A simple and automated HPLC column-switching method has with rapid sample pretreatmentbeen
developed for quantitative determination of b-carotene in food supplements. Commercially samples of
food supplements were dissolved in chloroform with help of saponification with 1 M solution of sodium
hydroxide in ultrasound bath. A 20-min sample dissolution/extraction step was necessary before chromatography
analysis to transfer b-carotene from solid state of food supplements preparations (capsules,
tablets) to chloroform solution. Sample volume – 3 lL of chloroform phase was directly injected
into the HPLC system. Next on-line sample clean-up was achieved on the pretreatment precolumn Chromolith
Guard Cartridge RP-18e (Merck), 10 4.6 mm, with a washing mobile phase (methanol:water,
92:8, (v/v)) at a flow rate of 1.5 mL/min. Valve switch to analytical column was set at 2.5 min in a
back-flush mode. After column switching to the analytical column Ascentis Express C-18, 30 4.6 mm,
particle size 2.7 lm (Sigma Aldrich), the separation and determination of b-carotene in food supplements
was performed using a mobile phase consisting of 100% methanol, column temperature at 60 C and flow
rate 1.5 mL/min. The detector was set at 450 nm. Under the optimum chromatographic conditions standard
calibration curve was measured with good linearity – correlation coefficient for b-carotene
(r2 = 0.999014; n = 6) between the peak areas and concentration of b-carotene 20–200 lg/mL. Accuracy
of the method defined as a mean recovery was in the range 96.66–102.40%. The intraday method precision
was satisfactory at three concentration levels 20, 125 and 200 lg/mL and relative standard deviations
were in the range 0.90–1.02%. The chromatography method has shown high sample throughput
during column-switching pretreatment process and analysis in one step in short time (6 min) of the
whole chromatographic analysis.