Carbon Dioxide in Wines - Denver Instrument

Carbon Dioxide in WinesIntroductionCarbon dioxide (CO 2 ) is generally present in wines. Thisis due to fermentation and the use of CO 2 for transferoperations during winemaking. The principle is to makethe sample strongly alkaline, by adding concentratedsodium hydroxide solution that converts all the CO2into CO 32- and titrating with 0.1M hydrochloric acid.PrincipleAs the wine made strongly alkaline (pH10-12) containsonly CO 32-, the titration occurs in two stepsCO 2- 3 + H+ HCO -3(end point at pH 8.6)HCO 3- + H+ CO2 + H 2 O(end point at pH 4.0)The end point titration is then performed with twosuccessive end points (pH 8.6 and pH 4.0) and thetitrant volume delivered from pH 8.6 to pH 4.0 is usedto quantify theCO 2 level in the wine in g/l. The molarweight of CO2 is 44.0 g/mol.A blank titration run with the same, but degassed, wineis necessary.Electrode and ReagentspHC2401-8 Combined pH Electrode(part no. E16M400)HCl 0.1 mol/l solution in distilledwater (see ApplicationNoteTTEP01-01MIN)This solution is also commerciallyavailable.NaOH 50% w/v in distilled waterDilution of 50 g of NaOH pellets in 100 ml of freshlyboiled distilled water is highly exothermic. The solutionis also very caustic for the skin and eyes. Observelaboratory safety regulations.Distilled waterIn order to have a reproducibleblank result, use freshlyboiled, distilled water which has been cooled to roomtemperature.IUPAC Series pH standardspH 4.005 (part no. S11M002) and pH 10.012 (part no.S11M007)End Point Titration SettingsBurette volume:25 mlStirring speed:500 rpmWorking mode:pHBlank:YES (see notes)Predose:0 ml (see notes)Stirring delay:10 secondsMaximum volume:40 mlMinimum speed:0.2 ml/minMaximum speed:10 ml/minDirection:Decreasing pHNumber of end points: 2End point 1:8.6 pHProportional band:2.0 pHEnd point delay:5 secondsEnd point 2:4.0 pHProportional band:2.0 pHEnd point delay:5 secondsSample unit:mlDilution:YESSample amount: 100Final dilution amount: 102 (see notes)Aliquot: 10ResultNo of results: 1Result by:differenceCalculate with EP: 2Result unit:g/lMolar weight:44.0 g/molReaction:1 smp + 1 titrProcedureCalibrate the combined pH electrode.Let the wine coolto 5°CBlank preparationDegassing a wine sample. Pour the wine into aBuchner flask and connect it to a vacuum system for 3minutes.Degassing is also possible by heating the wine andboiling for few seconds only. Then allow the wine tocool to room temperature. Pipette 100 ml of thisdegassed wine; add 2 ml or more of the NaOH 50%solution as accurately as possible. Make sure that thepH of this solution is around pH 10-12. Pipette 10 ml ofthis solution. Add the necessary volume of distilledwater; dip electrode and delivery tip in the solution.Run a blank titration. You can run more than one teston the blank; in this case the Titration Manager takes

into account the mean value.Sample preparationTaking care not to lose carbon dioxide, take 100 ml ofthe wine at 5°C using a measuring tube. Pour it in aconical flask, add the same volume of the NaOH 50%solution as for the blank, seal the flask and mixthoroughly. To avoid losing carbon dioxide, ensure thatthe flasks handling the sample are always at lowtemperature (near 0°C). Use an ice bath or refrigerator.Make sure that the pH of this solution is around pH 10-12. Pipette 10 ml of this solution. Add the necessaryvolume of distilled water, dip electrode and delivery tipin the solution. Run the titration.ResultsExpressed as g/l of CO2 (molar weight of CO 2 = 44g/mol)RCO2 = (Vtitr - Vblk) * Ctitr * 44 / VsmpVtitr = Delivered titrant volume between pH 8.6 and pH4.00 for sampleVblk = Delivered titrant volume between pH 8.6 and pH4.00 for blankCtitr = Titrant concentration in mol/l (generally 0.1)Vsmp = Sample volume (generally 10 ml)The above-mentioned END POINT SETTINGS take inaccount:- the blank calculation,- the dilution factor due to the addition of 2 ml ofNaOH 50% solution.Result on red wineNo carbon dioxide measuredVerification of the method by addition of Na 2 CO 3directly in the sample beaker before titration with thesame wine.Na2CO3 added in mg Vtitr - Vblk24 2.57 ml45 4.5 ml61 6.08 mlAs indicated in this table the method allows the addedNa 2 CO 3 be measured with a recovery ratio close to98%.Results on sparkling white wineSample dilution settings for this wineSample amount:50 mlFinal dilution amount: 52 mlAliquot:10 mlBlank on degassed wine5.37 ml of titrant (mean on 3 determinations)Results (3 determinations)Mean:Standard deviation:6.83 g/l CO20.02 g/l CO2Working RangeAccording to the formula mentioned under "Results":1 ml for (Vtitr - Vblk) corresponds to 0.44 g/l of CO2Note that this result is calculated for 10 ml of sampleand does not take into account the dilution factor dueto addition of NaOH 50% solution.NotesNote regarding the "blank"As the behaviour of every wine is different, it isnecessary to run a blank titration for every differenttype of wine.As the blank titration depends on the composition ofthe studied wine, do not forget to use the same sampleamount of wine and dilution settings for the blankdetermination and for the sample.Note regarding the "predose"To save time it is possible to use the "predose"function of the Titration Manager.Bear in mind that the "predose" volume of titrant iseffective during sample titration and also "blanktitration.Note that using "predose" can eliminate the first endpoint.Note regarding the final amount dilutionThis amount is the sum of the volume sample(generally 100 ml) and the volume of the NaOH 50%solution added (in this application note 2 ml).The volume of the NaOH 50% can change according tothe wine.Note regarding the resultAs the method itself offers good reproducibility, theaccuracy of the result depends on the handling ofthe non-degassed sample. It is important to avoidlosing carbon dioxide especially with sparkling wines.Ensure that a sufficient volume of NaOH 50% solutionis added.CurvesBlank

Sample: sparkling wineBibliographyTechniques for chemical analysis and qualitymonitoring during winemakingEd: Patrick ILAND wine promotionCampbelltown AUSTRALIA