Development of an assay for the extraction and quantification of nine 5-n-alkyl-5-ethyl barbituric acids in various rat tissues

Modeling Kinetics of Subcellular Disposition of Chemicals

“…Experimental techniques providing data for the calibration of the SBSP models can be classified as indirect and direct, depending on whether the phase, where the concentration of chemicals is determined, has been separated in the course of the experiment from the rest of the biosystem or not, respectively. The indirect techniques include measurement of the chemical's uptake into membranes, 76 vesicles, 77 subcellular organelles, 78 cells, 79 tissues, 80 and organs. 81 The direct approaches, suitable for simpler biosystems, are represented mainly by spectroscopic techniques: ultraviolet and visible (UV Vis) difference spectroscopy, [82][83][84][85] circular dichroism, [84][85][86] fluorescence lifetime measurements, 87 fluorescence quenching techniques, [88][89][90][91][92][93][94][95] fluorescence anisotropy, 96 Fourier-transform infrared (FT-IR) spectroscopy 84 combined with attenuated total reflection (ATR) 97 and high pressure, 98 electron paramagnetic resonance (EPR) with phospholipids containing spin labels in different positions, [99][100][101][102][103][104] and various nuclear magnetic resonance (NMR) techniques, 84,87,90,99, including the measurement of nuclear Overhauser enhancement spectroscopy (NOESY) 130,131 cross-relaxation rates.…”

“…Experimental techniques providing data for the calibration of the SBSP models can be classified as indirect and direct, depending on whether the phase, where the concentration of chemicals is determined, has been separated in the course of the experiment from the rest of the biosystem or not, respectively. The indirect techniques include measurement of the chemical’s uptake into membranes, vesicles, subcellular organelles, cells, tissues, and organs . The direct approaches, suitable for simpler biosystems, are represented mainly by spectroscopic techniques: ultraviolet and visible (UV Vis) difference spectroscopy, – circular dichroism, – fluorescence lifetime measurements, fluorescence quenching techniques, – fluorescence anisotropy, Fourier-transform infrared (FT-IR) spectroscopy combined with attenuated total reflection (ATR) and high pressure, electron paramagnetic resonance (EPR) with phospholipids containing spin labels in different positions, – and various nuclear magnetic resonance (NMR) techniques, ,,,,– including the measurement of nuclear Overhauser enhancement spectroscopy (NOESY) , cross-relaxation rates .…”

Quantification of tetramethyl-terephthalic acid in rat liver, spleen and urine matrices by liquid–liquid phase extraction and HPLC-photodiode array detection

“…Acidification with trichloroacetic acid of the homogenized samples contributed both to a complete extraction of TMT and to the precipitation of proteins, as previously reported for other biological matrices [14,15]. However, HCl treatment allowed the formation of a more compact protein precipitate than trichloroacetic acid, improving the sample purification and consequently, decreasing the number of peaks corresponding to endogenous compounds.Moreover, the use of the sodium acetate buffer also improved the extraction of TMT due to its reasonable solubility (0.5 mg ml −1 ) tested experimentally and to the presence of acetate ions with surface-active properties [16], which also favored the extraction of TMT gathered at the aqueous-organic interface [17][18][19]. On the other hand, the TMT extraction in urine spleen and liver matrices was studied after several stirring times (10-30 min).…”

“…Longer stirring times were required in more complex matrices, liver and spleen, in order to completely extract the TMT from cellular compartment.Liquid-liquid extraction using acetate buffer and chloroform was ideal for rat homogenates because both the aqueous and organic phases could be easily separated. The use of the easily removable chloroform, which is well-known to dissolve lipophilic molecules (alcanes, cycloalcanes), allowed a reduction of the endogenous lipophilic fraction [16]. Furthermore, this purification step did not reduce the TMT recovery since its solubility in chloroform is very low (< 0.1 g ml −1 ).…”