Chemical Composition Analysis and Testing Institution

Nanjing Aikang Quanxin Analysis and Testing is a third-party chemical product testing laboratory. We possess advanced technical equipment and a professional team, providing comprehensive, accurate, and reliable testing services for chemical products. Our professional team, with extensive experience, is always committed to offering you high-quality and professional testing and analysis services.
How to ensure the accuracy of test results?
All tests will produce testing errors, and there are many sources of analytical testing errors, such as the representativeness, uniformity, and stability of the sample. The task of quality assurance is to reduce all errors, including systematic errors and random errors, to an expected level.

Quality assurance in analytical testing can be divided into two major aspects: quality assurance of sampling and quality assurance of the analytical testing system.

Two Major Aspects of Quality Assurance 

Quality Assurance of Sampling:

A sample is a portion of material selected from a larger quantity;

The test result of the sample is an estimate of the overall characteristic quantity;

Due to the heterogeneity of the overall material, using the test result of the sample to infer the overall material inevitably introduces errors, known as sampling errors;

Sampling errors can be divided into random errors and systematic errors;

1. Random Sampling Error: Caused by uncontrollable random factors during the sampling process. Increasing the number of samples and the sample size can reduce random sampling errors.

2. Systematic Sampling Error: Caused by imperfect sampling plans, defective sampling equipment, incorrect operations, environmental factors, etc. This type of error can only be avoided or eliminated through strict quality assurance work in sampling.

● Sampling errors are always associated with measurement errors. By repeatedly testing multiple laboratory samples and conducting multiple tests on one laboratory sample, sampling errors can be estimated.


Quality Control in the Analytical Testing Process 


The analytical testing process generally includes sample processing, selection of measurement methods and measurement standards, calibration of measuring instruments, testing, statistical analysis of data, and reporting of measurement results. Each of these steps is closely related to the operator's skills, theoretical knowledge, and quality awareness.

How exactly are they related?


1. Sample Processing and Recovery Rate


During sample processing, incomplete dissolution, separation, or enrichment may occur, or the measured component may volatilize or decompose, resulting in negative systematic errors. On the other hand, contamination from utensils, chemical reagents, the environment, or the operator may cause positive systematic errors. Even if no obvious systematic errors occur during sample processing, significant random errors may still be introduced.


2. Control and Correction of Analytical Blanks


(1) Analytical Blanks and Their Role:

Analytical blanks and their variability play a decisive role in the accuracy, precision, and detection limits of trace and ultra-trace analysis results.

(2) Control of Analytical Blanks:

Mainly includes the following points:

① Eliminate or control contamination of the sample by the experimental environment;

② Contamination of the sample by chemical reagents varies with the purity and quantity of the reagents used;

③ Utensils used for storing and processing samples, if made of impure materials or not thoroughly cleaned, may contaminate the sample;

④ Avoid contamination of the sample by the analyst.

(3) Blank Test:

Based on the blank test value and its standard deviation, correct the sample measurement value for the blank.


3. Applicability of Measurement Methods


(1) Categories and Levels of Measurement Methods:

There are thousands of existing standard methods, which can be broadly divided into three types:

① Popular standard methods for testing product technical specifications.

② Standard methods developed for the implementation of certain regulations, known as official methods. For example, the Association of Official Analytical Chemists (AOAC) in the United States has developed standard methods for analyzing food, drugs, fertilizers, pesticides, and cosmetics to ensure the implementation of relevant agricultural and public health regulations.

③ Foundational standard methods, such as those developed by the Society for Analytical Chemistry (SAC) in the UK and the American Society for Testing and Materials (ASTM).

(2) Main Technical Parameters and Control Indicators of Measurement Methods:

Include: linear range, accuracy, precision, sensitivity, and detection limit.


4. Calibration of Measurement Methods


The purpose of calibrating measurement methods is to establish a functional relationship between the measurement signal and the quantity of the measured chemical component, i.e., the quantitative relationship between the physical signal and the chemical component. Creating an accurate and effective calibration curve is an important prerequisite for obtaining accurate and reliable measurement results.

(1) Use accurate and reliable measurement standards

(2) Eliminate or measure the effects of interference and matrix effects

(3) Control experimental conditions and design experiments rationally

Experiments should be designed according to the following principles:

① To maintain experimental conditions for measuring samples as consistent as possible with those used to create the calibration curve, the calibration curve should be created and used within a short time interval;

② The calibration curve should include at least five experimental points, and the range of values should be as wide as possible to improve the reliability and stability of the calibration curve;

③ Repeat measurements should be taken for each experimental point and averaged. At a minimum, repeat measurements should be taken at the endpoints of the calibration curve to reduce experimental errors.

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