Silica Xerogel Doped with Iron(III) as Sensor Material for Salicylhydroxamic Acid Determination in Urine

Salicylhydroxamic acid (SHA) is used as antimicrobic medicine and its concentration has to be monitored in urine. For the first time, silica xerogels doped with iron(III) have been proposed as sensor materials for SHA determination in biological samples. Three xerogels with iron(III) content in the range of 0.04-1.74% wt have been synthesized. BET surface area of these xerogels has varied in the range of 696-529 m²/g and total pore volume has varied in the range of 0.92-0.23 cm³/g. Complex formation between immobilized iron(III) and salicylhydroxamic acid has been investigated with solid phase spectrophotometry and IR spectroscopy. Orange-brown iron(III)-SHA complex with 1:1 stoichiometry is formed at pH 1-4 with half-reaction time of 17 min. Silica xerogel doped with 0.33% wt iron(III)) has been used as sensor material for SHA solid phase spectrophotometric determination (LOD 1.4 mg/L (n = 3), analytical range 4-230 mg/L). Proposed sensor material has been applied for SHA determination in biological samples of synthetic and human urine. The proposed procedure is characterized by a good level of accuracy (recovery values 97-120%) and precision (RSD values 4-9%) and can be recommended for pharmacokinetic-pharmacodynamic studies of hydroxamic acid-based medications.