Development of Semimicro LC/NMR and Its Applications in Cosmetic Ingredients Analysis

Abstract

An on-line LC/NMR system combining semimicro LC and 400MHz-NMR with a 3mm i.d. probe was developed. A semimicro LC column (1.5mm i.d.×250mm) was used for various studies with a mobile phase of D₂O/CD₃CN mixture at 100-125μL/min flow rates. This system required only 6-7.5mL/h of mobile phase, significantly improving cost-performance and allowing the use of expensive deuterated solvents so that solvent signals could be easily minimized. In addition, improvement of the sensitivity due to the condensation effect of semimicro LC was achieved, and the results fully supported the advantage of the semimicro LC/NMR system. Identification limits of ethyl p-hydroxybenzoate for this semimicro LC/NMR system were a few μg for ON-FLOW method and sub μg for STOP & FLOW method. This system also applied for the analysis of herb medicine powders of cosmetic ingredients. It was possible to monitor minor components without a preparative procedure, therefore it was useful for rapid screening of the effective components as cosmetic ingredients.