Browsing by Author "De Jongh, Tara"

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    Fluorescence detection of trace aluminium using a sequential injection analyser
    (Stellenbosch : Stellenbosch University, 2022-12) De Jongh, Tara; Roychoudhury, Alakendra N.; Samanta, Saumik; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Analytical instruments are either expensive to operate, prone to interferences, require a separate offline preconcentration step, or are not suitable for use onboard a ship when measuring dissolved Aluminium (Ald; < 0.2 µm fraction) in seawater. Thus far, Ald measurements have been performed most commonly using flow injection analysis (FIA), as it combines preconcentration, fluorometry and spectroscopy in a single manifold. Despite FIA’s compact and comprehensive design, the manifold has several drawbacks, including its laminar flow regime and the peristaltic pump, which causes tube stretching and generates measurement drift. As a result of these limitations, a third-generation flow analyser was developed, known as a miniaturized two-line sequential injection analyser (miniSIA-2). The miniSIA-2 incorporates similar design features to that of FIA, however, it operates on a bidirectional flow regime, enabling reverse fluid flow and encourages turbulence to allow complete sample and reagents reaction, while reducing the reagent consumption and waste generation. Thus far, the miniSIA- 2 has only been used to measure trace concentrations of Zinc (Zn) (Grand et al., 2011; Grand et al., 2016) and Iron (Fe) (Oliveira et al., 2015; Hatta et al., 2018) in seawater. This project therefore involves a novel and systematic approach to measuring Ald in seawater through fluorescence detection by an advanced miniSIA-2 manifold of Grand et al., (2016). The systematic approach involved integrating the experimental procedures outlined by Hatta et al., (2018) and the experimental protocols of Grand et al., (2011 & 2016) first and second design of Znd for measurements of Ald. This led to a method approach initiated with optimizing the batch method, followed by the Stop in Holding coil (SHC) procedure and finally incorporating a Solid Phase extraction (SPE) step with the SHC to ensure a fully automated instrument for measuring Ald in seawater. However, this project focused on developing and applying the well- established batch method from Hydes & Liss, (1976). The method details the development of a two-step method. Initially, a basic analytical setup was established by systematically adjusting parameters to achieve measurements at relatively higher Ald concentrations. During this step, a limit of detection (LOD = 9 nM) was achieved. The above-mentioned analytical setup was then used to achieve instrumental detection limits similar to the lowest Ald concentrations measured in global oceans (0.1 nM). In this second instant a lower LOD (7 nM) was achieved, however, the improvement was much less than the initial aim. This was the result of the instruments fluctuating baseline values, high Relative Standard Deviation (RSD), and the manifold’s inability to self-regulate internal temperatures during analysis time causing a weak peak configuration that resembled that of photobleaching and quenching.