The FDA has recently issued some guidance for managing nitrosamine impurities in pharmaceutical products [1]. Even in trace quantities, the presence of carcinogenic nitrosamine in medications risks patients’ safety. Controlling the nitrite concentration in pharmaceutical products and processes can help to prevent nitrosamine formation. For this reason, the determination of nitrite in pharmaceutical products and their raw materials with sensitive analytical methods is essential.
Often, dimethylamine is used to synthesize different medications. Under acidic conditions, it reacts with nitrite, forming nitrosamines [2]. This is also the case for the production of hydroxypropyl methylcellulose (Hypromellose), a common excipient. This Application Note covers the determination of nitrite in hydroxypropyl methylcellulose with ion chromatography (IC) using a Metrosep A Supp 10 column and direct UV/VIS detection at 215 nm. Sample preparation is performed with the Metrohm intelligent Pre-Concentration Technique with Matrix Elimination (MiPCT-ME).
Hydroxypropyl methylcellulose (Hypromellose) was received as a powder from a pharmaceutical company. A 0.1 g sample portion 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 for approximately 20 minutes and the flask was filled up to the mark with UPW. The prepared sample solution was filtered through a 0.2 μm syringe filter and kept in a sample processor under closed conditions prior to analysis.
A single-point calibration was used with 4 μg/L NO2- prepared from a 1000 mg/L NIST certified standard (Sigma TraceCERT No. 67276).
The sample was analyzed with a chromatographic separation technique as described in USP <621> [3] (Figure 1). A MiPCT-ME setup was used in conjunction with the method parameters in Table 1. A 2 mL sample was preconcentrated on a Metrosep A PCC 2 HC/4.0, and the matrix was eliminated with 3 mL of ultrapure water.
After injection, the anionic components were isocratically separated within 45 minutes on a Metrosep A Supp 10 - 250/4.0 column. The UV/VIS detector signal was recorded at 215 nm. Confirmation of the method accuracy was done with a spiking study. The sample was spiked with a nitrite standard at two concentration levels (1.0 μg/L and 4 μg/L), and the recovery values were evaluated.
Table 1. IC method parameters for the determination of nitrite impurities in hydroxypropyl methylcellulose (Hypromellose).
| 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/VIS detection at 215 nm |
Nitrite was quantified in hydroxypropyl methylcellulose (Figure 2). The method was sensitive enough to quantify trace levels of nitrite present in the sample matrix. A two-level spiking study confirmed the method accuracy, achieving recoveries between 80 and 120%.
Quantification of nitrite in hydroxypropyl methylcellulose according to USP <621> is possible with the presented IC method. Preconcentration of the sample offers higher sensitivity for the accurate determination of trace quantities of nitrite. Inline matrix elimination removes the interfering sample matrix before injection, further improving results. Separation of nitrite from other matrix components was achieved on the Metrosep A Supp 10 column. Method accuracy was confirmed by spiking studies.
This IC method is suitable for quality control of the impurity nitrite in pharmaceutical manufacturing processes involving the excipient hydroxypropyl methylcellulose.
- 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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