Development and Study of the Microfluidic Open Interface Coupled with Solid-phase Microextraction for Rapid Analysis
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Analytical chemistry mainly aims to identify and quantify analytes in matrices of interest. Analytical chemistry is an indispensable part of chemistry (and other scientific fields) because identification and quantification rely on repeatable and accurate measurements. Today's gold-standard systems for trace analysis are mainly chromatographic systems (liquid chromatography or gas chromatography) coupled to mass spectrometry. These methods attained the gold-standard status because of the overall method sensitivity and selectivity abilities. However, the main weakness of these systems is that they often require extensive sample preparation to reach outstanding performance regarding selectivity and sensitivity. Nevertheless, the chromatography step can be lengthy when selectivity is needed. Mass spectrometry has improved over the years, encouraging researchers to introduce samples directly to mass spectrometry, thus circumventing chromatographic separation. This field became known as direct-to-mass spectrometry. One of the main aims of this field is to avoid lengthy chromatography time and practically have real-time monitoring or high-throughput/rapid analysis of analytes at trace levels with little or no (laborious) sample preparation. However, these approaches serve only as the first line of study (rapid screening step), after which positive samples are submitted for thorough analysis using a gold-standard method. One of the main disadvantages of direct-to-mass spectrometry analysis is susceptibility to matrix effects (due to lack of separation), which internal standards can somewhat mitigate. Another disadvantage is instrument contamination resulting from inadequate or no sample preparation that is sacrificed for the overall rapid analysis. The most suitable sample preparation for direct-to-mass spectrometry analysis is solid-phase microextraction. It is a method developed to perform sampling and sample preparation in a single cohesive step. One of the advantages of this method is the non-exhaustive enrichment. The main advantages of this sample preparation method include using matrix-compatible coating, which offers analyte enrichment with minimal or no matrix interference co-enrichment. Additionally, the open-bed enrichment of solid-phase microextraction offers avenues for high-throughput sample preparation steps that minimize the overall analytical workflow time. When such analysis is used for the direct-to-mass spectrometry analysis, the general analytical workflow time is reduced by avoiding chromatography. Solid-phase microextraction has been coupled directly to mass spectrometry in many ways. One of the ways solid-phase microextraction can be coupled directly to the mass spectrometry is via a microfluidic open interface. The microfluidic open interface system coupled to mass spectrometry comprises a suction component (created by the ionization source of a mass spectrometer), an inflow component (pumping system), and a desorption chamber. All three components connect to a three-way chromatographic tee. The main requirement is that the suction component is constant. The liquid level in the desorption chamber can be introduced to the mass spectrometer by changing the inflow. Solid-phase microextraction devices (after the enrichment step) are then introduced to the very low-volume desorption chamber for analysis. The inflow stops after a short desorption time (e.g., 5 s). The suction component aspirates the volume of the desorption chamber, thus injecting the solution into the mass spectrometer for the analysis. The main highlights of the microfluidic open interface coupled to a mass spectrometer are desorption in a flow-isolated system and desorption into a low volume, which provides a tall Gaussian peak. The overall objective of this thesis is to redesign the microfluidic open interface system to demonstrate automation of the analysis workflow and make it suitable for rapid analysis. Firstly, Chapter 2 identifies the disadvantages of the existing microfluidic open interface system, which are used to improve the next design. The new system contains commonly available material to make the system approachable. Additionally, all system components are automated (by writing a homemade program from scratch), reducing the error from the manual operation. Nevertheless, this chapter depicts how the solid-phase microextraction coating design is essential for optimal desorption and analysis sensitivity. Chapter 3 expands on the fundamental idea raised towards the end of Chapter 2 by quantifying the mass transfer resistance in separation media. The effect of sorbent in matrix-compatible binders is crucial to understand for some applications. The extraction (or the desorption) of analytes will be controlled by the effective diffusion coefficient in the coating rather than at the interface or boundary layer, as it was a most common assumption before. The following two chapters, Chapter 4 and Chapter 5, contain applications that utilize the two designs of the microfluidic open interface for the analysis of immunosuppressive drugs and fentanyl analytes from the whole blood, respectively. For both works, the sample preparation is done in a high-throughput fashion. After the analysis with a microfluidic open interface, the overall method times (per sample) are substantially lower than gold-standard methods reported in the literature while maintaining similar detection and quantification limits compared to state-of-the-art reported methods. Therefore, solidphase microextraction coupled directly to mass spectrometry via a microfluidic open interface offers a suitable replacement for a gold-standard method. Chapter 6 contains an alternative and simplified use of the microfluidic open interface coupled to the homemade ultraviolet-visible light detection system. Finally, Chapter 7 encompasses the main findings and offers a future perspective on using solid-phase microextraction with a microfluidic open interface coupled directly to mass spectrometry or an alternative detector, such as ultraviolet-visible light detection.
Cite this version of the work
Emir Nazdrajic (2022). Development and Study of the Microfluidic Open Interface Coupled with Solid-phase Microextraction for Rapid Analysis. UWSpace. http://hdl.handle.net/10012/18835