Acetaldehyde (CAS 75-07-0): storage and disposal

Small glass bottles or sealed ampoules are the form it usually arrives in, and the seal counts for a great deal with a liquid this volatile. It should be kept cold and away from air, which means a spark-free refrigerator and nothing less, as an ordinary fridge could ignite the vapour. A warm prep room can build pressure in a bottle, so a cupboard is a poor second choice for it. Air also oxidises it to acetic acid, and traces of acid can start violent polymerisation, so tight caps protect against both problems. Metal caps, metal spatulas and shared funnels have no place near it. Oxidisers, oxidising acids and corrosive stock go elsewhere. Date the bottle on receipt and on opening, with a review at 12 months.

Look first at the cap and label: a loose or corroded closure, a faded label or no dates at all should stop you. Inside, old stock may show solid polymer as a white mass or deposit, and a thicker liquid can mean polymerisation has begun. A lower level in a bottle is common with something so volatile, and it also suggests air has been getting in. Pressure can build, so a bulged bottle or one that has been hissing should not be touched. Bottle age matters more than clarity, as peroxides give few visual signs. If it is old, undated or shows any warning sign, do not move it, do not open it, and get a specialist assessment. Peroxide testing is for competent staff only.

Forms peroxides and polymerises on standing.

This can form peroxides as it ages, especially after opening. Age and the opened date matter more than appearance, so a container with no opened date should be treated as old.

Review after 12 months: Review interval after opening from the cited peroxide former lists, not an expiry date from a manufacturer. Class C and all other chemicals are left null.

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a flammable laboratory pack with compatible chemicals.

Waste code 16 05 06* usually fits a laboratory bottle, but what matters more is that this item may not be fit to travel until it has been seen. Tell the collection team that it is acetaldehyde, what the dates show, and whether you can see any solid. Legacy school bottles deserve that note in particular, since they are the most likely to have polymerised. A specialist assessment comes first for anything old or undated. It must not go into a sink, a drain, a general waste bin or a skip, and nobody should try to treat it first. Neither should it be left in a fume cupboard to disappear, as peroxides would stay behind. Specialist collection is the only route, once a bottle is cleared.

Usually held as: neat, legacy stock.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.