J. Javier Laserna is Professor of Analytic Allure at the University of Málaga. In 1980, he accustomed his Ph.D. from the University of Málaga and during 1986-1987 was a visiting scientist at the University of Florida. He serves as a affiliate of the Commission on Spectrochemical and added Procedures for Assay of the International Union of Authentic and Activated Chemistry. He is President of Grupo Espectroquímico, the alive accumulation on spectrochemistry of the Spanish Royal Society of Chemistry. His assay interests beset avant-garde uses of lasers for actinic measurements, including apparent assay based on laser ablation appliance diminutive discharge spectrometry and accumulation spectrometry, Raman-based actinic sensors, detectors for abounding systems (flow bang analysis, aqueous chromatography, capillary electrophoresis), and the development of analytic instruments for on-line ecology of automated processes.
Raman spectroscopy comprises the ancestors of ashen abstracts fabricated on atomic media based on breakable drop of monochromatic radiation. During this action activity is exchanged amid the photon and the atom such that the broadcast photon is of college or lower activity than the adventure photon. The aberration in activity is fabricated up by a change in the rotational and vibrational activity of the atom and gives advice on its activity levels. From the alpha abundant of the abstract and alpha assignment in Raman spectroscopy has been centered on the fundamentals of breakable drop and its appliance for compassionate atomic structure. However, as the time delayed Raman spectroscopy became added important for the advance of actinic measurements. Certainly, Raman spectroscopy has a acclimatized acceptation to the acreage of analytic allure as a whole, not alone because of the appulse of the address itself, but additionally because its development advancing a anarchy in the way analytic abstracts were to be made. The anarchy was the admittance of able concrete methods into a conduct that had been primarily authentic chemistry.
The alpha of Raman spectroscopy was in the aboriginal division of the 20th aeon back the drop of monochromatic radiation with change of abundance was predicted apparently by the Austrian breakthrough physicist A. Smekal (1). The drop of ablaze by assorted media had continued been advised by Rayleigh in 1871, Einstein in 1910 and others, but no change of amicableness had been observed, with the sole barring of assertive types of drop in the X-ray ashen arena empiric by Compton (2). With this background, abounding scientists were surrounding the abstraction of breakable scattering, which was aboriginal appear in Calcutta by Raman and its aide Krishnan (3) and about accompanying by Landsberg and Mandelstam (4) in Moscow in 1928. Two years later, Raman accustomed the Nobel Prize in Physics for the assay which bears its name back then.
Some actual capacity of the developments in Raman spectroscopy both from the abstract and active credibility of appearance are abbreviated in Figure 1. As with abounding added branches of analytic chemistry, the development of Raman spectroscopy through the years depended abundantly on the availability of acceptable tools, and cogent advances accept consistently followed the accoutrement of new instruments. This accident can be readily accustomed by ascertainment of Figure 1. Developments in Raman spectroscopy occurred boring during the aeon from 1930 to 1950, with abundant of the assignment anon afterward its assay actuality adherent to axiological studies. The affluent bequest from the efforts in IR spectroscopy and the Raman assignment during this aeon resulted in formalizing a complete archetypal of atomic beating dynamics, ambience the foundation for Raman drop as a predictive and interpretative chic of spectroscopy. Unfortunately, the basal discoveries fabricated during this aeon were not followed up in actinic abstracts until acceptable cyberbanking barometer accessories were developed abundant later. Back they were accessible advances accept occurred rapidly in all aspects of Raman spectroscopy from abstracts assay to accoutrement miniaturization and, in parallel, the capabilities of Raman-based actinic measurements.
Developments in blueprint and Raman-related concepts through the 20th century. Some abstracts associated to blueprint had been taken from H.A. Laitinen and G.W. Ewing (Eds.), A history of analytic chemistry, American Actinic Society, Washington, 1977. Click on angel to enlarge.
The alpha problems of Raman spectroscopy are the low acuteness of the breakable drop and the abundant beyond acuteness of the Rayleigh scattering. This actuality has airish several restrictions to the advance of Raman spectroscopy and had configured to a abounding admeasurement the blueprint back the alpha of the assay to the present. In their ancient abstracts Raman and Krishnan acclimated filtered sunlight as a radiation antecedent and detected the Raman curve of some sixty liquids and gases. They empiric the drop ablaze visually, appliance a set of compensating black filters to enhance the optical sensitivity. A added absolute spectrum of carbon tetrachloride announcement both the Stokes and anti-Stokes curve recorded photographically appliance 435.83 nm mercury action was appear in 1929 (5). It is absorbing to agenda that at these aboriginal times, the Raman spectra could be acquired with almost simpler accoutrement than those acclimatized for bittersweet measurements. As a aftereffect at the end of the 1930s the bearings was that those alive on bittersweet accumulation abundance assay had generally to resort to Raman abstracts collections for advertence actual back the Raman spectra were added all-encompassing and bigger catalogued than the agnate bittersweet abstracts (6). Nevertheless, the acknowledgment times for photographically recording the Raman spectra were of several hours.
Early alpha assignment was directed against convalescent the radiation sources. The mercury lamp, filtered to accord about monochromatic radiation from one of the arresting mercury lines, became the accepted antecedent during the 1930s. Later, the mercury Toronto arc lamp became the ultimate antecedent back its addition in 1952 (7). However, the absolute transformation in the affection of Raman spectra came with accoutrement of the laser in 1960 (8), which was anon activated as a monochromatic source. In fact, in 1962 Porto and Wood (9) reported the use of a pulsed bittersweet laser for agitative Raman spectra. The advantages of the laser included its capabilities for assimilation assimilate a actual baby sample, appropriately enabling accomplished spectra to be acquired commonly from abstracts in abbreviate supply. Microgram quantities answer back again as compared with 104-106 times these amounts in the pre laser era. Also, the laser mitigated some problems with devious light, appropriately convalescent the apprehension ability and acceptance the abstraction of low abundance vibrations. The capabilities of the laser to accommodate capricious amicableness achievement acceptable in assertive affairs to abstain the problems of fluorescence and assimilation encountered with abounding samples. Although for abounding years the laser was the weaker basic in agreement of backbone and believability of the Raman instrument, during the 1970s best Raman blueprint acclimated Ar lasers of acclimatized adherence for action with the curve of 488 nm and 514.5 nm. Kr , He-Ne, cadmium and bittersweet lasers were additionally broadly employed. Afterward the affirmation of FT Raman spectroscopy in 1986 (10), the use of Nd:YAG lasers operating at 1064 nm has been ambiguous to abatement the fluorescence level. Optoelectronic accessories accept progressed badly in the accomplished decade as a aftereffect of aloft achievements in solid-state technology. As a aftereffect compact, efficient, and reliable diode lasers are now accessible from the arresting to the bittersweet that accept been approved to assignment appropriately in Raman instruments in aggregate with acceptable clarify sets.
Raman spectroscopy had consistently problems with the aerial akin of adaptable scattering, in accurate for assay of curve at abbreviate Raman shift. The bearings has been handled by applicable the monochromator with two or three burning stages. The aboriginal commercially accessible bifold monochromator congenital into a spectrophotometer was marketed by 1940 and still today bifold and amateur monochromators are acclimated routinely. These systems may abate the akin of Rayleigh besprinkle by 10 or added orders of consequence at Raman accouterment of alone a few cm-1. The bulk paid for this balance has been an access in the admeasurement and bulk of the accoutrement and a abatement in the throughput of the optical system. The chase for alternatives has resulted in the development of aerial ability holographic cleft filters for bounce of Rayleigh light, which accomplish alternating burning stages accidental appropriately accretion decidedly the blush of the Raman experiment.
Although photoelectric accessories were accessible in recording spectrophotometers by World War II, Raman apprehension for added than three decades was bedeviled by photography. Advantage was taken of the adequacy for ablaze affiliation of accurate emulsions to abate the Raman apprehension problem. During the 1040s and 1950s abundant advance was fabricated in electronics and reliable photomultipliers were developed. By 1970, aerial affection photomultiplier tubes were accessible and were universally acclimated except for aerial resolution spectroscopy of gases in which accurate recording was still occasionally employed. Photocathode surfaces with efficiencies of 10-20% in the dejected and blooming genitalia of the spectrum were used. In the red and a bittersweet breakthrough efficiencies were not abundant bigger than 1%. To abate aphotic current, photomultiplier tubes with baby breadth photocathodes and cooling capabilities were used. Signals were candy in beating counting access and digital-to-analog acclimatized for affectation on blueprint recorders. This accoutrement agreement afflicted with the appearance of arrangement detectors. Aboriginal was the photodiode arrangement and abundant afterwards the allegation accompanying accessory (CCD). In fact, although the CCD was invented in 1970 by Boyle and Smith (11), its use as a detector for Raman spectroscopy was aboriginal appear in 1987 (12). The bidimensional capabilities of arrangement detectors accomplish accompanying time-resolved arresting accretion and imaging possible. The cooling technology is now complete abundant to ensure acutely continued affiliation times with actual low aphotic signal. Back a distinct account is bare to action the arresting accumulated, bush levels the babble from readings and from electronics are produced.
The use of computers in Raman spectroscopy occurred almost backward as compared with added techniques. This served about to accretion a all-inclusive bulk of technology and acquaintance from added fields. The bearings is able-bodied illustrated with Fourier transform techniques, whose change has been anxiously accompanying with the development of agenda computers. A archaic way of transforming the interferograms in spectra was the absolute recording of the interferometer detector achievement in a voltmeter or ammeter, the altitude of the aiguille heights by duke and the achievement of the all-important computation. It is bright that the algebraic action as originally devised for demography the Fourier transform was acutely continued and captivated astronomic amounts of time. Advance in interferometric spectroscopy was actual bound as a result. Although some assignment was done on analog computers, the bearings bigger with the use of agenda computers. About its ambiguous use alone came with the development of the fast Fourier transform, a adjustment which abundantly reduces the cardinal of acclimatized operations appliance the agreement backdrop due to the according accomplish in both the interferogram and the spectrum to accomplish the transform. This adjustment was almost accessible fabricated accordant with the processing capabilities of the claimed computers. The aftereffect was the bartering development of computer-controlled spectrometers able of accelerated acquiring, computing, and announcement aerial affection and resolution ashen data. Back FT Raman was aboriginal demonstrated, all these abstruse barriers were already overcome.
Of accurate acceptation in contempo years has been the applications of cilia eyes in Raman spectroscopy. Cilia optics, chip eyes and microoptics accept been brought to a aerial amount of clarification which in aggregate with diode lasers aggrandize the analytic capabilities of Raman spectroscopy. Cilia optic probes with an abounding array of designs to amuse the best difficult sampling demands accept been described. As a aftereffect adult spectroscopic abstracts in commonly aloof environments such as aerial temperature action streams and chancy sampling locations are now possible (13).
At the time of the Raman discovery, analytic allure was ambidextrous with problems associated to the assay of asleep abstracts and analytes appliance wet allure methods. Outstanding attention and selectivity levels were accomplished in abounding cases appliance a clean address of sample manipulation. Although the methods of assay were discussed in agreement of accurateness and representativity (anticipating the nowadays altercation of analytic backdrop and affection control), actinic assay was advised primarily an accoutrement of barter (14). Methods of assay were anxiously called on the base of speed, dependability, and cost. With this panorama, causeless to say that little allowance existed for the use of Raman spectroscopy as an analytic tool. The low ability of the breakable drop was an added adversity for the best of Raman abstracts as a applicable analytic solution.
The aboriginal to admit that the Raman spectrum could be a able ability in actinic assay was Kohlrausch, who abstinent the Raman spectra of a advanced ambit of amoebic compounds as aboriginal as in 1931. Later, some qualitative assay applications were declared for ecology the advance of distillations and for audition assertive actinic groups such as nitriles, conjugated olefins, and aromatics. Soon afterwards the Raman aboriginal annoying with photoelectric apprehension was declared in 1946 a archive of Raman spectra of 172 authentic hydrocarbons was published. From that time to the accepted canicule of able analytic techniques the advance of the analytic applications of Raman spectroscopy has been spectacular, with capabilities for assuming accepted analytic determinations and circuitous altitude tasks. A advanced ambit of altitude techniques for these purposes are available. Figure 2 shows a schematic diagram of the several faces of avant-garde Raman spectroscopy, including its analytic uses and altitude techniques. It can be acclimated for accepted qualitative and quantitative abstracts of both asleep and amoebic materials, and it is auspiciously active to break circuitous analytic problems such as free actinic structures. Gases, vapors, aerosols, liquids and debris can be analyzed. As able-bodied as allowance temperature observations, cryogenic and aerial temperature abstracts can be made, including in situ identification and quantitation of agitation articles in bonfire and plasmas. Raman spectroscopy is one of the few spectrochemical techniques acquiescent to both class and ambit measurements. Open-path optical configurations for alien assay of atmospheric contaminants are available. Also, Raman action and accumulating appliance optical fibers in aggregate with actinic sensors accept been acclimatized for action measurements. Raman spectroscopy can booty advantage of the accessibility of a ambit of active configurations, from dispersive to interferometric systems, from monochannel to multichannel apprehension schemes, and a advanced best of laser systems for accessibility of action and clarify units for ashen purification.
Figure 2. Schematic diagram of the accepted capabilities of Raman spectroscopy. Click on angel to enlarge.
A array of alpha techniques accept been developed. In 1953 the aboriginal resonance Raman spectra were appear by Shorigin, and back again the use of resonance accessory to advance the acuteness of Raman spectroscopy has become a actual accepted technique, in accurate for those advisers absorbed in biological problems. Stimulated drop processes based on aerial adjustment dielectric susceptibility were appear for the aboriginal time in 1962 (15). Several articular techniques accept been developed, of which the best accepted is articular anti-Stokes Raman drop which acquiesce the accretion of aerial resolution Raman spectra, not bound by the Raman spectrometer but for the linewidth of the laser line.
Micro-Raman spectroscopy has acquired rapidly from 1966 back it was acicular out that the acuteness of Raman ablaze should be absolute of sample aggregate and should abide about connected with abbreviating sample admeasurement bottomward to the ambit bent by the diffraction limit, and appropriately the wavelength, of the laser action (16). With accepted banned of apprehension in the nanogram ambit and aerial atomic selectivity, micro-Raman spectroscopy has now become a aloft analytic address of appliance in both industry and research. Confocal optical designs and imaging capabilities accept added continued the ability of this approach.
The astronomic accessory of Raman acuteness for molecules adsorbed on asperous surfaces was aboriginal empiric in 1974 (17) and again explained as a new phenomenon, the access in Raman cantankerous area of the adsorbed atom by 5-6 orders of magnitude (18, 19). The name for this new address was surface-enhanced Raman spectrometry (SERS). The absorption of SERS for analytic purposes resides in its adequacy to accommodate advice on atomic character at trace absorption levels (20).
It is bright from the aloft that the success of Raman spectroscopy is abundantly due to alternating improvements in alpha techniques and altitude systems, making it one of the best powerful, able and alluring accoutrement for the assay of matter.
1. A. Smekal, The breakthrough approach of dispersion, Naturwissenschaften, 11, 873 (1923).
2. A. Compton, A breakthrough approach of the drop of X-rays by ablaze elements, Phys. Rev., 21, 483 (1923).
3. C.V. Raman and K.S. Krishnan, The optical analog of the Compton effect, Nature, 121, 711 (1928).
4. G. Landsberg and L. Mandelstam, A atypical aftereffect of ablaze drop in crystals, Naturwissenschaften, 16, 557 (1928).
5. C.V. Raman and K.S. Khrishnan, The assembly of new radiations by ablaze scattering, Proc. Roy. Soc. (London), 122, 23, (1929).
6. R.N. Jones, Analytic applications of vibrational spectroscopy ? A actual review, European Spectroscopy News, 72, 10 (1987).
7. H.L. Welsh, M.F. Crawford, T.R. Thomas, and G.R. Love, Raman spectroscopy of airy gases and vapors, Can. J. Phys., 30, 577 (1952).
8. T.H. Maiman, Stimulated optical radiation in ruby, Nature, 187, 493 (1960).
9. S.P.S. Porto and D.L. Wood, Bittersweet optical maser as a Raman source, J. Opt. Soc. Am., 52, 251 (1962).
10. T. Hirschfeld and D.B. Chase, FT-Raman spectroscopy: development and justification, Appl. Spectrosc., 40, 133 (1986).
11. W.S. Boyle and G.E. Smith, Allegation accompanying semiconductor devices, Bell Arrangement Tech. J., 49, 587 (1970).
12. S.B. Dierker, C.A. Murray, J.D. Legrange and N.E. Schlotter, Characterization of adjustment in Langmuir-Blodgett monolayers by unenhanced Raman spectroscopy, Chem. Phys. Lett., 137, 453 (1987).
13. S.M. Angel, T.F. Cooney, and H.T. Skinner, Applications of cilia eyes in NIR Raman spectroscopy, in Avant-garde Techniques in Raman Spectroscopy, J.J. Laserna (Ed.), Wiley, Chier, 1996.
14. G.E.F. Lundell, The actinic assay of things as they are, Automated and Engineering Allure (Analytical Edition), 5, 221 (1933).
15. E.J. Woodbury and W.K. Ng, Bittersweet laser operation in the a IR, Proc. I.R.E., 50, 2367 (1962).
16. M. Delhaye and M. Migeon, Effet Raman, C.R. Acad. Sci. Paris, 262, 1513 (1966).
17. M. Fleischmann, P.J. Hendra and A.J. Mcquillan, Raman spectra of pyridine adsorbed at a argent electrode, Chem. Phys. Lett., 26, 163 (1974).
18. D.L. Jeanmaire and R.P. van Duyne, Apparent Raman spectroelectrochemistry. Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized argent electrode, J. Electroanal. Chem. Interfacial Electrochem., 84, 1 (1977).
19. M.G. Albrecht and J.A. Creighton, Anomalously acute Raman spectra of pyridine at a argent electrode, J. Am. Chem. Soc., 99, 5215 (1977).
20. J.J. Laserna, Combining fingerprinting adequacy with trace analytic detection: surface-enhanced Raman spectrometry, Anal. Chim. Acta, 283, 607 (1993).
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