Equipment verification is often the laboratory quality control work is difficult, laboratories are prone to errors include: the scope of the verification of equipment is not clear, the verification method is not clear, on how to evaluate do not understand. This article focuses on how the laboratory to carry out the verification of equipment during the verification work, and how to evaluate and use the results of the verification, to truly ensure the credibility of the equipment.
1, terms and terminology
Period verification: is to maintain the credibility of the calibration state of the equipment, the verification carried out between the two verification / calibration.
2, the purpose and scope of the period verification
Equipment through the calibration, from the calibration results and the standard requirements of compliance can determine whether the accuracy of the equipment to meet the requirements; and the main purpose of the period verification is to check the stability of the state of the equipment, in order to improve the credibility of the testing equipment. Therefore, it is not necessary to carry out the period of verification of all the testing equipment, but only when needed or the stability of the equipment when in doubt. For example, in the following cases can be carried out during the verification:
2.1 performance is not very stable, prone to drift;
2.2 high frequency of use;
2.3 often taken away from the fixed place or use of the harsh environment;
2.4 in the operation of the process of the occurrence of doubtful phenomena or to give doubtful results;
2.5 acceptance of significant
2.5 Accepting a major testing contract or issuing test results that have a significant impact;
2.6 Non-compliance with the need to investigate the causes of non-compliance.
3, during the verification methods
Laboratories can choose the following methods according to their own situation and the specific characteristics of the equipment:
3.1 Verification by using certified standard substances or standard samples;
3.2 Comparison by using the same accuracy measurement equipment;
3.3 Selection of samples/items with good stability and high sensitivity Perform multiple repetitions of tests at different times and locations, and if necessary, use statistical techniques to evaluate the results of each test;
Laboratories that are in a position to do so may adopt the methods in 3.1, but the authors recommend more of the methods in 3.2. From the listed methods, it can be seen that the key to period verification is to select more stable items (e.g., standard substances) as the test object; if the selected verification items cannot meet the requirement of stability, it will have an impact on the credibility of the verification results. In the selection of equipment comparison should be noted that if the two devices at the same time when the same direction of drift, its comparison results may also indicate that the equipment is stable, so the method should be used with caution.
4, the period of verification plan, program development
Laboratory should be based on the equipment, the development of a fixed period of verification plan such as the annual period of verification plan, but also according to the specific circumstances of the development of a temporary verification plan, the plan should contain the verification of the time or frequency requirements and so on.
The different equipment should be developed for different verification program, the program should contain the selected verification methods, verification intervals, and the results of the assessment requirements, to facilitate the verification of the correct implementation, recording and evaluation to ensure the effectiveness of the verification results.
5, during the verification of the implementation
Equipment users in accordance with the verification plan, verification program requirements, in the specified time points to implement verification, and record the results.
6, the evaluation of the results of the period verification
According to the different requirements of the assessment, the evaluation of the results of the verification is different.
6.1 When using certified standard substances or standard samples for verification, it can be stipulated that the error should be no more than 2/3 of the allowable difference, and can also be carried out a number of repetitive testing after the use of the test to make a determination;
6.2 When re-testing of samples suitable for retention and comparing the test results, it can be stipulated that the deviation should be no more than the parallel tolerances specified in the relevant test method standards.
6.3 When taking the verification method of using stable items for multiple repetitive testing, statistical techniques can be used to evaluate, typically can choose the test to determine.
7, the use of the results of the verification of the period
When the verification proves that the equipment is stable, you can continue to use the equipment for testing; when the verification results proved that the equipment is not stable, but still in the acceptable range, should be verified by increasing the frequency of verification to ensure that the equipment's credibility; such as the results show that it has exceeded the permissible range, you should discontinue the use of the equipment, until the repair and through the calibration shows that it can be normal If the results of the verification confirm that the equipment cannot meet the requirements and cannot be repaired, consideration should be given to purchasing new equipment.
8, the use of examples
8.1 The use of known value of the article for verification
Configuration of the concentration of 100ng/?L propionic acid standard solution for verification of GC4011A gas chromatograph, in the development of the period of the verification plan, the program can be stipulated that: in the calibration of the equipment at the time of the 6 months after the 6 times of the standard substance repeat testing. Measurement results after implementation are shown in Table 1:
How to determine whether the balance is stable or not, the test can be used to carry out stability analysis, the second and third measurements were compared with the first results, the comparison results are as follows:
According to the data in Table 2 can be calculated:
It can be seen that the electronic balance can be proved to be stable at the time of the second verification, but in the The third verification proved to be unstable, at this time the equipment should be debugged and re-tested, the test is qualified to continue to use. In the development of the electronic balance of the next cycle of the period of verification program, should consider increasing the frequency to ensure its credibility, such as the verification interval for the verification of the first, the second interval of three months, and then the third interval of three months, and then the third interval of three months, and then the fourth interval of three months, and then again before the verification of the fifth, such as the implementation of the equipment is proved to be stable, it can be considered in the next cycle to reduce the frequency of verification as appropriate.