Q. Is a 1% Alconox solution stable in tap water? How long can 1% Alconox be stored as solution? Is pH measurement the best estimate of stability?
A. Alconox® Powdered Precision Cleaner, is stable in tap water (or any purity water- within reason) for 1-2 weeks when stored in a closed container. The mechanisms of degradation are microbial activity and hydrolysis of the polyphosphates. This of course differs from undiluted shelf life.
We have done studies that demonstrate no microbial growth occurred under closed lid controlled laboratory conditions for up to three weeks. However, for real life applications, the lid will be opened and closed to dispense the detergent solution, so you must account for possible microbial growth. Hence, the more conservative recommendation of 2 weeks to ensure stability.
The best way to monitor stability is to measure the pH of the solution over the course of the storage. Take and record a pH start point after initially preparing the solution as a reference point. Typically a drop in pH will detect the onset of microbial proliferation and activity.
Also, another early warning sign of microbial activity is a “characteristic” microbial odor. Monitoring with pH and odor during the storage period you are intending to qualify will give you some control to be sure that microbial activity had not started to cause concern.
The second possible mechanism is polyphosphate degradation. Detecting the onset of polyphosphate hydrolysis is more detailed than detecting microbial growth. Unfortunately the pH only rises slightly as the polyphosphates hydrolyze to ortho-phosphates, and to the best of our knowledge there is no quick and simple way to monitor this. It is in our experience that the amount of polyphosphate hydrolysis that occurs during these initial weeks is insufficient to perturb or interfere with detergent performance. So as long as you change the solution every 1-2 weeks, there is little concern for detergent performance loss.
Thus, the limiting factor in diluted detergent solutions’ storage remains microbial growth.
Many of these concepts of stability can be used across our detergent portfolio. However, factors like detergent format (liquid concentrate vs. powder), phosphate and enzymatic presence, as well as usage, will of course matter. You can contact us any time to discuss your process’ needs or read up further on shelf life.
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