On-line monitoring of Soxhlet extraction by chromatography and mass spectrometry to reveal temporal extract profiles.

Soxhlet extraction is a popular sample preparation technique used in chemical analysis. It enables liberation of molecules embedded in complex matrices (for example, plant tissues, foodstuffs). In most protocols, samples are analyzed after the extraction process is complete. However, in order to optimize extraction conditions and enable comparisons between different types of extraction, it would be desirable to monitor it in real time. The main development of this work is the design and construction of the interface between Soxhlet extractor and GC-MS as well as ESI-MS system. The temporal extract profiles, obtained in the course of real-time GC-MS monitoring, have been fitted with mathematical functions to analyze extraction kinetics of different analytes. For example, the mass transfer coefficients of pinene, limonene and terpinene in lemon sample, estimated using the first-order kinetic model, are 0.540h(-1), 0.507h(-1) and 0.722h(-1), respectively. On the other hand, the Peleg model provides the following extraction rates of pinene, limonene and terpinene: 0.370nMh(-1), 0.216nMh(-1) and 0.596nMh(-1), respectively. The results suggest that both first-order kinetic and Peleg equations can be used to describe the progress of Soxhlet extraction. On-line monitoring of Soxhlet extraction reveals extractability of various analytes present in natural samples (plant tissue), and can potentially facilitate optimization of the extraction process.