Light Absorption Measurements Research Articles

Characterization and bleaching properties of acid‐leached montmorillonite

AbstractAfter being subjected to preliminary purification, montmorillonite clay was leached with varying concentrations of sulfuric acid (0.5–2 mol L−1) at 90 °C for varying times (0.5–4 h). Acid leaching causes partial amorphization of the montmorillonite and increases its specific surface area by a factor of 3 (from 49.1 to 157 m2 g−1). The bleaching efficiency for Mongolian mare's milk oil, as judged by light absorbance measurements at 400 nm, was increased from 9.5% for the unleached clay to 93.8% for clay leached with 2 mol L−1 H2SO4 for 4 h. Copyright © 2006 Society of Chemical Industry

Thermodynamics of Interactions of Water-Soluble Porphyrins with RNA Duplexes

We characterized the interactions of meso-tetrakis(4N-(2-hydroxyethyl)pyridinium-4-yl) porphyrin (TEtOHPyP4), meso-tetrakis(4N-allylpyridinium-4-yl) porphyrin (TAlPyP4), and meso-tetrakis(4N-metallylpyridinium-4-yl) porphyrin (TMetAlPyP4) with the poly(rA)poly(rU) and poly(rI)poly(rC) RNA duplexes between 18 and 45 degrees C by employing circular dichroism, light absorption, and fluorescence intensity spectroscopic measurements. Our results suggest that TEtOHPyP4 and TAlPyP4 intercalate into the poly(rA)poly(rU) and poly(rI)poly(rC) host duplexes, while TMetAlPyP4 associates with these RNA duplexes by forming outside-bound, self-stacked aggregates. We used our temperature-dependent absorption titration data to determine the binding constants and stoichiometry for each porphyrin-RNA binding event studied in this work. From the temperature dependences of the binding constants, we calculated the binding free energies, DeltaG(b), enthalpies, DeltaH(b), and entropies, DeltaS(b). For each RNA duplex, the binding enthalpy, DeltaH(b), is the most favorable for TEtOHPyP4 (an intercalator) followed by TAlPyP4 (an intercalator) and TMetAlPyP4 (an outside binder). On the other hand, for each duplex, external self-stacking of TMetAlPyP4 produces the most favorable change in entropy, DeltaS(b), followed by the intercalators TAlPyP4 and TEtOHPyP4. Thus, our results suggest that the thermodynamic profile of porphyrin-RNA binding may correlate with the binding mode. This correlation reflects the differential nature of molecular forces that stabilize/destabilize the two modes of binding-intercalation versus external self-stacking along the host duplex.

Particle migration in a concentrated suspension flowing between rotating parallel plates: Investigation of diffusion flux coefficients

This paper reports an experimental and numerical study conducted to investigate the behavior of macroscopic monomodal concentrated suspensions (40%) undergoing a creeping torsional flow between two rotating plates. An experimental technique based on the detection of tracers by measurement of light absorption is developed and used to quantify the time evolution of the particles concentration profiles. Contrarily to results reported in the literature, an outward migration of the particles is observed. This shear-induced migration is confirmed by viscometric measurements where an increase in the apparent viscosity of the suspension has been observed for long periods of shear. Moreover, this increase is found to depend solely on the value of the applied strain, which is consistent with a shear-induced migration phenomenon. Experimental results are reproduced using a semi-quantitative model involving the balance of three diffusion fluxes induced, respectively, by the gradient of viscosity (Jη), the gradient of...

Efficient absorption and intense soft X-ray emission from gas cluster plasmas irradiated by 25-ps laser pulses

A highly efficient absorption is observed in multipicosecond laser pulse irradiation of argon and nitrogen gas cluster targets at moderate intensities of /spl sim/10/sup 15/ W/cm/sup 2/ using a 1.5 J/25 ps Nd : phosphate glass laser (/spl lambda/=1.054 /spl mu/m). Measurements of laser light absorption, side scattering, and extreme-ultraviolet (XUV) emission spectrum are performed for argon and nitrogen gases puffed through sonic or hypersonic nozzles in the pressure range from 10 to 60 bar. High values of 80%-85% of laser light absorption have been measured in both nitrogen and argon gas cluster plasmas. The X-ray line emission from argon plasma was /spl sim/ 30-40 times stronger than that from the nitrogen plasma, which is related to the formation of larger sized clusters in argon. The very high laser light absorption observed in these multipicosecond laser pulse irradiation experiments may be understood to be occurring due to intense heating of the near solid density clusters in the initial part of the laser pulse creating a plasma of a high degree of ionization, which continues to absorb the rest of the laser pulse energy through collisional processes during its expansion to subcritical densities.

Synthesis and performance of transparent casting polyurethane resin

A series of transparent casting polyurethane resins (TCPU) were synthesized from cycloaliphatic diisocyanate (IPDI or H12MDI), polyol, chain extender, crosslinking agents, catalyst and special aids (T), which were characterized by FTIR. The thermal stabilities of the obtained TCPU were examined by DSC and TGA, the glass transition temperature (Tg) was in the range of 95–110°C, the initial decomposition temperature (5% weight loss) was 250–265°C, and 10% weight loss at the temperature was in the range of 260–286°C in nitrogen atmosphere. The morphologies of the fractured surfaces of TCPU were revealed by a scanning electron microscope (SEM). The crystalline-amorphous characters of TCPU were studied by WAXD, the result shows that TCPU possesses amorphous glassy characters. The optical properties of TCPU were studied by a UV-7500 visible light absorbance measurement. All the samples exhibited excellent optical properties and possessed light transmittance in the range of 91%–93%.

Spatiotemporal Patterns of Dorsal Root–Evoked Network Activity in the Neonatal Rat Spinal Cord: Optical and Intracellular Recordings

Spatiotemporal patterns of dorsal root-evoked potentials were studied in transverse slices of the rat spinal cord by monitoring optical signals from a voltage-sensitive dye with multiple-photodiode optic camera. Typically, dorsal root stimulation generated two basic waveforms of voltage images: dual-component images consisting of fast, spike-like signal followed by a slow signal in the dorsal horn, and small, slow signals in the ventral horn. To qualitatively relate the optical signals to membrane potentials, whole cell recordings were combined with measurements of light absorption in the area around the soma. The slow optical signals correlated closely with subthreshold postsynaptic potentials in all regions of the cord. The spike-like component was not associated with postsynaptic action potentials, suggesting that the fast signal was generated by presynaptic action potentials. Firing in a single neuron could not be detected optically, implying that local voltage images originated from synchronously activated neuronal ensembles. Blocking glutamatergic synaptic transmission inhibited excitatory postsynaptic potentials (EPSPs) and significantly reduced the slow optical signals, indicating that they were mediated by glutamatergic synapses. Suppressing glycine-mediated inhibition increased the amplitude of both optical signals and EPSPs, while blocking GABA(A) receptor-mediated synapses, increased the amplitude and time course of EPSPs and prolonged the duration of voltage images in larger areas of the slice. The close correlation between evoked EPSPs and their respective local voltage images shows the advantage of the high temporal resolution optical system in measuring both the spatiotemporal dynamics of segmental network excitation and integrated potentials of neuronal ensembles at identified sites.

Seed Maturity, Germination, and Endophyte Relationships in Tall Fescue

Endophytic fungi were once considered detrimental components of cool season pasture grass seed because of their association with toxic compounds. Development of new cultivars of forage grasses infected with nontoxic endophytes suggests endophytes are an essential component of pasture ecosystems. The process of transmitting endophytes via the seed embryo is poorly understood, and little is known about harvest conditions and endophyte transmission or viability. The objective of this project was to develop methods of predicting seed maturity and determine the effect of harvest maturity on viable endophyte transmission to seedling plants. Sixty panicles of tall fescue (Festuca arundinaceae Shreb.) from fields in Georgia and Oregon were sampled from 15 d after flowering until seed freely shattered (Georgia) or seed fields were swathed (Oregon). All fields had previously tested >90% infection with endophyte before the study. Panicles were staged for maturity by scoring for color of the panicle and seed, as well as seed shatter. Chlorophyll was extracted from a fresh subsample of seed, and dry matter was determined from a second subsample. Chlorophyll was estimated by measuring light absorbance at 540 nm. Seed with varying maturity scores were germinated following different prechill conditions. Regression of chlorophyll and dry matter content (dependent variables) with maturity score (independent variable) suggest chlorophyll content (r2 = 0.90) provided a better estimate of maturity than did dry matter (r2 = 0.55). The more mature seed had greater mass, germinated faster, had a higher total germination, and produced more vigorous seedlings. Endophyte transmission into the developing seed was similar within different maturity seed, but infection of seedlings increased from 81 to 91% with seed maturity. We conclude that predicting tall fescue seed maturity by chlorophyll analysis provides a better estimate for seed quality when maintaining endophyte viability is of concern in the harvested seed.

Measurement of Wavelength-Resolved Light Absorption by Aerosols Utilizing a UV-VIS Extinction Cell

The principle, technical details, and performance of the long path extinction spectrometer (LOPES), a new folded-path extinction cell with a spectral range from the mid-UV (200 nm) to the near infrared (1015 nm), is presented. Using nonabsorbing glass beads the measured extinction spectrum of LOPES was validated by Mie calculations and was compared with scattering coefficients in the visible measured by a three-color integrating nephelometer (TSI, mod. 3563). For absorbing aerosols (here soot and biomass burning aerosol with single-scattering albedos of about 0.2 and 0.74 at 550 nm), LOPES was combined with a TSI 3563 nephelometer to determine the wavelength-dependent absorption coefficients from the difference of the extinction and scattering coefficients. These absorption coefficients were found to agree with the measurements by two state-of-the-art absorption techniques, the multiangle absorption photometry (MAAP) and photoacoustic spectrometry (PAS), which measure the absorption coefficient at the single wavelength of 532 nm and 670 nm, respectively. Finally, based on a comprehensive analysis of the TSI 3563 nephelometer errors and their propagation into the determination of the absorption coefficients from the LOPES and nephelometer data, we discuss implications for improving in situ measurements of the optical properties of atmospheric aerosols.

An animal model of venous hypertension: The role of inflammation in venous valve failure

Clinical observation suggests that chronic venous insufficiency is related to failure of venous valves. Duplex ultrasound studies of lower extremity superficial veins regularly show valve failure and venous reflux. Gross morphologic observation of venous valves in surgical specimens shows tearing, splitting, scarring, and disappearance of valves. Venous valve damage is acquired, linked with venous hypertension, and affected by inflammation. The objective of this study was to investigate the inflammatory process in valve remodeling associated with acute and chronic venous hypertension. A femoral arteriovenous fistula was created in study animals (Wistar rats, n = 60), and animals without an arteriovenous fistula were studied as controls (n = 5). At 1, 7, 21, and 42 days animals with the femoral arteriovenous fistula were anesthetized, and systemic pressure, the pressure in the femoral vein distal to fistula, and the pressure of the femoral vein in the contralateral hind limb were measured. Timed collection of blood backflow after division of the femoral vein distal to the fistula and in the alive, anesthetized animal was collected, measured, and calculated per unit time to be used as an indicator of valve insufficiency. The femoral vein distal to the fistula was harvested; valvular structures were examined and measured. Specimens were processed, and longitudinal sections were made and challenged with immunostaining antibodies against matrix metalloprotease (MMP)-2 and MMP-9. Sections were examined, and expression of molecular markers was determined by light absorption measurements after image digitization. One week after the procedure, all animals exhibited some degree of hind limb edema ipsilateral to the arteriovenous fistula. Pressure in the femoral vein distal to the fistula was markedly increased on average to 96 +/- 9 mm Hg. Reflux was increased in a time-dependent manner, with the 21-day and 42-day groups showing the highest values. Valves just distal to the fistula showed an increased diameter of the valvular annulus and a shortening of the annular height. Venous wall findings included fibrosis and fusion of the media and adventitia and scarring and disappearance of valves principally in the 21- and 42-day specimens. Immunolabeling for MMP-2 showed an increased level in the 21- and 42-day groups. MMP-9 showed an increased level at 1 day, followed by a more marked level in the 21- and 42-day groups. In this animal model of venous hypertension the findings of limb edema, increasing valvular reflux, and morphologic changes of increased annulus diameter and valve height are seen. Histologic changes included massive fibrosis of media and fusion with adventitia. Inflammatory markers MMP-2 and MMP-9 are strongly represented, and valve disappearance occurs after these markers are present. The gross morphologic changes seen are quite similar to those observed in human surgical specimens removed in treatment of venous insufficiency. When observed angioscopically at the time of vein stripping, saphenous vein valves show severe deformities including shortening, scarring, and tearing. The current model of induced venous hypertension demonstrates early venous valve changes that replicate those observed in humans. This observation provides a link from venous hypertension to an induced inflammatory reaction that stimulates the valve damage. Thus the model could be useful for defining the fundamental mechanisms that cause venous valve failure and varicose veins and in pharmacologic testing to prevent or treat venous insufficiency.

Control of oxidative stress in microcirculation of spontaneously hypertensive rats

One mechanism for organ damage in individuals with arterial hypertension may be due to oxygen free radical production. This study was designed to localize free radicals in a microvascular network of mature spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats. Because glucocorticoids play a role in pressure elevation of SHRs, we investigated their role in microvascular free radical formation. Oxygen radical production in mesentery was detected by tetranitroblue tetrazolium reduction to formazan aided by digital light-absorption measurements. Formazan deposits were observed in the endothelial cells and lumens of all microvessels and in lymphatic endothelia but were fewer in tissue parenchyma. The formazan distribution in younger (14-16 wk old) WKY rats and SHRs was heterogeneous with low values in capillaries and small arterioles/venules (<30 microm) but enhanced deposits in larger venules. Adrenalectomy served to reduce the formazan density in SHRs to the level of WKY rats, whereas dexamethasone supplementation of the adrenalectomized rats caused elevation in the larger venules of SHRs. In older (40 wk old) SHRs, formazan levels were elevated in all hierarchies of microvessels. After pressure reduction was employed with chronic hydralazine treatment, the formazan deposits were reduced in all locations of the microcirculation in both WKY rats and SHRs. Elevated formazan deposits were also found in lymphatic endothelium. These results suggest that oxygen free radical production is elevated in both high- and low-pressure regions of SHR microcirculation via a process that is controlled by glucocorticoids. Older SHRs have higher formazan levels than younger SHRs in all microvessels. Chronic hydralazine treatment, which serves to reduce arterial blood pressure, attenuates tetranitroblue tetrazolium reduction in WKY rats and SHRs even in venules of the microcirculation, which has no micropressure elevation. Free radical production may be a more global condition in SHRs and may not be limited to arteries and arterioles.

Evaluation of Multiangle Absorption Photometry for Measuring Aerosol Light Absorption

A new multiangle absorption photometer for the measurement of aerosol light absorption was recently introduced that builds on the simultaneous measurement of radiation transmitted through and scattered back from a particle-loaded fiber filter at multiple detection angles. The absorption coefficient of the filter-deposited aerosol is calculated from the optical properties of the entire filter system, which are determined by a two-stream-approximation radiative transfer scheme. In the course of the Reno Aerosol Optics Study (RAOS), the response characteristics of multiangle absorption photometry (MAAP) for white aerosol, pure black carbon aerosol from different sources, external mixtures of black and white aerosol, and ambient aerosol was investigated. The MAAP response characteristics were compared to basic filter transmittance and filter reflectance measurements. MAAP showed close agreement with a reference absorption measurement by extinction minus scattering. The slopes of regression lines vary between 0.99 ± 0.01 and 1.07 ± 0.02 for pure black carbon particles and external mixtures with ammonium sulphate to 1.03 ± 0.05 for ambient aerosol. No effect of the filter aerosol loading or the single-scattering albedo ω0 of the sampled aerosol on the MAAP response characteristics was observed. In contrast, transmittance and reflectance methods showed a clear impact of ω0 and the filter loading on the response characteristics, which requires the application of a correction function for the reliable determination of the aerosol absorption coefficient. In the case of nonabsorbing aerosol, the MAAP approach reduced the magnitude of the apparently measured absorption coefficient by one order of magnitude compared to a basic transmittance measurement.

Use of Two Different Serial Power Pulses for a Light Absorption Measurement at Low Gas Concentration

We propose a measuring method for low-concentration gas using two different power pulses for deducing of the noise level derived from spectroscopic systems including a light-emitting diode (LED) and an amplifier. After two-different pulse currents were applied to a LED, and the pulsed light beams emitted by the LED were passed through to a long-path gas cell with a multi-reflectional mirror, (path length, 105 cm). The pulse was divided into reference and sample beams. Each reference beam (I01, I02) and sample beam (I1, I2) obtained from two different power pulses were subtracted as (I01-I02) and (I1-I2), respectively. By using these two values, the sample concentration was estimated by using the Lambert-Beer law. Acetone gas was used as a test sample gas. Acetone gases of 0 ~ 90, 60 ~ 900 ppm concentration were measured with the present method. By calculating these signals differece, the electric noise in this apparatus was canceled, and we could measure low-concentration gas. The proposed method gave good calibration curves.

Modification, Calibration and a Field Test of an Instrument for Measuring Light Absorption by Particles

A filter-based single-wavelength photometer (Particle Soot Absorption Photometer, PSAP) for measuring light absorption by aerosols was modified to measure at three wavelengths, 467 nm, 530 nm, and 660 nm. The modified and an unmodified photometer were calibrated during the Reno Aerosol Optics Study (RAOS) 2002 against two absorption standards: a photoacoustic instrument and the difference between the extinction and scattering coefficient. This filter-based absorption method has to be corrected for scattering aerosol and transmission changes. A simple function for this was derived from the calibration experiment as a function of transmission and single-scattering albedo. For an unmodified PSAP at typical atmospheric absorption coefficients the algorithm yields about 5–7% lower absorption coefficients than does the usually used method. The three-wavelength PSAP was used for atmospheric measurements both during RAOS and during the New England Air Quality Study (NEAQS).

The Reno Aerosol Optics Study: An Evaluation of Aerosol Absorption Measurement Methods

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative humidity conditions and delivered to each measurement system. The aerosol mixing and delivery system was constantly monitored using particle counters and nephelometers to ensure that the same aerosol number concentration and amount reached the different instruments. The aerosol light-scattering measurements of four different nephelometers were compared, while the measurements of seven light-absorption instruments (5 filter based, 2 photoacoustic) were evaluated. Four methods for determining the aerosol light-extinction coefficient (3 cavity ring-down instruments and 1 folded-path optical extinction cell) were also included in the comparisons. An emphasis was placed on determining the representativeness of the filter-based light absorption methods, since these are used widely and because major corrections to the raw attenuation measurements are known to be required. The extinction measurement from the optical extinction cell was compared with the scattering measurement from a high-sensitivity integrating nephelometer on fine, nonabsorbing ammonium sulfate aerosols, and the two were found to agree closely (within 1% for blue and green wavelengths and 2% for red). The wavelength dependence of light absorption for small kerosene and diesel soot particles was found to be very near λ− 1, the theoretical small-particle limit. Larger, irregularly shaped graphite particles showed widely variable wavelength dependencies over several graphite runs. The light-absorption efficiency at a wavelength of 530 nm for pure kerosene soot with a number size distribution peak near 0.3 μ m diameter was found to be 7.5 ± 1.2 m2 g− 1. The two most fundamental independent absorption methods used in this study were photoacoustic absorption and the difference between suspended-state light extinction and scattering, and these showed excellent agreement (typically within a few percent) on mixed black/white aerosols, with the photoacoustic measurement generally slightly lower. Excellent agreement was also observed between some filter-based light-absorption measurements and the RAOS reference absorption method. For atmospherically relevant levels of the aerosol light-absorption coefficient (< 25 Mm− 1), the particle soot absorption photometer (PSAP) absorption measurement at mid-visible wavelengths agreed with the reference absorption measurement to within ∼ 11% for experiment tests on externally mixed kerosene soot and ammonium sulfate. At higher absorption levels (characterized by lower single-scattering albedo aerosol tests), this agreement worsened considerably, most likely due to an inadequate filter loading correction used for the PSAP. The PSAP manufacturer's filter loading correction appears to do an adequate job of correcting the PSAP absorption measurement at aerosol single-scattering albedos above 0.80–0.85, which represents most atmospheric aerosols, but it does a progressively worse job at lower single-scattering albedos. A new filter-based light-absorption photometer was also evaluated in RAOS, the multiangle absorption photometer (MAAP), which uses a two-stream radiative transfer model to determine the filter and aerosol scattering effects for a better calculation of the absorption coefficient. The MAAP absorption measurements agreed with the reference absorption measurements closely (linear regression slope of ∼ 0.99) for all experimental tests on externally mixed kerosene soot and ammonium sulfate.

Evidence that the spectral dependence of light absorption by aerosols is affected by organic carbon

The wavelength dependence of light absorption by aerosols collected on filters is investigated throughout the near‐ultraviolet to near‐infrared spectral region. Measurements were made using an optical transmission method. Aerosols produced by biomass combustion, including wood and savanna burning, and by motor vehicles, including diesel trucks, are included in the analysis. These aerosol types were distinguished by different wavelength (λ) dependences in light absorption. Light absorption by the motor vehicle aerosols exhibited relatively weak wavelength dependence; absorption varied approximately as λ−1, indicating that black carbon (BC) was the dominant absorbing aerosol component. By contrast, the biomass smoke aerosols had much stronger wavelength dependence, approximately λ−2. The stronger spectral dependence was the result of enhanced light absorption at wavelengths shorter than 600 nm and was largely reduced when much of the sample organic carbon (OC) was extracted by dissolution in acetone. This indicates that OC in addition to BC in the biomass smoke aerosols contributed significantly to measured light absorption in the ultraviolet and visible spectral regions and that OC in biomass burning aerosols may appreciably absorb solar radiation. Estimated absorption efficiencies and imaginary refractive indices are presented for the OC extracted from biomass burning samples and the BC in motor vehicle‐dominated aerosol samples. The uncertainty of these constants is discussed. Overall, results of this investigation show that low‐temperature, incomplete combustion processes, including biomass burning, can produce light‐absorbing aerosols that exhibit much stronger spectral dependence than high‐temperature combustion processes, such as diesel combustion.

Optical properties of nanocrystalline silicon within silica gel monoliths

Described herein is the incorporation of nanocrystalline silicon nc-Si from porous silicon (PSi) in a silica matrix fabricated by the sol-gel technique that yields highly photoluminescent (PL) and optically transparent monoliths with uniformly distributed nc-Si inclusions or nanoclusters. The sample monoliths were prepared with PSi-derived nanoclusters (PSi-n) with average diameters of 14–45nm. Concentrated samples of PSi-n-exhibited blueshifted orange emission bands with maximum peaks between 600 and 750nm with PL emission intensities ten times stronger than those of the original PSi, while diluted samples exhibited UV to blue (350–450nm) emission bands. The PL quantum yield of the typical PSi-n monoliths was 44% higher than the native PSi. Light absorption measurements showed a linear response to laser powers before the saturation threshold at 80mW. PL bleaching following 3h of constant laser power exposure resulted in 90% reduction of the maximum initial PL. Mechanical and thermal stability properties of nc-Si were greatly improved within the silica matrix, demonstrating that PSi-n monoliths’ are more manageable materials that enable the fabrication of samples with high densities of nc-Si for semiconducting and optoelectronic purposes. No special chemical passivation of the nc-Si surfaces was used in the preparation of the PSi-n monoliths. A strong relation between the optical properties of this nanophase material and the size distribution and concentration of nc-Si in the sample is demonstrated.

Studies Of Orientational Order Of Some Nematogens By Means Of Raman Scattering Spectroscopy

The orientational behaviour of some liquid crystals with various molecular structures was studied by means of the Raman scattering depolarization method. The Raman scattering spectra of linearly polarized light were recorded as a function of temperature in the nematic phase. On the basis of these spectra the order parameters 〈P2〉 and 〈P4〉 as well as the molecular distribution function were determined. The obtained data were compared with those estimated on the basis of polarized light absorption and emission measurements. The influence of the molecular structure on the orientational order of liquid crystals was discussed.

Pulse radiolysis system of OPU-LINAC in RIAST, Osaka Prefecture University

Micro- to milli-second pulse radiolysis apparatus using short electron pulse form 18 MeV linear accelerator (Linac) is in-service at the Research institute for advanced science and technology (RIAST), Osaka Prefecture University. This apparatus is an effective tool, not only for investigation of primary process on radiation chemistry, but also for research of electron transfer mechanism playing an important role in chemistry and bioscience. This apparatus is composed of an 18 MeV electron linear accelerator (electron pulse duration: about 4 μs) and a transient light absorption measurement system. We introduce the outline of this system, transient absorption spectrum of thiocyanate aqueous solution as an example of measured data and future plan.

Determination of formaldehyde in Brazilian alcohol fuels by flow-injection solid phase spectrophotometry

In this work, a solid phase spectrophotometric method in association with flow injection analysis for formaldehyde determination has been developed with direct measurement of light-absorption in C18 material. The 3,5-diacetyl-1,4-dihydrolutidine produced from the reaction between formaldehyde and fluoral P was quantitatively retained on C18 support and the spectrophotometric detection was performed simultaneously at 412nm. The retained complex was quickly eluted from C18 material with the eluent stream consisting of a 50% (v/v) ethanol solution. The results showed that the proposed method is simple, rapid and the analytical response is linear in the concentration range of 0.050–1.5mgL−1. The limit of detection was estimated as 30μgL−1 and the R.S.D. 2.2% using a sample volume of 625μL. The system presented an analytical throughput of 20 determinations per hour. The method was successfully applied in the determination of formaldehyde in ethanol fuel.

A silica matrix biosorbent of cadmium

Abstract In the process of preparation of a non-toxic metal biosorbent by entrapment of yeast cells in silica matrix by sol–gel technique, the homogeneity of yeast cell dispersion and prevention of precipitation during tetraethoxysilane pre-polymerization were found to be the parameters substantially influencing the sorption capacity for Cd2+. Ultrasonic treatment of cell walls increased the sorption capacity by 25% as a result of the suppression of their agglomeration. Precipitation during tetraethoxysilane (TEOS) pre-polymerization was tracked by measurement of light absorbance at λ=600 nm . The biosorbent formed from pre-polymer with a light absorbance of 0.3 had 50% less sorption capacity than that with an absorbance of 0.05. Modification of the TEOS:methanol:water ratio in the range from 1:10:8 to 1:10:40 and specific surface between 210 and 390 m 2 g −1 influenced the sorption capacity of biosorbents only within the limits of experimental error. The sorption capacity per unit weight of biosorbent was proportional to the yeast cell wall content. The content could be increased up to a cell walls: SiO 2 ratio ≅1.5 (w/w). Biosorbent with higher cell wall content was fragile and friable. Biosorbents were shaped by crushing and regular particles were prepared by moulding into millimetre-scale cylindrical moulds. In this shaping process, the loss of biosorbent mixture was small and the process could easily be scaled up. Using a mathematical model of a packed-bed adsorber, taking into account axial dispersion and mass transfer resistance the break-through curve for crushed and moulded biosorbent was predicted with high fidelity.