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Question

I am using the RapID RAMAN and to read KRAFT paper bag together with a transparent plastic bag the system indicates a low value of r, my question is, what should the parameters be to be able to read this type of container?

Mike Picollelli · Accepted Answer

We have a lot of success measuring materials through kraft paper (brown paper bags). The challenge with this packaging is the strong fluorescence background signal from the paper. To be successful with this packaging we often have to reduce the zero measurement conditions so the fluorescence background interference is not saturating the detector. At the same time we need optimum signal to noise spectra from both the zero and offset measurements. Here are some recommended measurement parameters that may help. These settings can be changed in the Edit Settings field. Zero measurement: Laser Power - 100% (initial setting) Exposure Time – 0.1 s (initial setting, the software will probably suggest shorter exposure time dependent on fluorescence intensity) Min and Max measurement times: set each to 1 s Note that the software will continue to suggest reducing exposure times to attenuate fluorescence until the shortest possible exposure time is reached. If the zero spectrum fluorescence is still saturating the detector at this point, the software will begin suggesting attenuating laser power to some values less than 100% until the detector is no longer saturated. Offset Measurement Laser Power – 100% Exposure Time – 0.1 s (initial settings) Min and Max measurement times: set each to 20 s Note in general, we haven’t seen a fluorescence saturation problem on the Offset measurement like we can see in the Zero measurement (described above). Check the SORS spectrum with these initial conditions. If the resulting spectrum has low S/N and an intensity less than 6000 counts, increase the Offset measurement times by 5 seconds at a time to optimize the SORS spectrum. If after 30 to 40 seconds, the resulting spectrum quality is still insufficient, then increase the Offset exposure time to 0.2 s. We generally recommend most measurements take less than 45 seconds to accomplish, if possible. The exposure time can be increased, generally up to 0.5 s with Offset measurement times in the 30 to 40 s range. The spectra can be processed with either the spline, polynomial, or iterative spline background correction to give the optimum SORS spectrum. The user can reprocess model spectra to see which of these gives more consistent results. The Pearson correlation threshold we typically suggest is 0.95. But we have seen customers reduce this to as low as 0.90 if required for difficult paper sack libraries / models. Finally, we have had models successful with up to triple layer brown paper sacks. But when the container is thicker than that, the useful signal is attenuated too much to be used. For example, fiber drum barrels or cardboard boxes are too thick to be used with SORS. In those cases it is necessary to open the container and measure through the clear plastic liner.

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