10 Best Common Methods Of Quality Control | IPQCCO

1. Reference Material Monitoring

① Quality control process
The usual practice is that the laboratory directly uses the appropriate certified reference materials or internal standard samples as the monitoring samples, and regularly or irregularly carries out the monitoring samples in the form of comparison samples or password samples at the same time as the sample testing in the same process and method. After the completion of the testing room, the testing results are reported to the relevant quality control personnel. The testing personnel can also arrange to insert reference materials during sample testing to verify the accuracy of the test results.

② Scope of application
Generally, it can be used for: Control of instrument status, control of sample testing process, instrument comparison within the laboratory, personnel comparison, method comparison and comparison equivalence between laboratories. This method is characterized by high reliability but high cost.

2. Personnel Comparison

① Quality control process
The testing personnel in the laboratory shall use the same method for the same sample and complete the testing task on the same testing instrument within a reasonable period of time, compare the consistency of the testing results, and determine the comparability and stability of the operation ability of the testing personnel. The laboratory shall conduct personnel comparison, and the comparison items shall be as complex as possible, especially with more manual operation steps. The operation of inspectors shall be independent of each other to avoid interference with each other.
Generally, the supervision frequency of the laboratory for new personnel is higher than that of normal on-the-job personnel, and it is best to always take the results reported by the experienced and stable testing personnel of the laboratory as the reference value when organizing personnel comparison.

② Scope of application
The main purpose of personnel comparison organized in the laboratory is to evaluate whether the testing personnel have the ability and qualification to work or change posts. Therefore, it is mainly used to assess the testing technical ability of new personnel and new trainees and supervise the testing technical ability of on-the-job personnel.

3. Method Comparison

① Quality control process
Method comparison is a comparison test between different analytical methods, which means that the same tester uses different detection methods for the same sample, detects the same item, compares the consistency of the determination results, determines its comparability, and verifies the reliability of the method.
The test object of method comparison is the test method, and the main purpose is to evaluate whether there are significant differences in the test results of different test methods. During comparison, the test results obtained by the standard method are usually used as the reference value and compared with the test results of other test methods. The difference of test results between methods should meet the evaluation requirements. Otherwise, it proves that the non-standard method is not applicable or needs further modification and optimization.

② Scope of application
Method comparison is mainly used to investigate the systematic error between different detection methods and monitor the effectiveness of detection results. Secondly, it is also used to confirm the non-standard methods involved in the laboratory.
The overall detection methods generally include sample pretreatment methods and instrument methods. As long as the pretreatment methods are different, whether the instrument methods are the same or not, they are classified as method comparison. However, if the pretreatment methods of samples in different detection methods are the same, but the detection instruments and equipment are different, they are generally classified as instrument comparison.

4. Instrument comparison

① Quality control process
Instrument comparison means that the same tester uses different instruments and equipment (including the same or different types of instruments) to test the same sample with the same test method, compare the consistency of the test results, and determine the comparability of instrument performance. The assessment object of instrument comparison is the testing instrument. The main purpose is to evaluate the performance differences (such as sensitivity, precision, anti-interference ability, etc.) of different testing instruments, the consistency of measurement results and existing problems. The selected test items and test methods shall be suitable for and fully reflect the performance of the instruments participating in the comparison.

② Scope of application
Instrument comparison is usually used to check and control the performance of newly added or repaired instruments and equipment in the laboratory, and can also be used to evaluate the difference degree of test results between instruments and equipment. For instrument comparison, pay particular attention to maintaining the consistency of all link conditions except the instrument in the comparison process, so as to ensure the full response of the result difference to the instrument performance.

5. Retest of reserved samples

① Quality control process
Retention retest means that the same sample is tested again at different times (or within a reasonable time interval). By comparing the consistency of the two test results, it can judge whether there are problems in the test process and verify the reliability and stability of the test data. If the two test results meet the evaluation requirements, it indicates that the laboratory’s test ability of the project is continuously effective; In case of nonconformity, the causes shall be analyzed, corrective measures shall be taken, and the previous test results shall be traced if necessary. In fact, the retest of reserved samples can be regarded as a special internal comparison in the laboratory, that is, the comparison at different times. For the retest of retained samples, attention shall be paid to the stability of the performance indicators of the samples used, that is, there shall be sufficient data display or expert evaluation to show that the assignment of retained samples is stable.

② Scope of application
As an internal quality control means, retained sample retest is mainly applicable to samples or positive samples with a certain level of test data, samples with relatively stable items to be tested, and when it is necessary to monitor the characteristics of retained samples and verify the reproducibility of test results. Retesting of reserved samples is conducive to monitoring the continuous stability of the test results of the project and observing its development trend; It can also urge inspectors to take each inspection seriously, so as to improve their own quality and technical level. However, it should be noted that the retest of reserved samples can only control the repeatability of the test results, and can not judge whether there is systematic error in the test results.

6. Blank Test

① Quality control process
Blank test, also known as blank test, is a process of quantitative analysis with the same methods and steps as the sample to be measured to obtain the analysis results without adding the sample to be measured (in special cases, it can be replaced by a blank sample without the component to be measured, but with a matrix basically consistent with the sample). The results measured by blank test are called blank test value, which is referred to as blank value for short. The blank value generally reflects the background of the test system, including the comprehensive impact of the noise of the test instrument, impurities in the reagent, environment and contamination during operation on the sample. It is directly related to the accuracy of the final test results and can be deducted from the analysis results of the sample. This deduction can effectively reduce the systematic error caused by reagent impure or reagent interference.

② Scope of application
On the one hand, the laboratory can effectively evaluate and correct the errors caused by the impurities carried by reagents, experimental water, utensils and environmental factors; On the other hand, while ensuring the effective monitoring of blank values, we can also master the differences between different analysis methods and testers. In addition, the blank test can accurately evaluate the detection limit, quantitative limit and other technical indexes of the detection method.

7. Repeat Test

① Quality control process
Repeated test is a repeatability test, also known as parallel sample test, which refers to two or more tests under repeatability conditions. Repeatability conditions refer to the test conditions in which the same tester uses the same equipment and the same test method to test the same tested object independently in a short time in the same laboratory.

② Scope of application
Repeated testing can be widely used in laboratories to monitor and evaluate the uniformity of sample preparation, the stability of testing equipment or instruments, the precision of testing methods, the technical level of testers and the analysis interval between parallel samples. It should be noted that with the different content levels of the components to be tested, the factors that may have an important impact on the test precision in the detection process will be very different.

8. Recovery Test

① Quality control process
Recovery test, also known as “spiked recovery test”, is usually a series of operations, such as adding the measured substance with known mass or concentration to the measured sample as the measurement object, measuring with a given method, comparing the obtained results with the known mass or concentration, and calculating the percentage of the increment of the analysis result of the measured substance in the added known amount. The calculated percentage is called the “spiked recovery rate” of the substance by the method, which is referred to as “recovery rate”. Generally, the closer the recovery is to 100%, the higher the accuracy of quantitative analysis results. Therefore, the accuracy of quantitative analysis results can be evaluated by the recovery.

② Scope of application
The recovery rate test has the characteristics of simple operation and low cost. It can comprehensively reflect the errors caused by various factors. It plays a very important role in the daily quality control of the testing laboratory. The main scope of application includes: the control of testing results of various chemical analyses, such as low content of heavy metals and organic compounds in various products and materials, the accuracy of chemical testing methods Verification of reliability, pretreatment of chemical test samples or effectiveness of instrument determination, etc.

9. Verification of calibration curve

① Process Overview
The calibration curve is used to describe the quantitative relationship between the concentration or quantity of the substance to be measured and the corresponding value or indicated value of the detection instrument. Simplified or identical analytical treatment is carried out by using standard solution according to normal sample detection procedures, and the drawn calibration curve is called standard curve and working curve accordingly.
In order to ensure that the calibration curve always has good precision and accuracy, corresponding methods need to be adopted for verification. For the verification of precision, three concentration points of low, medium and high are usually taken on the calibration curve for verification. The verification of accuracy is usually controlled by standard addition recovery test.

② Scope of application
Calibration curve method is often used in laboratory instrument analysis. Usually, the concentration of components in the sample to be measured fluctuates greatly, and the sample batch is large. The precision and accuracy of the calibration curve used in the detection process will be affected by many factors, such as the detection conditions of the laboratory, the response performance of the detection instrument, the operation level of the detection personnel and so on. On the one hand, regular verification can verify the response performance of the instrument, the operation specification and stability of the tester, on the other hand, it can also obtain the stability verification information of the standard solution used in drawing the curve.

10. Quality control chart

① Quality control process
In order to control the precision and accuracy of test results, it is usually necessary to continuously use monitoring samples for test control during the test process. Conduct statistical analysis on the accumulated monitoring data, and determine the center line, upper and lower control limits, upper and lower auxiliary lines and upper and lower warning lines by calculating the statistics such as average value, range and standard deviation, according to the production procedure of quality control chart, so as to draw the analysis control chart. Through the analysis control chart, after judging that the measurement process is in a stable or controlled state, the analysis control chart can be converted into the control chart, and the daily measured control data can be traced to judge whether there is system variation or trend.

② Scope of application
The quality control chart is applicable to the following scope:
– When it is desired to predict the variation range of process output;
– When judging whether a process is under statistical control;
– When the source of variation in the analysis process is random or non random;
– When deciding how to complete a quality improvement project, prevent the emergence of special problems or make basic changes to the process;
– When you want to control the current process, you can detect and take remedial measures when problems occur.

Quality control chart is undoubtedly an important evaluation method in quality control activities, but it should be noted that the conclusion evaluation of this method exists based on the test data of other quality control samples, and realizes the purpose of quality control through the statistical analysis of quality control data. Therefore, compared with other quality control methods, it is more inclined to be used as a tool to evaluate quality control data. In this regard, it is different from other internal quality control methods in the laboratory.