IR liquid transmission accessory — The Pearl

The Pearl™ from Specac is a novel liquid transmission accessory that has been developed especially for laboratory spectroscopic sample analysis in the mid-and near-infrared. The accessory consists of Specac’s innovative Oyster Cell assembly, which keeps the sample in a horizontal plane.

The design of the Pearl™ and Oyster Cell enables the quick and simple application of the sample, and for cleaning between samples with great benefits to sample throughput.

Key Features of the Pearl liquid transmission accessory

Highly Reproducible Pathlength

  • Pathlength reproducibility while assembling and disassembling a single Oyster Cell is within the range of 1 μm.
  •  Pathlengths can be altered in seconds by altering the bottom window.

Spacer-Free, Defined Pathlength Liquid Transmission Cell

  • ZnSe or CaF2 windows
  • Wedged or parallel window options with pathlengths ranging from 25 to 1000 μm

Handles Viscous Materials with Ease

  • There is no better choice than the Pearl for viscous samples. Poor pathlength reproducibility, which is common to demountable cells, has been removed as a result of the innovative design.
  • Effortless cleaning between samples also makes this an ideal choice for anyone tackling huge volumes of samples.

Interchangeable FTIR Transmission Windows

The Pearl™ has been equipped with an Oyster Cell consisting of either ZnSe or CaF2 windows, which can be exchanged in just a few seconds. Such Oyster Cells come in six pathlengths, 25, 50, 100, 200, 500 and 1,000 μm. Pathlengths can be altered by exchanging the bottom window for the pathlength needed.

Repeatable Pathlength

The Pearl™ has been developed to offer a highly precise pathlength that cannot be achieved while dismantling and reassembling a conventional liquid transmission accessory, with pathlengths repeatable to considerably less than 1μm as a result of the innovative Oyster Cell.

Wedged or Parallel Window Options

The Oyster Cells bottom window could be provided as either parallel or wedged (concerning the top window).

Parallel cells provide the potential to evaluate the real pathlength of the cell with the help of the interference fringing technique, even though they can lead to the appearance of a sinusoidal wave fringing pattern in users’ spectra when the refractive index of the material between the windows is diverse between sample and background spectra.

Parallel cells function well when examining an analyte dissolved in a solvent where a background spectrum could be achieved using the neat solvent.

Wedged cells greatly decrease the fringing pattern enabling better quality spectra to be achieved when the refractive index of background and sample needs to be different, such as when examining neat samples that necessitate an empty cell background.

As far as wedged cells are concerned, the company provides a heptane pathlength calibration tool to offer an approximation of the cell's pathlength.

Furthermore, the intensity of the interference fringing pattern is based upon the refractive index, having greater refractive index materials leading to a more pronounced pattern in users’ data. CaF2 wedged cells provide the biggest spectral quality (in regards to fringing), even though its spectral window is below ZnSe.

Window Specifications and Chemical Compatibility

Source: Specac Ltd

Material Range (cm-1) Refractive index
ZnSe 20,000 to 500 2.41
CaF2 50,000-1,180 1.31


ZnSe seems to be incompatible with acids and strong bases (suggested range pH 5.0–9.0). CaF2 is usually resistant to acids, water and bases — though it is slightly soluble in nitric acid and responds with sulfuric acid to form hydrofluoric acid.

The cell itself is built of corrosion-resistant stainless steel. Yet, this could be harmed on exposure to strong acids and bases or extended exposure to weak ones. It is always better to verify the compatibility of users’ samples and the cell materials before use.

Benefits of the Pearl over other Liquid Transmission Cells

The simple nature of the Oyster Cell enables rapid and simple cleaning, thereby increasing sample throughput. With a traditional cell, the pathlength alters every time it is dismantled and reassembled. The innovative design of the Oyster Cell eliminates these changes.

Improper assembly, or over pressurization resulting from injecting a sample into the cell, can cause a leakage in the traditional cell. This has been eliminated with the horizontal design of the Pearl and Oyster Cell system. To obtain a high throughput analysis of liquid samples, there is no better choice.

For highly viscous samples that should be loaded into a disassembled cell, pathlength reproducibility is impossible with a conventional cell. With the Oyster Cell, however, this issue is a thing of the past, as pathlengths can be reproduced every time the Oyster Cell is assembled. The Oyster also features an injection port to provide the utmost versatility for volatile samples.

Compatible with Measurement Standards

Source: Specac Ltd

Method Number
Determination of fatty acid methyl ester (FAME) content in middle distillates. Infrared spectrometry method (Click Here for Our App Note) EN 14078
In-Service Oil Condition Monitoring standard practice ASTM D7418
Phosphate Antiwear Additives in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis ASTM D7412
Monitoring of Oxidation in In-Service Petroleum and Hydrocarbon Based Lubricants ASTM D7414
Sulfate By-Products in In-Service Petroleum and Hydrocarbon Based Lubricants ASTM D7415
Nitration in In-Service Petroleum and Hydrocarbon Based Lubricants ASTM D7624
Standard Practice for Condition Monitoring of In-Service Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry ASTM E2412


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The Pearl by Specac

The Pearl in Aqua
The Pearl in Black
The Pearl in Green
The Pearl in Orange
The Pearl in Purple
The Pearl in Red
The Pearl in Yellow

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