Frequently Asked Questions

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  • How can I align a Cyclone Gas Cell?

      For mirror alignment of any version of Cyclone™ gas cell, but most especially for the variable pathlength cell options, Specac thoroughly recommend use of the laser alignment accessory P/N GS24500. This provides a coherent, visible source of light to assist in the initial cell alignment before the cell is placed into a spectrometer sample compartment for fine tuning against the spectrometers source and detection system. It is usually only necessary to adjust the input and output mirrors on the transfer optical unit rather than any adjustment of the mirrors inside the gas cell to achieve the correct alignment.

      Taking a C10 Cyclone™ cell as an example, this is factory aligned and set to a pathlength of 10.56 meters (40 passes of the beam through the cell). For a fixed pathlength cell the T shaped field mirror (FM) will show a line of 10 spots of light on the longest part of the T shaped FM, with 19 spots of light in total arranged as two parallel lines from side to side across the FM. If for any reason the objective mirrors (OM1 (input) and OM2 (output)) at the top of the cell become detached from their spring setting, then the pattern of light spots on the FM will not be observed.

      Consequently, no amount of adjustment on the input and output mirrors of the optical unit will allow for correct alignment. The objective mirrors must be remounted correctly in their spring setting. This is not a tricky job, but it does involve removal of the outer glass or metal cylinder of the gas cell to gain access to the mirrors for resetting. It is therefore crucial to establish a pattern of light spots on the FM to verify that the internal mirrors OM1 and OM2 are set correctly.

      For variable pathlength cells, if the OM2 has been adjusted via the micrometer screw for a different pathlength from the standard factory setting, it is necessary to establish some pattern of light spots on the FM to calculate for a set pathlength. Any slight misalignment either side of the next sequence of spots (next corresponding sequence of 4 passes through the cell) means there will be no passage of light through the cell and consequently no light will reach the output mirror of the optical unit.

      Therefore, for alignment of a FIXED pathlength Cyclone™ gas cell using the laser alignment accessory, mount the Cyclone™ gas cell on the alignment accessory such that the laser source will enter the optical transfer unit from the same beam direction as the spectrometer system.

      Rotate and/or tilt the input mirror to direct a beam of light up to the input objective mirror (OM1) at the top of the gas cell. If both objective mirrors (OM1 (input) and OM2 (output)) are in alignment then a pattern of spots corresponding to a particular pathlength setting are seen on the bottom T shaped FM. The final beam pass through the cell will be directed past the FM to the output mirror in the optical unit. This mirror can then be rotated and/or tilted to direct the beam of light to the target cross on the laser alignment accessory. The Cyclone™ gas cell can then be placed into the spectrometer for fine tuning and maximising the beam signal throughput.

      For alignment of a VARIABLE pathlength cell on the laser alignment accessory, mount the Cyclone™ gas cell on the alignment accessory such that the laser source will enter the optical transfer unit from the same beam direction as the spectrometer system. If NO light spots are seen on the FM when the beam of input light from the laser alignment accessory is directed to the OM1, then adjust OM2 by movement of the micrometer screw until a pattern of light spots is obtained. (It is assumed that OM1 and OM2 are correctly set in their mirror mountings.) When a particular beam pass sequence has been established, the final beam pass through the cell will be directed past the FM to the output mirror in the optical unit. This mirror can then be rotated and/or tilted to direct the beam of light to the target cross on the laser alignment accessory.

      The Cyclone™ gas cell can then be placed into the spectrometer and the input and output mirrors ONLY of the optical unit may need to be adjusted to peak up the signal for the pathlength selected. Only when this is done should the micrometer be adjusted to change the position of the OM2 and hence the pathlength of the cell. Changing of the OM2 should not alter the alignment of the cell from this point.

  • How can I troubleshoot my Manual Press?

      If there is a problem with an Atlas™ Manual 15T or 25T hydraulic press, before Specac can advise anything to help, certain details must be known about the actual press itself and the nature of the problem to clarify what may be required to solve the problem.

      The age of the press can be determined from a serial number found as a five figured number engraving at the rear of the pump block assembly (silver coloured part of the press where the crank and pump handle is attached).

      Presses built from 2008 onwards will have serial numbers with a letter preceding the five figure number and are metric threaded presses. Older presses where the five figured number is followed by the letter M it is a metric threaded press. If there is a five figured number but no letter M, or there is no serial number at all, then the press is an imperial threaded version.

      Presses with no serial number were built prior to March 1991. For imperial threaded presses it may now prove problematic in being able to supply relevant spares for the press to be fixed in situ. It may require sending the press to Specac for possible repair depending on the nature of the problem.

      Therefore, if confirmation is given of the serial number information, or some idea of the age of the press and its colour, or if there is no serial number, it will help in advising the best course of action for repair. Also, it is extremely helpful if a clear explanation of the nature of the problem is also supplied – e.g. if the press is leaking oil, where and how much oil is leaking? To solve this particular problem and possibly many others, it may only require a replacement seal and/or some specific advice, rather than the need for costly transportation of a press back to Specac.

  • How do I calibrate a Heated Golden Gate?

      Within the top plate area of the Heated Golden Gate diamond ATR accessory (P/N GS10540 – 200°C, or P/N GS10640 – 300°C), the temperature measuring thermocouple is situated as close as it can be to the diamond to record the actual surface temperature. Diamond is a very good heat conductor and so any discrepancies between the measurement position temperature and the surface temperature of the diamond should be small.

      If the actual surface temperature of the diamond is required to be known, it could be necessary to calibrate the heated Golden Gate top plate diamond surface itself using a range of solid samples with different melting point temperatures. If suitable standards can be found corresponding to say 50°C, 100°C, 150°C, 200°C and 250°C melting point temperatures they can be placed on the diamond and observed for their melting point as the temperature is reached and indicated on the temperature controller. The temperature should be raised slowly and steadily to account for any thermal lag etc. As the actual temperature when the standard sample should melt is known, the temperature could be raised to say within 10 degrees of the melt temperature and approached by 1 degree changes to get an accurate representation of the temperature melt figure.

      A graph can be constructed for the temperature displayed by the controller when the sample melts, against the actual known melting point temperature of the standard sample. The more samples you can measure the better as there would be a wider spread of more points to plot. A calibration curve can be constructed which should indicate the likely temperature of the diamond surface as opposed to the temperature being read by the thermocouple for the controller display.

  • How do I choose an ATR accessory for my application?

      Attenuated Total Reflectance (ATR) spectroscopy can be used for samples that are difficult to analyze by a transmission technique. Internal reflectance measurements are made by using an ATR crystal in contact with the sample. Choice of an appropriate ATR accessory is wholly dependent upon the amount and physical state of the sample that you wish to analyze.

      The physical state of the sample is an important factor in determining an appropriate ATR system. The sample must be in very good contact with the ATR crystal to obtain a good ATR spectrum. Hence liquids usually exhibit better ATR spectra than solid samples. A clamping system is used with solid samples to force the sample into good contact with the ATR crystal. It helps if the solid sample has a high degree of homogeneity to obtain consistent spectra between like samples. Issues such as reproducibility and sensitivity can become important, due to the way a sample makes contact with a specific ATR crystal.

      In summary, along with the sample amount and type, it is often a compromise between chemical performance and spectral range of a crystal material that determines the choice of an ATR accessory for a particular experimental application.

  • How do I clean my Evacuable Die?

      The Atlas™ Evacuable Pellet Dies are made from a grade of stainless steel 440C. If subjected to mineral acids (such as HCl) for prolonged periods then it will be attacked.

      For cleaning of the dies, it depends on the sample type being used inside the die and how it is being compressed as to the type of cleaning solvent(s) that might be needed to remove any solid material residues. However, Specac believe that, typically, most 13mm dies are used to prepare KBr discs with a solid sample for IR spectroscopy and if this is the case a recommended procedure is as follows.

      Clean the die body, two inner pellets and plunger (i.e. any of the parts that have potentially been in contact with the powder sample) with clean water or distilled water at room temperature. Dry these parts with a tissue or soft cloth (so as not to damage/abrade polished surfaces of the pellets) and then wash the parts again with methanol. Redry the parts with a clean tissue or soft cloth. The idea is that the water wash will remove any inorganic salt (KBr) deposits and then the methanol wash will remove further inorganics and most organic trace components (if say a pharmaceutical sample had been prepared). If the die is not to be used for a while, place in a dry and warm environment to prevent any build up of moisture.

      If many KBr disc samples are to be run, it can be best to have a couple of die sets to “rotate” during the preparation and cleaning procedures. Whilst one die is being cleaned and is drying on a warming plate, another die is being used for sample preparation and compression in the press.

  • How do I prepare high quality KBr pellets?

      Generally, it is easy to produce a good quality KBr pellet if an evacuable pellet die is used correctly. However, some faults in the produced sample pellet may occur due to a variety of reasons. Some of these faults and their remedies are tabulated below. The faults described are for pure KBr or other halide salts which do not contaminate the sample. When the sample is added to the halide salt the clarity of the disc will depend to a large extent on the quantity and type of sample. Usually 0.1 to 2% weight to weight of sample to KBr is perfectly adequate. The overall quality of a pellet is largely dependent upon the quality of the KBr or halide salt powder used, which should always be of a spectroscopic grade of purity.

      FaultCauseRemedy
      Sample pellet not clear. Lacks optical clarity.Sample damp, contaminated KBr powder or insufficient pressure when compacting.Dry the KBr powder or sample and increase the compacting pressure.
      Sample pellet is clear but shows opaque spots.Powder not uniformly flat in the die, leaving large particles which do not vitrify when pressed.Sieve powder to extract coarse grains, then re-grind and re-press.
      Sample pellet is cloudy.Insufficient evacuation time or leaky seals.Check seals on the die and lengthen evacuation period.
      Sample pellet is clear at first but quickly becomes cloudy.Damp powder or damp atmosphere.Dry the KBr powder or sample, check seals on the die and lengthen evacuation period.

      To ensure that a sample pellet is produced which will enable accurate spectra of samples to be obtained, it is essential that the sample is thoroughly blended with the halide salt powder. Blending can be achieved either by using a mortar and pestle (P/N GS03600) or by using a grinding mill.

      If a pellet breaks apart, then possibly not enough total mixture is being used in the die. Under compression the disc has become too thin and fragile. Excess moisture in a KBr disc could  cause it to fragment and insufficient pressure or load on the sample when in the die can mean that the KBr/sample mixture has not been sufficiently compacted. For a 13 mm diameter die with a total KBr/sample mixture mass of 400 mg, a load of 6 to 7 tons on the press gauge will produce a disc of approximately 1 to 1.5mm thickness.

  • How do I realign a Golden Gate ATR?

      The ZnSe or KRS-5 lenses of a Golden Gate ATR Accessory focus the beam of a light signal to pass through the small aperture of the diamond crystal assembly. As such a correctly aligned beam of light has to arrive at the lens before the beam is focussed to pass through the diamond crystal. If there is no registered signal whilst in a spectrometer system, even though a ZnSe or KRS-5 lens assembly has been replaced after it has been removed, alignment of the mirrors in the optical unit will need to checked.

      The best way to do this is by use of a visible light source. Specac has a specific Laser Alignment Accessory P/N GS24500 to help in this procedure. If this is not available, to use a discrete spot of light from a laser pointer is ideal, but if this is also not available then use a bright white light source.

      First remove the ATR top plate and the front cover plate from the Golden Gate optical unit to gain access to the mirrors. In a darkened environment, ensure that the bright light source is shone through the aperture port on one side of the optical unit. Start with the input side – before light reaches the diamond – of the optical unit as it would be in your spectrometer system. Ensure that the light image falls onto the centre of the first fixed mirror. It is also crucial that the light source is at the centre of the aperture port so the light will pass in a parallel line in relation to the base of the optical unit towards the first fixed mirror. (For a parallel centralised light beam, the Laser Alignment Accessory P/N GS24500 is the best tool to use.) The light will be reflected from this first mirror onto the second movable mirror at its centre point, if the initial light source is correctly positioned.

      The second mirror may then need to be adjusted for both its rotation and tilt so that the beam of light passes centrally through the first ZnSe or KRS-5 lens assembly. If the source of light is bright enough (and this is where a laser pointer light is preferred) the spot of light should be in the centre of the lens as it emerges from the top. There is no need to try and focus the lenses at this stage as it is more important to establish a correct beam path by alignment of the mirrors.

      Now, move the light source to the other side of the optical unit (the output side – after light has passed through the diamond) and repeat the process for mirror alignment to get a beam of light centrally in the second ZnSe or KRS-5 lens assembly.

      Once this condition has been achieved, replace the top plate onto the optical unit and place the accessory in the spectrometer system. Hopefully, the optical unit will now be roughly aligned to register some signal throughput by the spectrometers detector. At this stage start “fine tuning” the mirrors and the ZnSe or KRS-5 lenses for focus to get the optimum signal for the Golden Gate on your specific spectrometer system. Ensure that in any change of an optical component that you concentrate on one mirror or lens at a time, otherwise if the signal is lost you will need to start the alignment procedure from a visible light source again.

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  • How do I realign my Monolayer accessory?

      From installation of the Specac monolayer grazing angle accessory P/N GS19650 into a spectrometer sample compartment, if there is no signal throughput registered when the reference reflectance mirror is in position on the sampling platform and the “butterfly arms” have both been set to the same incidence angle (nominally 45°), then it is possible either one or both of the adjustable mirrors at the end of the butterfly arms is/are not correctly aligned.

      A monolayer grazing angle accessory will have been roughly aligned for a throughput before leaving Specac as new, but it needs to be finely tuned to best match the local environment within a specific spectrometer. If it is believed that the adjustable mirrors are not sending a signal correctly to and from the sampling area, you will need to recreate a beam path to and from the sample cup area to realign the mirrors using a source of visible light.

      Outside and away from the spectrometer sample compartment, place the monolayer grazing angle accessory on a flat surface. Have the solid sampling platform assembly fitted into the accessory and ensure that the platforms surface height is exactly level with a beam of light that would be running straight through the accessory over the central sample area line (marked on the platform)  if the light beam deflecting mirrors at the base of the butterfly arms were not present. The height of the solid sampling platform surface is adjustable by the rotatable screw mechanism as part of the complete sampling platform assembly.

      Set both butterfly arms to a nominal angle of 45° and fix them into position. Do not be concerned with position of the movable mirrors on the butterfly arm at this stage.

      Use a bright white light source beam (white light from an LED torch masked to a circle aperture of circa 10mm diameter is good ) in a darkened environment to project a beam of light to the angled, fixed, square mirror at the base of one of the butterfly arm assemblies fixed at the 45° angle. Ensure that the light beam image falls onto the centre of this first fixed mirror. It is also crucial that the light beam source passes in a parallel line in relation to the base of the accessory towards the first fixed mirror. The light will be reflected from the first fixed mirror towards the centre of the movable mirror at the end of the angled butterfly arm if the initial light source is correctly positioned for its overall beam height and parallel spatial positioning.

      Now adjust the movable mirror at the end of the butterfly arm for its rotation to direct the light beam towards the centre line of the sampling platform surface. You are looking to achieve an elliptical pool of light to cover this centre line position, such that the centre line acts as a bisecting diameter for two semi-circular pools of the light. Rotational movement of the mirror allows for central positioning of the incident angle light beam in a longitudinal direction across the sampling surface, but to centralise the beam of light now from the side to side direction, the tilt grub screw of the movable mirror is adjusted accordingly.

      When the white light beam spot has been established in the centre of the sampling platform area after passage through one of the butterfly arm assemblies set at a 45° angle from rotational and tilt adjustments of the movable mirror (which can be considered the light input beam side to the sample), repeat the process after moving the light source to the other side of the monolayer accessory (the output light beam side away from the sample). This is to project the light back through this second butterfly arm assembly via the adjustable mirror to the central area of the sample platform.  Centralisation of the spot of light from this direction is achievable from rotation and tilt of the adjustable mirror, provided the input source of light in the backwards direction is at the correct height, parallel positioned spatially and centred on the fixed, square mirror of this butterfly arm assembly.

      When this centralisation of the beam spot onto the sampling platform area has been achieved from both butterfly arm directions you should now have roughly aligned the movable mirrors such that a beam of light bought to the sampling area from installation of the accessory into a spectrometer and fitting of the reference mirror onto the platform surface will complete an IR radiant beam of light passage from source to sample to detector. There will be an energy level signal registered at the detector of the spectrometer from this rough alignment procedure.

      When installing the monolayer accessory into the spectrometer for a fine alignment that will be required now for an optimum energy throughput of the accessory, ensure that the reference mirror when fitted to the sampling platform is adjusted to its correct height for the reflecting surface. Therefore the sampling platform will need to be lowered by the same thickness as the reference mirror for a correct sample surface level to achieve an optimum energy throughput level.

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  • How do I realign my Selector Diffuse Reflectance Accessory?

      Throughput from a diffuse reflectance accessory is usually quite low in respect to an unobstructed beam. Typically, the Selector accessory P/N GS19900 with KBr as a reference material in the sample cup will give a signal responding to approximately 5% of overall throughput.

      The only mirrors that can be adjusted on the Selector accessory is the final output mirror (for rotation and tilt) and the two ellipsoid mirrors. A Selector accessory will have been roughly aligned for a throughput before leaving Specac as new, but it needs to be finely tuned to best match the local environment within a specific spectrometer. If it is believed that the mirrors are not sending a signal correctly to the sample cup area, you will need to recreate a beam path to and from the sample cup area to realign the mirrors using a source of visible light.

      Place the Selector on a flat surface and use a bright white light source in a darkened environment to project a beam of light to the first input fixed mirror. Over the sample cup surface area on the sample post, place a piece of fluorescent coloured tape (orange colour for example) and use the bright light source to trace the beam path from the source side of the Selector mirrors to the first ellipsoid mirror. This in turn should project an image of the light source onto the coloured tape surface. Ensure that the input beam of light is parallel to the first fixed mirror, such that the beam of light is projected correctly to the input ellipsoid from the first two fixed mirrors. At this stage adjust the input ellipsoid mirror only to bring the light spot into the middle of the sample cup. Raising and lowering the ellipsoid arm assembly by the micrometer screw will help adjust the spot of light for a focus. The light spot will get brighter (sharper) or dimmer (broader) depending on the focal point.

      When the spot of light is established in the centre of the sample cup from the input side, move the light source to the other side of the Selector (output side). This is to project light back through the Selector accessory via the final output adjustable mirror to the output ellipsoid and onto the sample cup. By a combination of the final output adjustable mirror and the output ellipsoid mirror, bring the spot of light again centrally to the cup with the orange tape. When this is achieved you should now have roughly aligned the optical components such that a beam of light bought to the sample cup and then being diffusely reflected would have traced its way through the path of the output optical components towards the detector. Therefore you should now be able to place the Selector into the sample compartment of the spectrometer and finely tune it against the detection system.

      Remove the fluorescent tape and use KBr powder as a reference material to register a signal throughput.

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  • How do I set up gas line plumbing of a long pathlength gas cell?

      For gas sampling and the types of operation achievable, it depends on how gas supplies are plumbed to be introduced into the internal gas cell cylinder area where the beam of light traverses between the internal mirrors for multiple passing to provide a long pathlength.

      For a typical type of set up, Specac suggest that there is the possibility of having a valve switching system fitted on the inlet gas tube to introduce a purge gas (e.g. N2) to pass and flow through the system and then the facility to switch to an analysis gas line to introduce a gas to measure.

      On the outlet tube side of the gas flow line, a switchable “side-line” can be plumbed in (use a “T” piece) to a vacuum pump. If the gas cell is to be evacuated, the outlet flow line should be switched off (closed) by use of its own in-line valve tap, the inlet tube valve should be closed and the vacuum pump side-line valve tap is opened to switch on the vacuum pump.

      From the outlet tube side, the flow line for the gases should be plumbed to a safe area to vent away. (e.g. a fume hood).

      Therefore, in combination of such a plumbed set up and specific opening and closing of valves from the inlet and outlet sides, the gas cell can be operated for:-

      1. Introduction and flow of a purge gas (N2).
      2. Introduction and flow of an analysis gas (or mixture of gases).
      3. Stop flow of an analysis gas to measure (static measurement).
      4. Evacuation of the cell, prior to introduction of an analysis gas under low pressure conditions and then allowing for flow of a purge gas  to “clean” the cell ready for a new sampling regime.

      If operating the gas for flow, then a flowmeter is needed to be plumbed in-line (possibly from the outlet side), to know that e.g. 3 liters of gas per minute is set as a flow rate.

      If the gas cell is pressurised from a stop flow analysis (static measurement), unless some type of safety over-pressure burst device is plumbed in as an additional outlet line stream which also vents to a safe area (e.g. the fume hood), any gaseous introduction for stop flow measurement must be set at pressure of less than +15psi for glass bodied cells or +125psi for metal bodied cells. (This value can be set on the pressure regulator of any gas cylinder being used if this is plumbed in line as an inlet gas supply.)

  • How do we measure the performance of a polarizer?

      The most important measure of polarization performance is called the extinction ratio. This is a measure of how efficiently the polarizer separates out the parallel and perpendicular components of polarization. An extinction ratio of 1000:1 indicates that for every 1000 photons of one polarization, there is only 1 of the contrary polarization passing through the grid. In the case of a wire grid it is the radiation polarized perpendicular to the grid wires that is transmitted.

      The extinction ratio of a wire grid polarizer varies by wavelength. It reaches a maximum at the longest wavelengths (λ) relative to the spacing of the grid (a). The ratio a/λ needs to be 0.5 or lower to have any polarizing effect, and ideally much, much less than this. When using a Specac holographic wire grid polarizer over the wavelength range 2.5 µm (4000 cm-1) to 25 µm (400 cm-1) the ratio a/λ varies from 0.1 to 0.01.

      Another important measure is transmittance of the polarizer. This will be affected by the substrate that the grid is deposited on. Not all IR-transparent materials can transmit across the full mid-IR range.  The thickness or diameter of the wires (d) relative to their spacing (a) also affects transmission. Increasing the ratio d/a will have the effect of lowering the overall transmission but tends to diminish the transmission of the ‘unwanted’ parallel component more. Up to a certain point, therefore, this causes an improvement in the extinction ratio.

      Graph of extinction rate over wave frequency for a holographic wire grid polarizer
      Typical extinction ratio curve for a holographic wire grid polarizer on a barium fluoride substrate

  • How easy is it to change a baseplate-mounted accessory?

      Most Specac accessories are installed into a spectrometer sample compartment via an adapter baseplate. The most commonly used type is known as a Benchmark ™ baseplate. The accessory locates onto the top of the Benchmark ™ baseplate and is held secure by a single thumbscrew fixing, usually into a location pillar at the front of the baseplate.

      There are three further support and location pillars arranged in a triangular configuration on the plate to match the height of the thumbscrew location pillar, such that the accessory is placed level to be presented at the correct beam height and spatial position in the spectrometer sample compartment. It is this arrangement of pillars (or location holes and pins for low beam height spectrometer systems) on a support plate that denotes a Benchmark ™ baseplate configuration.

      The metal plate that carries the pillars or location holes and pins is a particular shape and unique to a specific spectrometer sample compartment. It is this metal plate that is directly attached to the floor of a spectrometer. The Benchmark ™ baseplate may be suitable for a number of spectrometer models from the same manufacturer, and when placed into the spectrometer, will allow any Benchmark ™ baseplate compatible accessory to be correctly mounted for operation.

       The accessories can be changed over for operation simply by undoing the thumbscrew connection on the accessory itself. The Benchmark ™ baseplate part does not need to be removed from the spectrometer sample compartment. An advantage is that once an accessory has been finely aligned for operation in a particular spectrometer on the Benchmark ™ baseplate, as long as the optical settings on the accessory are not altered, it can be removed from the spectrometer as many times as required and is ready for use the next time it is installed.

      Specac accessories that are Benchmark™ baseplate compatible are:-

      • Golden Gate ATR systems
      • Quest ATR
      • Gateway ATR
      • Pearl Liquid Transmission Accessory
      • Cyclone Gas Cells
      • MiniDiff Plus Diffuse Reflectance
      • Microfocus Beam Condenser
      • Variable Temperature Cell Holders
      • Fixed Angle Specular Reflectance Accessory
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  • How thick should my film be when using the Film Maker?

      The quantity of sample placed into the film maker kit before melting and pressing is a major factor in the consistent thickness of film being produced. In addition the sample type, the load and the time that the load is applied to the sample (when the sample is cooling down) will all determine the overall thickness of the film to be produced.

      As an example, two sample discs of a PTFE type material were prepared in an Atlas™ High Temperature Film Maker Accessory P/N GS15800.  A temperature of 305°C was needed to melt the samples and they were compressed at a 1 ton load. The intention was to produce 0.1mm and 0.25mm thick films, therefore the 0.1mm spacing ring was used for one sample and the 0.25mm spacing ring for the other. Sufficient sample was placed into the kit so that on melting there was excess sample around the edge of the disc (acceptable overspill) for both thickness of discs. When the samples had cooled, their thicknesses were measured using an electronic micrometer.

       Interestingly, the 0.1mm spacing ring produced a 0.07mm thickness film and the 0.25mm spacing ring produced a 0.18mm thickness film. These values are surprising because it was expected to produce the MINIMUM thickness allowable from the ring value chosen i.e. a 0.1mm film and a 0.25mm film. However, it is the nature of the PTFE sample to “shrink” on cooling and comparison of the rates of shrinkage shows a reduction of 0.1mm to 0.07mm equates with a reduction from 0.25mm to 0.18mm. (A factor of 0.7).

  • What parts come with the Advanced High Temperature High Pressure Cell?

      When ordering the High Temperature High Pressure Cell (HTHP Cell) as the advanced version GS05855, there are 3 window assemblies supplied. The HTHP Cell will be supplied with the two pressure tested standard flat ZnSe window assemblies attached to the cell for transmission and decomposition experiments (as standard for GS05850). The wedged pressure tested ZnSe window assembly is supplied in the carry case along with an appropriate baseplate with mirrors and attachment parts for the HTHP Cell when the specular reflectance mode of operation is required. These additional specular reflectance mode parts can be ordered as GS05860 if the standard GS05850 HTHP Cell is to be upgraded.


      When the HTHP Cell is to be operated in the specular reflectance mode, the wedged cell window and the baseplate are attached in a specific way due to the beam direction in the spectrometer. Therefore, an upgrade kit GS05860 or the advanced version of the HTHP Cell GS05855 will only have the parts supplied for a specific spectrometer of a specific beam direction.

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  • What are the load limits for Evacuable Dies?

      The maximum load limits that are specified on the Evacuable Pellet Dies (e.g. 10 tons for the 13 mm die) are the maximum load that may be safely applied using any of Specac’s hydraulic presses.

      The pressure gauge on the Atlas™ Manual 15T and 25T should strictly be called the load gauge as it is this maximum tonnage load limit that is applied over a specific area under compression. As the dies grow in size for their diameter, so their recommended load limit increases as there is a larger area associated with being compressed for the die pellet. For the 13 mm diameter die the load of 10 tons (i.e. 22400 lbs) is being spread over an area of 132.73 mm2 (or 0.205 in2 ). This equates to a pressure of 109,268 lbs per square inch or 48.78 tons per square inch.

      Any increase above the maximum load limit could cause damage to the die set. For example, if the plunger was to “bulge” when inside the body because of over loading, the die set would completely seize and be totally unusable.

  • What Gateway ATR accessories are available?

      Gateway™ ATR is a six-reflection horizontal ATR sampling system designed to fit into a wide range of FTIR spectrometers. Samples to be analyzed can be either liquid or solid depending on which top plate assembly is being used. Sufficient sample is required to cover a crystal sampling surface area of at least 72mm long by 10mm wide.

      The parts that go to make up the Gateway™ ATR Kit system P/N GS11165, start with the in-compartment optical unit P/N GS11170.  The optical unit is provided with an appropriate Benchmark™ type baseplate for attaching to the spectrometer. You must specify which spectrometer when ordering this part number to receive the correct baseplate.

      The Gateway™ ATR Kit system is completed by a choice of trough top plate with 45° angle ZnSe crystal P/N GS11166 for liquids and pastes, or a flat top plate with 45° angle ZnSe crystal P/N GS11133 for solids and films. These top plates are compatible for use on the optical unit and are specifically designed for use at ambient temperatures. For the flat top plate you need a clamp kit P/N GS11171 (included with P/N GS11165) that affixes to the P/N GS11170 Gateway ATR optical unit. This allows for the necessary load/pressure to be applied to make good contact of a solid sample with the ATR crystal.

      For the study of samples at elevated temperatures up to 200°C, there is an additional option of the electrically heated trough top plate with 45° angle ZnSe crystal and dedicated temperature controller P/N GS11155. The plate is an open trough design similar to the standard trough top plate P/N GS11166, whereby a liquid is simply poured in to cover the crystal.  The thermostabilised open trough top plate P/N GS11139 is similar to the P/N GS11155 top plate but relies on a thermocirculating fluid for heating rather than from an electrically powered temperature controller.

      An alternative type of heatable top plate for Gateway™ ATR is the 550 microliter thermostabilized flow through top plate assembly with 45° angle ZnSe crystal P/N GS11118.

      A liquid sample can be flowed across the sampling surface of a ZnSe crystal in an enclosed chamber. The outer casing can be heated by the flow of a thermocirculating solution surrounding the sample/crystal area. The temperature achievable is dependent upon the thermocirculating fluid being used i.e. water or oil, etc. A liquid sample pumping system can be used for delivery of the liquid sample via peristaltic type flow through flexible tubing attached to the sample ports on the flow plate. The sample flow through the thermostabilized flow through top plate is rated up to a 60psi maximum.

      All of the Gateway™ ATR top plates are supplied with a 45° angle ZnSe crystal P/N GS11145, but alternative germanium P/N GS11147 and silicon P/N GS11146 crystals at a 45° angle are also available. They can be supplied on their own for placement into the trough or thermostabilized top plates, but they must be pre-affixed into a flat top plate assembly.

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  • What is a wire grid polarizer?

      A wire grid polarizing filter is an array of parallel conducting strips or wires, where the distance between the wires must be much less than the wavelength of light you wish to work with. As long as this condition is met, light whose electric field is oriented parallel to the wires will be reflected, while light whose electric field is oriented perpendicular to it will be transmitted. In this way the polarizer may be used to either filter out undesired polarizations, select for a specific polarization, or split light into two beams with opposite polarization.

  • What is Band Distortion and Band Shift in ATR?

      When obtaining an Infra Red spectrum via ATR spectroscopy, the spectrum will be different to that obtained for the same sample when collected as a transmission spectrum.

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  • What is reflectance spectroscopy?

      Reflectance measurements can be divided into two basic categories – internal or external reflectance. The technique of Attenuated Total Reflection (ATR) is employed for internal reflectance measurements as the beam of infrared radiation passes through an ATR element (crystal) in contact with the sample.

      For external reflectance measurements, the infrared beam of radiation is reflected directly from the sample surface. This type of external reflectance measurement can also be divided into two types – Diffuse or Specular.

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  • What is the difference between Specac’s standard and higher extinction ratio (HER) polarizers?

      The difference is in the amount of aluminium wire deposited on the surface of the substrate. The higher extinction ratio (HER) polarizers have more material, which is equivalent to increasing the thickness of the wires.

      In the case of free standing wire grids, we define the distance between the centrelines of the wires as ‘a‘ and the diameter or width of the wires as ‘d‘. As the ratio d/a increases the transmission of light through the polarizer decreases and begins to approximate a flat mirror. The transmission of light polarized parallel to the wires is affected by a greater amount, so the result is a higher overall extinction ratio. The light polarized perpendicular to the wires is affected only slightly, so the trade off between extinction ratio and overall transmittance is a good one.

      In the case of holographic wire grid polarizers, we cannot control the thickness of the ‘wires’ with the same precision, but we can still achieve a similar effect by increasing the amount of material deposited when the grid is laid on the substrate.

      Approximate difference in extinction ratio between standard (bold line) and HER (dotted line) holographic IR polarizers.

  • What is the difference between the Power and Autotouch presses?

      The Atlas Power 8T, Power 15T and Power 25T presses offer a load range capability of 1 to 8 tons, 2 to 15 tons and 3 to 25 tons respectively. 

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  • What is transmission spectroscopy?

      Light from a source passes through a sample to be registered by a detector. The method of analysis is based upon the absorption of the infrared beam by a sample at specific wavelengths or frequencies of light.

      A sample presented to the infrared beam in this configuration will produce an infrared spectrum unique to the sample itself. In this way, infrared spectroscopy is used as a qualitative measurement of a sample.

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  • What kind of measurements can I make with the High Temperature High Pressure Cell?

      The High Temperature High Pressure Cell (HTHP Cell) P/N 5850 has the capability of being operated at temperatures approaching 800C and pressures up to 1000psi.

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  • What pathlength gas cell do I need for my sample?

      Below is a table of typical Mid IR absorbence unit values for certain gases that have been expressed as concentration units of ppm per meter. All the gases have been measured in a one meter pathlength gas cell at 25C temperature and made up to 1 atmosphere pressure with a nitrogen gas mix. The absorbence value given for the concentration of gas is expected at the indicated wavenumber position.

      Gas speciesFormulaBand position (cm-1)PPM/meterAbsorbance
      Carbon dioxideCO223601000.40
      Carbon monoxideCO21701000.04
      MethaneCH430201000.10
      C2 to C6 n-alkanes29601000.10
      Nitrogen dioxideNO216301000.15
      Nitric oxideNO19001000.015
      Sulfur dioxideSO213701000.09
      Hydrogen sulfideH2S130010000.002
      AmmoniaNH39601000.12
      Hydrogen chlorideHCl29401000.04
      WaterH2O165010000.20
      Vinyl chlorideCH2CHCl950, 9001000.06
      AcetaldehydeCH3CHO27501000.015
      BenzeneC6H6670100.09
      TolueneC6H5CH3730, 6901000.10
      MethanolCH3OH10401000.10
      EthanolCH3CH2OH10501000.05
      Carbonyl sulfideCOS20701000.40
      Nitrous oxideN2O22351000.15
      Sulfur hexafluorideSF6950100.40

      The table of values indicates that typically for 100ppm of carbon dioxide gas, a gas cell at 1 meter pathlength will give an absorbance value of 0.4 absorbance units at 2360cm-1. For a 10 meter pathlength cell, a 100ppm per meter concentration would measure 4 absorbance units. Therefore you can “trade” the pathlength advantage for sensitivity, so a 10 meter pathlength cell with carbon dioxide gas measuring 0.4 absorbance units at 2360cm-1 would be equivalent to 10ppm per meter of gas.

      The other gas examples can be dealt with in exactly the same way. In comparison, carbon monoxide is ten times less sensitive than carbon dioxide to measure with an equivalent cell.

      For low ppm measurements you need a long pathlength gas cell and also, very importantly, a fast responding, sensitive detector such as a liquid nitrogen MCT detection system to discriminate for the weak signals from certain gas concentrations.

  • What samples can I analyze using a DC3?

      The DC3 diamond compression cell P/N GS02555 enables samples to be compressed to an ideal thickness for transmission experiments.

      The DC3 is for use with small compressible samples. It is not suitable for crushing large samples such as whole polymer pellets. These should be pre-crushed in a die, or a small fragment should be cut off prior to compression between the DC3 diamond windows. The DC3 should also not be used for crushing or compressing extremely hard samples. Care should be taken that the sample does not contain any hard particles (for example, some sand) that could cause failure of the thin diamond windows through “point” loading.

      The DC3, because of its small size and shape can also be used with Infrared Microscopes, where the large aperture allows for more than one sample to be loaded and compressed at one time. Each individual sample could then be selectively moved into the light beam from the IR microscope, saving on the time needed to mount and prepare each sample between analyses.

  • When to use a torque wrench for the Golden Gate

      On the Golden Gate™ ATR accessory a solid sample is bought into contact with the ATR crystal by pressure on the sample via an anvil.

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  • Which hydraulic press is best for my application?

      Specac makes a variety of Atlas hydraulic presses for a wide range of pressing applications.

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  • Which spectrometers are your accessories compatible with?