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A biosensor based on the optical signal of gold nanorods (GNRs) and an aptamer as the recognition element is reported to perform the rapid and selective spectrophotometric determination of profenofos. The GNR synthesized by the seed growth method have unique structures which binds with the aptamer through electrostatic adsorption and is well dispersed in a salt-containing solution. Upon the addition of profenofos, specific recognition caused aggregation of the GNRs. The optical signal therefore decreased and the response linearly related to the concentration of profenofos. The results demonstrate that ascorbic acid as the reducing agent plays an important role in the morphology of the GNRs. GNRs with the length-diameter ratio (L/D) of 12 stably combined with the aptamer. For the optimum conditions, spectrophotometric determination of profenofos was achieved using the biosensor with a linear relationship between the absorbance of GNR at 508 nm and the concentration of profenofos from 40 to 460 µg/L. The limit of detection of the method was 31.93 µg/L. In addition, this approach shows good selectivity for the analysis of fruits and vegetable. A valuable new method is reported for the determination of profenofos. [ABSTRACT FROM AUTHOR]

This work presents a simple, low cost, and portable spectrophotometer based on a digital microscope as a detector for the determination of the antioxidant activity and total phenolic content (TPC). The antioxidant activity was expressed as ascorbic acid equivalents (AAE) using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay. The TPC value was measured using the Folin-Ciocalteu method. The color of the products was captured using a digital microscope powered through the USB output of a laptop. A digital microscope, held in a 3D printing device was used to take photos of the reaction product that was illuminated with the stable light source of the digital microscope. The pictures were analyzed for quantitation. For the DPPH assay, the developed method provided a working range from 0.6 to 6 mg L−1 of ascorbic acid with a limit of detection (LOD) of 0.2 mg L−1 and a relative standard deviation (RSD) of 2.2%. The TPC method provided a working range from 4.6 to 100 mg L−1 for gallic acid, with a LOD of 1.4 mg L−1 and a RSD of 1.3%. Results of the proposed system agree well with a conventional spectrophotometric method and have been successfully applied to measure the antioxidant activity and TPC of local Thai tea samples. [ABSTRACT FROM AUTHOR]

A novel strategy for preparing polyethylene open tubular reactors coated with MnO2(s) was pioneered for flow analysis in order to minimize the inherent drawbacks of packed solid reagents. As an application, the determination of ascorbic acid in pharmaceuticals was selected. The method involved reduction of Mn(IV) by ascorbic acid, release of the formed Mn2+ion, reaction with formaldoxime, and spectrophotometric monitoring. The influence of flow pattern was investigated by using two similar flow systems relying on constant or pulsed flow delivered by peristaltic or solenoid pumps. With pulsed flow, system versatility and ruggedness were improved, and the analytical sensitivity (0.01143 L mg−1ascorbic acid), detection limit (0.6 mg L−1ascorbic acid), and sampling rate (60 h−1) evaluated compared to constant flow were improved by 2.1%, 40.0%, and 6.5%, respectively. At the same time, the reagent consumption (2.8 mg per determination) and analytical precision (relative standard deviation of approximately 2.5%) were maintained. One can conclude that the mixing conditions did not limit the analyte/reagent interaction. The results were in agreement with the British Pharmacopoeia method. [ABSTRACT FROM AUTHOR]

This paper describes a kinetic spectrophotometric method for the determination of L-ascorbic acid (AA) and thiols (RSH). Absorbance of Fe(II)-phen complex formed during the reaction of AA or RSH with Fe(III)-phen was continuously measured at 510 nm by double-beam spectrophotometer with flow cell. For determination some thiols, the catalytic effect of Cu2+ ions was used. AA and RSH can be determined in concentration ranges from 4.0×10-6 to 4.0×10-5 M and from 8.0×10-6 to 8.0×10-5 M, respectively. The applicability of the proposed method was demonstrated by determination of chosen compounds in pharmaceutical dosage forms. [ABSTRACT FROM AUTHOR]

A kinetic spectrophotometric method was developed for simultaneous determination of ascorbic acid (AA) and L-cysteine (Cys), based on detecting the colored final product. These compounds react differentially with Fe(III) in neutral medium, and the product of reduction, Fe(II), will form a colored compound with chromogenic reagent 1,10-phenanthroline, which shows a maximum absorbance at 510 nm. The absorbance was measured at 510 nm every 2 sec from 10 to 190 sec, and the data obtained were processed by chemometric approach, partial least squares (PLS). The experimental calibration set was composed with 25 sample solutions using orthogonal calibration design for two component mixtures. The concentration ranges for AA and Cys were 2.00–11.82 and 1.50–14.99 ppm, respectively. The effect of pH and temperature was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in pharmaceutical formulation. [ABSTRACT FROM AUTHOR]

A new spectrophotometric method for the on‐site determination of arsenic in contaminated water samples has been developed. The method is simple, rapid, and selective. It is based on reduction of As(V) to As(III) with ascorbic acid, complexation of As(III) with I− ions in strong HCl medium and extraction of the yellow colored iodo‐complex with N‐octylacetamide into chloroform solution. The optimum acidity range is 4.5–6.0 M HCl/2.5–3.5 M H2SO4. The apparent value (i.e., at two fold enrichment factor) of molar absorptivity in the term of arsenic is (5.00) × 104 L mol−1 cm−1 at λmax, 420 nm. The detection limit (i.e., absorbance causing more absorbance than 3s) of the method is 10 µg L−1 As. The method is free from interference of the ions commonly found to be associated with arsenic in environmental samples. The method has been tested for the field determination of arsenic in contaminated waters (i.e., surface, ground, rice field) of central India. #Accepted for poster presentation in IMA conference to held in Thessaloniki, Greece, 23–27 Sept., 2003. [ABSTRACT FROM AUTHOR]

Ascorbic acid present in pharmaceuticals and fruit juice was rapidly determined by the spectrophotometric method in association with flow injection analysis. The method is based on the inhibitory effect of ascorbic acid on the oxidation of pyrogallol red by iodate in sulfuric acid media. The calibration graph is linear in the range of 2.0 × 10[sup -6] M up to 1.0 × 10[sup -4] M. The throughput is 20 × 5 samples per hour and the detection limit is 0.5 µM ascorbic acid. The relative standard deviation for ten replicate determinations of 8.00 µM and 50.0 µM ascorbic acid is 3.4 and 0.60%, respectively. The influence of various species was studied for this determination. [ABSTRACT FROM AUTHOR]