Abstract: A solution of BH4- in aqueous 1% NaOH was injected into a carrier stream (2 ml/min) of water, which was mixed with a stream (2 ml/min) of 25 mM As(III) in 1 M HCl in a mixing coil (30 cm x 0.5 mm). The AsH3 formed diffused through the PTFE membrane of a gas diffusion unit into an acceptor solution (0.01 M H2SO4) and the resulting solution passed through the thin-layer flow cell of a BAS LC-17A amperometric detector equipped with dual Pt working electrodes maintained at 0.8 V vs. Ag/AgCl. The calibration graph was linear from 8 µM to 1 mM BH4-, and the detection limit was 1 µM. The RSD at 60 µM was 2% and the sample throughput was 60/h. Serious interference was caused by sulfide and sulfite.

Abstract: Samples containing Br- are injected into the flow injection analysis manifold (diagram given), where the Br- is converted online into Br by KMnO4, which diffuses from the donor stream through a hydrophobic membrane [see Nikolic et al., Analyst (London), 1991, 116, 49] into the acceptor solution The Br is carried to a flow-through amperometric cell (see Rocklin and Johnson, Anal. Chem., 1983, 55, 4) where it is reduced by a Pt electrode (vs. Ag - AgCl). The cathodic current is proportional to the sample Br- concentration. Calibration graphs are rectilinear up to 10 mM Br-. Use of a mixture of KMnO4 and NaCl reduces the detection limit to 1 µM (16 ng) Br-. The method was applied to the determination of Br- in Cl- and other reagents, as well as in natural waters. A rapid, indirect diffusion flow injection analysis (FIA) method with amperometric detection has been developed for the selective and sensitive determination of Br-. The method is based on permanganate oxidation of Br- to bromine. Bromine diffuses through a PTFE membrane and is quantified amperometrically at a platinum working electrode. Calibration graphs were linear up to the max. concentration. of Br- investigated (10.0 mmol/L). The precision of the technique was better than a relative standard deviation of 0.7% at 10.0 µmol/L, with a throughput of 30 samples per h. The effects of temp., acidity, working potential, composition of the reagent solution and interferents on the FIA signals were studied. The catalytic effect of Cl- on the permanganate oxidation of the analyte was utilized to lower the detection limit to 1 µmol/L (16 ng Br-). Similar detection limits were achieved by combining the effects of higher acidity (4.0 mol/L H2SO4) and elevated temps. (40°C). The method was successfully applied to the determination of Br- in chloride and other reagents, as well as in natural waters.

Abstract: Sample solution was injected into a carrier solution (1 ml/min) of 0.2 M HCl. the carrier stream merged with a reagent stream (1 ml/min) of 0.2 M HCl, passed through a mixing coil (30 cm x 0.5 mm i.d.) and into a diffusion cell with an acceptor solution 92 ml/min) of 0.01 M NaOH. The resulting solution went into a thin layer flow-through amperometric cell comprising a Ag working and Pt counter electrode with a Ag/AgCl reference electrode separated from the flowing stream by an ion exchange Nafion membrane. The cell was potentiostated and the current measured by a pulsed amperometric detector. The dynamic range of the FIA system was 0.001-5 µg/ml and recoveries of cyanide from all metal cyano complexes that produce free cyanides were 97.4-104.3% with RSD of 0.2-1.3% for 0.2 µg/ml cyanide and 98-103% with RSD of 0.2-0.7% for 2 µ/ml cyanide. The method was used to determine cyanide in industrial process waters. In the first part of this research, extensive species-dependent cyanide recoveries studies were performed using the approved standard methods available for determination of free cyanide. The data obtained show that serious problems are associated with both the CATC (cyanide amenable to chlorination) and WAD (weak and dissociable cyanide) methods. In the second part, a novel flow injection gas diffusion method for the determination of free cyanide was developed. Complete cyanide recoveries even in the presence of a large excess of the free CN- ion were found for the following species: 2-, 2-, 2-, 3-, -, 2-, and Hg(CN)2. No recoveries of CN- were obtained from the species that are considered as non free cyanide producing ones, such as 3-/4-, 3-, and -. The method developed is rapid, selective, reproducible, and easy to automate. Copyright 1995, American Chemical Society.

Abstract: Extensive species and concentration dependent cyanide recovery studies were carried out using a novel automated segmented flow injection-online UV digestion-amperometric (FI-UV) method for determination of total cyanide in water and wastewater samples. In addition, the response of the method to the presence of potential interferents was tested. The performance of the proposed method was compared with that of the standard method. The data obtained show that the FI-UV method has significant advantages over the EPA/ASTM approved procedures. Total cyanide levels and spike recoveries were determined for nine different industrial effluents. The precision and accuracy of the method, when applied to these effluents, expressed in terms of mean relative standard deviation and average percentage of spike recovery, were 1.5% and 101.0%, respectively. The technique developed eliminates the need for the time consuming, labor intensive distillation called for in the EPA/ASTM approved procedures. The method is rapid, selective and reproducible with a detection limit of 0.2 µg L-1 and a throughput of 30 analyzes per hour.