and also triggered from the pulse generator so that it is active for about 10 ns when the Raman photons from the probe laser fall on the detector but inactive for the remainder of the experimental cycle. This gating therefore rejects the scattered light from the high intensity pump pulse and also acts to remove luminescence. To give more wavelength tunability than is provided by the Nd : YAG lasers, the output pulses are either used to pump a dye laser or are Raman shifted with simple gases (H2, D2 or CH4).Raman shifting is a much less expensive means of generating a range of output wave- lengths than is a dye laser; both the initial cost of the equipment required and the running costs are lower, but it does not provide a continuously tunable wavelength range. However, a large number of output wavelengths can be generated using this system (the wavelengths generated by Raman shifting the fundamental and frequency doubled and tripled outputs of Nd : YAG lasers are given in ref. 42) and for most purposes it is not essential to be exactly on-resonance with a UV/vIS absorption band of the sample. Both pump and probe pulses must be focused into the same region of the sample. The simplest method of achieving this is to combine the beams and then to bring them into the sample colinearly.Normally the diameter of the pump beam at the sample is set slightly larger than that of the probe to ensure that only photolysed sample is Raman probed. The sample can be contained in a variety of ways, but the most usual methods for ensuring that the probed volume is constantly being regenerated are to flow the sample as a jet (or within a capillary) or to put the solution into a spinning cylindrical cell, such as an NMR tube. In an ideal e,vperiment, the sample is optically pumped at a wavelength where it is strongly absorbing but is then probed at a diflerent wavelength, where the transient species of interest is strongly absorbing but the unphotolysed sample is not. Until recently, experiments were limited to transient species which absorbed in the visible region, but methods for TR3 spectro- scopy with probe wavelengths in the UV region have now been developed and applied to both biological and simple chemical transients.4348 Under ideal absorption conditions, a high Samde I OMA I I I I Pulse Generator I------- I.__ Raman Shifter Nd/YAG Laser Fig.7 in the nanosecond time regime. Laboratory layout of a typical TR3 experimental system operating114R Analyst, November 1994, Vol. 121 proportion of the transient can be generated and its Raman signal will be strongly resonance enhanced. Indeed, the only signal, apart from solvent, which will be detected will be due to the transient, since the Raman signal of unphotolysed starting material will be vanishingly small. The best chance of achieving these conditions will be when pump and probe wavelengths are well separated, e.g., in stilbene, where the A,,, of the ground state is around 300 nm but that of the lowest excited singlet state is at 600 nm.I4 In the absence of a photolysing pulse, a dilute stilbene sample has no absorbance at 600 nm and the Raman signal is merely that of the solvent.The transient signal only appears upon photolysis and is therefore easy to d i s t i n g u i ~ h . ~ ~ However, for many samples the choice of pump and probe wavelengths is less clear because there is no wavelength at which the transient absorbs but the ground state does not. This gives the minor problem that the unphotolysed sample may give strong Raman signals, which will interfere with those of the transient unless the photolysis pulse is 100% effective in depopulating the starting material.More significantly, if the sample absorbs at the probe wavelength, then high irradiance probe pulses may generate a transient species, irrespective of whether the sample has been photolysed or not, and indeed this is the essence of the single-colour technique, but in TR3 experiments it has the effect of eliminating the dynamic information. To circumvent this secondary photolysis problem, it is necessary to reduce the irradiance of the probe pulse at the sample, with the associated loss in overall signal levels. Indeed, one of the reasons why the single-colour technique is experi- mentally simpler than two-colour methods is that in the former the transient signal is improved by increasing the probe laser irradiance (subject to sample damage limitations) whereas in the latter it is necessary to reduce the probe laser irradiance at the sample until no transient signal is present.In effect, the lowest irradiance level used in single-colour experiments is the upper limit in two-colour TR3 experiments. The major advantage which the TR3 approach provides over single-colour transient Raman experiments is the ability to monitor the dynamics of the transient species created in photolysis by monitoring the time evolution of the signal. In many cases the dynamics can be measured much more easily using conventional flash photolysis, so it might appear that little additional information is given by TR3, as opposed to a combination of single-colour Raman and conventional flash photolysis measurements.However, given the ease with which single laser pulses can generate even short-lived transients, it is important to confirm that the species probed in a single-colour experiment is indeed the transient of interest, rather than a species whose lifetime is similar to that of the laser pulse. Such a transient can dominate the spectrum recorded in a single- colour Raman experiment but can be very difficult to discern using flash photolysis. TR3 data can show that the dynamics of processes measured using flash photolysis and Raman scatter- ing techniques are similar. For example, in the TR3 spectra of ZnTPPS,”) shown in Fig. 8, a transient species with a strong band at approximately 1600 cm-l, is present 30 ns after photolysis and decays away within 10 ps; the species probed is the T1 state since its lifetime matches that recorded using flash photolysis measurements.Of course, the experimental conditions needed to record transient Raman data are critically dependent on the properties of the transient, so that the most efficient approach is to obtain as much information on the transient species as possible (e.g., using conventional flash photolysis) before embarking on Raman experiments. For example, in the ZnTTPS case discussed above, the lifetimes of the excited singlet and triplet states (approximately 2 ns and > 5 ps) and their absorption spectra (both absorbing strongly at approximately 430 nm) were determined in advance. On the basis of this information, it was clear that the optimum laser probe wavelength should be approximately 430 nm but that single-colour experiments with 10 ns pulses could give transient spectra with at least some excited singlet-state character in addition to the triplet.However, using the same probe laser wavelength (with low- energy pulses) but optically pumping at 532 nm, where the ground state absorbs, ensures that only the longest lived transient is observed. As expected, the spectra show the largest population of transient at the shortest delays and a simple regeneration of ground-state bands as relaxation proceeds. Another illustration of the advantages of TR3 over single- colour experiments is given by the studies of the transient species formed by excitation CuTMPyP in the presence of a high molar excess of a mononucleotide (5’dTMP).The single- colour data on this system (shown in Fig. 6) provided spectra of the transient, which was generated within the duration of a single 8 ns laser pulse, but gave little further information on the dynamics of its formation and subsequent decay. By moving to two-colour TR3 experiments with shorter pulses, it is possible to monitor both the formation of the transient (approximately 50 ps) and its subsequent decay (Fig. 9). In fact, for this system both processes are complete in about 1 ns so that within the 8 ns pulse duration used for the single-colour experiments several excitation-decay cycles can take place. The time resolution of TR3 experiments is set by the laser pulse duration and can be as fast as a few picoseconds or less,16 the ultimate limit set by the Heisenberg uncertainty principle.l 4 With Q-switched Nd : YAG lasers the resolution is typically tens of nanoseconds, but a recent report demonstrated that by using pairs of about 5 ns pulses from the same laser source it was possible to record the dynamics of a transient species whose lifetime was of the same order as the cross-correlation time of the laser pulses (approximately 100 ps).51 Sub-nanosecond events have also been characterized by ‘optical depletion timing’ using pulses of similar durati0n.5~ Data Analysis Most of the applications of TR3 listed in the following section are concerned with following structural changes in key components in the sample following excitation, but this is a Robe M Y 10 ps pump-probe time delays marked.The spectrum of the triplet state (At = 30 ns) is dominated by a strong band at approximately 1600 cm-I; recovery of the ground state is accompanied by loss of this band and growth of the strong feature at approximately 1350 cm-I. The similarity of the spectra obtained at 10 ps and and with the probe laser only shows that relaxation to the ground state is complete at this time delay. hpump = 532 nm, 8 mJ; hprobe = 447 nm, 1.5 mJ.Analyst, November 1996, Vol. 121 11SR - reflection of the interests of those who carried out the studies rather than a property of the method itself. TR3 has the potential to be used as a direct and highly selective quantitative analytical method since, at the simplest level, for analytical applications it is not strictly necessary to assign the features characteristic ofthe species of interest to particular vibrational modes provided that some c$ the bands are indeed character- istic of the species of interest and distinct from those ofpossible interfering molecules.The highly structured form of the spectra should allow identification of species of interest, and the method can be made highly selective by a combination of resonance effects (selection of the probe wavelength to match the absorption spectrum of the species of interest) and the use of the time domain to select, for example, only long-lived transient species from a complex mixture. Fig. 10 shows the ground-state and transient absorbance difference ( A A ) spectra of H2TPP along with the Raman excitation profile of the ground and TI states.53 It is clear that strong Raman scattering by the transient is only observed over a relatively narrow probe laser wave- length range.By selecting a probe wavelength outside this range or monitoring at longer delay times, it is easy to discriminate against the signal for this species. The most straightforward quantitative analysis used for TR3 data, and the one most commonly employed, is simply to measure the intensity of transient bands with respect to an internal standard, such as a solvent band. However, much more sophisticated multi-dimensional least-squares data analysis of excited state Raman spectra has been demonstrated for model systems.54.55 Such treatments are valuable in situations where saturation of the transient species is important, i.e., where the transient signal, even after correction for self-absorption effects, does not increase as the square of the incident irradiance.The single-colour technique clearly has potential as an analytical tool which has not been widely exploited, presumably because of the technical difficulties which were undeniably present until even a few years ago. Up to this time, the main objective of most transient Raman studies has not been direct quantitative analysis but rather structural determination of the transient species, and for this reason the simple fingerprint analysis has been supplemented by a range of vibrational mode assignments of varying complexity and rigour. At the simplest level, the vibrational features can be compared with model, chemically stable species.A clear example of this is in studies of Ru(Bpy)32+,38.39 whose excited- state spectrum contains two sets of features, one set in positions very close to those of the ground-state complex and a second set which are moved to a lower wavenumber and closely resemble those of chemically reduced Bpy in Li+Bpy- . The structure of the excited-state species can therefore be formulated as Ru"'Bpy2(Bpy-), the shifted bands arising from an excited state where the optically excited electron is localized on just one of the three available Bpy ligands. The next step upwards in sophistication in the analysis of TR3 data is to carry out some form of normal-mode analysis of the transient species investigated. This tends to be a much more difficult task but it has been completed for some systems such as the charge-transfer excited state of R~(Bpy)3~+ referred to above.56 Even in the ground state a full normal-mode analysis requires considerable experimental effort, typically involving studies of isotopically substituted compounds, use of a series of different excitation wavelengths, if resonance Raman spectra are required, and IR absorption spectra to find Raman-silent modes.57 With transient species the data sets are normally much more limited, so that even if series of isotopomers are available it is not normally possible to record spectra at a series of probe wavelengths.Similarly, although there have been major steps forward in time-resolved IR spectroscopy,-5x transient TR spectra are not normally available.However, it may be possible to assign bands in transient spectra by analogy to ground-state counterparts whose origin is known. For example, Fig. 1 1 shows the ground- and TI-state spectra of H2TPP. (The spectra were obtained in a manner very similar to that used for the ZnTPPS spectra discussed above.) A strong band is clearly visible at about 123.5 cm-I in both the ground- and triplet-state spectra of the complex. It is known that this band in the ground- state spectrum is v l , the stretching vibration of the bond connecting the phenyl ring to the porphyrin57 but the question to be addressed is whether the band which appears in a similar position in the T I spectrum has a similar origin. By recording spectra of a second isotopomer in which the aryl ring cubstituents have been deuterated (D20).it is possible to monitor the effect of phenyl ring deuteration on the position of this band in the ground and triplet states.59 As expected, the band is sensitive to this isotopic substitution, moving to about 1 186 cm-1 in the ground state. Moreover, the same frequency shift is also observed for the unidentified triplet state band, confirming that it has a similar composition to the well characterized ground-state band. In extreme cases, the band positions associated with particular modes can move by very large ~~ ~ 1200 1400 1600 Wavenumber /cm-' Fig. 9 TR3 spectra of Cu(TMPyP) in aqueous solution with excess S'dTMP. Pump-probe time delays as shown. Bands due to the transient species (marked with asterisks, as in Fig.6) build to a maximum at SO ps before decaying, at 950 ps, to the same level as is observed at 0 ps (where the probe pulse just precedes the pump pulse). hump = 540 nm, 15 pJ; hprobe = 418 nm, 0.5 pJ.116R Analyst, Noveniher 1996, Vol. 121 amounts. For example, in ground-state benzophenone the carbonyl C-0 stretching vibration is at 1665 cm-I, the lowest lying triplet state is n-n* in character and in its resonance I t a ) I I I 420 440 460 480 Wavelength /nm 430 440 450 460 Wavelength /nm Fig. 10 ( a ) Ground-state UV/VIS absorption spectrum and (b) transient absorbance difference spectrum (At = 30 ns) of H2TPP. (c) Resonance Raman excitation profiles of the ground and the triplet states of H2TPP. . , n.a. Triplet I 1000 1200 1400 16'00 Wavenumber / cm-l Fig.11 Resonance Raman spectra of the ground and triplet states of natural isotopic abundance (n.a.) H2TPP and its D20 isotopomer. Note this similarity in the isotope shifts of the V I band (marked) in both the ground [(a) and (b)] and triplet [(c) and (d)] states. Raman spectrum the band moves to 1222 cm-1.60 Many studies of the structural changes which occur following excitation have followed the approach of comparing changes in vibrational mode frequencies with calculated changes in structure and, as computational methods of reasonable sophistication become more accessible, this approach is likely to become even more widespread. Examples of Compounds Studied With Pulsed Laser Techniques Because the use of pulsed laser photolysis has been so very widely adopted as the best method of characterizing the transient vibrational spectra of so many different compounds, it is not possible to discuss all examples in sufficient depth to be meaningful or helpful.This is partly because the number of vibrational studies is large, but mostly because the vibrational studies are not carried out in isolation and a great deal of background information needs to be included to place the data from Raman studies within their wider context. In addition, some comprehensive reviews, which cover in useful detail all the relevant work carried out on particular classes of com- pounds in recent years, are available. For these reasons, detailed descriptions and comprehensive lists of references have been replaced in this review by Fig.12 and the text below, which is an attempt to illustrate some of the major classes of compounds that have been studied using pulsed laser techniques in the past 5 years, along with a very brief description of the type of information obtained, and recent references to work carried out by groups interested in these particular systems. It is hoped that this method of presentation will both illustrate the breadth of work available in the literature and demonstrate that TR3 methods need not be confined to a small set of particularly favourable compounds. Porphyrins and Metalloporphyrins The properties of the excited states of metalloporphyrins are extremely diverse but are dominated by the nature of the central metal i0n.3~ Their lifetimes vary by several orders of magnitude so that a range of transient Raman techniques have been used to characterize them.In broad terms, the photochemistry of the free-base (metal-free) and closed-shell metal complexes is dominated by porphyrin n-n* singlet and triplet excited states, with lifetimes of the order of a few nanoseconds and microseconds to milliseconds, respectively. TR3 studies of several free ba~e,s0,59,~~-66 Mg67 and Zn5",6*-72 porphyrins have been reported, as have spectra of closely related chlorins73 and even bacteriochlorophylls.74-77 The specific vibrational sig- nature of the TI states of tetraphenylporphyrins has been used to monitor intramolecular electron transfer to a covalently at- tached quinone m0iety.7~ With open-shell metal ions other low- lying d-d, metal-to-ligand and ligand-to-metal charge-transfer (MLCT and LMCT) states can be populated.Moreover, the energy differences between the various excited states is relatively small so that it is possible to switch the nature of the lowest excited state not only by changing central metal ion but also by altering porphyrin substituents or even the solvent. TR3 studies of Ni porphyrins, in which the d-d excited state lies lowest in e n e r g ~ 6 5 . ~ ~ and the MLCT state of RuI'TPP have been reported? For iron porphyrins the primary effect of photo- excitation is either photoreductionso or dissociation of axial ligandsg' (used extensively in studies of haem enzymes, shown below). Copper(I1) porphyrins show particularly complex behaviour which has been the subject of several publications.The Raman signature of the excited states change in solvents ofAnalyst, November 1996, Vol. 121 117R different polarity and when water-soluble derivatives interact with DNA or DNA model systems.82-90 Haem Enzymes Haem enzymes carry out a range of functions in living systems, from O2 transport and storage by myoglobin and haemoglobin, to electron transfer, by cytochromes b and c, and transformation of substrates, such as 0 2 to HzO in cytochrome c oxidase. Although the chemistry of most haem enzymes is not photo- chemically driven, extensive TR3 studies of haemoglobin and cytochrome c oxidase have been carried out by initiating their chemical reactions photochemically, through photodeligation of CO from CO adducts of their Fe" haem groups. The subsequent reaction pathway depends on the enzyme involved.With haemoglobin the primary interest has focused on the relaxation of the protein structure around the haem group, following either the evolution of the haem vibrational modes from the first picosecond until the structure has fully relaxed, or using UV probe wavelengths to monitor changes in the protein. For cytochrome c oxidase, TR3 methods have been used to follow the complex series of electron and proton transfer steps which follow 0 2 binding. Recent comprehensive reviews of the application of TR' methods (using both pulsed and CW photoinitiation) to haem enzyme reaction dynamics are avail- able. 34-36 Small Organic Molecules-Excited States and Radicals Studies of excited states of stilbene and its derivatives are inextricably linked to the development of picosecond optical spectroscopy and the molecule continues to provide a valuable testing ground for many of the phenomena associated with ultra-fast isomerization proce~ses.~4,~8,~9,5~~91-97 TR3 spectra, with extremely high S / N , of the first few picoseconds following excitation are now a~ailable.1~,~9,91 Although stilbene and its derivatives have been thoroughly examined by TR3 methods, it is by no means the only compound probed by picosecond or nanosecond methods.Indeed, the range of questions in organic photochemistry addressed by TR3 methods is almost as large as the field itself."-110 The particular strength of the method is that it allows structural characterization of excited states and therefore the investigation of links between structural changes upon photoexcitation and photochemical reactivity.Studies have ranged from investigation of the geometry (twisted or planar)97 of the singlet and triplet excited states of biphenyl to the structural changes which accompany excitation of photo- chromic compound^.^^ Radical formation is a common outcome of photoexcitation and free-radical reactions (or their suppres- sion) are physiologically important so that much interest has focused on this area, where the fact that technique can readily distinguish between excited states of different multiplicities and protonated and unprotonated radicals makes it particularly valuable. The spectra of large numbers of radical species generated either photochemically or by pulse radiolysis have 101 0 107 NH, 100 98 14,48,49,51,91- 97 99 102- 104,108 92,97 0 w:m R If0 ".SJrC0 fR X 92 6 105,106 109 108 - 111- 119 137,138 136 38,120- 135 120 50,59,61- 90 Fig.12 representative is shown for each general compound type. References cited under the structures cover both the compound shown and related compounds. Structures of some of the compounds whose excited states or radical products have been studied by resonance Raman spectroscopy. Only a singleI18R Analyst, November 1996, Vol. 121 been obtainedIo2-lI0 and in some cases the link between their electronic structure and chemical reactivity established. The structures of a representative range of compounds (not a comprehensive listing) are given in Fig. 12. Photosynthetic Reaction Centres, Carotenoids and Bacteriochlorophyll TR3 studies aimed at understanding photosynthetic systems have focused on both the bacteriochlorophyll, whose excited- state Raman spectra have been recorded,74-77 and on the photochemistry of carotenoids.The latter has been extensively investigated for many yearsL1 I but new insights continue to stem from the intensive scrutiny to which they have been subjected. In recent years, TR3 experiments have been carried out on a large number of carotenoids and their substituted derivatives in solution,l12-l 14 micelles1ls,l 16 and in vivo.117-119 The structural changes accompanying population of the lowest lyirig singlet and triplet excited states and radical cation formation have been determined. Metal Complexes The first resonance Raman studies of the lowest excited triplet metal-to-ligand charge-transfer excited states of R u ( B ~ ~ ) ~ ~ + by Bradley et al.,38 which showed that the optical electron was localized on a single Bpy ligand, firmly established transient Raman methods at the centre of studies of metal polypyridyl complexes.8 The technique has now been extended to studies of a wide range of complexes with different metal centres,I2()-lz6 and coordinated ligands.127-135 TR3 has now been used not only to find which ligand is reduced on excitation of heteroleptic complexes127 but also to find in which region of asymmetric ligands the optically excited electron resides,128,129 the effect of the environment on the excited state structure (including the changes brought about by interaction with DNA),'3&-'32 the nature of the excited states of polychromophoric com- plexes 33,1 34 and even the processes which occur during intramolecular electron transfer.l35 While most transient and time-resolved Raman studies of metal complexes have involved charge-transfer excited states, studies on the 6-6* excited states of Re2C18- and photoisomerization of metal carbene complexes137~138 and investigations of the nature (MLCT or intra-ligand) of the lowest excited state of Ru(halide)(CH3, CZHs)(CO)z(a-dii- mine),120 have also been carried out. The latter study compared both time-resolved IR absorption and Raman measurements on the same transient species. Bacteriorhodopsin and Visual Pigments The chemistry of vision is a natural area for exploration by photochemical techniques.TR3 methods have been extensively used to follow the sequence of reactions which follow initiation of the process through light absorption in the chromophore of bacteriorhodopsin and related molecules. I39 The photochemical cycle involves several steps which occur on a wide range of time-scales but which ultimately return the chromophore to its original state within milliseconds. 139,140 In recent years, several groups have been involved in carrying out the wide range of experiments (using both pulsed and CW lasers) needed to characterize the complex reaction sequence and in studying pigments related to the native protein. l4]-ls3 Conclusions Time-resolved Raman methods can be applied to a very large range of compounds, the exact experimental protocol depending on the time-scale of the measurement required and whether the process of interest must be initiated chemically, electro- chemically or photochemically.A range of protocols has been developed for each of these types of reaction. Technical advances have dramatically improved the signals obtainable from picosecond laser systems, but these systems are extremely expensive. Transient experiments based on CW and nanosecond pulsed lasers are considerably less expensive and based on a mature and established technology, so that for routine measure- ments they are more attractive. The technique offers the opportunity to monitor structural changes within samples undergoing time-dependent processes or the possibility of using the time domain simply as an additional variable with which to separate one component from a complex sample mixture.Sample concentrations are not excessively high, typically of the order IO-3-l(Y4 mol dm-3. The major disadvantages of the technique arise from the inherent weakness of the Raman effect, which demands sensitive optical detectors and high input light irradiances (with associated sample decomposition problems). In addition, strong luminescence from samples may prevent studies being carried out. 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B., Raap, J., Lugtenburg, J., and Mathies, R. A., Biochemistry, 1992, 31, 12546. Mukai, Y., Hashimoto, H., Koyama, Y., Kuroda. S., Hirata, Y., and Mataga, N., J . Phys. Chem., 1991, 95, 10586. Delaney, J. K., Atkinson. G. H., Sheves, M., and Ottolenghi, M., .J. Phys. Chem., 1995, 99, 7801. Delaney, J. K., Brack, T. L., Atkinson, G. H., Ottolenghi, M., Steinberg, G., and Sheves, M., Proc. Natl. Acad Sci. USA, 1995,92, 2101. Delaney, J. K., Brack, T. L., Atkinson, G. H., Ottolenghi, M., Friedman, N., and Sheves, M., J . Phys. Chen7., 1993, 97, 12416. Paper 6103777A Received May 30, I996 Accepted August 16, I996

ISSN:0003-2654    

DOI:10.1039/AN996210107R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, November 1996, Vol. 121 155N Book Reviews Supercritical Fluid Extraction By Larry T. Taylor. Techniques in Analytical Chemistry. Pp. xiv + 182. Wiley. 1996. Price f40.00. ISBN 0-47 1 - 1 1990-3. This is a welcome volume on supercritical fluid extraction (SFE) as it is written by a single author. Previous volumes have often been edited collections of chapters by a number of authors and therefore present the subject in a complex way. By contrast, this is a clear and less complicated account, which nevertheless addresses the important issues. The author has published research papers in supercritical fluids, although this is part of a wider analytical interest. He has run a series of successful analytical courses at this Institute, including ACS short courses on SFE and chromatography.He is thus well placed to provide an introduction to the subject. Reviewing this book inevitably raises the question of where SFE for analytical sample preparation is heading at the moment. It is undoubtedly going through a bad patch at present and seeing competition from new small-scale liquid separation techniques, which also reduce the use of organic solvents. The reasons for this are rather unfair. Firstly, it is apparent from research that SFE is only partially successful and the matrix does not always release all the analytes. This is unfair in comparison with liquid extraction because the detailed informa- tion about percentage recoveries obtainable from SFE is not available from liquid extraction because the latter technique is too time-consuming. Often SFE does better than liquid extraction.The second reason is that SFE appears very complex because of the way it is presented, often in ‘difficult’ papers. I hope the clear account given in this book will repair this second problem. For the analytical chemist this volume is an excellent and painless introduction to SFE for analytical sample preparation. It would be my first choice for someone contemplating the use of SFE. Those who routinely use liquid extraction should read this book to get a straightforward view of the SFE alternative. 6190038K A . A. Clifsord University of Leeds New Frontiers in Agrochemical lmmunoassay Edited by David A. Kurtz, John H. Skerritt and Larry Stanker. Pp. vii + 318; AOAC International. 1995. Price $93.00 (USA, Canada and Mexico); $97.00 (outside North America).ISBN 0-935584-58-7. Immunoassays in one form or another have been described for the vast majority of agrochemicals. In turn, many of these methods have been employed worldwide in routine analytical testing programmes. This book opens with a section devoted to outlining the analytical requirements of screening tests used in regulatory work. Pesticide and herbicide immunoassays are used as examples but the concepts discussed are applicable to most hapten immunoassays. The second section of the book addresses the chemical manipulation of haptens to yield high molecular weight conjugates suitable for generating immune responses and producing enzyme conjugates. This detailed review makes this an excellent reference point for those wishing to produce hapten derivitives suitable for developing an immunoassay.Section three is concerned with immunoassay formats. An interesting chapter within this section outlines some of the emerging techniques in developing field immunoassays. A further chapter deals with some aspects of immunoassay troubleshooting. There are notable absences of alternate immunoassays formats, particularly those using labels other than enzyme based. Similar descriptions for fluorescent, time resolved fluorescent and chemiluminescent applications would be a useful addition to future editions. Section four details some of the methods used to prepare samples for analyses by immunoassays. Solid phase extraction and immunoaffinity chromatography are described in reason- able detail.Many other techniques appear to have gone unmentioned. The penultimate section is centred on recent advances in immunoassay methods and here truly lies some of the ‘new frontiers’. The development and application of recombinant antibodies should be of particular interest to many workers in the field of immunoassay development. The book closes with descriptions of some of the methods used to analyse data generated by immunoassays. Though less exciting to read than some other areas of the book the importance of this subject should not be underestimated. This book covers many of the important aspects of develop- ing, validating and implementing immunoassays into routine monitoring programmes. There appears to be a strong bias towards pesticides and herbicides.Compounds such as antibiot- ics and steroids are notable absentees. Despite these limited shortfalls this book is quite an excellent guide to developing immunoassays in general and an even better guide to what might be possible in the future. 5190095F Chris Elliott Department of Agriculture of Northern Ireland Innovations in Supercritical Fluids: Science and Tech- nology Edited by Keith W. Hutchenson and Neil R. Foster. ACS Symposium Series 608. Pp. x + 470. American Chemical Society. 1995. Price US$125.95. ISBN 0-841 2-3324-1. This book is not primarily for the analytical chemist, as its subtitle implies. It has no chapters directly on supercritical fluid chromatography or analytical supercritical fluid extraction. It is a significant addition to the important volumes on supercritical fluids in the ACS Symposium Series.In this case it contains selected papers from those present at the ‘Symposium of Supercritical Fluid Science and Technology’ held as part of the 1994 Annual Meeting of the American Institute of Chemical Engineers. There is an introductory chapter by the editors reviewing current research on supercritical fluids. There are sections on molecular interactions and phase behaviour, chemical reactions, and an unusual section on ‘ Supercritical Fluids in the Forest Products Industry’ with an introductory chapter reviewing the area. Chapters of peripheral interest to the analytical chemistry are those on the choice of cosolvents for the extraction of pesticides, extraction from polymer matrices, two chapters on the extraction of contaminants from soils and extrdction from yew.For those working in general in supercritical fluids the book is an indispensible addition to their library. It would be of interest in those analytical laboratories which get involved in preliminary studies of possible processes. For analytical chemists, unless involved specifically in the applications listed above, this volume is only of minor interest. 61900220 A. A. Clifford University of Leeds156N Analyst, June 1996, Vol. 121 Electric Field Applications in Chromatography, Industrial and Chemical Processes Edited by Takao Tsuda. Pp. xiv + 312. VCH. 1995. Price DM298.00. ISBN 3-527-28687-X. At first sight this book may give the impression that the unsuspecting potential reader has acquired a kind of scientific ratatouille.On closer exploration into the various items presented, it transforms into a scientific kaleidoscope. Finally for those scientists interested in separation techniques the ingredients metamorphose into a collection of carefully selected themes, expressing the wide interests of Professor Tsuda. In mass transport phenomena, underlying all separation processes, almost always fundamental ‘classical’ driving forces are used. Amongst others a choice can be made from, e.g., gravity (centrifuge), pressure (gas, liquid chromatography), electric field strength (electrophoresis), or magnetism (mass spectrome- try). Nature makes it possible to create and apply these forces in different ways and magnitudes, to cover a wide range of solutes with a wide range of molecular weights.In experiments, sometimes phenomena occur that have to be suppressed or stimulated, e.g., electroosmosis. Applying just one kind of separation principle does not deliver the desired result. A combination of the above mentioned forces with physical phenomena such as adsorption, sieving, chemical reactions in well defined compartments, may result in a specific separation technique, which sometimes we believe we understand com- pletely. In these new horizon areas, this book has a lot to say. Although performance properties can create conditions for a specific separation principle, the rules of mass transport still form the basic assumptions, defining the potential and limits of separation. Nevertheless, the variations themselves are realised through a vast and highly diversified array of instruments and procedures described in the scattered literature.It is therefore sometimes difficult to collect information for a specific problem in separation science in order to optimize the solution, because as always many roads lead to Rome. In this book an attempt is made to create an intersection of applications and experiments, in which electric field and chromatography have been chosen for industrial and chemical processes. In addition to a well written clear introduction and summary (Chapter l), this book comprises three sections: in Chapters 2-6 main attention is paid to electrochromatography; in Chapters 7-1 1 applications in industrial processes are discussed; in Chapters 12-14 applica- tions to concentration, immunoassay and molecular orientation are given.‘On closer exploration into the various items presented, it transforms into a scientific kaleidoscope. ’ In Chapters 2 4 , dealing with electrochromatography, the reader is introduced into a world of analytical separation where zone profiles, created both with and without electroosmotic flow, play an important role. As a comparison, pressurised flow is discussed. The (dis)advantages are shown not only in simple formulae, but the information is larded with many pictures and photographs. In Chapter 5 attention is paid to the preparative separation of biomolecules. In Chapter 6 it is shown that combining various principles can be fun if you like to construct home-made equipment and are not simply hoping that elaborate equipment will produce all pre-programmed work. In the following chapters work is presented especially to stimulate young scientists of our computerized world.Optimization of processes such as industrial electroosmotic dewatering, electro- phoretic formation of ceramics, novel materials for electrorheo- logical fluids, electric fields and their role in both solvent extraction and in resolution of water-in-oil emulsions, is still possible. In Chapter 12 attention is paid to industrial concentra- tion or desalting purposes, a feature rather unknown amongst many scientists in analytical separation techniques, making use of electrophoretic and/or chromatographic principles. In Chap- ter 13 pulse immunoassay and pulse electrovoltage for cell manipulation is presented, techniques which will need more attention and will attract (as iontophoresis already does), more interest in the next decade.Finally, in Chapter 14, an interesting discussion on electric field organised photochemistry is pre- sented, an important item, as it can be linked to the growing interest in chiral chemistry. To conclude this review, I think that for those scientists looking for a profound treatise in theoretical aspects of electrical field applications in chromatography, this book may be disappointing, as it will be for those eager to collect detailed information on the items discussed. But for those interested in aspects of influencing, combining, reducing or amplifying electric, magnetic and chromatographic parameters it will give satisfaction.The unifying feature of the role of the electric field, as presented in this book is the displacement of solvent or migration and/or orientation of solutes. Much more thrilling phenomena are described and can be read between the lines. Therefore this book is especially valuable because important information is given with an introduction to up-to-date literature for creative readers. Moreover it may bring scientists in laboratories with different disciplines together. Therefore it is important to have this book in a scientific library to supply a good summary to researchers in this fascinating area from leading researchers in this field. 6190001 A F. M . Everaerts Eindhoven University of Technology The Netherlands A Practical Approach to Chiral Separations by Liquid Chromatography Edited by G.Subramanian. Pp. xvi + 406. VCH. 1994. Price DM178.00. ISBN 0-527-28288-2. This book consists of twelve chapters written by a mixture of European and North American authors. It is almost entirely concerned with high performance liquid chromatography (HPLC) though thin layer chromatography and capillary electrophoresis are mentioned. The first chapter is a brief introduction to chirality, industries in which chirality is important, the stationary phase types used in HPLC, and chiral mobile phase additives. Many aspects of this chapter are also covered in the introductions to other chapters; it nonetheless sets the scene for the forthcoming material. Chapter three is a short review of the regulatory implications of chirality focused on medicinal products.There is no mention of chiral separations in this chapter and it could perhaps have been combined with chapter one. Chapter two is concerned with molecular modelling of enantiodifferentation in liquid chromatography. This gives a necessary introduction to modelling and computational tools before reviewing the progress made in modelling Type I, I1 and 111 chiral stationary phases. The author discusses pitfalls as well as successes and the chapter is very readable even to those with little experience of molecular modelling. Chapter four is concerned with molecular imprinting and the possibility oi preparing tailor-made phases. ‘This is a worthwhile addition to the expand- ing chiral literature and the book should be of value to those working in this field.’ The larger part of the book then consists of chapters on some, but not all the different phase types.There is no chapter on theAnalyst, November 1996, Vol. 121 157N Type I phases first developed by Pirkle, for example, though they do get some mention in several other chapters. Cyclodex- trin, polysaccharide, protein, and polymer/silica composite phases are all covered in separate chapters. Mobile phase additives, ion-pair chromatography (as a separate chapter) and applications to pharmaceutical and biomedical analysis are then covered in the four subsequent chapters. As a compilation of contributions from different chapter authors, the book would have benefited from tighter editing. There is overlap between several chapters (e.g., the biological importance of chirality is covered repeatedly).There are inconsistencies in the use of English (conventional and American) and the lack of a chapter on Type I phases is an obvious omission. A chapter on preparative separations would also have been of interest as would more examples of applications outside of the drug area. Overall though, this is a worthwhile addition to the expanding chiral literature and the book should be of value to those working in this field. There are many references with each of the individual chapters and the book is well produced with plenty of helpful figures and tables. Both the contents list and the index are well prepared and helpful. Derek Stevenson 4190209B University of Surrey Special Trends in Thermal Analysis By Ferenc Paulik.Pp. xiii + 460. Wiley. 1995. Price f90.00. ISBN 0-471-95769-0. As the title implies this is not a book for the beginner. The author, and his brother Jeno, who is the silent partner in this text, are well known to thermal analysts not only in their native Hungary but throughout the world. The text comprises three sections and eighteen chapters. Part One is introductory in character and provides a well balanced history of the development of derivative thermogravimetry (DTG), simultaneous thermal methods (thermogravimetry; TG, DTG, and differential thermal analysis; DTA) and the factors affecting the result. Of particular importance is the treatment of sample size, heating rate and the development of variable mass- area crucibles.A wide range of well chosen examples emphasise the applications of the techniques. Although much of this material will be familiar to most experienced thermal analysts the content and tone of this section characterises the text as a whole and contains concepts which the author subsequently develops. Part Two deals with the kinetics and mechanism of thermal reactions. Treatment of this section is inevitably selective rather than comprehensive. In an attempt to develop a coherent framework, eight fundamental types of inorganic reactions are considered of which the treatment of dehydration and dehydrox- ylation reactions are arguably the most extensive and success- ful. The development of experimental techniques, in combina- tion with theoretical arguments, again leads into crucible design and simultaneous thermal methods.‘The price may deter all but University libraries but the book should be read by all serious workers and research students in the field. ’ Part Three is the most up-to-date and of the most interest to experienced thermal analysts. The quasi-isothermal, stop-start heating method (Q-TG), first introduced in Part One and now called Hi-Res TG, is further developed. The basis of the technique is the variation of heating rate as the rate of sample decomposition varies. The section refers to ideas and techniques introduced previously, especially in relation to sample size, heating rates, crucible geometry, etc., and develops them further. This enables the production of Q-TG/Q-DTG profiles. The interpretation of special profiles (e.g., beak-shape profiles) that improve the deconvolution of previously complicated decomposition profiles, especially in dehydration and nuclea- tion processes, and aid their understanding, are also dealt with. The section continues with other aspects of high resolution thermal analysis such as Q-DTG/Q-DTA, the combined techniques Q-TG/Q-DTG/Q-TA and thermomagnetic methods.Many examples and references, with excellent illustrations, are also provided in order to demonstrate the improved sensitivity and accuracy of the methods. The reader is left in no doubt that quasi-isothermal, and quasi-isobaric methods are the thermo-analytical methods of the future. The price may deter all but University libraries but the book should be read by all serious workers and research students in the field.E. S . Raper 51900.541 University of Northumbria at NewcastleFIVE CD-ROM PRODUCTS FROM THE ROYAL SOCIETY O F CHEMISTRY Analytical Abstracts - compiled especially for the analytical chemist, offering comprehensive coverage of key analytical journals worldwide Chemical Engineering & Biotechnology Abstracts - the world’s foremost database devoted to chemical engineering Chemical Business NewsBase - provides company, product and market information, plus environmental issues and regulations, for the chemical industry and its end-use sectors worldwide. Dictionary of Substances and their Effects - a unique guide to chemicals and their impact on the environment Environmental Chemistry, Health & Safety - contains information on chemicals deemed to cause actual or potential problems to humans or the environment, i ncl ud i ng m icro b io I ogi ca I and rad iat ion hazards. Unlimited Access Easy Budgeting Simple or Sophisticated Search Tools Your Choice of Output Options Please arrange for me to receive a FREE 30-DAY TRIAL of: Analytical Abstracts a Chemical Engineering & Biotechnology Abstracts a Chemical Business NewsBase a Dictionary of Substances and their Effects a Environmental Chemistry, Health & Safety [7 I would like further information about .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE ROYAL Name: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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ISSN:0003-2654    

DOI:10.1039/AN996210155N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, Noivmber 1996, Vol. 121 159N Conference Report I-7,1996 The historic and beautiful medieval city of Bologna, with its fabulous porticoed streetscapes, piazze, churches and palaces, was the venue for Euroanalysis IX from 1 to 7 September. This meeting attracted 673 registered participants from 53 countries, and the very full programme included 746 oral and poster presentations. Of these, 59% originated from Western Europe, while 39% were derived from Eastern European countries, reflecting the trend for increasing involvement from the latter sector. An informal Sunday evening mixer, which was held in the Palazzo d’ Accursi provided an atmospheric and convivial entre to the week’s activities. A somewhat more formal opening ceremony was held on Monday morning in the ‘Aula Magna Santa Lucia’ at the University of Bologna.The proceedings included the award of the prestigious Heinrich-Emanuel Merck Prize for Achievement in Analytical Chemistry jointly to Professor J. Harrison (University of Alberta, Canada) and Professor A. Manz (Imperial College, UK). Other medals and awards presented included those of the Italian Chemical Society to Professor L. Niinisto (Helsinki University of Technology, Finland), Emeritus Professor A. Liberti (University of Rome, Italy) and Professor R. Kellner (University of Technology, Vienna, Austria). Austrian Society for Analytical Chemistry awards were presented to Professor F. Adams (University of Antwerp, Belgium) and Professor M. Valcarcel (University of Cordoba, Spain). The proceedings were enlivened by the sublime music of Vivaldi, Respighi and Geminiani performed by the accomplished Ensemble Respighi.Poster sessions were given prominence at this meeting, and occupied a two hour time slot immediately post-lunch. A total of 690 posters were presented during five afternoons, and covered thematic areas of Pharmaceutical and Biomedical Analysis, Electroanalytical Chemistry, Surface and Materials Science, Flow Analysis, Bio- and Chemical Sensors, Environ- mental Analysis, Education in Analytical Chemistry, Food Analysis, Cultural Heritage, Chemometrics, Spectroscopy, Separation Science, Validation and Quality Assurance. A series of 29 invited lectures preceding each session of contributed papers (120 in all) were given on the same themes as those above. The opening plenary lecture was presented by Professor L.Caglioti (University ‘La Sapienza’, Rome, Italy), who outlined the role of chemical analysis in preserving Italy’s cultural heritage. Professor J. Grasselli (Ohio University, USA], in a stimu- lating Tuesday morning plenary, addressed the links between analytical and environmental chemistry (in a lecture entitled Analytical Chemistry-Feeding the Environmental Revolu- tion?), and argued that a high level of research in analytical chemistry should be maintained if understanding of environ- mental processes was to be further advanced. She emphasized the need for analytical chemists to improve their communica- tion of scientific issues such as risk assessment to the public, regulators and government. The Tuesday morning session included a journal sponsored segment on ‘Emerging Techniques in Environmental Analysis’ which included an invited lecture on laser induced photo- fragmentation spectroscopy by Dr.N. Ormenetto (European Commission-Joint Research Centre, Ispra, Italy), and seven other selected talks by younger scientists on topics such as traceability in nitrate measurements in water (J. C. Wolff, EC- JRC, Geel, Belgium), micellar electrokinetic capillary chroma- tography of algal toxins (W. John, University of Natal, South Africa) and use of novel conducting polymers for chiral molecular sensing (P. Evans, University of West England, UK) . In a later session on Environmental Analysis, Professor Jacques Buffle (Universite de Genkve Sciences 11, Switzerland), presented an inspiring lecture on techniques and developments in ‘In situ Monitoring and Speciation of Trace Elements in Natural Waters’.A special Tuesday evening session on Education in Analy- tical Chemistry was organized by the Working Party on Analytical Chemistry. This well attended session included a report by Professor R. Kellner on the Eurocurriculum in Analytical Chemistry. It was announced that the new Euro- curriculum Analytical Chemistry textbook would be launched at the Colloquium Spectroscopicum Internationale XXX meet- ing in Melbourne in September 1997. Professor P. Bartlett (University of Southampton, UK) presented a fascinating Wednesday plenary lecture on ‘Appli- cations of, and Developments in, Machine Olfaction’. In this lecture, he reviewed the neurophysiological processes involved in olfaction, and described how these processes could be mimicked by the use of gas sensing arrays and chemometrics.Lecture sessions on Pharmaceutical and Biomedical Analysis, Electroanalytical Chemistry, and Chemometrics followed. Within the Pharmaceutical and Biomedical session, Professor A. Roda (University of Bologna, Italy) delivered a lecture on ‘Quantitative High Performance Low-light Imaging in Bio- sciences’ which was noteworthy for both the quality of presentation and the excellent use of illustrative graphics. The highlight of the social programme was arguably the Wednesday evening concert in the City Theatre of Bologna by Corale G. Verdi, a noted choir from Parma, which presented a programme comprising works by Verdi, Rossini, Puccini.Bellini and others. ‘Advances in Scanning Electrochemical Microscopy’ was the topic of the Thursday morning plenary lecture by Professor A. Bard (University of Austin, Texas, USA). In his lecture, Professor Bard outlined the use of ultramicroelectrodes in scanning electrochemical microscopy (SECM), and gave a illuminating description of the application of this technique to reaction rate imaging at interfaces, and the detection of single electroactive molecules. Morning sessions on Chemometrics, Surface and Materials Science, and Bio & Chemical Sensors were followed by an afternoon free for social and sightseeing activities. The final plenary lecture, ‘The Role of Analytical Chemistry for Industrial Research’, was presented by Dr. M. Ehrat (Ciba- Geigy Ltd., Switzerland).Dr. Ehrat discussed the importance of issues such as speed of method development, selectivity, sensitivity, and sample throughput, in the pharmaceutical and agrochemical industries, and gave specific examples of how techniques such as MALDI-TOF mass spectrometry, on-line isotachophoresis, fast optical spectroscopic biointeractive anal- ysis (FOBIA), and optical mapping technologies could be applied advantageously.160N Analyst, November 1996, Vol. 121 Contributed paper sessions on Spectroscopy, Separation Science, Environmental Analysis and Bio & Chemical Sensors, and a poster session completed the formal scientific pro- gramme. The meeting concluded with lighthearted summaries by the Organizing Chairman (Professor Zambonin) and the Secretary General (Professor L. Sabbatini), and some meeting statistics from the Scientific Secretariat, Professor F. Palmisano. Dr. M. Widmer, Chairman of Euroanalysis X, gave a presentation on the direction and arrangements for the next meeting to be held in Base1 in 1999. He emphasized that budget price accommodation would be available for students, and suggested sagely that all other intending attendees should put aside one Swiss franc a day from now until 1999 in order to attend the meeting. Dr. Ian D. McKelvie Monash University, Australia

ISSN:0003-2654    

DOI:10.1039/AN996210159N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, November 1996. Vol. 121 161N Conference Diary Date Conference 1996 December 3 2nd Young Scientists Research Symposium-Current Research Trends in UK Air Quality 1st Asia-Pacific International Symposium on Capillary Electrophoresis and Related Techniques 17-20 Location Contact 1997 January 4-9 The Fourth International Symposium On: Giza. London, UK SCI Conference Department, 14/15 Belgrave Square, London SW 1 X 8PS, UK Singapore APCE ’96, c/o Dr. Sam F. Y. Li, Department of Chemistry, National University of Singapore, I0 Kent Ridge Crescent, Singapore 1 19260, Republic of Singapore Tel: +65 772 268 1. Fax: +65 779 1691. E-mail: chmlifys@leonis.nus.sg. New Trends in Chemistry The-Role of Analytical Chemistry in National Development International Conference on Flow Injection Analysis-XCFIA 97 12-1 6 12-17 1997 European Winter Conference on Plasma Spectrochemistry 20-24 First Asia-Pacific EPR/ESR Symposium 25-28 9th Sanibel Conference on Mass Spectrometry ‘Quadrupole Ion Traps’ 26-30 9th International Symposium on High Performance Capillary Electrophoresis and Related Microscale Techniques February 2-6 The Australian and New Zealand Society for Mass Spectrometry 16th Conference (ANZSMS 16) 3-5 2nd Symposium on Macromolecules Used as Pharmaceutical Excipients-New Opportunities, Characterization and Applications 18-1 9 Inbio ’97 Industrial Biocatalysis: The Way Ahead Orlando, (JSA Gent.Belgium Hong Kong Sanibel Island, FL, USA Anaheim, USA Hobart, Tasmania, Australia Stockholm, Sweden Manchester, UK Professor Dr. M. M. Khater, Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt ICFIA 97, Sue Christian, P.O.Box 26, Medina, WA Fax: + I 206 454 9361. E-mail: sue@ flow inject ion .corn. L. Moens, Secretariat, 1997 European Winter Conference, Laboratory of Analytical Chemistry, University of Gent, Proeftuinstraat 86, B-9000. Gent, Belgium l’el: +32 9 264 66 00. Fax: +32 9 264 66 99. E-mail: plasma97@rug.ac.be. Professor C. Rudowicz, Chairman, LOC & IOC, City University of Ilong Kong, Department of Physics and Materials Science, 83 Tat Chee Avenue, Kowloon, Hong Kong Tel: +8S2 2788 7787. Fax: -1-852 2788 7830. E-mail: apsepr@cityu.edu.hk. American Society for Mass Spectrometry, 120 1 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +I 505 989 4517. Fax: + I 505 989 1073.Shirley Schlessinger, Symposium Manager, HPCE ’97, 400 East Randolph Street, Suite 1015, Chicago, IL 60601, USA Tel: + I 312 527 201 1. 98039-0026, USA Mures Convention Management, Victoria Dock, Hobart, TAS 7000, Australia Tel: +61 002 3 12 121. Fax: +6 1 002 344464. E-mail: mures@ hba. trumpt.com.au; WWW:http://www .csl.edu.au/ANZSMS/ anzsms16.html. The Swedish Academy of Pharmaceutical Sciences, P.O. Box 1 136, S- 1 I 1 8 1 Stockholm, Sweden Tel: +46 8 723 50 00. Fax: +46 8 20 55 11. E-mail: academy@swephann.se or visit http://www.swepharm.pharmsoft.se. Spring Innovations Ltd., 185A Moss Lane, Bramhall, Stockport, Cheshire, UK SK7 1BA Tel: +44 (0)161 440 0082. Fax: +44 (0)161 440 9127.162N Analyst, November 1996, Vol. 121 Date 19 March 9-14 16-2 1 23-27 April 13-17 14-19 19-22 2 1-25 28-29 3 &2/5 May 4-8 Conference Advances in Analytical Chemistry: Miniaturisation and Sensors CANAS '97 Colloquium Analytische Atomspektroskopie 48th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy Electrophoresis '97 213th American Chemical Society National Meeting Genes and Gene Families in Medical, Agricultural and Biological Research: 9th International Congress on Isozymcs Scanning 97 Seventh International Symposium on Biological and Environmental Reference Materials (BERM-7) Computer & Process Validation in the Location Hudders field, Yorkshire, UK Freiberg/S ac hsen, Germany Atlanta, GA, USA Seattle, WA, USA San Francisco, CA, USA Texas, USA Monterey, CA, USA An twerp, Belgium M anches ter, Pharmaceutical and Fine Chemical Industries UK Flavours and Fragrances Warwick, UK PBA '97,Sth International Symposium on Pharmaceutical and Biomedical Analysis USA Orlando, FL, Contact Dr.Roger Jewsbury, Dept. Chemical and Biological Sciences, University of Huddersfield, Yorkshire HD1 3DH Tel: +44 (0)1484 472177. Fax: +1 (0)1484 472182. E-mail: r.a.jewsbury@hud.ac.uk; Internet: http://www.hud.ac.uk/ schools/applied~sciences/chem/aac97 .htm. G. Werner, Universitat Leipzig, Institut fur Analytische Chemie, Linnestrasse 3, D-04103 Leipzig, Germany Tel: +49 0341 973 6101. Fax: +49 0341 973 61 15. Linda Briggs, The Pittsburgh Conference, 300 Penn Center Blvd., Suite 332, Pittsburgh, PA 15235-5503, USA Tel: + I 412 825 3220, +I 800 825 3221. Fax: +1 412 825 3224. David Wiley, Electrophoresis Society, P.O.Box 1987, Lawrence, KS 66044-8897, USA Tel: +1 913 843 1221. Fax: +1 913 843 1274. E-mail: dwiley@allenpress.com. Department of Meetings, American Chemical Society, 115516th St. NW, Washington, DC 20036, USA Tel: +1 202 872 4396. Fax: +1 202 872 6128. E-mail: natlmtgs@acs.org. Mrs. Janet Cunningham, Barr Enterprises, 10 120 Kelly Road, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: + 1 301 898 5596. Mary K. Sullivan, FAMS Inc., SCANNING 97 Program Committee, Box 832, Mahwah, NJ Tel: +1 201 818 1010. Fax: +1 201 818 0086. E-mail: fams@holonet net; Internet: http:/*ww.scanning-fams.org. J. Pauwels, Institute for Reference Materials and Measurements, Retieseweg, B-2440 Geel, Belgium. Tel: +32 14 571 722; or Wayne Wolk, US Department of Agriculture, 10300 Baltimore Blvd, Beltsville, MD 20705, USA Tel: +1 301 504 8927.Spring Innovations Ltd,, 185A Moss Lane, Bramhall, Stockport, Cheshire, SK7 1BA Tel: +44 (0)161 440 0082. Fax: +44 (0)161 440 9127. Elaine Wellingham, Conference Secretariat, Field End House, Bude Close, Nailsea, Bristol BS19 2FQ, UK Tel: +44 (0)1275 853311. Fax: +44 (0)1275 85331 1. E-mail: confsec@dial.pipex.com. 07430-0832, USA Shirley E. Schlessinger (Symposium Manager), Suite 1015, 400 East Randolph Drive, Chicago, IL, 6060 1, USAAnulyst, November 1996, C'ol. 121 163N Date 11-15 12-13 12-16 18-22 27-28 June 1 4 1 -5 1-5 2-5 3-5 15-2 1 16-20 16-20 22-27 Conference Location 5th European Workshop on Modern Torquay, Developments and Applications in Microbeam UK Analysis Chiral USA '97 European Symposium on Photonics in Manufacturing 111 19th International Symposium on Capillary Chromatography and Electrophoresis IInd Miniaturisation in Liquid Chromatography versus Capillary Electrophoresis Conference 1997 International Symposium, Exhibit & Boston, USA Paris, France Wintergreen, VA, USA Ghent, Belg i um Washington, DC, Workshops on Preparative Chromatography, USA Ion Exchange, and Adsorption/Desorption Processes and Related Techniques 45th ASMS Conference on Mass Spectrometry and Allied Topics USA Palm Springs, CA, Geoanalysis '97,3rd International Conference Vail, CO, on the Analysis of Geological and Environmental Materials 6th Annual Course on Practical Methods of Digestion for Trace Analysis LIMS '97, 11th International LIMS Conference and Exhibition International Conference on Analytical Chemistry European Symposium on Environmental Sensing I11 European Symposium on Environmental and Public Safety I1 HPLC '97, 21st International Symposium on High Performance Liquid Phase Separations and Related Techniques USA Amherst, MA, USA The Hague, Netherlands Moscow, Russia Munich, Germany Munich, Germany Birmingham, UK Contact EMAS Secretariat, University of Antwerp, Department of Chemistry, Universiteitsplein 1, (3-261 0 Antwerp-Wilrijk, Belgium Fax: +32 3 820 2376.E-mail: vantdack@uia.ua.ac.be. Spring Innovations Ltd, 185A Moss Lane, Bramhall, Stockport, Cheshire, UK SK7 1BA Tel: +44 (0) 161 440 0082. Fax: +44 (0) 16 1 440 9127 or Brandon Associates, PO Box 1244, Merrimach, NH 03054, USA.Tel and Fax: + I (630) 424 2035. Francoise Chavel, Executive Secretary, European Optical Society, B.P. 147-9 1403 Orsay Cedex, France Tel: +33 1 69 85 35 92. Fax: +33 1 69 85 35 65. E-mail: francoise.chavel@iota.u-psud.fr. Joy Wise, P.O. Box 4153, Frederick, MD 21705-4153, USA Tel: +1 301 473 8311. Fax: +I 301 473 8312. E-mail: W isej oy@ aol . com. Prof. Ilr. Willy R. G. Baeyens, Chairman MINI-LC 11, University of Ghent, Faculty of Pharmaceutical Sciences, Department of Pharmaceutical Analysis, Laboratory of Drug Quality Control, Harelbekestraat 72, B-9000 Ghent, Belgium Tel: +32 9 264 80 97. Fax: +32 9 264 81 96. E-mail: wi lly .baey ens@rug . ac .be Janet Cunningham, Ban Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: + 1 301 898 3772.Fax: +1 301 898 5596. E-mail: Janetbarr@aol.com. American Society for Mass Spectrometry, 1201 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +I 505 989 4517. Fax: +I 505 989 1073. Belinda Arbogast, USGS, Dever Federal Center, Box 25046, MS 973, Denver, CO 80225, USA Tel: +1 303 236 2495. Fax: +1 303 236 3200. E-mail: plamothe@helios.cr.usgs.gov. Beverly Lissner, Questron Corporation, 4044 Quakerbridge Rd., Mercerville, NJ 086 19, USA Tel: + I 609 587 6898. Fax: + I 609 587 0513. Conference Secretariat, LIMS 97, 45 Hilltop Avenue, Hullbridge, Hockley, Essex, UK SS5 6BL Tel: +44 (0) 1702 23 1268. Fax: +44 (0) 1702 230580. E-mail: 101 320.1617@compuserve.com. Dr. L. N. Kolomiets, Scientific Council on Chromatography of the Russian Academy of Sciences Leninsky Prospect 3 1 , 1 1791 5 Moscow, Russia Tel: +7 95 952 0065.Fax: +7 095 952 0065. E-mail: Iarionov@Imm.phyche.muk.su. Franqoise Chavel, Executive Secretary, European Optical Society, B.P. 147-9 1403 Orsay Cedex, France Tel: +33 1 69 85 92. Fax: 33 1 69 85 33 65. E-mail: francoise.chavel@iota.upsud.fr. Francoise Chavel, Executive, Secretary, European Optical Society, B.P. 147-91403 Orsay Cedex, France Tel: +33 1 69 85 35 92. Fax: +33 1 69 85 35 65. E-mail: francoise.chavel@iota.u-psud.fr. HPLC '97 Symposium Secretariat, ICC, Broad Street, Birmingham B1 2EA, UK Tel: +44 121 200 2000. Fax: +44 121 643 0388.164N Analyst, November 1996, Vol. 121 Date Conference 30-3/7 Analytical Science and the Environment 30-3/7 6th European ISSX Meeting July 2 1-25 4th International Conference on Laser Ablation 23-26 4th International Conference on the Biogeochemistry of Trace Elements August 10-15 11th International Conference on Fourier Transform Spectroscopy 25-28 VII Flow Conference 25-29 IMSC '97-14th International Mass Spectrometry Conference September 7-1 1 7-1 1 7-12 8-12 8-1 2 111th AOAC International Annual Meeting and Exposition 214th American Chemical Society National Meeting 1 l t h International Conference on Secondary Ion Mass Spectrometry (SIMS XI) 4th International Conference on Nanometer Scale Science and Technology Biomedical Optics V Location Newcastle, Northumbria, UK Gothenburg, Sweden Monterey, CA, USA Berkeley, CA, USA Athens, GA, USA Aguas de Sao Pedro-Piracicaba, Brazil Tampere, Finland San Diego, CA, USA Las Vegas, NE, USA Orlando, FL, USA Beijing, China Poland Contact The Secretary, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London WlV OBN, UK Tel: +44 (0)171 437 8656.Fax: +44 (0)171 734 1227. Meeting Secretariat, 6th European ISSX Meeting, c/o The Swedish Academy of Pharmaceutical Sciences, P.O. Box 1136, S-1 11 81 Stockholm, Sweden Tel: +46 8 723 5000. Fax: +46 8 20 55 11. Richard E. RUSSO, Lawrence Berkeley Laboratory, MS 90-2024, Berkeley, CA 94720, USA Tel: +1 510 486 4258. Fax: +1 510 486 4260. E-mail: rerusso@lbl.gov;http://cola97.ornl.gov. I. K. Iskandar, U.S. Army Cold Regions Research and Engineering Laboratory, 72 Lyme Rd., Hanover, NH 03755, USA Tel: +1 603 646 4198. Fax: + I 603 646 4561. E-mail: iskander@crrel.usace.anny.mil. James A.de Haseth, Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA Tel: +1 706 542 1968. Fax: +1 706 542 9454. E-mail: dehaseth@dehrsv.chem.uga.edu. Henrique Bergamin Filho, CENA-USP, Caixa Postal 96, 13400-970 Piracicaba, SP, Brazil Tel: +55 194 335122. Fax: +55 194 228339. E-mail: flow97@ aguia.cena.usp.br. 14th IMSC Congress Secretariat, c/o Congress Management Systems, P.O. Box 151, SF-00141, Helsinki, Finland Margreet Lauwaars, P.O. Box 153,6720 AD Bennekom, The Netherlands. Tel: +3 1 3 18 4 18725; Fax: +31 318 418359; or Derek Abbott, 80 Chaffers Mead, Ashtead, Surrey, UK KT2 LNH Tel: +44 372 274856. Fax: +44 372 274856. Department of Meetings, American Chemical Society, 11 5516th St. NW, Washington, DC 20036, USA Tel: +1 202 872 4396.Fax: +1 202 872 6128. E-mail: natlmtgs@acs.org. SIMS XI, 1201 Don Diego Ave., Santa Fe, "I 87505, USA Tel: +1 505 989 4735. Fax: +I 505 989 1073. Shijin Pang, Beijing Laboratory of Vacuum Physics, Chinese Academy of Sciences, P.O. Box 2724, Beijing 100080, People's Republic of China Tel: +86 10 256 8306. Fax: +86 10 255 6598. E-mail: pang@image.blem.ac.cn. Francoise Chavel, Executive Secretary, European Optical Society, B.P. 147-9 1403 Orsay Cedex, France Tel: +33 1 69 85 35 92. Fax: +33 1 69 85 35 65. E-mail: francoise.chavel@iota.u-psud.fr.Analyst, November 1996, Vol. 121 165N Date Conference 15-19 3rd International Symposium on Speciation of Elements in Biological, Environmental and Toxicological Sciences 2 1-26 XXX Colloquium Spectroscopicum Internationale October 5-10 14-18 25-3 1 26-29 1998 4th international Symposium on Environmental Geochemistry BCEIA '97, The 7th International Beijing Conference and Exhibition on Instrumental Analysis 24th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies 8th Symposium on Handling of Environmental and Biological Samples in Chromatography.26th Scientific Meeting of the Group of Chromatography and Related Techniques of the Spanish Royal Society of Chemistry February 11-13 April 27-29 May 3-8 24-28 5th International Symposium on Hyphenated Techniques in Chromatography and Hyphenated Chromatographic Analyzers (HTC-5) 4th International Symposium on Hygiene and Health Management in the Working Environment HPLC '98-22nd International Symposium on High Performance Liquid Phase Separations & Related Techniques ESEAC '98,7th European Conference on Electroanalysis Location Port Douglas, Queensland, Australia Melbourne, Australia Vail, CO, USA Shanghai, China Providence, RI, USA Almeria, Spain Bruges, Belgium Ostend, Belgium St.Louis, MO, USA Coimbra, Portugal Contact Dr. J. P. Matousek, Department of Analytical Chemistry, University of New South Wales, Sydney, NSW 2052, Australia Tel: +61 2 3854713. Fax: +61 2 3856141. E-mail: j.matousek@unsw.edu.au. The Meeting Planners, 108 Church Street, Hawthorn, Victoria 3 122, Australia Tel: +61 3 9819 3700. Fax: +61 3 9819 5978. E-mail: http://ww w .latrobe.edu.au/CSIconf/XXXCSI .html. R. C. Severson, U.S. Geological Survey, Federal Center, Box 25046, MS 973, Denver, CO 80225, USA Tel: +I 303 236 5514. Fax: +1 303 236 3200. E-mail: iseg@helios.cr.usgs.gov. BCEIA '97 General Service Office, Room 585, Chinese Academy of Sciences Building, San Li He, Xi Jiao, P.O. Box 2143, Beijing 100045, China Tel: +86 10 8511133 Ext. 1585, +8 10 8511814. Fax: +86 10 851 1814. E-mail: bceia@aphyO 1 .iphy.ac.cn. Jo Ann Brown, Federation of Analytical Chemistry and Spectroscopy Societies, 210B Broadway Street, Frederick, MD 21701, USA Tel: +1 301 694 8122. Fax: +1 301 694 6890. E-mail: jbrownsas@aol.com M. Frei-Hausler, IAEAC Secretariat, Postfach 46, CH-4123 Allschwil 2, Switzerland Fax: +41 61 482 08 05. Royal Flemish Chemical Society, c/o Dr. R. Smits, BASF Antwerpen N.V., Haven 725, Scheldelaan 600, B-2040 Antwerp, Belgium Tel: +32 3 5612831. Fax: +32 3 8278439. E-mail: smitsr@innet.be. Technologisch Instituut vzw, Desguinlei 2 14, B-2018 Antwerpen, Belgium Tel: +32 3 216 09 96. Fax: +32 3 216 06 89. E-mail: hygiene@ ti .kviv. be. Janet Cunningham, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: + I 301 898 5596. E-mail: Janetbarr@ aol .corn. Professor Dr. C. M. A. BrettIESEAC '98, Departamento de Quimica, Universidade de Coimbra, P-3049 Coimbra, Portugal Tel: +351 39 35295.

ISSN:0003-2654    

DOI:10.1039/AN996210161N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

166N Analyst, November 1996, Vol. 121 Courses Date Conference 1996 December 9-12 An Introduction to ICP Spectrometry; An Introduction to TCP-MS Spectrometry Location Contact Omaha, NE, USA Robyn Castleman, Continuing Education Administrator, CETAC Technologies, 5600 S. 42nd St., Omaha, NE 68107, USA Tel: +I 402 733 2829, + I 800 369 2822. Fax: + I 402 733 5292. Dr. P. Tebbutt, Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL 10-1 3 Introduction to Mass Spectrometry Warw i c k , UK 1997 January 14 14 14 14 May 31-116 3 1-116 31-1/6 3 1-116 31-1/6 31-116 ICP-MS Instrumentation Gent, Belgium Secretariat 1997 European Winter Conference, Luc Moens, Laboratory of Analytical Chemistry, University of Gent, B-9000 Gent, Belgium Tel: +32 9 264 6600. Fax: +32 9 264 6699.E-mail: plasma97@rug.ac.be. Secretariat 1997 European Winter Conference, Luc Moens, Labortory of Analytical Chemistry, University of Gent, B-9000 Gent, Belgium Tel: +32 9 264 6600. Fax: +32 9 264 6699. E-mail: plasma97@rug.ac.be. Secretariat 1997 European Winter Conference, Luc Moens, Laboratory of Analytical Chemistry, University of Gent, B-9000 Gent, Belgium Tel: +32 9 264 6600;. Fax: +32 9 264 6699. E-mail: plasma97@rug.ac.be. Secretariat 1997 European Winter Conference, Luc Moens, Laboratory of Analytical Chemistry, University of Gent, B-9000 Gent, Belgium Tel: +32 9 264 6600. Fax: +32 9 264 6699. E-mail: plasma97@ rug.ac. be. Quality Assurance and Quality Control Gent, Belgium Plasma Spectrometry and Speciation Trends Gent, Belgium High Resolution ICP-MS Gent, Belgium ASMS Short Course-Interpretation of Mass Spectra Palm Springs, CA, USA American Society for Mass Spectrometry, 1201 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +1 505 989 4517.Fax: +I 505 989 1073. American Society for Mass Spectrometry, 120 1 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: + I 505 989 4517. Fax: + I 505 989 1073. American Society for Mass Spectrometry, 120 1 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +1 505 989 4517. Fax: + I 505 989 1073. American Society for Mass Spectrometry, 1201 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +I 505 989 4517. Fax: + I 505 989 1073. American Society for Mass Spectrometry, 1201 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +1 505 989 4517. Fax: +1 505 989 1073. American Society for Mass Spectrometry, 1201 Don Diego Avenue, Santa Fe, NM 87505, USA Tel: +1 505 989 4517. Fax: + I 505 989 1073. ASMS Short Course-Principles and Practice of Quantitative Mass Spectrometry Palm Springs, CA, USA ASMS Short Course-LC/MS: The Techniques of Electrospray and API Palm Springs, CA, USA ASMS Short Course-Proteins and Peptides Palm Springs, CA, USA ASMS Short Course-Principles of Ion Mass Spectrometry Palm Springs, CA, USA ASMS Short Course-Fundamentals of MALDI Palm Springs, CA, USA - Entries in the above listing are included at the discretion of the Editor and are free of charge. If you wish to publicize a forthcoming meeting please send full details to: The Analyst Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF. Tel: +44 (0)1223 420066. Fax: +44 (0)1223 420247. E-mail:Analyst@RSC.ORG.

ISSN:0003-2654    

DOI:10.1039/AN996210166N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Analyst, November 1996, Vol. 121 167N The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (O)171-437 8656. Fax: +44 (0) 17 1-287 9798. Telecom Gold 84: BUR21 0. Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society’s Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge. ~ Future Issues Will Include Amperometric Biosensor for Tyrosinase Inhibitors in Pure Organic Phase-Shaojun Dong, Qing Deng Rapid and Accurate Determination of Manganese in Washing PowdersDetergents Using Alkali Fusion and Inductively Coupled Plasma Techniques-Kym E.Jarvis, J. G. Williams, B. C. H. Gibson, E. Temmerman, C. De Cuyper Wall-jet Flow Cell for Stripping Potentiometry-Daniel Jagner, R. Ratana-Ohpas, W. Ratana-Ophas, P. Kanatharana Micro-optical Ring Electrode: Development of a Novel Elec- trode for Photoelectrochemistry-Colin Boxall, Gaelle I. Pennarun, Danny O’Hare Determination of Volatile Organic Compounds in Air by Dehumidified and Ventilated Diffusive Sampler, Thermal Desorption and Gas Chromatography-Flame Ionization Detec- tion-Y. S. Fung, Zucheng Wu Reagentless Amperometric Glucose Dehydrogenase Biosensor Based on Electrocatalytic Oxidation of Nicotinamide Adenine Dinucleotide Reduced Form by Osmium Phenanthrolinedione Mediator-Ioanis Katatis, Maria Hedenmo, Arantazu Narvaez, Elena Dominguez Flow System for Liquid Sample Introduction in Arc/Spark Excitation Sources-Celio Pasquini, Carlos Roberto Bellato Sensitive Densitometry for the Platelet-activating Factor and Other Phospholipid Determinations in Human Tears- Toshihisa Ohyama, Chiyo Matsubara, Kiyoko Takamura Application of Nafion-coated Mercury Film Electrodes to the Microdetermination of Formaldehyde by Differential-pulse Voltammetry-Wing Hong Chan, Hao Huang Competitive Enzyme-linked Immunosorbent Assay for the Determination of the Phenylurea Herbicide Chlortoluron in Water and Biological Fluids-Fawaz M.Katmeh, W. Aherne, D. Stevenson Volatile Organic Metabolites Associated With Some Toxic Fungi and Their Mycotoxins-Anna-Liisa Pasanen, Sanna Lappalainen, Pertti Pasanen Optical Sensor for Oxygen Concentrations Using a Porphyrin- doped Sol-Gel Glass-Sang-Kyung Lee, Ichiro Okura pK,, Values of the Opened Form of a Thieno-1,2,4-triazolo- 1,4-diazepine in Water-Beatrice Legouin, Jean-Louis Burgot Optical Chemical Sensors For Pharmaceutical Analysis Using 1,4-Bis( 1,3-benzoxazole)benzene as Sensing Material-Ying Wang, Kemin Wang, Wanhui Liu, Guoli Shen, Ruqin Yu Determination of Ammonia in Waste Waters by a Differential pH Method Using Flow Injection Potentiometry and the Nonactin-based Sensor-Robert W.Cattrall, Hongda Shen, Terence J. Cardwell Direct Determination of Butyl- and Phenyltin Compounds as Chlorides Using Gas Chromatography and Flame Photometric Detection-G. Lespes, C. Carlier-Pinasseau, M. Potin-Gautier, M. Astruc Simultaneous Stopped-flow Determination of Paracetamol, Acetylsalicylic Acid and Caffeine in Pharmaceutical Formula- tions by Partial Least Squares-Fourier Transform Infrared Spectrometry-Miguel de la Guardia, Zouhair Bouhsain, Salvador Garrigues Effect of Storage on the Recovery of Different Types of Pesticides Using a Solid-phase Extraction Method-A. Pena, C. de la Colina, F. Sanchez-Rasero, G. Dios, E. Romero Optical Biosensing of Nitrate Ions Using a Sol-Gel Im- mobilized Nitrate Reductase-Jonathan W. Aylott, David J. Richardson, David A. Russell Quantitative Analysis of Sulfated Calcium Carbonates Using Raman Spectroscopy and X-ray Powder Diffraction-Christos G. Kontoyannis, Malvina G. Orkoula, Petros G. Kou tsou kos COPIES OF CITED ARTICLES

ISSN:0003-2654    

DOI:10.1039/AN996210167N

出版商:RSC    

年代:1996

数据来源: RSC