Comparison of modifiers for determination of arsenic, antimony and selenium by atomic absorption spectrometry with atomization in graphite tube or hydride generation and in-situ preconcentration in graphite tube

The study was performed to compare the effect of magnesium modifier (magnesium nitrate) with that of other modifiers (palladium nitrate and nickel nitrate) in determination of arsenic, antimony and selenium by atomic absorption spectroscopy with atomization in a graphite tube, with generation of hydrides and in situ preconcentration in a graphite tube. The assumed criterion of a modifier performance was the magnitude of the analytical signal. It was found that in determinations with atomization in a graphite furnace the effects of all these modifiers were comparable, while in those with hydride generation and in situ preconcentration in a graphite tube the magnesium modifier showed poorer performance (25% decrease of the analytical signal). In determinations of arsenic and selenium the analytical signal obtained with magnesium salt as a modifier was comparable with those obtained in the presence of all other modifiers.     

Fluorination assisted slurry electrothermal vaporization in ICP-AES for the direct analysis of silicon dioxide powder

The performance of palladium as permanent chemical modifier electroplated on the surface of a graphite tube for the preconcentration of antimony hydride was examined and compared with thermally formed Pd-coatings. The application of Pd-electroplated tubes allows to perform at least 75 determination cycles without any significant change in the efficiency of hydride collection. This is an advantage over the thermally formed palladium coating which must be obtained individually before each measurement. After the optimization of the system parameters a concentration detection limit of 48 ng/L and an absolute detection limit of 71 pg for a 1.48 mL sample were obtained. The procedure was applied to the determination of antimony at a concentration level of 0.2 μg/L in a tap water sample. Received: 13 October 1997 / Revised: 8 December 1997 / Accepted: 11 December 1997     

Determination of Arsenic by Electrothermal Atomic Absorption Spectrometry Using Arsine Preconcentration on Palladium-Containing Adsorbents

A procedure was developed for the preconcentration of arsine on palladium-containing adsorbents followed by the determination of arsenic by electrothermal atomic absorption spectrometry. Aqueous suspensions of the adsorbent were placed in a graphite furnace at the determination step. The selection of the adsorbent was substantiated; adsorption properties of palladium-containing adsorbents were studied to validate their modifying properties. The absolute and concentration limits of detection for arsenic were 28 pg and 12 ng/L, respectively (sample volume of 100 mL).     

Investigation of thallium hydride generation using in situ trapping in graphite tube by atomic absorption spectrometry

Thallium hydride was generated from aqueous solutions by merging sample and sodium tetrahydroborate reductant in a batch system. In situ preconcentration of volatile thallium hydride in a preheated graphite furnace coated with palladium, which was used as both the collection medium and atomizer, greatly improved the sensitivity for the determination of thallium by hydride generation atomic absorption spectrometry. The presence of tellurium can increase the generation efficiency of thallium hydride. The operating conditions were optimized. The calibration graph is linear up to 100 ng and the characteristic mass for thallium was 0.92 ng which is seventeen times lower than that obtained with the heated quartz tube atomizer.     

Simultaneous determination of Se and As by hydride generation atomic absorption spectrometry with analyte concentration in a graphite furnace coated with zirconium

Conditions for the simultaneous determination of selenium and arsenic at ng l⁻¹ level were developed. Simultaneous determination of these elements was possible through the multielement capabilities of hydride generation, with in situ trapping and atomization in a graphite tube coated with zirconium and measurements using a dual channel atomic absorption spectrophotometer. The zirconium coating employed in this work was relatively stable; once formed it could stand ≈80 firings without any significant change in the efficiency of hydride collection. This appears to be an advantage over the palladium coating, which is usually formed individually before each measurement because of its thermal instability during the atomization step of the furnace temperature programme. As a result, two determinations of the two elements could be performed in 2.5 min. Under the optimized conditions, concentration detection limits of 17 and 13 ng l⁻¹ for a 7.1 ml sample volume were obtained for selenium and arsenic, respectively (absolute detection limits 120 and 92 pg for Se and As).     

Multivariate optimisation of hydride generation procedures for single element determinations of As, Cd, Sb and Se in natural waters by electrothermal atomic absorption spectrometry

Continuous flow hydride generation procedures for As(III), total inorganic As, Cd, total inorganic Sb, Se(IV) and total inorganic Se from sea and hot-spring water samples were optimised by experimental designs. Ir-coated graphite tubes were used as preconcentration and atomisation medium of the hydrides generated. Several factors affecting the hydride generation efficiency were studied. Results obtained from Plackett-Burman designs suggest that sodium borohydride flow rate and reduction coil length, are significant factors for total inorganic arsenic hydride generation. For cadmium hydride generation the significant factors are hydrochloric acid concentration, hydrochloric acid and sodium borohydride flow rates and reduction coil length. For total inorganic antimony hydride generation the factors affecting the hydride generation procedure are hydrochloric acid and potassium iodide concentrations and reduction coil length; finally, pre-reduction coil length and oven temperature for the pre-reduction step are statistically significant factors for total inorganic selenium hydride generation. In addition, the factors studied for the arsenic and selenium hydride generation from As(III) and Se(IV) are not significant. From these studies, the significant variables were optimised by central composite designs. Validation carried out analysis on three reference materials: SLRS-4 (Riverie water), CASS-3 (seawater) and NIST-1643d.     

Automated on-line separation preconcentration system for palladium determination by graphite furnace atomic absorption spectrometry and its application to palladium determination in environmental and food samples

A flow injection (FI) system was used to develop an efficient on-line sorbent extraction preconcentration system for palladium by graphite furnace atomic absorption spectrometry (GFAAS). The investigated metal was preconcentrated on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). The palladium is eluted with 40 μl of HCl 4 M and directly introduced into the graphite furnace. The detection limit for palladium under the optimum conditions was 0.4 ng ml⁻¹. This procedure was employed to determine palladium in different samples.     

Preconcentration of palladium in a flow-through electrochemical cell for determination by graphite furnace atomic absorption spectrometry

An electrochemical preconcentration at a controlled potential on the electrode in a flow-through mode followed by graphite furnace atomic absorption spectrometric (GFAAS) detection is proposed for determination of trace amounts of palladium. After electrolysis the polarization of the electrodes was changed and deposited metal was dissolved electrochemically in the presence of an appropriate stripping reagent. Conditions for the electrodeposition, such as pH of the solutions, a deposition potential, dissolution potential and a composition of stripping solution were optimised. The graphite electrode (GE) and glassy carbon electrode (GCE) were tested for the palladium reduction process. The detection limit of 0.05 ng ml⁻¹ Pd (1 pg) was obtained after palladium preconcentration on the GCE and dissolution with 0.2 mol l⁻¹ thiourea in 0.1 mol l⁻¹ HCl followed by GFAAS detection. The method was applied for the determination of palladium in spiked tap water and road dust samples.     

Determination of mercury in environmental samples by cold vapour generation and atomic-absorption spectrometry with a gold-coated graphite furnace

Mercury is determined at below the pg/ml level by a combination of cold vapour generation, trapping in a gold-coated graphite furnace and atomic-absorption detection. The mercury is reduced to the element by stannous chloride, stripped from solution by a stream of nitrogen and collected on a gold-coated porous graphite disk in a graphite furnace. It is then atomized by increasing the graphite furnace temperature and detected by an atomic-absorption spectrophotometer. The absolute detection limit and the characteristic mass were found to be 5 and 20 pg for 0.0044 absorbance, respectively. The concentration limit of detection was 0.1 pg/ml for a 50-ml sample, and the linear dynamic range covered three orders of magnitude. The precisions of the measurements were 2.7% for 0.1 ng and 2.6% for 2 ng of mercury. Analyses of NBS and NIES reference materials showed quantitative recovery. Analytical results obtained by the technique are presented for natural waters, marine biota and sediments.     

Electrolytic hydride generation electrothermal atomic absorption spectrometry – in situ trapping of As on different pre-conditioned end-heated graphite tubes

An automated analytical system for the determination of As combining an electrolytic hydride generator and a graphite furnace atomic absorption spectrometer has been developed. To investigate the trapping efficiency of permanent modifiers, the end-heated graphite tubes have been impregnated with Ir and mixed Pd/Ir pre-reduced modifiers, respectively, or pre-coated with Ir by electron beam evaporation under high vacuum. Furthermore, the influence of the modifier mass on the shape of the absorption signal has been studied and the performance of the modifier has been discussed. Using the pre-coated graphite tube the calculated detection limit (3s criteria ) for As was 3 pg and 15 ng/L (200 μL sample volume, two preconcentration steps) for the absolute mass and the concentration, respectively. The long-term stability of the permanent modifiers and their physical and or chemical changes during the lifetime of the tube have been observed.     

流动注射-氢化物-石墨炉原子吸收光谱法应用研究 Ⅲ.痕量锗的测定

本文采用自制的氢化物-石墨炉自动进样器及流动注射仪,直接测定了一些环境试样中的痕量锗,并研究了测定条件。该方法灵敏度高,线性范围宽,操作简单,速度快,耗样量少。特征质量:5.7 pg/0.0044A;检出限:1.3 pg;测定速度:30个样/h;回收率:99.5％～104％。     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Modifier effects from palladium and iridium in the determination of arsenic and antimony using electrothermal vaporisation inductively coupled plasma mass spectrometry

A study was made of the stabilising and carrying effects of palladium and iridium as modifiers in the determination of arsenic and antimony by electrothermal vaporisation inductively coupled plasma mass spectrometry. The signal intensities of arsenic and antimony were found to increase with decreasing volume (50–10 μl) and concentration (40–5 μg ml⁻¹) of the palladium modifier solution. Similar effects were not observed for iridium. Palladium and iridium had about the same stabilising effect on the analytes; significant loss of the analyte occurred at pyrolysis temperatures above 900°C. The two modifiers gave rise to about the same increase in signal intensity, but the transport mechanism is probably different. The results indicate that iridium interacts with the graphite surface such as to make carbon the main carrier. In contrast, palladium probably acts as an active carrier.     

Speciation analysis of inorganic form of arsenic in ground water samples by hydride generation atomic absorption spectrometry with insitu trapping in graphite tube

This paper presents the results of a study on the optimization of the determination of total arsenic and its species using the absorption atomic spectrometry method combined with hydride generation and in-situ concentration on the inner walls of the graphite tube. To ensure a maximum efficiency of the in-situ analyte concentration on the graphite tube walls, a palladium modifier subjected to preliminary thermal reduction was used. The limits of detection (3σ) were 0.019 ng/mL for total As and 0.031 ng/mL for As(III) at the preliminary analyte concentration for 60s. The optimised procedure of the analyte concentration on the inner walls of the atomiser (graphite tube) was applied for determinations of arsenic in samples of ground water. The content of arsenic in the samples studied varied from 0.21 ng/mL to 0.80 ng/mL for As(III), and from 0.19 ng/mL to 1.24 ng/mL for As(V).     

Microcolumn sorption of antimony(III) chelate for antimony speciation studies

Selective sorption of the Sb(III) chelate with ammonium pyrrolidine dithiocarbamate (APDC) on a microcolumn packed with C₁₆-bonded silica gel phase was used for the determination of Sb(III) and of total inorganic antimony after reducing Sb(V) to Sb(III) by l-cysteine. A flow injection system composed of a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was directly eluted with ethanol into the graphite furnace and determined by AAS. The detection limit for antimony was significantly lowered to 0.007 μg l⁻¹ in comparison to 1.7 μg l⁻¹ for direct injection GFAAS. This procedure was applied for speciation determinations of inorganic antimony in tap water, snow and urine samples. For the investigation of long-term stability of antimony species a flow injection hydride generation atomic absorption spectrometry with quartz tube atomization (FI HG QT AAS) and GFAAS were used for selective determination of Sb(III) in the presence of Sb(V) and total content of antimony, respectively. Investigations on the stability of antimony in several natural samples spiked with Sb(III) and Sb(V) indicated instability of Sb(III) in tap water and satisfactory stability of inorganic Sb species in the presence of urine matrix.     

Determination of palladium and platinum by electrothermal atomic absorption spectrometry after deposition on a graphite tube

The inner wall of a pyrolytically coated graphite tube served as the surface for adsorptive accumulation and/or for electrodeposition of palladium and platinum. A flow system for this preconcentration was constructed. For the electrodeposition a three-electrode arrangement was used. The flow rate for deposition, the medium and deposition potentials were optimized. After the deposition step, the graphite tube was placed into the graphite furnace and an atomization programme was applied. The procedure was applied for the determination of Pd and Pt in airborne particulates.     

Determination of antimony content in natural water by graphite furnace atomic absorption spectrometry after collection as antimony(III)-pyrogallol complex on activated carbon

Antimony(III) was preconcentrated on activated carbon (AC) as the antimony(III)–pyrogallol complex. Prior to the preconcentration, antimony(V) was reduced to antimony(III) with potassium iodide and ascorbic acid. The antimony adsorbed on the AC was determined by graphite furnace atomic absorption spectrometry as an AC suspension. The method was applied to differential determination of trace amounts of antimony in natural water.     

The atomic absorption determination of antimony,arsenic, bismuth, cadmium, lead, and tin in iron, copper,and zinc alloys with the graphite furnace

Antimony, arsenic, bismuth, cadmium, lead, and tin can be determined in metallurgical samples by flame atomic absorption spectrometry at levels of 0.005 wt%, but lower concentrations frequently necessitate preconcentration. The graphite furnace allows determination of these elements at concentrations 1–2 orders of magnitude lower than is possible with flame techniques. All six elements have detection limits at or below 1μg g⁻¹ in a variety of alloys. Calibration for antimony and load was done with standards containing the principal component of the alloy as a synthetic matrix. Bismuth, cadmium, and tin could be determined accurately only by the standard addition method. Arsenic could be determined in iron alloys with synthetic standards, but standard additions were required for copper alloys.     

Determination of major antimony species in seawater by continuous flow injection hydride generation atomic absorption spectrometry

The capabilities and limitations of the continuous flow injection hydride generation technique, coupled to atomic absorption spectrometry, for the speciation of major antimony species in seawater, were investigated. Two pre-concentration techniques were examined. After continuous flow injection hydride generation and collection onto a graphite tube coated with iridium, antimony was determined by graphite furnace atomic absorption spectrometry. The low detection limits obtained (∼5 ng l⁻¹ for Sb(III) and ∼10 ng l⁻¹ for Sb(V) for 2.5 ml seawater samples) permitted the determination of Sb(III) and total antimony in seawater with the use of selective hydride generation and on-line UV photooxidation. The number of samples that can be analyzed is about 15 per hour for Sb(III) determinations and 10 per hour for total antimony determinations. The analysis of seawater samples showed that Sb(V) was the predominant species, even in the presence of important biological activity.