2012 Volume 61 Issue 3 Pages 229-234
2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) nanoparticle-coated membranes were prepared by simple filtration of an aqueous dispersion of 5-Br-PADAP nanoparticles through a cellulose ester membrane filter (0.45 μm pore). By letting the dispersion stand for 3 min at room temperature for sufficient particle growth, more than 99.92% of the 5-Br-PADAP nanoparticles were coated uniformly and firmly on the membrane filter without any additives. A 5-Br-PADAP thin layer was located within 1 μm from the top surface of the filter. The membranes were cut into 6 pieces, and then test strips were immersed in 20 mL of a sample solution containing CdII and pH buffer (immersion test). The test strip changed color from yellow to reddish-orange based on complex formation with CdII. Stirring increased the reaction rate ; the color formation at 100 ppb was completed in ca. 30 min under stirring in contrast to more than 90 min without stirring. A very low extraction percentage (0.77%) of 700 ppb CdII to the 5-Br-PADAP thin layer was obtained by ICP-MS analysis. A detection curve was obtained using ΔE*(a*,b*) of a colorimeter. The equation is expressed as ΔE*(a*,b*) = 73.677 (1 − e−0.0036283 C) and the 3σ detection limit is 7.14 ppb based on 7 blank measurements. To improve the reaction rate and extraction percentage of an immersion test, a drop test was attempted by dropping 50 μL of a sample solution on the test strips equipped with No.1 filter paper as a water absorber. The extraction percentage by the drop test of 1 ppm CdII was 30.2% for ca. 15 min.
