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UHPLC Analysis of Structurally Similar Compounds: A Case Study of Ephedrine and Related Analogs on a Carbon Column

Abstract

The Supel™ Carbon LC column was used to baseline resolve polar structural similar compounds, ephedrine and related compounds, under normal phase conditions and is compared to another carbon based column available in the market. The results indicate that the Supel™ Carbon LC column is a suitable option for forensic and pharmaceutical analysis in counterfeit drug detection.

Section Overview

Introduction

Ephedrine and related analogs are used as the active components of many decongestants and bronchodilators. However, counterfeit versions of these products may have dangerous amounts of one or more analogs of ephedrine. Therefore, it is important to have analytical methods available to resolve these structurally similar compounds. The use of HPLC columns packed with carbon particles can fill this analytical need, as the polar retention effect on graphite (PREG) mechanism can discriminate compounds by differences in their three-dimensional structure. This application demonstrates the use of the Supel™ Carbon LC column to resolve ephedrine and its three structural analogs - norephedrine, pseudoephedrine, and synephrine, and compares it to another carbon based column available in the market.

Two-dimensional chemical structures of four compounds, each labeled with its corresponding name below the structure. From left to right, the compounds are—Norephedrine, Pseudoephedrine, Ephedrine, and Synephrine.

Figure 1.Chemical structures of compounds used in the study.

Experimental Conditions

Table 1.Chromatographic conditions for the analysis of ephedrine compounds
Table 2.Composition of Test Mix used in the study

Results

A chromatogram resulting from a UHPLC analysis performed on a Supel™ Carbon LC column with a geometry of 10 cm by 2.1 mm internal diameter (I.D.). The x-axis represents the retention time in minutes, ranging from 0 to 10 minutes, while the y-axis represents the absorbance in milli-absorbance units (mAU), ranging from 0 to 80 mAU. The chromatogram shows four distinct peaks at retention times of approximately 2.646 minutes, 3.105 minutes, 3.665 minutes, and 4.668 minutes, each corresponding to different analytes. The peaks are sharp and well-resolved, indicating effective separation of the compounds. The baseline is stable, with minor fluctuations, showing good chromatographic performance throughout the analysis.

Figure 2.Analysis of ephedrine compounds on Supel™ Carbon LC.

A chromatogram from a UHPLC analysis performed on a Competitor T column with a geometry of 10 cm by 2.1 mm internal diameter (I.D.). The x-axis represents the retention time in minutes, ranging from 0 to 10 minutes, while the y-axis represents the absorbance in milli-absorbance units (mAU), ranging from 0 to 80 mAU. The chromatogram displays four peaks at retention times of approximately 2.406 minutes, 2.662 minutes, 3.128 minutes, and 4.447 minutes, which correspond to different analytes. The peaks here are less sharp and more broadly spaced, indicating less effective separation of the compounds. The baseline shows some minor fluctuations, with slightly more noise.

Figure 3.Analysis of ephedrine compounds on a competitor carbon column.

Table 3.Retention time parameters for compounds seen in Figure 2
Table 4.Retention time parameters for compounds seen in Figure 3

Conclusion

This application has demonstrated the use of the Supel™ Carbon LC column in resolving ephedrine and related compounds. By employing the unique PREG effect, these compounds were baseline separated with excellent peak shape in under five minutes. In addition, the narrower particle size distribution and unique surface properties of the Supel™ Carbon LC column led to the generation of narrower peaks and better resolution compared to a column from an alternative vendor. The Supel™ Carbon LC column is an ideal choice for the resolution of mixtures of structurally similar compounds.

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