1. Editorial Now we have two volumes in the archive, all of us need to start thinking about citations. We have several on our books now and no-doubt people are thinking about citing work in hard copy publications. Citing in the form J.R. Bloggs, Internet J Vibr Spect., Vol. Ed. Pg looks fine, but it isn't very useful because the Journal is not 'taken' by libraries. We are about to invite libraries to download the material and hold it on their shelves, if they wish, but this will take time. Although not the traditional citation, the most useful to a reader would be J.R. Bloggs, Internet. J. Vib. Spect.,[www.ijvs.com] Vol. Ed. Pg. What do you, the readers and contributors think? Once we have some responses we will start negotiations with the Citation Index so we can get a rating. A decent rating is essential as I am sure you will all agree. With two volumes complete and nearly a thousand registered readers, now is the time for
you folks to tell us how the Journal is going. You will note the increased level of
colour, the large number of pictures and diagrams and the evolutions in format. Are they
acceptable? Have you any ideas where improvements can be made? We have had one edition
assembled by a guest editor and are negotiating for another. Is this a good idea from your
prespective? What keynote subjects should we be considering in the next twelve months? Our second contributed offering describes Raman microscopy mapping applied to sub cellular structure - again biology and biochemistry. Many feel that these are real growth areas in current science. Dave Batchelder and his colleagues from a whole range of Departments at the University of Leeds in the UK show that Raman is valuable in supporting Photodynamic Therapy, a rapidly developing method for the treatment of cancer. Now everyone needs to keep warm and wool is the textile par excellence . The CSIRO Wool Technology Laboratory at Belmont in Victoria, Australia is an internationally regarded centre of excellence in this field so we are honoured to publish Church and O'Niells paper on the use of NIR and chemometric applied to raw wool analysis - almost our first NIR paper and almost our first mention of chemometric data processing. Both subjects will be picked up on and featured later in this volume. Your Editor (poor soul) is getting fed up with writing rubbish for the first part of
our Journal! Pressed to write a piece to support an introductory talk to the Royal
Pharmaceutical Society one-day discussion forum on the value of Raman in pharmaceutical
analysis and the attitude of the drug regulators I thought - dammit I'll submit it to
myself. Louise sent it off to a referee and won't show me what he said except - accept
subject to some edits to the English. I have to admit his comments about incomprehensible
sentences were quite correct - so, here it is - the last of our submitted pieces. The second article describes the way near infrared is progressing - the complete analyser. Near infrared milk or wheat or flour or …….. analysers have been around for years but the n.i.r. folks are becoming clever. The article describes an analytical system offered by our sponsors Perkin Elmer called the Brewers Assistant. Now I don't like Beer (I drink too much wine) and hence could be suspected of yielding to sponsor pressure - not so. I insist in these cases that the article is scientifically sound and balanced not an advertisement. Remember, we have published articles like this before from instrument makers, but never yet from Perkin Elmer [Specialist CCD Raman from Kaiser - see M.J. Pelletier ijvs.com/volume1/edition3/section1.html, IR microscope from BioRad - see ijvs.com/volume2/edition4/section1.htm#Article4 and the Diamond ATR from Graseby Specac - see David Coombs ijvs.com/volume2/edition2/section1.htm]. Enthusiastic readers will remember that several editions ago I promised to write more pieces on the theory and practice of Raman Spectroscopy. Mindful of the fact some of you folk must be suffering from frustration Anne De Paepe and I have written a piece on the use of polarised light. We hope you find it interesting. Assistant Editorial My thanks to vigilant readers who pick up any crossed or broken links (Thanks Jerry Childers in Florida). I appreciate the messages so I can ensure that the web site runs smoothly, it's so easy to miss things when there's so much going into each edition. I did also get a comment from Paul Sayers from Gwynedd Wales, asking for PDF or PS version of the journal as he's having a problem with page breaks when printing out the journal. Now I wasn't sure about this, even if I print down the journal (in Explorer) figures get cut off at the bottom of pages. I asked the design agency who originally produced IJVS and they said that the problem of page breaks was just one of those things as we don't all use the same browser / printer etc. There was an alternative solution such as using Adobe Acrobat Reader software, but you have to buy the whole Acrobat package which is, as far as I am aware, about £500 (UK sterling). Any ideas anyone? As far as using PDF files for images, well everyone now seems to be supplying gif, tif or jpeg files now anyway which means the information is already in a digital form good enough for the web. Patrick tells me that there is a very good argument for NOT publishing PDF files of spectra as authors may not be too happy if readers copy down accurate spectra and manipulate the data for their own use. Can't say I blame them. Even as a non-scientist I thought that the idea of IJVS was to give readers operational information on vibrational spectroscopy with all it's technqiues, applications etc, then readers may try it for themselves and even come up with better results!? - Oh and then of course write their own papers and submit to IJVS!. One thing I will endeavour to do now that we receive most things in colour is to improve the presentation. If you don't have a colour printer yet you'll know that some colours just don't reproduce very well in monochrome. Diagrams are supplied to me in varying sizes and the max width we use for IJVS is 520 pixels wide. We plan to place them as full size on separate pages so you can click to view and then print down full size if wished. In fact I've done this in our first feature on Synchrotron Radiation. Let me know what you think of this idea? Louise Martin The 25th European Congress on Molecular Spectroscopy (EUCMOS XXV) is to be held in Coimbra from 27th August to the 1st September, 2000. The Congress official website is http://qui.uc.pt/~rfausto/eucmos_xxv It contains all the information regarding the meeting. Rui Fausto
13-14 APRIL 1999
University of Glamorgan
The School follows previous successful residential meetings and also draws on the highly successful work carried out previously by Dr Clara Craver and Professor Bill Fateley, notably at the Fisk Infrared Insititute, Nashville, Tennessee. This has established an enviable reputation as the leading course of its type for practical experience in the use of infrared and Raman spectroscopy in solving industrial and environmental problems involving materials identification and the characterisation of mixtures and polymers. Fees:
Fees include reception, accommodation, meals, course dinner and course materials. The School will be based in the Glamorgan Business Centre, a brand new facility within the attractive semi-rural campus of the University, which is set in a pleasant valley ten miles north of Cardiff. There are excellent residential, catering and recreational facilities. Motorway, rail or airport provides ready access. Registration commences at 18.00hrs on the evening of Monday 12 April. The School commences at 09.00 hrs on Tuesday 13 April and ends at 16.30hrs on Wednesday 14 April. The 160th IRDG meeting on Thursday 15 April 1999 will follow the School. The Programme Wednesday 14 April 1999 Course Organisers Prof Bill George, University of Glamorgan Teaching Staff Also IRDG Committee Members and Staff from School of Applied Sciences, University of Glamorgan. There will be a Reception on Monday 12 April and a Course Dinner on Tuesday 13 April with opportunities to visit areas of natural beauty viz. Heritage Coast and/or Brecon Mountains. To reserve a place, please contact
Allan Morris
Many spectroscopy papers appear these days where the source of radiation is one of the several Synchrotron Radiation sources available throughout the world. These sources are few in number and expensive to run, so the obvious question is "why do people go to the trouble of moving their entire infrared experiment to a huge fixed facility, a long way away and spend large amounts of money to run their spectra?" The answer of course lies in the properties of the radiation available from a Synchrotron Source. Synchrotron radiation is emitted when high-energy electrons are deflected as they pass
through a magnetic field. This phenomenon constitutes a considerable nuisance to the
designed of high-energy accelerators since it drains away the energy of a particle beam,
but it has properties which make it an excellent research tool in many areas of science. A
storage ring is a high energy electron accelerator devoted to the production and use of
synchrotron radiation, and the general method of production of radiation from such a
Synchrotron Radiation Source (SRS) is shown in Figure 1.
The spectrum of radiation from a typical storage ring is shown in Figure
2.
The main features of the spectrum are that it is:
The short wavelength cut-off in the spectrum is determined by the radius of curvature
of the electron beam in the magnetic field and hence by the magnetic field strength. At
one point in the ring there is a super-conducting Wiggler magnet with a magnetic field
(6T) higher than those in the storage ring dipoles; electromagnetic radiation of shorter
wavelength is produced at this point. At another point on the ring the beam passes through
a series of magnets of alternating polarity - an 'undulator' - which causes undulation
about its mean orbit as it passes through the pole gaps. The radiation emitted in
successive undulations adds coherently, so the intensity of the low energy x-ray spectrum
is greatly enhanced at this point. These methods of producing radiation are shown
schematically in Figure 3.
The world's first storage ring source was built at Daresbury in Cheshire in the UK, and an aerial view of the facility, showing the location of the ring and experimental area is shown in Figure 4.
The overall layout of the ring and experimental area is shown in Figure
5.
Electrons emitted from a hot cathode are first accelerated to 12MeV in a linear accelerator and injected into a booster synchrotron to raise this energy to 600MeV. Finally they are injected into a storage ring, where the energy is boosted to 2 GeV. The beam will continue to circulate for 20 hours or more in the high vacuum of the storage ring before more electrons need to be added. At suitable points on the ring, ports allow the radiation to shine down evacuated pipes into the experimental stations, each having an optical system to focus the beam into the experimental apparatus. Synchrotron sources are all similar but users are very dissimilar in their demands. Some users are interested in the X-rays, others in the visible etc. The management of the facility has built a series of systems on each of these beam lines designed to assist particular requirements and a large amount of data recording and processing equipment is permanently sited at Daresbury. In many cases some of the experiments people want to do can be run on the Daresbury equipment, and they do not have to transport their spectrometers to Warrington. They do, of course, have to take their samples and any cells they may need to contain them. Considering the mid infrared - the two properties that people find most useful are the intensity (or brightness) and the polarisation. The high brightness means than when there is a shortage of signal (the experiment is 'noise limited') they think of Synchrotron Sources. Infrared microscopy is notoriously difficult in some cases because the efficiency with which the infrared radiation passes through the microscope is low. The subject was aired in the last Edition [See ijvs.com/volume2/edition4/section1.htm]. Further, the low energy means that the time required to record a spectrum through a microscope is relatively long. This doesn't normally matter very much but if one is trying to scan an infrared map of a sample this time problems adds up to very long experiments indeed. The Synchrotron source speeds these measurements. Fast kinetic measurements or dynamic ones are frequently impossible using conventional sources and FTIRs in macro scale absorption or reflection measurements. Again the Synchrotron source is invaluable. Conventional infrared sources approximate to 'Black Body Sources' i.e. their emission falls on one of the plots given in Figure 6. As you can see, it is advantageous to have the source as hot as is practicable but the emission at long wavelengths is very poor indeed and is contaminated with overwhelming amounts of radiation at shorter wavelengths. The latter can be reduced with filters but the lack of intensity cannot be corrected. As a result, far infrared spectroscopy has always been a problem area. Operating much below 300cm-1 has always required high quality instruments and results have been slow to acquire and are of poor quality. Again, the use of Synchrotron radiation provides an advantage.
Although the reader's interest is in the near mid and far infrared, others users exploit different wavelength ranges. For example, radiation in the vacuum UV can be used to study the electronic structure of short-lived species using vacuum violet photoelectron spectroscopy. For these studies synchrotron radiation is extracted from a beam port and passed through a 5m normal incidence mono-chromator which allows the users to select radiation in the wavelength range 400-2000Å. A purpose-built photoelectron spectrometer which is used to study short-lived intermediate of atmospheric importance (like SO, CS, OH, O2(1Dg)) is shown in the photograph. Emission from the monochromater on the right of the photograph passes through the cylindrical interface chamber and then into the spectrometer.
Measurements on the photoelectron spectra of species of the type listed
above enable important electronic and vibrational parameters to be determined. Ionization
energies leading to various ionic states of a particular species can be determined, as
well as information on the vibrational structure of a particular electronic ion. This in
turn can provide important information on the bonding character of an electron involved in
the ionization process. Peter Boogaard and Sharon Cooke
Introduction The brewing process was probably discovered accidentally, air borne yeast cells having the ability to ferment cereals soaked in water [1]. Eventually it was discovered that if material from the top of one fermenting vessel was transferred to another, a new brew could be initiated thus the production of beer could be continuous. These processes were uncontrolled and many of the processes involved in making good beer were of a craft nature and at a scientific level only poorly understood. The beer produced by a master brewer is certainly interesting, but variations from brew to brew are inevitable and yields could vary widely. As a result these traditional methods are going out of favour. Local and global beer producers are in intense competition. In some cases the aim is to produce vast quantities of highly reproducible and comparable beer at many production sites. The argument is that beer X must be indistinguishable if it is bought in Toronto or Sydney. In other situations the strategy is totally different. The increasing popularity of 'traditional' or 'local' beers requires that brewers produce a range of products in small quantities but drinkers require that the beer does not vary from barrel to barrel or bottle to bottle. To control the process of beer making on-line analysis/monitoring/control would be an obvious solution, but the variability and complexity of the process means that this approach is not yet in widespread use. The combination of skill by the brewer and analysis at the finishing stage is much more attractive to the industry. The increasing level of control by regulators and the importance of product liability are also driving these changes. Beer analysis traditionally involves methods such as catalytic oxidation, fractional distillation and gas chromatography, all of which requires experienced and highly skilled laboratory staff. Further, the analysis of the product tends to be slow so that it is hard to respond to out-of-limits data. Alternative instrumental methods have therefore found a place in which simple dispersive near infrared and the less sophisticated filter based nir systems have been introduced. But often these systems are dogged by systematic errors, and required operation by relatively skilled and experienced technical staff. Perkin Elmer, who have been producing spectroscopic solutions to analytical problems for over 60 years perceived that what was required in the Brewing Industry was an instrument based total analytical solution, easy to use, fast and sufficiently rugged that it could reliably be used close to the production facility and by relatively unskilled staff. This article describes the Brewers Assistant; a near infrared based total analytical solution to the problem of beer analysis at the finishing (pre-packing) stage. Brewer's Assistant - technical details
The instrument part of the system consists of an F-T near infrared
spectrometer; a monitor and an auto-sampler, all controlled by the software, see Figure 1.
The beers (only about 5mls of each specimen) are filtered into simple vials made of glass
and these are loaded into the auto-sampler. The vials are selected one by one and the beer
is pumped into a quartz NIR cell with a path length of 0.5mm. A sample shuttle inserts the
cell into the beam where the spectrum of the beer is monitored in transmission. The cell
is then removed automatically, emptied and flushed with water to clean it before filling
from the next vial in the auto-sampler. While the cell is being cleaned and filled the
instrument runs a background spectrum. The system is illustrated in Figure 2.
A new background spectrum is recorded after each sample has been examined so that effects due to changes in the atmosphere, in temperature or in other environmental conditions are automatically removed. Scanning of the complete spectral range is completed in about 1 minute and the sample change and background acquisition routines are sufficiently fast, that about 50 specimens can be examined in 1 hour. Obviously, the data is logged on the computer and then processed. Typical nir spectra of a beer specimen is shown in Figure 3. It will be noted that only a relatively small pair of ranges are used in the analysis.
The near infrared data is then submitted to chemometric analysis using Partial Least squares #. This is done fully automatically; the operator is unaware of the procedures involved. The results are presented in tabular form on the screen and data logged for future use. # Editors Note: The mathematical routine used to analyse the data used is called Partial Least Squares analysis. There is little point in explaining the method and how it is done here because we will be featuring chemometrics in a future edition later this year. It is sufficient to accept that the methods look for trends in changes in the spectra in a series of samples where the changes vary as does a known difference between the samples eg. The alcohol content. If a trend can be established, the trend itself can be used as an analytical probe. Obviously, to establish the trend, suitable standards have to be made, examined and data logged. One catch with the method is that moving outside the range of the standards you have used (extrapolating the results) is very dangerous. Extrapolated results can frequently be meaningless so you must have decent standards and discipline yourself when doing the analysis. Some managers may not wish the tabulated data to be exposed to the system user. Management can therefore define limits within the system and the operative is then only shown a red or green light to define acceptability or failure. Standardisation Quite obviously sets of precisely analysed samples, which vary in only one respect from one to another, must be prepared and then examined as will be the unknown. Perkin Elmer have therefore acquired a huge range of specimens and examined them, defining in each case the data required to permit users to employ Brewer's Assistant without any sophisticated calibration by the end user. The name used to describe this procedure is the Scientist Inside. i) Alcohol Content (ABV) Samples used in the ABV calibration set cover the range zero to 12% alcohol. The software absorbs the spectra from the full set of standards and produces a plot of the variance against the alcohol content. To test how good the calibration is, it then removes one spectrum from one sample at a time, recomputes the plot using the remainder and uses the removed one as an unknown. After doing this for all the standards in turn it then displays the deviation in these calculated quantities against their known alcohol contents and calls this the Standard Error of Prediction in this case expressed as % alcohol content. ii) Original Gravity (OG) The original gravity is the density of the brew before the yeast has fermented
it. The value reflects the concentration of sugar and other constituents of the beer. In
this case the cross validation gives a value for the standard error of production of 0.49
within the range 19-95ºS [the units here are the specific gravity less that of water x 10-3
in gml-1] iii) Present Gravity (PG) This is the density of the beer once made and lies within the range -1.8 and 26ºS or 998.2 and 1.026kgl-1. The standard error of prediction is less than 0.2. Several other properties can be determined by FT NIR spectroscopy for example, real and apparent extract, degree of fermentation, the energy value in calories to name just a few. Conclusion We have shown that this new total analytical system can provide data to the Brewing analyst in minutes and do so with very acceptable accuracy. The ranges covered are summarised below: Alcohol by volume - 0-12% Original Gravity 1.020-1.100kgl-1 Present Gravity 0.998-1.030kgl-1 The beer market is rapidly changing - drinkers want special beers of different flavours, colour and alcohol content. They want exotic and reliable tastes and hence the industry is faced with both an increasing complexity of products, combined with more consistent beers. Ever more strict regulations of the industry is also to be considered. The Brewer's Assistant is aimed to satisfy the demand for a high performance analytical system requiring little of no skill by the operator, yet able to satisfy all regulatory requirements and customer ambitions. Reference
Anne De Paepe and Editor Raman spectra these days are normally recorded using polarised laser light but the polarisation is usually not used as an asset. We suppose the situation doesn't differ much from infrared - relatively few infrared users have ever recorded a spectrum through a polariser. In infrared this is a pity because considerable information on molecular orientation can be acquired very easily if you use polarised light. In the Raman much more information is available - read on! Let's assume your experiment operates in back-scatter (all F-T Raman accessories do and the microscope instruments (Dilor or Renishaw) also operate in back-scatter. Further, let's assume your laser is polarised (virtually all of them are) and that you have a sheet of Polarised sheet through which you can record the spectrum. Two experiments are possible on a normal isotropic sample (a liquid, gas or a lump of polymer).
The results of the THREE experiments
are shown below in Figure 2 for a cuvette of carbon tetrachloride.
So the basic experiment and the parallel one are similar
but the perpendicular spectrum is very different. Bands fall into two types - bands A, B
and C where the relative intensity of the equivalent bands in experiments 2 & 3 are ¾
and band D where Raman spectroscopists divide this behaviour into two characteristics. These bands which change in intensity by the ratio ¾ are so called depolarised bands. Those where the intensity ratio is less then ¾ are called polarised bands. So, if we stop there we notice that from a purely analytical point of
view Raman spectra can be recorded in two ways in these cases providing twice the
specificity of the sample spectrum. As a result, good collections of Raman spectra provide
both spectra || & We can take the matter further - those vibrations, which take place with the same symmetry as the molecule itself, give rise to the polarised bands. If we look back at the spectrum in Figure 1, above, Carbon Tetrachloride has four modes of vibration only one of which is fully terahedrally symmetrical - the "breathing" mode and it is this that causes the band near 460cm-1.
Let us go back to an earlier article your editor wrote telling student readers how to assign Raman spectra to fundamental modes of vibration. The example used was chloroform [3]. The arguments used were based solely on the frequency and intensity of the Raman bands. I also relied on a peculiarity of chlorine containing materials i.e. the fact that chlorine contains two isotopes 35Cl and 37Cl. I could have used polarisation to advantage had I wished to. In my earlier article the following assignments were made.
You will notice that three modes - and three only retain the symmetry of chloroform itself (C3v) vis those at 3019, 668 & 368cm-1. In the Figure 4 below, we show the spectrum of CHCl3 recorded with a polarisation analyser and you will see that indeed these three bands are polarised.
The argument so far is confined to isotropic systems - gases, liquids including solutions and non-oriented solids such as polymers. The reason is purely experimental - the particles and other inhomogeneities scramble the polarised radiation so that it loses its polarisation. There are of course, clear transparent highly oriented specimens such as crystals. These show very complex orientation effects. Let us again assume the experiment is carried out in backscatter and a crystal is available. A whole series of experiments can be carried out (not just two as described above). Let's also agree that the crystals can be said to have three orthogonal crystal axes (some crystals have non-orthogonal axes and for the moment we will ignore these). The experiments are drawn below in Figure 5.
i.e. 6 different experiments. Obviously, it is somewhat of a nightmare to describe these experiments so Porto many years ago came up with a simple shorthand nomenclature A| B C | D
- all these directions refer to the crystal axes. The first two experiments above can therefore be labelled. On the left, the laser is entering along axis 'y' with polarisation direction along the 'z' axis of the crystal. You collect again in the 'y' direction and the analyser is set in the 'z' direction. So the Porto nomenclature reads Y | Z Z |Y We have written the nomenclature in each case next to the drawings above. Just as we can relate the two Raman spectra described above on isotropic samples to the symmetry of the modes of vibration, the so called ANISOTROPIC experiments on crystals can be used to sort out the assignment of modes of vibration. The differences in the intensities from one experiment to another are considerable so it's not difficult from the experimental point-of-view to see what is happening. Below in Figure 6 we give an example recorded on a small crystal through a Raman microscope. We will not attempt to explain the spectra here because one needs to understand the theory of the Raman effect and the properties of the polarisation. We will cover this in the near future in another article. If the crystal axes are not orthogonal the situation becomes very complex.
In an oriented polymer the orientation is almost invariably cylindrical i.e. the orientation has only one defined axis - say the fibre axis or the axis along which the material was stretched during orientation - not three as in a crystal. So the comparison is as shown in Figure 7.
If we apply the anisotropic Raman experiments to a polymer only four different experiments can be performed because x & y are interchangeable. We give below in an example, the anisotropic scatter from a highly polyethylene as Figure 8.
Conclusion
|
experiment
is
very nearly zero.
