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Unique Beamsplitter Exchange Unit for a Research Grade Vacuum FT-IR Spectrometer

Allows automatic spectral range extension for the well-established VERTEX 80v under vacuum condition

View on VERTEX 80v equipped with automatic beamsplitter exchange option BMS-c.

View on the open automatic beamsplitter exchange unit BMS-c.

Three different beamsplitter background single beam spectra measured with the Platinum Diamond micro-ATR in the mid IR, far IR and THz spectral ranges.

Lactose Monohydrate measured with Platinum Diamond micro-ATR in the complete mid IR, far IR and THz spectral range from 4,000cm-1 (ca. 120THz) to 10cm-1 (ca. 0.3THz).

Bruker Optics is very proud to offer a new and unique automatic beamsplitter exchange unit BMS-c (fig.1) for its VERTEX 80v top-of the line bench-top vacuum FT-IR spectrometer. Its outstanding functionality enables the exchange of up to four different types of beamsplitter under vacuum conditions. With this new option for the high end research and development VERTEX 80v spectrometer, Bruker Optics now offers the real successor to the very famous IFS 113v FT-IR spectrometer which started the Bruker FT-IR product line in 1974 and also incorporated an automatic beamsplitter changer.

Additional value of an automatic beamsplitter exchange unit
Since the introduction of FT-IR spectroscopy, it is very well accepted by the research community that a spectrometer based on a vacuum optics bench provides IR spectra which are free of residual H2O- and CO2- absorption bands, which may mask very weak spectral features of the measured sample. Such residual absorptions of the laboratory room air are typically visible under purge conditions (for more details see Bruker Optics “Vacuum” product note T18-02/08).

Measurements of a sample in the complete IR or THz spectral range require different types of beamsplitter which makes it necessary to vent and re-evacuate the spectrometer optics bench for exchange of the beamsplitter. The new automatic beamsplitter exchange unit is particularly useful for more demanding applications such as working with liquid helium cooled cryostats or investigating samples which may change over time. Besides the shortened measurement time an additional benefit is the stable measurement condition and hence optimum spectral quality resulting from the permanently evacuated optics bench. The functionality outline of the new BMS-c unit is listed in Tab.I.

Tab. I: Functionality of the new BMS-c unit

  • Easy extension of spectral range
  • Use of up to 4 different beamsplitters
  • Shortened measurement times
  • Stable measurement conditions because optics is kept evacuated
  • No re-evacuating after beamsplitter exchange neccessary
  • Easy access to the terahertz spectral range
  • No interferences from atmospheric absorptions like water vapor and carbon dioxide

Operation of the BMS-c unit
Via the OPUS interface for measurement parameter settings, the desired type of beamsplitter can be selected. The used setup consisted of three installed beamsplitter which were the far IR / THz Mylar-BMS with 50μm thickness (T205/8) and the far IR multilayer Mylar BMS (T222/8) as well as the standard mid IR KBr beamsplitter (T304/8). The three beamsplitter have been used to acquire the spectra in the complete far and mid IR spectral ranges from 10cm-1 up to 4,000cm-1 without the need of venting and re-evacuation the spectrometer optics bench for BMS exchange. Both internal DTGS detectors equipped with KBr and PE windows as well as the standard internal IR source and the externally connected water cooled FIR/THz Mercury arc source have been permanently mounted and remotely selected. The related single beam spectra are shown in figure 3.

Measurement result
In order to demonstrate the performance of the new BMS-c unit the pharmaceutical filler lactose monohydrate has been measured in the spectral range from 4,000cm-1 down to the far IR/THz spectral range at 10cm-1(ca. 0.3THz) using the Platinum Diamond Micro-ATR unit (A225/Q). The long wavelength THz spectral range (1 THz = 33.3 cm-1) is increasingly important for polymorph characterization in the pharmaceutical industry. Instead of using traditional KBr and Polyethylene pellets, the applied ATR technique avoids time consuming sample preparation. Fig. 4 shows the merged measurement result which was acquired using three different set-ups of the optical components (sources, detectors and beamsplitters) without the need of venting and re-evacuation the spectrometer optics bench for BMS exchange. The excellent spectral matching for the used three different beamsplitter in connection with the new BMS-c unit is apparent.

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