Internal quality control of physical and chemical laboratory

1 Personnel training: in terms of experimental skills, the direct and effective way of personnel training is to conduct personnel comparison test In combination with participation in external ability verification, laboratory review and internal audit, health emergency testing and other activities, the expert group was organized to carry out personnel comparison test and personnel training The general practice is: first, determine the personnel to participate in the assessment or training The personnel are generally composed of experienced deputy director technicians, competent technicians, technicians and internship technicians Then, they are divided into two to three groups, one to two in each group After that, the expert group will comment on each group in detail In this way, young and middle-aged inspectors are trained, which makes a qualitative leap in the basic knowledge, experimental skills, quality control awareness and emergency detection ability of laboratory inspectors, so that the internal quality control of the laboratory can be put into practice and the accuracy and reliability of the detection results can be effectively guaranteed 2、 Sample quality control: the quality assurance of samples is often ignored in the inspection process Although it does not belong to the inspection process, it is the link to ensure the accuracy and reliability of the test results The quality of samples is affected by time and space, and restricted by many factors If the sample is not representative, uniform and stable, the clearer the test result is, the greater the harm will be When physical and chemical inspectors participate in sampling work, they should master sampling theory and plan Only by paying attention to the quality control of sampling can the test results truly represent and reflect the overall characteristics of the sample 3、 Determination and verification of detection methods: 1 Classification detection methods of detection methods are generally divided into standard methods, non-standard methods and standard methods with allowable deviation Among them, the standard methods include: international standards, such as IS0, wh0, ufa0, CAC, etc.; national (or regional) standards, such as GB, en, an-si, BS, DIN, JIS, AFNOR, r0ci ', Pharmacopoeia, etc.; industrial standards, local standards, enterprise standards filed by standardization authorities Non standard methods include: methods published by technical organizations, such as AOAC, FCC, etc.; methods published by scientific literature or journals; guidance methods provided by instrument manufacturers; internal methods developed by laboratories 2 The test methods shall be selected in the following order of priority: methods designated by customers; standards prescribed by laws and regulations; international standards, national (or regional) standards; industrial standards, local standards, enterprise standards filed by standardization authorities; non-standard methods and standard methods with allowable deviation 3 The validation of the test method should be verified before it is applied to the sample test It is found in the verification that the standard method or non-standard method is not detailed in the original text, but it will affect the test results, so the detailed operation steps shall be compiled into the operation instruction, which shall be used as the supplement of the method after being reviewed and approved 4 The standard methods for controlling the allowable deviation include: the standard methods used beyond the scope of the standard; the standard methods expanded or modified The standard methods that are allowed to deviate shall be verified, the operation instructions that deviate from the standard shall be prepared, and they can only be used after being reviewed and approved 4、 Traceability of measurement value: in chemical analysis, from a specific test result to the national standard, and then to the international unit of measurement, the traceability chain is realized through test methods and reference materials Therefore, in the laboratory quality control, it is necessary to ensure the traceability of reference materials and testing equipment 1 Traceability of reference materials the reference materials shall be purchased from qualified suppliers to ensure the reliable source of goods and facilitate the traceability of goods The imported reference materials shall be provided with the valid certificate traceable to the international measurement standard or the measurement standard of the exporting country or the certificate of conformity issued by the recognized foreign technical institutions, and the concentration, validity period, etc of the reference materials shall be confirmed The reference materials prepared in China shall have the serial number issued by the National Metrology Department and be attached with the certificate of reference materials When reference materials are used and traceability of measurement value cannot be carried out, effective certification provided by the manufacturer shall be provided, and the laboratory shall prepare procedures for technical verification 2 The traceability of instruments and equipment, including auxiliary measuring equipment, which has an important impact on the accuracy or effectiveness of test or sampling results, shall be verified / calibrated before being put into use to ensure the traceability and reliability of test results Instruments and equipment that have not been verified / calibrated shall not be used The measuring instruments listed in the national compulsory verification catalogue shall be verified by the legal metrology verification institution or the authorized metrology verification department, and the verification certificate shall be issued; the measuring instruments not subject to compulsory verification may be verified / calibrated by the legal metrology institution, the national accreditation institution or the calibration laboratory recognized by the members of APLAC and ILAC multilateral recognition agreements, and the verification / calibration certificate shall be issued It can also be calibrated by the laboratory according to the self inspection procedures, and the calibration results shall be reported The calibration personnel shall have the ability to engage in the operation and calibration of the instrument and equipment When it is impossible or not applicable to trace to the national measurement standard, the test reliability shall be provided by means of inter laboratory comparison, mutual comparison of similar equipment, and laboratory capability verification 3 During the period of two verifications / calibrations, the technical indicators of the instruments and equipment shall be checked during daily use, i.e during the period of verification, records shall be made to keep the instruments in good condition The main verification items in the national metrological verification regulations shall be selected for the periodic verification of instruments and equipment Generally, the following appropriate items shall be selected: zero point inspection, sensitivity, accuracy, resolution, quantity repeatability, linearity of standard curve, built-in self calibration inspection of instrument, test comparison of reference material or reference material, and technical indicators listed in instrument specification Reference materials also need to be checked during the period 5、 Quality evaluation of test data: the main quality index of test data refers to the accuracy and precision of data, as well as other technical elements of test method, such as test limit, linear range, specificity, resistance, sensitivity and uncertainty of the method 1 Accuracy accuracy is a comprehensive index reflecting systematic error and random error of the method The following methods can be used to check the accuracy: (1) the standard reference material is used for analysis and measurement, and the measured value and guarantee value are compared, and the error or relative error shall meet the requirements of the method Generally, 1-2 certified reference materials with concentration levels shall be determined At least 6 samples of the same reference materials shall be used for each concentration level, and the average value, standard deviation and relative standard deviation of the determination results shall be calculated Accuracy (%) = average detection concentration / marked concentration × 100 (2) In the absence of certified reference materials, analytes should be added to the sample matrix to determine the recovery At least 3 added concentrations shall be selected, and a certain concentration range shall be included The concentration within or close to the limit of quantification is the required concentration If the sample has an allowable limit, the allowable limit is also the required concentration Each concentration level shall be measured at least six times in parallel, and the average value, standard deviation and relative standard deviation of the measurement results shall be calculated Recovery (%) = (added standard sample measured value - sample measured value) / added concentration × 100 For organics to be tested, the recovery index shall meet the requirements of Table 1; for element analysis, the recovery index shall be between 90% and 110% (3) It is to test and compare the same sample with different analytical methods based on different principles The requirement of recovery rate is different in different concentration range 2 Precision precision refers to the consistency between independent test results under specified conditions The precision includes two sub indexes: method repeatability and method reproducibility Repeatability: refers to the degree of consistency between independent test results under repeatability conditions Repeatability condition refers to the condition that in the same laboratory, the same operator uses the same equipment, follows the same test method, and obtains mutually independent test results for the same tested object in a short time The repeatability shows the precision of the method in the laboratory The standard method must be tested for its precision to see if it is reliable In the process of repeatability test, three samples of different concentration levels were selected, and each concentration level was measured at least six times in parallel, and the average value, standard deviation and relative standard deviation were calculated Reproducibility: refers to the consistency between test results under reproducibility conditions The reproducibility condition is the condition that different operators use different equipment in different laboratories to obtain test results from the same tested object according to the same test method Reproducibility characterizes the precision of the method between laboratories to ensure that the method can be applied in different laboratories In the process of reproducibility experiment, at least three samples of different concentration levels or spiked concentration levels must be selected The concentration at the world limit or near the quantitative limit is the required concentration If the sample has the allowable limit, the allowable limit is also the required concentration There are two parallel samples, each of which is measured at least six times in parallel The data of each laboratory were analyzed statistically, and the total mean value, the standard deviation of reproducibility and the relative standard deviation of reproducibility were calculated 3 The linearity of linear analysis method is used to characterize the relationship between the concentration or quantity of the substance to be measured and the response value Its function is to get the test results directly or through mathematical formula in a given concentration range through the linear relationship The concentration range of the method should cover an order of magnitude as far as possible, at least 5 points (excluding blank) should be made, and the concentration of the tested component in the test solution should be within the linear concentration range For screening method, the value of linear correlation coefficient shall not be lower than o.98, and for confirmation method, the value of linear correlation coefficient shall not be lower than 0.99 4 Detection limit and quantitative limit detection limit and quantitative limit are two important indexes to characterize the detection ability of the method The detection limit can be determined in the following ways: (1) the average response signal value of at least 20 parallel determinations of blank samples plus 3 times of the standard deviation of the parallel determinations, and the corresponding sample analyte concentration or content is called the detection limit of this method (2) For spectrophotometry, the detection limit is the concentration value corresponding to 0.01 absorbance after deducting the blank value (3) The detection limit of chromatographic analysis refers to the small amount of substances that need to enter the chromatographic column when the detector can generate the response signal that is different from the noise phase Generally, it is determined as the concentration or content of the sample analyte corresponding to the response value of 3 times of the signal-to-noise ratio It is specified that the average response signal value of at least 20 parallel determination blank samples plus 10 times of the standard deviation of the parallel determination value, and the corresponding sample analyte concentration or content is called the quantitative limit of the method 5 Specificity refers to the ability of methods to distinguish analytes to be tested from other interfering substances (such as isomers, metabolites, degradation products, endogenous substances, matrix components, etc.) The ability of the method to determine analytes in a complex mixture without interfering with other components in the mixture (or sample) was characterized 6 The analysis method has the ability of anti-interference to the variable test factors When the test conditions change slightly, the method can keep the test results unaffected For the test of method resistance to denaturation, the sample pretreatment, purification, analysis and other factors that may affect the test results are usually selected for the pre-test, such as the source and storage time of reagents, solvents, standards, sample extracts, heating rate