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

Abstract

The elemental composition of fish otoliths is of considerable interest to those who wish to reconstruct temperature, migration, or environmental histories of individual fish based on assays of the otolith growth sequence. However, reported differences in otolith elemental composition 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 these four analytical tools, the International Otolith Composition Experiment distributed blind-labelled real and artificial otoliths of known but varied elemental composition to eight laboratories for assay of 10 selected elements. No one instrument type was sensitive to each element, nor was any one instrument preferred for use in all assays. In general however, abundant elements such as Na and K could only be measured accurately with an electron microprobe, while the trace elements required PIXE or LA-ICPMS. Strontium could be measured with considerable accuracy and precision by WD-EM, PIXE, and LA-ICPMS. The presence of significant, and occasionally large, differences among laboratories suggests that comparisons among published studies should be made cautiously and only after appropriate calibration.

Using otolith microchemistry to distinguish Atlantic salmon (Salmo salar) parr from different natal streams

“…Accuracy of LA-ICP-MS data is largely unknown; however, Sr and Ba can be accurately determined in otoliths by this method (Campana et al, 1997). This is likely owing to the fact that Ca is used as an internal standard and Sr and Ba are substituting for Ca in the otolith matrix.…”

Are there habitat salinity markers of the Sr:Ca ratio in the otolith of wild diadromous fishes? A literature survey

“…Similarly, Secor and Rooker (2000) once reported a significant difference (P \ 0.01) in Sr:Ca 9 1,000 among fish taxa collected from three different salinity regimes: freshwater 0.9, estuarine 2.3 and marine 3.4. The results of both Secor and Rooker (2000) and ours suggest that Sr:Ca 9 1,000 among fishes from freshwater, brackish and sea habitats must be a significant difference, although Sr:Ca ratio studies to date have been conducted separately by different authors even using different analytical methods with known differences in performance from each other (Campana et al 1997;Pontual and Geffen 2004). Noteworthily, the summarized Sr:Ca ratio results by Secor and Rooker (2000) were much lower than ours.…”

Stable Isotopic and Trace Elemental Compositions of Otoliths and the Stock Structure of Pacific Cod, Gadus macrocephalus

“…Due to the results from comparison of several elemental analytical methods (Campana et al 1997) we used a wet chemical method for analyzing trace elemental concentrations. A whole otolith piece (corresponding to the other piece of an otolith pair used for stable isotope analysis) was cleaned by 10% HCL for about 10 -15 s. According to their weights, sample powders were digested in 5 or 9 ml of 5% (v/v) HCL for 90 min.…”