Fluoride matrix modifiers for the determination of aluminum by graphite furnace atomic absorption spectrometry

A method was tested for the determination of aluminum by graphite furnance atomic absorption spectrometry using hydrofluoric acid and cesium fluoride as matrix modifiers. Alunimum trifluoride is stable to 1291°C, after which it sublimes to form AlF₃ gas. The subsequent gas-phase atomization of AlF₃ occurs rapidly, and produces clean, sharp absorption peaks. This method has a detection limit of 7 pg Al at a confidence interval of 95%. The method is fairly insensitive to interferences, with the exception of strongly complexing organic acids. The addition of CuF₂ to the matrix appears to eliminate interference from organic acids, but was found to produce a high background absorbance and to shorten the life of the graphite tube.     

On-line ion-exchange preconcentration and determination of traces of platinum by electrothermal atomic absorption spectrometry

A method to determine trace amounts of platinum in different samples based on electrothermal atomic absorption spectrometry is described. The preconcentration step is performed on a chelating resin microcolumn [1,5-bis(2-pyridyl)-3-sulfophenyl methylene thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex 1x8-200)] placed in the autosampler arm. The combination of a peristaltic pump for sample loading and the atomic absorption spectrometer pumps for elution through a selection valve simplifies the hardware. The peristaltic pump and the selection valve are easily controlled electronically with two switches placed in the autosampler, which are activated when the autosampler arm is down. Thus, the process is fully automated without any modification of the software of the atomic absorption spectrometer. Under the optimum conditions with a 60-s preconcentration time, a sample flow rate of 2.4 mL min(-1), and an injection volume of eluent of 40 microL, a linear calibration graph was obtained in the range 0-100 ng mL(-1). The enrichment factor was 14. The detection limit under these conditions is 1 ng mL(-1), and the relative standard deviation (RSD) is 1.6% for 10 ng mL(-1) of Pt. The method has been applied to the determination of platinum in catalyst, vegetation, soil, and natural water samples. The results showed good agreement with the certified value and the recoveries of Pt added to samples were 98-105%.     

Direct determination of cadmium in biological material using electrothermal atomization atomic absorption spectrometry with a metal tube atomizer and a matrix modifier

A direct determination of cadmium by electrothermal atomization atomic absorption spectrometry with a molybdenum tube atomizer has been investigated. Direct calibration method with cadmium standard solutions and ultrasonic agitation method of a solution including sample powder were used. Sulfur served as a matrix modifier for removal of interferences. Though this direct analytical method for cadmium determination in biological materials had a relatively large standard deviation, the accuracy was similar or superior to those of a sample digestion method and the direct analysis without sulfur. The advantages of this method are its simplicity, low cost, high speed of analysis, and rapid calibration.     

Semi-permanent lutetium modifier for the determination of beryllium in urine by electrothermal atomic absorption spectrometry

The determination of beryllium using electrothermal atomic absorption spectrometry with deuterium background correction in the presence of various isomorphous metals and Mg(NO₃)₂ was studied. While, Eu, Ir and Sm had no effect on the transient signals, the addition of Lu and Mg(NO₃)₂ improved the sensitivity of the beryllium signal with respect to that obtained in the absence of modifier. Although, Mg(NO₃)₂ has improved the signal with respect to its sensitivity, it also increased the tail and the background (BG) signals, specially when urine samples are under study. Whereas, when Lu was used the analytical signal is virtually free of BG interference indicating that the urine matrix interference was almost eliminated. Besides, the addition of 6 μg of Lu ensured that the signals were effectively constant for five firings following the furnace program, which included: three drying, and the pyrolysis, atomization, cleaning and cooling steps. The effect of some components, likely to interfere in the accurate determination of beryllium (such as: Al, Ca, Cl, Co, Cr, Fe, Mg and Mn) were investigated. At the physiological levels, most of these elements had no effect, except in the case of chloride when Mg(NO₃)₂ was used as modifier. In this case, the tolerance limit was of 3000 mg Cl⁻ l⁻¹. The characteristic masses were 1.19, 0.45 and 0.48 pg, when integrated absorbance was measured for beryllium without the addition of any modifier and in the presence of Lu and Mg(NO₃)₂, respectively. The limits of detection (3σ) were 85, 19 and 58 fg, respectively. The accuracy and precision with the use of Lu and Mg(NO₃)₂ was tested for the direct determination of beryllium in urine samples. Quantification was performed with aqueous standards. The results obtained for the determination of beryllium in reference materials (Trace Elements in Urine), together with good recovery of spiked analyte, using either Lu or Mg(NO₃)₂ modification demonstrate the applicability of the procedure to the analysis of real samples. However, Lu provided the most accurate results. Also, the addition of Lu enhanced the precision of the measurements to levels of 1.8% relative standard deviation instead of 5.6 and 3.3% for the case of beryllium alone and with the addition of Mg(NO₃)₂.     

Rapid determination of molybdenum in botanical material by electrothermal atomic absorption spectrometry

Low levels of molybdenum in plant samples are determined by simple digestion in nitric acid followed by electrothermal spectrometry. Sensitivity is enhanced by nitric acid whereas chloride, sulfuric acid, and perchloric acid have inhibiting effects. Recovery of molybdate added to plant samples averaged 94.3%, with a relative standard deviation of 10% for 0.50 μg Mo g^-1 of plant material. Large numbers of samples can be screened for molybdenum content without tedious organic extractions or long dry ashing processes.     

Silicon determination in milk by electrothermal atomic absorption spectrometry using palladium as chemical modifier

A direct method for silicon determination in milk samples by Electrothermal Atomic Absorption Spectrometry was developed. Palladium was used as chemical modifier at a concentration of 610 mg L(-1); with this modifier, silicon was stable up to 1800 degrees C. The precision and accuracy of the method were investigated. The detection limit was 16.2, 2.7 and 7.2 micro g L(-1) for cows' milk, human milk and infant formula, respectively. The method was applied to silicon determination in 17 infant formula samples, 13 human milk samples and 12 cows' milk samples.     

Simultaneous extraction and determination of traces of lead and arsenic in petrol by electrothermal atomic absorption spectrometry

The lead and arsenic compounds are converted to water-soluble iodides by reaction with a solution of iodine in toluene extraction into dilute nitric acid before determination by graphite-furnace atomic absorption spectrometry against aqueous standards. The method is simple, rapid, accurate and reasonably precise.     

Alkali metal fluoride matrix modifiers for the determination of trace levels of silicon by graphite furnace atomic absorption spectrometry

A method is described for the determination of silicon by graphite-furnace atomic absorption spectrometry with alkali metal fluorides as matrix modifiers. Alkali metal fluorides react with silicon to produce metal hexafluorosilicates, which are stable at temperatures as high as 1120– 1300°C, depending on the particular metal used. At higher temperatures, alkali metal hexafluorosilicates decompose into the metal fluoride and silicon tetrafluoride. The subsequent gas-phase atomization of silicon tetrafluoride occurs rapidly, and produces clean, sharp absorption peaks. When used in conjunction with a zirconium-treated graphite tube, this method has a sensitivity of 50 pg Si at a confidence interval of 95%. There is no evidence of silicon carbide formation in the graphite tube, and very little evidence of any deterioration of the zirconium-treated surface, as demonstrated by the fact that more than 200 samples can be processed on a single graphite tube without a decrease in sensitivity or change in the baseline.     

Coprecipitation with disulfide for the determination of traces of cobalt in water by electrothermal atomic absorption spectrometry

Nanogram quantities of cobalt (II) in 200 ml of water were quantitatively collected at pH 4 on a precipitate of disulfide, which is an oxidation product of dithiol (toluene-3,4-dithiol). The precipitate was separated by filtration and dispersed homogeneously in 2 ml of 0.05 mol l(-1) nitric acid with the aid of ultrasonic irradiation. The suspension was directly analyzed for cobalt by electrothermal atomic absorption spectrometry without serious background absorption. This simple preconcentration technique allows the detection of as little as 3 ng l(-1) (50 pmol l(-1)) of cobalt in water samples. The validity of the method was evaluated by using river and seawater certified reference materials.     

Determination of fluoride in sea-water by molecular absorption spectrometry of aluminium monofluoride after removal cation and anion interferences

Three procedures are proposed for the determination of trace levels of fluoride in sea-water, based on the formation of aluminium monofluoride in an electrothermal graphite furnace, followed by measurement of its molecular absorption at 227.45 nm. They involve the use of dilution, a matrix modifier, or a matrix modifier and an ion-exchange resin, and are all acceptably sensitive and specific for fluoride. Interferences from cations and anions are removed by a simple 20-fold dilution of the sample. At 10-fold sample dilution, chloride interference can be removed by adding 0.3M ammonium nitrate together with 0.01M aluminium + 0.01M strontium as a matrix modifier. The same matrix modifier is valid for use with 5-fold sample dilution and a cation-exchange step to avoid matrix affects from cations and chloride. The detection limit is about 8-10 ng/ml fluoride and the determination limit is 20 ng/ml. The precision of peak-height measurement at 0.2 mug/ml is 5-7%.     

Direct determination of traces of molybdenum in synthetic sea water by atomic absorption spectrometry with electrothermal atomization and selective volatilization of the salt matrix

A simple and rapid method is described for the direct determination by graphite-furnace atomic absorption spectrometry (HGA-2100) of traces of molybdenum (O.1–4 ng) in synthetic sea water. It is shown that the salt matrix can be removed completely by selective volatilization at 1700–1850°C, but the original presence of NaCl, Na₂SO₄, and KCl causes a considerable decrease in molybdenum absorbance, and MgCl₂ and CaCl₂ a pronounced enhancement. The presence of MgCl₂ prevents the depressive effects. Samples of less than 50 μl can be analyzed directly without using a background corrector, with a precision of<10%.     

Determination of traces of molybdenum in foods by electrothermal atomic absorption spectrometry

Low levels of molybdenum in different food samples were determined by atomic absorption spectrometry with electrothermal atomization after destruction of organic matter using four different methods, involving dry ashing at 600°C, wet digestion with heating with nitric/sulphuric and nitric/sulphuric/perchloric acid mixtures or direct extraction with dilute hydrochloric acid. In all cases the working conditions, reproducibility, precision and accuracy were investigated. The dry ashing method was generally the optimum destruction method.     

Mechanistic study of the aluminum interference in the determination of arsenic by electrothermal atomic absorption spectrometry

The interference effect derived from the presence of aluminum in the wall and platform atomization of arsenic using two sampling modes (aerosol vs. liquid drop) was revisited. The mechanistic action of the Al interference seems to be the result of the formation of some gas phase Al oxide, which would absorb at the arsenic analytical wavelength. A vaporization/condensation process for aluminum oxide seems to exist into the graphite tube with temperature. The effect of protons (as nitric acid) and activated carbon on the behavior of the Al interference was tested. A beneficial effect of overcoming the Al interference was derived from the presence of activated carbon. The mechanistic action of both, protons and activated carbon, was also proposed.     

Ammonium fluoride as a novel chemical modifier for the elimination of magnesium chloride interference on the determination of lead by graphite furnace atomic absorption spectrometry

Ammonium fluoride was found to be very efficient modifier for the elimination of MgCl₂ interference on Pb determination. Ammonium fluoride probably converts strongly interfering volatile MgCl₂ to less volatile MgF₂ matrix that makes possible the release of Pb analyte at lower temperature, before the matrix starts to vaporize. It was observed likewise that NH₄F removes the interferences mentioned, i.e. caused by MgCl₂ presence, much more effectively as compared with some modifiers, before now recommended for this purpose. The application of this modifier to the determination of Pb in 2% (m/v) MgCl₂ has ensured the characteristic mass and LOD value in the original sample of 12 pg and 60 ng g⁻¹, respectively (10 μl aliquots of sample). Applying the modifier to standards and samples enables the use of matrix-free standard solutions for attaining accurate analysis as verified by recovery studies.     

Flow injection determination of Pb and Cd traces with graphite furnace atomic absorption spectrometry

The preconcentration and recovery of lead and cadmium traces at ng l(-1) level were evaluated in standard solutions and natural aqueous samples using a FIAS (Flow Injection Atomic Spectrometry) apparatus. The method is based on retention of the complex formed between Pb or Cd and 1,2-dihydroxy-3,5-benzendisulphonic acid (Tiron) on a macroporous anion-exchange resin. The recovery of the analytes was obtained by elution with 0.1 M HCl and their determination was performed by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The detection limits were 9 and 7 ng l(-1) for Pb and Cd respectively. The effects of sample solution pH and composition and of interfering agents as well as reagent purity are discussed. The technique was applied to the analysis of natural waters.     

Some observations on the use of matrix modifiers in the determination of aluminum by electrothermal atomic absorption spectrophotometry

Some evidence demonstrating that the use of matrix modifiers is necessary to obtain good calibration lines in the determination of aluminum by graphite furnace atomic absorption spectrophotometry is provided. It was found that the most sensitive results were obtained when Mg(NO₃)₂ was used instead of NH₄H₂PO₄.     

Direct determination of aluminium in serum and urine by electrothermal atomic absorption spectrometry using ruthenium as permanent modifier

Ruthenium (Ru), thermally deposited on a integrated platform graphite furnace, was investigated as a permanent modifier for the determination of Aluminum (Al) in blood serum and urine by electrothermal atomic absorption spectrometry (ETAAS). The platform was treated with 500 μg of Ru as previously described. The pyrolysis and atomization temperatures for each material were of 1300 and 2300 °C, for serum sample and of 1000 and 2400 °C, for urine. The characteristic mass were of 31 and 33 pg for Al in serum sample and urine, respectively (recommended of 31 pg for Al in nitric acid 0.2% (v/v)). For this reason, the calibration was made with aqueous solutions for both the samples. Calibration curves presented r of 0.99145 and 0.99991 for serum and urine, respectively. With the optimized temperatures, being analyzed eight spiked blood serum samples, the recovery was between 95.90 and 113.50%. Two certified urines samples were analyzed with good agreement between experimental and reference values. In both the samples the R.S.D. were <5% (n=3). The detection limit (k=3, n=10) was of 0.40 μg of Al per liter for both the samples. The absorption pulses obtained were symmetrical, with very low background and without interferences. The life time of the tube-platform was higher than 600 cycles of atomizations for both the urine and serum samples.     

Iridium as permanent modifier in the determination of lead in whole blood and urine by electrothermal atomic absorption spectrometry

The behavior of Iridium as a thermally deposited permanent modifier for the determination of lead by GFAAS was studied. The iridium coating procedure was optimized using a two-level factorial design. Using the optimized coating procedure, up to 1100 firings were possible with the same coating without sensitivity losses. The system was used in the determination of lead in whole blood and urine. A mixture of 0.1% Triton X-100 and 0.2% nitric acid was used as diluent. Pyrolysis temperature was 800°C for both matrices. Spiked, low-level samples were used for calibration. Under these conditions, no significant difference was found in comparison to the results obtained using a validated conventional modification procedure employing phosphate as modifier. Also, good agreement between found and certified/reference values were observed in the analysis of certified and commercial quality control materials, respectively. Such agreement was observed even using a 1100 times fired Ir coated platform–graphite tube assembly.     

The determination of manganese by electrothermal atomic absorption spectrometry with a graphite furnace at constant temperature

Many of the interferences reported earlier for the determination of manganese in a graphite furnace were not found when a modern graphite furnace was used. At high levels of chloride matrix, an interference which was observed in the modern furnace was reduced when manganese was determined under constant temperature conditions. In this work, the sample was introduced on a tungsten wire after the graphite furnace had reached a constant, preset temperature. Drying and ashing were accomplished outside the atomization furnace, reducing contamination from matrix materials.