Determination of 27 metals in HISS-1, MESS-4 and PACS-3 marine sediment certified reference materials by the BCR sequential extraction.

The BCR sequential extraction procedure developed by the European Community Bureau of Reference was applied to the three marine sediment certified reference materials (CRMs). These CRMs are designated as HISS-1, MESS-4, and PACS-3 and comprise respectively pristine, moderately-contaminated, and highly-contaminated sediments, respectively. The study aimed to provide values of extractable elements in reference materials of varied geological origin to support method development and quality control efforts. Concentrations of 27 elements extracted in the three sequential extraction steps and in the residue were determined. The extraction steps consisted of: Step 1 - acetic acid extraction (targeting the exchangeable, water- and acid-soluble fraction); Step 2 - hydroxylammonium chloride extraction (targeting the reducible fraction); and Step 3 - hydrogen peroxide extraction (targeting the oxidizable fraction). The results from two independent laboratories using the sequential extraction procedure for the 27 elements were combined using the DerSimonian-Laird method of analysis implemented in the NIST Consensus Builder software. The percent recovery (sum steps vs total metal content) of 27 elements ranged from 68% to 125% in HISS-1, 76%-119% in MESS-4, and 70%-125% in PACS-3, based on the certified values. The combined uncertainty (k = 2) was from 1% to 39% for HISS-1, 3%-45% for MESS-4, and 3%-21% for PACS-3. Comparing the three extraction steps, the uncertainty of Step 3 was the highest for all the three CRMs. The agglomerate sediments in MESS-4 resulted in high uncertainty when compared to HISS-1 and PACS-3. The method validation showed the BCR sequential extraction procedure can apply to other elements including As, Co, Li, Mn, and V.

Direct mineralogical imaging of economic ore and rock samples with multi-modal nonlinear optical microscopy.

Multi-modal nonlinear optical (NLO) microscopy, including stimulated Raman scattering (SRS) and second harmonic generation (SHG), was used to directly image mineralogical features of economic ore and rock samples. In SRS/SHG imaging, ore samples generally require minimal preparation and may be rapidly imaged, even in their wet state. 3D structural details, at submicron resolution, are revealed tens of microns deep within samples. Standard mineral imaging based on scanning electron microscopy (SEM), with elemental analysis via energy dispersive X-Ray spectroscopy, was used to independently validate the mineral composition of the samples. Spatially-resolved SRS from dominant Raman-resonant bands precisely maps the locations of specific minerals contained within the samples. SHG imaging reveals locally non-centrosymmetric structures, such as quartz grains. Competing absorption and nonlinear scattering processes, however, can reduce contrast in SRS imaging. Importantly, the correlation between standard electron microscopy and multi-modal NLO optical microscopy shows that the latter offers rapid image contrast based on the mineral content of the sample.