RESUMO
The thick film semiconductor sensor for NO(2) gas detection was fabricated by screen-printing method using a mixed WO(3)-based as sensing material. The sensing characteristics, such as response time, response linearity, sensitivity, working range, cross sensitivity, and long-term stability were further studied by using a WO(3)-based mixed with different metal oxides (SnO(2), TiO(2) and In(2)O(3)) and doped with noble metals (Au, Pd and Pt) as sensing materials was observed. The highest sensitivity for low concentrations (<16 mg l(-1)) was observed using WO(3)-based mixed with In(2)O(3) or TiO(2). The NO(2) gas sensor showing the fastest response and recovery time (both within 2 min), good linearity (Y=0.606X+0.788 R(2)=0.991) for gas concentrations from 3 to 310 mg l(-1), low resistance (3 MOmega), high sensitivity, undesirable cross sensitivity effect and good long-term stability (at least 120 days) using WO(3)-SnO(2)-Au as sensing material.
RESUMO
A solid-phase microextraction method coupled with a flame photometric detector was developed for the analysis of organophosphorus pesticides in water. Two kinds of fiber (100 mum polydimethyl siloxane (PDMS) and 85 mum polyacrylate (PA) fibers) were used and compared. Parameters that may affect the extraction, such as the duration of absorption and desorption, temperature of absorption, ionic strength, elutropic strength, and concentration of humic acid were investigated. Higher sensitivity and lower detection limits were achieved using a PA fiber than using a PDMS fiber. The detection limit is less than 0.3 mug l(-1) for most of the analytes, except for mevinphos (420 mug l(-1)). The precision is better than 9%.
