Juliano da Silva Carlos, Pasquini Celio
Chemistry Institute, University of Campinas - UNICAMP, Caixa Postal: 6154, CEP: 13084-971, Cidade Universitária, Campinas, SP, Brazil.
Analyst. 2015 Jan 21;140(2):512-22. doi: 10.1039/c4an00836g.
Conventional reflectance spectroscopy (NIRS) and hyperspectral imaging (HI) in the near-infrared region (1000-2500 nm) are evaluated and compared, using, as the case study, the determination of relevant properties related to the quality of natural rubber. Mooney viscosity (MV) and plasticity indices (PI) (PI0 - original plasticity, PI30 - plasticity after accelerated aging, and PRI - the plasticity retention index after accelerated aging) of rubber were determined using multivariate regression models. Two hundred and eighty six samples of rubber were measured using conventional and hyperspectral near-infrared imaging reflectance instruments in the range of 1000-2500 nm. The sample set was split into regression (n = 191) and external validation (n = 95) sub-sets. Three instruments were employed for data acquisition: a line scanning hyperspectral camera and two conventional FT-NIR spectrometers. Sample heterogeneity was evaluated using hyperspectral images obtained with a resolution of 150 × 150 μm and principal component analysis. The probed sample area (5 cm(2); 24,000 pixels) to achieve representativeness was found to be equivalent to the average of 6 spectra for a 1 cm diameter probing circular window of one FT-NIR instrument. The other spectrophotometer can probe the whole sample in only one measurement. The results show that the rubber properties can be determined with very similar accuracy and precision by Partial Least Square (PLS) regression models regardless of whether HI-NIR or conventional FT-NIR produce the spectral datasets. The best Root Mean Square Errors of Prediction (RMSEPs) of external validation for MV, PI0, PI30, and PRI were 4.3, 1.8, 3.4, and 5.3%, respectively. Though the quantitative results provided by the three instruments can be considered equivalent, the hyperspectral imaging instrument presents a number of advantages, being about 6 times faster than conventional bulk spectrometers, producing robust spectral data by ensuring sample representativeness, and minimizing the effect of the presence of contaminants.
对近红外区域（1000 - 2500 nm）的传统反射光谱法（NIRS）和高光谱成像（HI）进行了评估和比较，以天然橡胶质量相关的特性测定作为案例研究。使用多元回归模型测定了橡胶的门尼粘度（MV）和可塑性指数（PI）（PI0 - 原始可塑性，PI30 - 加速老化后的可塑性，以及PRI - 加速老化后的可塑性保留指数）。使用传统和高光谱近红外成像反射仪器在1000 - 2500 nm范围内对286个橡胶样品进行了测量。样本集被分为回归子集（n = 191）和外部验证子集（n = 95）。使用了三种仪器进行数据采集：一台线扫描高光谱相机和两台传统的傅里叶变换近红外光谱仪。使用分辨率为150×150μm的高光谱图像和主成分分析对样品的不均匀性进行了评估。发现实现代表性所需的探测样品面积（5 cm²；24,000像素）相当于一台傅里叶变换近红外仪器1 cm直径探测圆形窗口6个光谱的平均值。另一台分光光度计只需一次测量就能探测整个样品。结果表明，无论高光谱近红外（HI - NIR）还是传统傅里叶变换近红外（FT - NIR）产生光谱数据集，通过偏最小二乘法（PLS）回归模型都能以非常相似的准确度和精密度测定橡胶特性。外部验证中MV、PI0、PI30和PRI的最佳预测均方根误差（RMSEP）分别为4.3%、1.8%、3.4%和5.3%。尽管这三种仪器提供的定量结果可被认为是等效的，但高光谱成像仪器具有许多优点，比传统的整体光谱仪快约6倍，通过确保样品代表性产生可靠的光谱数据，并将污染物存在的影响降至最低。
