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1. When we started planning for IJVS the Editorial Advisory Committee gave some considerable thought to the problem of page numbering and never quite sorted it out. We were fully aware that people would want to refer to articles, diagrams, or tables, but we ran across the technical problem of page length. If the default parameters on your software and printer match ours, your hard copy output will retain page integrity. Put another way - your page 27 will exactly match ours. If the conditions do not match, then gradually the page number you have differs from the input. As a result, we cannot number the pages for you. Various propositions were made, such as indicating the end of each input page, but they really were far from satisfactory. 2. All the best ideas are pinched from somebody else - why not re-invent what is done in the Bible - you know: Luke VI vs.10. The plan is to number each paragraph (we will skip very short ones) so that each Edition will be numbered from para. 1 - n. We will put the paragraph number at its beginning, in bold. As you can see, we have already started. The paragraph number is preceded by the Edition number, so if you wish to refer to this paragraph in the future, it would be 42 and thus the complete citation would read: P. J. Hendra, Internet J.Vib.Spect., 1 (1997) 42. We plan to produce six editions per year, so the first digit will never exceed six and it is unlikely that the number of paragraphs will exceed 99 in any one edition. Of course, it won't really matter if the number runs into the hundreds. 3. The advantages of this method are that it is unambiguous, very clear, simple, and very close to the system used in regular hard copy journals. In fact, it is more specific, defining a paragraph rather than a page. We plan to run the method for two editions, allowing you the readers to scream. If it seems to be acceptable, we will number Editions I, II and III and away we go. Last time I mentioned that we could not think of a good title for the section including responses, queries and answers from readers. Wendy came up with some ingenious suggestions, including R.E.A.R. (Readers' Enquiries and Responses) and then had some real inspiration - why not cash in on the current Jane Austen craze and entitle the section "Dear Reader". Having just seen "Pride and Prejudice", I fell in love with this idea immediately. Thus it is with some hesitancy, nay trepidation, that we impose on your patience and proffer the title in this Edition at paragraph 85. I would, of course, deem it a singular honour if you would respond and give us all the benefit of your thoughts on this delicate matter. 4. In this edition we are featuring reflection methods in the infrared. The coverage is far from exhaustive and will be taken up again and again, I am sure, in subsequent editions but here we "kick off" with a simplistic survey of the various methods. The physics of reflection can be a bit daunting, so in this introduction to the subject I have kept the theory very firmly at bay. Don't get complacent - it lurks in hiding and is sure to leap out in the future! 5. I am not in any way an expert in this field, so with some relief I persuaded Alex Shchegolikhin and his colleague Olga Lazareva to write the section on DRIFTS. In future editions we will pick up each of these techniques and cover them in much more detail. As time goes by I hope we will have an increasing flow of submitted papers. When I see an article I think would interest you folks, I write and ask the author to produce something for us. Many are in the pipeline but four have arrived for this edition. Thus, Alex Shchegolikhin and Olga Lazareva have sent in an interesting piece showing how a simple modification to the normal DRIFTS procedure makes it more easy to use, more routine and also more versatile. 6. One of our features is "Hot Sources" - the idea is that as time goes on so people will be able to find a good literature source very quickly; a source recommended by an experienced user. I have provided lots BUT you folks are not helping! We have received a couple of corrections and one suggestion - thanks - these are very valuable. PLEASE send me some more. 7. Wendy's son Rob is in the banking and commercial world and has received notification of some very nasty bugs which I suspect are circulating round a part of the Web fairly distant from our own. Hopefully they will not hit the scientific community, but you never know, so we reproduce these warnings - TAKE THEM SERIOUSLY. See IJVS 1 (1997) 412 8. Now that IJVS is settling down, I have to report a severe problem. People are doing what we ask and corresponding with us by e-mail - no problems. They are also following our instructions and sending in articles electronically. This is turning out to be a nightmare! Frequently we receive material in formats we simply don't know or cannot access. By the time we have identified the material and unsorted it, days can have passed, thereby defeating the whole object. People have problems with diagrams and we often receive manuscripts with diagrams and figures missing, or scrambled. We then FAX the authors and eventually receive the documents by FAX. I therefore suggest we change our methods. 9. Articles should initially be submitted by FAX. After refereeing and alteration - all by FAX or e-mail - the final manuscript must be sent on a disk in the correct format. We will not accept hard copy, as this has to be re-typed. It sounds a little odd to go back to snail mail but I am certain this will be faster in the long run. What do you authors and readers think??? 10. Our intention from the start of publication has been that the Journal should include short, easy to read, and up to date mini-reviews. The first is to hand and appears at IJVS 1 (1997) 4-68 11. Last time, the question of spectral data, its presentation, and use by readers, was raised. I mentioned the question of copyright. Nobody responded, so I presume few people are worried. Bob Lancashire and Tony Davies have written an authoritative piece on spectral data and it appears below at IJVS 1 (1997) 4-57 12. VIRUS ATTACK If you receive an e-mail entitled "JOIN THE CREW" DO NOT open it! It will erase EVERYTHING on your hard drive! Send this letter out to whoever you can - this is a new virus and not many people know about it. This information was received today from IBM. Also, if anyone receives mail entitled "PENPAL GREETINGS" please DELETE IT WITHOUT READING IT! This message appears to be a friendly letter asking if you are interested in a penpal, but by the time you read the letter it will be TOO LATE. The "Trojan Horse" virus will have already infected the boot sector of your hard drive, destroying all of the data present. It is a self-replicating virus and once the message is read, it will AUTOMATICALLY forward itself to anyone whose e-mail address is present in YOUR mailbox. This virus will DESTROY your hard drive and holds the potential to DESTROY the hard drive of anyone whose mail is in your box. If this virus keeps getting passed on, it has the potential to do a great deal of damage to computer networks worldwide. So please delete the message entitled "PENPAL GREETINGS" as soon as you see it. 13. There is another recent virus circulating. DO NOT OPEN or even look at any mail you receive that says "RETURNED or UNABLE TO DELIVER". This virus will attach itself to your computer components and render them useless. Immediately delete any mail items that say this. AOL has said this is a very dangerous virus and there is NO remedy for it at this time. PLEASE, BE CAREFUL. We have since discovered that these warnings, and all like them, are hoaxes. We include them here as a warning of the kind of hoaxes you might receive by email and also as a reassurance that your data is not under threat from this kind of attack. Please be aware though of the potential dangers of genuine viruses and take care to protect your computer from them. 14. Infrared Reflection Methods Everyone who uses infrared spectrometry is familiar with transmission methods; films of liquids and gums between KBr flats, free standing films of polymers, Nujol mulls and KBr discs - most of us have used them all. In Edition 1 we considered theory and practice in mulling and KBr disc making, but there are alternative methods of sampling. Many years ago pioneers demonstrated that excellent spectra could be recorded using reflection methods. As time went on, a bewildering range of these appeared, but in a sense they were of very limited value and only of real interest to the specialist. The problem with them all was that the reflection process was inefficient and the older dispersion instruments were not sensitive enough to give good quality results - or to be more correct, unless used with considerable skill and backed by experience, the results were unacceptable. 15. In the 70's and 80's, FTIRs penetrated first the research and then the routine laboratory. These instruments had vastly improved sensitivity and as a result the reflection methods got a shot in the arm. The FT instrument did not make these methods possible, although some of the accessory manufacturers imply that it did, but rather its development made them routine. What are these reflection methods? Basically there are three - specular reflection, diffuse reflection, and attenuated total internal reflection, although all of them have been subdivided and developed into seemingly newer and more advanced techniques. To assist readers who are not familiar with them, I will now very briefly and simplistically describe each. In articles to follow, this brief introduction will be expanded. 16. Specular Reflection Everyone is familiar with this - the mirror is an example. Light incident on a smooth surface is reflected at the angle with which it hits the surface. Note that the angle of incidence and reflection is conventionally referred to the normal, not the surface itself. Don't ask me why - it just is! So glancing incidence - light slithering along the surface itself - has a high angle of incidence, say 85°. 17. Light reflected off a surface is not identical in characteristics to that which is incident. Some attenuation is normal. The nature of the reflector itself causes this attenuation. Thus, my car is red - white light is severely attenuated in the blue/green by the paint, so it appears to me to be red (I conveniently forgot to mention the dirt and the rust). Also, the reflection process causes polarization. White light from all sources is non-polarized - the electric vector of the electromagnetic radiation is not controlled. Reflection is more efficient for light polarized normal to the reflector than it is for radiation polarized parallel to it. So we can redraw the first diagram: 18. Thus, to the observer, the reflection process has caused the radiation to be somewhat polarized. Many of us exploit this effect when we buy Polaroid sunglasses. The Polaroid sheet in the glasses is set to transmit only the horizontally polarized light. Hence the eye sees 50% of the light reaching the Polaroid, (in fact a bit less than 50% due to absorption losses), thus reducing the light level as is desired. However, the reflected light is more severely attenuated so that reflection off smooth surfaces seems to the wearer to be dimmed. That is why Polaroid sunglasses reduce the glare of the sun reflected off water or polished surfaces and makes them ideal for motorists or fishermen (you really can see the fish more easily when wearing Polaroid rather than any other sunglasses). 19. If you illuminate a surface with infrared radiation, the light will be attenuated and polarized exactly as it would be in the visible. The efficiency of reflection is related to the refractive index of the reflector. The theory will come up later but it is sufficient here to accept that as a sample absorbs, its index of refraction changes as well. As a result, infrared absorbers show an efficiency of reflection that wanders up and down with the absorbance. Hence, the reflected light contains information in it about the absorption spectrum. It would be nice if the reflection spectrum was the same as the absorption one, but it is not. It is related to it. Here is a comparison 20. There is an obvious connection between the two but the reflection spectrum is hard to recognise. Fortunately, computer processing of the reflected spectra can unscramble this lot and produce an output very close to the conventional absorption spectra. The software (or algorithm) is due to Kramers and Krönig and almost all FTIRs have it as part of the software suite. So we have - Highly polished metal mirrors can reflect ~97% of the light falling on them but fairly smooth organic ones (say a lump of plastic) will only reflect 10-25%, but this is ample for a modern FTIR. Accessory manufacturers make Specular Reflection accessories and most enable users to vary the angles of incidence and reflection at will. 21. Sampling in specular reflection can be a problem. If the sample readily transmits, the reflection can be weak and of less diagnostic value. The method works best on 'optically dense' samples e.g. carbon loaded plastics where the carbon soaks up the transmitted radiation and the reflection bounces off the surface. If a sample is oriented - say a mineral or polymer - the absorption spectrum is dichroic, i.e. it is direction dependant, hence the reflection efficiency is dichroic as well and as a result measurements can yield orientation data. If the reflection is carried out at high angles of incidence, grazing angle reflection information can be acquired from very thin films. 22. So, the message is clear - reflection is valuable and versatile. The problem is that unless a diagnostic protocol has been worked out in a particular case, it is difficult to use, requires computer processing, and is certainly not a universal method for the casual user. A variant on specular reflection is transflectance, although it has been called other names in its time. If you have a thin sample - a piece of film or a liquid film - you can examine it like this 23. Two processes occur - reflection off the top surface and also transmission and reflection off the mirror, followed by a second transmission. If the reflection off the top surface could be eliminated, the light collected would be a true absorption spectrum typical of a sample of thickness 2t/Cos(i). The reflection off the mirror, as we have seen, is much more efficient than our organic material hence the combined radiation collected in the experiment illustrated above is predominantly the transmitted stuff and many users ignore the reflection off the sample surface and assume their spectrum is due to transmission. 24. Diffuse Reflection This technique is often called DRIFT - Diffuse Reflection Infrared Fourier Transform - but the Fourier Transform part of the name is irrelevant. Diffuse reflection occurs off rough surfaces. The reflected radiation comes off in the specular direction and in all other directions as well. The specular component arises very much like it does off a smooth surface but the diffuse bit occurs to at least some extent from penetration and multiple reflection/absorption inside the bulk of the specimen. The result is that if one can separate the two, the diffusely scattered radiation resembles an absorption spectrum, the specularly reflected part, the spectrum described in paras 16 to 23 above. 25. When it appeared, DRIFT seemed to be the answer to the analyst's prayer - a simple, almost universal analytical tool - but it transpires that it is good in the hands of the experienced expert. Sampling is fiddly and requires skill. Alexander Shchegolikhin and Olga Lazareva have provided a piece to follow which tells you more about DRIFT and a variant they find more useful - DRAFT (and I'm not going to tell you what DRAFT stands for!). Thank goodness it didn't come out as DRAUGHT! REF: Int.J. Vib. Spect.,[www.ijvs.com] 1, 4,
14-25 (1997) 26. Diffuse Reflectance for the routine
analysis of Liquids and Solids Alexander Shchegolikhin and Olga Lazareva 27. Diffuse reflection requires that an infrared beam illuminates a powdered sample and that the system collects light over a wide range of angles excluding the specular reflection angle. We have used commercially available DRIFT accessories for several years and two of them are illustrated below. 28. An optical diagram of the Perkin-Elmer Diffuse Reflectance (PEDR) accessory is shown in Fig.1. This accessory is mounted in the spectrometer sample compartment by placing its side slide support into the sample slide holder of the instrument. Access to the sample is accomplished from the front of the attachment by sliding the sample holder horizontally toward an operator. The sample height is fully adjustable by means of a single focus adjustment knob. The PEDR accessory design, shown in Fig.1, uses five flat reflectors, one of which (M1) is double-sided. It uses one aspherical reflector (M4), which both focuses the incident beam on the sample and collects the reflected beam with 8X condensation power. The collecting angle of the PEDR accessory is a full pi steradians, so that it is able to collect approximately 50% of the reflected energy. The angle of incidence is 38° [11].
29. Although it is not obvious in the diagram, the sample is tilted out of the plane so that the specular reflection misses the ellipsoidal collector. An optical diagram of the other DRIFT accessory used in our work, "The Collector" from the Barnes Analytical Spectra-Tech, is shown in Fig.2. The design employs 4 flat and 2 aspherical reflectors. The aspherics are off-axis ellipsoids which focus and collect infrared energy with 6X condensation of the beam. The collection angle is a full pi steradians, collecting about 50% of the available reflected energy. The fixed mean angle of incidence is 50°. The accessory is mounted onto the bottom of the sample compartment of the spectrometer.
30. Here again the sample is tilted to avoid the specular component. Some of the accessory makers use a blade to discriminate the diffuse from the specularly reflected light. The idea is as below the radiation must pass beneath the blade and hence through the powdered sample. Barnes provided a 'Blocker' i.e. a small gold coated blade, which can be placed across the sample surface during normal diffuse reflectance experiments. 31. Access to the sample is from the top, by sliding the ellipsoids out of the way. The sample height is fully adjustable by the adjustment micrometer screw. All diffuse reflectance systems involve concentrating the beam from the interferometer onto the sample and collection over a wide angle for onward passage to the detector (Ideally the HgCdTe cooled super-sensitive device rather than the normal routine DTGS detector). The laws of optical physics hence require that the area viewed on the sample surface is smaller than the normal beam cross-section in the sample area. 32. The Perkin-Elmer 1725-X FTIR beam has an 8mm spot size at the focus, so the spot sizes with the DRIFT accessories are 1.0mm and 1.3mm for the PEDR and the "Collector" respectively. In diffuse reflection it is essential that the infrared beam enters the sample. It has to be bounced around beneath the surface in order that absorption can occur before it leaves the surface for collection and subsequent analysis. To achieve this, powdered samples are almost invariably examined. 33. Neat powders often absorb far too strongly - remember the path followed by the radiation through the specimen is quite long. As a result, it is normal to dilute a specimen with an infrared transparent powder - say KBr. The concentration of sample is quite low. Organics are usually diluted with KBr over a wide range of concentration, 10% down to 0.5% are quite usual, but inorganics seem to work well over a narrower concentration range, around 1%. However, to get good spectra the grinding and mixing must be really carefully done. The subject is well covered in the literature [1]. Solid lumps like polymers cannot be sampled by grinding and dilution. In these cases abrasion with course silicon carbide abrasion paper is the solution. The accessory makers supply small paper discs with an open texture coated with SiC. These are lightly rubbed on the specimen and then examined. The amount of powdered material stuck to the abrasive sheet is very small, so no dilution is required - the discs are examined as they come. The SiC does not interfere in the spectrum. 34. With care and skill a wide range of problems have been tackled with diffuse reflection. Since its introduction in 1978 by Fuller & Griffiths [1], it has been employed to characterise the molecular orientation in injection-molded polymeric products [2], to study the light-induced yellowing of paper [3], for surface analysis of polymer films [4], polymer fibers [5] and glass fiber mats [6,7], for the analysis of functional groups in polymer films [8], or for the determination of crystallinity in fiber reinforced composites [9,10]. The main limitation in sampling in DRIFT accessories is space - the sample stage must be small and lie close to the collector mirror. 35. However, accessory manufacturers are ingenious and they have produced many clever sampling stages over the years, enabling users to heat or cool samples. Perhaps the most elaborate encloses the sample in a stainless steel cell with ZnSe windows. The sample inside can be exposed to vacuum or gases and it can be heated. The whole cell is very small ~30mm in diameter and 20mm high. Using these devices, a wide range of catalytic studies have been reported. Examples are the reduction of NO by ammonia over vanadia - titania areogels [11] and reactions between CO+H over complex alumina catalysts [12]. 36. When it was introduced, DRIFT was predicted to make significant progress in routine analysis. It seemed to be simpler and quicker than transmission methods and it was thought to be really versatile. The latter has been so, but for routine use there is a major weakness; the quality of the spectra recorded requires considerable skill. The grinding and mixing with diluent, the concentration, and the way the mixture is loaded into the cup which holds it in the accessory, are all important. The abrasive disc method must be carried out carefully. So, as an analytical tool DRIFT is excellent but it has tended to be confined to the specialist user - the skilled analytical spectroscopist or the research worker. We have more recently developed a variant of DRIFT. Using the normal diffuse reflectance accessory, we examine samples in a specular mode, but for solids we do not get specular reflection spectra. Sounds confusing, doesn't it - SO, please read our paper at para 95. We have called our method DRAFT. 37. References
38. Attenuated Total Internal Reflectance (often abbreviated as
A.T.R.) you will note the phenomenon called refraction. If the indices of refraction Ng and Na are those for glass and air respectively, then Sin(i)/Sin(r) = Na/Ng
i.e. r > a law due to the very early physicist, one Snell. 39. If you increase i there comes a point where r runs away to 90°. It is when Sin(i) = Na/Ng. At greater angles of incidence than this the light stays inside the glass and reflects - none is refracted. 40. Although few people do the experiment at school, you can place any two materials in 'optical contact', say glass and oil, and observe the same effects. The same relationships apply except that now Nair becomes Noil. This phenomenon makes the optical fibre possible Index Nglass or Nquartz > Nsilicone rubber The rays totally internally reflect down the core and none leaks into the sheath. 41. In 19 I said that in an absorbing material the index of refraction changes as one crosses an absorption band. As a result, if one carried out the total internal reflection experiment using infrared radiation, the angle at which total internal reflection would occur would vary as one crossed an absorption band. You would need an infrared optical crystal of high index - say, zinc selenide or ThBrI(KRS-5) and a method of placing your sample on its surface. If the angle of incidence was just right, as one crossed an absorption band internal reflection would be switched off and on. All a bit difficult but possible. It turns out life can be a bit simpler than this. If the experiment is set up so that total internal reflection is comfortably occurring, i.e. Sin(i) > Nsample/Ncrystal a different but related phenomenon occurs. 42. Light comes in at incident angle i and reflects at r where i = r. Now total internal reflection is occurring at the interface but the radiation is not perfectly confined inside the crystal. Over a very short distance, (a shallow penetration) the radiation permeates the sample. The jargon is that the 'Evanescent wave' penetrates the sample - to a depth of the order of the wavelength of the radiation (but this penetration depends amongst other things on angle i). As a result, the totally internally reflected light carries information about the infrared absorption of the sample. The attenuation of the infrared beam is subtle, so in most ATR accessories multiple reflections are used e.g. in the horizontal ATR systems the optical arrangement is 43. The sample is poured, spread or squashed onto the upper surface of the crystal. Ours, from Grazeby Specac, has a ZnSe crystal with dimensions 60x7mm x 4.5mm thick and it fits into the sample area of our 1720 or 2000 Perkin Elmers. The spectrum produced is very close to the absorption spectrum of the sample. Because the penetration of the beam is so small, a thin smear of a liquid gives excellent results. ATR has recently been extended a great deal and is now a really versatile, supremely easy, and fast sampling system and we will cover the technique in detail in future editions. You do not have to restrict yourself to oils or squashy solids, powders, films, solutions, minerals, hard plastics -almost anything other than a gas can now be examined. 44. So, we have a set of reflection methods, applicable in the infrared. All have their attractions, some can give unique data whilst others are more routine in their application. All can be used on commercial spectrometers, thanks to the accessory manufacturers and incidentally all are useable in infrared microscopes - another subject to be covered in future editions. REF: Int.J. Vib. Spect.,[www.ijvs.com] 1, 4,
38-44 (1997) 45. The Ultimate in "Downskilling": Infrared Spectroscopy in Automobile Scrapyards Patrick Hendra and Peter Mucci The alternative - high-tech yards - remove the engines and transmissions and then smash the rest into small pieces (~ 5x3cm in size). Magnetic and other crude separations produce steel and other outputs but the plastics, upholstery and small metal parts are then usually buried in the ground. Since they are inevitably horrible mixtures contaminated with oil and hydraulic fluid, this can be very environmentally unfriendly and costly. 46. In Europe, an EU directive has been agreed requiring manufacturers to re-use materials to certain degrees, ever increasing over the years, and Ford were concerned with this problem. If plastic bits were removed from cars, could these be categorised and sorted so that the recovered material would be marketable, hence making the whole dismantling process more financially viable? The Prototype Group therefore asked us to work with them and Fords to come up with a fast, gorilla-proof, analytical procedure. 47. We tried various hairbrained ideas and then, in collaboration with Dr. John Graham, found the answer - mid i.r. specular reflectance. As explained above in para. 19 the mid-infrared reflection spectrum of a plastic is very different from the absorption one. Further, the most specific data comes from optically opaque specimens such as carbon loaded polymers - just the kind of rubbish we were being asked to sort. We recorded specular reflection spectra of several polymers typical of the motor industry, all loaded with carbon or ground slate. A few examples are given in Fig.1.
Quite clearly the spectra, as spectra, are dreadful but they are different. Our first intention was to use the Kramers Kronig algorithm to derive the absorption component and then use this for search purposes, but the KK process is too slow. We returned to the differences between the reflectance spectra - why not create a library of these and use them as a base for a library search? The problem here was the level of background. We quickly found that examples of the 'same' polymer - say polypropylene used in bumpers, heater casings, or air cleaner covers, gave similar spectra but very different backgrounds. A simple way of overcoming this problem is to differentiate. Let me explain. 48. The first differential of a spectrum with respect to cm-1 makes all absorption bands look bisignate. 49. The background is a signal fairly constant in absorbance as the wavenumber is traversed, hence it has very little gradient, i.e. dA/dcm-1 is small. As a result, we have become very similar 50. If it turns you on to see your spectra looking like such, a second differential will return the peaks (but not the background), i.e. we have We chose to stop at the first differential. The process takes milliseconds so there is no real penalty in time. The derivative reflectance spectra of various specimens of the same polymer look fairly similar to absorption ones - similar enough that they can be used to generate a database. See Fig.2.
51. Initial results were very encouraging - view a specimen of a piece of automobile for about six seconds - differentiate - library search - analysis, a total time of about eight seconds. Two problems remained - samples had to be prepared for analysis i.e. they had to fit into the accessory on the spectrometer - hardly an operation appropriate to a scrapyard. The second problem was grease, dirt and a generally non-spectroscopic environment. Ruggedisation was critical. To tackle the first problem, a special accessory was designed which placed the sampling point above the instrument lid and the viewed plane horizontal and downwards facing - see Fig.3.
Obviously, inclusion of a window and perhaps a gentle flow of air would remove any possibility of contamination of the optics with dust, oil, or grease. It also made the construction of an all-enveloping case over the spectroscopic system easy. With careful design, the optical system was very efficient with an excellent signal reaching the detector. 52. Now sampling - bits of old car are rarely flat, almost never clean, and may be coated with paints. Plastic bumpers are a good example. Exposed unpainted ones are often polypropylene or polycarbonate filled with short strands of glass fibre, rubber modifiers, plus ground up slate and perhaps some talc, and carbon black. 53. Painted bumpers can be of polyester filled with long glass fibre, as used in boat hulls, or polybutylene terepthalate or even a polymer 'alloy' based on a variety of typically impact resistant compounds, all covered in several layers of paint (which itself will be inhomogeneous - primer, paint, overglaze layer, etc.). On top of all this, a bumper is large, unwieldy and far from flat. To solve the sampling problem a simple rotary cutter can be incorporated in the complete machine or be mounted nearby on a bench. This shaves off a millimetre or two of the surface, removing greases and of course any paint, and producing a small area of flat surface. Experience, however, has shown that only about 10% of analysis needs surface preparation.
54. The instrument works, see Fig.4 - the process was patented by Ford and a commercial machine duly produced by the Prototype Group. To our delight, the machine caught the eye of the Science Museum (Britain's collection of things scientific and technological, based in a large building near Central London's Imperial College and the Royal Albert Hall). The Museum was creating a new "Challenge of Materials" gallery and hence our beast had found instant fame! The time required for an unskilled operator to examine a lump of rubbish with infrared and see the analysis displayed on a VDU is less than 8 seconds. 55. The obvious next question is cost - is it worth it? Perhaps the question doesn't need answering because somehow the plastics have to be re-used to satisfy the EU regulations, but in the end economics always rears its ugly head. However, the machines are getting cheaper and a complete system is now around the price of a luxury car. Polypropylene, P.V.C., polyethylene and polystyrene all cost around $1000 a ton as virgin material but nylon, polyesters and polycarbonates are two or three times more valuable. Recovered scrap is of variable value - poor quality, dirty, poorly sorted material has almost no value and can even be costly to dump. At the other extreme, because some retailers want to be GREEN, some scrap is in short supply!! Even though it is expensive to clean up and re-use. 56. The story is then clear - recovering large bits of cheap plastics is worthwhile and even medium sized lumps of valuable ones. It is not worth removing small widgets of anything, but bumpers, headlights, tailgates, air cleaners, dashboards, and the myriad of larger pieces, are worth the effort of dismantling and identification. Just think, a bumper weighing 10kg, even at only $150 a ton, is worth $1.50. Removal and sorting need take no more than a minute - sounds viable to me. REF: Int.J. Vib. Spect.,[www.ijvs.com] 1, 4,
45-56 (1997) 57. Using Chemistry properly on the Internet/Intranet Antony N. Davies1 and Robert
J.Lancashire2 1 ISAS, Inst. für Spektrochemie und Angewandte Spektroskopie, Bunsen-Kirchhoff-Str.11, 44139 Dortmund, Germany 2 Department of Chemistry, University of the West Indies, Mona, Kingston 7, Jamaica Introduction The reporting of scientific advances has basically not changed since the arrival of the printing press made scribes redundant. Finally we have - in the Internet Journal of Vibrational Spectroscopy - a medium to report our scientific advances by showing our science. We can now display in a scientific report our spectra as spectra and our chemical structures as chemical structures not just as pictures. 58. Chemical MIME To enable this the Internet required an agreed protocol defining data types that are likely to be encountered. Agreed protocols are called Multipurpose Internet Mail Extensions (MIME) and have to be agreed by the Internet Engineering Task Force (IETF). Well recognised types are TEXT, IMAGE, AUDIO, VIDEO. For Chemistry the draft definitions are called Chemical MIME and have been pioneered by Henry Rzepa of Imperial College, London, UK and his colleagues. A table of some of the chemical MIME types is given in table 1. The latest information can be found at the following URL: http://www.ch.ic.ac.uk/chemime/
What this basically means is that any internet aware software should recognise a file called mydata.gau as a gaussian input file. Of more relevance for this article, a file called myspectrum.dx should be recognised as a JCAMP-DX spectrum and treated as such. 60. The JCAMP-DX MIME type for spectra display So, having agreed on using the JCAMP-DX format for your spectrum on the Internet what is needed is a viewer which can display the spectrum as something more useful than a line of text! This has been made possible by the work of Robert Lancashire and co-workers who have written a utility which runs either as a stand-alone spectrum viewer or as an integrated part of your Web software as a plug-in for say Netscape. This is freely available and can be downloaded from http://wwwchem.uwimona.edu.jm:1104/software/jcampdx.html . If you wish to run the the software as a plug-in, the file (npjdx.dll) must be located in the program\plugins subdirectory of your browser. You can check that the plug-in has been installed correctly by using the "About Plug-ins" menu from the Help menu item. The next step is to try out your spectrum-enabled browser. You can do this by looking at some of the data available at http://wwwchem.uwimona.edu.jm:1104/spectra/index.html 61. If the plug-in is correctly installed (copied to the correct directory) you should see something like:
62. Alternatively look for some of the test data we have on our site here at ISAS: http://www.isas-dortmund.de/projects/lisms/biorad/difdup.dx which should show up as:
If you are not running a 32 bit system, then you should install the external viewer (jcampvw.exe). Select General Preferences and then Helpers.You can then use the Browse feature to locate the program which you have downloaded from Jamaica. Finally, test the implementation on your own data by either writing a Web page with a link to one of your own JCAMP-DX files or by simply using the OPEN FILE command within your browser. 63. Chemical Structures To activate your browser for chemical structures there are a number of plug-in's available. One is MDL's CHIME package available at http://www.mdli.com/chemscape/chime/. With this installed you can produce great internet chemically active reports such as the 'molecule-of-the-month' pages. Try http://www.bris.ac.uk/Depts/Chemistry/MOTM/motm.htm for some good examples. 64. Support and Development The JCAMP-DX standard has been adopted by IUPAC [1,2] and has a wide spread implementation amongst the spectrometer manufacturers. Following several meetings with the IUPAC Databases Committee it was decided that, in order to avoid competing development work on the same standard, an agreement should be drawn up between the JCAMP executive and IUPAC. This agreement committed the IUPAC Committee on Printed and Electronic Publications (CPEP) to set up a Working Party to support and develop the JCAMP-DX range of standards in return for financial support from the JCAMP organisation. The working party has been very lucky in recruiting many of the people who have been developing the use of JCAMP-DX data standards world-wide. Bob McDonald, an author of the first JCAMP-DX standard for infrared spectroscopy [3] had been pushing the adoption of these standards and publishing test data sets. He has also developed the use of the Internet for information on the JCAMP-DX standards with a very extensive reference site at http://members.aol.com/rmcdjcamp/index.htm. 65. In the European Community the standard had been adopted for food research within the Quest 'Quality Established through Spectroscopic Techniques' project. Here a lot of work was put in by Peter McIntyre of the University of Glamorgan, UK and Doug Rutledge of the Institut National Agronomique in Paris, France. An extended and unified version of the standard for food research was written and an extensive software suite developed to support this use. The largest spectroscopic database project in recent years, the German government 'Informationssystem Spektroskopie' adopted the JCAMP-DX standards. It was used for data exchange between various project partners as well as for downloading data from the on-line version of the 'SpecInfo' databases available over STN International. During this project the next two Standards were published, JCAMP-DX for Nuclear Magnetic Resonance spectroscopy in 1993 [4] and JCAMP-DX for Mass Spectrometry in 1994 [5]. Both protocols were co-authored by Tony Davies, who is chairman of the IUPAC Working Party and Peter Lampen, who now works for the Deutsche Forschunganstalt für Lüft- und Raumfahrt in Berlin, Germany. JCAMP-DX is one of the Chemical MIME types defined within Chemical MIME. Henry is not a member of this working party but is also leading a parallel working party on Chemical MIME reporting to the CPEP. Robert Lancashire of the University of the West Indies (UWI), Mona, Jamaica started using the JCAMP-DX standards as the most reliable method of moving spectroscopic data from his spectrometer for storage and into other applications such as spreadsheets. This interest developed into writing Windows programs to handle and display spectra via the JCAMP-DX standards. His group is now very active producing plug-ins and helper applications as well as Java scripts for JCAMP-DX standards to run with commercial Internet browser packages. This allows scientists to place spectroscopic data in the IUPAC recommended format on the Internet where it can be handled as spectra and not as purely graphical data. 66. Conclusions Now we have the tools to produce a truely 'active' journal for vibrational spectroscopy on the internet. So I hope from now on all the spectra will be submitted as spectra and not as graphics or 'high resolution' PDF files !!! On this note the CLIC group have recently produced the first "enhanced" Chem Comm article [6] which includes a JCAMP-DX file of an infrared spectrum. 67. References 68. SERRS - a sensitive spectroscopic technique Suzanne D. Cooper, W. Ewen Smith*,
Caroline Rodger and Peter C. White Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK *to whom correspondence should be addressed Introduction
70. However the technique has two significant limitations in that:
In addition, in practice the method can be used semi-quantitatively in some cases, but many workers have experienced significant difficulty in obtaining reproducible results. This short article explains the nature of the effect and postulates that the lack of reproducibility is due to shortcomings in the understanding and control of the chemistry used. 71. Nature of method Although SERRS is best considered as a single process it is often thought of as a combination of surface enhanced Raman scattering (SERS) and resonance Raman scattering. SERS was discovered experimentally some years ago and basically involves the interaction between the molecule adsorbed on the surface and the plasmons present on the surface of certain metals [4]. This greatly enhances the Raman scattering cross section of the molecules, but for this to occur the surface must be roughened. Although the mechanisms whereby surface enhancement is obtained are still the subject of controversy, the nature of the effect is well established and enhancements of Raman band intensities in the range 103 to 106 are often quoted. 72. There have been various attempts to explain the process. Most commonly it is believed that two processes can occur, namely electromagnetic and charge transfer enhancement. In the electromagnetic mechanism the electric field on a rough surface becomes greatly enhanced if the incident photon energy is in resonance with a normal mode of the free electrons in the metal. Where the size of the roughness feature is much less than the wavelength of the incident light it is the dielectric constant of the metal that determines the electric field enhancement. Only certain metals such as silver, gold and copper produce maximum values of the electric field in the visible wavelength region and thus give a large SERS enhancement. A molecule on a rough surface of one of these metals will experience an enhanced electric field from the metal in addition to the electric field from the incident light, thus will scatter light with an enhanced intensity compared to an isolated molecule. This contribution to SERS does not require direct bonding between the adsorbate and the metal surface; enhanced sensitivity has been recorded up to 40 Å from the metal surface. In the charge transfer mechanism, the enhancement effect is dependent on the nature of the molecules involved. It involves transfer of charge from the metal surface through a bond. The enhancement mechanism requires new electronic transitions between adsorbate and metal, made possible when a molecule is at the surface. This mechanism accounts for the high specificity of SERS to the first layer of adsorbed molecules. 73. Resonance Raman scattering occurs when the energy of the incident photons matches (or nearly matches) the energy of an electronic transition in a molecule [5]. This process enhances the efficiency of the scattering process by about a factor of three or four orders of magnitude compared to ordinary Raman scattering. Electronic information as well as vibrational information can be obtained from the frequency dependence of the intensity of the scattering. In practice, resonance Raman scattering is limited to only certain molecules with chromophores, due to problems with fluorescence, photodecomposition, and self-absorption. Most SERRS spectra are interpreted on the basis that the resonance and SERS effects can be treated separately. This method is practical where the combination is between resonance Raman and the electromagnetic SERS term. If the charge transfer effect and resonance make the greatest contribution, the chromophore and the charge transfer involved in SERS are likely to be coupled. 74. The substrates used for SERRS can be created in several ways, but the most common are: electrochemical (oxidation and reduction of metal electrodes), evaporation (vacuum deposition of metallic films on a substrate) and chemical reduction (metal colloids formed in solution). Electrode systems for SERRS have the advantage that the surface roughness is easily created and regenerated, and electron transfer and voltage dependence can be easily studied. The problem is that the nature of the surface is difficult to characterise. In the technique extensively studied at Strathclyde, aggregated colloid (usually silver) is used to provide the roughened surface. 75. Experimental Design
If the excitation is at molecular resonance (position 1 in figure 1(a)), the interaction with the chromophore partially depolarises the incident light beam which reduces, but may not eliminate, the dependence of the signal on the orientation of the adsorbate on the surface. This makes the technique less sensitive to small changes in experimental conditions, and is the ideal condition for quantitative detection at attomolar levels. If the excitation is off-resonance for the molecular chromophore but at resonance for the surface plasmons (position 2 in figure 1(a)), the condition is sometimes known as SE(R)RS. Pre-resonance still gives selectivity or sensitivity for the species containing the chromophore, but the scattering intensities are dependent on the molecular orientation at the surface, providing more information on the nature of the bonding. 76. Figure 1(b) illustrates an alternative situation where the molecular absorbance and plasmon resonance maxima coincide. The enhancement will be similar to the first case described for figure 1(a) but the enhancement factor is likely to be greater.
Many types of surfaces have been used for SERRS. The most traditional surface and one of the best is a roughened silver electrode. This is achieved by carrying out an electrochemical step prior to the adsorption of the molecules onto the substrate. Figure 2 shows a possible electrode system. The advantages of a system of this type is that it can be incorporated into a 1 cm fluorescence cell making sampling relatively simple. However, the flexibility of sampling arrangements in Raman are one of its big advantages, and consequently many cell types can be used. In particular, the correct positioning of the secondary electrode can be better achieved by other designs of cell. 77. Many other SERS active surfaces have been suggested. Some examples are cold deposition of silver island films on surfaces and ruled gratings. Lately, the use of aggregated silver colloids has become quite widespread. These aggregated colloids provide very good roughened surfaces with high electric fields in the interstices, and consequently provide a very effective scattering surface. Two particular colloid types are most commonly used. In one, borohydride reduction is used to obtain the colloid. The alternative is to use a citrate reduction process. In this laboratory, the citrate reduction process is preferred since the resultant colloids have a long lifetime. A sample of colloid can be used for periods of up to 6 months following preparation. This particular colloid is rather more difficult to make but if made successfully can be more reproducible than the borohydride colloid. Silver colloids are prepared at Strathclyde using a modified Lee and Meisel procedure [6]. Before use all glassware is cleaned using aqua regia,
followed by gentle scrubbing with soap solution and is then successively rinsed in
distilled water and methanol. 500 ml of distilled water and 90 mg of silver nitrate are
added to a round bottomed flask. The flask is then heated to boiling with vigorous
stirring, then 10 ml of a 1% solution of trisodium citrate is added. The heating is then
reduced and the solution is left to boil gently for 90 minutes with continuous stirring.
The flask is then left to cool and the volume adjusted to 500 ml with addition of
distilled water. The quality of the colloid produced is analysed using a uv-vis
spectrometer; the 78. Characterisation of a standard SERRS colloid To obtain a rough surface suitable for SERRS, the colloid must first be aggregated. A fractal cluster is then obtained where the electric field intensity is very high in the interstices of the aggregates; an enhancement of 106 is expected for SERS with this method. Aggregation can be performed in several ways by the addition of a suitable aggregating agent chosen to be appropriate to the adsorbate studied. 79. A critical feature required to obtain reproducible spectra on colloid is that the aggregation step must be carefully controlled. The most standard aggregating agents are either inorganic salts such as sodium nitrate or acid solutions. More recently, other methods using poly-L-lysine to aggregate the colloid have been suggested. The advantages of these methods are that the poly-L-lysine contains positive charges which can attract negative species to the negative colloid particle surfaces, and also poly-L-lysine helps to act as an aggregation control agent. It is essential that stable aggregates are obtained for a period of time significantly longer than that required to take the spectrum.
Transmission and scanning electron microscopy were used to characterise the colloid particles; the particles were found to hexagonal in shape with a largest face dimension of 36 nm. Aggregated colloid was also analysed; figure 3 shows a TEM photograph of poly-L-lysine aggregated silver colloid. Colloid aggregated with poly-L-lysine consists of small clumps of particles, but physical contact between them is prevented by a layer of poly-L-lysine on each particle. Conversely acid aggregated colloid consists of clumps of particles but with no space between the particles; as the amount of acid added is increased the size of these aggregates also increases. 80. SERRS Applications
The sensitivity of the SERRS technique is now well understood. A number of papers claiming very sensitive detection and indeed single molecular detection are appearing [8, 9]. An example of this is shown for Rhodamine in figure 4. Smaller and smaller quantities of Rhodamine were added to a suspension of colloid. Eventually, a concentration of Rhodamine in colloid which would effectively be 6 x 10-18 M if no Rhodamine was adsorbed on the surface was obtained. This corresponds to approximately 20-40 molecules present in the laser beam at any one time. The experiment was not limited by the sensitivity of the instrument, but was instead limited by the difficulty of dealing with contamination problems at this level. It will be noted that the concentration dependence is not linear and this may well be because of a desorption/adsorption process occurring between the glass and silver surfaces and the solution. At this point in time, the main purpose of this diagram is to illustrate the enormous sensitivity which is possible. Above monolayer coverage, the spectra are affected by fluorescence from non-attached dye molecules.
SERRS has also been used to study biological molecules; for example, studies of enzymes on proteins are well known. An illustration is given in figure 5 for cytochrome c adsorbed on silver colloid. The intense bands in the spectra correspond to those found in resonance, but the relative intensities do vary when compared to resonance. The band at 1375 cm-1 (v4) is a marker for the oxidation state and v3 at 1506 cm-1 is a marker for the spin state. By gradually titrating cytochrome c into a silver colloid, adsorption layers on the surface have been built up from below to above monolayer coverage. When this occurs, there is a relative intensity change in a number of the bands. Specifically, the ratio of the intensity of the band at 1375 cm-1 (A1g, v4) to the band at 1640 cm-1 (B1g, v10) changes. By plotting this intensity the formation of the monolayer can be observed. The reason for this change is that SER(R)S, provided the effect contains an appreciable SERS contribution, is dependent on selection rules related to those obtained from SERS alone. Thus, as the monolayer builds up on the surface, the protein packs and the orientation of the haem in the protein relative to the surface changes. This change is reflected in the relative intensity changes between v4 and v10. In fact at close to monolayer coverage more subtle reorganisation of the layer occurs, as shown in figure 5. 81. Analytically, the first papers on quantitative SERRS are beginning to appear. They require very careful control of the aggregation and the use of adsorbates which ensure that there is efficient dye-metal surface adhesion [10, 11]. Additionally, it must be recognised that the field gradients in aggregated colloid vary within the aggregate and consequently even distribution of the adsorbate is essential. Furthermore, for quantitative use it is essential that concentration dependence calibration curves and relative standard deviation (RSD) values are reported. Many reported SERRS experiments do not give these so it is difficult to evaluate the results. To aid the reliability of quantitative SERRS a new series of dyes designed to complex onto the silver surface have been produced. With these dyes RSD values of between 2 and 4 % have been obtained using a Raman microscope. Given that RSD values of 2 % are normally obtained for Raman spectra with this instrument; this suggests that quantitative SERRS is possible. 82. An alternative approach of value for qualitative analysis is to coat colloid onto a suitable coloured surface. This procedure has been used to determine in situ, in a single cotton fibre, the nature of the covalently bound dye [12]. The intention of the work was to provide a rapid test for use in forensic science to match a fibre found at a crime scene to a garment. This review has concentrated on SERRS applications using colloid, but many other applications are currently being developed; for example, it is possible to use evaporated silver to determine the nature of thin films of non-linear optic materials [13]. Further, electrodes are used to provide SERRS detection for chromatography [14]. The advantage of the electrode system is that the electrode surface can be regenerated between determinations. 83. Conclusion 84. References
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approximately 404 nm and the full width at half height less than 60 nm. The advantage of
the method is that the colloid is reproducible and if produced in this manner can be
stable for several months. 
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