Quality control of Aloe vera (Aloe barbadensis) and Aloe ferox using band-selective quantitative heteronuclear single quantum correlation spectroscopy (bs-qHSQC)

In the present study, band-selective quantitative heteronuclear single quantum correlation spectroscopy (bs-qHSQC) was applied for the quality control of the two Aloe species present in the European Pharmacopeia. After development and validation of a complete spectral range (csr-) qHSQC assay, a specific pulse program with selective excitation was applied and the measuring time was reduced from 135 to 32 min, while maintaining the same resolution. This bs-qHSQC method (method I) showed slightly higher RSD values compared to the csr-qHSQC method (maximum RSD of 2.80%), but better recovery rates in comparison to the assay of the Pharmacopeia (97.3% for Aloe vera and 96.6% for Aloe ferox). Apart from quantifying the total anthranoid content, the method moreover allows the quantitation of aloin among other aloin derivatives, such as 7-hydroxyaloin, as well as the differentiation of the two investigated species. Additionally, a second bs-qHSQC method (method II) for the fast (4 min) determination of the aloin A/B ratio was developed and compared to C-13 qNMR measurements. Showing the same results in much less analysis time, the latter approach contributes to a general problem in natural product chemistry, the co-occurrence of structurally similar compounds and their analysis in complex matrices, e.g. plant extracts.