Impurity profiling of l-asparagine monohydrate by ion pair chromatography applying low wavelength UV detection

l-asparagine is a non-essential amino acid being used for a variety of pharmaceutical applications. The compound may be produced following synthetic or fermentative pathways leading to the formation of distinct impurities such as organic acids, other amino acids, dipeptides, or cyclic amino acid derivatives. Analysis of the respective analytes is challenging due to the lack of a chromophore, thus the monograph of the European Pharmacopoeia describes a thin layer chromatographic test for detection of other amino acids. Thus, a sensitive and robust liquid chromatographic method was developed and validated applying detection at 210nm for determining the related substances. Separation and quantification of the analytes was achieved on a reversed phase C₁₈ column using a mobile phase composed of a mixture of a phosphate buffer, sodium octanesulfonate, and acetonitrile in an isocratic elution mode. In contrast to the currently used thin layer chromatographic test, the method is capable of separating and quantitatively assessing expected ninhydrin-positive and -negative impurities from synthetic and enzymatic production pathways.