Probe Selection for Time-gated Raman Measurements

The PicoRaman M3 spectrometer enables the use of a wide variety of first- and third-party probes. This includes probes that are compatible with sample enclosures, probes for immersion measurements, adapters that enable microscope measurements, and many others. This text goes through some of the options that are offered by Timegate Instruments and when a user may want to choose a certain option.

Solid and powder samples, sample vials and sampling enclosures

Eye safety is an important factor when considering time-gated Raman measurements. Sample enclosures are often used with Raman techniques to minimize ambient light interference. Ambient light is not a significant interference source with time-gated Raman and sample enclosures are mainly used for eye safety and sampling purposes.

Timegate offers a SampleCube enclosure that has a closing door, and it also rotates the sample while moving the inserted probe back and forth (vertical probe position) for representative surface sampling. The surface scanning speed and the scanned area can be adjusted.

The SampleCube is compatible with B&W Tek BAC100 probes and other probes with similar dimensions and it is well suited for non-contact measurements of e.g., leveled powder samples or liquids in vials (horizontal probe position). This measurement option is versatile and has been used for e.g., pharmaceutical, mineral, ionic liquid, and catalyst-related applications.

Placing the probe in the vertical position enables representative surface sampling from powder and solid samples.

The horizontal probe position enables eye-safe measurements from vials and cuvettes.

The B&W Tek BAC100 probes come with a front spacer piece that also enables contact measurements where the tip of the probe (attached spacer piece) is pressed against the sample.

Attaching a spacer piece to the BAC100 probe's shaft enables contact measurements. Laser safety precautions should be followed.

Watch the SampleCube demonstration video:

Microscope measurements

In many applications, the user needs to focus on certain small surface areas or particles. This can be achieved by connecting a PicoRaman M3 spectrometer to a microscope using a Microprobe adapter. The adapter supports Olympus BX, CX, and MX series upright microscopes.

PicoRaman M3 spectrometer connected to an Olympus microscope using a Microprobe adapter.

Focusing the measurements is done using the microscope’s own controls and when the image is focused, the measurement will be carried out on the in-focus measurement spot. A reticle helps the user to further assess the size and location of the measurement spot. The Microprobe adapters include an integrated camera, and the image can be studied using the microscope’s eyepieces or by looking at the camera feed which also enables easy recording of the visual findings.

The measurement’s spot size and magnification depend on the utilized microscope objectives. The spot size range is roughly 210 µm – 21 µm with magnifications of 10X – 100X. This measurement option has been used for a variety of different use cases including mining, mineral, and polymer-related applications.

The integrated USB camera enables easy image recording through the MicroProbe adapter. The figure shows the laser illumination of a sample.

Watch the Microprobe demonstration video:

Immersion and cell culture measurements

Timegate Instruments offers a ProbePro family for a wide variety of measurement needs including slurry, liquid, and cell culture measurements. The ProbePro probes include detachable and replaceable shafts, and the shafts can be changed to match the application no matter if the measured material is an abrasive mineral slurry, a cell culture media solution, or something else. The ProbePro Mini probes are compatible with SCHOTT ViewPort^® solutions that enable easy and sterile sensor integration to bioreactors.

ProbePro Mini attached to a PicoRaman M3 spectrometer.

The ProbePro Mini probes used in combination with SCHOTT ViewPort^® variants enable the adjustment of the working distance (distance between the front window and focus point from where most of the data is collected). Optimal working distance depends on the optical properties of the measured material and an adjustable working distance enables optimal data collection efficiency from different types of liquids, slurries, gels, and bioreactor applications. Generally speaking, optimal results are achieved when the working distance is short for opaque and dark samples as the material may absorb and block light that travels longer distances within the material. Longer working distances may be used with transparent materials, and the results are often better when the whole measurement spot is slightly deeper within a see-through material.

Another interface option is SCHOTT ViewCell™ which allows the user to easily measure liquids that are pumped through the ViewCell™. As with the ViewPort^® variants, a ProbePro Mini probe is placed inside the ViewCell™ for measurements.

Tubing can be connected to a SCHOTT ViewCell™ and liquid sample material can then be measured while it is moving through the ViewCell™.

SCHOTT ViewCell™ interface.

Watch the PicoRaman M3 spectrometer and ProbePro Mini demonstration video:

Author

This blog was written by Timegate Instruments’ Senior Application Specialist Bryan Heilala. Bryan is a young and energetic chemist with a degree in M.Sc. (chemistry) and experience and background in analytical chemistry. Read more about him and the whole Timegate team.