Reference material is a measurement standard to ensure accurate value and value traceability. It is widely used in calibrating measuring instruments, evaluating measurement methods, and assigning material characteristic values. It plays an important role in quality management, quality assurance, and technical arbitration.

　　Traceability System for Definition, Classification, Numbering and Quantity of Reference Materials

　　(1) Definition

　　Certified standard substances are standard substances certified by authoritative departments, and one or more of their characteristic values are determined through the establishment of traceability procedures, and can be traced back to the measurement unit that accurately reproduces the characteristic value. Certified standard substances in our country are approved, promulgated and authorized by the national standard measurement department.

　　(2) Classification

　　Our country divides reference materials into primary and secondary, which all meet the definition of certified reference materials.

　　first-class reference material(Primary Reference Material) has high accuracy and is mainly used to evaluate standard methods and conduct arbitration analysis　　　　① Use absolute measurement or two or more accurate and reliable methods of different principles to determine the value. In the case of only one method, use multiple laboratories to determine the value by the same accurate and reliable method.

　　secondary reference materialThe number of the second-level reference substance code "GBW (E) " is preceded by the front of the number. The first two digits of the number are the major category number of the reference substance, and the last four digits are the serial number of the major category of reference substance. The copy batch number is indicated by English lowercase letters and is ranked last in the reference substance number.

　　(4) Traceability system of magnitude

　　The traceability system of the magnitude is shown in the figure below.

　　(1) Save and transfer characteristic values and establish measurement traceability

　　The reference material is a measurement standard with good accuracy, uniformity and stability of the characteristic quantity. It has the function of maintaining the characteristic value in time and transferring the value in space. By using the reference material, the actual measurement results can be traceable.

　　(2) Ensure the consistency and comparability of measurement results

　　By calibrating the measuring instruments and evaluating the measurement process, the measurement results are traced back to the national unit system (SI) by the reference material to ensure the consistency and comparability of the measurement results, so as to achieve the uniformity of the magnitude.

　　(3) Research and evaluation of measurement methods

　　Reference materials can be used as substances with known characteristic values to study and evaluate methods for measuring these components or characteristics, so as to judge the accuracy and reproducibility of the method, and to evaluate the adaptability of the detection method in specific occasions by verifying and improving the accuracy of the measurement method, so as to promote the development of testing technology.

　　(4) Establish the quality assurance of the measurement system

　　Testing institutions use standard materials for quality control to achieve quality assurance, which is a good way to ensure that testing data is accurate, reliable, and comparable.

　　Use and management of reference materials

　　(1) The procurement of reference materials should be unified, and the requirements for use should be taken into account when purchasing, such as the range of values, the composition of the matrix, and the uncertainty of the standard value. The purchase of reference materials can be made on the National Standard Network.

　　(2) Establish a general ledger of reference materials and implement a registration system for receipt. The general ledger of reference materials includes: name, composition, supplier, batch number, purchase date, validity date, certificate number, acceptance status or conclusion, storage location and other information;

　　(3) The standard substances shall be disposed of safely according to the requirements of the certificate or relevant storage conditions, designated for safekeeping, and a special storage area shall be set up. The storage area shall be clearly marked and there shall be anti-pollution measures to ensure that the standard substances are in a standard state and maintain their validity.

　　(4) Use certified reference materials officially approved by the state or relevant departments in order to be traceable to national benchmarks, national measurement benchmarks or national reference material benchmarks. For the use of unapproved reference materials, they must be analyzed, compared and verified to prove that they meet the requirements before use;

　　(5) The value of the standard solution must be tested, verified, and compared according to the specified methods, and can be traced back to the national benchmark; if it cannot be traced back to the national benchmark, it can only be used when the data of the standard test proves that the requirements are met. The preparation, setting, and storage of the standard solution shall be carried out in accordance with relevant regulations.

　　(6) The reference material has exceeded its validity period, or within the validity period, but an abnormal situation has arisen, and changes have occurred after testing and analysis. The management personnel shall fill in the application for scrapping the reference material, and deal with it in a timely manner after approval.

　　(7) Reference materials and standard solutions belonging to highly toxic chemicals shall be managed in accordance with the regulations on the management of highly toxic chemicals, and the use shall be tracked.

　　Key Points of Standard Solution Preparation Management

　　(1) Accurately weigh (measure) the solute

　　For solid reagents, it should be fully dried and cooled to room temperature as required, and then weighed immediately for preparation. When weighing, accurately weigh to 0.1 mg. For liquid reagents, the required volume should be calculated according to the needs, and then directly measured. Standard solution preparation should use qualified Class A volumetric bottles.

　　(2) Choose the correct solvent

　　The general principle for selecting a solvent is that the purity of the solvent should be roughly the same as the purity grade of the reagent. If necessary, the quality of the solvent should be tested, and if its purity does not meet the requirements, it should be treated to ensure the quality of the standard solution.

　　(3) Control the number of preparations

　　The standard solution should be prepared according to the stability, concentration and required amount of the standard solution. The standard solution with higher concentration and better stability can be prepared for about a month at a time, and the standard solution with lower concentration and poor stability should be prepared in small quantities in batches.

　　(4) Do a good job in calibration

　　The standard solution concentration should be calibrated regularly, especially for standard solutions with unstable concentrations, it is best to calibrate before each use to ensure accuracy.