The stability of the standard sample is used to describe the change of the characteristic value of the standard sample over time, which means that the standard sample is stored for a long time. Under the influence of external environmental conditions, the physical and chemical properties of the sample and the ability to remain unchanged. So how to judge the stability of the standard sample? The following is a small edition of Bolinda to introduce you.

According to the basic theory of standard sample technique, when measuring and determining the characteristic value of standard sample, the measurement uncertainty of the value is composed of three independent components. These are: the measurement uncertainty component introduced by the measurement method, the measurement uncertainty component introduced by the non-uniformity between bottles and bottles, and the measurement uncertainty component introduced by the sample instability over time.

Because the standard sample is in transit or stored in the warehouse, the characteristic value of the standard sample may change with the transport conditions or with the change of time under the specified storage conditions. In the field of standard sample technology, we refer to the degree of change of standard sample characteristics during transport under suitable transport conditions as short-period stability; The degree to which the characteristics of a standard sample change over time under suitable storage conditions is called long-period stability.

Therefore, in the process of developing the standard sample, it is necessary to carry out short-period stability research, the purpose is to determine the suitable transport conditions of the standard sample through the test analysis. That is to ensure that when the standard sample is distributed under specified transport conditions, changes in the characteristics of the standard sample due to transport do not increase the measurement uncertainty of its characteristic standard value.

At the same time, it is necessary to carry out a long period stability study, the purpose is to determine two problems through test analysis: one is the suitable storage conditions of standard samples; The second is the time period in which the standard sample characteristics and standard values remain effective under such storage conditions. That is to ensure that during the validity period, when the standard sample is stored under the specified conditions, the change of the standard sample characteristics will not increase the measurement uncertainty of its characteristic standard value.

If we further study and analyze the internal mechanism of standard sample stability research, we can also find the following two situations:

The first case is that all samples change uniformly over time. The expression is: although the characteristic value of the whole batch of samples has changed, the standard sample characteristic standard value is very consistent at each selected test time point. In other words, the characteristic standard value of the standard sample is not the same at different time points, but at any specific time point, the characteristic standard value of the batch of standard samples is consistent. The characteristic of this situation is that at any test time point, the sample material of the whole batch of standard samples still remains uniform, but the standard value of the standard sample characteristic at each test point changes, and the corresponding measurement uncertainty does not change.

The second case is: at each detection time point, the change of the whole batch of samples is uneven (some samples in the same bottle have changed, some have not changed, that is, the uniformity of the bottle has changed; Or some bottles have changed the sample, some bottles have not changed, that is, the uniformity between bottles has changed), in the form of: at any test time point, the sample uniformity of the standard sample has changed, so the corresponding characteristic standard value and measurement uncertainty have changed.

It can be seen that the stability problem is essentially the problem of studying the change of the uniformity of the standard sample over time. We can therefore divide stability studies into three types according to this principle:

The first is the case where the sample material changes uniformly over time. At this time, we can find out the correlation between the change of the characteristic value of the sample and the time through the stability study, and adopt the method of regression analysis to study and find out the appropriate regression equation. If the regression equation can be obtained, the stability change of the standard sample can be predicted.

The second type is the case of uneven changes in the sample over time. Through the stability study, we can judge and determine whether the standard value change of the standard sample characteristics at each detection time point is within the corresponding measurement uncertainty range.

The third category is the stability of transport conditions. Since the transportation environment and conditions are often harsh and unavoidable in the actual transportation, the purpose of stability research becomes to find the measurement uncertainty introduced by the transportation conditions, and then add this measurement uncertainty component to the measurement uncertainty of the standard sample characteristic value.

The above content is how to judge the stability of the standard sample, at the specified time interval and environmental conditions, the characteristic value of the standard sample is maintained within the specified range of nature. The longer the specified period indicates the better the stability of the standard sample, and this period is called the validity period of the standard sample. When issuing and selling a standard sample, the validity period of the standard sample should be clearly given, so that the use of the standard sample within the specified validity period can guarantee the accuracy of the calibrated measuring instrument, the evaluated measurement method or the determination of other materials.