The standard substance is a measurement standard with accurate quantity, and it has been widely used in the fields of chemical measurement, biological measurement, engineering measurement and physical measurement. Standard substances have the following characteristics:
The batch value of the standard substance is only related to the properties of the substance, not to the quantity and shape of the substance;
There are many types of standard substances, and there are thousands of standard substances for chemical composition alone, and their quantitative limits span 12 orders of magnitude;
The reference material has strong practicability and can be applied under actual working conditions. It can be used not only for calibration and verification of measuring instruments, but also for evaluating the accuracy of measurement methods, as well as for quality evaluation of the measurement process and measurement certification and measurement arbitration of laboratories. wait;
Standard substances have good reproducibility and can be prepared in batches and reproduced after use.
According to "International General Metrology Basic Terminology" and "ISO Guide 35", reference materials are defined as follows.
(1) Reference material (reference material, RM) has one or more sufficiently uniform and well-determined characteristic values for calibrating equipment, evaluating testing methods, or materials or substances that assign values to materials.
(2) A certified reference material (CRM) refers to a reference material with a certificate, one or more of its characteristic values are determined by a procedure that establishes traceability, so that it can be traced to an accurately reproduced reference material, expressed in thousands The unit of measure for the value of the property, and each certified value is accompanied by an uncertainty for a given level of confidence.
(3) Primary reference material (PRM) is a relatively new concept. The International Committee for Planning and Design (CIPM) established the Material Machinery Consultative Committee (CCQM) in 1993, and proposed it at the 1995 Material Consultative Committee meeting. It is defined as follows: a primarymethedofmeasurement (PMM) is a measurement method with the highest metrological quality, its operation can be completely described and understood, its uncertainty can be expressed in SI units, and the measurement results do not depend on the measurement standard being measured . The reference reference material refers to a reference material with the highest measurement quality and whose value is determined by the reference method.
It can be seen from the above definition that standard substances have two notable characteristics: O has the highest accuracy; @ is used for measurement purposes. This clarifies some vague concepts about standard substances, and puts those "product series standard samples" (cotton, grain, wool, hemp and other products) that are not used to calibrate measuring instruments and measurement methods, and have no accuracy requirements Standard samples) are distinguished from standard substances.