The Quantification of Nitrite in Excipients and Chemicals

The trace level quantification of nitrite in excipients and chemicals is of major interest to the pharmaceutical industry due to the formation of carcinogenic nitrosamines from potentially present secondary amines and nitrite in the API and/or drug product. I would like to share this excellent article by Markus Baumann and Kevin N?f "Quantification of Nitrite in Excipients and Chemicals: A Versatile and Highly Sensitive Method Using Headspace Gas Chromatography Coupled to Mass Spectrometry".

The aim of this work was the development of a method for the quantification of nitrite down to a level of 0.05 mg nitrite per kg material (ppm) that can be versatilely used for a wide range of excipients and chemicals. The detection of cyclohexene from the reaction of cyclamate with nitrite in water by gas chromatography coupled with mass spectrometry was selected due to its presumed great potential in terms of sensitivity, robustness, reliability, and specificity. The root cause for the presence of a significant blank peak, which was the key limiting factor, was identified and eliminated to achieve the desired sensitivity. Consequently, a method for the quantification of nitrite down to the targeted level of 0.05 ppm was developed and validated for 19 different excipients and chemicals. Specific sample preparation for challenging excipients and chemicals, such as magnesium stearate and carbonates, was developed and successfully applied. It was shown that the quantification range can be expanded up to 50 ppm covering a wide concentration range. See the article as shared on pharmaexcpients.com

Method Development (from the free pdf ofd the article)

Buffer Capacity Evaluation. Buffer capacity was assessed with regards to pH shift due to material, by weighing 50 mg of each material in a 20 mL headspace vial and the addition of 4.0 mL of 100 or 500 mM phosphate buffer pH 3, using universally applicable pH indicators after shaking the mixtures well, Figure S1. The 100 mM buffer solution was not capable to prevent a pH shift for sodium croscarmellose and magnesium stearate ending up in pH values of 5 and 4 respectively. However, the buffer strength of a 500 mM buffer solution was able to do so. The importance of sufficient buffer capacity is shown in Table S2 shows the pH shifts caused by various excipients. Recovery values of spiked nitrite content in solutions at pH around 3 were acceptable, whereby the solutions with pH ≥ 4 showed a bad recovery due to incomplete reaction of cyclamate to cyclohexene. The spiking experiment was not successful because of a matrix effect, but because the pH conditions were not optimal resulting in no conversion of cyclamate to cyclohexene.

Buffer Versus Acidified Solution. For feasibility trials, the elaborated reaction mix, containing 2.5 mg/mL sodium cyclamate, was assessed against the initial approach of sulfuric acid conditions by comparison of the cyclohexene response (Figure S2). The sulfuric acid solution was thereby mixed with cyclamate directly and stirred for 5h like the procedure for the buffer. Thus, the comparison is not biased by the preparation procedure due to presence of a large blank peak in the sulfuric acid solution. In conclusion, no difference in the cyclohexene response could be observed and it could be shown that the buffer is appropriate.

Access the full pdf on the method development here

#excipients #nitrites #nitrosamines