COMPARISON OF ACCURACY, PRECISION, AND SENSITIVITY IN ELEMENTAL ASSAYS OF FISH OTOLITHS USING THE ELECTRON-MICROPROBE, PROTON-INDUCED X-RAY-EMISSION, AND LASER-ABLATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The elemental composition of fish otoliths is of considerable interest to those who wish to reconstruct temperature, migration, or environme ntal histories of individual fish based on assays of the otolith growt h sequence. However, reported differences in otolith elemental composi tion among studies may be due in part to performance differences among four of the most popular instruments for targeted elemental analysis: wavelength-dispersive electron microprobe (WD-EM), energy-dispersive electron microprobe (ED-EM), proton-induced X-ray emission (PIXE), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS ). To rigorously compare the sensitivity, accuracy, and precision of t hese four analytical tools, the International Otolith Composition Expe riment distributed blind-labelled real and artificial otoliths of know n but varied elemental composition to eight laboratories for assay of 10 selected elements. No one instrument type was sensitive to each ele ment, nor was any one instrument preferred for use in all assays. In g eneral however, abundant elements such as Na and K could only be measu red accurately with an electron microprobe, while the trace elements r equired PIXE or LA-ICPMS. Strontium could be measured with considerabl e accuracy and precision by WD-EM, PIXE, and LA-ICPMS. The presence of significant, and occasionally large, differences among laboratories s uggests that comparisons among published studies should be made cautio usly and only after appropriate calibration.