Two methods for determination of 1-methylpyrrolidine

Introduction

1-Methylpyrrolidine, also known as N-Methylpyrrolidine, is a cyclic secondary amine that appears as a colorless or slightly yellow liquid.(Figure 1) 1-Methylpyrrolidine has a wide range of applications and can be used to prepare broad-spectrum antibiotics such as cefepime and as an intermediate for the preparation of Tolmetin; It can also be used as a dye stabilizer, preservative, high boiling point selective solvent, and organic amine catalyst. 1-Methylpyrrolidine is an organic base and inactive to UV absorption. Therefore, it is difficult to determine this impurity in cefepime for injection by using conventional HPLC method.[1] Two methods for determining methylpyrrolidine are as follows.

1.Capillary electrophoresis method

1-Methylpyrrolidine is one of the potential known degradants of cefepime hydrochloride, and it is also a residual process impurity from synthesis. 1-Methylpyrrolidine is reported to be an inert of unknown toxicity by US Environmental protection agency. It is also observed that the increase in 1-methylpyrrolidine content is proportional to the decrease in potency of cefepime. Consequently, monitoring and control of N-methylpyrrolidine in cefepime for injection is essential for preserving the desired quality of active moiety during release as well as throughout its shelf life. The present study relates to a new capillary electrophoresis method for the determination of 1-methylpyrrolidine. The newly developed capillary electrophoresis method for determining the content of 1-methylpyrrolidine in cefepime for injection has been validated as per International Conference on Harmonization (ICH) guidelines to prove the selectivity, sensitivity, suitability, robustness, and ruggedness of the method. This simple, efficient, and rapid methodology may be used by pharmaceutical industry for routine analysis as well as during stability studies. The newly developed capillary electrophoresis method to determine the content of 1-methylpyrrolidine in cefepime for injection requires 10 min for data acquisition, and uses an indirect UV photometry method to detect the analyte signal at 240 nm against the reference signal at 210 nm. The electrophoretic system is optimized to get stable base line, higher signal to noise ratio and peaks with narrow peak width. The method employs bare fused silica capillary with extended light path, effective length of capillary is 56 cm and inner diameter of capillary is 50 μm, 5 mmole of imidazole buffer adjusted to pH 5.1 with 3 molar acetic acid solution is used as background electrolyte. The sample is introduced in hydrodynamic mode employing pressure of 50 mbar for 5 s, and the desired separation is achieved with constant applied voltage of 25 kV at ambient temperature (~25°C).

This optimized capillary electrophoresis method to determinethe content of N-methylpyrrolidine in cefepime for injection issimple, efficient, rapid, selective, and sensitive. The low cost peranalysis, shorter analysis time, ambient temperature during theanalysis, no sample plug formation, and stable baseline are notedto be specific advantages of this optimized capillary electrophoresis method over the ion chromatography methodsreported so far. The selection of background electrolyte as imidazole buffer, and its optimum concentration and pH, in additionto sample concentration are the critical electrophoretic parameters that have been suitably optimized in this method to achievenarrow peak shape, stable baseline and higher signal to noiseratio.[2]

2. Dispersive liquid–liquidmicroextraction method

The US Pharmacopeia monograph specifies the limit of NMP to ＜0.3% in cefepime hydrochloride and ＜1% in cefepime for injection. The latter is a dry mixture of cefepime hydrochloride and L-arginine. The current US Pharmacopeia method uses cation-exchange chromatography with non-suppressed conductivity detection to determine the limit of NMP in cefepime. There are several disadvantages to this method,such as the ≈3–4 h time required per injection, a lack of retention time stability for NMP in standard and sample solutions and a lack of sensitivity.Several methods have been reported for direct measurement of NMP concentration in cefepime samples by GC ,HPLC, ion chromatography and CE. But each of them has some disadvantages and limitations. A simple, rapid and efficient sample preparation technique, dispersive liquid–liquid microextraction, coupled with gas chromatography-flame ionization detection has been developed to determine 1-methylpyrrolidine in cefepime. The effect of various experimental factors on the preparation procedure, such as the nature and volume of extraction and disperser solvents, extraction time, the nature of buffer and its pH,and salt effect, was investigated, optimized and the following results were obtained:extraction solvent, chloroform; dispersive solvent and solvent for dissolving cefepime, a mixture of methanol/water (88:12, v/v); salting out agent, NaCl; and buffer, carbonate/bicarbonate (C = 0.5 M, pH=12). The optimized conditions were applied to the real sample (cefepime) for the extraction and determination of 1-methylpyrrolidine. The calibration graph is linear from 0.02 to 850 mg/L with the square of correlation coefficient 0.999. LOD and LOQ are 6.4 and 21.2μg/L in solution, respectively, and 0.2 (2×10⁵)and 0.6 (6×10⁵) mg/g (%, w/w) in cefepime powder, respectively, using sample size50 mg. Repeatability of the method is good and RSD% for six repeated experiments(C=170 mg/L) is 6.35%.

References

[1] Yan Hl, Li Yxn, Liu Hr, et al. Research on the Synthesis of Heterocyclic Compound N-Methylpyrrolidine [J]. Journal of Qufu Normal University (Natural Science Edition),2009,35(01):79-81.

[2] Prasanna SJ, Sharma HK, Mukkanti K, Kumar VJ, Raja G, Sivakumaran M. Validation of capillary electrophoresis method for determination of N-methylpyrrolidine in cefepime for injection. J Chromatogr Sci. 2010;48(10):830-834. doi:10.1093/chromsci/48.10.830

[3] Farajzadeh MA, Goushjuii L, Bashour Y. A simple and rapid dispersive liquid-liquid microextraction method followed by GC-FID for determination of N-methylpyrrolidine in cefepime. J Sep Sci. 2010;33(23-24):3767-3773. doi:10.1002/jssc.201000510

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