Analytische Chemie
Filtern
Dokumenttyp
- Vortrag (1)
- Posterpräsentation (1)
Referierte Publikation
- nein (2)
Schlagworte
- PAT (2) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
Raman spectroscopy is becoming a powerful process analytical technology (PAT) tool. Until now Raman technology has not shown its full potential in bioprocess on-line monitoring due to several technical challenges. Because of only small? interference from water molecules, Raman-spectroscopy is in contrast to IR spectroscopy able to follow changes of metabolite concentrations in dilute aqueous solutions. Results from common CCD-based process Raman-spectrometers reveal only barely identifiable peaks with a dominating (fluorescence) background. To solve this, Raman spectroscopy needs: (A) an enhancement to increase the limit of detection (LOD), and (B) a reliable method to distinguish the Raman signal from the sample-related auto-fluorescence.
SERS (surface enhanced Raman spectroscopy) acts as an optical "nano-antenna"-effect. It causes a dipolar localized surface Plasmon resonance effect due to noble metallic nanoparticles or roughened metal and improves the limit of detection (LOD) significantly. Another new process-monitoring technique, which removes the fluorescence background in Raman-measurements is called time-gated Raman spectroscopy. It uses a picosecond pulsed Nd:YVO4-laser as emission source (exc= 532 nm) and a gated SPAD-array (Single Photon Avalanche Detector) detector instead of commonly used CCD (Charged Coupled Device)-detectors and CW (Continues Wave) laser emission. Time-Gate can measure the Raman-signal before the stronger fluorescence signal reaches the detector.
In this study we utilized both SERS (Surface Enhanced Raman Spectroscopy) and time-gated Raman spectroscopy (TG-Raman) in combination on cell-free supernatant samples of an Escherichia coli cultivation with mineral salt media and a lactic acid bacteria fermentation with complex media. As a reference method for the estimation of amino acids and other metabolites, HPLC-RID and HPLC-FLD were used to evaluate the Raman-based detection. The quantitative evaluation of Raman data was performed by multivariate data analysis such as principal component analysis (PCA) and partial least squares regression (PLSR). For the first time, we can show that both qualitative and quantitative measurements are conducted successfully with both, SERS and time-gated Raman methods in industrially relevant media, so that a fast and reliable in situ or bypassed concentration measurement becomes feasible.
Intensified continuous processes are in focus of current research. Compared to traditional batch processes, intensified continuous production allows the synthesis of new and difficult producible compounds with better product uniformity and reduced consumption of raw materials and energy. Flexible (modular) chemical plants can produce various products using the same equipment with short down-times between campaigns, and quick introduction of new products to the market. Consequently, the demand for powerful Process Analytical Technologies, which can monitor key variables like component concentrations in real-time, is increasing. Low-Field NMR spectroscopy presents itself as such an upcoming smart sensor1,2 (as addressed, e.g., in the CONSENS project3,4).
Continuous measurement approaches can usually be differed in On- or In-line which both have advantages and drawbacks. On the one hand On-line measurements are easy to integrate even in existing setups through bypass systems, on the other hand issues like the representativity of the sampling must be considered. In the case of Inline analysis, where the whole fluid stream is analyzed, this issue can be avoided. Nevertheless, homogeneity of the mixture must be assured using NMR spectroscopy.
This talk shall give a brief summary of current Online and Inline Low-Field NMR approaches. Furthermore, current research results using a tailor-made flow cell for inline analysis are shown pointing out the working range as well as limitations of these method in combination with NMR spectroscopy.