Laboratory ashing dishes: how can loss on ignition and ash content be determined?

Indispensable in gravimetric analysis, incineration dishes deliver clean, controlled ashing to determine loss on ignition (LOI), ash content or sulphated ash. Designed for muffle furnaces, they are available in porcelain, silica/quartz or platinum to cover a range of temperature and chemical reactivity requirements. Their shallow profile maximises surface area and speeds oxidation of organic matrices. The result: weighings to constant mass, optimised cycle times and reproducible results, from quality control to analytical development.

What types of incineration capsules are available, and how do you choose the right one?

Ignition crucibles are defined by their material, form and capacity. Models in glazed porcelain (low-form, sometimes with a pouring lip) offer good chemical inertness (except HF and strong bases), uniform heat distribution and a typical rating up to ~ 1000–1100 °C. Crucibles in silica/quartz prioritise thermal shock resistance and low blanks, for rapid calcinations up to ~ 1050–1100 °C. Platinum dishes are the benchmark for gravimetric accuracy and demanding matrices, thanks to exceptional chemical inertness and thermal resistance (beyond 1000 °C), while avoiding halides and certain metals that can attack it when hot.

On the form side, shallow crucibles speed up oxidation (high surface-to-mass ratio) and make residue handling easier. A lid can limit early spattering if left slightly ajar to ensure oxygenation. Key selection criteria: service temperature, chemical compatibility (acids, salts, bases), usable volume vs surface area, mechanical robustness, and compliance with Ph. Eur./USP/ISO protocols. Good practice: pre-ignite the empty crucible, heat with a temperature ramp to prevent foaming, cool in a desiccator and weigh to constant mass.

At-a-glance comparison (see table) to guide selection by use case:

Type	Max temperature	Principle & benefits	Typical applications
Glazed porcelain	~1000–1100 °C	Great cost/robustness balance, uniform heat distribution	Ash content in agri-food samples, residues after ignition, routine QC
Silica / Quartz	~1050–1100 °C	Excellent thermal-shock resistance, very low blanks	Fast Loss on Ignition (LOI), sensitive matrices, short runs
Platinum	>1100 °C (method-dependent)	Top-tier inertness and dimensional stability	Pharma (sulphated ash), materials, traceability

In which fields are ashing crucibles used?

• Food industry : determination of ash content and minerals in flours, milk, cereals and additives; verification of regulatory compliance and formulation stability.
• Pharmaceutical : sulphated ash and residue on ignition tests (Ph. Eur./USP) to quantify inorganic impurities and control excipients.
• Environment : loss on ignition (LOI) on sludge, sediments and waste; volatile matter; ash characterisation for disposal or recovery.
• Chemicals & materials : quantification of mineral fillers, carbon black and binders; control of cement/lime by LOI; preparation of residues prior to analyses ICP-OES/ICP-MS.
• Cosmetics : quantification of inorganic phases (pigments, talc, fillers) to ensure consistent colour/texture.
• Research : thermal studies, oxidation kinetics, validation of calcination ramp and gravimetric protocols.

Available types of ashing crucibles

Incineration capsule

Incineration capsules: frequently asked questions

Which material to choose for which temperature?
Porcelain up to ~1100 °C, silica/quartz ~1050–1100 °C with good thermal-shock resistance, platinum for precision and demanding cycles beyond 1000 °C.

How can you avoid losses during ashing?
Ramp the temperature, start with the lid slightly ajar and, if needed, use an ashing aid; do not overload the crucible.

Why weigh to constant mass?
To confirm the end of decomposition/oxidation and remove moisture effects; the difference between two successive weighings should be negligible.

What common chemical incompatibilities?
HF and strong bases attack porcelain/quartz; avoid halides and certain metals with hot platinum; always check matrix/material compatibility.

How do you clean a crucible in routine use?
Brush off residue, rinse (water/mild acidification if compatible), dry, then lightly re-ignite; avoid thermal shock and harsh abrasives.

What sample load is recommended?
Aim for one-third to one-half of the working volume to keep a large surface area and limit foaming; use several crucibles rather than a single overloaded one.

Is a lid necessary?
Useful at the start to prevent spattering; leave it slightly open for oxygenation, then remove it once combustion has stabilised.