Optimization of a chemical modifier in the determination of selenium by graphite furnace atomic absorption spectrometry and its application to wheat and wheat flour analysis.

A method for the determination of total selenium in wheat and wheat flour using graphite furnace atomic absorption spectrometry (GFAAS) with palladium/ascorbic acid as a chemical modifier was studied. The effects of nickel nitrate, palladium/ascorbic acid, and palladium/magnesium nitrate as chemical modifiers on the sensitivity in the determination of selenite, selenate and selenomethionine by GFAAS were compared. The palladium/ascorbic acid modifier was used for the determination of total selenium in wheat and wheat flour, because the oxidation states of the selenium ion are not important in the determination. The detection limit was estimated to be 1 microg L(-1) (calculated as 3sigma of the blank); the calibration curve was linear for the concentration range 5 - 50 microg L(-1) and the recovery range was 96.66 - 101.80%. The optimal ashing and atomizing temperatures were 1300 degrees C and 2250 degrees C, respectively. The proposed method was successfully applied to the determination of total selenium in wheat and wheat flour.     

Determination of tin in lead/tin solder leachates from copper piping by graphite platform furnace atomic-absorption spectrometry

A stabilized-temperature platform furnace/atomic-absorption spectrophotometric(STPF-AAS) method has been developed for the determination of tin leached from lead/tin-soldered copper pipes. The method involves the use of a modifier composed of diammonium hydrogen phosphate, magnesium nitrate and nitric acid. Aqueous tin standards in the composite matrix modifier are used for calibration. The characteristic mass and detection limit (three standard deviations of the blank) for peak-height measurement of tin are 5 pg and 1.7 microgl., respectively. The corresponding peak-area values are 26.8 pg and 12.8 microgl., respectively. The accuracy, precision, and interferences (especially of sulphate) have been assessed.     

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.     

Determination of tributyltin in toluene extract from sea water by graphite furnace atomic absorption spectrometry with a new matrix modifier

A new matrix modifier composed of calcium and chromium[VI] was proposed for the determination of tributyltin (TBT) in toluene extract from sea water containing sediment by graphite furnace atomic absorption spectrometry (GFAAS). Fourteen inorganic and organic compounds (barium, calcium, chromium[VI], lanthanum, magnesium, nickel, palladium, strontium, calcium-chromium[VI], calcium-strontium, nickel isocaprylate, 5%-, 10%-aqueous solution of ascorbic acid and toluene-saturated solution of ascorbic acid) as a matrix modifier were comparatively studied and a matrix modifier composed from 5 microg of calcium and 1 microg of chromium[VI] was found to give the best performance. The interference effects of co-existing elements in sea water containing sediment (aluminium, iron, magnesium, sodium and strontium) were studied. TBT in eight toluene extracts was determined by GFAAS with the proposed matrix modifier. The relative standard deviation was 3.0% for 63 ng ml(-1) of TBT (n = 11). The recoveries were 88-104%. The characteristic mass was 7 pg. The linearity range was 0-250 ng mg(-1).     

Direct determination of selenium in a wild fruit juice by electrothermal atomic absorption spectrometry

A matrix modifier composed of platinum and nickel is proposed for the determination of selenium in a wild fruit juice made from Lantingguo (Vuccinium uliginosam). Five matrix modifiers (copper/nickel, palladium/magnesium, platinum/magnesium, platinum/nickel and platinum/copper) for suppressing the interference effects of seven co-existing elements (potassium, phosphorus, calcium, magnesium, manganese, zinc and iron) in a wild juice were studied and a matrix modifier composed fro;m 10 mug of platinum and 200 mug of nickel was found to give the best performance. Selenium in three juices was determined by electrothermal atomic absorption spectrometry employing the proposed matrix modifier without matrix preseparation. The relative standard deviation was 14% for 0.20 mg l(-1) of selenium. The recoveries were 95-110%. A characteristic mass was 28 pg.     

Influence of citric acid as chemical modifier for lead determination in dietary calcium supplement samples by graphite furnace atomic absorption spectrometry

Citric acid was used as a chemical modifier for Pb determination by graphite furnace atomic absorption spectrometry in dietary supplement samples (calcium carbonate, dolomite and oyster shell samples) and its efficiency was compared to the use of palladium. Pyrolysis and atomization curves were established without use of chemical modifier, with the addition of 20, 100 and 200 μg of citric acid, and with 3 μg of palladium. The citric acid modifier made possible the interference-free Pb determination in the presence of high concentrations of Ca and Mg nitrates. Acid sample digestion involving closed vessels (microwave-assisted and conventional heating) and acid attack using polypropylene vessels at room temperature were compared. All digestion procedures presented similar results for calcium carbonate and dolomite samples. However, for oyster shell samples accurate results were obtained only with the use of closed vessel systems. Analyte addition and matrix-matched standards were used for calibration. The characteristic mass for Pb using citric acid and palladium were 16 and 25 pg, respectively. The relative standard deviation (RSD) was always less than 5% when citric acid was used. The relative and absolute limits of detection were 0.02 μg g^− 1 and 8 pg with citric acid and 0.1 μg g^− 1 and 44 pg with the Pd modifier, respectively (n = 10, 3σ). The recovery of Pb in spiked calcium supplement samples (10 μg l^− 1) was between 98% and 105%. With the use of 100 μg of citric acid as chemical modifier, problems such as high background absorption and high RSD values were minimized in comparison to the addition of 3 μg of palladium.     

Comparative study of magnesium nitrate,palladium nitrate and reduced palladium for the direct determination of mercury in sea water by electrothermal atomization atomic absorption spectrometry

A comparative study of different chemical modifiers in graphite furnace atomic absorption spectrometry for the direct determination of mercury in sea water samples, in synthetic sea water sample of high (72.8%) and low 34.2%) salinity and in aqueous solutions, was carried out. The use of reduced palladium produces better results. The mixture of palladium nitrate and ascorbic acid, gives the best limit of detection (1.9 gl^–1). The use of reduced palladium and magnesium nitrate produced excellent recoveries (close to 100%) in the whole salinity range for all mercury concentration tested. The use of palladium nitrate alone or combined with magnesium nitrate gave good recoveries with respect to a real sea water sample for low salinities. The interference from the major components of sea water were completely removed by using reduced palladium and magnesium nitrate modifiers. Thus, a single calibration curve with synthetic sea water may be applied to the analysis of sea water samples of widely differing salinities.     

Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 3: Chemical interference of sulphate using palladium modifiers

The interference caused by sulphate (as the sodium salt) in the electrothermal atomization atomic absorption analysis of selenium was investigated for prereduced and unreduced palladium nitrate modifiers. Kinetic parameters of the selenium atomization were calculated for both types of modifier with varying amounts of sulphate added. Prereduced palladium was a better modifier since it tolerated higher amounts of interferent. For high levels of interferent, the kinetic parameters approached that of selenium without modifier. It was postulated that the interference was caused by the formation of palladium sulphate which reduces the number of active palladium sites available for selenium stabilization. The poorer performance of the unreduced modifier was explained in that the formation of stabile palladium sulphate hindered the reduction of Pd(II) to palladium metal which was needed for the selenium stabilization. Sulphate only interfered on the high temperature stabilization process; the low temperature stabilization, linked to the formation of a [Pd,Se,O] compound, was unaffected. The results support earlier literature reports that selenium loss occurs by covolatilization with the matrix and gives a reason why palladium modifiers are rendered useless by the sulphate interferent.     

Reduction of effects of structured non-specific absorption in the determination of arsenic and selenium by electrothermal atomic absorption spectrometry

The presence of iron and phosphates in biological matrices causes deuterium arc background-correction systems to overcompensate at several arsenic and selenium resonance lines. The addition of platinum as matrix modifier has a significant effect on both the absorbance/time profile of iron and the formation of gaseous phosphate decomposition products. A nickel/platinum matrix modifier is shown effectively to control the problems in the determination of selenium arising both from thermal instability and spectral interferences. The same combination eliminates the spectral interferences found at the arsenic resonance lines. Remaining problems are the thermal stabilization of organometallic arsenic compounds present in biological samples. When radioactived-labelled ⁷⁴As compounds prepared in vivo were applied, none of the tested matrix modifiers (Ni, Cu, Ag, Pd, Zr, Ce, Ce + magnesium nitrate) showed a significant influence on the volatility of arsenic in whole blood and urine from rats.     

Effectiveness of palladium as a chemical modifier for the determination of lead in biological materials and foodstuffs by graphite furnace atomic absorption spectrometry

Summary A combination of 6 g palladium and 15 g magnesium nitrate is proposed as chemical modifier for lead determinations in biological materials and foodstuffs. The applicability of this modifier was investigated by the analysis of several types of samples, as compared to the classical NH₄H₂PO₄ and Mg(NO₃)₂ modifier. Direct determinations of lead against aqueous standard solutions can be performed in 3-fold diluted urine, 2-fold diluted milk and 6-fold diluted blood, when the proposed modifier is added. A method for lead determinations in potatoes using the combined palladium and magnesium nitrate modifier, after a microwave acid digestion, is described. The optimum GFAAS pyrolysis temperature remains dependent on the matrix and should be determined for each type of sample. A wider linear range of the calibration curve is observed when the proposed Pd modifier is used.     

Effectiveness of palladium as a chemical modifier for direct silver and manganese determination in cocaine and heroin by electrothermal atomic absorption spectrometry

Methods for the direct determination of silver and manganese in cocaine and heroin by electrothermal atomic absorption spectrometry using palladium as chemical modifier have been developed. Cocaine samples, 0.5 g, were dissolved in 2 ml of 35.0% (m/v), HNO(3) diluting to 10 ml with ultrapure water. A comparative study of palladium, magnesium nitrate, palladium-magnesium nitrate and nitric acid used as chemical modifiers was carried out, and it was found that palladium alone is adequate to stabilize silver and manganese at charring temperatures of 1000 and 1300 degrees C respectively. A study was made on the insertion of a cooling step before the atomization step, and this approach was not advantageous. Limits of detection of 2.3 and 6.9 microg kg(-1) were obtained for silver and manganese respectively. The analytical recovery oscillated between 95.9 and 103.6% for silver and between 99.7 and 103.0% for manganese. Finally, a study of some interferences and a study of the precision and analytical recovery of the amount of sample were also carried out.     

Multielement electrothermal atomic absorption spectrometry: A study on direct and simultaneous determination of chromium and manganese in urine

A study was carried out on the direct determination of Cr and Mn in urine using simultaneous atomic absorption spectrometry (SIMAAS). The heating program conditions, the absorbance signal profiles, the influence of different chemical modifiers, and the urine sample volume delivery into the tube were optimized to perform the calibration with aqueous solutions. Among several chemical modifiers tested, the best recovery and repeatability results were obtained for 3 microg Mg(NO3)2. On using this modifier, the pyrolysis and atomization temperatures for simultaneous determination of Cr and Mn were 1,300 degrees C and 2,500 degrees C, respectively. Urine samples were diluted (1+1) with 2.0% (v/v) HNO3 + 0.05% (w/v) Triton X-100 prepared in high purity water. A 20-microL aliquot of analytical solution and 10 microL of chemical modifier solution were delivered to the graphite tube. The characteristic masses were 7.8 pg for Cr (RSD=4.0%) and 4.6 pg for Mn (RSD=2.6%). The limits of detection were 0.08 microg L(-1) (n=20, 3s) for Cr and 0.16 microg L(-1) (n=20, 3s) for Mn. Recovery studies for 1.0 or 2.5 microg L(-1) of Cr and Mn added to different urine samples showed acceptable results for Cr (100%, RSD=14%) and Mn (88%, RSD=5.6%).     

Spectrophotometric determination of etodolac in pure form and pharmaceutical formulations

Background

A routine method for the quantification of beryllium in biological fluids is essential for the development of a chelation therapy for Chronic Beryllium Disease (CBD). We describe a procedure for the direct determination of beryllium in undigested micro quantities of human blood and serum using graphite furnace atomic absorption spectrometry. Blood and serum samples are prepared respectively by a simple 8-fold and 5-fold dilution with a Nash Reagent. Three experimental setups are compared: using no modifier, using magnesium nitrate and using palladium/citric acid as chemical modifiers.

Results

In serum, both modifiers did not improve the method sensitivity, the optimal pyrolysis and atomization temperatures are 1000°C and 2900°C, respectively. In blood, 6 μg of magnesium nitrate was found to improve the method sensitivity. The optimal pyrolysis and atomization temperatures were 800°C and 2800°C respectively.

Conclusion

In serum, the method detection limit was 2 ng l^-1, the characteristic mass was 0.22 (± 0.07) pg and the accuracy ranged from 95 to 100%. In blood, the detection limit was 7 ng l^-1, the characteristic mass was 0.20 (± 0.02) pg and the accuracy ranged from 99 to 101%.     

Determination of Antimony in Sediments by Zeeman-Corrected Electrothermal Atomic Absorption Spectrometry with Ultrasonic Slurry Sampling

A method was developed for the determination of antimony in slurried sediments (on the basis of samples of three Certified Reference Materials) by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. Slurried samples were prepared in 6% nitric acid containing 0.02% of Triton X-100. A mixed palladium/magnesium chemical matrix modifier, L'vov platform atomization and a temperature-time program with a relatively short (10 s) sample pyrolysis stage were used. The results of the determinations by this technique are in very close agreement with certified values and the repeatability of this analytical procedure expressed in terms of relative standard deviation was typically better than 9% at the slurry concentration of approx. 90 mg/2 mL. The characteristic mass of Sb (at the spectral line 231.1 nm) was 25.6 pg and the limit of detection (calculated for 100 mg/2 mL slurry) was about 0. 04 μg/g.     

Determination of arsenic, cadmium, lead and selenium in highly mineralized waters by graphite-furnace atomic-absorption spectrometry

A graphite-furnace AAS method using the stabilized-temperature platform furnace (STPF) concept, mixed palladium and magnesium nitrates as chemical modifier and Zeeman background correction has been applied to the direct determination of As, Cd, Pb and Se in highly mineralized waters used for medicinal purposes. These contain 20-40 g/l. concentrations of salts, mainly sodium and magnesium chlorides, bicarbonates and sulphates. The use of a pre-atomization cool-down step to 20 degrees in the graphite-furnace programme reduced the background absorption. Increasing the mass of magnesium nitrate modifier to 5 times that originally proposed improved the analyte peak shape. Under these conditions, no interference was found in analysis of the chloride/bicarbonate type of water, but the sodium and magnesium sulphate type of water had to be diluted, and even then an interference remained. Calibration with matrix-free standard solutions was used, but use of spike recovery is strongly recommended for testing the accuracy. The limits of determination (4.65sigma) of the proposed method for undiluted samples are 2.0 mug/l. for As, 0.05 mug/l. for Cd, 1.0 mug/l. for Pb and 1.5 mug/l. for Se.     

Mechanism of modification by palladium in graphite furnace atomic absorption spectrometry

The effects of palladium and mixtures containing palladium on the absorbance characteristics of lead, thallium, cadmium, selenium, manganese and cobalt are described. These data, together with results of scanning electron microscopy showing the distribution of palladium on the graphite surface, indicate that palladium has a physical mechanism of analyte modification. During furnace heating, the analyte dissolves in molten palladium and may combine with it chemically. However, the rate limiting step leading to atomization appears to be diffusion of the analyte from palladium. The addition of magnesium, molybdenum or powdered carbon increases the speed of diffusion by causing palladium to form smaller droplets, and hence produces sharper absorbance peaks. Palladium becomes less effective as the atomization temperature increases, because the rate of diffusion is higher. This accounts for palladium having only a small stabilizing effect on less volatile elements such as manganese and cobalt. The addition of ascorbic acid to palladium has no significant effect on its modifying properties in a dilute nitric acid matrix. Results of kinetic studies on the atomization of gold are consistent with analyte diffusion out of palladium as the rate-limiting step leading to atomization.     

Direct determination of germanium in botanical samples by graphite furnace atomic absorption spectrometry with palladium-zirconium as chemical modifier

A method has been described for the direct determination of trace levels of germanium by graphite furnace atomic absorption spectrometry (GFAAS) using chemical matrix modification technique. The stabilization and the pyrolysis temperatures for germanium were investigated with various chemical modifiers including palladium, palladium–magnesium, palladium–strontium and palladium–zirconium. The highest pyrolysis temperature and highest integrated absorbance were obtained using palladium–zirconium modifier, and the severe matrix interference from sulfate can be eliminated. The characteristic mass and absolute detection limit (3σ) of germanium were found to be 16 and 12 pg, respectively. The proposed method was applied to the determination of trace levels of germanium in botanical samples with a recovery range of 92–106%. The hydride generation atomic fluorescence spectrometric (HGAFS) method was employed to analyze the samples and the results agree well with those obtained by GFAAS. The contents of germanium in standard reference materials were determined and the results were in good agreement with the reference values.     

The selection of a chemical modifier for vanadium determination in various types of natural waters by electrothermal atomic absorption spectrometry

Various modifiers (ascorbic acid, NH₄NO₃, EDTA, NH₄SCN and a mixture of Pd/Mg(NO₃)₂) are compared for the accurate determination of vanadium in natural waters by electrothermal atomic absorption spectrometry. The interferences of compounds commonly present in natural waters, such as NaCl, CaCl₂, MgCl₂ and FeCl₃ are studied. Matrix interferences were effectively eliminated by ascorbic acid or ammonium nitrate. For comparison, the standard addition method was applied without a modifier which provided satisfactory results. The accuracy of the method was confirmed by analysis of certified reference materials of waters (‘Trace Metals in Drinking Water’ and SRM 1643e ‘Trace Elements in Water’) as well as by recoveries of vanadium spiked to tap water, mineral water, synthetic riverine and synthetic sea waters. The limits of detection and characteristic masses for ascorbic acid and ammonium nitrate as the modifiers were 1.71 and 1.56?µg?L^?1 and 70 and 67?pg, respectively. Recovery was in the range of 98–105% and RSD was less than 5%.     

Chemical modifiers in the determination of molybdenum in human serum by electrothermal atomic absorption spectrometry

Summary Various modifiers were investigated for the molybdenum determination in human serum samples by electrothermal atomization atomic absorption spectrometry. Methods with magnesium nitrate, barium difluoride, nitric acid, palladium-magnesium nitrate and palladium-hydroxylamine were studied by introducing the serum samples directly into the graphite furnace with 0.2% triton X-100. The mineralisation and atomization curves, the amount of modifier and the calibration and addition graphs were studied in all instances. The characteristic masses were 18, 22, 17, 12 and 13 pg of molybdenum for magnesium nitrate, barium difluoride, nitric acid, palladium-magnesium nitrate and palladium-hydroxylamine, respectively. The precision, accuracy and interferences of the methods were also investigated.     

电感耦合等离子体原子发射光谱法测定纯银中镉、铋、铁、铅、锑、钯、硒、碲

样品用硝酸溶解,加入过量盐酸沉淀分离银,过滤后利用电感耦合等离子体原子发射光谱法测定镉、铋、铁、铅、锑、钯、硒、碲,方法检出限分别为:0.0028,0.0075,0.0036,0.011,0.010,0.021,0.0075,0.0039μg/mL;加标回收率为98.1%～114.3%;RSD小于4.2%,方法能同时准确测定镉、铋、铁、铅、锑、钯、硒、碲,满足日常分析要求。