Any detection will generate detection errors, and there are many sources of analysis and testing errors, such as sample representativeness, uniformity, and stability. The task of quality assurance is to reduce all errors, including systematic errors and random errors, to the expected level.

The quality assurance of analytical testing can be divided into two aspects: quality assurance of sampling and quality assurance of analytical testing systems.

The two main aspects of quality assurance

Quality assurance of sampling
A sample is a subset of substances selected from a large number of materials;
The measurement result of the sample is an estimated value of the overall characteristic quantity.

Due to the non-uniformity of the overall material, inferring the population based on the measurement results of the sample inevitably introduces errors, which are called sampling errors.

Sampling errors can be divided into random errors and systematic errors:
1.Random error in sampling: caused by uncontrollable random factors during the sampling process. Increasing the number and quantity of samples can reduce the random error in sampling.
2.Systematic sampling error: Due to incomplete sampling plans, defective sampling equipment, incorrect operation, environmental factors, and other influencing factors, this error can only be avoided or eliminated through strict sampling quality assurance work.

Sampling error is always associated with measurement error, and can be estimated by repeatedly measuring multiple laboratory samples and multiple measurements of a laboratory sample.

Quality control in the analysis and testing process
The analysis and testing process generally includes sample processing, selection of measurement methods and standards, calibration and determination of measuring instruments, statistical analysis of data, and reporting of measurement results. Each step is closely related to the operational skills, theoretical knowledge, and quality awareness of the measurer. How exactly is it related?

1Sample processing and recovery rate
During the sample processing, incomplete dissolution, separation, and enrichment may occur, or negative systematic errors may occur due to the volatilization and decomposition of the tested components; On the other hand, positive systematic errors may also occur due to contamination of the tested components by vessels, chemical reagents, environment, and operators. Even if no significant systematic errors are generated during the sample processing, significant random errors can still be introduced.

2Control and correction of blank analysis
（1）Analyze the blank and its role:
The analysis of blank and its variability plays a decisive role in the accuracy, precision, and detection limit of trace and ultra trace analysis results.
（2）Control of blank analysis:
There are mainly the following points:
① Eliminate or control contamination of the sample by the experimental environment;
② The contamination of the tested component in the sample by chemical reagents varies with the purity and dosage of the reagents;
③ The containers used for storing and processing samples may contaminate the samples if the material is impure or not thoroughly washed;
④ Avoid contamination of the sample by analysts.
（3）Blank experiment:
Perform blank correction on the measured values of the sample based on the blank test values and their standard deviations.

3Applicability of measurement methods
（1）Categories and levels of measurement methods:
There are thousands of existing standard methods, which can be roughly divided into3Types:
① The universal standard method for testing product technical specifications.
② The standard methods developed to implement certain regulations are called square methods. Like the American Society of Analytical Chemists（AOAC）Standard methods for analyzing food, drugs, fertilizers, pesticides, and cosmetics have been developed to ensure the implementation of relevant agricultural and public health regulations.
③ Basic standard methods, such as the British Society for Analytical Chemistry（SAC）Proposed analysis method and American Society for Testing and Materials（ASTM）Proposed standard methods.
（2）Main technical parameters and control indicators of measurement methods:
Including: linear range, accuracy, precision, sensitivity, detection limit.

4Calibration of measurement methods
The purpose of measuring method calibration is to establish a functional relationship between the measured signal and the measured chemical composition value, that is, a quantitative relationship between the physical signal and the chemical composition. Creating accurate and effective calibration curves is an important prerequisite for obtaining accurate and reliable measurement results.
（1）Use accurate and reliable measurement standards;
（2）Eliminate or measure the effects of interference and matrix effects;
（3）Control experimental conditions and design experiments reasonably.

The experiment should be designed according to the following principles:
① In order to maintain the consistency between the experimental conditions of the measured sample and the conditions for making the calibration curve as much as possible, the calibration curve should be made and used within a short time interval;
② The optimal number of experimental points on the calibration curve is5More than one, and the range of experimental points should be as wide as possible to improve the reliability and stability of the calibration curve;
③ It is recommended to repeat measurements at each experimental point and take the average value. Repeat measurements should be taken at least at the endpoints of the calibration curve to reduce experimental errors.

5Standard analysis methods and standardization of analysis methods
Standard analytical methods, also known as analytical method standards, are a type of technical standard. There are often multiple methods available for determining a project, each with different sensitivities. The requirements for instruments and operations are different. Moreover, due to the different principles of the methods, the interference factors are also different, and even the meaning of the results is not the same.
Laboratories attach great importance to inspection work and meet the quality requirements of society for inspection data. Therefore, it is necessary to comprehensively control the various factors that affect inspection data, such as technical personnel, instruments and equipment, sample disposal, testing methods, drug reagents, environmental conditions, quantity traceability, etc., as an organic whole. The entire process of inspection work involves the effective control of the interrelationships and relationships between various activities that affect the quality of inspection and the formation of its quality. Only then can the accuracy, fairness, authenticity, and reliability of inspection data be ensured, and the continuous improvement and enhancement of laboratory analysis and testing work quality be guaranteed.

The specific explanation is as follows:
（1）Personnel
Personnel are the most valuable resource. The quality of a laboratory largely depends on the quality and proficiency of its personnel.
（2）Instrument and equipment
Instruments and equipment are important resources necessary for laboratory testing work, and are the foundation for ensuring the quality of testing work and obtaining reliable measurement data.
（3）Pharmaceutical reagents
Pharmaceutical reagents refer to consumable materials used for testing. With the development of society, people have increasingly high requirements for detection accuracy, from constant to trace, and then to trace and ultra trace analysis. The content of the tested elements is very low and extremely small, and the purity and quality requirements for drug reagents are very strict.
The quality of experimental reagents directly affects the quality of detection work, mainly in two situations:
One is that the reagent is impure (containing the tested component itself), which leads to higher results;
Another type is when the sensitivity of the reagent decreases or becomes ineffective, which affects the accuracy of the detection results. The laboratory should establish a procurement and acceptance system for drug reagents, establish a system for reagent validation, qualified (unqualified) records, and qualified supplier list to ensure that reagents meet technical specifications and provide a basis for correct procurement.
The procurement of consumables such as chemical reagents is an important component of the entire testing process. Reagents directly affect the quality of testing work, so it is necessary to strictly control the quality of external support services and supplies to ensure that the testing quality is not affected.
（4）Testing method
The testing method is the basis for implementing testing work in the laboratory and is the most important factor in ensuring the analysis of data. Different detection methods result in varying levels of quality.
（5environment
Environment refers to experimental facilities and environmental conditions. To ensure the quality of inspection work, the laboratory facilities and environmental conditions must meet the work requirements.
（6）Traceability of measurement values
Traceability of measurement values refers to the characteristic of linking measurement results or standard values with specified reference standards (national or international measurement standards) through an uninterrupted comparison chain with specified uncertainty. Traceability of measurement values is a key link in inspection work.
（7）Sample disposal
Sample disposal refers to the analysis and testing of the submitted samples. The laboratory should develop procedures for sample collection, sealing, transportation, handover and acceptance, and sample retention in accordance with national technical specifications or standards; For samples with special testing requirements, equipment and facilities that meet the storage conditions of the samples should be equipped to avoid deterioration, damage, or cross contamination during storage or inspection, ensuring the integrity of the tested samples and the validity of the test results.

Article source: Internet