The wine is ashed at oC in presence of an excess of soda lime. A solution of the residue at pH 4. Spectrophotometer capable of measuring absorbance at wavelengths between and nm. Calcium hydroxide suspension containing g of CaO per liter. Phenolsulfonephthalein solution:. Oxidizing solution:. Storage: two weeks at 4 oC. Reducing solution:. Potassium bromide solution corresponding to 1 g of bromide per liter. How to obtain ash and ash solution.
Place 50 mL of wine in a silica dish of 7 cm diameter, add 0. Check that the pH is at least pH Leave the dish covered with a watch glass for 24 hours. Evaporate the liquid until dry on a boiling water bath. To accelerate the evaporation, a hot air current can be used in the final stages. Ash as follows: place the dish 30 minutes in a furnace 2. After cooling, mix the residue with a little distilled water.
Evaporate on the boiling water-bath. Mix the residue with 5 mL boiling distilled water. Add Crush the precipitated calcium sulfate with a glass rod. Transfer the content of the dish to a centrifugation tube. Centrifuge for 10 min. Place 8 to 9 mL of the clear supernatant into a test tube. Qualitative test. If the coloration obtained is yellow, brownish yellow or greenish yellow, the ash solution can be used undiluted.
Quantitative method. Measure using a spectrophotometer set at nm with a 1 cm cell, the difference in absorbance between the sample and the blank obtained by adding the same quantities of reagents to 5 mL of distilled water. Note: When the bromide content is low yellow coloration, slightly greenish determine the absorbance in a cell of 2 cm optical path.
Preparation of the calibration curve. In a set of 8 test tubes, place 0. The solutions are equivalent to 0. Continue as in 4. Determine the absorbance of these solutions and a blank, as in 4. The absorbance obtained corresponding to the bromide concentration is plotted on a line that curves slightly towards the origin. The bromide content in wine is obtained by plotting on the calibration curve, the net absorbance of the ash solution taking into account the thickness of the cell used and any dilution of the ash solution and interpolating the bromide concentration.
