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W. Nischkauer, C. Herwig, F. Vanhaecke, A. Limbeck:
"Dried-droplet Laser-Ablation in combination with ICP-OES and ICP-MS for the determination of major and minor elements in heavily matrix-loaded fermentation media";
Poster: 2014 Winter Conference on Plasma Spectrochemistry, Amelia Island, Florida, US; 06.01.2014 - 11.01.2014; in: "2014 Winter Conference Program and Abstracts", (2014), ISSN: 0161-6951; 145 S.

The determination of the elemental composition in fermentation media used for bioprocesses in bioreactors (e.g., based on yeast as host) is of major interest for economic media development and to monitor and correspondingly adjust the availability of nutrients during the process. Apart from these tasks, experimental investigations aiming at understanding limitations in biomass production as a function of nutrient shortage also require reliable determination of nutrients.
From the analytical viewpoint, elemental analysis in these media is not overly challenging, only the presence of sugars and other organic constituents as well as the rather high concentrations of some mineral elements (e.g., Na, Ca, K) require adequate dilution and acidification of the samples, the application of internal standards and the use of matrix-matched standards in external calibration. Although being well-established, these procedures are labor-intensive and time-consuming.
Fermentation samples taken from bioreactors are not stable since micro-organisms are still present, which calls for immediate analysis. Also, accurate sample dilution and the addition of internal standards can only be performed by trained personnel and in many cases, these operations cannot be accomplished on-site. Therefore, alternatives for improved sample stabilization and sample transport are required which allow for straight-forward sample collection, storage and analysis.
The investigation of dried sample droplets via an appropriate solid-sampling technique can meet these requirements and Laser Ablation (LA) offers the possibility of repeated analysis of a single sample (provided that the analyte distribution is homogeneous), as well as high sample throughput. Moreover, the amount of sample introduced into the ICP can be adjusted by choosing adequate Laser parameters. Sample stability of dried droplets is excellent, and sample preparation can be accomplished in an uncomplicated manner. LA ICP-MS has been previously deployed for the elemental analysis of dried droplets of, e.g., urine or drinking water and was used in this contribution for obtaining deeper insight into sample preparation by studying the spatial distribution of analytes within the dried sample residues.
Besides ICP-MS, we also studied the performance of ICP-OES in combination with LA for dried sample residues from a biochemical reactor. Although ICP-OES is more limited in terms of sensitivity, spectral interferences only play a minor role.
In this contribution, we will compare the performance of different sample preparation approaches (application of samples on cellulose filters vs. on polymer targets) as well as different strategies for internal standardization and calibration in terms of analytical performance (reproducibility, trueness, sensitivity) and in terms of ease of operation.

Dried droplet analysis, LA-ICP-OES/MS, fermentation media