Physico-chemical studies on the charge-transfer complex formed between sulfadoxine and pyrimethamine with chloranilic acid.

Thermodynamic studies on the charge-transfer complexes of sulfadoxine and pyrimethamine with chloranilic acid in non-aqueous 1,4-dioxan were investigated by spectrophotometric method. The absorption maxima for sulfadoxine and pyrimethamine were observed at 500 and 520 nm, respectively. We observed a bathochromic shift in the transitions of these complexes with respect to chloranilic acid, which absorb at 420 nm. The enthalpy of complexation was found to be -3.044 kJ/mole for pyrimethamine and -5.934 kJ/mole for sulfadoxine. Equilibrium constant values were generally high, that is 261.202 l/mole and 344.29 l/mole for pyrimethamine and sulfadoxine, respectively, at 303 K. Free energy values were negative, of the order of -14.420 kJ/mole for pyrimethamine and -15.384 kJ/mole for sulfadoxine, indicating that complex formations were exothermic. These data suggest that the complexes are very stable. Arguments are presented to support the application of charge-transfer interactions in the quantitative analysis of these drugs.

Analysis of trimethoprim, lincomycin, sulfadoxin and tylosin in swine manure using laser diode thermal desorption-atmospheric pressure chemical ionization-tandem mass spectrometry.

A new extraction method coupled to a high throughput sample analysis technique was developed for the determination of four veterinary antibiotics. The analytes belong to different groups of antibiotics such as chemotherapeutics, sulfonamides, lincosamides and macrolides. Trimethoprim (TMP), sulfadoxin (SFX), lincomycin (LCM) and tylosin (TYL) were extracted from lyophilized manure using a sonication extraction. McIlvaine buffer and methanol (MeOH) were used as extraction buffers, followed by cation-exchange solid phase extraction (SPE) for clean-up. Analysis was performed by laser diode thermal desorption-atmospheric pressure chemical-ionization (LDTD-APCI) tandem mass spectrometry (MS/MS) with selected reaction monitoring (SRM) detection. The LDTD is a high throughput sample introduction method that reduces total analysis time to less than 15s per sample, compared to minutes when using traditional liquid chromatography (LC). Various SPE parameters were optimized after sample extraction: the stationary phase, the extraction solvent composition, the quantity of sample extracted and sample pH. LDTD parameters were also optimized: solvent deposition, carrier gas, laser power and corona discharge. The method limit of detection (MLD) ranged from 2.5 to 8.3 µg kg(-1) while the method limit of quantification (MLQ) ranged from 8.3 to 28µgkg(-1). Calibration curves in the manure matrix showed good linearity (R(2)≥ 0.996) for all analytes and the interday and intraday coefficients of variation were below 14%. Recoveries of analytes from manure ranged from 53% to 69%. The method was successfully applied to real manure samples.