Neutral red (CAS 553-24-2): storage and disposal
A red dye that changes colour with acidity, neutral red is used as a stain and as an indicator in school, college, university, pathology and histology labs, held as powder and as made-up solution. It is classified for skin and eye irritation, respiratory irritation and suspected genetic defects. The suspected genetic effect is what shapes storage, and the fact that solutions change colour with acidity changes what an apparent colour change means.
- CAS number
- 553-24-2
- Form
- Solid
- Storage class
- Toxic
- Signal word
- Warning
- Usual EWC code
- 16 05 06*
Harmful or irritant
Serious health hazard
What to do this week
- Check the label is readable and write down the opened date if it is not already there.
- Check it is stored as toxic stock and apart from the items listed under "Do not store with".
- If you no longer need it, add it to your disposal list so it goes on the next collection.
Safe storage in a school or lab
Keep neutral red away from oxidisers and separate from acids to prevent incompatible contact and changes to its pH-sensitive colour. A locked cabinet with a stock record is where powder belongs, as the suspected genetic effect calls for controlled access. Because the dye changes colour with acidity, contamination by acids could alter the colour of a neutral red solution, which is one more reason to keep the containers separate. Keep the powder jar capped, the thread wiped and the date of receipt on the label. Dust is irritating to the airways, so open it only where there is ventilation.
How to tell it has deteriorated
The dye is red in acid and shifts towards yellow as the liquid becomes more alkaline, so a bottle of solution that has changed colour may simply have picked up a contaminant rather than aged. It is a warning to treat the bottle as unknown, not as proof of what happened. Look also for a crust around the cap, a stained label, a lower level than the record and sediment. Powder that is caked or damp has absorbed moisture, and a faded label or lost record is enough reason to list the stock. Do not test the solution to find out what changed it. A bottle whose colour no longer matches its label should be described as such.
How it must be disposed of
By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a toxic laboratory pack with compatible chemicals.
A school, college or university prep room uses the discarded laboratory chemical code 16 05 06*, and a pathology service clearing human healthcare stock uses 18 01 06*. Describe whether the stock is powder, solution or both, with the container size, and mention any bottle whose colour has changed so the carrier does not pack it beside acids or oxidisers. Leaving a sink for the colour test is not a route, and neutral red is never poured away or wiped off a bench into general waste. Containers stay sealed and upright until the collection.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded organic chemical, not a laboratory pack | 16 05 08* |
| Human healthcare setting | 18 01 06* |
| Hazardous waste | Yes |
The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.
Do not store with
- OxidiserToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- AcidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- Acetic acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Calcium hypochloriteToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Hydrochloric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Hydrogen peroxideToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Nitric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Potassium nitrateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Potassium permanganateToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
- Sulfuric acidToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Common quantities we collect
Usually held as: solid, solution.
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.
Where it is commonly held
Hazard statements
- H315 Causes skin irritation.
- H319 Causes serious eye irritation.
- H335 May cause respiratory irritation.
- H341 Suspected of causing genetic defects.
Precautionary statements
- P203 Obtain, read and follow all safety instructions before use.
- P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
- P264 Wash hands and exposed skin thoroughly after handling.
- P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
- P271 Use only outdoors or in a well-ventilated area.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P318 If exposed or concerned, get medical advice.
- P319 Get medical help if you feel unwell.
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P332+P317 If skin irritation occurs: Get medical help.
- P337+P317 If eye irritation persists: Get medical help.
- P362+P364 Take off contaminated clothing. And wash it before reuse.
- P403+P233 Store in a well-ventilated place. Keep container tightly closed.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Our neutral red solution has changed colour. Is it still usable?
The dye changes colour with acidity, so a shift may mean contamination rather than age. Do not test it. Record the change, treat the bottle as unknown and list it for collection if it no longer matches its label.
Why is neutral red kept away from acids?
Keep neutral red separate from acids to prevent contamination and changes to its pH-sensitive colour. Oxidisers should also be segregated because they may react with the organic dye.
Does neutral red need locked storage?
Its classification includes suspected genetic defects, so a locked cabinet with a stock record is the sensible arrangement, with the powder kept capped and away from food and drink.
Do we list the powder and solution as one item?
No. They are different forms in different containers, so list each separately with its container size, and say on the request whether any solution bottle has changed colour since it was made up.
