A modified selective optical sensor for selenium determination based on incorporating xylenol orange in a poly(vinyl...

A novel optical sensor has been developed to measure selenium ions. The sensor membrane was created by mixing xylenol orange (XO) and sodium tetraphenylborate (NaTPB) with a plasticized poly(vinyl chloride) membrane that contained o-nitrophenyl octyl ether (o-NPOE) as a plasticizer. XO was previously established for use in a colorimeter to measure selenium in water and other media. At pH 6.6, the color of the detecting membrane changed from orange to pink when in contact with Se⁴⁺ ions. Various variables affecting the uptake efficiency were evaluated and optimized. Under optimum conditions (i.e., 30% PVC, 60% o-NPOE, and 5.0% of both XO and NaTPB for 5.0 min as the response time), the proposed sensor displayed a linear range 10-175 ng mL^-1 with the detection and quantification limits of 3.0 and 10 ng mL^-1, respectively. Also, the precision (RSD%) was better than 2.2% for six replicate determinations of 100 ng mL^-1 Se⁴⁺ in various membranes. For the detection of Se⁴⁺, the selectivity of the sensor membrane was investigated for a number of possible interfering inorganic cations, but no appreciable interference was found. With the use of a 0.3 M HCl solution, the sensor was successfully restored, and the response that may have been reversible and reproducible exhibited an RSD% of less than 2.0%. The sensor has been successfully used to analyze Se⁴⁺ ions in environmental and biological materials.