Potenciometric and biamperometric determination of sulphur dioxide in wine

Jedan od bitnih tehnoloških parametara i parametar kakvoće vina čije je praćenje definirano zakonskim propisima jest sadržaj SO2 u vinu. S obzirom na važnost praćenja tog parametra, predložene su brojne metode za analizu SO2 u vinu. U praksi se zbog svoje brzine i jednostavnosti najčešće primijenjuje jodometrijska titracija SO2 uz vizualno određivanje završne točke titracije uz škrob kao indikator, tzv. Ripperova metoda. Jedan od glavnih nedostataka te metode je otežana detekcija završne točke titracije kod titracije jako obojenih, crnih vina. U ovom radu istražene su dvije alternativne metode određivanja završne točke titracije – potenciometrijska i biamperometrijska detekcija završne točke. Te su metode naročito prikladne za automatizaciju analize uz uporabu automatskog titracijskog uređaja (titratora), a njihovom se primjenom izbjegava vizualna detekcija završne točke. Ispitan je utjecaj sastava uzorka i parametara titracije, kao što su brzina titracije, inicijalno dodani volumen titranta i jakost struje kod biamperometrijskih titracija, na točnost titracije i oblik titracijske krivulje. Ustanovljeno je da su pogreške u titraciji minimalne ako se u uzorak inicijalno doda volumen titranta za 1–2 cm3 manji od ekvivalentnog volumena, te ako se titracija provodi brzinom od 0,5 cm3/min. Kod biamperometrijskih titracija ustanovljeno je da se točne vrijednosti sadržaja SO2 u uzorku dobivaju uz narinutu struju manju ili jednaku 200 nA. Rezultati analize SO2 u vinu dobiveni pomoću obje metode slažu se s rezultatima dobivenim klasičnom, Ripperovom metodom. U usporedbi s potenciometrijskom titracijom, biamperometrijska titracija pokazuje bolju reproducibilnost i daje bolje definirane titracijske krivulje pa je treba preferirati.One of the most important technological parameters and quality parameter of wine, the monitoring of which is defined by governmental regulation, is content of SO2 in wine. Due to the great importance of this parameter, numerous methods were proposed for the determination of SO2 in wine. Because of its simplicity and the speed of the analysis, the method most frequently employed in practice is the Ripper method, based on iodometric titration of SO2 with visual determination of the titration end-point using starch as an indicator. One of the main disadvantages of this method is difficult detection of the titration end-point in the case of SO2 determination in highly coloured, red wines. In this work, two alternative methods for determination of titration end-point – potenciometric and biamperometric detection – were explored. These methods are particularly suitable for the automatization of analysis using automated titration device (titrator) and they allow the drawbacks associated with visual end-point detection to be avoided. The influence of the sample composition and titration parameters, such as the speed of titration, initial volume of added titrant, and current applied in the biamperometric titration, on the accuracy of titration and the shape of titration curves, has been examined. It was found that the titration errors are minimal if the volume of titrant about 1–2 cm3 smaller than the volume needed to reach the equivalence point is initially added to the titrated sample and if the titration is conducted with the titrant dosing rate equal to 0.5 cm3/min. For biamperometric end-point detection, it was shown that the correct value of the SO2 content in the sample can be obtained only if the current applied to the electrodes is less than or equal to 200 nA. The results of SO2 determination in wine samples obtained by both the potentiometric and amperometric method are in good agreement with the results obtained by commonly employed Ripper method. In comparison to the potenciometric titration, the biamperometric titration exhibits better reproducibility and provides better defined titration curves, so it shoud be preferred