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One mistake not to make on assay calculation

Recently, a customer asked us for advice on assay calculation of Oxytetracycline Hydrochloride by using reference materials from the European Pharmacopoeia (Ph. Eur.). The Pharmacopoeia (Ph. Eur.) provides two reference materials for Oxytetracycline, which are mentioned in the monograph for Oxytetracycline Hydrochloride: “Oxytetracycline” and “Oxytetracycline HCl”. However, in some cases this seems to cause confusion about the correct reference standard for assay calculation. Having the same name, “Oxytetracycline HCl” is often considered to be the correct one to use for assay calculation of Oxytetracycline Hydrochloride. But when calculating the assay of Oxytetracycline Hydrochloride it is often overlooked that the reference material “Oxytetracycline” has an assigned content and “Oxytetracycline HCl” is only a qualitative standard. Therefore, for assay calculation of “Oxytetracycline Hydrochloride” you must choose the quantitative “Oxytetracycline” standard and use an equivalency factor. Do not use the qualitative “Oxytetracycline HCl” reference standard to obtain the assay by assuming the content as 100 %! This standard is only used in the identification test by thin-layer chromatography. picture: dreamstime

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