传统中药在世界范围的需求量巨大, 尤其是屠呦呦在2015年获得诺贝尔医学奖以来, 中药的受欢迎程度进一步得到了提高。 然而, 中药的质量标准管理中还存在较多关键性问题, 其中, 中药水分含量的检测是中药质量一致性控制中的一个重要因素。 基于近红外LED吸收光谱的中药水分传感器, 通常采用电平信号或锁相放大来实现信号的探测。 方波激励可以获得水吸收光谱信号丰富的时域和频域响应信息, 故常被用来作为水分传感器的激励源。 针对待测样品的不平整度、 提离效应及噪声等因素严重影响水分含量的时域特征量的问题, 提出了一种基于方波激励的近红外吸收信号频谱分析的中药水分传感器。 首先, 利用中心波长为1 450 nm的LED作为水吸收光谱信号的光源, 并采用快速傅里叶变换获得水直接吸收光谱信号的频谱特征量。 其次, 分析和优化了激励方波信号参数, 优化结果表明, 当方波激励源的频率、 幅值及占空比三个参数分别为100 Hz, 1 500 mV及50%时, 水的吸收光谱信号最好。 最后, 制备了8组用于标定的肚痛丸样品和4组用于验证的肚痛丸样品, 在优化激励方波参数基础上, 建立了肚痛丸水分含量与奇次谐波信号幅度之间的线性关系。 标定与验证实验结果表明, 谐波分量中基频分量(100 Hz)和三次谐波分量(300 Hz)的幅值与肚痛丸的水分含量的线性相关系数r值分别为0.992和0.993, 平均后的最小误差为1.0%, 最大误差小于6.5%。 该水分传感器把方波作为激励源, 利用小波滤波算法对水吸收光谱信号进行去噪, 并采用快速傅里叶变换算法将光谱吸收信号转换到频域后进行特征量提取, 具有精度高、 适用性强、 实时在线测量等优点, 在中药制药质量控制和过程分析中具有广阔的应用前景。

Traditional Chinese medicines (TCMs) are in great demands around the world, and their popularity increased even more when Tu Youyou was awarded the 2015 Nobel Prize in Medicine. However, many key issues regarding the current quality standards remain and moisture content (MC) of TCM is one of the important elements of the quality control inspection. MC detection of TCM is usually implemented by using a voltage level or lock-in amplifier based on a Near-infrared Light-Emitting Diode (NIR-LED) absorption spectroscopy sensor. Square signal is frequently used as excitation source due to its abundant absorption features both in the time-domain and frequency-domain. However, the planeness, lift-off effect, and measurement noise negatively affect the time-domain features during MC measurement. A MC sensor has been developed to precisely measure the MC of Dutong pills based on NIR-LED spectrum analysis in this work. Firstly, a broadband NIR-LED with a central wavelength at 1 450 nm was adopted for the water absorption source. The spectrum features of the direct absorption signals were extracted by Fast Fourier Transform (FFT) algorithm. Secondly, the parameters of the excitation square signal were analyzed and optimized. The optimization results showed that the direct absorption spectrum signal was optimal when the excitation frequency, amplitude and duty ratio were set as 100 Hz, 1500 mV and 50% respectively. Finally, eight calibration groups with different MCs and four validation groups of Dutong pills were prepared. The linear relationship between the MC of the Dutong pills and the odd harmonic signal amplitude was established on the basis of the optimized square parameters of the excitation source. The calibration and validation results demonstrated the fundamental frequency components (100 Hz) and the 3rd harmonic components (300 Hz) have a high linear correlation with the MCs of the Dutong pills and the linear correlation coefficient R values were 0.992 and 0.993, respectively. The minimum measurement error and maximum error after averaging were 1.0% and less than 6.5%, respectively. The MC sensor took the square wave as excitation source. The noise of the water absorption spectrum signal was removed by wavelet filtering algorithm. The FFT algorithm was adopted to extract the feature of spectral signal. Therefore, the sensor has the advantages of high precision, wide applicability, real-time online measurement, and has the potential to be used for quality control and process analytical technology in TCM.