Commercial Spectrophotometer Research Articles

Construction and application of a portable microcontrolled turbidimeter for the in situ determination of sulfate

This study reports on the construction of a turbidimeter employing light emitting diodes as radiation source at a wavelength of 405 nm, a photodiode as detector, a temperature sensor and a microcontroller used for data acquisition and processing. The turbidimeter was applied to determine sulfate concentrations in natural water employing barium chloride as reagent. Potential interferences and recovery studies were performed and an interference of 3.5 % and a recovery between 97.8 and 108 % were estimated. The analytical performance of in situ turbidimeter for the determination of sulfate was evaluated and compared with two commercial spectrophotometers and a good agreement was obtained.

Construction of a low-cost laser-based multiplexed spectrometer: a potential probe for environmental pollution monitoring

A low-cost, sensitive, laser-based (Helium Neon; He-Ne) optical Fourier-transformed (multiplexed) spectrometer has been constructed for the quantification of suspended particulates in the air. The optomechanical features of the spectrometer are presented together with a theoretical framework of its operation. The apparatus is calibrated by using a standard commercial spectrophotometer and has been successfully used to detect smoke of various densities. The simplicity in the design of the apparatus and sensitivity in its measurement would expectedly attract high school and college students and definitely help to spread the awareness of environmental pollution among younger generation.

Measurement uncertainty in colourcharacterization of printed textile materials

The subject of uncertainty of spectrophotometric measurement of printed textile materials is one of the major unsolved technical problems in textile colourimetry today. Textile manufacturers are often trying to maintain co-lour difference tolerances which are within the range or even less than the uncertainty of the measurement system controlling them. In this paper, two commercial spectrophotometers with different measuring geometries (GretagMacbeth Eye-One Pro with 450/0° geometry and ChinSpec HP200 with d/8° geometry) were comparatively investigated in terms of measurement uncertainty in colour characterization of textile products. Results of the study indicate that, the despite of different measuring geometry, instruments had the similar measurement repeatability behaviour (repeatability of readings from different parts of the same sample) in the case of used digitally printed polyester materials. The important influence on measurement variability had the material preparation method (were the materials triple folded, placed on a black backing or a white backing). On the other hand, instruments showed difference concerning the inter-model agreement. Although this difference was not confirmed as significant with visual assessment, observers evaluated the measurement readings from the Eye-One Pro spectrophotometer as more accurate colour appearance characterization of textile materials.

Off-normal solar optical property measurements using an integrating sphere

Shading devices attached to windows can be used to control solar gain and hence reduce building peak load and annual energy consumption. The performance of a shading device in this regard is strongly dependent on its solar optical properties. The current study discusses a unique measurement technique that was used to obtain off-normal solar optical properties of flat shading materials. The off-normal properties were needed in order to develop solar optical property models both for shading materials and shading devices. These models provide useful input to building peak load calculation and annual energy simulation tools. Special sample holders were designed and fabricated to facilitate measurements using a commercial spectrophotometer with integrating sphere attachment. A combination of theory and companion tests were used to confirm the validity of the approach.

In-office dental bleaching efficacy assessment in function of the light exposure regime by digital colorimetric reflectance spectroscopy

In-office dental bleaching has been subject of several studies. Generally those studies quantify through visual analysis, the shade reduction of the teeth submitted to different bleaching protocols (light sources, bleaching agent concentrations and irradiation time). The objective of this work is the determination of the influence of four irradiation protocols on the obtainment of better aesthetic results using a colorimetric spectrophotometer that quantifies color changes in each situation imposed. Forty bovine incisors were selected in function of similar anatomic characteristics; a concentrated coffee solution was used to stain the teeth. A commercial spectrophotometer was used to measure the color changes during evolution of the experiment (stain and bleaching phases) and the obtained data was analyzed by the ANOVA test. The obtained data showed the evolution of teeth color during the staining period, as well as, the color reduction that each bleaching protocol achieved. Based on our findings it is possible to conclude that bleaching protocols with larger irradiation periods did not showed significant differences when compared with shorter irradiation protocols, in that way the use of protocols with 30 min or more of consecutive irradiation are not clinically justified and also can cause several side effects. Key words: Dental bleaching, light emitting diodes (LEDs), spectrophotometer, objective measurements.

A method to correct for spectral artifacts in optical-CT dosimetry

The recent emergence of radiochromic dosimeters with low inherent light-scattering presents the possibility of fast 3D dosimetry using broad-beam optical computed tomography (optical-CT). Current broad beam scanners typically employ either a single or a planar array of light-emitting diodes (LED) for the light source. The spectrum of light from LED sources is polychromatic and this, in combination with the non-uniform spectral absorption of the dosimeter, can introduce spectral artifacts arising from preferential absorption of photons at the peak absorption wavelengths in the dosimeter. Spectral artifacts can lead to large errors in the reconstructed attenuation coefficients, and hence dose measurement. This work presents an analytic method for correcting for spectral artifacts which can be applied if the spectral characteristics of the light source, absorbing dosimeter, and imaging detector are known or can be measured. The method is implemented here for a PRESAGE® dosimeter scanned with the DLOS telecentric scanner (Duke Large field-of-view Optical-CT Scanner). Emission and absorption profiles were measured with a commercial spectrometer and spectrophotometer, respectively. Simulations are presented that show spectral changes can introduce errors of 8% for moderately attenuating samples where spectral artifacts are less pronounced. The correction is evaluated by application to a 16 cm diameter PRESAGE® cylindrical dosimeter irradiated along the axis with two partially overlapping 6 × 6 cm fields of different doses. The resulting stepped dose distribution facilitates evaluation of the correction as each step had different spectral contributions. The spectral artifact correction was found to accurately correct the reconstructed coefficients to within ∼1.5%, improved from ∼7.5%, for normalized dose distributions. In conclusion, for situations where spectral artifacts cannot be removed by physical filters, the method shown here is an effective correction. Physical filters may be less viable if they introduce strong sensitivity to Schlieren bands in the dosimeters.

Alternative UV Sensors Based on Color-Changeable Pigments

Photochromism is a chemical process in which a compound undergoes a reversible change between two states having separate absorption spectra, i.e. different color [1]. In our previous work we have published some solutions of problems of measuring photochromic textile sample by standard commercial spectrophotometric systems [2]. Main problem with measurement of kinetic behavior of photochromic pigments by standard spectrophotometer is relatively long time period between individual measurements (5 s) and impossibility of measuring whole color change during exposure without interruption of illumination of sample during measurement. It means, standard commercial spectrophotometers enable off-line measurement of kinetic behavior during exposure period and quasi on-line measurement during reversion period. Based on this problem, it is only possible to obtain precise data during reversion—decay process and growth process (exposure) is affected by high variability of data. Following this knowledge, we developed original experimenttal system with short time scanning of color change of photochromic samples during growth and decay period of color change. In this study it is presented new view on the relationship between intensity of UV-A radiation and color change half-life t1/2. Via this relation, it is demonstrated the possibility of the flexible textile-based sensors construction in the area of the radiation intensity identification.

以较高空间分辨率测量可变形薄膜的透射率

An apparatus for localized transmittance measurements of optical coatings with spatially non-uniform performance is presented. The setup allows spectral acquisition in the range of 400–1000 nm with spatial resolution higher than 20 µm. Examples of its implementation for the characterization of linearly variable optical components of portable spectrometers are given. OCIS codes: 120,0120. 310,0310. doi: 10.3788/COL201008S1.0103. Optical coatings for specific applications where an intentionally designed non-uniform surface induces spatially variable optical performance may have performance variations at a micrometer scale. To characterize the optical devices of this kind, a dedicated measurement technique is required to allow surface mapping of optical behavior. As long as commercial spectrophotometers have insufficient spatial resolution for acceptable results, dedicated apparatuses are needed for localized measurements. Recently, two instruments developed for localized photometry were compared [1] . In this letter, we present a novel setup with an extremely simplified construction for the purpose of transmittance measurement with enhanced spatial resolution and high spectral accuracy. Any type of structured material for which the transmittance is not constant over the surface can be measured by this apparatus, from biological samples to components for space applications. To illustrate the functionality of the proposed instrument, this study analyzes the optical performance of linearly variable filters manufactured in the frame of research programs for spatial applications. Such filters [2,3] are employed for the construction of miniaturized spectrometers for image spectroscopy of Earth and other planets from space. In particular, we report on the characterization of two different types of filters: an inducedtransmittance narrowband filter with linear variation of a transmittance peak over the surface and an all-dielectric low bandpass filter with nonlinear spatial profile. The filter transmission peak in the first case, as well as the edge of the pass-band in the second case, are moved from a minimum to a maximum wavelength (430–930 nm and 300–900 nm, respectively) over a spatial length of a few millimeters, with a gradient of about 200 nm/mm. The measurement setup (Fig. 1) consists of illuminating and collecting optics and a spectral analyzer connected to the computer. The radiation from a hybrid deuterium-tungsten source is delivered by an optical fiber with a 5 µm in-diameter core to the sample surface. The output fiber end is positioned at a distance of less that 1 mm from the sample to avoid scratching the fiber against the sample surface during the sample movement. At this distance, the numerical aperture of the illuminating fiber guarantees a light spot size less than 20 µm. The two-dimensional translation micrometric system insures accurate sample positioning for bi-dimensional scanning with a minimum motor step of 0.25 µm. A lens block focuses the transmitted light onto the entrance of a fiber with a 600 µm core, which is connected to the Ocean Optics HR2000 spectrometer. This spectrometer allows signal acquisition in the range of 300–1100 nm with a resolution of 2 nm. These range extremes are actually slightly shortened to 400–1000 nm due to a relatively high noise-to-signal ratio caused both by a low signal level (small core of illuminating fiber and non-optimized fiber-to-lamp connection) and a lower sensitivity of the spectrometer at the extremes of its working range. Both spectral range and spatial resolution may be improved if a spectrometer with an enhanced spectral resolution and sensitivity is employed or if the gap between the sample and the illuminating fiber is decreased. Both analyzed filters are multilayer optical coatings deposited on glass substrates. The first coating is comprises 21 alternating layers of silicon oxide and tantalum

Toward the reflectance measurement of micro components

Today, the controls by reflection of optical coatings are most of the time made with flat samples thanks to commercial spectrophotometers. However, components become smaller and more complex, curvature radius of lenses or mirrors are larger, so that measures are not so accurate and sometimes are not possible. Flat samples don’t represent anymore the real reflection ability of the component. So to perform this kind of measurements, special devices are needed. A new means developed by the French Atomic Energy Commission (CEA) is proposed to fill in this gap. This device has a accuracy of 0.06% on flat sample over the 400 nm to 950 nm wavelength range with a spot size of 100 µm. It can measure the reflectance of samples even if their shapes are spherical. We investigate stainless steel balls and optical micro components (mirrors and lens) thanks to the tiny size of the analyzing spot of our reflectometer. Herein we introduce our first results on small optical components and show the limiting factors of our device.

Spectrophotometer Calibration by a Double Integrating Sphere Reference Light Source and Display Panel Measurement Using Dark Sphere

We succeeded to develop a reference light source in the range of very low luminance using a double integrating sphere system, and calibrated a commercial spectrophotometer below 1 × 10-5cd/m2 levels, which is 1/100 lower than the specified limit for measurement. And we improved measurements in the ultra low luminance range of displays using the calibrated commercial spectrophotometer and a dark sphere to suppress the influence of the surround.

Highly sensitive photonic crystal fiber based absorption spectroscopy

We have reported a highly sensitive evanescent field based absorption spectroscopy using an optimized structure of PCF with defected-core. The absorption sensitivity up to 10.8 mol−1 has been achieved which is six times improvement compared with the previous reported 1.6 mol−1 sensitivity in a defected-core PCF. Moreover, this structure can achieve a twice higher sensitivity compared with commercial spectrophotometer. Excellent linear relationship has been obtained between absorption and aqueous sample concentrations which suggested that the PCF is a satisfactory candidature as an absorption spectroscopy for off-chip or on-chip analyte quantitation.

A Novel Opto-Mechanical System Coupled to a Spectrophotometer for Measuring Coatings on Small Size Substrates and Optical Fiber Filters

A novel opto-mechanical system coupled to a commercial spectrophotometer using optical fibers was developed to measure optical transmittance of small samples, like filters deposited on optical fiber tips or micrometric substrates, as well as to investigate transmission uniformity of filters by surface scanning. It consists of two identical modules, reference and sample, both inserted in the chamber of the spectrophotometer. Each module was formed by an optical fiber, 200 µm core diameter and numerical aperture of 0.22, supported by adjustable positioning mounts for easing alignment. The system was validated by measuring the transmittance spectrum of a coated glass substrate with and without the opto-mechanical system, showing no significant differences between both methods. To determine the system versatility were undergone two transmittance experiments: one for a filter deposited on the tip of an optical fiber and the other by scanning the surface of a coated glass substrate. It can be concluded that the opto-mechanical system allows to measurement the transmittance of small size filters and optical fibers filters, as well as to scan over large coated surfaces to investigate coating uniformity.

Semiquantitative method for the evaluation of grease barrier coatings

Many tests are known for testing the grease barrier performance of coatings in paper or paperboard. Some are manifested in standard procedures such as TAPPI, ASTM, or ISO, but as many procedures were developed and modified by companies and research groups. Mainly the test methods are based on visually detecting the amount of oil, which is in most cases dyed for better contrast, penetrating through the coating, meaning the procedures are based on a subjective visual evaluation and thus often not linked for instance to a statistical meaningful physical value. We found that by using a slightly modified ASTM D 722 test the L* a* b* color coordinates determined with a commercial handheld spectrophotometer are related to the grease barrier performance of an organic coating. By applying this new method the penetration time of an oil/dye mixture could be correlated to the lightness L* and chromaticity b* and fitted by an exponential function. Furthermore, the coating was slightly modified and an improvement or worsening of the grease barrier could be detected clearly outside of the statistical scatter of a control series. We call this method semiquantitative, since the level of grease barrier of a coating is not measured directly by a quantitative value, but color coordinates are correlated in a series to the effectiveness of the grease barrier.

A Phototransistor-Based High-Sensitivity Biosensing System Using 650-nm Light

A miniature optical biosensing system based on a PMOS phototransistor and absorption photometry is proposed. The phototransistor was manufactured in a standard 0.35-mum CMOS process, and it exhibited a responsivity higher than 1000 A/W for 650-nm light. For biochemical applications, the TMB/H2O2/HRP method was adopted as a useful basis in our system. A sample volume of only 10 mul was required to be dropped on the slide above the phototransistor. Experimental results demonstrated that a high sensitivity of 2.5 muA/pM was achieved, and the minimum HRP concentration successfully detected was 2.7 pM. This detection limit is three orders of magnitude better than that of a lately reported silicon biosensor, and is even comparable to that of a commercial spectrophotometer.

A High-Sensitivity CMOS-Compatible Biosensing System Based on Absorption Photometry

An optical biosensing system based on a standard CMOS technology and absorption photometry is proposed. Within the compact prototype, a CMOS sensor consisting a P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">well</sub> finger photodiode and a transimpedance amplifier was implemented in a standard 0.35-mu m CMOS technology. The ABTS/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /HRP method was adopted to be coupled with various analytes of interest, such as glucose and histamine, which can serve as the basis for medical diagnosis. The experimental results demonstrate that the minimum concentrations successfully detected for H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , glucose, and histamine are 1 muM, 1 muM, and 10 muM, respectively. The detection limits are at least one order of magnitude better than those of reported CMOS biosensors, and are even comparable to those of a commercial spectrophotometer.

On-Line UV Spectrophotometric Analysis for Organic Chemistry of Novel Inorganic Polymer Derived Microreactor

The use of microfluidic or lab-on-a-chip system has shown great promise for many applications. We have previously reported fabrication and application of preceramic polymer derived chemically and mechanically stable microfluidic devices in organic synthesis. Even though organic reactions are successfully performed, it is hard to analyze product to evaluate yields without any time delay except for integration of detecting module in the devices. Moreover small sample volume makes it even difficult to analyze sample by conventional analytical tools. Removal of catalyst and by product before analysis is another hurdle in evaluating performance of microrector. In this paper we describe preliminary results for simple on-line (real-time) quantitative analysis of microchemical reaction in preceramic polymer derived microreactor without reconstruction of microreactor or expensive components. A commercial UVNIS spectrophotometer is used to monitor well established Knoevenagel reaction. To evaluate the performance of presented on-line UV/IS monitoring system, UV/IS data are compared with off-line gas chromatography based analysis system.

Singlet oxygen quantum yields (Φd) in water using beetroot extract and an array of LEDs

It is proposed a simple and inexpensive strategy to determine singlet oxygen (¹O2) quantum yields (ΦΔ) of photosensitizers (PS) in water using beetroot extract containing betacyanin (Bc) and a set of light emitting diodes (LEDs) for excitation. Bc, a cationic natural dye, was obtained by flash chromatography purification from the red beet extract (Beta vulgaris) and employed as a convenient probe for ¹O2 detection. Solutions of Bc and PS were illuminated with an array of LEDs adapted in the cuvette compartment of a commercial spectrophotometer, and the decrease in Bc absorbance was followed as a function of time. Bc photobleaching decreased in de-aerated solution and increased in D2O, indicating the involvement of ¹O2. The observed photobleaching rate constant (k obs) was proportional to the LED intensity, concentration and ΦΔ of the PS. By keeping the light source constant we could estimate the overlap integral (R) between the LED emission and PS absorbance for different PS concentrations. The slope of R versus k obs is the value of the photobleaching rate constant (k), which was shown to be proportional to ΦΔ. Values of ΦΔ obtained by this method were compared with those obtained by measuring NIR (near infrared) emission for a series phenothiazine dyes.

A portable, inexpensive and microcontrolled spectrophotometer based on white LED as light source and CD media as diffraction grid

A portable, microcontrolled and low-cost spectrophotometer (MLCS) is proposed. The instrument combines the use of a compact disc (CD) media as diffraction grid and white light-emitting diode (LED) as radiation source. Moreover, it employs a phototransistor with spectral sensitivity in visible region as phototransductor, as well as a programmable interrupt controller (PIC) microcontroller as control unit. The proposed instrument was successfully applied to determination of food colorants (tartrazine, sunset yellow, brilliant blue and allura red) in five synthetics samples and Fe 2+ in six samples of restorative oral solutions. For comparison purpose, two commercial spectrophotometers (HP and Micronal) were employed. The application of the t-paired test at the 95% confidence level revealed that there are not significant differences between the concentration values estimated by the three instruments. Furthermore, a good precision in the analyte concentrations was obtained by using MLCS. The overall relative standard deviation (R.S.D.) of each analyte was smaller than 1.0%. Therefore, the proposed instrument offers an economically viable alternative for spectrophotometric chemical analysis in small routine, research and/or teaching laboratories, because its components are inexpensive and of easy acquisition.

Radiation hardness study on fused silica

Radiation hardness tests have been carried out on fused silica samples of the highest optical grade from three different manufacturers (Suprasil, Lithosil and Corning). The samples were irradiated with protons in order to emulate the expected accumulated radiation damage over the entire life span of the future PANDA experiment. Changes in optical properties were the primary focus of this study. The optical transmission over a broad wavelength band ranging from UV to visible light was investigated using a commercial spectrophotometer. In addition, changes of the polished surface were studied using an interferometer. No evidence for changes in transmission and surface quality was found within the obtained precision.

Cavity-enhanced absorption spectroscopy with a red LED source for NOx trace analysis

Incoherent broad-band cavity-enhanced absorption spectroscopy (IBB-CEAS) based on arc lamps has been around for a few years, but only two reports exist using light-emitting diodes (LEDs). We present a setup based on a 643-nm LED which is of interest for the simultaneous detection of NO3 and NO2. The latter is chosen for testing as it is stable and available in calibrated diluted samples. A detection limit in the ppbv range is obtained with 2-min averaging (5×10-9 /cm rms baseline noise level), comparable to the best performance of chemiluminescence devices used for pollution monitoring. At 1-s acquisition time, the detection limit is below 10 ppbv. Extrapolation to NO3 yields a detection limit of a few pptv for a few minutes averaging. We also test the retrieval of absolute sample absorption (and concentration) using the cavity mirror reflectivity obtained with a commercial spectrophotometer, and we conclude that a calibration based on a reference sample of known concentration is preferable for accurate concentration measurements with IBB-CEAS. Finally, we present a rigorous frequency-domain derivation of cavity transmission as a function of wavelength for a broad-band spectrally smooth source, which complements the time-domain derivation by Fiedler et al. This derivation exposes an issue with multiple transverse mode excitation inherent to this technique, which may result in slightly distorted spectral profiles.