The method of analysis used in a practical is determined by the concentration of the species being analysed. The relatively high level of tartaric acid in grapes allows it to be determined by direct titration, while the lower concentration of the preservative sulfur dioxide employs a back titration (where the concentration is determined from the difference between the sample and a blank titration). The analysis of species present at trace levels requires a much more sensitive technique, such as colorimetry (which we will look at in a future ‘Lab page’). For these examples we used the wine Marquis de la Ligne Bordeaux Blanc, but the analyses will work equally well with any white wine. Before commencing any lab work, make sure that you carry out a risk assessment (Box 1).
■ Do not conduct practical work unless you are being supervised.
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