Average mass scan of the total ion chromatogram versus percentage chemical composition in multivariate statistical comparison of complex volatile mixtures

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Abstract

The analysis of complex volatile mixtures by gas chromatography-mass spectrometry (GC-MS) is a time-consuming process. It involves separation and identification of the components based on their retention times and fragmentation patterns, followed by determination of their relative percentages from integration of their peak areas. Herein we show that multivariate statistical analysis of the relative abundances of the m/z values obtained from the average mass scans (AMS) of the complex mixture is a faster and potentially more reliable method of assessing these mixtures. To achieve this, 15 model complex mixtures, were prepared comprising varying amounts of 10 different constituents. The AMS profile and chemical composition of each mixture were compared to one another using agglomerative hierarchical cluster analysis and principal component analysis. The results obtained strongly suggest that multivariate statistical analysis of AMS profiles is a promising, time saving and reliable tool for analyzing complex volatile mixtures, in particular essential oils.

Translated abstract

A análise de misturas voláteis complexas usando cromatografia gasosa-espectrometria de massa (CG-EM) é um processo demorado. Este processo envolve a separação e identificação de componentes baseados em seus tempos de retenção e padrões de fragmentação, seguido da determinação de suas porcentagens relativas a partir da integração das áreas dos picos. No presente trabalho mostramos que análise estatística multi-variada das abundâncias relativas dos valores m/z obtidos a partir das varreduras médias de massa (VMM) da mistura complexa é um método mais rápido e potencialmente mais confiável de avaliação destas misturas. Foram preparadas 15 misturas modelo complexas contendo quantidades variadas de 10 constituintes diferentes. O perfil VMM e a composição química de cada mistura foram comparados uns aos outros utilizando análise de cluster hierárquica aglomerante e análise de componentes principais. Os resultados obtidos indicam fortemente que análise estatística multi-variada dos perfis VMM é uma ferramenta promissora, eficiente e confiável para analisar misturas voláteis complexas, em particular óleos essenciais.

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Accelerated proteolysis in alternating electric fields for peptide mapping.

Sheng WANG, Huimin Bao, Ting Ting Liu … (2008)

Sinusoidal alternating voltages (typically 5 V) were employed to enhance the efficiency of proteolysis for peptide mapping in this work. Protein solutions containing trypsin were allowed to digest with the assistance of alternating electric fields (AEFs) between a pair of platinum wire electrodes in Eppendorf tubes. The feasibility and performance of the novel proteolysis approach were investigated by the digestion of several standard proteins. It was demonstrated that AEFs significantly accelerated in-solution proteolysis and the digestion time was substantially reduced to 5 min. The digests were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) with sequence coverages that were comparable to those obtained by using conventional 12-h in-solution proteolysis. The suitability of AEF-assisted proteolysis to real protein samples was demonstrated by digesting and identifying human serum albumin in gel separated from human serum by sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE). The present proteolysis strategy is simple and efficient and will find a wide range of applications in protein identification.