| Abstract |
The use of Inductively Coupled Plasma – Mass Spectrometry (ICP – MS) in the analysis of metal content, in a wide range of different samples and matrices, is both widespread and well-known for decades. In cases of suspensions containing relatively low particle concentrations (~106 particles/ml), single particles can be detected as a result of the system’s capability for very short reading time per datapoint. This parameter is called dwell time, and the technique is also known in the literature as single particle Inductively Coupled Plasma – Mass Spectrometry (sp – ICP – MS). The following thesis is a presentation of the further development of a method for studying the presence and fate of metal – containing nanoparticles in seawater samples. This approach was subsequently applied on samples acquired for the needs of two different studies: First, from a mesocosm experiment in 2019, as part of a larger experiment taking place in Cretacosmos, the Greek branch of Aquacosm (EU network of mesocosms facilities). And second, from Santorini island, as part of a program investigating the occurrence and nature of nanoparticles in the proximity of islands (NanoIsland, ELIDEK) during different times throughout the year. For the needs of these analyses, in addition to the inductively coupled plasma mass spectrometry system, and the application of the single particle detection technique, an on-line dilution system was also incorporated. For the mesocosm experiment two different types of samples have been investigated, spiked with low ppt concentrations of Ag nanoparticles and ionic Ag respectively. Also, two different dwell times have been used, and three different threshold criteria for the identification of particles have been applied. For the analysis of samples from seawater tanks spiked with Ag nanoparticles, analyzed using 10 ms dwell time, the μ + 3std threshold criterion proved suitable. ‘’μ’’ stands for the average intensity value and std for the standard deviation of the dataset, after a process that is well documented in literature. For the analysis of samples from seawater tanks spiked with Ag nanoparticles, analyzed using 75 μs dwell time, a different kind of threshold has been proven more reliable. It is equal to 𝜇 + 2.71 + 3.29 ∗ √𝜇, where ‘’μ’’ stands for the mean intensity of the dataset, as it was mentioned before. For the analysis of samples from seawater tanks spiked with Ionic Ag, analyzed using 10 ms dwell time, both the μ + 3std and μ + 5std threshold criteria performed similarly well. And finally, for the analysis of samples from seawater tanks spiked with Ionic Ag, analyzed using 75 μs dwell time, the μ + 5std threshold proved sufficient. During the analysis of the samples from the ionic Ag spiked tanks, pulse events usually associated with particles were observed, whose nature and origin are addressed. Regarding the NanoIsland samples, an investigation of temporal and spatial variations has been conducted, focusing on the occurrence and Cu content of Cu containing nanoparticles. The data processing of these samples incorporated a developing, python – based coding script, specifically made for the needs of this project. The processing revealed generally higher particle concentration in sites associated with boats activity during the Chronakis Michail Ioannis Master’s Degree Thesis 2 summer period. Also, particles with higher Cu content were generally found in deeper waters, while there have been indications about their precipitation, beginning around the same period as the high particle concentrations observed. Finally, the system itself also exhibited sufficient ruggedness and the capability of continuous analysis for more than 10 hours of continuous operation, for a number of months, without significant equipment downtime, despite the aggressive seawater matrix.
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