1. Editorial In this edition we don't really feature any particular subject and it is with regret that I have to admit that we are not innovating either. A-ha I hear you say - the Editorial team is running out of steam! My response - you wait until the next edition! Down to business - Stewart Parker and David Champion are experts in inelastic neutron scattering and Stewart has been our main source of background material. One of the major limitations with INS (apart from the huge cost/spectrum) is the lack of easily accessible databases - of spectral libraries. As Stewart and David point out in their piece, an ever-growing database does exist and they describe and explain it. Last Christmas I bumped into Herbert Shurvell and persuaded him to write us a piece on the subject closest to his heart - paper very old and new. Our second feature by Herbert and his colleagues in the Art Conservation Dept at Queen's University in Kingston, Ontario describes how infrared is particularly useful in identifying pigments and whiteners in papers. They include a wide range of both current papers and also some a century old. I have a feeling their paper* will prove to be of considerable interest amongst conservationists. (*what a horrible pun) IJVS has extensively covered diamond ATR. We have published descriptions of the technique, commercial products and its applications. One of the reasons, I must confess, is that I am a real enthusiast - to me, it is THE method of sampling in the mid infrared. As always, progress continues and Jim Fitzpatrick has generated an article on micro-sampling. Jim reviews progress to date and then goes on to explain the latest creation from SensIR which combines some features of a microscope and a diamond ATR. Jim then tells us about applications. I'm sure you will find the article useful. On a more philosophical point - one might ask why Jim Fitzpatrick's article appears as a feature article in a scientific journal. Isn't it really just a press announcement from a manufacturer? My answer as your Editor is definitely no Jim's article, like several others we have included, have significant value as pieces of science because they introduce the subject rather, explain the background and history behind the technique, offer a clear description and give examples of applications - a far more comprehensive and useful offering than a short piece of advertising copy. In the submitted section we have three papers this time - one from Andrew Brookes and Derek Craston on reaction kinetic measurements using Raman methods, an offering on the calculation of fundamental mode frequencies from Dr Ridha, Salima and Bahoueddine and finally another offering on Micro-spectroscopy, this time in the Inorganic field and by Jon Schoonover, George Harilla and Patrick Treado. The last paper shows that coupling Micro Raman spectroscopy with elemental analysis mapping can be particularly valuable in the study of complex inorganic mixtures. Schoonover and his colleagues show how valuable the technique can be in the nuclear waste industry but I can envisage it being valuable in geology and many other areas. Dr Ridha and his colleagues have calculated from first principles the vibrational frequencies of PI3 PI2H and PIH2. The hydrides are of interest because it is very difficult to make pure samples so calculated frequencies are valuable in sorting out the spectra. Personally, I find this type of work a little frustrating because the calculated frequencies are very different from the experimental ones. In a complex molecule I just wonder how useful the calculated values are. Perhaps one of you experts in this field would like to comment. Andy Brookes and Derek Craston's work in kinetic field should be of widespread interest because they show how Raman can produce data through glass windows and does not, of course, involve sampling. I recommend all these papers to you.
Stewart F. Parkera and David J.
Championb bH H Wills Physics Laboratory, Introduction Neutron scattering experiments are expensive. Thus it is incumbent upon the users of such facilities that the best possible use is made of the data. Usually, the data is analysed, published and (hopefully) archived by the experimentalist and co-workers. At this stage the data can be considered to be "lost" to the wider scientific community, since only the published material is available. While many facilities archive the raw data from the instruments, this is not always readily available or in a user-friendly form. A notable exception is the Institut Laue Langevin (ILL) that makes all of its data available as ASCII files via the WorldWideWeb [1]. This situation may be contrasted with the practice in analytical chemistry. There, it is recognised that considerable effort is devoted to the acquisition of spectroscopic data and that once the initial purpose has been served, such as identification or characterisation of a material, the data is still valuable. Most such companies hold spectroscopic data in a database both for legal requirements and as a resource in its own right. Spectroscopic databases have also been created as commercial enterprises. The result is that the major forms of analytical spectroscopy have spectral libraries of enormous size. For instance, the Sadtler library of infrared spectra has over 150,000 compounds, whilst mass spectroscopy libraries contain over 400,000 compounds. Such libraries greatly increase the power of the techniques. The inelastic neutron scattering (INS) spectrometer TFXA [2] at ISIS and its successor TOSCA [3] span the energy range 0 - 4000 cm-1 (0 - 500 meV), the traditional mid-infrared. The instruments are unusual among INS spectrometers in that they follow a single trajectory through momentum transfer (Q, Å-1) energy transfer (w , cm-1) space [4]. The resulting spectra are complementary to conventional infrared and Raman spectra. (TFXA and the relation of INS spectra to infrared and Raman spectra are described in an IJVS article [2]). During the time that it was operating (May 1985 -February 1998) TFXA recorded 4499 spectra from a huge variety of materials. These included biological materials [5], catalysts [6], fullerenes [7], superconductors [8], hydrogen-in-metal systems [9], polymers [10], organic [11], inorganic [12] and organometallic compounds [13]. (The references are selected examples, a complete list of publications can be found at http://www.isis.rl.ac.uk/CrystalAnalysers/TFXApubs.htm). As a first step to increase access to the spectra we have created a small database from the spectra. The spectra selected for the database are well-characterised, pure compounds, recorded at low temperature (generally below 30K). In the remainder of this paper, we describe the philosophy adopted, how to access the database and how the database will be further extended. The Philosophy At an early stage it was recognised that the provision of data to potentially anyone on the planet was a sensitive issue. To overcome this problem, a twofold strategy was adopted. The only data that would be included were spectra for which the originators had given permission and those that had already been published and were thus in the public domain. In the latter case it is at least conceivable that anyone who wanted the data could digitise the spectra in the original publications and so obtain it. Every spectrum is labelled with either the originators name or the full literature citation. The units of energy transfer were chosen to be wavenumbers (cm-1) since this is the most commonly used unit for this spectral region. It also emphasises the partnership with infrared and Raman spectra. Conversion to other units is trivial since the transformations are linear (e.g. 1 cm-1 = 0.12397 meV = 0.02997 THz). Initially it was also decided to restrict the spectra to "parent" compounds, isotopomers would not be included. The reason for this is that it is very difficult to obtain 100% labelled materials and the presence of an isotopic impurity can have dramatic effects on the spectra. This is particularly marked in the case of deuterium for hydrogen substitution, the difference in incoherent cross-section (D 5 barns, H 80 barns) means that a few percent of H in a nominally 100% D labelled compound will give impurity features of comparable intensity to the fully labelled material, as shown in Figure 1.
It was also decided to exclude spectra of the compounds adsorbed on catalysts, since the spectra may be very different from the parent compounds. Figure 2 shows a comparison of solid formic acid and the difference spectrum of formic acid adsorbed on CuO, the features in the later are due to adsorbed formate [15]. For the future, it is planned to address both of these issues.
The Database The database is located at: http://www.isis.rl.ac.uk/INSdatabase/ There is a search facility which operates on the chemical name and the formula. This brings up a list of hits at the bottom of the page, clicking on the desired one will bring up the reference and a "thumbnail" sized GIF image. Clicking on the spectrum will give a full-screen image. Four file formats are available, two graphical and two ASCII versions and all of the spectra can be downloaded in all of the formats.
GIF
EMF DAT
The first line is the name of the compound, its principal investigator, their affiliation and the literature reference (if known). The second line defines the units, for the energy transfer (i.e. x) axis all the spectra are given in units of wavenumbers, cm-1. The counts (i.e. y) column is the scattered intensity and is directly proportional to the scattering function S(Q,w ). The error column (i.e. z) is given by the square root of the number of counts, since Poisson statistics apply to the measurement process. JCAMP-DX An example is shown below. Lines beginning with ## are comment lines. The first five lines define the origin of the spectrum, the next 12 give information as to how the data is organised, the data then follows and is terminated by ##END=.
Conclusions At present there are 70 materials available on the database in all four formats. It is planned to increase this during the summer of 1999 and in the longer term it is intended that as work on TFXA and TOSCA is published, the INS spectra will be made available on the website. To our knowledge this is the first time that INS data have been made readily accessible, the hope is that it will bring the advantages of INS spectroscopy to the wider community. The Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. References
*Please send correspondence and proofs to: Sharon D. Wightman and Herbert F. Shurvell
Introduction Coatings on coated papers contain pigments, an adhesive or binder and various additives, which facilitate the coating process. The latter are present in minor amounts. Modern coatings are of two general types: pigmented or functional. For the improvement of printing and graphic reproduction, pigment coatings level the microscopic irregularity of the paper surface and make it more uniformly receptive to printing inks. Functional coatings are applied for various specific purposes. For example, in the food packaging industry, functional coatings provide barriers to fluids and grease, and retard the oxidation of package contents. Coated papers have been known for hundreds of years. In the fifteenth and sixteenth centuries, artists used coatings of animal glue and calcium carbonate on single sheets of handmade paper. The traditional inventory of pigments was restricted prior to the nineteenth century to calcium carbonate and kaolin (china clay). Other materials, which became available in the twentieth century, include: blanc fixe (precipitated barium sulphate), satin white (calcium sulphate), titanium dioxide, talc, and aluminum trihydrate. In recent years, use of the traditional binders, gelatin and animal glue has declined in favour of casein, latex, starch, soya protein, and natural adhesives. Other materials found in paper coatings include urea-formaldehyde and styrene-butadiene polymers, polyvinyl alcohol and modified celluloses. A coated paper cannot always be detected visually. Calendared finishing processes give gloss and smoothness to both coated and uncoated papers. Both the presence of and the type of paper coating are important considerations that affect conservation treatment . Various methods for the identification of pigments and binders in coatings are available. These include chemical spot tests for protein starch and cellulose, coating removal and analysis, and ashing for the preparation of samples for detection of inorganic pigments. Various Infrared spectroscopic techniques have been used for the analysis of paper and paper coatings. Most of the reported infrared studies employed the Attenuated Total Reflection (ATR) technique. Other reported methods include infrared microscopy, and a transmission method in which samples were crushed between diamond anvils. The use of near infrared spectroscopy has also been reported. Using ATR-FT-IR spectroscopy, historical papers have been characterized by their gelatin (hide glue) content and the determination of polymer and mineral content of coatings on papers has been reported. In this paper a simple sampling method is described using infrared transmission measurements for the identification of the main components of coatings on paper. Samples and Sample Treatment Table 1 lists the various papers examined in this study. Samples were taken from several general types and weights of papers: bond typing paper, magazine, wallpaper, art stock, gift wrap, post card, and printed catalogue papers. The papers ranged in age from late nineteenth century to the 1990's. Some of the papers were unused. The typing paper was taken from a pad of sheets. The 1990's wallpapers were cut from store rolls. The unpasted pre-1970's wallpaper had been used as a drawer lining. Both of the coloured art stocks were from storage inventories. The remaining papers had been in circulation.
Table 1. Details
of papers studied To obtain a sample for infrared spectroscopy, 1-2 milligrams of material is scraped, with a stainless steel scalpel, from the surface of selected areas of the paper. Printed papers should be scraped in uninked areas such as margins. All papers should be scraped, where possible, on interior surfaces well away from the edges, to reduce the amount of contamination, which might be present from handling and exposure. The scraping must be done lightly and with even pressure in one direction only. The scrapings are transferred to an agate mortar and approximately 200 milligrams of dry KBr powder is added. Scrapings and KBr are ground together until the sample is dispersed homogeneously. The mixture is transferred to a stainless steel die between two 13mm diameter polished anvils, which are wiped free of contamination with lens tissue. Air is evacuated from the die using a vacuum pump. A transparent, or nearly transparent pellet, is obtained, by pressure using a hydraulic press. An article on making good KBr discs can be found in Volume 1/Edition 1 of IJVS [www.ijvs.com]. In addition to the sample spectra, a set of reference spectra of known coating materials was also recorded. Samples of reference materials were obtained from the paper conservation laboratory at Queen’s University and from various commercial suppliers. The reference spectra were recorded of seven common pigments, five protein binders, four different cellulose samples and four starches. Infrared Spectra Attenuated Total Reflection (ATR) spectra can be recorded using a KRS-5 crystal with ends cut at 45o. The infrared radiation is directed into the crystal and collected as it leaves by means of mirrors. The spectra reported in this article were obtained using an RIIC Model four-mirror system. The crystal is mounted in a stainless steel holder with strips of the paper sample clamped against each side. A more up to date technique, diamond ATR, is available these days. (See IJVS Volume 2 Edition 2 [www.ijvs.com]) Reference Spectra
Pigments
Table 2. Characteristic features of infrared spectra of some pigments. The two oxide pigments ZnO and TiO2 and talc have very simple spectra. Kaolin has a more complex spectrum, with several characteristic peaks. The most notable feature of the infrared spectrum of a coating containing kaolin is a sharp doublet at 3620/3695 cm-1, which is due to stretching vibrations of OH groups in the kaolin structure [10]. Confirmation of the presence kaolin is found from the presence of three peaks of decreasing intensity at 540, 470 and 430 cm-1 and a strong broad band centred near 1030 cm-1. The two compounds CaSO4 and BaSO4 have broad absorption bands near 1100 cm-1 and several other sharp characteristic peaks in their spectra. CaCO3 occurs in two polymorphic forms, calcite and aragonite. The infrared spectrum of the pigment, whiting has a very strong, very broad band centred near 1420 cm-1. This feature is characteristic of the calcite form of CaCO3. Binders
Celluloses
Starches
Sample Spectra Figure 5 shows the infrared spectra of three different papers. A variety of pigment materials are evident in these spectra. Figure 6 shows the spectra of 3 different wallpapers. It is clear from the absence of absorption near 1720 cm-1 that the pre-1970 wallpaper has no plastic coating. Figure 7 compares the spectra of two different coloured card stocks. Figure 8 compares the printed and unprinted sides of a wrapping paper. Figures 9 and 10 show infrared spectra of two old papers. Detailed interpretation of these sample spectra is given below. Magazine and erasable
typing papers
Wallpapers
Coloured card stocks
Printed wrapping
paper
A 1897 postcard
An old furniture
catalogue (circa 1920)
Comparison of infrared ATR and transmission
spectra
Sumary & Conclusions Table 3 summarises the main inorganic pigments found to be present in the coatings of the paper samples studied.
Table 3. Pigments identified in coatings on the sample papers The procedure described here offers a simple rapid method for the qualitative analysis of pigments and other compounds in paper coatings. Information is readily obtained on both organic and inorganic compounds present in the coating materials. Other materials such as synthetic polymers also have been observed in the coatings. The spectra recorded in this study generally did not reveal the presence of materials such as protein binders and starches. Infrared spectra of these materials are relatively weak and the broad features of their spectra form part of a general background. For older papers, which have little or no pigment coating, the infrared spectrum is essentially that of cellulose. Jim Fitzpatrick Sensir Technologies Samples that would have been difficult if not impossible to analyze on traditional small element diamond ATR accessories are now simple to do on the DuraScope. In addition to all of the advantages of the small element diamond ATR element, the DuraScopeTM incorporates a video camera beneath the diamond for assistance in positioning of the sample and observing contact between the sample and the diamond. For the first time, the power of these two techniques has been combined in a system that works in the sample compartment of the FT-IR. The addition of the video camera with output to a PC video board allows image manipulation and control that had been seen before only on infrared microscopes. Being able to see the sample allows the user to select discrete areas for analysis while ignoring others. This technology offers many advantages to the FT-IR user. The evolution of Diamond ATR
microanalysis Infrared spectral analysis, using ATR, is gaining wide acceptance among chemists because these FT-IR accessories are a unique interface for solid and liquid samples [1]. Diamond ATR has all of the advantages of traditional ATR in addition to some unique benefits [2]. In addition to being a very versatile analysis system for large samples, this technique has been referred to as a poor mans’ microscope [3]. Diamond ATR accessories are microanalysis devices. The high cost of cutting and polishing the diamond ATR element to the required shape and the requirement to minimize the pathlength of the infrared beam in the diamond imposes a practical limit on the size of the sensing element surface. To offer affordable accessories with minimal spectral interference from the ATR element itself, diamond ATR manufacturers offer systems that have sensing surfaces approximately 1 mm in diameter. A variety of innovative optical designs concentrate 15-30% of the spectrometer energy through these small diamond elements (Figure 1). As a result, sample size requirements for ATR have been reduced by more than 100X over traditional 45 degree ZnSe ATR systems. Achieving intimate contact with the diamond element is critical for successful ATR analysis. Using small ATR diamond elements, it is much easier to achieve contact as element size decreases. As Lewis and Sommer point our, " Since pressure is a force divided by area, the pressures obtainable in a micro-configuration can be four to five times greater for equal applied pressure. The reduced area also provides uniform pressure, eliminating baseline distortions associated with uneven pressure across much larger internal reflection elements"[4]. Everyone using ATR accessories has experienced the futility of getting a quality spectrum of a powder on a large 6-reflection ZnSe crystal. Single crystals of this same powder are now routinely analyzed on small element diamond ATRs. Only the users’ eyesight, patience and steadiness of hand limit the sample size. Small element single and multi-reflection diamond ATRs have an active area in the center of the diamond. Samples larger than 500 microns will usually cover the entire diamond after compression. As a result, sample positioning is not as critical. However, as users try for smaller and smaller samples, it becomes important to position the sample accurately in the center and make sure that it stays in place when it is compressed. Samples as small as 20 microns are now possible [2]. Most pressure devices prevent the user from seeing the sample positioned on the diamond (Figure 1). Unable to see, the user can not observe shifting of the sample on the active area of the diamond (and sometimes across the room).
The DuraSamplIRTM configuration, as represented in Figure 1 is the basis for the universal ATR [5] offered by Perkin Elmer in their new Spectrum OneTM FT-IR spectrometer and the SmartTM DuraSamplIR offered by Nicolet in the new AvatarTM FT-IR spectrometer. At PittCon 1998, SensIR Technologies introduced the ViewIRTM. The ViewIR allows a user to look through the pressure device, position the sample in the active area of the diamond and watch the sample being compressed (Figure 2).
Apparent contact with the sample is observed as a "wetting" effect on the glass pressure plate. It is assumed that the samples behave as hydrostatic fluids and therefore the same effect is occurring on the reverse side between the sample and the diamond interface. The ViewIR is ideal for small contaminants that have been removed from a matrix such as black inclusions in a white pharmaceutical tablet in addition to single crystals and single fibers. However, samples that continue to provide a challenge are opaque samples, ink on paper etc. In essence, samples that can not be seen through or around are not suitable for the ViewIR. To address this problem, a new accessory developed. The DuraScope (SensIR Technologies, Danbury, CT) is a small element diamond ATR accessory that views through the diamond so that sample-to-diamond contact is directly observed (Figure 3). One of the advantages of the SensIR Technologies diamond ATR design is that the element is neither faceted nor a prism. The diamond element is flat on both sides. In addition, the ZnSe focusing crystal is visibly transparent. This allows the placement of a high-resolution miniature CCD camera beneath the diamond.
Now it is possible to observe the samples’ contact with the diamond instead of contact with the glass pressure device as the user is actually looking through the diamond. In addition, a key feature of this design is the 30-100X magnification provided by the camera. The electronics of the camera compensate for the yellow color of the ZnSe focusing element. The camera focus is set at the diamond-sample interface. Samples are in focus as soon as they are placed on the diamond. Positioning the sample on the diamond is greatly aided by a high quality video image displayed on the integrated video monitor. Sample-to-diamond contact is observed as a wetting effect and appears as a visible change in sample size and transparency. Different areas of the sample can be selectively analyzed through careful positioning and compression. The sample press has interchangeable sample compression tips for optimal analysis. For example, a clear plastic tip serves as an illuminator for transparent samples by focusing ambient light behind the sample, a concave stainless steel tip is included for pellets etc. An integrated force readout system allows the user to reproducibly return to the same pressure each time in addition to having both a visual and audible force overload alarm. This is achieved using a LED display (Figure 4). As the pressure increases, more of the LEDS are illuminated. The red LED indicates that no more pressure should be applied.
A 4 inch video monitor is standard on the DuraScope system. In addition, the DuraScope has outputs for additional NTSC and S-Video (Figure 5) through the use of the electronics interface module. This allows photodocumentation and report generation through the use of an optional PC video card. All that is required is the connecting cable to the PC.
Options such as extended spectral range to 230 cm-1 are available through the use of KRS5 as the focusing element instead of ZnSe. An additional benefit of the SensIR Technologies design is that multiple reflection configurations are possible through the use of an air gap between the diamond and the ZnSe in specific locations. This refractive index difference between the diamond and the air pocket cause additional internal reflections. This multi-reflection option is ideal when enhanced sensitivity is required. The diamond element in this configuration is approximately 3 mm so all of the advantages of a small element ATR are still retained.
Application Examples Analysis of ink on a business card
Forensic Applications
LSD analysis has proven to be a difficult sample to analyze because
in street form, concentrations are quire low. The most popular distribution
method is as "stamps" where the LSD is deposited onto paper
tabs. The user can then lick the LSD from the back of the "stamp".
The usual method of analysis is to extract the LSD using a solvent
such as chloroform. The sample is then analyzed using a GC/MS. This
method is difficult and time consuming. A novel method was employed
by Harris using a wick and capillary action [6]. The LSD was allowed
to migrate up the wick where it crystallized overnight and was picked
off for infrared microscopy. While still an improvement over GC/MS,
it was still time-intensive. An alternative method is described here.
2 microlitres of street sample dissolved in chloroform were deposited
on a multi-reflection diamond ATR DuraScope using a GC syringe. The
chloroform evaporated in less than ten seconds, allowing the LSD to
crystallize out onto the diamond. A spectrum was collected and the
crystal was wiped clean with an appropriate solvent. Collection and
cleaning took less than one minute.
These beads are approximately 100 micrometers in diameters and would be very difficult to manipulate and observe without the viewing enhancement that the DuraScope or an FT-IR microscope provides [9]. Notice the difference in illumination between the sample, before and after compression. The sample compression tip in this example is a glass rod. It serves as a light conduit and focuses ambient light at the back of the crystal. In the uncompressed image, the pressure device has been rotated completely out of the way for easy access to the sample area. As a result, there is no enhancement in the illumination behind the sample. Hair Analysis
Experimental
To collect a sample spectrum with the DuraScope, simply place the sample on the diamond and position it in the center. The integrated video monitor aids in this step. Rotate the pressure arm into position over the diamond and apply pressure by turning the steel post. Observe contact and then initiate scanning. That’s all there is to it. Summary By allowing the analyst to view through the diamond element of the ATR accessory The DuraScope offers capability to the FT-IR user that has never before been available in an in-compartment FT-IR accessory. The DuraScope offers all of the capabilities that were once reserved for those users who had ATR objectives on infrared microscopes [11]. In addition to allowing analysis that was previously impossible, the DuraScope brings simplicity and ease of use to samples that were possible but difficult. The ideal analysis technique has improved. DuraScope is a trademark of SensIR Technologies. One or more of the following patents cover the DuraScope: USP 5,552,604, USP 5,703,366, and USP 5,172,182
DuraScope Components References
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