Bachelor of Environmental Science (Honours)
School of Earth & Environmental Sciences
King, Joshua J., Ultra-trace determination of aluminium and gallium in marine waters, Bachelor of Environmental Science (Honours), School of Earth & Environmental Sciences, University of Wollongong, 2013.
A rapid and simple analytical procedure was developed for the determination of aluminium and gallium at ultra-trace concentrations in marine waters. Pre-concentration and matrix removal was achieved via Solid Phase Extraction (SPE), using the Chelex-100 ion exchange resin. Extraction conditions such as sample and column pH (pH 5.5 ± 0.1), sample flow rate (4.00 mL.min-1), as well as the column rinsing solution (1.0 M ammonium acetate) were optimised to ensure quantitative recovery, while minimising sample preparation times.
Quantification was conducted using an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) equipped with a collision/reaction cell. Instrumental conditions were optimised specifically for aluminium and gallium detection. Optimisation of the hydrogen and helium collision/reaction cell flow rates enabled polyatomic and doubly charged interferences to be minimised, allowing for accurate quantification at the ng.L-1 level of aluminium in hydrogen or helium cell gas modes, and gallium in hydrogen or no gas modes.
The newly developed SPE method was applied to a number of coastal marine samples collected off the coast of Sydney, New South Wales. Dissolved aluminium concentrations ranged from 1.2 μg.L-1 in the Port Hacking estuary, to 7.3 μg.L-1 in Botany Bay. Dissolved gallium concentrations shared a similar trend to aluminium concentrations with the lowest concentrations found in the Port Hacking estuary (1.3 ng.L-1), increasing in both Sydney Harbour and up to a maximum of 110 ng.L-1 in Botany Bay. All samples contained dissolved aluminium concentrations above the current ANZECC marine Environmental Concern Level (ECL) of 0.5 μg.L-1.
The method detection limits for aluminium (10 ng.L-1) and gallium (0.1 ng.L-1) are sufficiently low, and the method itself is simple and fast enough to be applied in routine water quality monitoring programs to determine dissolved aluminium at and below the current ANZECC marine Environmental Concern Level (ECL) of 0.5 μg.L-1, as well as dissolved gallium concentrations at and below the current ANZECC freshwater ECL for gallium of 18 μg.L-1 (used in place of a marine ECL due to lack of data).