Pure steam and its numerous definitions
Our investigations showed that a legal standard for “Pure Steam” did not exist. There has not been any recognized authoritative body which defined Pure Steam for use in high purity applications, as opposed to “plant steam“ which may be used in non-sterile environments where there is no product contact.
The pharmaceutical industry requested guidance from the USP in the form of a definition for steam. To answer that call, the USP Pharmaceutical Water Expert Committee developed a new monograph – Pure Steam.
Pure steam – now legally described in the USP
Pure Steam can be described qualitatively as vaporized water that meets all the chemical quality attributes requirements of WFI.
The requirements for Pure Steam are the following:
- The source water is drinking water or better
- it is produced by vaporization > 100 °C with appropriate prevention of source water entrainment
- the condensate meets <645> Water Conductivity and <643> Total Organic Carbon
- the condensate has a Bacterial Endotoxin limit of 0.25 Endotoxin/mL
Note that the chemical tests cannot be performed on the vapor. Unlike HTM 2010 which specifies limits on non condensable gasses and % saturation, the USP monograph notes specifically that these physical requirements are not contained in this monograph, but the monograph adds “The level of steam saturation or dryness, and the amount of non condensable gases are to be determined by the Pure Steam application”.
This means the user to determine appropriate physical properties of the Pure Steam. When steam is used as a sterilizing agent, these physical tests may be required to assure appropriate heat is delivered. When the steam is used as an ingredient in a product, these physical attributes may be of no value to the quality of the product. Regardless of the use of Pure Steam, METTLER TOLEDO THORNTON offers high quality measuring systems to support you in the determination of water conductivity and TOC in the condensate.
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