Application of Laser Ablation Inductively Coupled Plasma−Mass Spectrometry in Dendrochemical Analysis

The potential of laser ablation sampling (LAS) in conjunction with inductively coupled plasma−mass spectrometry (ICP−MS) for multi-element analysis of tree rings in Acer pseudoplatanus L. (sycamore) growing in urban U.K. is evaluated. Annual growth increments in xylem tissue are readily observed. Individual rings formed between 1975 and 1992 were sampled and analyzed by ICP−MS after LAS or after conventional nitric acid digestion. To correct for differences in ablation, 13 C was used as in internal standard. Significant linear relationships were found for Pb, Mg, and Mn concentrations recorded after acid digestion and values determined by LAS. Lead in xylem declined steadily after 1975 until the late 1980s, clearly reflecting a reduction in lead deposition in urban U.K. during this period. Using acid digestion, Cd was detected only in a tree close to a Cu−Cd refinery; concentrations generally remained steady in this tree through the study period. A similar response was found in this tree with LAS. Cadmium was also detected in one of the two other trees 6 km from the refinery using LAS, but at much lower concentrations. Distribution of Mg and Mn within tree rings differed between trees; more likely reflecting differences in soil chemistry rather than atmospheric deposition. The results indicate that LAS coupled with ICP−MS can be used directly to determine changes in xylem chemistry, which reflect changes in exposure to metal deposition or changes in soil chemistry. This provides a repeatable, non-destructive sensitive method for determining many elements in wood, with high spatial resolution.