Aluminum ions in analysis of released fluoride from glass ionomers

Objectives: Aluminum ions interfere with fluoride determination when an ion-selective electrode (ISE) method is used. This study examined the effect of the presence of aluminum ions on the determination of fluoride ions released from glass ionomers. Methods: Disk-shaped specimens of five different commercial glass ionomers were immersed in deionized distilled water at 37 °C for one day or up to seven weeks. The amounts of released aluminum were determined by atomic absorption spectrophotometry, whereas the released fluoride was quantitated using a fluoride ISE with TISAB plus two different decomplexing agents for aluminum (CDTA or sodium citrate-potassium nitrate) or TISAB only. Results: Released amounts of aluminum and fluoride ions were found to be significantly different among the five different glass ionomers tested. Based on preliminary examination of the effect of the amount of aluminum ions on the measured value of fluoride, it was found at the end of one day for some of the glass ionomers that the fluoride concentrations measured without decomplexing agents were significantly lower than those measured with decomplexing agents, depending on the amounts of aluminum in the solution. However, since all the glass ionomers tested leached out most of the aluminum ions by seven days, the measured fluoride concentrations were not affected by a small amount of released aluminum from the glass ionomers immersed longer than seven days. Conclusions: When fluoride release from the glass ionomer is determined using ISE, care must be taken with the experimental design and analytical procedures to eliminate the interference by aluminum ions.