Flow Injection Inductively Coupled Plasma-Mass Spectrometry With Ultrasonic Nebulizer for the Quantification of Trace Elements in Seawater: An Innovative Method Targeting Cadmium, Cobalt, Lead, Manganese, Molybdenum, Tin, Uranium, and Vanadium

Abstract

The accurate determination of trace elements in seawater is essential for environmental monitoring and the study of oceanic biogeochemical processes. However, traditional analytical techniques often face limitations due to the ultra-trace concentrations of metals and the high salinity of seawater, which introduces significant matrix effects. In this study, a novel flow injection-inductively coupled plasma mass spectrometry (FI-ICP-MS) method coupled with an ultrasonic nebulizer was developed and optimized for the direct quantification of cadmium, cobalt, lead, manganese, molybdenum, tin, uranium, and vanadium in seawater samples. The method was optimized by evaluating the effects of eluent concentration (0.05-0.20% HNO3, with 0.05% selected as the minimum effective value to ensure analyte stability, prevent precipitation, and minimize salt-related stress on the FI system), flow rate (0.4-1.0 mL/min), and sodium chloride matrix composition, ensuring minimal spectral interferences while maintaining high sensitivity. The selected operating conditions (0.05% HNO3 eluent at 0.70 mL/min with 103Rhodium and 193Iridium as internal standards) provided a robust analytical performance with low procedural limits of detection and quantification (ranging from 0.003 to 0.2 µg/L for LoDs and from 0.01 to 0.7 µg/L for LoQs) and excellent instrumental repeatability (1.2%-6.6%). The overall method was validated using the IAEA-443 seawater certified reference material, yielding recoveries between 104%-118% and procedural reproducibility ranging from 3.8% to 15%. The optimized FI-ICP-MS method was applied to real seawater samples collected from two distinct Mediterranean transects: offshore Livorno, a site influenced by intense maritime and industrial activities, and Montecristo Island, a protected marine reserve with minimal anthropogenic impact. Results indicated no significant differences in trace metal concentrations between the two areas, suggesting that natural geochemical processes predominantly regulate elemental distributions. Most elements followed a conservative vertical distribution, with localized anomalies observed for manganese and cadmium. Furthermore, all measured cadmium and lead concentrations were well below the regulatory thresholds set by Directive 2013/39/EU, confirming compliance with environmental quality standards.

Keywords: direct analysis; flow injection ICP‐MS; seawater; trace elements.

FIGURE 1

Schematic representation of the fluidic connections to the 6‐port Rheodyne PEEK valve in its two operational positions (load position and inject position). Dashed lines indicate internal connections within the valve, while solid lines represent external fluidic pathways. The coil represents the injection loop, which is internally mounted between Ports 3 and 6.

FIGURE 2

Schematic representation of the fluidic connections to the DEX MXP9900‐000 2‐position/6‐port PEEK switching valve in its two operational positions (Positions 1 and 2). Dashed lines represent internal connections within the valve, while solid lines indicate external fluidic pathways.

FIGURE 3

Sampling location areas.

FIGURE 4

Effect of flow rate on peak area (left), peak height (center), and FWHM (right) for a 200 µL injection of 0.2 µg/L U in 0.20% HNO₃ carrier stream.

FIGURE 5

Effect of NaCl concentration on peak area (left), peak height (center), and FWHM (right) for a 200 µL injection of 0.1 µg/L U in 0.05% HNO₃ carrier stream at 0.70 mL/min.

FIGURE 6

Surface‐to‐Deep (S/D) ratios of average concentrations for the eight target elements: Livorno samples (green) and Montecristo samples (yellow).