Determination of bismuth in nickel-base alloys by atomic absorption spectrometry with introduction of solid samples into an induction furnace

Atomic absorption spectrometry with an induction furnace is applicable'to the determination of bismuth at 0.02–10 μg g^-1 levels in 1–30-mg samples of nickel-base alloys dropped into the furnace. Calibration graphs of peak absorbance versus mass of bismuth are constructed by use of standardised alloys. Samples of alloys can be added to the furnace at 2.5-min intervals. Calibration graphs, accuracy, precision and limits of detection of the method are discussed for 26 alloys. Accuracy is assessed by comparing the induction furnace results with results supplied with the alloys, and with results obtained for solutions of the alloys by atomic absorption spectrometry in association with hydride generation or a mini-Massmann furnace. With alloys containing more than 0.1 μg Bi g^-1, relative standard deviations by the induction furnace method are usually < 15%. The limit of detection for bismuth is 0.02 μg g^-1     

Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina

A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid‐phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2‐mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type, and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng/L level and the limit of detection (3s) were found to be 2.3% and 12 ng/L, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.     

Flow Injection On‐line Preconcentration Coupled with Hydride Generation Atomic Fluorescence Spectrometry for Ultra‐Trace Amounts of Bismuth Determination in Biological and Environmental Water Samples

Abstract

A simple and sensitive flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG‐AFS) was developed for ultra‐trace bismuth determination in water and urine samples. The preconcentration of bismuth on a nylon fiber‐packed microcolumn was carried out based on the retention of bismuth complex with Bismuthiol I. A 15% (v/v) HCl was introduced to elute the retained analyte complex and merge with KBH₄ solution for HG‐AFS detection. Under the optimal experimental conditions, an enhancement factor of 20 was obtained at a sample frequency of 24/h with a sample consumption of 13.0 ml. The limit of detection was 2.8 ng/l and the precision (RSD) for 11 replicate measurements of 0.1 µg/l Bi was 4.4%.     

Study on stable coatings for determination of lead by flow-injection hydride generation and in situ concentration in graphite furnace atomic absorption spectrometry

Lead hydride was generated by flow-injection from 0.05 M oxalic acid sample solution by using 0.1 M HCl carrier solution and the reaction with 1.5% sodium borohydride in the presence of 2% potassium hexacyanoferrate(III) as a mild oxidizing agent. Pb was determined by in situ concentration in graphite furnace AAS. The hydride generation by flow-injection and trapping in the graphite tube coated with a highly stable trapping reagent (e.g. tungsten) allows automatic Pb determination. In a systematic investigation, the in situ concentration of Pb was studied in the temperature range 50–600° on graphite tubes coated with noble metals (Ir, Ir/Mg, Pd/Ir), and with W or Zr. The highest response was found on the Ir coatings at trapping temperatures of 200–300°, followed by the W and Zr coatings. The radiotracer ²¹⁰Pb was used to measure hydride generation (95%) and trapping efficiency (71%) on a W-coated tube. Signal stability and reproducibility was tested over 400 trapping and atomization cycles, and the better performance was found with the W and Zr coatings at a precision of 3%. Trapping temperatures above 450°C can lead to errors in absorbance values owing to an adsorptive “carry-over” effect. A characteristic mass of about 21 pg Pb for W-coated tube (283.3 nm) and a detection limit (3σ) of about 0.25 ng was obtained with a 0.5 ml sample loop. The problem with Pb hydride generation is the relatively high reagent blank (1.3 ng in 30 s trapping time) even using chemicals of the highest purity. The method has been tested by applying it to the determination of Pb in a sediment certified reference material.     

Atomic absorption spectrometric determination of trace tellurium after hydride trapping on platinum-coated tungsten coil

In this work, a sensitive and simple method for the determination of tellurium was developed by hyphenation of electrically heated quartz tube atomic absorption spectrometry and tellurium hydride trapping on platinum-coated tungsten coil. With a mixture of Ar and H₂, tellurium hydride was transported to tungsten coil for trapping at 390 °C and releasing at 1200 °C. A limit of detection (LOD, 3σ) of 0.08 ng mL^{− 1} was obtained with 1 min trapping (1.5 mL sampling volume), and enhancement factor was 28 compared to conventional hydride generation atomic absorption spectrometry. The LOD was better or at least comparable to literature levels involving on-line trapping and some other sophisticated instrumental method such as graphite furnace atomic absorption spectrometry (GF-AAS) and inductively coupled plasma mass spectrometry (ICP-MS), and it can be further lowered down to 0.03 ng mL^{− 1} by increasing the trapping time to 4 min. The platinum coating was stable for 300 firings without sensitivity loss. Interference and its alleviation were studied in detail. The proposed method was applied to the determination of tellurium in several geological standard reference materials, and the results were found in good agreement with the certified values.     

Determination of arsenic by inductively coupled plasma mass spectrometry – comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL^–1), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100–200 pg mL^–1), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH₄ which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Determination and interference studies of bismuth by tungsten trap hydride generation atomic absorption spectrometry

The determination of bismuth requires sufficiently sensitive procedures for detection at the μg L⁻¹ level or lower. W-coil was used for on-line trapping of volatile bismuth species using HGAAS (hydride generation atomic absorption spectrometry); atom trapping using a W-coil consists of three steps. Initially BiH₃ gas is formed by hydride generation procedure. The analyte species in vapor form are transported through the W-coil trap held at 289 °C where trapping takes place. Following the preconcentration step, the W-coil is heated to 1348 °C; analyte species are released and transported to flame-heated quartz atom cell where the atomic signal is formed. In our study, interferences have been investigated in detail during Bi determination by hydride generation, both with and without trap in the same HGAAS system. Interferent/analyte (mass/mass) ratio was kept at 1, 10 and 100. Experiments were designed for carrier solutions having 1.0 M HNO₃. Interferents such as Fe, Mn, Zn, Ni, Cu, As, Se, Cd, Pb, Au, Na, Mg, Ca, chloride, sulfate and phosphate were examined. The calibration plot for an 8.0 mL sampling volume was linear between 0.10 μg L⁻¹ and 10.0 μg L⁻¹ of Bi. The detection limit (3 s/m) was 25 ng L⁻¹. The enhancement factor for the characteristic concentration (C_o) was found to be 21 when compared with the regular system without trap, by using peak height values. The validation of the procedure was performed by the analysis of the certified water reference material and the result was found to be in good agreement with the certified values at the 95% confidence level.     

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％。     

Continuous flow hydride generation laser induced fluorescence spectrometry for trace determination of lead in water and sediment samples

Continuous flow hydride generation coupled with laser induced fluorescence spectrometry (HG-LIF) has been used for the determination of Pb in aqueous samples. Lead hydride is generated in K₃Fe(CN)₆-HCl medium using NaBH₄ as the reducing agent. Parameters such as acidity and the concentrations of oxidising and reducing agents have been studied in order to obtain the highest sensitivity. Laser excitation of Pb has been performed at 283.306 nm and fluorescence has been detected at 365 nm and 405.8 nm. The limit of detection calculated for the optimised conditions (1% K₃Fe(CN)₆ in 0.3% Oxalic Acid, 0.055 mol L^?1 HCl, 1% NaBH₄ in 0.1% NaOH) is 0.3 ng mL^?1. However, a significant Pb background was observed for blank measurements, which degraded the limit of detection. The limit of detection that is estimated for a Pb free blank was determined by detuning the laser to a wavelength of 282.806 nm and was found to be 0.45 pg mL^?1. Method repeatability is 3.5% RSD at the 10 ng mL^?1 level. The accuracy of this method has been evaluated by analysis of a water reference material. The results obtained for a multielement standard determined using the HG-LIF approach have been found to be in agreement with those obtained by using a comparison ICP-AES approach. The HG-LIF approach has been applied to the measurement of Pb in a contaminated sediment sample material. The results of this study demonstrate that a small tunable laser system combined with hydride generation sample introduction can be used to measure Pb with high sensitivity, precision and selectivity in different sample matrices.     

Optimization of Continuous Flow Hydride Generation Inductively Coupled Plasma Optical Emission Spectrometry for Sensitivity Improvement of Bismuth

Experimental variables in continuous flow hydride generation inductively coupled plasma-optical emission spectrometry (CF-HG-ICP-OES) were optimized for determination of bismuth. Concentrations of NaBH₄, HCl, and NaOH, flow rates of NaBH₄, sample solution, waste and carrier argon, radio frequency power, lengths of reaction, and stripping coils were optimized to obtain lower detection limits. Under optimum conditions, the detection limit was calculated as 0.16 ng mL^?1, and the calibration plot was linear between 1.0–50.0 ng mL^?1. An improvement in detection limit of 5.75 times by CF-HG-ICP-OES was reached vs. ICP-OES. Relative standard deviation (RSD) for ten replicate measurements of 10.0 ng mL^?1 Bi was calculated as 3.9%. Effect of possible interferic ions on Bi signal was evaluated. Accuracy of method was verified by using a standard reference material, SRM 1643e. Results found for Bi were in satisfactory agreement with certified values. The proposed method was then employed to determine trace concentration of Bi in milk samples. Bi amounts in samples were found in the range from lower than the quantitation limit to 14.5 ng mL^?1, whereas Bi concentrations were lower than the detection limit in three samples.     

Development and Application of a Hydride Generation Laser Induced Fluorescence Method for Measurements of Bismuth

A hydride generation laser induced fluorescence (HG LIF) approach has been investigated for trace level measurements of bismuth. The technique uses a tunable dye laser operating at 306.7 nm as the excitation source and bismuth fluorescence is measured at 472 nm. The optimized HCl and NaBH₄ concentrations for bismuth measurements were 1.2 M and 2.0%, respectively. The current technique has a limit of detection of 0.03 ppb and 0.01 ppb for blank measurements performed with the laser tuned on and off the bismuth excitation wavelength, respectively. Measurements of bismuth in different sample matrices have demonstrated the effectiveness of thiourea and ascorbic acid as masking agents for measuring samples containing interfering ions. Measurements of bismuth have been performed in reference materials, a bismuth-containing medication, and tea leaves. The results demonstrate that the HG LIF approach has feasibility for measuring bismuth in various samples at environmentally relevant concentrations.     

Determination of selenium in blood serum by ICP-OES including an on-line wet digestion and Se-hydride formation procedure

Summary An analytical procedure for the determination of Se, as well as of other trace elements of clinical interest, in undiluted blood serum samples is presented. This procedure allows the on-line wet ashing of the sample, the hydride generation and the determination of the SeH₂ formed in one step. For this purpose, carrier solution and the injected sample (300 l) were merged with an acid stream (80% H₂SO₄, 12% HClO₄, 8% HNO₃) and passed through a reaction coil heated up to 240°C. To increase the dispersion, the wet digestion was carried out in an ultrasonic field. After trapping of the gas bubbles, 5 mol/l HCl and 0.053 mol/l NaBH₄ solutions were added via T-junctions for Se-hydride generation. The nebulizing system of the ICP-OES was used as gas/liquid separator. The hydride was swept from the spray chamber into the plasma by an argon gas flow with droplets containing other sample constituents. This allows the simultaneous determination of other trace elements of clinical interest, for example Fe, Cu and Zn. The relative detection limit for Se in blood serum was 5 g/l. The quality of the developed procedure was verified in two ways: by measuring SRM Seronorm 116 and by comparing the results for different serum samples with the results obtained with ETAAS. Our results were in good agreement in both cases.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Determination of ultratrace bismuth in milk samples by atomic fluorescence spectrometry

A sensitive procedure was developed for determination of bismuth (Bi) in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion with HNO3 and H2O2. The method provides a sensitivity of 1832 fluorescence units (ng/mL) with a detection limit of 0.01 ng/mL, which corresponds to 20 pg absolute limit of detection, equivalent to 0.50 ng/g in the original sample. Application of the methodology to cow milk samples from the Spanish market showed the presence of Bi at a concentration of 11.8-28.8 ng/g, which compared well with data obtained after dry ashing of samples and with data obtained by inductively coupled plasma-mass spectrometry after microwave-assisted digestion.     

Improvement of the Detection Limit in Capillary Gas Chromatographic Trace Analysis of C2–C4 Hydrocarbons by Post Column Cryogenic Trapping

A method for the improvement of signal-to-noise ratios and hence detection limits in capillary gas chromatographic trace analysis of C₂–C₄ hydrocarbons was developed. It is based on the post column cryogenic trapping of the separated hydrocarbons using liquid nitrogen as coolant and its fast reinjection into the detector by rapid heating of the capillary tubing used for trapping. The improved signal-to-noise ratios were applied to decrease the sample volume and/or to lower the detection limit 10 to 27 times. The concentrations of these hydrocarbons in an urban air sample determined without and with post column cryogenic trapping were in good agreement but the precision was better when applying the cryogenic trapping mode.     

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     

Determination of selenium in infant foods using electrothermal atomic absorption spectrometry with direct slurry sample introduction

Slurry sampling electrothermal atomic absorption (SS ETAAS) was applied to the development of a sensitive and precise method for selenium determination in infant foods without sample pretreatment. Suspensions prepared in a medium containing 0.1% Triton X-100, 0.5 or 5% v/v concentrated HNO₃ were directly introduced into the furnace. The accuracy of the procedure was confirmed by analysis of a standard reference material and comparison with hydride generation atomic absorption spectrometric (HGAAS) procedure. The characteristic mass is 44 pg and detection limit 0.43 μg·l⁻¹.     

The determination of bismuth in serum and urine by electrothermal atomic absorption spectrometry

A method for the determination of bismuth in serum and urine is presented. The method includes 1 + 1 dilution of the sample with 1 mM EDTA followed by charring in a graphite furnace under an oxygen atmosphere. The use of oxygen results in the formation of more homogeneous bismuth salts (probably bismuth oxides) during charring, and more efficient burning of the protein and organic components of the sample matrix. The procedure formulated is a standard additions method and is verified for serum and urine samples. The method reduces matrix interferences, gives a detection limit of 0.05 μg l^-1, and has a relative standard deviation of less than 5% for bismuth in the reference range of 2.6–6.0 μg l^-1. The method displays a recovery accuracy of 91, 96, and 100% for urine, serum, and aqueous samples, respectively.     

Solid phase extraction and graphite furnace atomic absorption spectrometric determination of ultra trace amounts of bismuth in water samples

A simple and reliable method for the selective extraction and determination of bismuth in water as well as alloy samples using octadecyl bonded silica cartridge modified with cyanex 301 and graphite furnace atomic absorption spectrometry is described. Extraction efficiency and influence of sample matrix, optimum amount of extraction ligand, type and least amount of proper eluent and flow rates were evaluated. The limit of detection of the proposed method is 0.01 ng ml(-1). The influence of potential interfering cations in water samples on the recovery of bismuth was investigated. The method was successfully applied to the extraction and determination of bismuth in natural water and alloy samples.     

Flow injection chemical vapor generation of Au using a mixed reductant

Sodium tetraethylborate was used to enhance the chemical vapor generation (CVG) efficiency of gold. Volatile species of Au in a weakly acidified buffer medium were generated at room temperature by reaction with a mixed reductant containing 0.1% NaBH₄ and 0.01% NaBEt₄ in the presence of 0.03% sodium diethyldithiocarbamate (DDTC). A flow injection (FI) system was coupled to a heated quartz tube atomizer for atomic absorption spectrometry (AAS) detection. A precision of 2.5% RSD (n=11, 0.4 mg/L level) was realized at sampling frequencies of 110/h. A detection limit of 2.8 ng/mL (3σ) was obtained based on a 500-μL sample volume. Compared with FI-CVG-AAS using NaBH₄ as the sole reductant, sensitivity was increased 8- to 10-fold. In situ trapping of the analyte in a graphite furnace followed by electrothermal AAS detection, as well as signal monitoring using ICP-OES, was used to study the system. Generation efficiency is estimated to be in the range of 0.8–6%.