Sensitive determination of chromium (VI) in paint samples using a membrane optode coupled to a multisyringe flow injection system.

In this work, the potential of a membrane optode coupled to a multisyringe flow injection system (MSFIA) was assessed for determining the Cr(VI) concentration in paint samples. The detection is based on the color obtained from the reaction of Cr(VI) with 1,5-diphenylcarbazide in the presence of sulfuric acid (H(2)SO(4)). The redox product was immobilized on a poly(styrene-divinylbenzene) (SDB-XC) membrane optode. The analyte in the sample was then directly quantified at the surface of the disk by measuring the intensity of reflected incident light using a bifurcated optical fiber at 540 nm. Experimental parameters (concentration of reagents, sample volume, flow rate of sample solutions, eluent concentration, and effect of diverse ions) were studied in detail. The overall time required for the complete procedure was 4 min and only required 0.2 mL of the sample volume. The dynamic working response of Cr(VI) was found within the concentration range of 2.4-1000 µg L(-1) with a limit of detection (LOD) of 0.7 µg L(-1), while the relative standard deviation (RSD) for 400 µg L(-1) Cr(VI) was lower than 2% (n=6). This developed method was used to determine Cr(VI) concentrations in the paint samples, for which an alkaline extraction procedure was proposed. The extraction procedure was based on the use of a 7.5% Na(2)CO(3)/5% NaOH solution at 90 °C for 30 min. Under optimal conditions, the recoveries ranged from 99% to 101%. The complete method was validated using a certified reference material (ERA-QC540, soil sample) and by comparing the results with those obtained using atomic absorption spectrometry (AAS).

Controlled release of theophylline from inert matrices: effect of channeling material on release rate.

Sustained release theophylline tablets containing stearic acid wax and lactose fast flo as chanelling agent were prepared and evaluated. The fusion technique was used for dispersing the drug in the different levels of stearic acid. The release rate of theophylline from the prepared tablets increased with the increase of the level of the channeling material in the formula. The drug release from tablets containing high level of wax (30 and 60%) and low level of channeling material (59% and 29%) followed the diffusion controlled model for inert porous matrix. The drug release increased significantly with the increase of lactose fast flow level in the formula. After 2 hours of testing dissolution, the tablets start to erode and the mechanism of drug release deviate from the diffusion controlled model. The mechanism of drug release was dependent on the level of the channeling material in the matrix.