A low-pressure liquid chromatography system for the on-line quantification of caffeine loaded into lipid nanoparticles that permeates pig skin was developed. The apparatus includes a Franz diffusion cell with computer-controlled sampling that allows collection of acceptor solution with automatic compensation for sample withdrawing, and a C-18 reversed-phase monolithic column integrated in a typical Flow Injection Analysis (FIA) set-up where separation between caffeine and other matrix elements is performed before spectrophotometric quantification at 273 nm. Several parameters regarding chromatographic analysis (propulsion element, column length, mobile phase composition, and flow rate) were studied along with the establishment of the sampling procedure. Under the selected conditions (monolithic column Chromolith® RP-18 15 mm × 4.6 mm i.d., acetonitrile:water 10:90 (v/v), flow rate 0.45 mL min(-1)) a detection limit of 4 μM and RSD values for caffeine concentration <2% were achieved. High recovery values were obtained when Hepes buffer incubated as acceptor solution in presence of pig skin for 8 h was spiked with caffeine (103±5%). The developed system also accounts for low organic solvent consumption, low operating costs, low generation of waste and high sample throughput (24 h(-1)). Due to the real time automated sampling and high throughput, transdermal permeation profiles of nanoformulations can be established within a time frame seldom observed by conventional techniques.

Department of Analytical Chemistry Faculty of Pharmacy in Hradec Kralove Charles University Prague Czech Republic

UCIBIO REQUIMTE Departamento de Ciências Químicas Faculdade de Farmácia Universidade do Porto Rua de Jorge Viterbo Ferreira 228 4050 313 Porto Portugal

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