Energy Dispersive X-Ray Fluorescence Methodology And Analysis Of Suspended Particulate Matter In Seawater For Trace Element Compositions And An Intercomparison With High-Resolution Inductively Coupled Plasma-Mass Spectrometry

A modification of energy dispersive X-ray fluorescence (ED-XRF) for analysis of trace element concentrations in suspended particulate matter (SPM) in seawater and intercomparison with high-resolution inductively coupled plasma-mass spectrometry (HR ICP-MS) is presented. Approximately 250 SPM samples were collected on polycarbonate track-etched filters in the Indian Ocean during the U.S. CLIVAR/CO2 Repeat Hydrography meridional section I09N cruise in 2007. Samples were first analyzed by ED-XRF, a nondestructive technique, for Al, P, Ti, Mn, Fe, Ni, Cu, and Zn and subsequently digested and quantified by HR ICP-MS, creating two blind, basin-scale data sets used for a paired statistical comparison. Our results found (1) ED-XRF analysis using thin-film principles can quantify the elemental composition of SPM at nanomolar concentrations found in the open ocean; (2) there was excellent agreement between ED-XRF and HR ICP-MS analyses for Al, Fe, and Mn and good agreement for P and Ti; (3) analytical differences were the largest for Cu, Ni, and Zn; (4) HR ICP-MS methods have lower detection limits for most elements when compared to the ED-XRF; (5) ED-XRF analysis has a closer agreement to reported values for the NIST SRM 2783 standard and lower relative standard deviations when compared to the HR ICP-MS. We recommend continued refinement of nondestructive ED-XRF methods as this would allow for the easy exchange of filtered samples between lab groups for intercalibration and intercomparison of basin-scale hydrographic cruises and archival for future analysis.