Preconcentration and determination of trace silver ion using benzothiazole calix[4]arene modified silica by flow injection flame atomic absorption spectrometry.

The silica gel modified with benzothiazole calix[4]arene (APS-L1) via Schiff's base reaction was applied as a sorbent in an online system for preconcentration and determination of silver ion by flame atomic absorption spectrometry (FAAS). APS-L1 was used as an effective sorbent for solid phase extraction (SPE) of silver(I) ion in both batch and column methods. The optimum experimental parameters such as pH, eluent type, sample flow rate, eluent volume and eluent flow rate including the effect of interfering ions were investigated. Silver(I) ion was determined at pH 6-7. The capacity of APS-L1 sorbent was found to be 12.2 mg/g of sorbent. The high affinity was obtained without interference from the interfering ions. The optimum conditions of the online flow injection preconcentration coupled with the FAAS (FI-FAAS system) were evaluated. The sample flow rate was 3.0 mL min(-1) using sample volume of 5-10 mL. Elution was performed with 250 µL of 0.1 mol L(-1) thiosulfate at the flow rate of 1.5 mL min(-1). The analytical characteristics and performance of the FI-FAAS system were studied under optimum conditions using a solution spiked with standard silver(I) ion at 20 and 50 µg L(-1). The detection limit of 0.44 µg L(-1) was obtained. The accuracy of the proposed method was evaluated and percentages of recovery at 20 and 50 µg L(-1) were 100.2 and 99.5%, respectively. The percent relative standard deviations (%RSD) at 20 and 50 µg L(-1) were 6.1 and 3.3%, respectively. The developed method was successfully applied to determine trace silver(I) ion in drinking and tap water samples.

Single strand hollow fiber membrane (SSHFM): an on-line sample preparation for the flow based colorimetric determination of free iron in fruit juices.

A single strand hollow fiber membrane (SSHFM) was developed for the on-line sample preparation for the flow based colorimetric determination of free iron levels in fruit juices. The SSHFM, as used, could separate Fe(2+) from some spectrophotometric interfering agents in the fruit juice, such as pigments, solid suspensions and polysaccharides. The screening process was likely to have been primarily based on dialysis, wherein only ions or molecules that are smaller than the pores of the membrane can diffuse through while relatively larger molecules or particles could not. Two flow modes, a continuous and stopped flow, were studied. Factors that influenced the sensitivity (%dialysis) of the method, such as the flow rate, sample volume, flow direction and stopped flow time, were optimized. The stopped flow mode was found to be relatively more sensitive than the continuous flow mode and displayed a linear range of 1-30 mg L(-1) Fe(2+), a limit of detection of 0.5 mg L(-1), and a % relative standard deviation of less than 2% (n=8) for the analysis of 10 mg L(-1) Fe(2+) spiked grape juice samples. A sample throughput of 24 samples h(-1), was attained without any further sample treatment.

Bulk optode sensors for batch and flow-through determinations of lead ion in water samples.

A sensitive optode consisting of highly lead-selective ionophore (Lead IV), proton-selective chromoionophore (ETH 5294) and lipophilic anionic sites (KTpClPB) in plasticized polyvinyl chloride (PVC) membrane was fabricated. The optode membranes were used for determination of Pb(2+) by absorption spectrophotometry in batch and flow-through systems. The influence parameters such as pH, type of buffer solution, response time and concentration of regenerating solution were optimized. The membrane responded to Pb(2+) by changing its color from blue to pinkish purple in Tris buffer containing different concentration of Pb(2+) at pH 7.0. The optode provided the response range of 3.16x10(-8) to 5.00x10(-5) mol L(-1) Pb(2+) with the detection limit of 2.49x10(-8) mol L(-1) in the batch system within the response time of 30 min. The dynamic range of 1.26x10(-8) to 3.16x10(-5) mol L(-1) Pb(2+) with detection limit of 8.97x10(-9) mol L(-1) were obtained in the flow-through system within the response time of 15 min. Moreover, the proposed optode sensors showed good selectivity towards Pb(2+) over Na(+), K(+), Mg(2+), Cd(2+), Hg(2+) and Ag(+). It was successfully applied to determine Pb(2+) in real water samples and the results were compared with well-established inductively coupled plasma optical emission spectrometry (ICP-OES). No significant different value (t(critical)=4.30>t(exp)=1.00-3.42, n=3 at 95% of confidence level) was found.

Cost-effective flow cell for the determination of malachite green and leucomalachite green at a boron-doped diamond thin-film electrode.

An electrooxidation and a cost-effective flow-based analysis of malachite green (MG) and leucomalachite green (LMG) were investigated at a boron-doped diamond thin-film (BDD) electrode. Cyclic voltammetry as a function of the pH of the supporting electrolyte solution was studied. Comparison experiments were performed with a glassy carbon electrode. A well-defined cyclic voltammogram, providing the highest peak current, was obtained when using phosphate buffer at pH 2. The potential sweep-rate dependence of MG and LMG oxidation (peak currents for 1 mM MG and LMG linearly proportional to v 1/2, within the range of 0.01 to 0.3 V/s) indicates that the oxidation current is a diffusion-controlled process on the BDD surface. In addition, hydrodynamic voltammetry and amperometric detection using the BDD electrode combined with a flow injection analysis system was also studied. A homemade flow cell was used, and the results were compared with a commercial flow cell. A detection potential of 0.85 V was selected when using a commercial flow cell, at which MG and LMG exhibited the highest signal-to-background ratios. For the homemade flow cell, a detection potential of 1.1 V was chosen because MG and LMG exhibited a steady response. The flow analysis results showed linear concentration ranges of 1-100 microM and 4-80 microM for MG and LMG, respectively. The detection limit for both compounds was 50 nM.