Determination of fluoride content in drinking water and tea infusions using fluoride ion selective electrode

Abstract

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 odredjivanje sadrzaja 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 jacine rastvora i kontrolisanje koncentracije hidroksid-jona i interferirajucih jona metala. Uticaj pH i kompleksirajucih jona metala moze se uspesno regulisati rastvorom TISABa i odrzavanjem pH vrednosti u oblasti od 5,00 do 7,00. Sadrzaj fluorida u uzorcima moze se odrediti metodom direktne potenciometrije, a u slucaju veoma niskih koncentracije, metodom standardnog dodatka. U radu je vrseno odredjivanje koncentracije F--jona u flasiranim mineralnim vodama ('Vujic voda', 'Rosa', 'Duboka', 'Voda-voda', 'Aqua viva', 'Knjaz Milos') i vodi iz beogradskog vodovoda sa dve beogradske opstine (Palilula i Novi Beograd) i u cajevima (Divlja nana (Mentha piperitae folium), Caj od zalfije (Salviae officinalis), Caj od kantariona (Hypericum perforatum), 'Domaca nana' (Mentha piperita L.), Caj od kamilice (Chamomillae flos)), upotrebom fluorid-selektivne elektrode. Uoceno je da sadrzaj fluorid-jona u flasiranim mineralnim vodama znatno odstupa od vrednosti koje su date na deklaraciji, ali i da sadrzaj fluorid-jona varira tokom vremena. Sadrzaj fluorid-jona u vodi iz vodovoda sa dve beogradske opstine, u vreme analiziranja je znatno povecan i premasuje vrednosti propisane Pravilnikom o kvalitetu vode za pice. Dobijeni rezultati ispitivanja fluorida u cajevima ukazuju da se fluoridi nalaze u cajevima u razlicitim koncentracijama. Do razlike dolazi i medju istim vrstama caja, sto je zabelezeno kod nane (Mentha piperitae folium), sto je posledica pre svega zemljista na kojem je nana uzgajana. Kako je, saglasno preporukama Svetske zdravstvene organizacije (SZO), unosenje fluorida limitirano u opsegu 2 do 4 mg dnevno, na svim proizvodima koji se koriste u humanoj upotrebi potrebno je navesti i sadrzaj fluorida.