Towards a More Reliable Identification of Isomeric Metabolites Using Pattern Guided Retention Validation

Reliable analyte identification is critical in metabolomics experiments to ensure proper interpretation of data. Due to chemical similarity of metabolites (as isobars and isomers) identification by mass spectrometry or chromatography alone can be difficult. Here we show that isomeric compounds are quite common in the metabolic space as given in common metabolite databases. Further, we show that retention information can shift dramatically between different experiments decreasing the value of external or even in-house compound databases. As a consequence the retention information in compound databases should be updated regularly, to allow a reliable identification. To do so we present a feasible and budget conscious method to guarantee updates of retention information on a regular basis using well designed compound mixtures. For this we combine compounds in “Ident-Mixes”, showing a way to distinctly identify chemically similar compounds through combinatorics and principle of exclusion. We illustrate the feasibility of this approach by comparing Gas chromatography (GC)–columns with identical properties from three different vendors and by creating a compound database from measuring these mixtures by Liquid chromatography–mass spectrometry (LC–MS). The results show the high influence of used materials on retention behavior and the ability of our approach to generate high quality identifications in a short time.

FEASIBILITY STUDY ON THE DEVELOPMENT OF REFERENCE MATERIAL OF PESTICIDE IN BLACK TEA

In this paper, a study on development of reference material (RM) for α-endosulfan and bifenthrin in black tea as a matrix is reported. The study was conducted on the basis that such RMs was presently not available in Indonesia. To obtain a good and proper RM, a feasibility study of RM development is extremely required. The RM was firstly prepared by grinding the tea leaf to have particle size of about 150-106 μm and water content of about 5.99%. A small portion of the grinded tea leaf was then spiked with hexane solution containing both target analytes at certain concentrations, followed by a proper drying to obtain initial candidate of RM (iCRM). The iCRM was then well-mixed properly with another portion of non-spiked grinded tea material to get final candidate reference material (fCRM) powder. A gas chromatography equipped with electron capture detector was used for analyte identification and the feasibility of the method was evaluated in term of spiking technique and homogenization process. The evaluation by ANOVA showed that fCRM was statistically considered to be homogeneous and having α-endosulfan and bifentrin mass fraction ± U of 380.32 (±120.32) ng.g-1 and 522.74 (±148.65) ng.g-1 in dry weight basis, respectively.