Core Tip: The stability of standard samples is based on the basic theory of standard sample technology. When measuring and determining the characteristic values of standard samples, the measurement uncertainty of this value is composed of three independent components

Stability of standard samples
According to the basic theory of standard sample technology, when measuring and determining the characteristic value of a standard sample, the measurement uncertainty of that value is composed of three independent components. This is: the measurement uncertainty component introduced by the measurement method, bottle-The measurement uncertainty components introduced by non-uniformity between bottles and the measurement uncertainty components introduced by sample instability over time.
Due to the fact that the characteristic values of standard samples may vary with changes in transportation conditions or over time under specified storage conditions during transportation or storage in the warehouse. In the field of standard sample technology, we refer to the degree of change in the characteristics of standard samples during transportation under appropriate transportation conditions as short-term stability（short-termstability）； The degree to which the characteristics of standard samples change over time when stored under appropriate storage conditions is called long-term stability(long-termstability).
Therefore, in the process of developing standard samples, it is necessary to conduct short-term stability studies, with the aim of determining suitable transportation conditions for standard samples through experimental analysis. Ensure that when distributing standard samples under specified transportation conditions, changes in the characteristics of the standard samples caused by transportation will not increase the measurement uncertainty of their characteristic standard values. At the same time, long-term stability studies must also be conducted to determine two issues through experimental analysis: first, appropriate storage conditions for standard samples; The second is the effective time period for maintaining the standard values of standard sample characteristics under such storage conditions. Ensure that within the validity period, when storing standard samples under specified conditions, changes in the characteristics of the standard samples will not increase the measurement uncertainty of their characteristic standard values.

If we further study and analyze the internal mechanism of stability research on standard samples, we can also discover the following two situations:
The first scenario is:
All samples undergo uniform changes over time (or transportation conditions). The manifestation is that although the characteristic values of the entire batch of samples have changed, the consistency of the standard sample characteristic values is very good at each selected testing time point. That is to say, the characteristic standard values of standard samples are not the same at different time points, but at any specific time point, the characteristic standard values of the batch of standard samples are consistent. The characteristic of this situation is that at any testing time point, the sample material of the entire batch of standard samples remains uniform, but the standard values of the characteristics of the standard samples at each testing point have changed, while the corresponding measurement uncertainty has not changed.
The second scenario is:
At each testing time point, the changes in the entire batch of samples are uneven (some samples in the same bottle have changed, some have not changed, that is, the uniformity inside the bottle has changed; or some samples in the bottle have changed, and some bottles have not changed, that is, the uniformity inside the bottle has changed)-The uniformity between bottles has changed, manifested as a change in the uniformity of the standard sample at any testing time point, resulting in changes in the corresponding characteristic standard values and measurement uncertainties.
From this, it can be seen that stability issues are essentially the study of changes in the uniformity of standard samples over time. Therefore, we can classify stability studies into three types based on this principle:
The first type is the situation where the sample material changes uniformly over time. At this point, stability studies can be conducted to identify the correlation between changes in sample characteristic values and time. The "Regression Analysis" method can be used to study and find a suitable regression equation. If the regression equation can be obtained, the stability changes of the standard sample can be predicted.
The second type is the situation where the sample material undergoes uneven changes over time. Stability studies can be conducted to determine whether the standard value changes of the standard sample characteristics at each testing time point are within the corresponding measurement uncertainty range. The statistical testing method for this determination isFInspection ortTesting.
The third category is research on the stability of transportation conditions. Due to the harsh and unavoidable transportation environment and conditions in actual transportation, the purpose of stability research becomes to find the measurement uncertainty introduced by transportation conditions, and then add this measurement uncertainty component to the measurement uncertainty of the characteristic values of standard samples.

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