Total ionic solubility acid buffer

Fluoride release is most frequently determined using an ion-selective electrode. Because such electrodes are incapable of detecting complexed fluoride, a decomplexing agent is generally added to the mixture prior to analysis. This frees up fluoride from most complexes as the F ion, and the total quantity of fluoride released can then be determined by the ion-selective electrode. The usual complexing agent is TISAB (total ionic solubility acid buffer) [250]. 

Release of fluoride under acidic conditions is associated with the occurrence of fluoride in complexed form. Under acidic conditions, aluminium ions are released in greater quantities than under neutral conditions, and it may be that the fluoride becomes complexed as species such as AIF " [104]. There is also the possibility of the formation of the complex HF " with protons from the acid or, indeed, of forming undissociated HF [105]. None of the possible complexes of fluoride (nor undissociated HF) yields free fluoride ions, so they are not detectable with fluoride-ion selective electrodes. Instead, fluoride must be decomplexed and released as F ions by the addition of total ionic solubility acid buffer. 

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