Dmitri A. Katskov

Determination of trace elements in automotive fuels by filter furnace atomic absorption spectrometry

Abstract The determination of Cd, Cr, Cu, Pb and Ni was performed in gasoline and diesel fuel samples by electrothermal atomic absorption spectrometry using the Transverse Heated Filter Atomizer (THFA). Thermal conditions were experimentally defined for the investigated elements. The elements were analyzed without addition of chemical modifiers, using organometallic standards for the calibration. Forty-microliter samples were injected into the THFA. Gasoline samples were analyzed directly, while diesel fuel samples were diluted 1:4 with n-heptane. The following characteristic masses were obtained: 0.8 pg Cd, 6.4 pg Cr, 12 pg Cu, 17 pg Pb and 27 pg Ni. The limits of determination for gasoline samples were 0.13 μg/kg Cd, 0.4 μg/kg Cr, 0.9 μg/kg Cu, 1.5 μg/kg Pb and 2.5 μg/kg Ni. The corresponding limit of determination for diesel fuel samples was approximately four times higher for all elements. The element recovery was performed using the addition of organometallic compounds to gasoline and diesel fuel samples and was between 85 and 105% for all elements investigated.

Method development for the determination of lead in wine using electrothermal atomic absorption spectrometry comparing platform and filter furnace atomizers and different chemical modifiers

A method has been developed for the determination of lead in wine by electrothermal atomic absorption spectrometry without any sample preparation and calibration against aqueous standards, using 7.5 microg Pd as a chemical modifier. The results obtained for seven wines using the proposed method and an acid digestion procedure did not show any significant difference using a Students t-test. Atomization in a transversally heated filter atomizer (THFA) was compared with atomization in a conventional transversally heated platform furnace. The former provided a 2.6-fold higher sensitivity, improving the characteristic mass from 34 to 12 pg and a 1.6-fold better limit of detection (0.3 microg L(-1) compared to 0.5 microg L(-1)) for aqueous solutions using the same injection volume of 20 microL. However, the average precision, expressed as the relative standard deviation for the determination of lead in wine under routine conditions was improved from 4.6% with platform atomization to 0.6% in the THFA. The lead content found in seven arbitrarily chosen white and red wines, five from Brazil, one from Chile and one from Spain, ranged from 6 to 60 microg L(-1) Pb with an average content of 11.4 microg L(-1) Pb for the wines from South America.

Atomic and molecular spectra of vapors evolved in a graphite furnace. Part 3: alkaline earth fluorides

Abstract Slurries of alkaline earth fluorides in aqueous and toluene media, 100 μg as element, were vaporized in a pyrocoated and Ir-sputtered graphite furnace during fast heating from 400 to 2500°C. Absorption spectra in the 200–475-nm range were obtained using a dedicated CCD spectrometer. The vaporization of Be, Mg, Ca, Sr and Ba fluorides showed the signs of the evolution of the di-fluorides at low temperature followed by the appearance of the mono-fluorides and atomic vapor. The exothermal interaction of sample vapor with graphite caused the evolution of heat into the furnace gas that substantiated light scattering below 400 nm, emission continuum above 400 nm and reversal of some molecular bands into emission. All the thermal effects were displayed more intensely in the presence of the hydrolysis products in the aqueous slurry. The hydrolysis was suppressed, and the thermal effects were reduced, when the toluene slurries were used. The vapor interaction with graphite was reduced in a great extent in the Ir sputtered tubes, and hence, the spectra of the mono-fluorides were not affected by the overlapping of simultaneous thermal effects.

Direct determination of Cd and Pb in edible oils by atomic absorption spectrometry with transverse heated filter atomizer

A transverse heated filter atomizer (THFA) was employed for the direct determination of Cd and Pb in edible oils, using a PerkinElmer atomic absorption spectrometer (SIMAA-6000). Twelve samples of olive, avocado, grape seed, sunflower, salad and cooking oils were examined. The determination was performed directly, after sample dilution with n-heptane. The metal–organic standard in oil, Conostan S-21, was employed for calibration. Results of determination were verified using the external calibration and analyte addition methods. Reduction of spectral and chemical interferences from the organic matrix, and reduction of losses of the analyte as volatile compounds, provided limits of detection of 0.06 and 0.7 μg L−1 for Cd and Pb, respectively, with the lowest recovery of the analyte above 60%. Omission of chemical modification, a shorter thermal program and stability of analytical signals during 600–700 temperature cycles within 15% deviation with the use of single filter, represent additional advantages in application of AA spectrometry with THFA atomizer for food analysis.

Determination of lead and cadmium in organic solutions by electrothermal atomic absorption spectrometry with a transverse heated filter atomizer

The performance of a transverse heated filter atomizer (THFA) is investigated for the atomic absorption determination of Pb and Cd in organic solutions and compared with that of a conventional transverse heated graphite atomizer (THGA). Organometallic species of Pb and Cd are stabilized in the THFA at 1100 and 900 °C, respectively, without matrix modification. Pd and Ir modifiers can be used to increase the stabilization temperature by 100 and 200 °C, respectively. Ir provides permanent stabilization during, at least, 75 heating cycles with a cleaning temperature of 2450 °C. Sensitivity improvement (3–4 times), better repeatability, large sample volumes (up to 100 µl) and a short thermal program provide the advantages of the THFA over the THGA in the analysis of organic liquids. The precision and accuracy of the method is verified by the analysis of certified reference materials.

Sulfur determination in coal using molecular absorption in graphite filter vaporizer

The vaporization of sulfur containing samples in graphite vaporizers for atomic absorption spectrometry is accompanied by modification of sulfur by carbon and, respectively, appearance at high temperature of structured molecular absorption in 200-210 nm wavelength range. It has been proposed to employ the spectrum for direct determination of sulfur in coal; soundness of the suggestion is evaluated by analysis of coal slurry using low resolution CCD spectrometer with continuum light source coupled to platform or filter furnace vaporizers. For coal in platform furnace losses of the analyte at low temperature and strong spectral background from the coal matrix hinder the determination. Both negative effects are significantly reduced in filter furnace, in which sample vapor efficiently interacts with carbon when transferred through the heated graphite filter. The method is verified by analysis of coals with sulfur content within 0.13-1.5% (m/m) range. The use of coal certified reference material for sulfur analyte addition to coal slurry permitted determination with random error 5-12%. Absolute and relative detection limits for sulfur in coal are 0.16 μg and 0.02 mass%, respectively.

Vaporization of indium nitrate in the graphite tube atomizer in the presence of chemical modifiers

Abstract The CCD spectrometer coupled with the graphite tube furnace was employed to investigate the vaporization of micrograms of In (as nitrate). Fifty absorption spectra between 200 and 475 nm were collected during 10 s while the tube temperature increased from 700 to 2600–2700 K. The vaporization was carried out in the pyrocoated, Ir-sputtered and Ta-lined tubes in the presence of Cu, Co, Ni, Pd and Mg nitrates, sodium tungstate, ascorbic acid and ammonium hexachloroiridate monohydrate after thermal pretreatment. In the pyrocoated tube the vaporization of In occurred at 1350–1550 K with fast evolution of molecular vapor. The observed broad bands with maxima at 225, 290 and 275 nm were attributed to In 2 O and InO, according to their thermal behavior. Cu, Co, Ni, Pd, Ir modifiers, Ta-lining and Ir sputtered surface suppressed the release of In oxides and induced the delayed appearance of In atomic lines simultaneous with a broad band at 205 nm, tentatively attributed to In dimer. Tungsten caused faster and more complete reduction of In oxide than carbon. Indium oxide bands were substituted between 1100 and 1350 K by a band at 244 nm assigned to gaseous tungsten oxide. Ascorbic acid caused the decrease of indium oxide fraction in gas phase. The presence of MgO in the tube led to the decrease of the band at 205 nm. The vaporization of micrograms of Cu, Co, Ni, Pd and MgO in the pyrocoated tube caused the appearance of absorption and emission continuum, superimposed to In atomic lines at temperatures above 1550 K. This effect had been earlier explained as induced by exothermal interaction of the vaporized substance with carbon. SEM observations of Ir deposits on the graphite surface confirmed the interaction of Pt group metals with carbon at high temperature. A similar effect is advanced for other metal modifiers.

Transverse heated filter atomizer: atomic absorption determination of Pb and Cd in urine

A transverse heated filter atomizer (THFA) was applied to the direct determination of Cd and Pb in urine, and its analytical performances were investigated using a PerkinElmer SIMAA 6000 atomic absorption spectrometer. Seronorm certified human urine reference materials and six realistic samples collected locally were used for the method validation. The urines were diluted ten- or five-fold with 0.2% HNO3. Cd and Pb nitrate solutions were employed as standards. Recoveries of the elements from the urine samples were investigated with the analyte addition method. Compared to the transverse heated graphite atomizer (THGA) with a platform, the THFA provided a significant reduction of spectral background and chemical interferences from the urine matrix, without the use of chemical matrix modifiers, a 1.5–2 times increase of the determination sensitivity and, therefore, a reduction of limits of detection up to 0.018 and 0.2 µg L−1 for Cd and Pb, respectively. The use of a THFA collector made from carbon fiber and a tungsten wire improved recoveries of lead and cadmium in urine (≥92%). A sampling temperature 150 °C enabled us to skip the drying period, thus a significantly reduced temperature program was obtained. The accuracies of the measurements of Cd and Pb in the Seronorm urine materials were in good agreement with the recommended values: 4.1 ± 0.1 µg L−1 of Cd (recommended 5) and 92 ± 1 µg L−1 of Pb (recommended 85). The lifetime of the THFA for Pb determination was longer than 700 firings, with the sensitivity loss not more than 25% after 500 firings.

Atomic and molecular spectra of vapors evolved in a graphite furnace.Part 5: gallium, indium and thallium nitrates and chlorides

Abstract The vaporization behavior and vapor spectra of Ga, In and Tl nitrates and chlorides in the tube furnace was investigated using an UV spectrometer with CCD detector. Fifty spectra in the wavelength range of 200–475 nm were collected in each experiment during the vaporization step, with temperature increase from 473 to 2673 K. The vaporization patterns were compared for the pyrocoated, non-pyrocoated graphite tubes, and Ta-lined tubes. Nitrate and chloride aqueous solutions and chloride slurries in chloroform were used to distinguish the impact of hydrolysis on the vaporization behavior of these chlorides. The spectra of oxygen and chlorine containing molecules, presumably of suboxides, chlorides and dichlorides were identified upon variation of the experimental conditions. The release of suboxide vapors due to the reduction of oxides by carbon was promoted after the decomposition of nitrates. The presence of other elements on the vaporization surface, or the isolation of the sample from the graphite surface by Ta-lining, impeded the vapor release and reduced the intensity of molecular bands. Adsorption of chlorine onto graphite caused a decrease of chloride and dichloride bands. The suboxide bands were observed in the spectra of Ga and In chlorides introduced in the tube as aqueous solutions, due to partial hydrolysis.

Transverse heated filter atomizer: atomic absorption spectrometric determination of Pb and Cd in whole blood

A transverse heated filter atomizer (THFA) was applied to the direct determination of Cd and Pb in blood, and its analytical performances were investigated using a Perkin Elmer SIMAA 6000 atomic absorption spectrometer. Seronorm human blood reference materials (RM) and samples of bovine whole blood spiked with Pb were used for the method validation. The blood samples diluted 5 or 10 times with water to reduce their viscosity were injected in the THFA at temperature about 110–120 °C together with blank or analyte solution in 0.2% HNO3. Compared to the transverse heated graphite atomizer with a platform (THGA), the THFA provided significant reduction of non-specific background absorption and more than 90% recovery of Cd and Pb, without the use of chemical modifiers. The ‘hot’ sampling and injection of ethanol together with the blood solution improved repeatability of analytical signals. Periodical cleaning at elevated temperature after each 15–20 measurements prevented building up of solid residues in the THFA cavity. Limits of detection achieved for Cd and Pb were 0.05 and 1 µg L−1, respectively.