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Chemical collection and stock control for UK schools, universities and hospitals

Guanidine hydrochloride (CAS 50-01-1): storage and disposal

Guanidine hydrochloride is the white crystalline salt that protein chemists use to unfold proteins, held in university and pathology labs as powder and as strong 6 M solution. It is classed as harmful if swallowed and as a skin and serious eye irritant. Its chief nuisance is how readily the solid takes up water, and that decides how it is shelved and how old stock looks.

CAS number
50-01-1
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Harmful or irritant pictogramHarmful or irritant

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as general stock and apart from the items listed under "Do not store with".
  3. 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

Because the powder pulls water from the air, the lid matters more than the shelf. Keep the bottle tightly closed on a general shelf in a dry cupboard, with a label that gives the date of opening. Holders who keep the 6 M solution should store it in a tray on a lower shelf, as a fall or a cracked bottle spreads a lot of liquid, and keep it apart from acid and oxidiser stock. A plain cupboard in a university protein lab is typical. Pathology stores may hold small amounts for assay kits. Do not return unused powder to the bottle, since that carries moisture and grit in.

How to tell it has deteriorated

This salt dissolves in the water it absorbs, so an old bottle changes in a distinct way. The crystals first clump, then turn damp and may collapse into a wet paste or a solid block that has set to the glass. A bottle that looks half full of hard rock was probably left uncapped. The strong solution shows a different sign. At this concentration crystals can deposit at the bottom of the bottle or on the cap thread, and the thread then seizes. Look also for crust round the neck, a faded label and a cap that has cracked. None of this suggests the contents are safer than before.

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 non-regulated or low hazard laboratory pack with compatible chemicals.

Powder and solution are grouped separately in a lab pack, each with compatible stock. Record whether you hold powder or the 6 M solution, how much remains and where it was kept. The code is 16 05 06* in a research lab, 16 05 08* if it is a discarded organic chemical outside a pack, and 18 01 06* in human healthcare. Solutions go in leak-proof, upright containers, away from the solids. Whether wet or dry, it must not go into a sink or drain, and no one should try to dry out a damp block or break it up for convenience. A seized cap should be left as it is.

Waste codes and transport details for Guanidine hydrochloride
EWC code, laboratory chemicals16 05 06*
Discarded organic chemical, not a laboratory pack16 05 08*
Human healthcare setting18 01 06*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Common quantities we collect

Usually held as: solid, 6 M.

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

  • H302 Harmful if swallowed.
  • H315 Causes skin irritation.
  • H319 Causes serious eye irritation.
Precautionary statements
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P270 Do not eat, drink or smoke when using this product.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • 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.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Why has our guanidine hydrochloride turned into a block?

The salt takes water from the air and dissolves in it, then sets as the bottle dries. That means the cap was loose at some point. Do not force it out, record the bottle and ask for collection if it is not wanted.

Do the 6 M solution bottles need different handling?

Yes. Keep them upright in a tray on a low shelf, because a break releases a large volume of liquid. Check for crystals and a seized cap, and describe the solution separately from any powder on the paperwork.

What hazards are recorded for guanidine hydrochloride?

Harmful if swallowed, skin irritation and serious eye irritation. Those statements place it as an irritant and a hazardous waste, so it goes for specialist collection and is described accurately on the stock record.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula CH6ClN3. EC number 200-002-3.

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