Silica-titania xerogel doped with Mo,P-heteropoly compounds for solid phase spectrophotometric determination of ascorbic acid in fruit juices, pharmaceuticals, and synthetic urine

Abstract

BackgroundAscorbic acid is one of the most important vitamins to monitor in dietary sources (juices and vitamins) and biological liquids.ResultsSilica and silica-titania xerogels doped with Mo,P-heteropoly compounds (HPC) have been synthesized varying titanium(IV) and HPC content in sol. Their surface area and porosity have been studied with nitrogen adsorption and scanning electron microscopy, their elemental composition has been studied with energy-dispersive X-ray analysis. The redox properties of the sensor material with sufficient porosity and maximal HPC content have been studied with potentiometry and solid phase spectrophotometry and it has been used for solid phase spectrophotometric determination of ascorbic acid. The proposed method is characterized by good selectivity, simple probe pretreatment and broad analytical range (2–200 mg/L, LOD 0.7 mg/L) and has been applied to the analysis of fruit juices, vitamin tablets, and synthetic urine.ConclusionsNew sensor material has been used for simple and selective solid phase spectrophotometric procedure of ascorbic acid determination in fruit juices, vitamin tablets, and synthetic urine.Graphical abstractWe synthesized several silica-titania xerogels doped with Mo,P-heteropoly compounds, studied their properties, and designed the sensor material for solid phase spectrophotometric determination of ascorbic acid in fruit juices, pharmaceuticals, and synthetic urine.

Silica and Silica–Titania Xerogels Doped with Iron(III) for Total Antioxidant Capacity Determination

“…Gallic acid and ascorbic acid determination procedures were chosen for this comparison because they are some of the most popular model antioxidants. LOD values are similar to our previous results [21,29] and comparable with other solid phase spectroscopic procedures. Time of analysis and sensor material stability are important for on-site analytical applications.…”

“…For SiTi12.5Fe100 xerogel, Si:Ti:Fe ratio in atomic % was measured as 100.0:12.8:5.3 by EDX analysis, while the ratio calculated by the molar amounts added to the sol is 100.0:12.8:7.7. The Si:Ti ratio agrees well with the expected values which we had observed for our silica-titania xerogels before [29]. We believe the difference in the amount of iron can be explained by the fact that EDX analysis measures the elemental composition of the surface of the xerogel particles.…”

“…The micropore area, on the contrary, increased. The same effect was described earlier for silica-titania xerogels [29,30]. It means that iron(III) in the sol mixture did not substantially influence the gelation process.…”

“…The time of reaching the equilibrium (when the absorbance of the xerogel stopped increasing) depended on the titanium(IV) content (Table 2). Titanium(IV) incorporated in the matrix of the xerogel accelerated the reduction of iron(III) similarly to heteropoly compounds reduction [29]. Selected conditions were used for sensor materials preparation.…”

“…The time of reaching the equilibrium (when the absorbance of the xerogel stopped increasing) depended on the titanium(IV) content (Table 2). Titanium(IV) incorporated in the matrix of the xerogel accelerated the reduction of iron(III) similarly to heteropoly compounds reduction [29]. The interaction of all the modified xerogels (SiFe/Phen, SiTi5Fe/Phen, and SiTi12.5Fe/ Phen) with different antioxidants was studied in the 1.0 × 10 −5 M-1.0 × 10 −2 M range and the calibration curve slopes were determined (Table 2).…”