Evolving from the 100 Year Old USP <231> Method to USP <232/233>

USP 232/233

Many of our clients are concerned because they are not sure how they should implement the Permissible Daily Exposures (PDEs) laid out in the new USP guidelines. We discuss unique routes of administration and unlimited serving sizes on a weekly basis. But the most common issue is how to “update” the use of USP <231> limits to the guidelines published on January 1, 2018.

For clients who have historically used the USP <231> method, the question becomes how to integrate the summation limit of the ten heavy metals (Ag, As, Bi, Cd, Cu, Hg, Mo, Pb, Sb & Sn) into the current PDE calculations. We now use whichever is lower:

  • 1/10 of the total HM specification for each individual element. For example: If the summation of the HM must be <10 ppm, this would equate to 1 ppm for each element.  


  • The USP <232> Oral Daily PDE for the element, divided by the serving size. For example, let’s use mercury’s oral PDE of 30 ug/day. If a product’s serving size is 2 grams, the specification becomes 30 ug/day divided by 2 grams, giving a specification of 15 ug/g or 15 ppm.

In this case, we would default to the top calculation of 1 ppm for the mercury specification in this product.

To view USP <232> limits, click here.

Note: For products with smaller serving sizes, the specifications for elemental impurities may change once you are dealing with USP <232/233>. For example, PQLs can increase dramatically, particularly with small serving sizes.

For USP testing of your product(s), please contact us at (717) 697–7536 or submit a request here.

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