Određivanje sadržaja fluorida u vodi za piće i čajevima fluorid-selektivnom elektrodom

Potentiometric analysis of fluoride content (as F- ion) in solutions by using fluoride ion-selective electrode is simple, reliable and cheap. Very small concentrations of fluoride-ions (to 10-6 mol/dm3) can be determined by fluoride selective electrode, with regulation of ion strength of a solution and control of concentration of hydroxide ions and interfering ions of metals. The influence of pH and complexing ions of metals can be successfully regulated by the TISAB solution and by preserving pH value in the range from 5.00 to 7.00. The content of fluorides in the samples can be determined by the method of direct potentiometer, and in the case of very low concentration by standard addition method. In this paper it was analyzed the determination of fluoride ions concentration in bottled mineral waters and water from Belgrade plumbing in two Belgrade districts (Palilula and Novi Beograd) and in tea, by using the fluoride selective electrode. It was determined that the content of fluoride ions in bottled mineral water significantly differs from values given on declaration, and that content of fluoride ions varies over a period of time. The content of fluoride ions in water from plumbing in two Belgrade districts at the time of analysis was significantly increased and exceeded values given in Regulation for drinking water quality. The received results from the analysis of fluorides in teas show that fluorides exist in teas in different concentrations. There are also differences between the same kinds of tea, which is noted with mint (Mentha piperitae folium), as a consequence of differences between soils where it was planted. As taking of fluorides, according to World Health Organisation recommendation (WHO), is limited in the range from 2 to 4 mg per day, it is necessary to give the content of fluorides on all products that are used in human consumption.Potenciometrijsko određivanje sadržaja fluorida (kao F-jon) u rastvorima upotrebom fluoridne jon-selektivne elektrode je jednostavno, pouzdano i jeftino. Fluorid-selektivnom elektrodom mogu se odrediti veoma niske koncentracije fluorid-jona (do 10-6 mol/dm3), uz regulisanje jonske jačine rastvora i kontrolisanje koncentracije hidroksid-jona i interferirajućih jona metala. Uticaj pH i kompleksirajućih jona metala može se uspešno regulisati rastvorom TISABa i održavanjem pH vrednosti u oblasti od 5,00 do 7,00. Sadržaj fluorida u uzorcima može se odrediti metodom direktne potenciometrije, a u slučaju veoma niskih koncentracije, metodom standardnog dodatka. U radu je vršeno određivanje koncentracije F--jona u flaširanim mineralnim vodama ('Vujić voda', 'Rosa', 'Duboka', 'Voda-voda', 'Aqua viva', 'Knjaz Miloš') i vodi iz beogradskog vodovoda sa dve beogradske opštine (Palilula i Novi Beograd) i u čajevima (Divlja nana (Mentha piperitae folium), Čaj od žalfije (Salviae officinalis), Čaj od kantariona (Hypericum perforatum), 'Domaća nana' (Mentha piperita L.), Čaj od kamilice (Chamomillae flos)), upotrebom fluorid-selektivne elektrode. Uočeno je da sadržaj fluorid-jona u flaširanim mineralnim vodama znatno odstupa od vrednosti koje su date na deklaraciji, ali i da sadržaj fluorid-jona varira tokom vremena. Sadržaj fluorid-jona u vodi iz vodovoda sa dve beogradske opštine, u vreme analiziranja je znatno povećan i premašuje vrednosti propisane Pravilnikom o kvalitetu vode za piće. Dobijeni rezultati ispitivanja fluorida u čajevima ukazuju da se fluoridi nalaze u čajevima u različitim koncentracijama. Do razlike dolazi i među istim vrstama čaja, što je zabeleženo kod nane (Mentha piperitae folium), što je posledica pre svega zemljišta na kojem je nana uzgajana. Kako je, saglasno preporukama Svetske zdravstvene organizacije (SZO), unošenje fluorida limitirano u opsegu 2 do 4 mg dnevno, na svim proizvodima koji se koriste u humanoj upotrebi potrebno je navesti i sadržaj fluorida