Water used for all solutions was obtained from a Milli-Q
water purification system (Millipore; Bedford, MA). Stock solutions
of L-ascorbic acid were prepared daily in acidified Milli-Q water
(0.1% v/v formic acid) and stored in amber flasks at 4 C prior to
chromatographic analysis. Working standard solutions were prepared by dilution.
2.2. Samples
Seventeen samples from different manufacturers, including: orange juice, apple juice, grape and pineapple juice, orange drink, lemon drink, apple drink, tea drink, isotonic drink and isotonic
drink with orange and cola flavour were purchased in local supermarkets.
The samples were analysed directly, filtered and diluted when necessary, in order to keep the concentration within the calibration range.
Each sample was analysed in duplicate. Once the samples were analysed they were stored in a refrigerator.