A HEPES/CHES buffer according to Wilson and Horne (Wilson &
Horne, 1984) was used for diluting FA stock solutions and juice
samples. Stock solutions of the FA standard and the IS (2 mg/ml)
were prepared in an aqueous solution of NaOH (0.1 mol/l). These
solutions were diluted with HEPES/CHES buffer and stored in small
portions at 80 C until use. The working solution of the IS was
1 lg/ml, various concentration of the FA standard were prepared
by appropriate dilution with the HEPES/CHES buffer.