Mitigating Volatile Element Loss During ICP, AAS Sample Preparation.

In trace element analysis, inaccurate results for Hg, As, Se, Sb, and B are frequently attributable to analyte loss during sample preparation rather than instrumental error.
These elements form volatile species and are readily lost if digestion protocols are not appropriately controlled.

Elements of concern and loss mechanisms:
1. Mercury: Volatilizes above 60°C and adsorbs to polymeric containers.
2. Arsenic, selenium, antimony: Lost as volatile chlorides during open-vessel acid digestion above 90°C.
3. Boron: Lost as BF₃ during HF digestion unless complexed.
4. Cadmium, lead, zinc: Subject to volatilisation during high-temperature ashing above 400°C.

Common points of failure in laboratory workflows:
– Open-vessel hotplate digestion with evaporation to dryness
– Fuming of HF without the addition of complexing agents
– Dry ashing or loss-on-ignition procedures at elevated temperature
– Inappropriate storage conditions leading to adsorption or precipitation

Controls implemented in high-performing laboratories:
1. Closed-vessel microwave digestion: Prevents evaporative loss and is the preferred method for Hg, As, Se, and Sb.
2. Elimination of dry-down steps: Digests are cooled and diluted to volume without evaporation.
3. Chemical stabilisation: Use of 1% HCl with gold for Hg; 2–5% HCl for As, Sb, and Se; mannitol or boric acid for B following HF digestion.
4. Container selection: Glass or FEP for mercury; acidified HDPE for As, Se, and Sb.
5. Appropriate detection systems: Cold vapour for Hg and hydride generation for As/Se/Sb, as conventional ICP nebulization is insufficient at trace levels.

Quality indicators of volatile loss:
Consistent recovery of base metals, combined with low recovery of Hg, As, or Se in certified reference materials, indicates a preparation issue. Similarly, agreement between XRF, AAS, and ICP for non-volatiles, but divergence for volatiles, is diagnostic.

Summary: For volatile elements, containment and chemistry take precedence over temperature. Once an analyte is lost to the fumehood, it cannot be quantified.