Search results for "colorimetry"
showing 10 items of 85 documents
Chromogenic Detection of Nerve Agent Mimics by Mass Transport Control at the Surface of Bifunctionalized Silica Nanoparticles
2010
Chemical warfare (CW) agents are toxic chemicals that have been used in several terrorist attacks in recent years. Among CW species, nerve agents are probably the most dangerous; their high toxicity and facile synthesis underscores the need to detect these lethal compounds with quick, reliable procedures. Analytical methods based on enzymatic assays and physical measurements have generally been used to detect these hazards. However, these protocols usually have limitations such as low selectivity, poor portability, and a certain level of complexity. In recent years, several chromogenic and fluorogenic sensors, and reagents for the detection of nerve agents have been described. For instance,…
Aldicarb residues in citrus soil, leaves and fruits
1990
Aldicarb was applied to the soil of Late Valencia orange field plots. A comparative study between four analytical methods is reported, the NPD-gas chromatography method being the best choice. The work also reports the study of accumulation and persistence of aldicarb and its biologically active metabolites in the soil, leaves and fruits (rind and pulp, separately). Residue content, at the ppb level, was found in the order leaves much greater than rind greater than pulp. Carbamate was found to accumulate mainly in its oxidized forms. Residues had reached a maximum level in about 90 days after application.
Application of the S-CIELAB color model to processed and calibrated images with a colorimetric dithering method.
2009
This work uses the S-CIELAB color model to compare images that have been calibrated and processed using a colorimetric dithering method which simulates increments in viewing distance. Firstly, we obtain XYZ calibrated images by applying the appropriate color transformations to the original images. These transformations depend on whether the image is viewed on a display device or encoded by a capture device, for example. Secondly, we use a colorimetric dithering method consisting of a partitive additive mixing of XYZ tristimulus values. The number of dithered pixels depends on simulated viewing distance. The dithered tristimulus values are transformed to digital data to observe the dithering…
Polydimethylsiloxane composites containing 1,2-naphtoquinone 4-sulphonate as unique dispositive for estimation of casein in effluents from dairy indu…
2015
A unique dispositive to determine casein which is the most abundant protein in dairy sewages has been proposed. In this sensing technology, the derivatization reagent 1,2-naphtoquininone 4-sulphonate (NQS) is embedded into a polydimethylsiloxane-tetraethylortosilicate-SiO2 nanoparticles composite (PDMS-TEOS-SiO2NPs). When the composite is immersed into the samples, casein is extracted from the solution and derivatized inside the PDMS matrix after 10 min at 100°C. The sensing support changes its color from yellow to orange depending on the casein concentration. Quantitative analysis can be carried out by measuring the absorbance with a reflection probe or by image-processing tool (GIMP). Thi…
Continuous-flow tristimulus colorimetry: a new approach for gradient scanning techniques
1991
Abstract A flow-injection gradient scanning technique for colour evaluation by means of tristimulus colorimetry is described. Equipment and data acquisition requirements are discussed. The program CHROMA.FIA data the treatment and comparative chromatic analysis is presented. The chemical and flow conditions were optimized. Comparative studies using metallochromic indicators with both the flow-injection and the conventional batch procedures were made. The continuous-flow procedure provides good results and is more than fifteen times faster than the manual titrimetric procedure.
Colorimetric Characterization of Mobile Devices for Vision Applications
2015
Purpose: Available applications for vision testing in mobile devices usually do not include detailed setup instructions, sacrificing rigor to obtain portability and ease of use. In particular, colorimetric characterization processes are generally obviated. We show that different mobile devices differ also in colorimetric profile and that those differences limit the range of applications for which they are most adequate. Methods: The color reproduction characteristics of four mobile devices, two smartphones (Samsung Galaxy S4, iPhone 4s) and two tablets (Samsung Galaxy Tab 3, iPad 4), have been evaluated using two procedures: 3D LUT (Look Up Table) and a linear model assuming primary constan…
Measurement of Lymphocyte Proliferation: Critical Analysis of Radioactive and Photometric Methods
1992
Different methods of lymphocyte proliferation are compared to identify a non-radioactive alternative to 3H-thymidine-test. The enzymatic assays evaluating the turnover of mitochondrial dehydrogenases (MTT-test) and lysosomal hexosaminidase (NAG-test) proved not sensitive enough to substitute for 3H-thymidine incorporation. The incorporation of the nucleotide analog 5-bromodeoxyuridine (BrdU) can be exploited using an ELISA-system (enzyme linked immunosorbent assay) employing a monoclonal anti-BrdU antibody to measure cell proliferation. An optimized test protocol of the BrdU-ELISA which fulfills the requirements for a sensitive and practicable non-radioactive alternative to 3H-thymidine-tes…
Quantification of Imidacloprid in Honeybees: Development of a Chemiluminescent ELISA
2010
A Chemiluminescente Enzyme-Linked Immuno-Sorbent Assay (CL-ELISA) for determination and quantification of the fungicide imidacloprid in honeybees was developed in an indirect competitive format. The assay was optimized by determining: the optimal coating conjugate concentration and anti-imidacloprid antiserum dilution, the effect of the incubation time on the competitive step, the tolerance to organic solvents. The IC50 and the limit of detection (LOD) values were 14.8 ng mL-1 and 0.11 ng mL -1, respectively, similar to those of colorimetric ELISA with a calibration range of 0.1 – 2600 ng mL-1. Cross reactivity of some related compounds such as three imidacloprid metabolites, 6-chloro nicot…
3,3?,5,5?-Tetramethylbenzidme for the colorimetric determination of manganese in water
1998
Manganese can be determined by colorimetry with previous oxidation of Mn(II) in a strong basic medium, using 3,3′,5,5′-tetramethylbenzidine as a chromogenic reagent. The molar absorptivity of the reaction product is 3.4 × 104 mol−1l cm−1l, the detection limit 3 ng/ml, the RSD (0.5 mg/l,n = 8) 0.9% and the calibration range (1-cm cells) 0.02–0.8 mg/1 V(V), Cr(VI) and Co(II) are the most significant interferences. The new method was compared with an AAS procedure (air-acetylene flame) with previous solvent extraction and also with a colorimetric method for the determination of manganese in sea and drinking water.
A Colorimetric Membrane-Based Sensor with Improved Selectivity towards Amphetamine
2021
Due to their simplicity, speed and low cost, chemical spot tests are increasingly demanded for the presumptive identification of illicit drugs in a variety of contexts such as point-of-care assistance or prosecution of drug trafficking. However, most of the colorimetric reactions used in these tests are, at best, drug class selective. Therefore, the development of tests based on chemical reactions with improved discrimination power is of great interest. In this work, we propose a new colorimetric assay for amphetamine (AMP) based on its reaction with solutions of alkaline gold bromide to form an insoluble yellow–orange derivative. The resulting suspensions are then filtered onto nylon membr…