Seikh Mafiz Alam

Optical ascorbic acid sensor based on the fluorescence quenching of silver nanoparticles.

A sensitive and selective fluorimetric sensor for the assay of ascorbic acid (AA) using silver nanoparticles as emission reagent was investigated. In this study, silver nanoparticles were prepared based on aqueous-gaseous phase reaction of silver nitrate solution and ammonia gas. The nanoparticles were water-soluble, stable and had a narrow emission band. They were used as a fluorescence probe for the assay of ascorbic acid on its quenching effect on the emission of silver nanoparticles. The principal reason for quenching is likely to be a complexation between ascorbic acid and silver nanoparticles. The quenching mechanism was established by Stern-Volmer law. Under the optimum conditions, the quenched fluorescence intensity was linear with the concentration of ascorbic acid in the range of 4.1 x 10(-6) to 1.0 x 10(-4) m (r = 0.9985) with a detection limit of 1.0 x 10(-7) m. The RSD for repeatability of the sensor for the assay of ascorbic acid concentration of 3.0 x 10(-5) and 4.0 x 10(-6) m was found to be 1.5 and 1.3%, respectively. The proposed method was applied to the determination of ascorbic acid in vegetables and vitamin C tablets.

Development of a sensitive flow‐injection–chemiluminescence detection method for the determination of laevodopa

A simple chemiluminometric method using flow injection has been developed for the determination of levodopa, based on its sensitizing effect on the weak chemiluminescence (CL) reaction between Na(2)SO(3) and acidic KMnO4. Under optimum experimental conditions, the CL intensity was linearly related to the concentration of levodopa from 3.4 x 10(-8) to 2.4 x 10(-5) mol/L and the detection limit was 1.1 x 10(-8) mol/L (s:n = 3). The relative standard deviation (RSD) of the proposed method calculated from 20 replicate injection of 3 x 10(-7) mol/L levodopa was 3.3%. The correlation coefficient was 0.997. The method was successfully applied to the determination of levodopa in commercial pharmaceutical formulations and spiked urine samples.

Application of a lanthanide composite nanoparticle‐sensitized luminescence method for the determination of salicylic acid in pharmaceutical formulations and human plasma

Terbium-acetylacetone (Tb-acac) composite nanoparticles were synthesized using the ultrasonic method. The nanoparticles are water-soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorimetric probes in the determination of salicylic acid (SA), based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution was investigated. Under the optimum conditions, a linear calibration graph was obtained over the SA concentration range 5 x 10(-7)-1 x 10(-4) mol/L. The limit of detection was found to be 2.5 x 10(-8) mol/L. The relative standard deviation (RSD) for six repeated measurements of 1 x 10(-4) mol/LSA was 1.75%. The method was applied to the determination of SA in pharmaceutical formulations and human plasma. We believe that the proposed approach has great potential for clinical purposes.

CL sensitisation of tris-(bipyridyl) ruthenium (II) – cerium (IV) reaction system by AgNPs for determination of GFX

The flow injection combined with tris-(bipyridyl) ruthenium (II)-cerium (IV) chemiluminescence (CL) method based on the sensitisation of silver nanoparticles (AgNPs) has been established for the quantitative analysis of gatifloxacin (GFX). AgNPs were synthesised using the reaction between ammonia gas and silver nitrate solution and was used to increase the CL intensity of the proposed system. The enhancement of CL intensity was linear with the concentration of GFX added. Effects of different experimental parameters were studied. Under the optimal conditions, the linear relationship was established between the concentration range of 1.4 × 10-10-4.5 × 10-8 M, with the correlation coefficient (r2) 02E9999. The limit of detection was found to be 4.6 × 10-11 M. The relative standard deviation obtained was 3.2% for six replicate measurements of GFX (1.2 × 10-9 M). The proposed CL method was applied to the commercial drug and the result was in agreement with the labelled amount. The technique was further adopted to the analysis of GFX in spiked urine samples. Negligible interference was found (variation in CL intensity <5%) from a few common foreign excipients applied in preparation of pharmaceutical drug. The comparative results with a few reported methods indicates that the proposed method is more sensitive than other methods..