Authors:Long Han, Deepak Doraiswamy, and Rakesh K. Gupta
Light emitting devices containing conjugated polymers are conveniently fabricated using ink-jet printing. A common problem in the processing of these materials is that the Newtonian viscosity of the polymer solution is not sufficient to describe the jetting performance because the molecular weights and concentrations employed are such that the resulting solutions are elastic. These differences in fluid elasticity levels cannot be measured using traditional techniques like dynamic mechanical experiments or the first normal stress difference in shear, but strongly impact the jetting behavior of the liquid. In this study, a variety of polystyrene solutions in DECALIN having a shear viscosity of ~5 mPa s but different elasticity levels were examined for their jetting behavior. The jetting behavior of these solutions was studied visually using drop-on-demand jetting equipment and their rheology was characterized using a custom extensional rheometer designed for measuring the elasticity of such low viscosity liquids. If elasticity effects are absent as in Newtonian liquids (corresponding to a Trouton ratio of 3) satellite drops are formed resulting in loss of liquid and poor positioning. On the other hand, if elasticity effects are very large (Trouton ratios ≫4) separation problems occur at the nozzle with undesirable “tailing.” The optimum range for stable, efficient jetting occurs at Trouton ratios in a narrow band between 3 and ~5. A very slight degree of elasticity corresponding to a Trouton Ratio around four thus seems to be optimum for the jetting process. This appears to be the first time that such a design criterion has been outlined for this process. Such an approach complements thermal techniques for elucidating the role of molecular and flow properties on the processing behavior of polymeric systems.
Authors:Ravi Bhushan, Deepak Gupta, and Aishwarya Jain
A simple and sensitive method for separation and quantitative determination of antidiabetic drugs in pharmaceutical preparations has been established and validated. Commercial formulations of five antidiabetic drugs (metformin, pioglitazone, rosiglitazone, glibenclamide, and gliclazide) were chosen for the studies. The compounds were extracted, isolated, purified, recrystallized, and characterized by measurement of melting point,
, and IR. Quantitative determination was performed by HPLC, TLC, and column chromatography supplemented with UV spectrophotometry. Two of the combinations, metformin + pioglitazone and metformin + gliclazide, were separated by open-column chromatography. Detection was by UV spectrophotometry in HPLC and by use of iodine vapor in TLC.
Authors:Ravi Bhushan, Hans Brückner, Virender Kumar, and Deepak Gupta
A simple and rapid method has been established for indirect separation of the optical isomers of seventeen DL
amino acids by reversed-phase and normal-phase TLC. Amino acids derivatized with 1-fluoro-2,4-dinitrophenyl-5-L
), or 1-fluoro-2,4-dinitrophenyl-5-L
) were spotted on precoated plates. Diastereomers of all the DL
amino acids were separated most effectively by normal-phase TLC with phenol-water, 3:1 (
), as mobile phase. In reversed-phase TLC the diastereomers were separated most effectively by use of mobile phases containing acetonitrile and triethylamine-phosphate buffer (50 mM, pH 5.5). The results obtained by use of the classical
) were compared with those obtained by use of FDNP-L
. The effects of buffer concentration, pH, and concentration of organic modifier were studied. This indirect method enabled resolution of DL
amino acids at nanomolar concentrations.