NanoSIMS Imaging of D/H Ratios on FIB Sections.
Anal Chem
; 91(21): 13763-13771, 2019 11 05.
Article
em En
| MEDLINE
| ID: mdl-31549804
ABSTRACT
The D/H ratio imaging of weakly hydrated minerals prepared as focused ion beam (FIB) sections is developed in order to combine isotopic imaging by nanoscale secondary ion mass spectrometry (NanoSIMS) of micrometer-sized grains with other nanoscale imaging techniques, such as transmission electron microscopy. In order to maximize the accuracy, sensitivity, precision, and reproducibility of D/H ratios at the micrometer size, while minimizing the surface contamination at the same time, we explored all instrumental parameters known to influence the measurement of D/H ratios in situ. Optimal conditions were found to be obtained with the use of (i) a Cs+ ion source and detection of H- and D- at low mass resolving power, (ii) a primary beam intensity of 100 pA, and (iii) raster sizes in the range of 8-15 µm. Nominally anhydrous minerals were used to evaluate the detection limits and indicate a surface contamination level of â¼200 ppm equivalent H2O under these conditions. With the high primary intensity used here, the dwell time is not a parameter as critical as found in previous studies and a dwell time of 1 ms/px is used to minimize dynamic contamination during analysis. Analysis of FIB sections was found to reduce significantly static contamination due to sample preparation and improved accuracy compared to using polished sections embedded not only in epoxy but in indium as well. On amphiboles, the typical overall uncertainty including reproducibility is â¼20 on bulk FIB sections and â¼50 at the 1.5 µm scale using image processing (1σ).
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Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Anal Chem
Ano de publicação:
2019
Tipo de documento:
Article