Structural analysis of triacylglycerols and edible oils by near-infrared Fourier transform Raman spectroscopy

Fourier transform Raman spectroscopy was employed for structural analysis of triacylglycerols and edible oils. Raman spectra sensitively reflected structural changes in oils. Even slight structural fluctuation between triacylglycerols and free fatty acids led to obvious differences in Raman bands as shown by C-O-C stretching from 800 to 1000 cm(-1) and the band at 1742 cm(-1). Structural difference in geometric isomers was easily distinguished as proved by C = C stretching at 1655 cm(-1) (cis) shifting to 1668 cm(-1) (trans) and by =C-H in-plane bending at 1266 cm(-1) in cis disappearing in the trans isomer. Raman intensity at 1266, 1302, and 1655 cm(-1) changed concomitantly with the change of double-bond content in oils. It showed that FT-Raman was capable of precisly reflecting the content of double bonds in oils. A linear correlation with high consistency between the Raman intensity ratio (v1655/v1444) and the iodine value was obtained for commercial oils. Based on the results, FT-Raman spectroscopy proved itself a simple and rapid technique for oil analysis since each measurement could be directly completed in 3 min without any sample modifications.     

Concentration measurements of multiple analytes in human sera by near-infrared laser Raman spectroscopy

Our primary goal in this study is to demonstrate that near-infrared Raman spectroscopy is feasible as a rapid and reagentless analytic method for clinical diagnostics. Raman spectra were collected on human sera by use of a 785-nm excitation laser and a single-stage holographic spectrometer. A partial-least-squares method was used to predict the analyte concentrations of interest. The prediction errors of total protein, albumin, triglyceride, and glucose in human sera ranged from 1.0% to 10%, which are highly acceptable for clinical diagnosis, of their mean physiological levels. For investigating the potential application of near-infrared Raman spectroscopy in screening of therapeutical drugs and substances of abuse the concentrations of acetaminophen, ethanol, and codeine in water solution were measured in the same fashion. The errors of the Raman tests for acetaminophen and ethanol are lower than their toxic levels in human serum, and the sensitivity for detection of codeine fails to reach its toxic level.     

Rapid, noninvasive concentration measurements of aqueous biological analytes by near-infrared Raman spectroscopy

Accurate concentration measurements of glucose, lactic acid, and creatinine in saline solution have beena chieved with near-IR Raman spectroscopy and a partial least-squares analysis. The Raman spectra were acquired remotely through optical fibers. A root-mean-squared prediction error of 1.2 mM for glucose concentration was achieved in 100 s. Concentrations of other analytes were predicted with similar accuracy.     

In vivo noninvasive measurement of blood glucose by near-infrared diffuse-reflectance spectroscopy

This paper reports in situ noninvasive blood glucose monitoring by use of near-infrared (NIR) diffuse-reflectance spectroscopy. The NIR spectra of the human forearm were measured in vivo by using a pair of source and detector optical fibers separated by a distance of 0.65 mm on the skin surface. This optical geometry enables the selective measurement of dermis tissue spectra due to the skin's optical properties and reduces the interference noise arising from the stratum corneum. Oral glucose intake experiments were performed with six subjects (including a single subject with type I diabetes) whose NIR skin spectra were measured at the forearm. Partial least-squares regression (PLSR) analysis was carried out and calibration equations were obtained with each subject individually. Without exception among the six subjects, the regression coefficient vectors of their calibration models were similar to each other and had a positive peak at around 1600 nm, corresponding to the characteristic absorption peak of glucose. This result indicates that there is every possibility of glucose detection in skin tissue using our measurement system. We also found that there was a good correlation between the optically predicted values and the directly measured values of blood samples with individual subjects. The potential of noninvasive blood glucose monitoring using our methodology was demonstrated by the present study.     

Noninvasive investigation of blood oxygenation dynamics of tumors by near-infrared spectroscopy

The measurement of dynamic changes in the blood oxygenation of tumor vasculature could be valuable for tumor prognosis and optimizing tumor treatment plans. In this study we employed near-infrared spectroscopy (NIRS) to measure changes in the total hemoglobin concentration together with the degree of hemoglobin oxygenation in the vascular bed of breast and prostate tumors implanted in rats. Measurements were made while inhaled gas was alternated between 33% oxygen and carbogen (95% O(2), 5% CO(2)). Significant dynamic changes in tumor oxygenation were observed to accompany respiratory challenge, and these changes could be modeled with two exponential components, yielding two time constants. Following the Fick principle, we derived a simplified model to relate the time constants to tumor blood-perfusion rates. This study demonstrates that the NIRS technology can provide an efficient, real-time, noninvasive means of monitoring the vascular oxygenation dynamics of tumors and facilitate investigations of tumor vascular perfusion. This may have prognostic value and promises insight into tumor vascular development.     

Quantitative analysis of vitamin A degradation by Raman spectroscopy

Vitamin A is known to support cell growth promotion, maintenance, and differentiation of epithelial tissues. Retinol is currently used in cosmetic formulations and products to deliver these and other benefits to the skin. However, retinol is known to be unstable and, therefore, remains of great concern to the cosmetic industry. The decomposition pathways of the retinoids in general have been previously postulated and investigated mostly by high-performance liquid chromatography (HPLC) with UV/Vis spectroscopy. In our studies, we examined specific conditions at which retinol degrades and subsequently identified and quantified the products of retinol decomposition by Raman spectroscopy. We reveal which experimental settings and computational tools allow monitoring of in situ evolution of an all-trans retinol solution when submitted to UV light in the presence of oxygen.     

Single-pollen analysis by laser-induced breakdown spectroscopy and Raman microscopy

The application of laser-induced breakdown spectroscopy to the analysis of single biological microparticles (bioaerosols) is described, exemplified here for a range of pollens. Spectra were recorded by exposure of the pollen to a single laser pulse from a Nd:YAG laser (lambda = 1064 nm, Ep approximately 30 mJ). The intensities of the single-pulse laser-induced breakdown spectra fluctuated dramatically, but an internal signal calibration procedure was applied that referenced elemental line intensities to the carbon matrix of the sample (represented by molecular bands of CN and C2). This procedure allowed us to determine relative element concentration distributions for the different types of pollen. These pollens exhibited some distinct concentration variations, for both major and minor (trace) elements in the biomatrix, through which ultimately individual pollens might be identified and classified. The same pollen samples were also analyzed by Raman microscopy, which provided molecular compositional data (even with spatial resolution). These data allowed us to distinguish between biological and nonbiological specimens and to obtain additional classification information for the various pollen families, complementing the laser-induced breakdown spectroscopy measurement data.     

Investigating dehydration from compacts using terahertz pulsed, Raman, and near-infrared spectroscopy

The purpose of this study was to investigate the dehydration of piroxicam monohydrate (PRXMH) in compacts using terahertz pulsed spectroscopy (TPS), Raman spectroscopy, and reflectance near-infrared (NIR) spectroscopy. Compacts were prepared by using PRXMH and poly(tetrafluoro)ethylene powders and combining them in three different manners before compression to produce compacts in which the PRXMH was dispersed throughout the compact, deposited on one face of the compact, or included as a layer within the compact. TPS was a suitable technique to assess the effect of sample preparation on dehydration, whereas Raman and NIR spectroscopy were limited by their sampling depth and the interference of the polymer matrix. TPS revealed that the dehydration behavior depended largely on the compact preparation method. Non-isothermal dehydration was investigated with all three spectroscopic techniques, combined with principal component analysis (PCA) on samples where the PRXMH was deposited on one face of the compact. In addition, variable temperature X-ray powder diffractometry (VT-XRPD) was used to verify the transformation from PRXMH to anhydrous PRX form I, while thermogravimetric analysis (TGA) was used to monitor the water loss. All three spectroscopic techniques allowed in situ monitoring of the dehydration from the surface layers of the compacts. TPS and Raman spectroscopy detected structural changes of the crystal, while NIR spectroscopy was more sensitive to water loss. PCA of the TPS, Raman spectroscopy, and XRPD data revealed similar dehydration profiles. In contrast, the NIR spectroscopy profile was more similar to the TGA results. The spectroscopic techniques were more suitable than slower techniques such as VT-XRPD for monitoring rapid structural changes that occurred during the dehydration.     

Real-time monitoring of distillations by near-infrared spectroscopy

A simple device is described to couple a fast-scanning acoustooptic tunable filter-based NIR spectrophotometer to a distillation apparatus for monitoring the condensed vapor in real time. The device consists of a small funnel whose glass neck (2-mm diameter) is bent into an "U" format to produce a flow cell of approximately 150-microL inner volume. A pair of optical fibers is used to deliver the monochromatic light and to collect the fraction passing through the glass tube. The end of the condenser of the distillation head touches the wall of the small funnel. The condensed liquid flows uncoupled from pressure changes in the interior of the distillation head. Absorbance spectra were obtained, during the distillation, as averages of 50 scans (4 s) every 5 s in the spectral range 950-1800 nm with nominal resolution of 2.0 nm. In the first experiments, the distillations were performed at constant power supplied to the sample (25 mL) in a microdistillation apparatus working without any type of reflux column. The usefulness of the real-time monitoring of distillation is demonstrated using some prepared binary mixtures and by comparing the distillation behavior of adulterated and regular gasoline samples. Data analysis and interpretation are facilitated by employing principal component analysis. The system accesses the composition of the condensate, which can separate and concentrate one or more compounds present in the original sample.     

Analysis of sticky cotton by near-infrared spectroscopy

"Stickiness" in cotton is a major problem affecting throughput in cotton gins and spinning mills alike. Stickiness is thought to be caused by the deposition of sugars by insects, principally aphid and whitefly, on the open boll. Fourier transform near-infrared (FT-NIR) spectroscopy was used to develop models for sugar content from high-pressure liquid chromatography (HPLC), thermodetector, and mini-card data. A total of 457 cotton samples were selected to represent both Upland and Pima varieties and cotton processing before and after ginning. The Unscrambler was used to develop the models. A successful model was made to determine the mini-card value and successfully detect "stickiness". The standard error of cross-validation (SECv) was 0.26 with an R2 of 0.96. The model was not improved by increasing the range of "stickiness" as measured by the mini-card from the usual 0-3 scale to a scale of 0-8. If a value is determined to be greater than 1 it will be difficult to blend bales at a spinning plant "opening line" to allow for maximum efficiency of spinning.     

Discrimination of bacteria and bacteriophages by Raman spectroscopy and surface-enhanced Raman spectroscopy

Detection of pathogenic organisms in the environment presents several challenges due to the high cost and long times typically required for identification and quantification. Polymerase chain reaction (PCR) based methods are often hindered by the presence of polymerase inhibiting compounds and so direct methods of quantification that do not require enrichment or amplification are being sought. This work presents an analysis of pathogen detection using Raman spectroscopy to identify and quantify microorganisms without drying. Confocal Raman measurements of the bacterium Escherichia coli and of two bacteriophages, MS2 and PRD1, were analyzed for characteristic peaks and to estimate detection limits using traditional Raman and surface-enhanced Raman spectroscopy (SERS). MS2, PRD1, and E. coli produced differentiable Raman spectra with approximate detection limits for PRD1 and E. coli of 10(9) pfu/mL and 10(6) cells/mL, respectively. These high detection concentration limits are partly due to the small sampling volume of the confocal system but translate to quantification of as little as 100 bacteriophages to generate a reliable spectral signal. SERS increased signal intensity 10(3) fold and presented peaks that were visible using 2-second acquisitions; however, peak locations and intensities were variable, as typical with SERS. These results demonstrate that Raman spectroscopy and SERS have potential as a pathogen monitoring platform.     

近红外光谱数据处理的独立分量分析方法研究

从数学的角度分析比较了主成分分析(PCA)与独立分量分析(ICA)的原理和特点,给出光谱矩阵在两种不同分析方法下的不同分解;同时结合线性回归和神经网络回归,提出"两步法"来确定不同成分含量测定的最优模型.进而采用PCA与ICA对实际测得的玉米近红外光谱进行了处理,比较分析了两种不同分解所得矩阵的化学含义,以及PCA与ICA两种不同分解对玉米光谱分析结果的影响.仿真结果表明,ICA从独立性角度对光谱数据矩阵进行分解,所得结果更接近实际光谱.最后,利用"两步法"对玉米三种主要成分水、淀粉、蛋白质分别建立了各自最优含量测定模型.结果表明,所建模型符合快速测定要求,具有一定的实用价值.     

ICA的近红外光谱分析软件的研制

研制了基于独立分量分析方法的近红外光谱分析软件.该软件包括光谱解析、光谱建模和未知成分含量测定三个模块,使用了小波分析、ICA和BP神经网络等数据处理方法.将这种软件用于实测的玉米近红外光谱分析,所得结果令人满意.使用LabVIEW与MATLAB软件混合编程,充分利用了各软件的优点,不仅程序简单,而且界面友好.     

Scattering and absorption effects in the determination of glucose in whole blood by near-infrared spectroscopy

Optical properties of whole bovine blood are examined under conditions of different glucose loadings. A strong dependency is established between the scattering properties of the whole blood matrix and the concentration of glucose. This dependency is explained in terms of variations in the refractive index mismatch between the scattering bodies (predominately red blood cells) and the surrounding plasma. Measurements in the presence of a well-known glucose transport inhibitor indicate that variations in refractive index mismatch are related to the penetration of glucose into the red blood cells and demonstrate that increased scattering involves the uptake of glucose by red blood cells. Finally, multivariate calibration models are presented for the measurement of glucose in a whole blood matrix. These models are based on near-infrared spectral data collected from 80 different samples prepared from a single whole blood matrix. Calibration studies are performed over the combination, first-overtone, and short-wavelength spectral regions. The best calibration model is generated from combination region spectra, providing a standard error of prediction (SEP) of less than 1 mM over the concentration range of 3-30 mM. The model based on the first-overtone region is slightly degraded but still provides acceptable performance (SEP = 1.20 mM). The model based on the short-wavelength region is further degraded (SEP = 2.53 mM). To rationalize these results, an analysis of the selectivity of the calibration models is performed by computing the glucose net analyte signal. It is established that the models based on the combination and first-overtone regions are dominated by glucose absorption information, while the model computed from the short-wavelength region is based primarily on scattering information. This result provides evidence that absorption information is needed in order to obtain a glucose calibration model with acceptable performance.     

Multicomponent direct detection of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy using silver nanoparticles functionalized with the viologen host lucigenin

Silver nanoparticles (NPs) functionalized with the molecular assembler bis-acridinium dication lucigenin (LG) have been used as a chemical sensor system to detect a group of polycyclic aromatic hydrocarbon (PAH) pollutants in a multicomponent mixture by means of surface-enhanced raman scattering (SERS). The effectiveness of this system was checked for a group of PAHs with different numbers of fused benzene rings, namely anthracene, pyrene, triphenylene, benzo[c]phenanthrene, chrysene, and coronene. In order to determine the host capacity of this sensor system, the self-assembly of the LG viologen on a metallic surface has been checked by analyzing SERS intensities of PAH bands at different LG concentrations. The NP-LG-analyte affinity is derived from the analysis of PAH band intensities at different concentrations of pollutants, the adsorption isotherm of each PAH on NP-LG cavities has been studied, and the corresponding adsorption constants have been evaluated. The limit of detection at trace-level concentration is confirmed by the presence of their characteristic fingerprint vibrational bands. The SERS spectra of PAH mixtures confirm that LG viologen dication shows a higher analytical selectivity to PAHs constituted by four fused benzene rings, mainly pyrene and benzo[c]phenanthrene, in agreement with their higher affinity which is also related to their better fit into the intermolecular LG cavities. As a conclusion, SERS spectra recorded on modified NP-LG surfaces are a powerful chemical tool to detect organic pollutants.