Methods: A tissue equivalent material, ferrous benzoic xylenol orange gel, was prepared using gelatine, ferrous ammonium sulfate, sulfuric acid, xylenol orange tetrasodium salt and benzoic acid.
In our experiment, ferrous benzoic xylenol orange (FBX) gel was prepared using gelatine (from bovine skin, Type B), ferrous ammonium sulfate (Aldrich ammonium iron (II) sulfate hexahydrate, 99% American Chemical Society (ACS) reagent), sulfuric acid (Sigma-Aldrich), xylenol orange tetrasodium salt (Sigma-Aldrich) and benzoic acid (Sigma-Aldrich) formulated in 1998 by Kelly RG16 and others.13,14
Upon complettion of (1), add 25ml of ferrous ammonium sulfate (0.4N) and allow to stand one minute.
Run a blank titration on25 ml of the ferrous ammonium sulfate solution, as used above, in 50ml of water and 5ml of 25% sulfuric acid.
Ferrous ammonium sulfate
solution (FAS) then is added drop by drop until the pink color completely and permanently disappears, signaling the endpoint of the reaction.
Solution 1 (Maleic acid) Maleic acid 25 g Distilled water 1000 mL Solution 2 (Redox) Ferric nitrate 30 g Ferrous ammonium sulfate
80 g Citric acid 20 g Distilled water 1000 mL Solution 3 (Detergent) n-Dodecylamine acetate 3 g Synperonic-N 4 g Distilled water 1000 mL Solution 4 (Silver nitrate) Silver nitrate 200 g Distilled water 1000 mL Processing Procedure
In the assay without digestion, the addition of potassium thiocyanate ( [greater than or equal to] 0.1 mmol/ L), ascorbic acid ( [greater than or equal to] 4 mmol/L), or ferrous ammonium sulfate ( [greater than or equal to] 16 mmol/L) significantly increased the estimated concentration of iodine in the iodate solution.
Regarding interference, ascorbic acid, potassium thiocyanate, and ferrous ammonium sulfate in concentrations up to 16 mmol/L did not affect the Sandell-Kolthoff reaction after digestion in our study, which is consistent with a previous report by Pino et al.