A typical approach to establish solution stability is to analyze the solution following the method, and then store it under the required conditions. It is re-analyzed after a specified period of time. The original results and results obtained for the stored samples are compared to evaluate the stability. Alternatively freshly prepared samples may be used for comparison. Typical storage conditions include refrigerated and, stored protected from light, over a period of 24 hours to several days.
The comparison may take the form of an absolute measure, i.e. the re-analysis is within specified limits, or statistical tests based on confidence intervals may be used:
- Percent recovery of the initial value at all next points of the period of time should not be less than 98% of the initial value;
- Percent difference in the initial and at the end of the period of time should not be more than 2% of the initial value;
- The % relative standard deviation for the results (individual percent differences) should not be more than 2.0;
- T test for the mean percent differences;
- Confidence interval of mean percent difference should include zero.
Calculations of fast two tests are comparatively easy and interchangeable. However it would be highly appreciable if someone can send me some example protocols-reports which includes last statistical tests or any other specific tests for Analyte solution stability in method validation.
Thanks.