OTHER NONMONOGRAPHED WATERS
In addition to Drinking Water, this compendium discusses waters with various other designations. These include waters of various quality levels for special uses such as, but not limited to,
cleaning and testing purposes.
Both General Notices and Requirements (Water in a Compendial Procedure) and Reagents, Indicators, and Solutions clearly state that where the term “water” is indicated for use in analyses without grammatical qualification or other specification, the quality of the water must be Purified Water. However, numerous such qualifications do exist.
Some of these qualifications involve adjectives describing methods of preparation, ranging from specifying the primary purification step to specifying additional purification.
Other qualifications call for specific attribute “absences” to be met that might otherwise interfere with analytical processes.
In most of these cases, the required attribute absences are not specifically tested.
Sometimes, a further “purification process” is specified that ostensibly allows the water to adequately meet this required “absence attribute”.
However, preparation instructions for many reagents were carried forward from the innovator’s laboratories to the originally introduced monograph for a particular USP–NF article or general test chapter.
The quality of the reagent water described in these tests may reflect the water quality designation of the innovator’s laboratory.
These specific water designations may have originated without the innovator’s awareness of the requirement for Purified Water in USP–NF tests.
Regardless of the original reason for the creation of these numerous special analytical waters, it is possible that the attributes of these special waters could now be met by the basic preparation steps and current specifications of Purified Water.
In some cases, however, some of the cited post-processing steps are still necessary to reliably achieve the required attributes.
Users are not obligated to utilize specific and perhaps archaically generated forms of analytical water where alternatives with equal or better quality, availability, or analytical performance may exist.
The consistency and reliability of operations for producing these alternative analytical waters should be verified so that the desired attributes are produced.
In addition, any alternative analytical water must be evaluated on an application-by-application basis by the user to ensure its suitability.
The following is a summary of the various types of nonmonographed analytical waters that are cited in the USP–NF.
This is not an exhaustive listing.
Those listed below are used in multiple locations.
Several nonmonographed analytical waters are not included below because they are only found in one or perhaps two locations within this compendium.
Note that the names of many of the waters below imply a very low chemical impurity level.
For example, “deionized water” implies that all the ions have been removed. However, in most cases discussed below, exposure of the water to air will result in the ingress of carbon dioxide (CO2), leading to the formation of bicarbonate and hydrogen ions. Therefore, the removal of ions cannot be completely maintained for most analytical applications.
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