Automated high-throughput Raman detection of fluidic samples: measurement setup and methods preventing air bubble interference.

Raman spectroscopy has widely been recognized as an analytical tool of high potential in biopharmaceutical downstream processing, and the use of flow cells has been suggested for use in in situ or in-line Raman spectroscopy measurements at least for development-scale processes. However, there remains a need for Raman analysis of samples that cannot be accessed through an in-line monitoring system, particularly for low-volume samples in micro-to-milliliter range. This article presents a new setup that enables automated Raman measurements of liquid samples with low injection volume of 300 µL. A designed adapter links a Tornado Micro Flow Cell to a Tecan liquid handling system, allowing direct sample delivery. This work focuses on a set of methods implemented on this setup to address the issue of air bubbles, which can significantly interfere with Raman signal quality during measurement. These methods include adapted residence time, a three-step purging/cleaning method, combined with a vertical and upflow flow-cell orientation. A series of experiments demonstrates the effectiveness of these methods in reducing air bubbles and improving spectral robustness. The presented setup and methods enable automated high-throughput Raman detection of fluidic samples with small injection volumes and high-quality spectral data.