Monitoring Bath Life Extension in Medical Device Cleaning

Q. What is the best way to monitor for bath life extension in medical device cleaning?

A.To avoid potential for cross contamination, only freshly made up cleaning solutions should be used for the highest levels of critical cleaning. However, there are certainly times were bath life extension is practical, and warranted.  For critical cleaning applications, high levels of cleaning can also be achieved with extended bath life.

In general, a pH change of 1 unit towards neutral indicates an exhausted cleaning solution. Bath life can be extended by physical filtration of particulates, cooling and settling of sludge and skimming of oils. Bath life can also be extended by adding one half as much detergent, of the initial load, after partially depleting the cleaning life of the bath. With frequent daily use, detergent solutions can rarely be used longer than a week even with these bath life extension techniques.

Conductivity, pH and % solids, by refractometer, can be used to control bath detergent concentration. Free alkalinity titration can be used to control bath life of alkaline cleaners where the soil being cleaned depletes free alkalinity—as is often the case with oily soils.

The process:

  1. Titrate a new solution to determine free alkalinity.
  2. Titrate the used solution to determine the percent drop in free alkalinity.
  3. Add more detergent to the bath to bring the free alkalinity back to the level of the new solution. (For example if the initial solution is made up with 100 ml of cleaner concentrate and a 25% drop in free alkalinity is observed, try adding 25 ml of cleaner concentrate to recharge your solution.)

Perform a new free-alkalinity titration to confirm the recharge the first few times this recharging method is used. This is to ensure that the detergent being used is linear with respect to free alkalinity depletion. This form of bath life extension cannot run indefinitely, sludge will eventually form. Fresh solutions must be made up periodically. Bath lives can also be extended using conductivity.

Most cleaners contain conductive salts which can be detected using conductivity. Once the conductivity response of the detergent is determined, the depletion of those conductive salts can be measured. Typically, this kind of measure the bath and recharge with detergent process can be done 2-3 times before a new bath is needed.

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