Potency Assay

Potency Assay
USP <621> <797>

The vast majority of potency assays in our lab are performed by means of UltraHigh Performance Liquid Chromatography (UHPLC) instrumentation.  These instruments determine potencies by isolating the desired ingredients from the other substances in a formulation and thus can provide accurate quantitation without interference.  For this reason, it is the technique most favored by the FDA and also most often sited in USP monographs.  Our UHPLC instruments are coupled with Diode Array UV Detectors (DAD) which use absorbance of UV light to detect and quantify the desired substance.  These detectors can also use the UV absorbance spectrum to verify the identity of ingredients.  Thus, quantitation and identification can be accomplished simultaneously.  In addition, some of these instruments are also coupled with Mass Spectrometers which detect, quantify, and identify based upon molecular weight of an ingredient.  These very sophisticated instruments are often employed for highly complex formulations or those ingredients which are present at very low concentrations.
(USP <621> <797>)

Potency Assay

Potency Assay
$ 150 / API

Titrations

At times, the USP monograph calls for the use of titration techniques to quantify certain API's in a formulation.  This technique is highly accurate for certain substances.  It utilizes very specific chemical reactions between the ingredient of interest and another chemical substance to determine the amount present.  The basis of this is chemical stoichometry which states, for example, 1 mole of a certain ingredient will react with precisely 1 mole of another specific chemical.  For instance, the amount of chloride in a solution can be determined by titrating with silver nitrate.  In this reaction, silver ions will react and bind with the chloride ions forming an insoluble precipitate.  When all of the chloride ions are bound, the endpoint is reached, and by observing how much silver nitrate is used, the amount of chloride can be determined.

Titration

Potency Assay
$ 150 / API

Mass Spectrometry
USP <621> <797>

Molecules of active ingredients in a formulation are separated by means of UHPLC then are passed into the Mass Spectrometer (MS) for detection, quantification, and identification.  When entering the MS, molecules are first ionized, then separated by radio frequency oscillations on the basis of their mass/charge ratio.  This process can be used to determine the molecular weight of a compound or can be used to ignore all other compounds in a formulation except the one having desired molecular weight.  This makes MS highly specific for a desired API and, therefore, we often use it for testing very complex formulations.  It is also very sensitive, able to detect low microgram to high nanogram amounts.
(USP <621> <797>)

Mass Spectrometry

Potency Assay
$ 180 / API

Protein / Peptide
USP <621> <797>

These biomolecules can be very large and fragile, often easily broken apart by shaking.  They are usually temperature sensitive and can bind to glass, plastic, and/or filters during formulating processes.  We have specialized instrumentation and special handling techniques for testing their potencies.  Among the several separation techniques we use to analyze proteins are those based upon size, charge, polarity, and hydrophobicity.

 

Protein / Peptide

Potency Assay
$ 200 / API

Porcine Thyroid

The active Liothyroxine (T3) and Levothyroxine (T4) compounds in this natural thyroid form are bound within the thyroid protein.  To determine their potencies the protein must first be enzymatically digested to free the T3 and T4.  This process takes 28 hours* under controlled conditions before analysis by UHPLC. 

*Requiring 28 hours to perform, same-day rushes are not possible
 

Porcine Thyroid

Potency Assay
$ 230

API Powder
USP <621> <797>

It is often a good idea to determine the potency and verify the identity of an Active Pharmaceutical Ingredient (API) before using.  We often see potencies which are less than that claimed by the manufacturer or supplier, and on occasion, we have seen errors in their identity as well.  Sometimes, there is more water present than what is listed on the Certificate of Analysis (CoA).  We test for potency and determine the identity of all API’s we test.  When appropriate, Infrared (FT-IR), UV, or other means is used are used for identity per the USP.  Water, or Loss on Drying (LoD) is not automatically included, but we suggest it be ordered as well.
(USP <621> <797>)

API Powder

Potency Assay
$ 300