A solution of TISAB with \(1 \mathrm{M} \mathrm{NaCl}\) is available to treat drinking water samples for fluoride determination using a fluoride ISE and a \(\mathrm{Ag} / \mathrm{AgCl}\) reference electrode in \(3 \mathrm{M} \mathrm{KCl}\). The expected fluoride concentration in these samples is \(1 \mathrm{mg} / 1\). How much TISAB should be used per \(100 \mathrm{ml}\) sample solution to reach a reasonable IS and minimize junction potentials?