Several fruit juices and alcoholic beverages (red wine, white wine, apple cider) were treated with different alkaline solutions to examine the best conditions for sulfite liberation. The liquids were diluted 1:100 (v/v) with either carbonate buffer (pH 9.1 and pH 10.6), sodium hydroxide solution (pH 10.3) or with a mixture of 90% carbonate buffer (pH 10.6) and 10% NaOH (1 mol/L). After dilution, the mixture was injected into HPLC–IMER seven times within 11 h to monitor the changes in recovery over time. Each sample was analyzed in quintuplicates.
In a second experiment, two parts of sodium hydroxide solution (View the MathML sourcec=1mol/L) were added to one part of the sample, and 22 parts of carbonate buffer (B) were added after different waiting periods, immediately prior to injection. Sulfite peak areas of the chromatograms were compared to determine the minimum reaction time for maximum sulfite recovery.
All sample preparation was carried out by the autosampler. Thus, it was possible to execute experiments over long periods of time without interruptions and with very high reproducibility.