Dipotassium hydrogen phosphate (CAS 7758-11-4): storage and disposal

Bought as a tub of buffer stock, it should go on a dry shelf with the lid screwed tight after each use, as damp air gets into this salt quickly. Because it irritates skin, gloves are sensible when scooping, and spilt crystals should be reported and not wiped into other stock. The dibasic and monobasic phosphates look the same, so write the full name on the label and date the tub on arrival. A dry, labelled, well organised store is the baseline, with food grade supplies kept separate from laboratory stock. Pathology and university labs often hold several phosphate salts together.

This salt draws water readily, so an old tub is often one solid cake or a damp, sticky mass instead of loose crystals. A crust around the neck and a wet ring on the shelf below show the lid has not been sealing. Buffer solutions made from phosphate go cloudy or grow mould once they have stood too long. Check also for a faded label, a cracked tub and an unknown date of receipt. Everything is described as found. A caked tub is not a reason to open it or break the lump.

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.

The asterisk on 16 05 06* marks hazardous waste, which is the usual code for this item. A pathology store in human healthcare would use 18 01 06*, and a discarded inorganic chemical outside a lab pack takes 16 05 07*. Dry stock and any bottled solution travel in separate groups, and a leaking cap is described so the packers know. No sink, drain, general waste bin or skip is the route, and staff should not try to treat it first. Record the tub size, the amount left and whether it has caked or run damp.

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.