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Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

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Fast Inspection of Quality of Indigo Naturalis by Multiple Light Scattering
03:40

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Published on: August 18, 2023

Composition of Indigo naturalis.

Inken Plitzko1, Tobias Mohn, Natalie Sedlacek

  • 1Institute of Pharmaceutical Biology, University of Basel, Basel, Switzerland.

Planta Medica
|March 20, 2009
PubMed
Summary

A new quantitative assay using (1)H-NMR offers a more accurate method for determining indigo content in Indigo naturalis, overcoming solubility issues seen with HPLC-UV. This advance aids in better quality assessment for future European Pharmacopoeia monographs.

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Area of Science:

  • Pharmacognosy
  • Analytical Chemistry
  • Quality Control

Background:

  • A proposed European Pharmacopoeia monograph for Indigo naturalis suggests using High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV) for quantifying indigo and indirubin.
  • Initial testing revealed significant challenges with the HPLC-UV method, primarily due to the poor solubility of indigo, leading to inaccurate dosage estimations.

Purpose of the Study:

  • To develop and validate an alternative quantitative assay for indigo in Indigo naturalis.
  • To compare the performance of the new assay with the proposed HPLC-UV method.
  • To investigate simple wet chemistry methods for detecting undeclared additives in Indigo naturalis.

Main Methods:

  • Quantitative Nuclear Magnetic Resonance ((1)H-NMR) spectroscopy was employed to develop a new assay for indigo.
  • High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV) was used for comparative analysis.
  • Eight samples of Indigo naturalis were analyzed using both HPLC-UV and (1)H-NMR.
  • Wet chemistry assays were performed on artificially spiked samples to determine limits of detection for sugars and starch.
  • Sulfate ash determinations were conducted for overall impurity assessment.

Main Results:

  • The (1)H-NMR assay provided more reliable indigo concentrations compared to HPLC-UV.
  • HPLC-UV consistently underestimated indigo content due to solubility limitations during sample preparation.
  • Sucrose was identified as an additive in one Indigo naturalis sample using (1)H-NMR.
  • Limits of detection were established for sugars and starch using wet chemistry methods.

Conclusions:

  • Quantitative Nuclear Magnetic Resonance ((1)H-NMR) is a suitable alternative for accurate indigo quantification in Indigo naturalis, overcoming solubility issues inherent in HPLC-UV.
  • The findings support the development of more robust quality control measures for Indigo naturalis.
  • Further investigation into additives and impurity profiles is recommended for future European Pharmacopoeia monographs.