Standard materials, please pay attention to these questions!

(1) Types of characteristic quantities and methods of setting values:

Some reference materials may only be suitable for a specific method or application in a specific field, and the values ​​of some reference materials have special provisions, such as the value of crystal water, which should be noted in the certificate to prevent mis-selection and mis-use;

(2) Characteristic level:

The characteristic quantity level of the reference material should match the level of the daily measurement sample;

(3) Acceptable uncertainty levels:

The relevant uncertainty level of the characteristic quantity of the reference material should match the precision and correctness limit requirements in routine measurement;

(4) Matrix and possible interference:

When the reference material is used for method validation, quality control and calibration of some measurement methods with serious matrix effects, the matrix should be as close as possible to the matrix of the daily measurement sample;

(5) Form:

Reference materials can be prepared in different forms, such as freeze-dried and frozen samples.

(6) Minimum sampling amount:

As long as the minimum sampling volume is specified in the reference material certificate, the sampling volume used for measurement should not be less than the minimum sampling volume, so whether the minimum sampling volume can meet the requirements of the measurement method should be considered when purchasing;

(7) Dosage:

The amount of reference material purchased should be sufficient for the application in the entire experimental plan, including sample preparation as needed;

(8) Stability:

Before purchasing, confirm the validity period of the purchased batch of reference materials to avoid the situation of expiration when using

How to verify newly purchased certified reference materials?

For the purchased reference materials, after receipt, you should first confirm whether the transportation conditions of the reference materials meet the requirements, and then check whether the variety and quantity are consistent with the purchase requirements, whether the packaging and appearance are normal, and whether the marking is clear and complete; No certificate, whether it is within the validity period of the certificate statement,

Is a reference material with a certificate a certified reference material (CRM)? 

To answer this question, we must first understand the meaning of "Certified Reference Material"

Certified reference materials should have the following basic characteristics:

(1) Traceability and uncertainty statement;

(2) The preparation, determination and identification of reference materials conform to the valid procedures given by ISO Guide 34 and Guide 35.

What is the difference between certified reference materials and other reference materials?

First of all, it should be clear that only certified or certified values ​​provided by certified reference materials can be used for calibration, assignment of other substances, and confirmation of measurement correctness, and through their use to declare the metrological traceability of measurement results

Occasionally, in the absence of certified reference materials, these reference materials have to be used for calibration and other activities, but it should be further evaluated whether these reference materials meet the characteristics of certified reference materials, or whether traceability and quantitative uncertainty levels can be used.

Reference value or information value of a certified reference material

Some additional reference or informative values ​​are sometimes provided in the certificate of a certified reference material, which often lack clear metrological traceability, lack uncertainty information, or incomplete uncertainty assessments

Does the reference material have to be used within the validity period?

The validity period of the reference material is determined by the research unit according to the stability research data, in order to ensure the reliability of the standard material quality value and uncertainty.

Why must the reference material be used and stored in accordance with the conditions specified in the certificate?

The conditions of use and storage specified in the reference material certificate are necessary conditions for assurance

How to save the opened reference material?

"One-time use" is sometimes specified in the reference material certificate.

For certified reference materials that can be used multiple times, it is very important to ensure proper storage and packaging of the reference material packaging unit after opening, and the integrity of the certificate

What is the significance of the minimum sampling amount of reference materials?

The minimum sample size of the reference material is specified in the homogeneity study

Does the measured value of the reference material have to be within the uncertainty?

If the measured value of the reference material by the laboratory exceeds the uncertainty range of the characteristic value of the reference material, it cannot directly draw the conclusion that the measurement result is biased, because the uncertainty of the reference material U Uncertainty related to the determination, homogeneity, and stability of the reference material does not involve the random uncertainty related to the user's measurement of the reference material in the laboratory

S represents the standard deviation, n represents the number of repetitions, and the t value can be obtained by looking up the table according to n and the confidence probability level

What should be paid attention to during the dilution and use of standard materials for calibration?

The standard materials for calibration purchased by users are often of high concentration and cannot be used directly.

In addition to the necessary control of the blank, different diluents have different stabilizing effects.
In principle, they should be prepared according to the types and concentrations of diluents specified in the testing standard method
.
The measuring instruments used in the weighing and dilution of standard substances, such as balances, pipettes, volumetric flasks, etc.
, should be properly calibrated or verified to meet the precision and accuracy requirements, especially the microsyringes and pipettes used in organic analysis.
The error of the liquid gun is large, and daily calibration should be paid attention to
.

How to carry out quantity verification for reference materials?

How to do a good job in the quantitative control of reference materials in the use process is often a problem that users are confused about
.
Specific measures should be formulated for the quantity control of reference materials according to the following situations:

(1) For certified reference materials, as long as they are stored in accordance with the conditions and methods specified in the reference material certificate, and used within the validity period, the value is guaranteed.
The verification of such reference materials should be simplified to check the packaging, labels and Integrity, validity period, storage conditions, etc.
of the certificate; if it is a certified reference material that can be used multiple times after opening, in addition to the above verification, the laboratory should formulate corresponding documents to regulate its subsequent use and management, and regularly check its use.
, and if necessary, check the value by comparing it with another unopened unit or batch of standard substances
.

(2) For internal reference materials or calibration solutions prepared by certified reference materials, etc.
, due to insufficient homogeneity and stability data, strict quantitative control is very necessary
.
The methods that can be taken are flexible depending on the economic and technical conditions of the laboratory, such as using the quality control chart to check the trend, comparing the quality values ​​of the previous batches of standard substances, or verifying the accuracy of the values ​​through the comparison between laboratories
.
In addition, the frequency of verification should be determined according to the characteristics of the reference material.
For reference materials with good stability expectations, the time interval for verification can be relatively relaxed
.