PIXE Analysis of Lake Sediment, as a Complementary Technique for ICP Analysis

An ion beam analysis method has been developed to non-destructively measure elemental concentrations in sediments. Particle-Induced X-ray Emission (PIXE) spectrometry was used to quantitatively determine the concentrations of minor and trace elements in a series of different types of lacustrine sediments from W. Michigan and aeolian dust samples from California, as well as NIST Standard Reference Material sediments. A number of these sediments were also analyzed by inductively-coupled plasma–atomic emission spectrometry (ICP-AES) using standard (EPA reference method) protocols. Analytical results for splits of the same samples evaluated by both techniques initially appeared quite different: to reconcile this apparent discrepancy, a mass balance study was conducted using PIXE measurements of bulk sediments, their residues after acid digestion, and measurements of the eluent by ICP-AES. Interpretation of combined data from both techniques helped resolve mass closure issues likely related to sample preparation, matrix effects, and detection limits.

An exciting feature of the ion beam analysis method is that it can be performed on dried solid sediment samples, both before and after acid extraction processes. The difference in the elemental concentrations before and after acid digestion occurs can be used to determine the fraction of each element eluted. Since the fraction of metals eluted during digestion depends strongly on the geological matrix of the sediment, this ion beam analysis method is an excellent complementary technique for routine environmental analyses of sediments via acid digestion. Data will be presented that show the strong matrix dependence of the eluted metals extracted from a variety of lake sediments.