Development of Tannin Modified Membrane for Spectrophotometric Determination of Lead

Tannin modified membrane (TM) was developed for preconcentration and detection of trace level of lead (Pb) using a complex formation between Pb2+ and (4-2-pyridylazo)-resorcinol (PAR). The extraction membrane was prepared by immobilizing tannin on a rectangular cellulose filter paper sized 7 x 9 cm2 and then cut into a small circular shape of 13-mm diameter to fit with a commercially available syringe filter holder. The 4-layered of the TMs was employed for preconcentration of Pb2+. An aliquot of 50 mL of standard or sample containing Pb2+ was loaded by using a 50-mL syringe that connected with a filter holder. To accelerate speed of analysis, peristaltic pump was used by connecting to a bottom side of the filter holder. For loading step, a flow rate of 4.4 mL/min was used. Elution of Pb2+ was accomplished by manually passing 5 mL of 0.1 M HCl through the membrane. An aliquot of 3 mL of the eluent was then mixed with the PAR reagent under the controlled pH of 9. Absorbance of 522 nm was monitored. Various optimization parameters affecting the immobilization of tannin on the cellulose filter paper were investigated. Under optimized conditions, linear calibration was obtained from 0.1 mg/L to 1.25 mg/L of Pb2+ solution. Acceptable precision of 2.0% (n = 5) was obtained. Good recoveries of 90.40 and 91.99 were achieved for drinking water samples

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 x 2 x 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffe reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm(-1))

Transparent Cross-Flow Platform as Chemiluminescence Detection Cell in Cross Injection Analysis

This work presents the use of a transparent ‘Cross Injection Analysis’ (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. A photomultiplier tube placed above the reaction channel detects the emitted luminescence. The system was applied to the analysis of (i) Co(II) via the Co(II)-catalyzed H2O2-luminol reaction and (ii) paracetamol via its inhibitory effect on the catalytic activity of Fe(CN)63− on the H2O2-luminol reaction. A linear calibration was obtained for Co(II) in the range of 0.002 to 0.025 mg L−1 Co(II) (r2 = 0.9977) for the determination of Co(II) in water samples. The linear calibration obtained for the paracetamol was 10 to 200 mg L−1 (r2 = 0.9906) for the determination of pharmaceutical products. The sample throughput was 60 samples h−1. The precision was ≤4.2% RSD. The consumption of the samples and reagents was ca. 170 µL per analysis cycle

Contactless conductivity detector from printed circuit board for paper-based analytical systems

This work presents a capacitively coupled contactiess conductivity detector ((CD)-D-4) etched out from a printed circuit board (PCB) as potential sensor for paper-based analytical systems. Two lines of any desirable pattern forming 35-mu m thick planar copper electrodes were produced on a PCB plate (40 mm x 60 mm) by photolithography. The final PCB plate was covered with polypropylene film to serve as the insulating layer for the (CD)-D-4 detector. The film also protected the copper electrodes from corrosion. Electrodes made in this planar geometry make the PCB-(CD)-D-4 suitable as sensor for flat devices such as paper-based analytical devices. For this work, plain paper strips were employed as sample reservoir and as fluidic channel without hydrophobic pattern. A dried paper strip was first placed over the sensor, followed by dispensing a fixed volume of the liquid sample onto the paper. Entrapment of the liquid sample in the paper strip leads to reproducible size and position of the detection zone of the sample liquid for the capacitive coupling effect. High precision was obtained with %RSD <= 1% (n = 18) for standard solutions of KCl. Soil suspensions could be analyzed without prior filtration by placing a drop onto the paper strip extending away from the detector zone. The paper strip filtered out soil particles at the surface of the paper. Therefore, only soil filtrate moved towards the detection zone by lateral flow. The (CD)-D-4 detection using paper strip showed high tolerance to soil suspension with turbidity up to 6657 NTU, offering direct analysis of soil salinity. Cleaning with moist tissue paper between samples is adequate even for dirty samples such as soil suspension. We also monitored conductivity of acid-base reaction in the microfluidic paper channels, which was later applied to the quantification of bicarbonate in water and in antacid tablet ("Soda Mint Tablet")