Recently, the FDA released a guidance document for pharmaceutical manufacturers regarding the control of nitrosamine impurities in medications [1]. Nitrosamine presence in drugs can be risky for patients as these compounds are carcinogenic, even at trace levels. However, nitrosamine formation can be avoided by controlling and monitoring the nitrite concentration in pharmaceutical products and raw materials. Developing processes to reduce or eliminate nitrosamine formation requires sensitive analytical methods for the determination of nitrite in complex matrices.
Dimethylamine is used during the synthesis of many pharmaceuticals. Under acidic pH, dimethylamine reacts with nitrite to form nitrosamines [2]. Duloxetine hydrochloride is an active pharmaceutical ingredient (API) against depression and other nervous system diseases. This Application Note describes the analysis of nitrite in duloxetine hydrochloride with ion chromatography (IC) using a Metrosep A Supp 10 column with direct UV/VIS detection at 215 nm. The Metrohm intelligent Pre-Concentration Technique with Matrix Elimination (MiPCT-ME) is used for sample preparation.
Duloxetine hydrochloride was received as a powder from a pharmaceutical company. Approximately 0.05 g of sample was accurately weighed and transferred into a clean 10 mL volumetric flask containing 5.0 mL of ultrapure water (UPW). The content was dissolved using a vortex mixer (approx. 5 min) and filled up to the line with UPW. A 0.1 mL aliquot of 1.0 mol/L sodium hydroxide was added, and the contents were mixed. The prepared sample solution was filtered using a 0.2 μm syringe filter and then passed through an IC-Ag sample preparation cartridge to remove any chloride ions. With automated sample preparation (MiPCT-ME), 2 mL of the sample solution was preconcentrated and the matrix was eliminated using 3 mL UPW.
A single-point calibration was made with 4 μg/L NO2- prepared from a 1000 mg/L NIST certified standard (Sigma TraceCERT No. 67276).
The prepared sample solution was injected directly using MiPCT-ME (Figure 1) and analyzed using the method parameters given in Table 1.
Anionic components were isocratically separated on a Metrosep A Supp 10 - 250/4.0 column and the background was reduced to a minimum with sequential suppression. The UV/VIS detector signal at 215 nm was recorded. The total run time was 40 minutes. The method accuracy was confirmed by a study where samples were spiked with 4 μg/L NO2- and the recovery values were evaluated.
Table 1. IC method parameters for the determination of nitrite impurities in duloxetine hydrochloride API.
| Column | Metrosep A Supp 10 - 250/4.0 |
|---|---|
| Eluent | 5.0 mmol/L sodium carbonate 5.0 mmol/L sodium hydroxide |
| Flow rate | 1.0 mL/min |
| Column temp. | 45 °C |
| Injection volume | 2 mL (preconcentration volume) |
| Detection | UV detection at 215 nm |
Nitrite was quantified in duloxetine hydrochloride with a chromatographic separation method as described in USP <621> (Figure 2) [3].
Using the MiPCT-ME setup, the method was found to be highly sensitive, able to quantify trace levels of nitrite present in the sample matrix. The method accuracy, confirmed by the spiking study, achieved recovery values between 80 to 120 %.
The presented IC method with the Metrosep A Supp 10 column can be used to quantify trace levels of nitrite in duloxetine hydrochloride according to USP <621>. The high sensitivity was achieved by using preconcentration, and the interfering sample matrix was eliminated with an inline matrix elimination technique. This procedure is accurate and robust, and in contrast to manual preconcentration techniques, no additional work is needed for this automated inline process.
- U.S. Department of Health and Human Services Food and Drug Administration; Center for Drug Evaluation and Research (CDER). Control of Nitrosamine Impurities in Human Drugs - Guidance for Industry. Pharmaceutical Quality/Manufacturing Standards/ Current Good Manufacturing Practice (CGMP) 2021.
- U.S. Pharmacopeia. USP-NF Nitrosamine Impurities. General chapter. https://doi.org/10.31003/USPNF_M15715_02_01.
- 〈621〉 Chromatography. https://doi.org/10.31003/USPNF_M99380_01_01.
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