Abstract: An automated flow system for the determination of vitamins A, D3 and E in butter and margarine was constructed by coupling a sample treatment system (alkaline hydrolysis and SPE) with LC. A sample stream containing 2 g of butter or margarine in 25 mL of 3% Triton X-100 was merged with an alcoholic NaOH reagent stream (reagent details given) and the mixture was passed through a reactor coil (RC; 5 m x 0.05 mm i.d.). The flow from the RC was merged with 2.2 M acetic acid and passed through the Sep-Pak plus C18 SPE cartridge at 1 ml/min for 6 min. The cartridge was washed with water/methanol (3:2) for 4.5 min and then the retained analytes were eluted (1 ml/min) with methanol through a 100 µL injection loop. After 4 min the contents of the loop was injected into the LC system. The chromatography was performed on a 5 µm OD-224 RP18 column (22 cm x 4.6 mm i.d.) with a 7 µm RP18 pre-column (1.5 cm x 3.2 mm i.d.) with 2.5 mM acetic acid/sodium acetate in methanol/water (99:1) as the mobile phase (1 ml/min) and electrochemical detection at at 1.3 V vs. Ag/AgCl. Linear calibration graphs were obtained and the detection limits were 0.035, 1.8 and 0.31 µM for vitamins A, D3 and E, respectively. The day-to-day RSD (n = 10) of the method was 2.4-5.8%. Results were in agreement with those obtained by classical methods.

Abstract: An automated sample treatment and analysis system for the determination of vitamins A, E and cholecalciferol in both powdered and liquid milk is described. Powdered milk (0.5-2 g) was dissolved in 25 mL water and liquid milk was diluted with water to 30%. The samples were hydrolyzed using a two-channel system in a coiled PTFE tubing reactor (5 m x 0.5 mm i.d.) using 60% aqueous NaOH/10% ascorbic acid/ethanol (3:1:10). A third channel containing 2.5 M acetic acid was used to neutralize the solution before pre-concentration on a Sep-Pak C18 cartridge for 5 min. The cartridge was washed with H2O/methanol (3:2) for 4 min. The vitamins were eluted with methanol into a 100 µL injection loop, then analyzed on a 5 µm Brownlee OD-224 RP-18 column (22 cm x 3.2 mm i.d.) with a 7 µm RP18 guard column (1.5 cm x 3.2 mm i.d.), 2.5 mM acetic acid/sodium acetate buffer in aqueous 99% methanol as mobile phase (1 ml/min), UV detection at 280 nm and electrochemical detection at 1.3 V. Recoveries (n = 10) were 80-105% and day-to-day RSD (n = 10) were 1.2-6.8%.

Abstract: A prototype automated system involving continuous-flow analysis and high performance liquid chromatography (CFA/ HPLC) has been developed for the analysis of fat-soluble vitamins in individual pharmaceutical tablets. The novel features are the front-end coupling of CFA to HPLC, injection of hexane solutions on reversed phase columns, separation/quantitation of vitamins A, D2 and E within single chromatographic runs for a wide variety of tablets, and a dynamic range sufficient to accommodate the 1000-fold higher levels of vitamins A and E over D2 in the same tablets. The analysis rate is 10 samples per hour, the precision better than 6% for all three vitamins, and the recovery is 70-90% of that obtained by the standard AOAC method. Although the system is a prototype, it already greatly outperforms current manual analyzes which are time consuming, tedious, and demanding in terms of the level of skill and experience of the experimenter. Included in this work are some retention comparisons of commercial columns.