Questions on Dynamic Light Scattering from the Second Supplement to the 18th Edition of the Japanese Pharmacopoeia

Many of you may already be aware, but as of June 28, 2024, dynamic light scattering has been added to the Japanese Pharmacopoeia as General Test Method 3.07: Method for Measuring Particle Size in Liquids Using Dynamic Light Scattering.

Speaking of our dynamic light scattering equipment, we are referring to the Zetasizer Advance Series. This compact equipment can measure particle size, zeta potential, and molecular weight all in one machine.

Now, returning to the topic of the Japanese Pharmacopoeia, in the section of the second supplement to the 18th edition, under the last part of section 3 on Management/Verification of Instrument Performance, the following statement can be found.

The difference between the measured average particle size and the certified value must be within 2%. In the cumulant method, the measurement value of the polydispersity index (PDI) must be 0.1 or less, and the relative standard deviation of at least five consecutive measurements must also be 2% or less.

Because of this wording, many people have asked us the same question, which we would like to explain here. The question is, “Is the requirement for a relative standard deviation of 2% or less concerning the polydispersity index?”

We inquired with the Pharmaceutical Evaluation and Licensing Division of the Ministry of Health, Labour and Welfare and received the following explanation.

The relevant section of the Japanese Pharmacopoeia is intended to convey the following three points:

1. The measured average particle size should have a difference of 2% or less from the certified value.
2. In case of using the cumulant analysis method, the polydispersity index (PDI) should also be 0.1 or less.
3. The relative standard deviation of the average particle size for five consecutive measurements should be 2% or less.

Therefore, the standard deviation requirement for five consecutive measurements applies to “particle size,” and not to the PDI.

We hope this information will be useful to those who had similar questions.

The Zetasizer Advance Series offers six different models! Try the Zetasizer Diagnostic Tool to easily determine which model fits your measurement needs best by simply choosing your options.

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