Determination Of Total Inorganic Arsenic Research Articles

Sequential injection analysis system for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry

A sequential injection analysis system is proposed for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry. The sample, a reducing sodium tetrahydroborate solution and a blank solution containing HCl, ascorbic acid and potassium iodide are sequentially aspirated and then dispensed into a gas–liquid separation cell. An Ar flow sweeps the arsine into the flame of an atomic fluorescence spectrometer. An auxiliary H2 flow was necessary to support the flame. Linear calibration graphs were obtained for arsenic concentrations between 2.5 and 50μgl−1, the detection limit (3σb/S) being 0.67μgl−1. The relative standard deviation of the method was 1.8% (n=9) when 0.5ml of a 20μgl−1 As standard solution was aspirated. The sample throughput was 33 samples per hour. The proposed method has been validated by means of reference materials and the results obtained were in good agreement with the certified values.

On-line cryogenic trapping with microwave heating for the determination and speciation of arsenic by flow injection/hydride generation/atomic absorption spectrometry

An on-line flow injection-hydride generation/atomic absorption spectrometry method was developed for the preconcentration and selective determination of inorganic arsenic [As(III) and As(V)] and its methylated species. The separation of the arsenic species was performed by an automated pH-selective arsines generation technique, using sodium tetrahydroborate(III) as reductant. Each arsine was cryogenically trapped in a PTFE coil, knotted and sealed inside another wider diameter tube, through which liquid nitrogen was suctioned by negative pressure. Then, based on their different boiling points, the arsine species were selectively liberated by using a heating cycle of microwave radiation, followed by atomic absorption detection. A sample solution aliquot mixed with 1% citric acid was used for the determination of As(III) alone, while a second sample aliquot mixed with 2 mol l −1 nitric acid was used for the quantitative determination of total inorganic arsenic, monomethylarsonic acid and dimethylarsinic acid. Based on 10 ml sample, the detection limits lie within the range 20–60 ng As l −1, which are sufficiently low to detect the arsines-forming species in natural waters. These values are negatively affected by the reagents purity and background noise due to flame flickering, but the sensitivity can substantially be improved by increasing sample size or running several consecutive reactions.

A FIA-system for As(III)/As(V)-determination with electrochemical hydride generation and AAS-detection.

A flow-injection system with electrochemical hydride generation and atomic absorption detection for As(III)/As(V) determination is described. A simple electrolytic flow-through cell has been developed and optimized. Several cathode materials like Pt, Ag, Cu, C and Pb have been tested. The influence of the electrolysis current, concentration of sulfuric acid, carrier stream, flow rate, sample volume and interferences by other metals on the arsenichydride generation have been studied. For the determination of total inorganic arsenic, As(V) is reduced to As(III) on-line by postassium iodide or L-cysteine at 95 degrees C. The influence of the temperature and the reduction medium on this pre-reduction step has been tested. The calibration curve is linear in the range of 5 to 50 microg/L for As(III) and total inorganic arsenic and shows a higher sensitivity than in case of reduction with sodium tetrahydroborate. The detection limit is 0.4 microg/L for As(III) and 0.5 microg/L for total inorganic arsenic at a sample volume of 1 mL.

Generation of AsH 3 from As(V) in the absence of KI as prereducing agent: Speciation of inorganic arsenic

It is shown that the potassium iodide to the samples to reduce As(V) to AS(III) is not essential when total inorganic arsenic is determined by molecular spectrophotometry (trapping AsH 3 in Ag—DDTC) or by atomic-absorption spectrometry (if Ar flow-rate and NaBH 4 addition rate are controlled in 6 M hydrochloric acid medium). Furthermore, in the presence of low concentration of organic arsenic, a method is reported for the selective determination of inorganic As(III) and As(V), based on the use of citrate/citric acid medium to determine As(III) and hydrochloric acid to determine total inorganic As. As(V) is determined by the difference between total inorganic As and As(III). The interference level of organic arsenic species (monomethylarsenic acid and dimethylarsenic acid) in the determination of total inorganic arsenic and AS(III) in 6 M hydrochloric acid and citrate/citric acid medium respectively, is reported in the text. The developed method is applied to determine As(III) and As(V) in spiked, tap and waste waters and in lake sediments.

On-line preconcentration of arsenic from water samples with an anion-exchanger column coupled to a hydride generation ICP system

An on-line anion-exchange preconcentration hydride generation ICP system for the determination of total inorganic arsenic in water is described. The column was packed with strongly basic anion-exchange resin (AG 1-X8). Experimental conditions including pH of the sample solution, eluent, flow rate of eluent, oxidation states of arsenic and competing anion ions were studied. Compared with the conventional continuous hydride generation ICP, a 9.2-fold improvement in sensitivity was obtained with RSD 1–2% at 100 ng/ml. The detection limit (3σ) was 0.08 ng/ml. The recoveries in water samples were satisfactory. The system provides complete automation of sample loading, eluting and regenerating of the resin.

Determination of total inorganic arsenic in fish, shellfish and fish products.

Two methods are described for the determination of total inorganic arsenic in fish and fish products. The first method involves separation of the inorganic arsenic by distilling it from 6.6 N hydrochloric acid. The second method involves chelation and extraction of inorganic arsenic after sample dissolution in sodium hydroxide solution, with subsequent back-extraction and oxidation. In both methods the arsenic concentration is measured, after hydride generation by atomic-absorption spectrophotometry with atomisation in a flame-heated silica tube: with the first method the solution contains arsenic(III), and in the second the solution contains arsenic(V). Results obtained by both methods are in agreement over a range of samples. The distillation method is favoured for reasons of efficiency and economy in time. The derived limit of detection and confidence intervals are given.

Determination of total inorganic arsenic in fish, shellfish and fish products : Brooke, P.J. and W.H. Evans, 1981. Analyst, Lond., 106(1262): 514–520

Determination of total inorganic arsenic in fish, shellfish and fish products : Brooke, P.J. and W.H. Evans, 1981. Analyst, Lond., 106(1262): 514–520