G.E. Pacey

Solution ionic strength effect on gold nanoparticle solution color transition.

Unmodified and modified gold nanoparticles are proposed as sensors using the red to blue transition as an indicator. This work indicates that ionic content is an important variable to track in analytical samples and during the sensor fabrication processes. Mono and multivalent salts where the titrants for a standard gold nanoparticle solution. Multivalent cation salt titrants exhibited a greater sensitivity to color change than monovalent cation salts. The data suggest that specific surface adsorption is the predominant mechanism for the red to blue color change not aggregation. The 3-7nm Debye length for divalent cations versus the 0.5-1.5nm for monovalent cations indicates surface electrodynamic resonance effects are an important factor in the observed color changes.

Metal speciation by flow-injection analysis

A two-channel switching valve is incorporated in the flow-injection manifold for on-line control of the metal speciation of Fe(II)/Fe(III) and Cr(III)/Cr(VI). 1,10-Phenanthroline is used for the iron determinations and diphenylcarbazide for chromium. The absorbances are measured at 512 and 540 nm, respectively. When a 30-mul injection loop is used, the response is linear for 0.5-30.0 ppm Fe and 0.5-40.0 ppm Cr. The relative standard deviation in each case is approximately 1%. The method allows at least 180 injections per hour.

Arsenic speciation by ion-exchange separation and graphite-furnace atomic-absorption spectrophotometry

As(III), As(V), monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA) were determined by graphite-furnace atomic-absorption spectrophotometry after separation of the species by ion-exchange chromatography. The detection limits (ng/ml) were DMA 0.02, MMA 2.0, As(V) 0.4 and total arsenic 4.0. As(III) was determined by difference. This system gave better detection limits and/or shorter analysis times than previously reported systems.

Utilisation of kinetic-based flow injection methods for the determination of chlorine and oxychlorine species

Abstract Automated selective iodometric methods for the determination of chlorine and oxychlorine species have been developed for use in the drinking water industry. By utilising kinetic-based methods, linear ranges observed were: chlorine, 0.2–10 mg l −1 ; chlorine dioxide, 0.3–10 mg l −1 ; chlorite ion, 0.08–5 mg l −1 ; and chlorate ion, 0.08–5 mg l −1 .

Rapid analysis of perchlorate, chlorate and bromate ions in concentrated sodium hypochlorite solutions

A sensitive, rapid, and rugged liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for measuring concentrations of perchlorate, chlorate, and bromate ions in concentrated sodium hypochlorite solutions is presented. The LC-MS/MS method offers a practical quantitation limit (PQL) of 0.05 microg L(-1) for ClO(4)(-), 0.2 microg L(-1) for BrO(3)(-), and 0.7 microg L(-1) for ClO(3)(-) and a sample analysis time of only 10 min. Additionally, an iodometric titration technique was compared with the LC-MS/MS method for measurement of chlorate ion at high concentration. The LC-MS/MS method was the most reproducible for chlorate concentrations below 0.025 M while the iodometric titration method employed was the most reproducible above 0.025 M. By using both methods, concentrations of chlorate can be measured over a wide range, from 0.7 microg L(-1) to 210 g L(-1) in hypochlorite ion solutions. Seven quenching agents were also evaluated for their ability to neutralize hypochlorite ion, thereby stopping formation of perchlorate ion in solution, without adversely impacting the other oxyhalide ions. Malonic acid was chosen as the quenching agent of choice, meeting all evaluation criteria outlined in this manuscript.

Improvements in the N,N-diethyl-p-phenylenediamine method for the determination of free and combined residual chlorine through the use of FIA.

In the determination of free and combined chlorine, the reaction of permanganate standards with N,N-diethyl-p-phenylenediamine (DPD) exhibits nonlinearity presumably because both the colored semiquinoid product and the colorless quinoid product are both formed. The titrimetric DPD method titrates both of the products while the colorimetric method monitors only the colored semiquinoid products. This results in a nonlinear response for the colorimetric method above 1.0 mg/l. as Cl(2). Under FIA conditions, the nonlinearity of the DPD colorimetric method is eliminated in the 0.1-5.0 mg/l. (as Cl(2)) range and the linear range is expanded to 0.1-8.0 mg/l. as Cl(2). Also, relative standard deviations are improved by 0.5-11% relative to the colorimetric method and 1.5-4.0% relative to the titrimetric method. The FIA method was developed further to sequentially determine both free and combined chlorine, since chloramine was found to have a negligible interference in the free chlorine determination.

Interaction of ozone with gold nanoparticles

Gold nanoparticles interact with aqueous ozone to produce a surface plasmon resonance shift without aggregation of the nanoparticles. Given ozones destructive nature, the surprising finding was that the gold nanoparticles returned to their original color and were able to cycle between the wavelengths as ozone was introduced and removed. Gold islands were made and tested for a gaseous ozone response. Similarly to the aqueous system, the gold islands show a cycling effect. Potentially, this system would be useful as a sensor that identifies the presence of ozone in gaseous media.

Spectrophotometric determination of bromate ions using phenothiazines

Abstract A highly sensitive spectrophotometric method for the determination of bromate ion is described. The method is based on the reduction of aqueous bromate ion by a phenothiazine in acidic conditions to produce a colored species. The method is suitable for bromate ion determination in the 1–700 μg/l range. For the most sensitive reagent, trifluoperazine, the limit of detection and limit of quantitation were calculated to be 0.67 and 2.25 μg/l, respectively.

Optimization of parameters for gas-diffusion flow-injection systems

Abstract The effects of flow rate, flow direction, flow ratio, pressure, membrane area, channel depth and channel shape on the optimization of gas-diffusion flow-injection systems are described in detail. A nonreacting chemical system, chlorine dioxide, was used to study the physical dispersion of the gas-diffusion systems. It was found that slow flow rates and shallow channels are optimal. Stopped-flow conditions in a nonreacting chemical system may not be worth the cost in time. For chemical systems in which the analyte is consumed, the optimized parameters included stopped flow.

The investigation of the behavior of a long period grating sensor with a copper sensitive coating fabricated by layer-by-layer electrostatic adsorption

Sensors based on changes of refractive index in response to sorption of an analyte on the coating or film of a long period grating fiber (LPG) fiber have recently been reported. In most prior work the coating or film swelled during interaction with the analyte. The swelling mechanism produced a kinetic response that slowed both the sensors time for steady-state measurement and the reversibility of the sensor. Here, the analytical utility of fabricating these nanometer thin films using the layer-by-layer (LBL) electrostatic assembly method is evaluated using Cu(II) as the test analyte and Cibacron Blue as the reagent immobilized in the LBL assembly; a generation-4 poly(amidoamine) dendrimer served as the spacer in the assembly. Detection of 1.3mgCu(II)L(-1) was observed when six bilayers comprised the coating. The stable response was achieved with 0.6mgL(-1) in less than 1min. When 0.1M HCl was used as the rinsing solution, this LPG sensor was reversible and the signal to similar concentrations of Cu(II) reproducible.