counterion analysis active pharma ingredient ion chromatographyThis blog post features a new application that demonstrates ion chromatography (IC) with suppressed conductivity (great write by Dr. Joachim Weiss) to be an excellent technique for determining the counterion of an active pharmaceutical ingredient in a drug substance or a drug product.

The drug substance Tolterodine (a quaternary ammonium compound used to treat urinary incontinence) is typically prepared as a salt, and pharmaceutical companies assay the counterion–in this case, tartrate–in the drug substance to ensure it is present at the appropriate levels. The counterion assay can also serve as a check of the amount of active pharmaceutical ingredient in the sample.

Previously, Application Note 190, Determination of Sulfate Counter Ion and Anionic Impurities in Aminoglycoside Drug Substances by Ion Chromatography with Suppressed Conductivity Detection, (downloadable PDF) showed IC to be an excellent technique for determining the counterion of an active pharmaceutical ingredient in a drug substance or product.

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Application Note 1002, Determination of Tartaric Acid in Tolterodine Tartrate Drug Products by IC with Suppressed Conductivity Detection, (downloadable PDF), developed at our Bangkok Applications Lab, updates Application Note 190 by demonstrating the determination of a counterion not previously shown. It also describes two new IC methods that reduce time and labor, are accurate and reproducible, and have analysis times as low as 10 minutes. Both approaches use an electrolytic suppressor, which eliminates the time and effort to prepare dilute sulfuric acid regenerant.

The first method uses our Reagent-Free™ IC (RFIC™) system (Thermo Scientific Dionex ICS-3000 system), and, therefore, requires only the addition of deionized water for eluent and suppressor regenerant production. This 10-minute method demonstrates improved accuracy and productivity because both eluent and regenerant are prepared automatically, eliminating the time and effort required to manually prepare these reagents while also reducing the possibility of errors and contamination. The second method uses a carbonate/bicarbonate eluent and has an analysis time of 12 minutes. The two methods use two of our columns: carbonate eluent anion-exchange column and hydroxide-selective anion-exchange column (Thermo Scientific Dionex IonPac AS22 Analytical column and Dionex IonPac AS20 Analytical column respectively).

Let us know in the Comments box below if this application was helpful to you in your work. We look forward to hearing from you.