Sequential Hydride Generation Research Articles

Speciation analysis of inorganic As and Sb in urban dust using slurry sampling and detection by fast sequential hydride generation atomic absorption spectrometry.

In this work, a methodology for chemical speciation analysis of inorganic As and Sb in urban dust using slurry sampling and detection by fast sequential hydride generation atomic absorption spectrometry is proposed. Doehlert design and desirability function were used to find the optimum conditions for hydride generation (1.0molL-1 HCl and 0.9%mv-1 NaBH4). The accuracy of the analytical method was evaluated by analysis of reference material fly ash (BCR 176R), addition and recovery tests for inorganic As species, and comparison of independent methods for Sb determination in urban dust samples. The determination of the total concentrations of As and Sb and their inorganic species presented good accuracy, between 80 ± 1 and 101 ± 6%. Precision was expressed as the relative standard deviation and was better than 4.7% (n = 3). The limit-of-quantification values were 0.23 and 1.03mgkg-1 for As and Sb, respectively. The methodology was applied to eight samples of dust collected in an urban area of Salvador and Jaguaquara cities, Bahia, Northeast, Brazil, with an aerodynamic size lower than 38μm. Concentrations of pentavalent inorganic species (iAs5+ and iSb5+) in relation to trivalent species (iAs3+ and iSb3+) were found in urban dust collected in the city of Salvador, which are regarded as more toxic for both elements. The enrichment factor and geoaccumulation index (Igeo) values showed that for some samples, the concentrations of iAs and iSb presented strong enrichment and, and regarding environment, strong to moderately polluted by iAs and iSb, with an indication of anthropogenic contributions. The occurrence of these inorganic constituents in the urban area of Salvador can be related with intense industrial activities and vehicular traffic.

Automated determinations of selenium in thermal power plant wastewater by sequential hydride generation and chemiluminescence detection

After the Fukushima disaster, power generation from nuclear power plants in Japan was completely stopped and old coal-based power plants were re-commissioned to compensate for the decrease in power generation capacity. Although coal is a relatively inexpensive fuel for power generation, it contains high levels (mgkg−1) of selenium, which could contaminate the wastewater from thermal power plants. In this work, an automated selenium monitoring system was developed based on sequential hydride generation and chemiluminescence detection. This method could be applied to control of wastewater contamination. In this method, selenium is vaporized as H2Se, which reacts with ozone to produce chemiluminescence. However, interference from arsenic is of concern because the ozone-induced chemiluminescence intensity of H2Se is much lower than that of AsH3. This problem was successfully addressed by vaporizing arsenic and selenium individually in a sequential procedure using a syringe pump equipped with an eight-port selection valve and hot and cold reactors. Oxidative decomposition of organoselenium compounds and pre-reduction of the selenium were performed in the hot reactor, and vapor generation of arsenic and selenium were performed separately in the cold reactor. Sample transfers between the reactors were carried out by a pneumatic air operation by switching with three-way solenoid valves. The detection limit for selenium was 0.008mgL−1 and calibration curve was linear up to 1.0mgL−1, which provided suitable performance for controlling selenium in wastewater to around the allowable limit (0.1mgL−1). This system consumes few chemicals and is stable for more than a month without any maintenance. Wastewater samples from thermal power plants were collected, and data obtained by the proposed method were compared with those from batchwise water treatment followed by hydride generation-atomic fluorescence spectrometry.

Arsenic leached by step-wise ions addition under aerobic and anaerobic: Speciation by Sequential Hydride Generation Flow Injection Analyzer (SHGFIA)

Leaching behavior of arsenic has been investigated by step-wise ions addition of river sediment near arsenic mine; arsenic was contained in sediment 450 mg kg-1. Leachates were characterized by discriminating arsenite and arsenate under both aerobic and anaerobic. Results indicate that arsenite As(III) and arsenate As (V) were leached from the sediments by step-wise ions addition especially phosphate ion enhanced more leaching of arsenic from sediment under anaerobic mostly was As (V). DOI: http://dx.doi.org/10.3329/bjsir.v49i3.22135 Bangladesh J. Sci. Ind. Res. 49(3), 195-198, 2014

Leaching behavior of arsenite and arsenate from the contaminated sediment by the effect of phosphate ion under anaerobic conditions

This article presents the effect of phosphate ion on the potential leaching of arsenic from the contaminated sediment under anaerobic conditions near neutral pH for 120 h. Arsenic content in the selected sediments was 450 mg/kg. In the leaching experiment, 50 g of sediment sample was added into 400 mL of five different concentrated 0 (no phosphate), 3, 10, 15, and 20 mg/L phosphate solutions, and leachates were analyzed by distinguishing As(III) and As(V) with the sequential hydride generation flow injection analyzer (SHGFIA). The results indicate that arsenic concentration in the leachates was increased for As(V) up to 72 h, and subsequently As(V) concentration was decreased in the suspension. The leached amount of As(V) concentration in the aqueous phase was increased with increasing the phosphate concentration in the suspensions, and statistically significant correlation (R2 = 0.9959) was found. Conversely, As(III) concentration in the leachates was almost constant up to 24 h then As(III) concentration was decreased in the suspension. The phosphate ion was potentially leached arsenic, especially As(V) as phosphate (PO43−) ion has more charge density than arsenate (AsO43−) resulting more As(V) was leached from the contaminated sediment with increasing the phosphate concentration in the suspensions.

High Sensitivity Arsenic Analyzer Based on Liquid-reagent-free Hydride Generation and Chemiluminescence Detection for On-site Water Analysis

In this work, a portable and reliable instrument based on manual hydride generation and subsequent ozone induced chemiluminescence analysis was developed and optimized for measurement of aqueous arsenic in drinking water. The aim was to develop a system for use in the field in villages in developing countries where water treatment systems have been installed. Consequently, it is beneficial that the system could be operated without reagent solutions or purified water. Arsenic trihydride (arsine) was generated by reaction with solid acid and solid borohydride, and then introduced to a chemiluminescence cell where the arsine was mixed with ozone to generate chemiluminescence. The measurement could be repeated with the throughput of 60 times h(-1), and the limit of detection was 0.4 µg L(-1). The measurable arsenic concentration was up to 1 mg L(-1) for 2 mL samples. The system was evaluated for analysis of natural water samples, and the obtained data agreed well with those from ICP-MS and sequential hydride generation flow analysis. We expect this small and inexpensive instrument will be used in developing countries.

Measurements of arsenite and arsenate contained in mining river waters and leached from contaminated sediments by sequential hydride generation flow injection analysis

In this work, a new analytical method for gasifiable compounds based on sequential hydride generation flow injection analysis (SHGFIA) was applied to water analysis and leaching investigation. For water analysis, it was confirmed that 1μgL−1 As(III) and As(V) were stable for a few days when EDTA was added in the sample waters. Dissolved As(III) and total arsenic (As(III)+As(V)) were converted to AsH3 in neutral and acidic medium, respectively, to transfer to a miniature gas scrubber (100μL in absorber volume). The collected arsenic was successively measured by flow analysis based on molybdenum blue chemistry. With this system, changes in As(III) and As(V) concentrations of water placed with arsenic-contaminated-sediment was monitored in near real time. From these data, kinetic analyses were carried out and kinetic constant was obtained from plot of ln{(C∞−C)/C∞} where C and C∞ were leached arsenic concentration and its final concentration, respectively. It was found that rate of As(III) leaching was much faster than that of As(V) while As(V) leached more in amount compared to As(III). In this work, it was demonstrated that kinetic investigation is also one of the important application of flow analysis. The SHGFIA system showed excellent performance for leaching analysis of arsenic with discrimination of As(III) and As(V).

Investigation of arsenic removal in batch wise water treatments by means of sequential hydride generation flow injection analysis

Arsenic water pollution is a big issue worldwide. Determination of inorganic arsenic in each oxidation state is important because As(III) is much more toxic than As(V). An automated arsenic measurement system was developed based on complete vaporization of As by a sequential procedure and collection/preconcentration of the vaporized AsH3, which was subsequently measured by a flow analysis. The automated sensitive method was applied to monitoring As(III) and As(V) concentrations in contaminated water standing overnight. Behaviors of arsenics were investigated in different conditions, and unique time dependence profiles were obtained. For example, in the standing of anaerobic water samples, the As(III) concentration immediately began decreasing whereas dead time was observed in the removal of As(V). In normal groundwater conditions, most arsenic was removed from the water simply by standing overnight. To obtain more effective removal, the addition of oxidants and use of steel wools were investigated. Simple batch wise treatments of arsenic contaminated water were demonstrated, and detail of the transitional changes in As(III) and As(V) were investigated.