Investigation of the fundamental behavior of long-period grating sensors

A new class of fiber optic sensor, long period gratings (LPG) optical sensors, has been investigated. The characteristics of the bare fiber LPG were studied. The LPG response to different refractive index standards, mixtures of methanol and ethanol were observed. The temperature dependence of LPG sensors was determined. A commercial LPG sensor for copper determination was evaluated.     

The investigation of the behavior of a long period grating sensor with a copper sensitive coating fabricated by layer-by-layer electrostatic adsorption

Sensors based on changes of refractive index in response to sorption of an analyte on the coating or film of a long period grating fiber (LPG) fiber have recently been reported. In most prior work the coating or film swelled during interaction with the analyte. The swelling mechanism produced a kinetic response that slowed both the sensor's time for steady-state measurement and the reversibility of the sensor. Here, the analytical utility of fabricating these nanometer thin films using the layer-by-layer (LBL) electrostatic assembly method is evaluated using Cu^II as the test analyte and Cibacron Blue as the reagent immobilized in the LBL assembly; a generation-4 poly(amidoamine) dendrimer served as the spacer in the assembly. Detection of 1.3 mg Cu^II L⁻¹ was observed when six bilayers comprised the coating. The stable response was achieved with 0.6 mg L⁻¹ in less than 1 min. When 0.1 M HCl was used as the rinsing solution, this LPG sensor was reversible and the signal to similar concentrations of Cu^II reproducible.     

Degradation of β-Carbolines Harman and Norharman in Edible Oils during Heating

The β-carbolines, mainly including harman and norharman, are a group of naturally occurring, plant-derived alkaloids, and are also considered as nonpolar heterocyclic aromatic amines. Sesame seed oils contain a high level of β-carbolines (harman and norharman). In China, sesame seed oil blends are one of the most popular types of vegetable oils blends, which can be used as cooking oils or frying oils. Thus, it is meaningful to investigate the degradation of β-carbolines (harman and norharman) in sesame seed oil blends as frying oils during heating. In this work, the loss of harman and norharman in different types of sesame seed oil blends have been investigated. The results showed that the degradation of harman and norharman were dependent both on the type of oil blends, heating temperature and time. Harman and norharman were more degraded during heating (150 °C, 180 °C) in oleic acid-rich oil blends compared to polyunsaturated acid-rich oil blends. Mechanistic investigation suggested that the reduction in harman and norharman in oil blends during heating was mainly due to the oxidative degradation reaction between β-carbolines and lipid oxidation products. Therefore, the contents of β-carbolines (harman and norharman) in sesame seed oil blends when used as frying oils and heated can be decreased with prolonged cooking time.     

Gas chromatographic sensing on an optical fiber by mode-filtered light detection

A chemical sensor for gas phase measurements is reported which combines the principles of chemical separation and fiber optic detection. The analyzer incorporates an annular column Chromatographic sensor, constructed by inserting a polymer-clad optical fiber into a silica capillary. Light from a helium-neon laser is launched down the fiber, producing a steady intensity distribution within the fiber, but a low background of scattered light. When sample vapor is introduced to the sensor, and an analyte-rich volume interacts with the polymer cladding, Chromatographic retention is observed simultaneously with a change in the local refractive index of the cladding. An increase in cladding refractive index (RI) causes light to be coupled out of the fiber, with detection at a right-angle to the annular column length to provide optimum S/N ratio. This detection mechanism is called mode-filtered light detection. We report a gas Chromatographic separation on a 3.1 m annular column (320 microm i.d. silica tube, 228 microm o.d. fiber with a 12 microm fluorinated silicone clad) of methane, benzene, butanone and chlorobenzene in 6 min. The annular column length was reduced to 22 cm to function as a sensor, with selected organic vapors exhibiting unique retention times and detection selectivity. The detection selectivity is determined by the analyte RI and the partition coefficient into the cladding. The calculated limit of detection (LOD) for benzene vapor is 0.03% by volume in nitrogen, and several chlorinated species had LOD values less than 1%. For binary mixtures of organic vapors, the detected response appears to be the linear combination of the two organic standards, suggesting that the annular column may be useful as a general approach for designing chemical sensors that incorporate separation and optical detection principles simultaneously.     

Prediction of the acid value,peroxide value and the percentage of some fatty acids in edible oils during long heating time by chemometrics analysis of FTIR-ATR spectra

Edible oils are used in the preparation of foods as a part of their recipe or for frying. So to ensure of food safety, checking the quality of the oils before and after usage is an important subject in food control laboratories. In this study, edible oils from four different sources (canola, corn, sunflower and frying) were heated for 36 h at 170 °C and sampling was done every 6 h. The free fatty acid, peroxide value and the content of some fatty acids (C16:0, C18:0, C18:1, C18:2, C18:3) of the oil samples were determined by standard methods. Then, the ATR-FTIR spectra of the samples were collected. The partial least squares (PLS) regression combined with genetic algorithm was performed on the spectroscopic data to obtain the appropriate predictive models for the simultaneous estimation of acid value, peroxide value and the percentage of five kinds of fatty acids. The effect of some preprocessing methods on these models was also investigated. Preprocessing of data by orthogonal signal correction (OSC) resulted in the best predictive models for all oil properties. The correlation coefficients of calibration set (>0.99) and validation set (>0.86 and in most case >0.94) of the OSC–PLS model suggested suitable predictive modeling for all studied parameters in the oil samples. This method could be suggested as a rapid, economical and environmental friendly technique for simultaneous determination of seven noted parameters in the edible oils.     

Carbonyl value in monitoring of the quality of used frying oils

In this study, a set of frying oil samples of different compositional properties but passed qualitative and quantitative standards, which were of various vegetable oil sources (individually or as blends), were obtained from seven of big oil factories in Iran. Before starting the frying process, all the frying oils had carbonyl values (CV) higher than 2 micromol g(-1). The CV of most frying oils linearly increased until the end of the frying process, whereas for some of them, the CV increased and reached a maximum and then decreased to some extent. However, in a set of frying oil samples on average, the CV linearly increased as the frying time increased. There was a linear relationship between the CV and total polar compounds (TPC) throughout the frying process with a high determination coefficient (R(2)=0.9747). The values found for carbonyl compounds of the frying oils during frying process ranged from 7.76+/-0.00 to 123.45+/-3.70 micromol g(-1). Assuming that the limit of acceptance for TPC is 24%, this was roughly corresponded to 43.50 micromol g(-1) for CV.     

A simplified UV spectrometric method for determination of peroxide value in thermally oxidized canola oil

The aim of present study was to develop a simple method on UV spectrometer for the determination of peroxide value (PV) of the frying oil. The basis of the PV determination was the stoichiometric reaction of triphenylphosphine (TPP) with the hydroperoxides present in frying oil to produce triphenylphosphine oxide (TPPO), which exhibits a readily measurable absorption band at 240 nm by ultraviolet region. The PV ranged between 0.15 and 11.66 meq. of active oxygen per kilogram of oil as the canola oil was heated from 0 to 12 h in the fryer at 180 °C. The proposed method was correlated with official AOCS titration method and best correlation coefficient (R² = 0.99525) was achieved, proving that there is no significant difference in the results. Therefore, developed method could serve as an alternative to the titration method, for the determination of PV in frying oils.     

温度敏感水凝胶包覆长周期光纤光栅传感器研究

以N-异丙基丙烯酰胺(NIPAM)为单体、N,N'-亚甲基双丙烯酰胺(MBAA)为交联剂、安息香二甲醚(DMPA)为引发剂,利用紫外光引发聚合制备了一系列温度敏感性聚(N-异丙基丙烯酰胺)(PNIPAM)水凝胶,并对其性能进行了测定.结果表明,PNIPAM水凝胶的平衡膨胀比随着交联程度的变化而改变.当交联程度适当时,水凝胶可具有最大的溶胀比.在此研究基础上,利用浸渍提拉法在长周期光纤光栅(LPFG)包层外制备了PNIPAM水凝胶薄膜包覆层.研究了得到的LPFG传感器对温度和湿度的响应性,该类型传感器表现出对温度的灵敏响应性.     

Thin film composite optical waveguides for sensor applications: a review

We review the design and fabrication of thin-film composite optical waveguides (OWG) with high refractive index for sensor applications. A highly sensitive optical sensor device has been developed on the basis of thin-film, composite OWG. The thin-film OWG was deposited onto the surface of a potassium-ion-exchanged (K⁺) glass OWG by sputtering or spin coating (5–9 mm wide, and with tapers at both ends). By allowing an adiabatic transition of the guided light from the secondary OWG to the thin-film OWG, the electric field of the evanescent wave at the thin film was enhanced. The attenuation of the guided light in the thin film layer was small, and the guided light intensity changed sensitively with the refractive index of the cladding layer. Our experimental results demonstrate that thin-film, composite OWG gas sensors or immunosensors are much more sensitive than sensors based on other technologies.     

Determination of silicon in fats and oils by electrothermal atomic absorption spectrometry with in-furnace air oxidation

A graphite-furnace atomic absorption spectrometric emthod is reported for determination of dimethylpolysiloxane (silicone) in edible fats and oils. It incorporates an air-oxidation step in the furnace program to reduce matrix interferences. The detection limit is 0.3 mg kg^?1 in soils, and short-term precision is about 6% at silicon concentrations of 1.7–2.0 mg kg^?1. The procedure was successfully applied to a variety of commercial frying fats and oils, to quantify silicone loss during polish filtration during oil manufacture, to quantify sorption of antifoam onto fried food, and to detect fugitive sources of silicone encountered in deep-fat frying operations.     

Mode-filtered light methane gas sensor based on cryptophane A

A mode-filtered light sensor has been developed for methane (CH₄) gas determination at ambient conditions. The proposed chemosensor consisted of an annular column which was constructed by inserting an optical fiber coated with a thin silicone cladding of cryptophane A into a fused-silica capillary. When CH₄ was introduced to the sensor, selective inclusion of CH₄ into the silicone layer would cause a change in the local refractive index of the cladding, resulting in the change of mode-filtered light that emanated from the fiber. Three detection windows were set alongside the capillary to propagate the light to a charge-coupled device (CCD). The changes of mode-filtered light on exposure to various concentrations of CH₄ were thus simultaneously monitored. The mode-filtered light intensity decreased with the increase in concentration of CH₄. The dynamic concentration range of the sensor for CH₄ was 0.0-16.0% v/v with a detection limit of 0.15% v/v. The highest sensitivity was found at the channel furthest away from the excitation light source. The response time (t_95%) was about 5 min. The reproducibility was good with a relative standard deviation (RSD) of less than 7% from evaluating six cryptophane A-coated fibers. Oxygen, hydrogen and carbon dioxide showed very little interference on detection but interferences from dichloromethane and carbon tetrachloride were observed. The proposed mode-filtered light sensor has been successfully applied to determine CH₄ samples and the accuracy was good. Our work offers a promising approach for CH₄ detection.     

A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection

We have developed a planar, optofluidic Mach-Zehnder interferometer for the label-free detection of liquid samples. In contrast to most on-chip interferometers which require complex fabrication, our design was realized via a simple, single-layer soft lithography fabrication process. In addition, a single-wavelength laser source and a silicon photodetector were the only optical equipment used for data collection. The device was calibrated using published data for the refractive index of calcium chloride (CaCl(2)) in solution, and the biosensing capabilities of the device were tested by detecting bovine serum albumin (BSA). Our design enables a refractometer with a low limit of detection (1.24 × 10(-4) refractive index units (RIU)), low variability (1 × 10(-4) RIU), and high sensitivity (927.88 oscillations per RIU). This performance is comparable to state-of-the-art optofluidic refractometers that involve complex fabrication processes and/or expensive, bulky optics. The advantages of our device (i.e. simple fabrication process, straightforward optical equipment, low cost, and high detection sensitivity) make it a promising candidate for future mass-producible, inexpensive, highly sensitive, label-free optical detection systems.     

Optical fiber evanescent wave absorption spectrometry of nanocrystalline tin oxide thin films for selective hydrogen sensing in high temperature gas samples

SnO₂ nanocrystalline material was prepared with a sol-gel process and thin films of the nanocrystalline SnO₂ were coated on the surface of bent optical fiber cores for gas sensing. The UV/vis absorption spectrometry of the porous SnO₂ coating on the surface of the bent optical fiber core exposed to reducing gases was investigated with a fiber optical spectrometric method. The SnO₂ film causes optical absorption signal in UV region with peak absorption wavelength at around 320 nm when contacting H₂-N₂ samples at high temperatures. This SnO₂ thin film does not respond to other reducing gases, such as CO, CH₄ and other hydrocarbons, at high temperatures within the tested temperature range from 300 °C to 800 °C. The response of the sensing probe is fast (within seconds). Replenishing of the oxygen in tin oxide was demonstrated by switching the gas flow from H₂-N₂ mixture to pure nitrogen and compressed air. It takes about 20 min for the absorption signal to decrease to the baseline after the gas sample was switched to pure nitrogen, while the absorption signal decreased quickly (in 5 min) to the baseline after switching to compressed air. The adhesion of tin oxide thin films is found to be improved by pre-coating a thin layer of silica gel on the optical fiber. Adhesion increases due to increase interaction of optical fiber surface and the coated silica gel and tin oxide film. Optical absorption spectra of SnO₂ coating doped with 5 wt% MoO₃ were observed to change and red-shifted from 320 nm to 600 nm. SnO₂ thin film promoted with 1 wt% Pt was found to be sensitive to CH₄ containing gas.     

Analysis of the Dynamic Decomposition of Unsaturated Fatty Acids and Tocopherols in Commercial Oils During Deep Frying

The decomposition of unsaturated fatty acids and tocopherols in 10 commercial edible oils during deep frying was investigated. The dominant tocopherol in oils rich in polyunsaturated fatty acids (PUFAs) was γ-tocopherol, except for natural perilla oil (δ-tocopherol dominant), and the main tocopherol in oleic acid-rich oils was α-tocopherol. The PUFA-rich oils had higher tocopherol contents than the oleic acid-rich oils. Both the reduction rate of total unsaturated fatty acid (TUFA) and total tocopherol (TToc) were linear with frying time (t). The decomposition rate of TToc is faster than that of TUFA since the slope values obtained from fitting equations (Y?=?k t) k_TToc (1.520–14.483) were obviously larger than for k_TUFA (0.155–0.270). By establishing a dynamic decomposition index, unsaturated fatty acids and tocopherol in oils showed dynamic decomposition over multiple frying cycles. The obtained results showed that decomposition characteristics of oils are related to their fatty acid compositions.     

掺硼p型非晶硅薄膜的制备及光学性能的表征

以高氢稀释的硅烷(SiH₄ )为反应气体,硼烷(B₂H₆)为掺杂气体,利用RF-PECVD方法,在玻璃衬底上制备出掺硼的氢化非晶硅(a-Si:H)薄膜,研究了硼掺杂量对氢化非晶硅(a-Si:H)薄膜的光学性能的影响.利用NKD-7000 W光学薄膜分析系统测试薄膜的透射谱和反射谱,并利用该系统的软件拟合得出薄膜的折射率、消光系数、吸收系数等光学性能参数,利用Tauc法计算掺硼的非晶硅薄膜的光学带隙.实验结果表明,随着硼掺杂量的增加,掺杂非晶硅薄膜样品在同一波长处的折射率先增大后减小,而且每一样品均随着入射光波长的增加而减小,在波长500 nm处的折射率均达到4.3以上;薄膜的消光系数和吸收系数随着硼掺杂量的增大而增大,在500 nm处的吸收系数可高达1.5×10⁵cm^-1.在实验的硼掺杂范围内,光学带隙从1.81 eV变化到1.71 eV.     

Quantitative characterization of the optical properties of absorbing polymer films: Comparative investigation of the internal reflection intensity analysis method

Nondestructive, three‐dimensional refractive‐index measurements are used for the determination of both the crystallinity and orientation in thin polymer films. The prism wave‐guide coupler is particularly suited for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to determining only the refractive index of transparent or weakly absorbing thin‐film samples. On the basis of thin‐film optics, this study develops a new internal reflection intensity analysis (IRIA) method, which uses the intensity information rather than the conventional mode angle values to acquire both the refractive index and the extinction coefficient over a range of transparent to highly absorbing polymer films. Therefore, the IRIA method overcomes the limitations of this prism wave‐guide coupler technique, which can only measure the refractive index of a weakly absorbing sample. With a Metricon PC‐2010 as the skeletal framework, a prototype instrument has been developed to apply and test the IRIA method. A study comparing both the refractive index and extinction coefficient obtained with ellipsometry, ultraviolet–visible/near‐infrared reflectometry, and IRIA for solvent blue 59 dyed polystyrene films confirms that the IRIA method is effective for obtaining the three‐dimensional refractive indices and extinction coefficients of polymer films. In addition, the refractive index and extinction coefficient spectrum (400–800 nm) of solvent blue 59 have been determined with the effective media theory. Furthermore, the three‐dimensional complex refractive indices of highly absorbing black electrical tape, inaccessible to other optical measurement because of its surface character, has been determined by the IRIA method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 842–855, 2003     

Effect on rheology and frying stability of edible oil before and after addition of fenugreek seeds

Rheological parameters of vegetable oils showed great changes during frying. The correlation between rheological behavior and viscosity measurements during frying can give a good overall estimate of frying oil quality. In the present study, rheological properties of rice bran oil (RBO) and soybean oil (SBO) during deep-frying of 13 ​min were investigated for consecutive 1st, 2nd, 3rd, and 4th frying at an interval of one week. To enhance the frying stability of RBO and SBO, fenugreek seeds (Trigonellafoenum graecum) was added during frying. The shear stress versus shear rate data was fitted to Newtonian and Herschel-Bulkley rheological models. The flow behavior of RBO and SBO with and without fenugreek seeds in before and after frying were measured at 30 ​± ​2 ​°C. The increase in viscosity, acid values and flow behavior index (n) with frying times for both RBO and SBO can be controlled with the addition of fenugreek seed up to 3rd frying with n ​< ​1 values, where without fenugreek seeds for RBO and SBO it showed a shear thickening properties (n ​> ​1) after 2nd and 3rd frying respectively.     

New low-index liquid refractive index standard: SRM 1922

A new standard for the calibration of refractometers has been developed. Standard Reference Material (SRM) 1922 is a mineral oil with a refractive index nD = 1.46945 at 20 degrees C, which is within the range of the Brix scale (% sucrose). The change in refractive index with temperature (dn/dT) has been characterized for the range 15 degrees C to 35 degrees C to allow for calibrations within that range of temperatures. The refractive indices were measured at 5 wavelengths in the visible spectrum by using the method of minimum deviation with a +/- 2-3 x 10(-5) uncertainty at 20 degrees C. The values of nD and dnD/dT were determined by fits of a two-term Cauchy function to the values at the measured wavelengths with a +/- 6 x 10(-5) uncertainty in nD at 20 degrees C.     

Chromium speciation using sequential injection analysis and multivariate curve resolution

This work proposes a new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy (NIRES). The method is based on heating an oil sample at a fixed temperature, followed by the acquisition of the emission spectra with time using a home-made spectrometer with an acousto-optical tunable filter (AOTF) as monochromator. The induction time, related to the oxidative stability, is determined by means of the emission band at 2900 nm and its increase and broadening during the heating time. After the induction period, this band also provides information related to the oxidation rate of the sample. Twelve samples of edible oils, of different types and from different manufacturers, were analyzed for oxidative stability with mean repetitivity of 3.7%. The effects of nitrogen insertion, heating temperature and the presence of antioxidant compounds on the oxidative stability were evaluated.     

Authentication of vegetable oils on the basis of their physico-chemical properties with the aid of chemometrics

In food production, reliable analytical methods for confirmation of purity or degree of spoilage are required by growers, food quality assessors, processors, and consumers. Seven parameters of physico-chemical properties, such as acid number, colority, density, refractive index, moisture and volatility, saponification value and peroxide value, were measured for quality and adulterated soybean, as well as quality and rancid rapeseed oils. Chemometrics methods were then applied for qualitative and quantitative discrimination and prediction of the oils by methods such exploratory principal component analysis (PCA), partial least squares (PLS), radial basis function-artificial neural networks (RBF-ANN), and multi-criteria decision making methods (MCDM), PROMETHEE and GAIA.In general, the soybean and rapeseed oils were discriminated by PCA, and the two spoilt oils behaved differently with the rancid rapeseed samples exhibiting more object scatter on the PC-scores plot, than the adulterated soybean oil. For the PLS and RBF-ANN prediction methods, suitable training models were devised, which were able to predict satisfactorily the category of the four different oil samples in the verification set. Rank ordering with the use of MCDM models indicated that the oil types can be discriminated on the PROMETHEE II scale. For the first time, it was demonstrated how ranking of oil objects with the use of PROMETHEE and GAIA could be utilized as a versatile indicator of quality performance of products on the basis of a standard selected by the stakeholder. In principle, this approach provides a very flexible method for assessment of product quality directly from the measured data.