Chromatography Forum

Hello,
Can anybody tell me the excact calculation method for PSD indicated in batch validation reports of silica ? More precisely what means "D(10)/D(90) ratio" ? Sometimes I found 40/90 ratio, and even 50 ratio . Also I found Dv90/Dv10.
All information I found is so confusing, because different use of symbols (D)(Dv). I thought D=mean and Dv=Standardeviation. Maybe this is question of language ?
Thanks a lot.

I think that it is more a question of terminology (and consistent terminology) rather than language.

Different manufacturers/groups use different terms and values. The "D" or "Dv" perhaps just refers to "distribution" or "distribution value" (that is partly my guess and partly my understanding of the common usage of the terminology). The numbers of 10, 50 and 90 are the commonly used values.

I don't recall the terminology of the USP and the EP (I don't have those guidances readily available at the moment). However, the FDA uses D10, D50, D90 and Span. Please see this FDA guidance with respect to particle size distributions for spray patterns for spray drug products:

http://www.fda.gov/cder/guidance/4234fnl.pdf

I always confuse myself over the terminology, so I am not going to attempt to explain it. I recommend that you look at that FDA document and that you look in the USP and/or EP for the best description. You can also look at the manuals for various particle size distribution instruments.

I hope that I did not confuse things for you.

Regards,
Dan

An accumulative particle size distribution is an S-shaped curve. You look for the 10%, 50% and 90% value of this S, and then calculate the appropriate ratio. We use the 90/10 ratio as a measure of the width of the distribution, and the 50% point as the center of the distribution. The subscript v stands for the distribution based on the particle volume. One can commonly also plot the same thing for the number of particles, rather than the particle volume. (D stands for particle diameter, v stands for volume.)

If you want to know more, I can give you a giant lecture on the subject over e-mail.

Thanks a lot for both reactions. I catched what to calculate. Only I don't understand why some QC-reports on batch validation bring confusion with definitions as "weighted" or "average weighted" . These are well-defined terms in mathematics, and cannot be used inappropriote in QC reports. I thought this is science, no advertisements hoping nobody understands. But your answers solved my problem, thanks again.

Dear Dr. Neue

I would like to see your giant lecture on this subject, so could you send it on my e-mail? I'm interested in this subject while i am awaiting for your book on HPLC columns to hit my address

Thanks a lot
Regards