Quantitative determination of tetracycline hydrochloride by thin-layer chromatography

Comparison of polyethylene glycol and polyoxyethylene stearate as excipients for solid dispersion systems of griseofulvin and tolbutamide I: Phase equilibria

“…This polymorph is the most stable a t room temperature (21,22). In view of the reported polymorphism of tolbutamide (19)(20)(21)(22), it may seem surprising that no polymorphic transitions were observed in the present work; this finding is illustrated by the differential thermal analysis plot shown in Fig. 1.…”

“…The only form of tolbutamide encountered under the conditions of the present work was the commercial form which melted a t 127" (19), namely, Modification A (20) or I (21,22). This polymorph is the most stable a t room temperature (21,22).…”

Separation and Quantitative Determination of Impurities in Tetracycline

“…Van den Bulcke (14) studied the influence of the binder and polyalcohols in the stationary phase and of the solvent systems both on the separation of tetracyclines and the detection of their impurities. Microcrystalline cellulose was used to separate I and other impurities from IV (15)(16)(17)(18).Gyanchandani et al (19) first impregnated the plates with the solvent system, a process that conditioned them so that they could be stored for several weeks. Finally, van Hoeck et al (20) separated I, 11, and I11 from IV on a solvent-impregnated plate and determined IV by direct fluorometry.…”

“…Van den Bulcke (14) studied the influence of the binder and polyalcohols in the stationary phase and of the solvent systems both on the separation of tetracyclines and the detection of their impurities. Microcrystalline cellulose was used to separate I and other impurities from IV (15)(16)(17)(18).…”

“…Microcrystalline cellulose is also unsatisfactory because the support, as described by Simmons et al (15)(16)(17), is difficult to prepare and does not allow a good separation while the use of citrate and/or phosphate buffers may markedly increase the epimerization of the tetracy- clines (19,21,22). For the same reason, the temperature should be controlled during the development (21).…”