I. 操作摘要
??????????? 使用Brimrose自由空間光譜儀收集含有聚合物添加劑的五種化合物的光譜，其中的三種樣品含有高濃度的添加劑，另外兩種樣品是含有這些添加劑的樹脂。光譜顯示了所有五個樣本之間的明顯區別，PCA回歸證實Brimrose自由空間光譜儀能夠區分這五種化合物。光譜顯示了清晰的波峰，包含了可以用于定量分析此類化合物中添加劑水平的相關光譜信息。下一步是獲取含有已知不同水平添加劑的樣品，并使用Brimrose光譜儀收集用于PLS1分析的光譜，該光譜可用于創建一個模型，可以定量分析添加劑在這些化合物中的水平。
II.簡介
聲光可調濾波器（AOTF）的原理基于光在各向異性介質中的聲折射。裝置由粘在雙折射晶體上的壓電導層構成。當導層被應用的射頻（RF）信號激發時，在晶體內產生聲波。傳導中的聲波產生折射率的周期性調制。這提供了一個移動的相柵，在特定條件下折射入射光束的部分。對于一個固定的聲頻，光頻的一個窄帶滿足相匹配條件，被累加折射。RF頻率改變，光的帶通中心相應改變以維持相匹配條件。
光譜的近紅外范圍從800nm到2500 nm延伸。在這個區域最突出的吸收譜帶歸因于中紅外區域的基頻振動的泛頻和合頻。是基態到第二激發態或第三激發態的能級躍遷。因為較高能級躍遷連續產生的概率較小，每個泛頻的強度連續減弱。由于躍遷的第二或第三激發態所需的能量近似于第一級躍遷所需能量的二倍或三倍，吸收譜帶產生在基頻波長的一半和三分之一處。觸簡單的泛頻以外，也產生合頻。這些通常包括延伸加上一個或多個振動方式的伸縮。大量不同合頻是可能的，因而近紅外區域復雜，有許多譜帶彼此部分疊加。
現在，NIRS被用作定量工具，它依賴化學計量學來發展校正組成的參照分析和近紅外光譜的分析的關聯。近紅外數據的數學處理包括多元線性回歸法（MLR）、主成分分析法（PCA）、主成分回歸法（PCR）、偏最小二乘法（PLS）和識別分析。所有這些算法可以單獨或聯合使用來得到有價值組成的定性描述和定量預測。
III.? Methodology
- Data Collection
A Brimrose Free Space spectrometer was used to collect absorbance spectra of five samples containing additives.? Each sample was placed in a large petri dish and leveled out.?? The instrument was tested and adjusted for maximum signal.??? 200 scans were collected for each reading and averaged into one spectrum.? As the instrument was scanning, the petri dish was moved back and forth and around in circles to allow the instrument to scan the entire surface of the sample contained in the dish.?? The samples were kept at the objective distance of 40 mm.? 5 spectra were taken for each sample for a total of 25 spectra.? All raw spectral data was taken in reflectance mode with 2nm resolution.? Wavelength range was between 1100nm and 2300nm.? Spectra were processed into absorbance and first derivative and imported into Unscrambler for modeling.
IV.Results
- Spectra
Figure 2.?? Absorbance spectra of all 5 samples containing additives.
The spectra show clear peaks around 1200, 1400, and 1550 nm.? The loading weights for the PCA analysis will confirm that these peaks can be used to distinguish between these 5 compounds and could also probably be used for quantitative analysis of additive level in these compounds.
Figure 3.?? Absorbance spectra of sample PPM 11174
Figure 4.? Absorbance spectra of sample PPM11421E63
Figure 5.? Absorbance spectra of sample PM 11025E4
Figure 6.? Absorbance spectra of LDPE RESIN
Figure 7.? Absorbance spectra of PP RESIN
2.Modeling and Regressions
PCA analysis was performed on the absorbance spectra using Unscrambler.? PCA analysis was also performed on the first derivative spectra but the results were much better using the absorbance data.? The PCA analysis shows that all 5 samples can be clearly distinguished from one another using the Brimrose spectrometer and that the information used to distinguish the samples from one another comes from the wavelength ranges where the spectral peaks occur.
Figure 8.? Scores plot for PCA analysis of all 5 sample sets.
Figure 9.?? X-Loading weights plot for PCA analysis of 5 samples.
The scores plot shown in Figure 8 shows that the Brimrose Free Space Luminar 2030 is able to distinguish between all 5 samples in this study.? The 5 sets of data points are clearly separated from one another.? Figure 9 shows that the information used for separating the samples using the spectra comes from the same wavelength ranges where the spectra peaks occur.? Both the absorbance spectra and the loading weights have peaks around 1200, 1400, and 1550 nm.? This is a good indication that these peaks contain the spectral information necessary to create a regression model that could quantify the amount of additive in the samples.
V. Conclusions and Recommendations
It is concluded that the Brimrose Free Space spectrometer can be used to qualitatively analyze the 5 samples used in this study.? There are clear spectral differences that can be seen from looking at the spectra and the PCA analysis makes it even clearer that the five samples can be distinguished using spectral data.? The fact that the PCA analysis takes its information from the same wavelengths where the spectral peaks occur indicates that these peaks can probably be used to quantify the amount of additive found in these samples.? It is recommended that Brimrose receive quantities of the same samples with known different amounts of additives.? Brimrose will conduct a similar study collecting spectral data and using the data for PLS1 analysis, which will show if it is feasible to set up a model to quantitatively analyze the amount of additives in the samples.
