Standard analysis methods and standardization of analysis methods

1. Standard analysis methods The determination of a project often has a variety of alternative analysis methods. These methods have different sensitivities and different requirements for instruments and operations; and because the principles of the methods are different, the interference factors are also different, and even the results The meaning is different. When different methods are used to measure the same item, the problem of incomparable results will arise, so it is necessary to carry out standardization activities of analytical methods. The selection of the standard method must first reach the required detection limit. Secondly, it can provide sufficiently small random and systematic errors. At the same time, it can obtain similar accuracy and precision for various environmental samples. Of course, technology and instruments must also be considered.
Second, the standardization of analytical methods The standard is the result of standardization activities. Standardization is a highly policy-oriented, economic, technical, rigorous and continuous work. To carry out this work, a strict organizational structure must be established. Due to the special nature of these works, these institutions are required to be bound by standardized regulations.
3. Collaborative experiment to monitor the experimental space. Collaborative experiment refers to the cooperative research activities carried out for a specific port and in accordance with a predetermined procedure. The collaborative test can be used for the standardization of analytical methods, the determination of the concentration of reference materials, the arbitration of laboratory disputes and the technical evaluation of analysts.
The purpose of standardization and collaborative testing of analytical methods is to determine the precision and accuracy that can be achieved as the standard analytical method under actual application conditions, and to formulate the allowable limits of analytical errors in practical applications as method selection, quality control and Basis of analysis results arbitration.

4. Environmental Standard Substances

1. Environmental standard substances and their classification
(1) Environmental measurement Environmental measurement is a measurement system that quantitatively describes the distribution and concentration (or intensity) of harmful substances or physical quantities in different media in the environment. Environmental measurement includes environmental chemical measurement and environmental physical measurement.
Environmental stoichiometry is a chemical substance salt measurement system centered on the determination of harmful substances in the atmosphere, water, soil and people and organisms; environmental physical stoichiometry is a physical measurement system centered on the determination of noise, vibration, electromagnetic waves, radioactivity, thermal pollution, etc. .The relevant measurement items are described in the previous chapters.
(2) Matrix and matrix effect In environmental samples, the content of various pollutants is generally at the ppm or ppb level, and other substances that are present in large amounts are called matrix. Most of the measurement methods used in pre-oral environmental monitoring are relative analysis methods, that is, a method for comparing and measuring the reference reagent or standard solution with the sample to be tested under the same conditions. The standard solution made up of "pure substances" differs greatly from the actual environmental matrix. The difference between the composition of the matrix and the matrix, the error caused by the difference in physical and chemical properties in the actual measurement is called the matrix effect.
(3) Environmental standard materials Environmental standard materials are a class of standard materials. Different countries and different institutions have different names for standard substances, and there is still no generally accepted definition so far.
The International Organization for Standardization (ISO) defines a reference material (referred to as RM for short) as this material has one or several properties that have been fully determined, and these properties can be used as a calibration instrument or verification measurement method. RM can transfer measurement data (including physical, chemical, biological or technical) between different locations. It can be pure or mixed gas, liquid or solid, or even simple artificial objects. Before a batch of RM is issued, one or several properties given and sufficient stability should be determined. Usually within the specified uncertainty range, an appropriate small amount of RM samples should have the complete RM properties. ISO also defines that certified reference materials (CRM) should be accompanied by a certificate. The certificate should have the relevant characteristic values, use and storage methods, and validity period. The certificate is issued by the national authoritative measurement unit.
The standard substance defined by the National Bureau of Standards (NBS) is called the standard reference substance (SRM for short). It is issued by NBS, and the certificate with the certificate is also called CRM. The value of the reference material is obtained by one of the following three methods: â‘  a standard method with known accuracy; â‘¡ two or more independent and reliable methods; â‘¢ a specially established laboratory collaboration network. SRM is mainly used to: â‘  help develop standard methods; â‘¡ calibrate measurement systems; â‘¢ ensure the long-term improvement of quality control procedures.
2. Preparation and setting of standard materials (1) General process of standard material preparation The preparation of solid standard materials can be roughly divided into sampling, crushing, mixing and sub-packaging. Figure 1 is the process of making river sediments, our country's environmental standard substance. Solid reference materials are usually prepared from environmental samples. Environmental samples that have been selected as standard materials include fly ash, river sediment, soil, and coal: plant leaves, roots, stems, and seeds: animal offal, muscle, blood, urine, hair, etc.
Most environmental liquid and gas samples are very unstable, and the composition has a large dynamic change. Therefore, the standard substances of liquid and gas are prepared by simulating the composition of natural samples. For example, SRM1643a (19 trace elements in water) in the United States is based on The concentration of various elements in fresh water in natural ports is accurately weighed by various chemical reagents and accurately diluted.
(2) Research and inspection of stability and uniformity Uniformity is the first and most fundamental requirement of standard materials, and it is the premise to ensure that the standard materials have spatial consistency, especially for solid samples. Uniformity is a relative concept. First, absolute uniformity is impossible. If the unevenness of the sample is much smaller than the error in the analysis, the sample can be considered to be uniform. The uniformity of the sample is targeted, because the distribution of different components in the sample is very different. Some components are difficult to achieve uniformity, such as solid samples, the inspection of the uniformity of these components is the focus of inspection.
The amount taken is also a factor related to uniformity. In order to ensure the uniformity of the sample, the standard sample certificate usually specifies the minimum sampling volume. Because when the sampling volume is reduced below a certain limit, the unevenness of the sample will increase sharply.
Uniformity inspection can be divided into pre-packaging inspection and post-packaging inspection. The inspection before sub-packaging includes inspection during the mixing process and inspection after mixing.
Stability is another important property of reference materials, and it is a prerequisite for making reference materials consistent in time. Compared with solid reference materials, the uniformity of liquid and gaseous materials is easy to achieve, but it is much more difficult to maintain stability.
The stability of reference materials is affected by environmental conditions such as temperature, humidity, and light. The activity of microorganisms will also lead to changes in the composition of the sample, so many standard materials must be sterilized by radiation or high temperature sterilization. Choosing an appropriate storage container and adding an appropriate stabilizer may greatly improve the stability of the standard substance.
The stability test adopts the method of follow-up test. After preparation, regularly check whether the components change with time, and whether the degree of change can meet the requirements of the allowable limit of the uncertainty of the reference material.
The inspection of uniformity and stability usually adopts a high-precision measurement method in order to find small differences in the time and space distribution of reference materials.
(3) Analysis and value determination of standard materials At present, the value determination of environmental standard materials mostly adopts a variety of analysis methods, which are completed by collaborative tests of multiple laboratories. The preparation of environmental standard materials is a highly technical, highly accurate requirement. The work environment and personnel operation skills must have high water, large workload, and high preparation cost. This is also the main reason why the types of reference materials increase slowly and are expensive.
On the basis of accurate analysis, the method of mathematical statistics is often used for the setting of standard materials. At present, China's environmental standard materials mostly process data according to the following steps:
(1) For a group of experimental data, after discarding the outliers in the original data according to the Grubbs test, find the mean, standard deviation, and relative standard deviation of the group of data:
(2) The average value of each measurement in different laboratories and different methods of an element mountain is regarded as a set of equal precision measurement values. After discarding outliers using the Grubbs test, the total average and standard deviation are obtained:
(3) The total average value is used to represent the setting value of the element, and the single uncertainty of the measurement is expressed by twice the standard deviation (2s), and the relative uncertainty is expressed by dividing the 2s by the total average value.

American analytical standards

Analytical Standards Introduction

Standards are materials containing a known concentration of an analyte. They provide a reference to determine unknown concentrations or to calibrate analytical instruments.

The accuracy of an analytical measurement is how close a result comes to the true value. Determining the accuracy of a measurement usually requires calibration of the analytical method with a known standard. This is often done with standards of several concentrations to make a calibration or working curve.

Primary Standards

A primary sta

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