Here, I am pleased to present a recently developed fast ion chromatography method for the simultaneous determination of lithium, sodium, and calcium in the drug lithium carbonate (link to U.S. National Library of Medicine) without the handling hazardous reagents.
As you know, the drug lithium carbonate is used to treat a number of mental health problems associated with chemical imbalance in the brain, particularly bipolar disorder. Because lithium is the key ingredient and sodium and calcium are possible cationic impurities in lithium carbonate preparations, the United States Pharmacopeia (USP) requires determination of these compounds and the monograph defines three separate antiquated assays for lithium, sodium, and calcium that use hazardous reagents. In the USP monograph, sodium is determined with a flame photometer at 589 nm and corrected for the background transmission at 580 nm. To determine calcium, the USP describes a chelometric titration assay that uses oxalate precipitation and permanganate titration and requires more than 4 h to complete.
One of the chemists in our Sunnyvale Applications Lab (USA) has designed an assay that uses cation ion chromatography to determine all three impurity analytes in a single injection while at the same time determining the high-concentration lithium. The method she designed meets all the requirements of the USP monograph, and is described in Application Note 1090, IC Assay for Lithium, Sodium, and Calcium in Lithium Carbonate, (downloadable PDF). This new method takes 25 minutes to complete and is a simple, accurate, and robust alternative to the time-consuming assays for these three analytes in the current USP monograph.
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For the method development, the system setup included one of our high-pressure ion chromatography systems (Thermo Scientific Dionex ICS-5000+ HPIC system), one of our high-capacity, cation-exchange columns (Thermo Scientific Dionex IonPac CS16 cation-exchange column), electrolytically generated highly pure methanesulfonic acid (MSA) eluent, and suppressed conductivity detection. The eluent was generated using our eluent generator cartridge (Thermo Scientific Dionex EGC III MSA Eluent Generator Cartridge) and was purified on line using one of our cation trap columns (Thermo Scientific Dionex CR-CTC II Continuously Regenerated Cation Trap Column).
By the way, in this past year, we have released several ion chromatography applications for pharmaceutical analysis; they have been blogged here but here are the links to the PDFs for easy access:
- Application Note 1057, Determination of Methylamine in Drug Products (downloadable PDF)
- Application Note 1062, Determination of Morpholine in Linezolid by Ion Chromatography (downloadable PDF)
- Application Note 1072, Ion Chromatography Assay for Ammonia in Adenosine (downloadable PDF)
- Application Note 1073, Determination of Ammonia in Sodium Bicarbonate (downloadable PDF)
- Application Note 1075, Ion Chromatography Assay for Chloride and Sulfate in Adenosine (downloadable PDF)
- Application 1076, Determination of Monochloroacetic Acid in Carbocisteine (downloadable PDF)
If you have questions on the method, instrument, or column, do enter them in the Comments box below; our experts look forward to hearing from you.