Dry Ashing
Definition
Viscera or hair is dried and incinerated in a muffle furnace at 450 to 550 degrees Celsius. Inorganic ash is dissolved in dilute HNO3 for instrumental analysis. Simple and clean for Pb and stable metals, but loses Hg entirely and partially loses As, so unsuitable for those analytes.
- Process
- Thermal decomposition in a muffle furnace until white mineral ash remains, then dissolved in dilute acid.
- Temperature range
- 450 to 550 degrees Celsius
- Works well for
- Lead and stable metals
- Not suitable for
- Mercury (lost entirely) and arsenic (partially lost)
Common questions
What temperature is used in dry ashing?+
Dry ashing uses a muffle furnace heated between 450 to 550 degrees Celsius. The sample is incinerated at this temperature until only white mineral ash remains.
Why would a forensic chemist choose dry ashing over other methods?+
Dry ashing is simple and clean for analyzing lead and stable metals. However, it completely loses mercury and partially loses arsenic, so it is unsuitable if those elements are the target analytes.
What happens to the ash after incineration?+
The inorganic ash remaining after incineration is dissolved in dilute nitric acid (HNO3) for instrumental analysis.
Related terms
- Wet Digestion
- Viscera is digested with HNO3 + H2SO4 + HClO4 (or HNO3 + H2O2) at controlled temperature. Closed-vessel microwave-assisted digestion in Teflon bombs...
- Acid Blank
- A parallel digestion of reagents in an empty vessel, subtracted from the sample to correct for trace metal contamination in the acids.
- Arsenic (As)
- Metalloid; trivalent arsenite (As III) is 60 times more toxic than pentavalent arsenate (As V). Thiol-group blocker that poisons mitochondrial enzymes (pyruvate...
- Ashing Aid
- A salt (typically magnesium nitrate) added before dry ashing to fix volatile elements as less volatile salts that survive the furnace.
- Hydride Generation (HG-AAS)
- Sensitivity booster for As, Sb and Se. Sample plus NaBH4 in acid liberates AsH3 / SbH3 / SeH2 gas, which is swept...
- Lead (Pb)
- Cumulative neurotoxin from chronic occupational exposure (battery recycling, smelter work), leaded paint, contaminated cosmetics (low-grade sindoor, surma, kohl), and adulterated Ayurvedic preparations....
- Marsh Test (1836)
- Confirmatory test for arsenic devised by James Marsh after the Bodle case (1832), in which Marsh was unable to convince a jury...
- Matrix Destruction
- Breakdown of organic tissue into water, CO2 and mineral residue so bound metals are released as free ions. Without it, AAS reads...
- Mercury (Hg)
- Three toxic forms: elemental (vapour from broken thermometers, dental amalgam), inorganic salts (mercuric chloride, corrosive sublimate), and organic (methylmercury from biomagnification, ethylmercury...
- Microwave-Assisted Digestion
- Closed-vessel digestion in PTFE or quartz bombs at 1200 to 1800 W, reaching 200 degrees Celsius and 1500 psi in 30 to...
- Reinsch Test
- Classical screen for arsenic, antimony, mercury and bismuth. A clean copper strip is immersed in the acidified sample (concentrated HCl, near-boiling) for...
- Thallium (Tl)
- The 'poisoner's poison' because thallium sulphate is tasteless, odourless and colourless. Substitutes for potassium in cellular transport. Alopecia at 2 to 3...
Explained in these topics
- Dry Ashing and Wet Digestion for Metallic PoisonsThermal decomposition in a muffle furnace at 450 to 550 degrees Celsius until only white mineral ash remains, then dissolved in dilute acid.
- Metallic Poisons: Arsenic, Mercury, Lead and ThalliumViscera or hair is dried and incinerated in a muffle furnace at 450 to 550 degrees Celsius. Inorganic ash is dissolved in dilute HNO3 for instrumental analysis...