Spectrophotometric Approach Research Articles

Designing visually optimal shade guides

Dental shade guides do not provide a broad coverage of tooth colors. There is a need for shade guides that can provide closer color matches. The purpose of this study was to propose and assess a visually optimal shade guide for tooth color matching. With the use of a spectrophotometric approach, the color distribution (L*a*b*) of 150 extracted human teeth and 3 commercially available shade guides (Vita Lumin V, Trubyte Bioform Color Order Shade Guide, and Vitapan 3D-Master Shade System) was measured. With the use of a hierarchical clustering approach, a series of shade guides was designed with a varying number of tabs. The average error (DeltaE) between colors from each shade guide and the extracted teeth was computed. The proposed visually optimal shade guide had the smallest average error of all guides tested. The new guide achieved lower error with fewer shade tabs than the 3 commercial systems evaluated. Within the limitations of this study, it was demonstrated that a hierarchical clustering technique can be used to design a visually optimal shade guide for a given population with a flexible degree of control over the mean error and number of tabs.

Sandwich-Type Complexes of Alkaline-Earth Metal Cations with a Bisstyryl Dye Containing Two Crown Ether Units

The formation of complexes between a bisstyryl dye containing two benzo-15-crown-5 ether groups, 2, and Mg2+, Ca2+, Sr2+, and Ba2+ ions was studied in acetonitrile solution by using a spectrophotometric approach. In contrast to its monostyryl analogue 1, which shows a rather low cation-binding selectivity, the bisstyryl dye 2 selectively binds the Sr2+ and Ba2+ ions because of formation of intramolecular sandwich complexes. Alkaline-earth metal cations induce substantial blue shifts of the absorption maximum of 1 and 2, particularly in the case of sandwich complex formation. The emission behavior of 1 and 2 and their Ba2+ complexes in acetonitrile solution has also been studied. In both cases, complex formation leads to a blue shift of the fluorescence maximum and a decrease in the emission quantum yield. The fluorescence decay is monoexponential for the complex of 1 and biexponential for that of 2. The longer-lived fluorescence component, which corresponds to the lower-energy band in the steady-state spectrum, is assigned to an intramolecular excimer state.

Ultraviolet and visible light spectrophotometric approach to blood typing: objective analysis by agglutination index

A new blood typing technology based on ultraviolet (UV) and visible light spectroscopy (UV/visible spectroscopy) has been developed. Blood groups and types are determined by quantifying reproducible changes in the UV and visible light spectra of blood in the presence of agglutinating antibodies. Samples of red cells in the presence and absence of agglutinating antibodies were examined by UV/visible spectroscopy. Blood groups and types were determined by comparing the optical density spectra obtained between 665 and 1000 nm. These comparisons generate numbers (agglutination index) ranging from 0 to 100, with smaller numbers corresponding to lack of agglutination and larger numbers corresponding to agglutination. The optical density of agglutinated blood is dramatically different from that of unagglutinated blood. The agglutination index derived from the relative slopes of the spectra is an objective indicator of agglutination strength. An agglutination index greater than 17 consistently and accurately established blood group- and type-specific agglutination. The method accurately predicted A, B, and O blood groups, and D type in over 275 samples. Scattering theory-based calculations of relative volumes of red cells before and after agglutination show a direct correlation with the agglutination index and provide the theoretical basis of the analysis. This quantitative technique is reproducible and has the potential for automation.

Polymer-Mediated Extraction of Porphirinato Chelates for a Spectrophotometric Approach to Sub-ppt Level Detection of Metal Ions

Abstract Negatively charged copper(II) and zinc(II) chelates with 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphine were incorporated into the precipitates formed from the aqueous solutions of thermo-responsive polymer; poly(N-isopropylacrylamide). In the presence of an appropriate kind and amount of quaternary ammonium ion, the recovery of the chelate was quantitatively. Sub-ppt level zinc(II) in water by the photometric detection in HPLC was successfully achieved, because of the highly efficient concentration.

Multiwavelength spectrophotometric determination of acid dissociation constants of ionizable drugs

A multiwavelength spectrophotometric approach has been developed to determine acid dissociation constants (p K a values) of sparingly soluble drug compounds. UV absorption spectra of the drug solution are acquired using a versatile device based on a fiber optics dip probe, a light source and a photodiode array (PDA) detector while the pH and the ionic strength of the chemical system is manipulated precisely by means of a commercially available titrator. Target factor analysis (TFA) has been applied to deduce the p K a values from the multiwavelength UV absorption data recorded at different pH values. We have called this multiwavelength approach the WApH technique because the p K a results are determined from changes in Wavelength and Absorbance as a function of pH (WApH). The WApH technique is exemplified by using several pure drugs, namely, niflumic acid, nitrazepam, pyridoxine, quinine and terbutaline. The p K a values obtained agree well with those derived from pH-metric titrations. It has been demonstrated that the WApH technique is able to deduce p K a values with high accuracy even if the absorption spectra of the reacting species are very similar.

Dissolution of Silica and Formation of a Dispersed Phase Induced at Low pH by the Association of Soluble Aluminum Ionic Species with Solid Silica Gel

It is shown that the overall behavior of silica in the presence of hydrolyzed Al solutions (pH range 3 - 4) is drastically modified: the total amount of dissolved silica and the initial rate at which silica passes into solution are increased compared to what is observed for a porous silica in water. By using a simple spectrophotometric approach, an estimate of the amount of monomeric and polymeric silica aqueous species can be obtained as a function of time. For all hydrolyzed solutions, the presence of a dispersed phase is also observed. Furthermore, when it is treated with these Al solutions the initial silica gel has its texture, surface charge, and global reactivity modified. This complex chain of events which occurs at acidic pH is in fact triggered by the presence in solution of highly charged Ails polymeric cations, which after adsorption onto the silica sample depolymerize in a process which involves the surface hydroxyls. This leads to the inclusion of tetrahedral Al in the silica famework and the presence of surface-coordinated octahedral Al. This globaly leads through a weakening of the Si-O bonds to an increased release of silica into solution. The Al cations left in solution interact with the aqueous Si species, leading with time to the formation of a metastable silica-aluminum dispersed phase which differs strongly from the treated silica beads. These interactions between Al hydrolyzed solutions and solid silica are therefore quite effective in spatially redistributing the initial silica beads. Many of these conclusions have been made possible by the use of solid-state NMR.

Chemical synthesis of optical grade ceramic precursors: A spectrophotometric approach for analysis

Extremely controlled hydrolysis of a rapidly water-absorbing alkoxide was performed so as to achieve a gel of high optical transmittance. An aluminium sec-butoxide precursor was structurally modified using ethyl acetoacetate in varying stoichiometric ratios. The sol-gel synthesis of the chelated alkoxide was conducted under closely monitored conditions of humidity, temperature and ultrasonic power and the hydrolysing water was added at extremely slow rates using callibrated micropipettes. Molecular level homogeneity was ensured by adopting an intense, contact mode probe type ultrasonication of the chelated alkoxide in presence of excess alcohol, until the alumina sol sonogelled on the addition of a stoichiometric amount of water. The sonogels were seen to possess an extremely high optical transmittance as a result of the novel processing and synthesis technique proposed and developed by us. Uv-visible spectrophotometric analysis of the sonogelling sol at every water addition was performed and a gel of over 95% transmittance could be obtained at a chelate ratio of 1:2, with 15 ml isopropyl alcohol, at a water addition rate of 0.4 ml h −1 g −1 of alkoxide, under an ultrasonic power of 90 watts.

Kinetic spectrophotometric determination of iron oxidation states in geological materials

A kinetic spectrophotometric approach is applied to the determination of iron oxidation states in geological materials. Silicate rock samples were sealed in a Teflon vial under argon atmosphere and were decomposed with a mixture of hydrofluoric acid and sulphuric acid by the microwave digestion technique. The absorbance of iron(III)-Tiron complex was followed at 560 nm and the absorbance/time relation was analyzed by non-linear least squares fitting. The FeO and Fe2O3 determinations in silicate rocks by the proposed kinetic method agree with those done by the static o-phenanthroline method. The analytical results for standard igneous rock samples are compared with published data.

Micellar Electrokinetic Capillary Chromatography of Porphinato Chelates as a Spectrophotometric Approach to Sub-Femtomole Detection of Metal Chelates

Micellar Electrokinetic Capillary Chromatography of Porphinato Chelates as a Spectrophotometric Approach to Sub-Femtomole Detection of Metal Chelates

On the strength of solid acids

The objective of the present work was to establish the relative strengths of some common solid acids and to put them on a scale familiar to chemists. A modified spectrophotometric approach involving Ho and HR indicators was developed. The red-shifts of spectra from the adsorbed neutral forms of 4-nitrotoluene and 4-nitrofluorobenzene were used to deduce the equivalent H 2S0 4 concentrations. Thus, values of 70 to 80%, and 90 to 98% H 2S0 4 were determined for silica-alumina and HY preparations, respectively. HM preparations were found to be mild superacids (stronger than 100% H 2S0 4). On the other hand, H 2S0 4/ZrO 2 preparations had surface acidities about equivalent to 100% H 2S0 4, and SbF 5/silica-alumina was a superacid with − 14.5 < H 0 < − 13.7. These data were correlated with the catalytic activities of the solid acids expressed either as In (reaction rate) at 370°C or as the temperature required to obtain 0.5% conversion of isobutane. The extent and nature of the secondary reactions also varied with the acidity. These results demonstrate that the intensive factor of the acidity (acid strength) dominated over the extensive factor (surface concentration of Brønsted sites) in controlling the acidity, and therefore the catalytic properties, of these solids.

SPECIATION OF IRON IN ENVIRONMENTAL WATER AND GEOLOGICAL SAMPLES BY KINETIC SPECTROPHOTOMETRY

A kinetic spectrophotometric approach is applied to the determination of iron oxidation states in environmental groundwater and silicate rock samples. The method is based on the rapid formation of iron(III)-Tiron complexes, while the oxidation of iron(II) is remarkably accelerated in the presence of Tiron. The increase of absorbance was followed at 560nm and kinetic data were analyzed by non-linear least squares fitting. The proposed method does not require precise control of temperature, unlike most kinetic measurements.

Chromogenic diazirine: A new spectrophotometric approach for photoaffinity labeling

[[2-Nitro-4-[3-(trifluoromethyl)-3 H-diazirin-3-yl]]phenoxy]acetic acid and its derivatives have been synthesized as a special carbene precursor with a chromogenic group. Photolysis of the diazirine in methanol and cyclohexane gave intermolecular OH and CH insertion products, respectively. Spectroscopic properties of the diazirine derivatives and the photo-products revealed that irradiation and detection can be performed in a spectral region where the absorption due to most biological macromolecules is negligible. The application of this reagent will provide a useful approach for simple spectrophotometric detection of labeled products without recourse to conventional radioactive techniques in the photoaffinity labeling methodology.

Zinc/Chromium (II) reduction for nitrate determination in agricultural materials by colorimetry or ion‐selective electrode

AbstractTo phase analytical pathways within this laboratory, recent approaches to nitrate analysis have been studied; of particular interest were the U V spectrophotometric approach (Heanes 1982, 1986) and zinc/chromium (II) reduction procedure (Pruden et al 1985). By combining and modifying various aspects of the aforementioned procedures with an adaption of an indophenol blue colorimetric procedure (Mitchell 1972) it was possible to measure nitrate‐nitrogen 0.10‐8.00 g kg−1 DM routinely on a range of agricultural materials (at present hays, straws, grasses, calabrese, potato leaves, cereals, soils and perlites) on a sophisticated high‐volume‐throughput microprocessor‐controlled auto‐sampler/spectrophotometric system.

Chemically immobilised bi-enzyme electrodes in the redox mediated mode for the flow injection analysis of glucose and hypoxanthine.

Flow injection analysis systems incorporating amperometric bi-enzyme electrodes for glucose and hypoxanthine determination are described. The sensors were based on glucose oxidase-peroxidase for the determination of glucose and xanthine oxidase-peroxidase for the determination of xanthine and hypoxanthine and the enzymes were immobilised on nylon mesh and held over a platinum electrode. The hydrogen peroxide product of the enzymatic catalysis was monitored amperometrically in a three-electrode Stelte cell, adapted for flow injection analysis, after its peroxidase-catalysed reaction with hexacyanoferrate(II).The use of the hexacyanoferrate(II) mediator permitted a low applied potential (–100 mV vs. Ag-AgCl) to be used, enabling the determination of glucose in blood serum samples without difficult sample pre-treatment. The xanthine oxidase-peroxidase bi-enzyme electrode was used to determine hypoxanthine in fish meat as an indicator of deterioration during storage and the results compared favourably with an alternative spectrophotometric approach recommended by the Analytical Methods Committee (AMC) according to the equation [hypoxanthine]Electrode= 1.01[hypoxanthine]AMC+ 4.0 × 10–3, with a correlation coefficient of 0.998.

The spectral evolution of galaxies. I - an observational approach

In the present paper, two major new surveys are discussed, taking into account a photometric and a spectrophotometric approach. It is demonstrated that the optical color selection of galaxies is a superior technique for selecting a more homogeneous sample of distant galaxies than other methods such as radio flux density, which is rather arbitrary, or selecting rich clusters of galaxies. The comparison of phenomenological models of spectral evolution with the observed data indicates that the present epoch age for giant elliptical galaxies is much older than 8 Gyr. These models provide an adequate description of the evolution of giant elliptical galaxies with a present epoch age of about 16 Gyr and an exponentially decaying star-formation rate with an e-folding time of about 0.9 Gyr. 76 references.

The solution state of nickel(II) and nickel(I) in the presence of diphosphines in acetonitrile. A combined electroanalytical and spectrophotometric approach

The equilibria involving nickel(II), nickel(I) and nickel(0) in the presence of bidentate phosphine ligands in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry. The obtained results show that when both cone angles and PP distance make the diphosphine well-suited to act as a chelating ligand, only bis-chelate complexes of the type NiL 2 are formed by nickel in all the three achieved oxidation states. Longer methylene chains interposed between the phosphorus atoms make the diphosphine less suited to act in a bidentate fashion, thus allowing lower-order complexes, e.g. NiLS 2 (S = solvent), to be obtained for nickel in the +2 and +1 oxidation states. Evidence for the poor stability of the [Ni ILS 2] + complexes and for a higher-order complex of the type NiL 3 for nickel(II) have also been obtained. The dependence of the reduction potentials on the nature of the diphosphine employed is discussed.

Some Factors Affecting Assay Variability in the Determination of Chlortetracydine in Premix Feeds

There are many sources of error in the microbiological determination of high levels of chlortetracycline in premix. Among the critical factors that can be controlled by the analyst are careful weighing of the reference standard and careful dosing of cylinders. A spectrophotometric approach and automatic filling of cylinders are suggested to ensure proper monitoring of these operations. Among factors that cannot be controlled by the analyst is the assay design. A 3-point design which is a modified version of the (3+3) design is considered, and its advantages are illustrated.

The secondary structure of E. coli ribosomes and ribosomal RNA's: a spectrophotometric approach.

The thermal denaturation spectra of E. coli 50s and 30s ribosomal sub units and of their isolated RNA's were studied over the wavelength range of 2300-3000 Angstrom. It was possible to fit the experimental denaturation spectra with super positions of the reference spectra for denaturation of A - U and G - C base pairs derived from model polyribonucleotides. The coefficients of these linear combinations were used to calculate the fractions of A - U and G - C base pairs in the samples. It was found that the helical content of the RNA's inside the subunits is smaller than that of the isolated RNA's, thus suggesting that proteins may affect the secondary structure of RNA in the ribosome.