Abstract: Biological fluids were deproteinized and I was adjusted before centrifugal filtration (Amicon Centrifree filter; 20 min). The filtrate was analyzed for amino-acids by HPLC on a column (15 cm x 3 mm) of cation-exchange resin (7 µm; Li+ form) at 45°C with Li citrate buffers (pH 2.75 and 7.5) as gradient eluents (0.3 mL min-1), post-column derivatization with phthalaldehyde and fluorescence detection at 425 nm (excitation at 334 nm). Iohexol and trometamol were eluted near or on the tyrosine peak, phenylpropanolamine was co-eluted with tyramine in the following chromatogram and amikacin gave a post-arginine peak which carried over on to the subsequent 2 to 3 chromatograms.

Abstract: A 2-g sample (yogurt, cheese or infant formula) was homogenized with ~40 mL of methanol, the homogenate was heated at 60°C for 15 min and the cooled product was diluted to 50 mL with methanol. A 20 µL portion of the filtered solution was analyzed by HPLC on a radially compressed column of Nova-Pak C18 (5 µm) equipped with a guard column of µBondapak C18/Corasil (37 to 50 µm). The mobile phase (1.5 mL min-1) was methanol - 0.05 M Na2HPO4 (3:17) containing heptanesulfonic acid as counter-ion, adjusted to pH 3.0 with 6 M H3PO4. Post-column derivatization was effected with phthalaldehyde and the products were detected by fluorimetry at 425 nm (excitation at 338 nm). The calibration graph for 20 to 400 ng of tyramine was rectilinear. Average recoveries (and coefficient of variation) were 95.3% (9%) for infant formula, 102% (1.6%) for yogurt and 95.2% (8.4%) for cheese.