Basic knowledge of sample collection and preparation

1.
Sample collection and samples

Sample collection is abbreviated as sampling, also known as sampling or sampling
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The first step in testing a sample is sample collection

Second, the importance of sample collection

Sample collection is an important and very careful operation process
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To collect small quality samples from a large batch of tested products that can represent the entire batch of tested substances, certain principles must be followed, appropriate methods must be mastered, and the loss of certain components or contamination of foreign components during the sampling process must be avoided.

Through the analysis, inspection and testing of samples, an objective and true evaluation of the quality and safety level of the inspected object is the functional requirement of the inspection and testing organization
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Therefore, it is necessary to correctly collect and prepare samples to ensure the objectivity, uniformity and representativeness of the tested samples

Three, the basic principles of sample collection

(1) Representativeness

The collected samples should be representative, so that the measurement results of the sampled products can represent the characteristics of the sample population
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(2) Authenticity

During the sample collection process, the sampling personnel should record relevant information about the sampling in a timely and accurate manner
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(3) Fairness

The sampling personnel should personally come to the site to take samples, and no personnel shall interfere with the sampling by the sampling personnel
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Four, sampling error

(1) Random sampling error

Sampling random error is the deviation caused by some uncontrollable accidental factors in the sampling process, which cannot be avoided
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Increasing the number of repetitions of sampling can reduce this type of error

(2) Sampling system error

Factors such as sampling plan, sampling equipment, operator, and environment can all cause systematic errors in sampling
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The deviation of the systematic error is fixed and should be avoided as much as possible

Random errors and systematic errors may exist in sampling.
Therefore, the difference in characteristic data obtained by testing samples includes both sampling error and test error
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Five, sample preparation

Sample preparation is the process of crushing, shrinking, and mixing the original sample using economical and effective processing methods
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The prepared analysis sample can not only meet the requirement of sufficiently fine particle size, but also make the sample sample uniform after preparation, ensuring that the material composition and content of the original sample remain unchanged

First, avoid chemical changes in the components during the preparation process
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Second, prevent and avoid contamination of the components to be measured
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Third, minimize the introduction of irrelevant compounds into the preparation process
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The sample collection of agricultural quality inspection agencies mainly includes agricultural products, farmland soil, agricultural irrigation and so on
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The sampling method, preparation and storage requirements of different samples are different

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