Abstract
In this work, multivariate detection limits (MDL) estimator was obtained based on the micro-electro-mechanical systems–near infrared (MEMS–NIR) technology coupled with two sampling accessories to assess the detection capability of four quality parameters (glycyrrhizic acid, liquiritin, liquiritigenin and isoliquiritin) in licorice from different geographical regions. 112 licorice samples were divided into two parts (calibration set and prediction set) using Kennard–Stone (KS) method. Four quality parameters were measured using high-performance liquid chromatography (HPLC) method according to Chinese pharmacopoeia and previous studies. The MEMS–NIR spectra were acquired from fiber optic probe (FOP) and integrating sphere, then the partial least squares (PLS) model was obtained using the optimum processing method. Chemometrics indicators have been utilized to assess the PLS model performance. Model assessment using chemometrics indicators is based on relative mean prediction error of all concentration levels, which indicated relatively low sensitivity for low-content analytes (below 1000 parts per million (ppm)). Therefore, MDL estimator was introduced with alpha error and beta error based on good prediction characteristic of low concentration levels. The result suggested that MEMS–NIR technology coupled with fiber optic probe (FOP) and integrating sphere was able to detect minor analytes. The result further demonstrated that integrating sphere mode (i.e., MDL0.05,0.05, 0.22%) was more robust than FOP mode (i.e., MDL0.05,0.05, 0.48%). In conclusion, this research proposed that MDL method was helpful to determine the detection capabilities of low-content analytes using MEMS–NIR technology and successful to compare two sampling accessories.
Highlights
Most wet chemistry methods have been used for a long time, such as high-performance liquid chromatography (HPLC)
This paper focuses on establishing an mechanical systems (MEMS)–near infrared (NIR) method of four quality parameters coupled with two sampling accessories
The results indicated that NIR spectroscopy combined with two sampling accessories could be successfully applied to determine the low content of glycyrrhizic acid, liquiritin, liquiritigenin and isoliquiritin in licorice
Summary
Most wet chemistry methods have been used for a long time, such as high-performance liquid chromatography (HPLC). These technologies usually have some disadvantages like tedious sample preparation procedures, time-consuming, labor-intensive and consumption of organic solvent. The advantages of NIR spectroscopy over other analytical techniques have increased its acceptance in agriculture, food, pharmaceuticals, chemical and oil industry.[3,4,5]. The growing demand has fostered the development of sensitive and expeditious NIR techniques, which were capable of determining low concentration (below 1000 parts per million (ppm)) of Chinese herbal medicine (CHM), such as Holographic Grating, Fourier Transform, Acousto-Optic Tunable Filter and micro-electro-mechanical systems (MEMS). Important drawbacks of NIR technology, low spectral intensities and overlapping bands, result in high detection limit.[4,6,7,8]
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