Capturing Solid-Phase Extraction Concepts by the Naked Eye: An Undergraduate Laboratory Experiment

Abstract

Solid-phase extraction (SPE) is a widely used sample treatment method for extraction, preconcentration, and cleanup of liquid samples, based on similar principles of chromatographic methods. In this experiment, we propose the use of food dyes to assist the acquisition of the main theoretical and practical aspects of SPE. Various experiments were implemented in a laboratory session to teach the concepts and techniques of cartridge conditioning, sample load, and sample elution, together with key concepts such as breakthrough volume and recovery rates. The use of food dyes represents a straightforward approach that fostered the acquisition of the basic principles of SPE in particular and chromatographic methods in general. Simple spectrophotometric measurements allowed the rapid calculation of recovery rates and the visualization of breakthrough volume curves. Among the concepts addressed and put into practice in this laboratory session are (i) describe the principles and experimental setup of SPE as applied to analyte extraction, preconcentration, and purification; (ii) apply chromatographic concepts such as retention and elution in the context of SPE; (iii) identify potential analyte losses during sample preparation and propose strategies to minimize them; (iv) interpret breakthrough volume curves to assess cartridge performance; (v) perform quantitative analysis and calculate recovery rates using UV–vis spectrophotometric data. The main innovation of this study lies in its emphasis on enhancing students’ understanding of the theoretical principles underlying each stage of the SPE technique, unlike most published studies, which focus on explaining the fundamentals of column liquid chromatography. This was achieved through the use of the intrinsic color properties of the analytes as a visual and didactic tool. At the same time, the study also connects laboratory-based experiments with real-world applications, emphasizing the practical relevance of the technique.