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.     

A fast method for the determination of lead in paprika by electrothermal atomic-absorption spectrometry with slurry sample introduction

A rapid procedure for the determination of lead in commercial paprika samples is described. The samples are first calcined at 350 degrees , then suspensions are prepared in water containing 0.1% v/v Triton X-100 and 0.1% w/v ammonium phosphate and injected into the electrothermal atomiser. The use of platform atomisation with a preatomisation cooling step allows for simple calibration with aqueous standards. When using 0.4% suspensions the detection limit is 0.2 ug/g. The results for seven paprika samples agree with those obtained by an alternative method involving calcination and dissolution in acid.     

Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 microL of these suspensions (4 mg/mL) are diluted to 1000 microL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400 degrees C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800 degrees C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5-75 and 0.2-5 microg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.     

Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 μL of these suspensions (4 mg/mL) are diluted to 1000 μL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400?°C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800?°C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5–75 and 0.2– 5 μg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.     

Fast determination of lead in lake sediment samples using electrothermal atomic absorption spectrometry with slurry samples introduction

An analytical method for the determination of glutamic acid by the sequential perturbation caused by different amounts of glutamic acid on the oscillating chemical system involving the Cu(II)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium is proposed. The method relies on the linear relationship between the changes in the oscillation amplitude of the chemical system and the concentration of glutamic acid. The reaction is implemented in a continuous-flow stirred-tank reactor, and changes in the oscillation amplitude on each perturbation are proportional to the glutamic acid concentration. The use of the analyte pulse perturbation (APP) technique permits sequential determinations on the same oscillating system owing to the expeditiousness with which the steady state is regained after each perturbation. The dynamic range lies between 2.5x10(-6) and 3.2x10(-4) M of glutamic acid, with the regression coefficient is 0.9987. The precision is excellent (less than 0.68% as relative standard deviation (R.S.D.)). Some aspects of the potential mechanism of action of glutamic acid on the oscillating system are discussed.     

Determination of tin and titanium in soils, sediments and sludges using electrothermal atomic absorption spectrometry with slurry sample introduction

Fast-heating programmes for determining titanium and tin in soils, sediments and sludges using electrothermal atomic absorption spectrometry (ETAAS) with slurry sampling are developed. For titanium determination, suspensions are prepared by weighing 5-40 mg of sample and adding 25 ml of a solution containing 50% (v/v) concentrated hydrofluoric acid. For tin determination, suspensions are prepared by weighing up to 300 mg of sample and then adding 1 ml of a solution containing 25% (v/v) concentrated hydrofluoric acid. Palladium (30 μg) and ammonium dihydrogen phosphate (7% w/v) are used as matrix modifiers for titanium and tin, respectively. Prior mild heating in a microwave oven is recommended for titanium determination. Calibration is carried out using aqueous standards. The tin and titanium contents of a number of samples obtained by using the slurry approach agree with those obtained by means of a procedure based on the total dissolution of the samples using microwave oven digestion. The reliability of the procedures is also confirmed by analysing several certified reference materials.     

Determination of aluminium and manganese in human scalp hair by electrothermal atomic absorption spectrometry using slurry sampling

Methods for the determination of aluminium and manganese in human scalp hair samples by electrothermal atomic absorption spectrometry using the slurry sampling technique were developed. Palladium and magnesium nitrate were used as chemical modifiers. Hair samples were pulverized using a zirconia vibrational mill ball, and were prepared as aqueous slurries. Determinations can be performed in the linear ranges of 1.9–150 μg l⁻¹ Al³⁺ and 0.03–10.0 μg l⁻¹ Mn²⁺. Limits of detection of 0.9 mg kg⁻¹ and 27.6 μg kg⁻¹ were obtained for aluminium and manganese, respectively. The analytical recoveries were between 99.6 and 101.8% for aluminium and in the 98.3–101.3% range for manganese. The repeatability of the methods (n=11), slurry preparation procedure and ETAAS measurement, was 16.0 and 7.9% for aluminium and manganese, respectively. The methods were finally applied to the aluminium and manganese determination in 25 scalp hair samples from healthy adults. The levels for aluminium were between 8.21 and 74.08 mg kg⁻¹, while concentrations between 0.03 and 1.20 mg kg⁻¹ were found for manganese.     

Rapid determination of lead, cadmium and thallium in cements using electrothermal atomic absorption spectrometry with slurry sample introduction

 A method is proposed for the determination of Pb, Cd and Tl in cements by ETAAS. The samples are suspended in a medium containing 10% v/v ethanol and 1% v/v both conc. nitric and hydrofluoric acids and are directly introduced into the electrothermal atomizer. The drying stage is performed by programming a 400 °C temperature, a ramp time of 5 s and a hold time of 30 s on the power supply to the atomizer. No ashing step is used. Atomization is carried out at 2100, 1800 and 1700 °C for Pb, Cd and Tl, respectively. For Cd determination, ammonium dihydrogen phosphate is added to the suspension medium. No modifier other than hydrofluoric acid is required for the Pb and Tl determination. It is shown that the results obtained by using direct calibration with aqueous standards for five commercial samples agree with those found by means of the standard additions method. Received: 29 March 1996/Revised: 24 May 1996/Accepted: 30 May 1996     

Determination of lead in fish samples by slurry sampling electrothermal atomic absorption spectrometry

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry (USS-ETAAS) was been applied to the determination of lead in several fish samples. The influences of instrument operating conditions and slurry preparation on the signal were examined. Palladium and ammonium nitrate were used as the modifier to improve the signal. Since the sensitivity to lead in various fish slurries and aqueous solutions was different, the standard additions method was used for the determination of lead in these fish samples. The method was applied to the determination of lead in dogfish muscle reference material (DORM-2) and a swordfish muscle sample purchased from the local market. The analysis results agreed with the reference value. The accuracy was better than 6%. The precision between sample replicates was better than 16% with the USS-ETAAS method. The detection limit of lead estimated from standard additions curve was about 0.053-0.058 microgram g-1 in different samples.     

Determination of cadmium in biological and environmental samples by slurry electrothermal atomic absorption spectrometry

The retention of cadmium by the bacteria Escherichia coli and Pseudomonas putida was optimized in order to develop a rapid and selective preconcentration method for cadmium from biological and environmental samples prior to determination by electrothermal atomic absorption spectrometry. Living and lyophilized cells for both bacteria were used, but the method using dead cells shows better analytical capabilities. Cadmium from aqueous solutions is easily retained on the outer membrane of both bacteria in the pH range 4-10, although the selected working pHs for E. coli and P. putida were 5 and 9, respectively. Cadmium retained by the bacteria was dispersed in 3.5 M nitric acid and the slurry was introduced directly into the graphite tube. The best sensitivity and detection limit were obtained for E. coli (0.03 ng ml(-1) and 0.04 ng ml(-1) respectively, in the absence of any chemical modifier). A strong spectral interference from nickel chloride was found and methods to overcome it were developed. The proposed extraction procedure was tested by the determination of cadmium in different standard biological and environmental samples.     

Development of a slurry atomization method for the determination of cadmium in food samples by electrothermal atomization atomic-absorption spectrometry

Matrix modifiers have been compared for the determination of cadmium in foodstuffs by ETA-AAS with the sample injected in the form of a slurry. Addition of 800 mug/ml Pd stabilized cadmium to a similar extent as did ammonium dihydrogen phosphate, but avoided the increase in background signal associated with the latter. An analytical procedure was developed, based on palladium matrix modification, platform atomization with a pre-atomization cooling step and integrated absorbance measurements. The method allowed the analysis of milk, liver and olive leaf slurries at concentrations up to at least 50 mg/ml by direct calibration with aqueous standards. The accuracy of the analytical results was within 15% and the detection limit for cadmium in analysis of a 50 mg/ml slurry was 10 ng/g.     

Determination of aluminium in aerosols by flameless atomic-absorption spectrometry

A method is reported for the determination of aluminium in aerosols collected on Whatman 41 cellulose filters. In the destruction procedure, provision was made to eliminate silica by hydrofluoric acid treatment. Analysis of the solutions was performed by the flameless atomic-absorption technique. The accuracy was checked by using data from instrumental neutron-activation analysis (INAA) and standard reference materials. An analogue integrator gave a better linearity and detection limit than conventional peak-reading.     

Determination of aluminium and chromium in slurried baby food samples by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometry was used to determine aluminium and chromium in different types of baby foods. Samples without previous treatment were introduced into the atomizer as suspensions, which were prepared in a medium containing 0.1% (w/v) Triton X-100 (for chromium) or 10% (v/v) ethanol (for aluminium), 5% (v/v) concentrated hydrogen peroxide, and 0.5% (v/v) concentrated nitric acid. The slurries were homogenized with a potter and introduced directly into the furnace. The presence of nitric acid allowed a substantial amount of analyte to be extracted to the liquid phase. No matrix effect was observed and aqueous standard solutions were used for calibration. The detection limits were 4 and 50 pg for chromium and aluminium, respectively; characteristic masses were 3.8 pg for chromium and 18 pg for aluminium. Reliability of the procedures was checked by statistically comparing the results with those obtained with a previous microwave oven mineralization stage and by analyis of several certified reference materials. Values for the aluminium content ranged between 0.4 and 3.0 microg/g, and for chromium between 0.003 and 0.06 microg/g.     

Determination of lead in biological samples by use of slurry sampling electrothermal atomic absorption spectrometry

Slurry-sampling electrothermal atomic absorption spectrometry has been applied to the determination of lead in several biological samples (fish and marine algae). The slurries were prepared both by magnetic shaking and microwave-heating and the effect of instrument operating conditions and slurry preparation conditions on the signal were examined. In addition, results from slurry sampling were compared with those obtained by microwave-assisted acid digestion of the same samples and no significant differences were found between them when the analysis of variance (ANOVA) was applied. The between-batch precision of the slurry techniques employed was similar to that for the microwave-assisted digestion procedure; values were always below 6.7%, except for the Dicentrarchus labrax sample for which the value obtained was 9.5% when using slurry magnetic shaking and 7.6% when using the slurry microwave heating. The accuracy of the slurry methodology employed was also evaluated by analysis of two biological reference materials (NIST-1577b and IAEA-V10); percentage recoveries obtained were between 95.6 and 98.5% of the values certified for lead.     

The influence of atomization pressure on the behaviour of aluminium in electrothermal atomic-absorption spectrometry

Pressurized atomization in argon purge gas considerably enhances the peak area in AAS determination of aluminium, owing to the decrease in the diffusion rate of atoms with increasing pressure. If lower heating rates are used, the diffusional loss mechanism becomes more important. Thus pressure then has an even more pronounced influence on signal strength. Atomization under pressure in argon purge gas is shown to be beneficial only for light elements. It can be expected that if instrumental matrix modification is made by using hydrogen as purge gas, increasing the atomization pressure may prove beneficial for all elements.     

Determination of cadmium, chromium and lead in marine sediment slurry samples by electrothermal atomic absorption spectrometry using permanent modifiers

A procedure for the determination of cadmium, chromium, and lead in marine sediment slurries by electrothermal atomic absorption spectrometry is proposed. Slurry was prepared by mixing 10 mg of ground sample with particle size smaller than 50 μm completed to the weight of 1.0 g with a 3% nitric acid and 10% hydrogen peroxide solution. The slurry was maintained homogeneous with an aquarium air pump. For cadmium, the best results were obtained using iridium permanent with optimum pyrolysis and atomization temperatures of 400 and 1300 °C, respectively, a characteristic mass, m_o (1% absorption), of 2.3 pg (recommended 1 pg). Without modifier use, zirconium, ruthenium, and rhodium m_o were 3.4, 4.1, 4.6, and 4.8 pg, respectively. For chromium, the most sensitive condition was obtained with zirconium permanent with optimum pyrolysis and atomization temperatures of 1500 and 2500 °C, m_o of 6.6 pg (recommended 5.5 pg); and without modifier use, rhodium, iridium, and ruthenium m_o were 5.3, 8.8, 8.8, and 8.9 pg, respectively. For lead, the best modifier was also zirconium, m_o of 8.3 pg for the optimum pyrolysis and atomization temperatures of 600 and 1400 °C, respectively, (recommended m_o of 9.0 pg). For iridium, ruthenium, without modifier, and rhodium, m_o were 14.7, 15.5, 16.5, and 16.5 pg, respectively. For all the modifiers selected in each case, the peaks were symmetrical with r² higher than 0.99. Being analyzed (n = 10), two marine sediment reference materials (PACS-2 and MESS-2 from NRCC), the determined values, μg l⁻¹, and certified values in brackets, were 2.17 ± 0.05 (2.11 ± 0.15) and 0.25 ± 0.03 (0.24 ± 0.01) for cadmium in PACS-2 and MESS-2, respectively. For chromium in PACS-2 and MESS-2 the values were 94.7 ± 5.6 (90.7 ± 4.6) and 102.3 ± 10.7 (106 ± 8), respectively. Finally, for lead in PACS-2 and MESS-2, the results obtained were 184 ± 7 (183 ± 8) and of 25.2 ± 0.40 (21.9 ± 1.2), respectively. For cadmium and lead in both samples and chromium in PACS-2, calibration was accomplished with aqueous calibration curves. For chromium in MESS-2, only with the standard addition technique results were in agreement with the certified ones. The limits of detection (k = 3, n = 10) obtained with the diluents were 0.1, 3.4, and 3.6 μg l⁻¹ for cadmium, chromium, and lead, respectively.     

Determination of total magnesium in biological samples using electrothermal atomic absorption spectrometry

Magnesium content is an important diagnostic parameter in medicine. It is recognized that its determination in one compartment is not sufficient for reliable information about the magnesium status in the body. In addition to the common procedures of magnesium determination in blood by flame atomic absorption spectrometry, the procedure of electrothermal atomization has also been developed and applied to the analysis of blood fractions, mononuclear cells and isolated nuclei of liver cells.Electrothermal atomization is preferred in cases where the sample size is limited and the magnesium content low. The total errors are in the order of 3–4%. Various techniques of sample pretreatment have been tested and direct dilution with 0.05 mol l⁻¹ nitric acid was optimal when the samples were not mineralized. The calibration graph based on standards containing albumin was found to give the best results, as the form of magnesium in the samples may influence the ashing and atomization processes. Good agreement was obtained for determination of magnesium in standard serum. The results are compared with those obtained by the standard flame atomization technique.     

Hot-injection procedures for the rapid analysis of biological samples by electrothermal atomic-absorption spectrometry

The combination of palladium/hydrogen matrix-modification and injection of samples into a graphite tube at 120 degrees has allowed the accurate determination of copper, iron, lead and nickel in biological reference materials (urine, milk powder and bovine liver). Palladium modification allowed the use of a standard ashing temperature of 1000 degrees for all four elements. Direct aqueous calibration was applied without the need for standard additions. The total heating cycle, from the start of sample injection, took 45 sec.