Relevant requirements for testing in the laboratory
Chemical reagents are high-purity chemicals that meet certain quality requirements and are the material basis for analytical work. The purity of the reagent is very important for the analytical test. It will affect the accuracy of the result. If the purity of the reagent does not meet the requirements of the analytical test, accurate analytical results cannot be obtained. The correct selection and use of chemical reagents will directly affect the success or failure of the analytical experiment, the accuracy of the experiment and the cost of the experiment. Therefore, the instrument user must fully understand the nature, type, use and use of the chemical reagent.
According to the quality standards and uses, chemical reagents can be broadly divided into standard reagents, common reagents, high-purity reagents and special reagents.
1 General requirements for inspection methods
- 1 Weighing: refers to the weighing operation with the balance, the accuracy requirement is expressed by the effective digit of the value, such as “weigh 20.0g…” The accuracy of the weighing is ±0.1g; “weighing 20.00g…” The accuracy of the quantity is ±0.01g.
- 2 Accurate weighing: refers to the weighing operation with a precision balance with an accuracy of ±0.0001g.
- 3 Constant amount: refers to the difference in quality after the two consecutive drying or burning under the specified conditions does not exceed the specified range.
- 4Measurement: refers to the operation of measuring the liquid substance by the measuring cylinder or the measuring cup, and the precision requirement is represented by the effective digit of the numerical value.
- 5 suction: refers to the operation of taking liquid substance with a pipette and a graduated pipette. The accuracy requirement is represented by a significant digit of the value
- 6 Blank test: refers to the results obtained by parallel operation, except that no sample is added, using the same analytical procedure, reagents and dosage (except for the amount of standard titration solution in the titration method). Used to deduct the detection limit of the reagent background and the calculation test method in the sample.
2 reagent requirements and basic representation of the solution concentration
The water used in the test method refers to distilled water or deionized water when no other requirements are indicated. When it is not specified which solvent is used to prepare the solution, it means an aqueous solution. When the specific concentration of H2SO4, HNO3, HCL, NH3·H2O is not specified in the test method, it refers to the concentration of the commercially available reagent specification. The drop of liquid refers to the amount of distilled water flowing down from the standard dropper. At 20 ° C, 20 drops is equivalent to 1.0 mL.
The representative methods of solution concentration are:
1 is expressed in the standard concentration (ie, the concentration of the substance): it is defined as the amount of the substance containing the solute per unit volume of the solution, and the unit is Mol/L.
2 is expressed in terms of proportional concentration: it is expressed as the mixed mass fraction of several solid reagents or the mixed volume fraction of the liquid reagent, and can be recorded as (1+1) (4+2+1)
3 expressed in mass (volume) fraction: expressed as the mass fraction or volume fraction of the solute in the solution, which can be recorded as w or ф.
4 If the solution concentration is expressed in mass or volume units, it can be expressed as g/L or in its appropriate fractional number (eg, mg/mL).
Requirements and other requirements for formulating solutions:
The purity of the reagents and solvents used in the preparation of the solution should be in accordance with the requirements of the analytical project. The reagents are usually stored in hard glass bottles. The lye and metal solutions are stored in polyethylene bottles and stored in brown bottles in the dark.
Parallel tests must be performed during the test. The method of representation of the test results shall be consistent with the representation of food hygiene standards. The calculation and value of the data shall follow the valid numerical rules and numerical trade-off rules.
During the inspection process, the inspection shall be carried out in strict accordance with the analytical procedures specified in the standard. Protective measures shall be taken for the unsafe factors (poisoning, explosion, corrosion, burns, etc.) in the experiment. The physical and chemical testing laboratory implements analytical quality control. On the basis of establishing good technical specifications, the physical and chemical testing laboratory should have technical parameters such as detection limit, precision, accuracy, and drawing standard curve data. The inspector should fill out the inspection record.
