Determination of chromium (III) using a homogenous mixture of water-ethanol-methylisobutylketone solvents

The use of organic solvents to increase metal ion determination sensitivity by atomic absorption spectrophotometry with flame is quite common. The most employed organic solvent is 4-methyl-2-pentanona (methylisobutylketone, MIBK) which optimizes sample vaporization and combustion. In this work, we present the use of a homogeneous mixture of water-ethanol—MIBK solvents (1:14:10 v/v, respectively), named the single-phase solution instead of employing pure organic solvents to determine chromium (III) ions by atomic absorption spectrophotometry with flame. The analytical calibration curve in single-phase solution evaluated up to 8 μg ml⁻¹ was linear and was described as Abs=0.0048 C_Cr(III)-0.0010 (r²=0.9998). Stability in the measurement as well as an increase in sensitivity more than twice as high when compared to determinations exclusively made in aqueous solutions were observed. The exactness of the determinations was evaluated with the same steel standards.     

Determination of natural levels of lithium and strontium in human blood serum by discrete injection and atomic emission spectrometry with a nitrous oxide—acetylene flame

A sensitive technique is described for the rapid, direct determination of normal levels of lithium and strontium in 100-μl samples of human blood serum without separation or preconcentration. Nitrous oxide—acetylene flame emission spectrometry, using conventional atomic absorption apparatus is used, with discrete sample injection. Lithium and strontium standards were prepared in 21% (v/v) glycerol which approximates the viscosity of serum. It is recommended that serum samples be analyzed by either calibration with artificial serum and glycerol standards or by immediate standard microaddition procedures. Results for pooled human serum indicate accuracy and precision of better than 6% at the 10 ng ml^-1 level. The method is free from nebulizer clogging and matrix interferences and should be useful as a routine clinical laboratory procedure.     

Determination of Cu,Cd, Ni,Pb and Zn in Edible Oils Using Reversed-Phase Ultrasonic Assisted Liquid–Liquid Microextraction and Flame Atomic Absorption Spectrometry

A simple and green reversed-phase ultrasonic assisted liquid?liquid microextraction method for determination of Cu, Cd, Ni, Pb and Zn in edible oils was developed. Detection was carried out by flame atomic absorption spectrometry. The influence of main parameters including ultrasonic time and temperature, disperser solvent, volume of extracting solvent and centrifuging time on the extraction efficiency of target analytes were investigated and optimized. In the proposed method, a few microliters of water (containing 3%, v/v, nitric acid) as extracting solvent was injected into the oil sample and mixture transferred to ultrasonic bath. Then, the mixture was centrifuged in order to accelerate in phase separation. Finally, the aqueous phase was removed and delivered to flame atomic absorption spectrometer. Calibration curves for all metals were linear in the range of 5?100 ng/mL. The limit of detections for Cu, Cd, Ni, Pb and Zn were 0.8, 0.3, 0.5, 1.5 and 0.5 ng/mL, respectively. Relative standard deviation (RSD) values were in the range of 0.6?1.9%. The recoveries were in the range of 95.2–101.2% with RSD values ranging from 0.8 to 1.9%. The proposed method was applied successfully for the determination of interested metals in commercial edible oils.     

Atomic absorption spectrometric determination of copper,zinc, and lead in geological materials

An atomic absorption spectrometric method is described for the determination of copper, zinc, and lead in geological materials. The sample is digested with HF—HCl—H₂O₂; the final solution for analysis is in 10 % (v/v) HCl. Copper and zinc are determined directly by aspirating the solution into an air—acetylene flame. A separate aliquot of the solution is used for determination of lead; lead is extracted into TOPO-MIBK from the acidic solution in the presence of iodide and ascorbic acid. For a 0.50-g sample, the limits of determination are 10–2000 p.p.m. for Cu and Zn, and 5–5000 p.p.m. for Pb. As much as 40 % Fe or Ca. and 10 % Al, Mg, or Mn in the sample do not interfere. The proposed method can be applied to the determination of copper, zinc, and lead in a wide range of geological materials including iron- and manganese-rich, calcareous and carbonate samples.     

Analytical applications of emulsions. determination of lead in lubricating oils by atomic absorption spectrometry

Lead used in lubricating oils (ca. 0.2%) is determined by direct nebulization of oil-water emulsions into the flame of an atomic absorption spectrometer. The method is as accurate and precise as a similar method involving mineralization of the oil, and has the advantage of simplicity, speed and the use of aqueous standards for calibration.     

Evaluation of the analytical capabilities of frequency modulated sources in multielement non-dispersive flame atomic fluorescence spectrometry

Frequency modulated sources of Cd and Zn are used to produce modulated atomic fluorescence signals (at two different frequencies) in a non-dispersive flame atomic fluorescence spectrometer. To reduce the flame background level, a chlorine filter, a separated air—acetylene flame, and a solar blind photomultiplier are used. Even so, there is shown experimentally and theoretically to be a multiplex disadvantage, as compared to the conventional single slit scanning dispersive spectrometer, as a result of the flame background photon noise and an additional multiplex disadvantage at high concentrations of an interference, e.g. in the measurement of Zn (213.9 nm), Cd (228.8nm) results in a reduced S/N for Zn when the Cd signal level becomes comparable with the flame background signal level. Little future for multiplexed techniques in atomic flame spectrometry in the u.v.- Visible is predicted.     

Suppression of interferences in the determination of lead in natural and drinking waters by graphite-furnace atomic absorption spectrometry

The problem of matrix interference encountered in the determination of lead in natural and drinking waters by graphite furnace atomic absorption spectrometry is examined by looking at the individual effects of various constituent salts (NaCl, KCl, MgCl₂ and CaCl₂, Na₂SO₄, KH₂PO₄ and Mg(NO₃)₂), of which MgCl₂ and Na₂SO₄ interfered most severely. The use of the L'vov platform decreased the sulphate interference, but was not successful in removing the other interferences. The mixture of 0.05% (w/v) lanthanum (as LaCl₃) and 1% (v/v) nitric acid previously proposed for wall atomisation was found to be effective in controlling the interferences. Nitric acid alone removed almost completely the effects of MgCl₂ and CaCl₂, but had little effect on the interference of sulphate, which required the addition of lanthanum for suppression. The removal of interferences in real water samples by the lanthanum/nitric acid mixture is demonstrated by comparison of results obtained by this approach with those obtained by atomic fluorescence spectrometry and by flame atomic absorption spectrometry after preconcentration by evaporation.     

Flame Atomic Absorption Spectrometry Assay for Copper Determination in Pharmaceutical Products for Veterinary Use

Abstract

The scope of the present study is to quantify copper in pharmaceutical products of veterinary use, using flame atomic absorption spectometry (f_AAS). The determination is carried out after samples' mineralization in a HCl:HNO₃ (20∶1, v:v) mixture followed by the instrument quantification and the validation of the result. The validation indicates that the interferences from the whole analytical system and their measurement do not influence the results and ensure that there are no other effects which have not been considered.     

The role of various flame constituents in the production of atoms in the air—acetylene flame

Atom-formation processes in the premixed air—acetylene flame used in atomic absorption spectrometry are examined. Flame profiles of copper, indium and calcium atoms for five flames of differing acetylene: air ratios are compared with the flame profiles of temperature and the natural flame species C₂, CH and H. The flame profiles of the metals bear little resemblance to the temperature profile. C₂ and CH radicals are shown to be confined to the lower region of the flame (approximately to the region of the reaction zone), whereas H radicals persist far beyond the reaction zone. The strong resemblance of the profile of indium atoms to that of H radicals suggests the participation of H radicals in indium atom formation. Experiments on the action of the flame on solid calcium oxide similarly suggest the involvement of H radicals in the reduction of calcium oxide.     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix. Received: 20 February 1997 / Revised: 2 June 1997 / Accepted: 7 June 1997     

An Ion Exchange Separation-Atomic Absorption Spectrophotometric Method for the Determination of Microgram Quantities of Copper,Iron and Zinc in Infant Milk Formula: Powder Form.

Abstract

An atomic absorption spectrophotometric method is described for the determination of microgram quantities of copper, iron and zinc in infant formula powdered milks. After sample digestion in concentrated nitric acid in a pressure vessel, the solution is evaporated till dryness, and then a solution of 6M HCl is added, in order to form the chlorocomplexes of the metals. This acid solution is passed through an ion-exchange column (anion exchange resin, chloride form). The metals are eluted from the column with diluted acid mixture of 0.005M HCl + 0.5% (v/v) HNO₃, and then the eluate is evaporated till dryness. The residue is dissolved in 1% (v/v) HNO₃, and then atomized into an air-acetylene flame. A standard addition procedure was employed as a back-up technique. The results obtained by this proposed method and those obtained by the standard addition technique were statistically treated, compared and discussed in this paper.     

Determination of vanadium by atomic absorption spectrophotometry

Methods for the determination of vanadium, in the range 0.5–100 mg/l, by atomic absorption spectroscopy in an oxy-acetylene as well as in a nitrous oxideacetylene flame are presented. For use with oxy-acetylene flames, vanadium is extracted as vanadium cupferrate into a mixture of methyl isobutyl ketone and oleic acid (78:22, v/v) and the organic phase is aspirated to the flame. The sensitivity is 0.7 mg/l of vanadium in the organic phase. For nitrous oxide-acetylene flames, an aqueous solution of vanadium is aspirated directly. The sensitivity is further improved by the use of methyl isobutyl ketone, the addition of Al³⁺ and diethylene glycol diethyl ether. Many potential interferences were examined and methods to overcome those found are given.     

Optimization of Fatty Acid Determination in Selected Fish and Microalgal Oils

The use of ten fatty acid methyl ester reference standards coupled with a detailed quantification method was shown to significantly optimize the fatty acid determination of selected fish and microalgal oils when compared to methods that use only one reference standard (C19:0 or C23:0) as a relative response factor. When using the mixture of ten reference standards after transesterifying oils with NaOH/BF₃, determination of total fatty acids, eicosapentaenoic acid and docosahexaenoic acid improved by an average of 7.3, 11.5 and 8.4%, respectively. Furthermore, improvements of 13.9, 18.9 and 6.8% of total fatty acids, EPA and DHA, respectively, were obtained when using the mixture of reference standards for fatty acid determination after directly extracting and transesterifying oil contained in microalgal cells with a mixture of methanol, HCl and chloroform. Fatty acid methyl ester standards dissolved in isooctane showed <5% variability throughout 130 days of stability testing when stored at ?20 °C. The optimized method can be used for improving the quantification of fatty acids in both oils (fish and microalgal oils) and dry microalgal cells.     

Flow injection flame atomic absorption spectrometry for slurry atomization. Determination of iron, calcium and magnesium in samples with high silica content

A study on the use of slurries in flame atomic absorption spectrometry is reported. Samples with a very high silica content are ground and then slurried in a solution containing 2% hydrochloric and 3% v/v hydrofluoric acids. The suspensions are prepared in the 0.01-1% m/v range and introduced into the flame by means of a simple flow injection manifold. Relative standard deviations for the measurements of iron, calcium and magnesium in diatomaceous earth samples are in the 1.5-2.8, 2.2-5.3 and 2.8-5.0% ranges, respectively. To avoid the use of suspensions prepared with a very low percentage of solid sample and to improve the reproducibility, an on-line dilution manifold is tried. The use of an easy-to-construct variable volume dilution chamber allows the on-line dilution of the slurries, thus permitting the determination of calcium and magnesium over a wide range of concentrations. Calibration is performed using aqueous standards. The experimental conditions, optimized for the determination of iron, calcium and magnesium in diatomaceous earth samples, can also be applied to other silica-based materials, as is shown by the analysis of several standard reference materials.     

Determination of trace impurities in electronic grade quartz: Comparison of inductively coupled plasma mass spectroscopy with other analytical techniques

An analytical procedure for the determination of uranium and thorium in the sub-ng/g range as well as of other trace elements in the ng/g to g/g range in high purity quartz samples is described. The results obtained by inductively coupled plasma mass spectroscopy (ICP-MS) are compared to those obtained by other analytical techniques (instrumental neutron activation analysis, INAA; flame atomic absorption spectrometry, AAS; Zeeman graphite furnace atomic absorption spectrometry, ZGFAAS; total reflection X-ray fluorescence analysis, TRFA; direct current arc optical emission spectrometry, DC-arc OES; and X-ray fluorescence analysis, XRFA). For the ICP-MS measurements, the decomposition of the samples is carried out with HF/HNO₃/H₂SO₄-mixtures. The results obtained by the different methods show reasonable agreement. For uranium and thorium, ICP-MS proves to be the most sensitive method: detection limits of about 50 pg/g can be achieved for both elements.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Burntgas composition of the heliumoxygenacetylene flame

The burnt gas composition of a potentially important atom reservoir, the HeO₂C₂H₂ flame, is calculated. This flame, compared to the air—acetylene flame, provides a slightly more reducing and a much less quenching environment.     

Determination of cadmium and lead at low levels by using preconcentration at fullerene coupled to thermospray flame furnace atomic absorption spectrometry

A new and sensitive method for Cd and Pb determinations, based on the coupling of thermospray flame furnace atomic absorption spectrometry and a preconcentrator system, was developed. The procedure comprised the chelating of Cd and Pb with ammonium pyrrolidinedithiocarbamate with posterior adsorption of the chelates on a mixture (40 mg) of C₆₀ and C₇₀ at a flow rate of 2.0 ml min⁻¹. These chelates were eluted from the adsorbent by passing a continuous flow of ethanol (80% v/v) at 0.9 ml min⁻¹ to a nickel tube placed in an air/acetylene flame. After sample introduction into the tube by using a ceramic capillary (0.5 mm i.d.), the analytical signals were registered as peak height. Under these conditions, improvement factors in detectability of 675 and 200 were obtained for Cd and Pb, respectively, when compared to conventional flame atomic absorption spectrometry. Spiked samples (mineral and tap waters) and drinking water containing natural concentrations of Cd were employed for evaluating accuracy by comparing the results obtained from the proposed methodology with those using electrothermal atomic absorption spectrometry. In addition, certified reference materials (rye grass, CRM 281 and pig kidney, CRM 186) were also adopted for the accuracy tests. Due to the good linearity ranges for Cd (0.5–5.0 μg l⁻¹) and Pb (10–250 μg l⁻¹), samples with different concentrations could be analyzed. Detection limits of 0.1 and 2.4 μg l⁻¹ were obtained for Cd and Pb, respectively, and RSD values <4.5% were observed (n=10). Finally, a sample throughput of 24 determinations per hour was possible.     

Cloud point preconcentration and flame atomic absorption spectrometric determination of Cd and Pb in human hair

Cloud point methodology has been successfully used for the preconcentration of trace amounts of Cd and Pb as a prior step to their determination by flame atomic absorption spectrometry. O,O-Diethyldithiophosphate and Triton X-114 are used as hydrophobic ligand and non-ionic surfactant, respectively. After phase separation at 40 °C based on cloud point of the mixture, the surfactant-rich phase is diluted with methanol. The enriched analyte in the final solution is determined by flame atomic absorption spectrometry using conventional nebulization. After optimization of the complexation and extraction conditions, enhancement factors of 22 and 43 were obtained for Cd and Pb, respectively. Under the experimental conditions used, preconcentration of only 10 ml of sample in the presence of 0.05% (v/v) Triton X-114 permitted the detection of 0.62 μg l⁻¹ of Cd and 2.86 μg l⁻¹of Pb. The proposed method was applied to the determination of Cd and Pb in human hair samples.     

γ-Radiation produced supported metal complex catalysts V. Determination of rhodium by atomic absorption spectroscopy

Rhodium in polymer-supported catalysts as well as in organorhodium complexes can be determined conveniently by atomic absorption spectroscopy. Following oxidative destruction of the organic material in a mixture of concentrated sulphuric acid and hydrogen peroxide, an aqueous solution to which 2% lanthanum nitrate has been added is aspirated into an air/acetylene flame. A linear calibration graph is obtained at 343.5 nm for rhodium concentrations in the range 0–20 ppm. Standards are prepared by oxidising [RhH(CO)(PPh₃)₃] in the same way as the sample. In this way interference by chloride is avoided. This interference is important when large amounts of chloride are present as in commercial rhodium trichloride in aqueous hydrochloric acid solution standards.     

Multivariate technique for optimization of digestion procedure by focussed microwave system for determination of Mn, Zn and Fe in food samples using FAAS

This article describes the development by response surface methodology (RSM) of a procedure for iron, zinc and manganese determination by flame atomic absorption spectrometry (FAAS) in food samples after digestion employing a focussed microwave system. A Doehlert matrix was used to find optimal conditions for the procedure through response surface study. Three variables (irradiation power and time and composition of oxidant solution—HNO₃ + H₂O₂) were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 12 min, 260 W and 42% (v/v) for irradiation time, irradiation power and percent of H₂O₂ in solution, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials and by comparison with a well-established closed vessel microwave dissolution methodology.