In order to ensure that the analytical test results have a certain degree of accuracy, and have comparability and consistency, it is often necessary to calibrate the instrument, calibrate the concentration of the solution and evaluate the analytical method of the substance, which is called the standard substance.

The standard material requires uniform material, stable performance, mass production, quasi-certain value, and a standard material certificate.

Standard substances have been identified with one or more sufficiently uniform characteristic values of the substance or material, as a "measuring tool" in the analytical measurement industry, in the calibration of measuring instruments and devices, evaluation of measurement analysis methods, measurement of material or material characteristic values and assessment of the analyst's operational technical level, as well as in the production process of product quality control and other fields play an indispensable role.

By definition, a reference material has three distinctive characteristics:

1. Accuracy, uniformity and stability of characteristic quantity value;

2. Quantity value is transitive;

3. Measurement standards in physical form.

Among them, accuracy, uniformity and stability are the characteristics and basic requirements of standard material quantity value. The following is a specific analysis:

1) Accuracy

Accuracy and reliability are the main characteristics of the standard material, usually the standard value of the standard material and the uncertainty of the measurement will be given at the same time in the standard material certificate, and the sources of uncertainty including weighing, instruments, uniformity, stability, uncertainty between different laboratories and different methods should be calculated.

2) Uniformity

Material uniformity is the first condition of the standard material, the precision of the measurement method, that is, the standard deviation can be used to measure the uniformity of the standard material, the precision is affected by the sampling amount, the uniformity of the standard material is for the given sample amount, the small sample amount of the uniformity test will generally be given in the standard material certificate.

3) Stability

Stability refers to the ability of a reference substance to maintain its characteristic value within a specified range under specified environmental conditions and time.

According to the characteristics of reference materials, reference materials are usually divided into primary reference materials and secondary reference materials.

1. Primary standard material:

It is mainly used to calibrate the standard substances lower than it, calibrate high accuracy measuring instruments, research and evaluation standard methods;

2. Secondary standard material:

It is mainly used to meet some general detection and analysis needs, as well as the general requirements of the social industry, as a working standard material directly used for field method research and evaluation, for daily analysis and measurement with lower requirements.

A reference substance is a substance or material having one or more sufficiently good, highly stable, and defined physical, chemical, and metrological properties used to calibrate a measuring instrument, evaluate a metrological method, or assign a value to a material. The reference material includes: the reference material for chemical composition analysis, the reference material for measurement of physical and chemical properties, and the reference material for measurement of engineering and technical properties. The standard substances used to unify the value of quantities belong to the category of measuring instruments.