Post-optimization of Py-GC/MS data: A case study using a new digital chemical noise reduction filter (NOISERA) to enhance the data quality utilizing OpenChrom mass spectrometric software

摘要

Noise is a known drawback in the mass spectrometric analysis of chromatographic data. Different tech-niques exist to avoid or to remove noise before and after data acquisition. Noise occurs in two different types, electronic and chemical. The former can be lowered by applying smoothing filters. The latter needs more sophisticated methods since the distinction between chemical noise and real chromato-graphic data is not straightforward. Several approaches have been published with different scopes and algorithms. This work describes a new algorithm (NOISERA - Noise Reduction Algorithm) for a dynamic reduction of chemical noise in mass spectrometric, chromatographic data of nominal mass resolution. It offers an approach to detect and to reduce chemical noise with a minimum of required user interaction and adjustments. Due to the assumption, that chemical noise varies in its intensity and is dependent of the time, the algorithm tries to calculate and reduce noise locally along the retention time axis. Electronic noise will not be covered by the presented algorithm. It can be reduced by applying further filters, since OpenChrom provides methods for smoothing.The presented algorithm NOISERA is capable of reducing noise with minimal user interaction. It combines existing ideas and extends them to achieve a parameter-free chemical noise detection and reduction. NOISERA improves the signal-to-noise ratio of peaks, but as a drawback of all chemical noise filters, it tends to remove either too much, respectively, not enough data from chromatograms than necessary. That is why the algorithm should not be used without supervision of an analyst. The noise reduction filter NOISERA is available as a plug-in for OpenChrom and is released under the Eclipse Pub-lic License 1.0 (EPL). OpenChrom is available free of charge at http://www.openchrom.net. The noise reduction algorithm NOISERA is included in the latest OpenChrom release.