The Principles of Medical Device Decontamination

High sodium content can cause frothing and foaming, which in turn can impede impingement and the resulting decrease in washer-disinfector efficacy. Certain conditions can cause deposition of dissolved or suspended species, such as the coating of dissolved metals on instrument surfaces, which can cause staining. Chlorine can cause pitting corrosion on stainless steel surfaces, and is typically present as metal salts in the water supply, e.g. NaCl, MgCl 2 , CaCl 2 , etc.

Sequestrants and chelating agents

In order to allow a greater spectrum of detergent efficacy in a range of water quality supplies, certain chemicals can be added to address these negative effects of hard water and metal ions. These chemicals are typically known as sequestrants. These sequestrants have a specific chemical structure that allows them to bond or react with metal ions in the hard water. A specific form of sequestrant is known as a chelating agent; these chelating agents have a structure like a claw which can bind the free metal ions, and hence make water act as though the metal ions (that impart water hardness) were not present, thus enhancing the effects of the detergent system used. The ions for which chelates are particularly useful are multivalent ions such as Ca, Mg, Fe, Cu, Zn, Ni, etc. Chelates typically prevent deposition onto instruments and allow the detergent to perform the cleaning as expected. They can also inhibit scale formation and remove scale deposits, as well as destabilise secondary protein structures and hence contribute towards cleaning. It is important to note that the best chelant or sequestrant for the system is not always the one that can handle the most water hardness; a combination of at least one chelant and at least one sequestrant can typically outperform each individual component. Chelants perform stoichiometrically, meaning that they have a specific molar ratio to the metal ions, whereas sequestrants do not.

Advantages of certain detergent formulations

Rust (Fe 2 O 3 ) is a corrosion product sometimes found on medical devices containing iron (which of course includes stainless steel). Depending upon its oxidation state, this corrosion can be reddish-brown through to black.

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