Paolo Tittarelli

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.

Evaluation and validation of instrumental procedures for the determination of nickel and vanadium in fuel oils

A direct method for the determination of Ni and V in fuel oils by flame atomic absorption spectrometry has been developed which is sufficiently rapid, accurate and precise for monitoring batches of fuel oil. Fifty-four European laboratories participated in the round-robin test (RRT), which was carried out on six fuel oil samples in order to evaluate the precision of the method. Various procedures and instrumental techniques such as electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence, inductively coupled plasma mass spectrometry and neutron activation analysis were employed to control the accuracy of the results. The participating laboratories provided 1879 results for Ni and 1945 results for V. The precision of the flame direct method (FDM) was calculated according to the ISO 5725 method. The repeatability and reproducibility data for the FDM showed definite improvements on comparison with the precision data given by the Institute of Petroleum (IP) 288 method. The limit of determination (six times the interlaboratory standard deviation of the FO01NV sample) was 5.6 µg g–1 for Ni and 4.2 µg g–1 for V. In the concentration range investigated (1–70 µg g–1 of Ni and 2–180 µg g–1 of V) the repeatability (r) and reproducibility (R) showed a linear relationship with both element contents. The r values were 3.4 µg g–1 for an Ni content of 30 µg g–1 and 3.8 µg g–1 for a V content of 50 µg g–1, while the R values for the same element contents, were, respectively, 8.1 µg g–1 for Ni and 11.1 µg g–1 for V. Evaluation of the accuracy of the method was also performed using standard reference materials. The instrumental techniques showed the results to be in excellent agreement. The control of accuracy and the comparison of results obtained by the independent techniques allowed validation of the proposed method. Therefore, it was possible to advance consensus values for the Ni and V content in the six fuel oil samples examined in the RRT.

Reduction of Background Absorption in the Measurement of Cadmium, Lead and Selenium in Whole Blood Using Iridium-sputtered Graphite Tubes in Electrothermal Atomic Absorption Spectrometry

The thermal behaviour during pyrolysis and of the vapour phase during atomization for Cd, Pb and Se in acid-digested whole blood using Ir-sputtered tubes is described. The performance of Ir as a permanent modifier was affected unfavourably by the complex matrix compared with conventional modifiers. Background absorption was measured using an atomic absorption spectrometer in addition to a diode-array spectrometer and compared with the background obtained in pyrolytic graphite-coated graphite tubes. Both methods of measurement indicated that the background was much reduced in the Ir-sputtered tubes. The decrease in background absorption improves conditions for the measurement of these elements. Background molecular absorption was also measured as a function of time. Molecular species such as NO were detected in the vapour phase using pyrolytic graphite-coated tubes, whereas CS and CO were detected using Ir-sputtered tubes.

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.

Design, operation and analytical characteristics of the filter furnace, a new atomizer for electrothermal atomic absorption spectrometry☆

Abstract The design of a filter furnace (FF), a new atomizer for electrothermal atomic absorption spectrometry (ETAAS) introduced earlier, has been optimized for applications in conventional analytical instrumentation. The factors controlling the analytical characteristics of the FF, i.e. the general geometry of the FF, the configuration of the dosing hole, pyrocoating, the spatial distribution of the shield gas around the FF, the amount of thread, and the porosity of the filter graphite are examined. The analytical characteristics of the improved design of the FF have been investigated and compared with those of tube and platform furnaces. The determination of high- and medium-volatility elements is evaluated in the presence of an excess of volatile matrix. The new FF has a number of advantages: the potential to set the sampling volume in the range 10–100 μl while maintaining short drying times for any volume; sensitivity levels comparable with those attainable by the stabilized temperature platform furnace (STPF) technique, without the use of matrix modifier; and significant reductions in background and chemical interference. The speed and accuracy of the method is shown in the determination of various elements in the presence of halides, seawater, nitric acid, whole blood and other chemicals. The main disadvantage of the method is that the FF components are destroyed at the temperatures required for the determination of low-volatility and carbide-forming elements.

Determination of sulphur in fuel oils by absorption spectrometry of electrothermally generated carbon sulphide molecules

Molecular absorption spectra of CS are observed during the vaporization of crude and fuel oils in an electrothermal atomizer. The CS absorbance at 257.6 nm is used to determine the sulphur content of the oil, based on measurements in a conventional electrothermal atomic absorption spectrometer. The results for various fuel oils generally agree with those obtained by x-ray fluorescence spectrometry (ASTM D2622). The detection limit referred to the undiluted oil is 50 mg kg−1, and the repeatability is 3% at the 250 mg kg−1 level. Some oils exhibit uneven vaporization of sulphur species.

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.

Vaporization of silicon and germanium as molecular species in electrothermal atomizers

The vaporization of Si and Ge and their respective oxides was recorded using an ultraviolet spectrometer with diode-array detection. The samples were analysed as aqueous slurries using thermal programmes that are normally employed for trace analysis. Both the elements and the respective oxides form the monoxides SiO(g) and GeO(g) during atomization. In the presence of compounds containing S, CaSO4 or FeS2, the gaseous sulfides SiS and GeS were observed. While in the case of Si it is possible to obtain SiS as a unique species from wall vaporization, with Ge the presence of GeS is always associated with that of GeO. The spectral characteristics of the compounds identified are reported. The presence of SiS has also been detected during the atomization of a bituminous coal.

Effect of magnesium nitrate vaporization on gas temperature in the graphite furnace

Abstract The vaporization of magnesium nitrate was observed in longitudinally-heated graphite atomizers, using pyrocoated and Ta-lined tubes and filter furnace, Ar or He as purge gas and 10–200-μg samples. A charge coupled device (CCD) spectrometer and atomic absorption spectrometer were employed to follow the evolution of absorption spectra (200–400 nm), light scattering and emission. Molecular bands of NO and NO 2 were observed below 1000°C. Magnesium atomic absorption at 285.2 nm appeared at approximately 1500°C in all types of furnaces. The intensity and shape of Mg atomization peak indicated a faster vapor release in pyrocoated than in Ta-lined tubes. Light scattering occurred only in the pyrocoated tube with Ar purge gas. At 1500–1800°C it was observed together with Mg absorption using either gas-flow or gas-stop mode. At 2200–2400°C the scattering was persistent with gas-stop mode. Light scattering at low temperature showed maximum intensity near the center of the tube axis. Magnesium emission at 382.9, 383.2 and 383.8 nm was observed simultaneously with Mg absorption only in the pyrocoated tube, using Ar or He purge gas. The emission lines were identified as Mg 3 P°– 3 D triplet having 3.24 eV excitation energy. The emitting species were distributed close to the furnace wall. The emitting layer was thinner in He than in Ar. The experimental data show that a radial thermal gradient occurs in the cross section of the pyrocoated tube contemporaneously to the vaporization of MgO. This behavior is attributed to the reaction of the sample vapor with the graphite on the tube wall. The estimated variation of temperature within the cross section of the tube reaches more than 300–400°C for 10 μg of magnesium nitrate sampled. The increase of gas temperature above the sample originates a corresponding increase of the vaporization rate. Fast vaporization and thermal gradient together cause the spatial condensation of sample vapor that induces the light scattering.