Oxytetracycline EP Impurity A

A thin-layer chromatographic (TLC) method using densitometry is described for the assay and purity control of oxytetracycline and doxycycline. With a mobile phase of dichloromethane-methanol-water (59:35:6, v/v/v) and a silica gel thin-layer, previously sprayed with 10% sodium edetate solution adjusted to pH 9.0, all the potential impurities of oxytetracycline or doxycycline are well separated from the main components and from each other. Results obtained with TLC are compared with those obtained by previously established liquid chromatography (LC) methods using poly(styrene-divinylbenzene) stationary phases. A good correlation was obtained (r greater than 0.9999). For TLC the relative standard deviation (RSD) for the assay of the main component was less than 2%, for LC the RSD was less than 1%.

Pharmaceuticals, especially antibiotics, constitute an important group of aquatic contaminants given their environmental impact. Specifically, tetracycline antibiotics (TCs) are produced in great amounts for the treatment of bacterial infections in both human and veterinary medicine. Several studies have shown that, among all antibiotics, oxytetracycline hydrochloride (OTC HCl) is one of the most frequently detected TCs in soil and surface water. The results of the photocatalytic degradation of OTC HCL in aqueous suspensions (30 mg·L-1) of 0.5 wt.% cobalt-doped TiO2catalysts are reported in this study. The heterogeneous Co-TiO2photocatalysts were synthesized by two different solvothermal methods. Evonik Degussa Aevoxide P25 and self-prepared TiO2modified by the same methods were used for comparison. The synthesized photocatalysts were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV/vis diffuse reflectance spectroscopy (DRS), and N2adsorption (BET) for specific surface area determination. The XRD and Raman results suggest that Ti4+was substituted by Co2+in the TiO2crystal structure. Uv/visible spectroscopy of Co-TiO2-R showed a substantial redshift in comparison with bare TiO2-R. The photocatalytic performance of the prepared photocatalysts in OTC HCL degradation was investigated employing Uv/vis spectroscopy and high-performance liquid chromatography (HPLC). The observed initial reaction rate over Co-TiO2-R was higher compared with that of Co-TiO2-HT, self-prepared TiO2, and the commercial P25. The enhanced photocatalytic activity was attributed to the high surface area (153 m2·g-1) along with the impurity levels within the band gap (2.93 eV), promoting the charge separation and improving the charge transfer ability. From these experimental results, it can be concluded that Co-doping under reflux demonstrates better photocatalytic performances than with the hydrothermal treatment.

The fate of oxytetracyclines (OTCs) in soil interstitial water was investigated and the structure of a number of degradation products elucidated in a time-related experiment. A previously developed separation method for LC-MS-MS able to base separate and quantify OTC and three of its epimers and degradation products was applied. Compounds detected were 4-epi-oxytetracycline (EOTC) (t(R)=3.0 min), OTC (t(R)=4.4 min), alpha-apo-oxytetracycline (alpha-apo-OTC) (t(R)=11.4 min) and beta-apo-oxytetracycline (beta-apo-OTC) (t(R)=18.4 min). Furthermore, we tentatively identified 4-epi-N-desmethyl-oxytetracycline (E-N-DM-OTC) (t(R)=3.0 min), N-desmethyl-oxytetracycline (N-DM-OTC) (t(R)=3.5), N-didesmethyl-oxytetracycline (N-DDM-OTC), 4-epi-N-didesmethyl-oxytetracycline (E-N-DDM-OTC) (t(R)=3.7 and 4.7 min) and 2-acetyl-2-decarboxamido-oxytetracycline (t(R)=8.7) in all samples. Most compounds were only present in trace concentrations (less than 2%) relative to the parent OTC. EOTC was on the other hand formed up to a ratio of 0.6 relative to parent OTC concentration. Only EOTC, E-N-DM-OTC, N-DM-OTC, N-DDM-OTC and E-N-DDM-OTC were formed during the time-related experiment. All other compounds were probably only present as impurities in the spiked OTC formulation as they declined in concentration from the start of the experiment. Half-lives (T(1/2), days) of the OTCs in soil interstitial water were in the order of 2 days (EOTC) to 270 days (beta-apo-OTC).