No abstract

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Deltalambda=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Deltalambda=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 microg ml(-1) (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 microg ml(-1) (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40-102% for acetylsalicylic acid and 90-100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97-99% for acetylsalicylic acid and 97-98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 microg ml(-1) and 0.0306 microg ml(-1) for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 microg ml(-1) of acetylsalicylic acid is 2.75% and for 2.2 microg ml(-1)of caffeine is 1.7%.

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.

Bilirubin is a metabolic breakdown product of blood haem, of great biological and diagnostic importance. A new chemiluminescence (CL) method has been developed for the quantification of bilirubin. The method is combined with the flow injection analysis (FIA) technique and based on the inhibition effect of bilirubin on the CL from the lucigenin-hydrogen peroxide system in an alkaline medium. Under the optimum conditions, the decreased CL intensity was proportional to the concentration of bilirubin, in the range 0.0585-58.47 microg/mL. The detection limit estimated from the calibration graph was about 7.8826 ng/mL. The relative standard deviation (RSD) of 10 parallel measurements (1 x 10(-4) mol/L bilirubin) was 2.5%. Recoveries of bilirubin were found to fall in the range 94-97.5% using control sera. The method is interference-free, fast and easy to carry out.