Do you really understand the electronic balance? - those things that explore the "minimum weight"

The medicine should have curative effect, the paint should have the correct color, the adhesiveness of the glue should be guaranteed, the taste of the cake should be pure, the building cement should have a certain strength, the quality of the gold jewelry should be correct... all of this needs to be accurate. Weighing is guaranteed. As one of the most commonly used weighing tools in the laboratory, electronic balances have a very high rate of appearance, especially in the development and production of the pharmaceutical industry. In the whole drug experiment process, accurate weighing results are very important, which directly affects the reliability of the research and development results and the quality of the final product. The most critical one is the “minimum weighing value” of the balance closely related to the precision weighing. .

Blind spot on "minimum weight"

Regarding the “minimum weighing value” of the electronic balance, because of the slightly ambiguous pharmacopoeia rules and comparative professional calculation formulas, there is currently a reality that cannot be ignored, even for the majority of manufacturers with years of experience in balance sales. Personnel or dealer friends, because there are more or less blind spots on the professional knowledge of the balance, it is inevitable that this problem will be misunderstood.

According to the United States Pharmacopoeia, if the analytical balance is required to accurately weigh the substance, it must comply with the requirements of the United States Pharmacopoeia General 41, that is, the mass of the weighed item cannot be less than a certain minimum weighing value. To this end, Ohaus engineers threw a question at a new product dealer meeting: an electronic balance weighing range 0-220g, its readability is 0.01mg, then you can use this balance Is weighing 10mg of the drug? There are many dealers on the spot who have given the affirmative answer. Since the readability of the balance is 0.01mg, the 10mg sample can definitely be accurately weighed. Even if it is 1 or 2mg, accurate weighing should be no problem. of. After a while, the engineer smiled and gave the answer: "Your answer is wrong!" Obviously everyone mistakenly regarded the minimum weight as readability. So how do you calculate the minimum weight of the balance?

How to define and calculate the "minimum weight value"

The minimum weight, also known as the minimum net weight of the sample, is clearly defined in the United States Pharmacopoeia, General Principles 1251, which describes the acceptable lower limit for the sample size while maintaining the required weighing accuracy. In order to meet the required weighing accuracy, the sample mass (eg net weight) must be equal to or greater than the minimum weighing value when the sample is weighed. The minimum weight value is only applicable to the net weight of the sample, except for tare or gross weight. It can be expressed by the following formula:

m _min = k × s _RP / U

Where k is the expansion factor (usually ≥ 2), s _RP is the standard deviation of the test weight not less than 10 repeated weighing values ​​(eg in milligrams), and s _RP varies with the environment, the specific value measured Also, U is the required weighing accuracy. Among them, the Chinese Pharmacopoeia stipulates that U should take 0.10% when “precision is determined” and “1%” when “weighed”.

For those materials that must be accurately weighed, the US Pharmacopoeia General Regulations 41 make the following provisions: If the standard deviation of the weight value is divided by the weight value, the result is not more than 0.10%, then the repeatability is satisfactory. Under this condition, the above formula can be simplified as: m _min = 2000 × s _RP . If the obtained repeatability is less than 0.41 d, where d is the display division value (specified as 0.01 mg), it is replaced by 0.41d. Under this condition, the above formula can be simplified to m _min = 820d.

How to use 4Q certification to correctly select and use the right balance

After listening to so many introductions about the minimum weight value, I think that everyone already has a concept in mind, then on this basis, how do we choose and use the balance correctly? In fact, for the most widely used pharmaceutical industry for electronic balances, the Good Manufacturing Practice (GMP) stipulates that pharmaceutical production verification should include plant design, facility and equipment design confirmation, installation confirmation, operation confirmation, and performance confirmation, ie 4Q certification. The main procedures for device verification are:

Drug safety is life-threatening. If the 4Q certification fails, it will not meet the mandatory certification requirements of GMP, which will affect the safety of drug production and bring security risks. In contrast to the selection of the balance, the 4Q certification refines the selection of the balance, and the minimum weight value is explicitly mentioned in the Operational Confirmation (OQ) section:

A. Design Confirmation (DQ)

    — Select the appropriate balance parameters according to the customer's weighing requirements

B. Installation Confirmation (IQ)

— Verify product transportation, unpacking, initial installation

C. Operational Confirmation (OQ)

- various function checks of the balance, such as buttons and automatic doors

— test four corners, linearity, repeatability

- calculate the minimum weight value

D. Performance Confirmation (PQ)

— Verify that the product meets the set specifications

- Users need to develop standard operating procedures

— It is recommended that trained technical service personnel perform periodic functional and performance tests

The performance of the balance depends on the facility environment in which it is installed. The calculation of the minimum weighing value repeatability must be based on the performance confirmation of the balance after the installation is installed (installation confirmation) and the operation permit (operation confirmation). Sex determines the minimum weight of the electronic balance . Therefore, when you choose to buy a balance, you can't see Taishan in a blind spot. You should choose the repeatability of the corresponding electronic balance according to the readability of the balance and the minimum value of your own weighing sample, so that you can purchase a suitable electronic balance and get twice the result with half the effort. Effect.

Why choose Ohaus electronic balance

Ohaus electronic balance is widely used in the pharmaceutical industry. In order to meet the high-precision weighing requirements of pharmaceuticals, Ohaus has specially designed the Explorer quasi-micro series balance, and then follow the small series to see this accurate What is one of the 100,000 Explorer micro-balances that wins user recognition and love?

1. Intelligent hardware and software: equipped with high-speed integrated sensor, with AutoCalTM automatic calibration system, convenient for professional linearization test and calibration, reducing cumulative error;

2. Zero-contact operation: In order to prevent cross-contamination of powder samples, Explorer quasi-micro balances are equipped with 4 wireless sensors to provide non-contact peeling, clearing, printing and other common functions;

3. Eliminate external influences: the presence of wireless induction automatic hood doors and built-in static eliminators minimizes the influence of external factors on accurate weighing;

4. Administrator rights: Each balance can create 10 normal user privileges, an administrator user rights. The administrator can manage the permission opening options of each user to protect the important weighing parameter settings from being modified;

5. Set the minimum weighing value: In the parameter setting, you can determine the minimum weighing value to be used to determine whether the sample meets the USP requirements. If the actual weight is below the set minimum weight, the color of the weighing data display value will change to yellow to alert the user.

Knowing so much, do you also have a preference for EX micro-balances? If you want to know more about the Explorer Quasi-micro series balance or Ohaus other balance family products, or are looking for more professional and detailed selection guide, please call 4008-217-188, our professional engineers will be in the first Contact you at one time!

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