Filters/filtering metabolite detection

Zhang, H., Ray, K., Ma, L., Zhang, D., Drexler, D., and Sanders, M. (2005a). Applicability of mass defect filters (MDF) to drug metabolite detection in biological matrices. In Proceedings of the 53rd ASMS Conference on Mass Spectrometry and Allied Topics, San Antonio, TX. 

Zhang, H. et al., Mass defect profiles of biological matrices and the general applicability of mass defect filtering for metabolite detection, Rapid Commun. Mass Spectrom., 22(13), 2082, 2008. 

Several MS acquisition and data processing strategies are used for detection and structure elucidation of metabolites. The common metabolite detection strategies are summarized in Section 9.2.1, which include full MS scan, constant neutral loss, parent ion scan, multiple reactions monitoring, and mass defect filtering. The structure elucidation strategies feature product ion scan, multistage scan, and accurate mass measurement, which are reviewed in Section 9.2.2. 

Two of the most widely used and detected UV filters in the environment and WWTPs are BP3 and 4-MBC. Thus, they were the selected compounds to study individually their degradation by fungi [44, 49]. Studies with BP1, not only a BP3 metabolite but also an industrial UV filter (but its use in cosmetics is not allowed) itself have also been performed. Studies in liquid media allow a better analysis and monitoring of many parameters, both the contaminant concentration and the fungal metabolic state such as glucose consumption and enzyme production. In these studies, the degradation process was performed with the fungus in form of pellets. 

Dobutamine hydrochloride may be determined in plasma levels, after extraction, on a C18 reversed-phase column eluted with 22% aceto-nitrile-78% 0.1 M phosphate buffer (pH 2.0) at 2 ml/minute. The drug and its metabolite are detected by a fluorescent detector with an excitation wavelength of 195 nm and a 330 nm emission cut off filter. The retention times of dobutamine and the 3-methoxy metabolite are 5.2 and 7.9 min., respectively. The lower limit of sensitivity is 10 ng/ml. Reproducibility is 5% over a 25-300 ng/ml range. Nylidrin is used as an internal standard (6). 

Detection and characterization of metabolites in biological matrices using mass defect filtering of liquid chromatography/high resolution mass spectrometry data. Drug Metab. Dispos. 2006, 34, 1722. 

The idea of back transformation of a three-dimensional NMR experiment involving heteronuclear 3H/X/Y out-and-back coherence transfer can in principle be carried to the extreme by fixing the mixing time in both indirect domains. Even if one-dimensional experiments of this kind fall short of providing any information on heteronuclear chemical shifts, they may still serve to obtain isotope-filtered 3H NMR spectra. A potential application of this technique is the detection of appropriately labelled metabolites in metabolism studies, and a one dimensional variant of the double INEPT 111/X/Y sequence has in fact been applied to pharmacokinetics studies of doubly 13C, 15N labelled metabolites.46 Even if the pulse scheme relied exclusively on phase-cycling for coherence selection, a suppression of matrix signals by a factor of 104 proved feasible, and it is easily conceivable that the performance can still be improved by the application of pulsed field gradients. 

Exact mass filter exclusion based on the decimal places of a parent dmg, is a post processing filter which allows complete removal of unexpected entities (ions) which do not agree with the criteria preset by the user. Such a filter is fully adjustable once the samples have been processed. This process can dramatically reduce the number of ions in the analyte sample by filtering out the vast majority of matrix-related ions. This will also allow use of very low threshold values to detect low-level metabolites without having to go through the very tedious and long task of manual exclusion of false positives. Typically, extracted ion chromatogram windows of 0.1 mDa allow the... 

Zhu, M., Ma, L., Zhang, H., and Humphreys, W. G. (2007). Detection and structural characterization of glutathione-trapped reactive metabolites using hquid chromatography-high-resolution mass spectrometry and mass defect filtering. Anal. Chem. 79 8333-8341. 

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