Rapid Identification of Traditional Chinese Medicine Alumen and the Counterfeit Ammonium Alum by Mid-infrared Spectroscopy
Objective:The mid-infrared(MIR)spectroscopic characteristic peaks were determined for the discrimination of Alumen,ammonium alum and their mixture to establish a simple and low-carbon method for the identification of Alumen and the examination of ammonium salt in Alumen.Methods:MIR spectra of Alumen,ammonium alum and their mixtures were directly measured by the attenuated total reflection method.The differential absorption peaks between Alumen and ammonium alum were examined.The feasibility of the differential absorption peaks to discriminate Alumen and ammonium alum as well as to detect the adulterated Alumen with ammonium alum was evaluated by statistical analysis.Results:The mian difference in MIR spectra between Alumen and ammonium alum was that there was the N-H bending vibration peak of ammonium ions near 1436 cm-1 in the latter.Alumen and ammonium alum could be discriminated intuitively according to the presence or absence of this characteristic peak.Ammonium ion can be qualitatively identified based on the height or area of the N-H bending vibration peak when Alumen was adulterated with not less than 5%of ammonium alum,meeting the requirement for the limit of detection of ammonium salt in the Section of Alumen Detection in Chinese Pharmacopoeia(version 2020).Conclusion:MIR spectroscopy can accurately identify Alumen,ammonium alum and their mixtures,and can be used as a simple,rapid,cheap and green method for the identification of Alumen and the examination of ammonium salt in Alumen.