Apple juice (50 ml) was adjusted to pH 7.0 and pH 1.5, respectively, and extracted three times with ethyl acetate (50 ml). The combined extracts were evaporated to dryness, and the residue was dissolved in 10 ml of water. The solution was passed through a C solid-phase extraction cartridge which had been preconditioned with methanol and 0.1% HCl, respectively. After washing with water, the analytes were eluted with methanol (5 ml) and used for chromatographic analyses. Alternatively, the combined ethyl acetate extracts were dried over sodium sulfate without using solid-phase extraction cartridges.