Analyte Stability in Solution

It is important to include sufficient replicate analyses in the experiment to ensure that any variability observed is real and not simply within the range of variability that should be expected for the analysis of replicates. No significant loss of analyte (p = 0.05) should be observed for any of the conditions of storage and use that are established for subsequent routine use. In addition, a working life for standard solutions should be established by testing the stability over the time period typically used in the laboratory for both stock standard solutions and working standards, and this information should be included in the method. 

Decision 2002/657/EC recommends procedures for assessment of analyte stability in solution. Sufficient standard solution should be prepared to provide at least 40 replicate aliquots of the standard solution for testing. From this stock, 10 replicate portions should be taken to assess each of the proposed conditions of temperature for storage, which typically are temperatures such as -20°C, - -4°C and - -20°C (typical temperatures in a freezer, a refrigerator and room temperature ). Two sets (10 aliquots per set) should be prepared for testing at - -20°C, one to be stored in light, the other in the dark. The tests should be conducted at time intervals such as  

Analytical results at each time point should be compared with the results obtained for analysis of an aliquot of the standard when it was freshly prepared. 

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