Bromothymol blue (CAS 76-59-5): storage and disposal

In a school prep room the indicator bottles tend to live together on one shelf near the burettes, which is a sensible place for the dropper bottles but not for the powder, since a splash or a leak from an acid or alkali bottle nearby would change colour in the stock. Keep powder and solution in closed bottles on a general shelf, separate from food supplies, and keep dropper bottles upright in a tray. Put the opening date on the 0.04% solution, as the colour may fade and the solvent can escape through a loose cap, so stock that is years old has changed without anyone looking. A university store follows the same pattern.

A faded or smudged label is often the first thing seen, because indicator drips run down the side of the bottle and bleach the print. Inside, the colour of the solution may fade, and the level may drop where solvent has escaped through the cap, leaving a dried blue or yellow ring around the neck. A bottle that is meant to be blue in alkaline stock but has gone green or yellow has probably taken up acid, possibly carbon dioxide from the air through a poor seal. Powder should be loose, so damp or caked powder suggests moisture has entered. Stock with an unknown date of receipt is awkward to describe.

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

A weak solution of a dye still needs to be described properly. Bromothymol blue is not normally classified as hazardous, so the ordinary waste transfer note usually covers it, but it remains a chemical waste, usually under code 16 05 09, and must be recorded accurately by form, strength and volume. Powder and solution are listed separately, and the dropper bottles are packed upright in a lab pack with other compatible items. Colour fading or solvent loss does not change that. Stock should not be rinsed into a sink or drain, however pale the solution, and nobody should try to clear it by diluting it.

Usually held as: solid, 0.04% solution.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.