Potassium dihydrogen phosphate (CAS 7778-77-0): storage and disposal

A quick check that costs nothing: pick up the tub and see whether the salt moves. If it rattles loose, the lid has been doing its job. Keep it in a dry, labelled, well organised store, dated on arrival, with the full name on the label, since the monobasic and dibasic phosphates are easy to swap. Histology and pathology labs usually hold both and should shelve them apart. Food grade supplies stay separate from laboratory stock. It is not classified as hazardous on the sources we checked, so no cabinet is needed, but a stock record still applies.

The salt itself keeps well, so the first change is caking: a tub that has taken up damp sets into a hard lump at the base, and a crust forms around the neck. Buffer solutions made from phosphate are a different matter, because a cloudy bottle, floating threads or mould on the surface show the liquid has stood too long. This substance gives few other distinctive signs. Faded labels, a cracked tub and an unknown date of receipt are the remaining checks. Each is recorded as found, and old solutions are listed separately from dry stock.

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

Hospital and pathology holders would use 18 01 07, while a school or university holder would use 16 05 09, which is the waste code for this item as a non-hazardous chemical. The distinction is the setting, so say where it came from. Not being classified as hazardous on the sources we checked does not make it a sink or bin item: it never goes down a drain, into general waste or a skip, and staff should not try to treat it first. Dry salt and any solutions are described and packed separately. Record the size, quantity and condition.

Usually held as: buffer 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.