Application Note 1003 USP24 Compliance for LTH Instruments

Conductivity Instrument meets US Standards
US Pharmacopoeia 24 (USP24) is used by all pharmaceutical companies as a standard set of procedures to ensure that they will comply with FDA requirements. This is applied to conductivity measurements, which are used to determine if the water used as either a washing solution or as part of the product being manufactured meets strict quality standards.

The Directive
Conductivity is used as the first (Stage 1) test and can be an on-line measurement. The measurement is used to determine the maximum level of dissolved minerals that are in solution, which it is ideally suited to do. However the conductivity of a solution varies with temperature as well as the contaminants in it, and this temperature dependence varies with the type of contaminant. In order to compensate for this most conductivity instruments apply a temperature compensation factor, usually 2%/C, but due to the wide variation in the quality of different manufacturers temperature compensation systems USP24 has specified that all measurements must be made uncompensated. The table below lists the maximum allowed conductivity values at a series of different temperatures.

The Difficulty
This is fine until you have applications where the process water temperature varies considerably. The conductivity table varies between 0.6 to 3.1 uS/cm over a 0 – 100 C temperature range, with an on-line measurement where do you set the limit?

The Solution
LTH has resolved the problem by incorporating a USP24 set-point option into the MCD53 instrument (see Application Note 9907). With this selected, the table of temperature vs. conductivity values is automatically applied and the output relay is energised should the Stage 1 test values be exceeded. The MCD53 has other features that further improve this monitoring. Two separate 4-20 mA outputs are also provided for the uncompensated conductivity reading and temperature, which can be used for independent recording and archiving of the systems performance. All LTH conductivity systems can be provided with traceable certification, and cells can be supplied which are steam sterilisable and with FDA approved materials.

To summarise, the full requirements for USP24 can be adhered to by fitting the LTH Conductivity controllers at the final stage of your water treatment system, so allowing an alarm to be raised when the water is non-compliant.

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