Leaching of loosely bound elements during wet grain size separation with sodium hexametaphosphate: implications for selective extraction analysis
Bibliographic record
Abstract
Sodium hexametaphosphate, Na 6 (PO 3 ) 6 , is often used as a dispersant in wet grain size separation procedures to obtain the clay-sized (<0.002 mm) fraction of till and soil samples. However, the complexing properties of this reagent can lead to a loss of elements through chemical leaching during the separation process. This work examines potential losses of Cr, Zn, Fe, Mn, Ni, Sb, and Hg from glacial sediment (till) to dispersant solution. Compared to dissolution by conventional aqua regia digestion, these losses are insignificant at <0.3%. However, if the elements in a loosely bound form are under study using selective or sequential leaches, then the losses can be viewed as substantial. Sodium hexametaphosphate solution, used as dispersant at a strength of 0.5%, was found to dissolve as much as 68% of the Hg in a bulk till sample (<4 mm) that would be brought into solution by a 1 M sodium acetate extractant at pH 5, designed to dissolve the adsorbed/exchangeable/carbonate phase of a geological sample. Up to 10% of the Hg and 7% of the Cr leached from the clay-sized fraction by 1 M NaOAc could have been lost to the Na 6 (PO 3 ) 6 dispersant during the clay-sized separation. Consequently, the concentrations of labile or weakly bound forms of elements reported in a sequential extraction scheme could be reduced because of a loss to the Na 6 (PO 3 ) 6 dispersant.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".