An Energy-dispersive Miniprobe Multielement Analyzer (EMMA) for direct analysis of Pb and other trace elements in peats

Abstract

An Energy-dispersive Miniprobe Multielement Analyzer (EMMA) was designed and constructed for sensitive, rapid, and non-destructive analysis of trace elements (As, Cr, Cu, Fe, Ga, Ge, Hf, Mn, Ni, Pb, Rb, Se, Sr, Th, Y, U, Zn) in small (e.g. 50 μm) samples such as individual mineral grains from rocks. An alternative configuration of the EMMA instrument is described here for use with larger samples such as powders of coal, soil, sediments, and plant materials. To minimize heterogeneity problems, a larger X-ray beam size (0.1 × 6 mm) was used by installing a different collimator, and the sample holder rotated 25 times per minute. Using this approach, Rb, Sr, Cu, Zn and Pb were measured in peat samples collected from bogs in Switzerland and northern Scotland. The detection limit for Pb, for example, is approximately 0.3 μg/g which is one order of magnitude better than conventional XRF analyzers. For comparison, Pb was also measured in acid digests of the same samples using GFAAS. The Pb results obtained using EMMA are comparable to the GFAAS data for the continental peat samples. However, in the Cl-rich samples from the maritime bogs, the GFAAS signal was strongly suppressed, and an accurate comparison of the two methods was not possible. The EMMA technique, therefore, has three advantages over conventional GFAAS: first, no sample dissolution is required; second, several elements of interest are determined simultaneously; and third, the EMMA technique is not subject to matrix interferences.