Determination of Mo, Zn, Cd, Ti, Ni, V, Fe, Mn, Cr and Co in crude oil using inductively coupled plasma optical emission spectrometry and sample introduction as detergentless microemulsions

A procedure to prepare crude oil samples as detergentless microemulsions was optimized and applied for the determination of Mo, Zn, Cd, Si, Ti, Ni, V, Fe, Mn, Cr and Co by ICP OES. Propan-1-ol was used as a co-solvent allowing the formation of a homogeneous and stable system containing crude oil and water. The optimum composition of the microemulsion was crude oil / propan-1-ol / water / concentrated nitric acid, 6 / 70 / 20 / 4 w/w/w/w. This simple sample preparation procedure together with an efficient sample introduction (using a Meinhard K3 nebulizer and a twister cyclonic spray chamber) allowed a fast quantification of the analytes using calibration curves prepared with analyte inorganic standards. In this case, Sc was used as internal standard for correction of signal fluctuations and matrix effects. Oxygen was used in the nebulizer gas flow in order to minimize carbon building up and background. Limits of detection in the ng g^− 1 range were achieved for all elements. The methodology was tested through the analysis of one standard reference material (SRM NIST 1634c, Residual Fuel Oil) with recoveries between 97.9% and 103.8%. The method was also applied to two crude oil samples and the results were in good agreement with those obtained using the acid decomposition procedure. The precision (n = 3) obtained was below 5% and the results indicated that the method is well suited for oil samples containing low concentrations of trace elements.     

Comparison of parallel flow and concentric micronebulizers for elemental determination in lubricant oil, residual fuel oil and biodiesel by Inductively Coupled Plasma Optical Emission Spectrometry

Two micronebulizers, PFA-100 and Miramist, were evaluated using a method for elemental determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) in lubricant and residual fuel oils diluted in xylene. The facility and speed of direct sample dilution in organic solvents, without additional pretreatment, combined with the multielemental capacity and robustness of ICP OES are advantageous. The operational conditions were optimized through factorial design. Improvement in the signal-to-background ratio was observed for Ag, Al, B, Ba, Ca, Cr, Cu, Fe, Mn, Si, Ti and V. Higher sensitivity was obtained with the PFA-100 micronebulizer, although the limits of detection (LOD) obtained for both micronebulizers were similar, between 0.3 μg kg^-1 (Mg) and 18 μg kg^-1 (Ni). The certified reference materials NIST 1634c and NIST 1085b were used for method validation and good recoveries were obtained with values between 93% (Pb) and 102% (P) for PFA-100 and 90% (Pb) and 103% (P) for Miramist. The method was also validated for analysis of biodiesel samples by recovery tests, with results from 89% to 103%. The proposed method was employed for the analysis of crude oil, lubricant oil and biodiesel from different raw materials.     

Investigations on the use of chemical modifiers for the direct determination of trace impurities in Al2O3 ceramic powders by slurry electrothermal evaporation coupled with inductively-coupled plasma mass spectrometry (ETV–ICP–MS)

The direct determination of trace impurities in Al₂O₃ ceramic basic powders by ICP–MS using electrothermal evaporation (ETV) with slurry sampling has been investigated. To increase interference-free analyte volatilization, the use of the palladium-group modifiers (PGM) IrCl₃, Pd(NO₃)₂, and PdCl₂ for the determination of Ca, Fe, Ga, Mg, Mn, Na, Ni, and V in Al₂O₃ powders was studied. Their role, which in ETV–ICP–MS and ETV– ICP–OES is to stabilize the investigated analyte during the ashing phase, to increase vaporization of the matrix, and to reduce transport losses was investigated. Optimum analysis results were obtained with PdCl₂ modifier when 500 ng Pd was used for a sample weight of 100 μg Al₂O₃ injected into the ETV. Calibration was performed by standard addition with aqueous solutions of the analytes. The RSDs calculated from triplicate analysis ranged form 5 to 10%. Detection limits between 0.07 μg g^–1 (Ga) and 1.1 μg g^–1 (Na) were achieved. The accuracy was proven for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V by analyzing an NIST standard reference Al₂O₃ material (SRM 699) with a middle grain size of 16.4 μm. The analytical method was used for the analysis of Al₂O₃ powder (AKP 30, Sumitomo, Japan) with impurities in the low μg g^–1 range and a middle grain size of 1.1 μm. The results obtained for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V were comparable with those obtained by ICP–MS subsequent to conventional decomposition with hydrochloric acid at high pressure.     

Evaluation of residual fuel oil standard reference materials as trace element standards

National Bureau of Standards residual fuel oil Standard Reference Materials, SRM 1619, 1620a, 1634a, and former SRM 1634 were analyzed for 20 trace elements by instrumental neutron activation analysis to determine whether these materials are suitable trace element standards for elements other than the 6 elements certified in SRM 1634a. The SRM 1634a is a suitable standard for Ni, V, Se, Na, Zn, As, Cr, Fe, Ce, Sm and La but Co, Ba, Nd, Cs, Eu, Sc, and Sb appear to be heterogeneously distributed and are probably present in mineral particulates. The SRM 1619 is a convenient standard for V and for low Ni content oils, but SRM 1620a does not appear to be a suitable standard for any trace element investigated.To whom correspondence should be addressed.     

Electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry for the determination of Fe,Co, Ni,Cu, and Zn in biological samples

Slurry sampling electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry (ETV-DRC-ICP-MS) has been applied to determine Fe, Co, Ni, Cu, and Zn in biological samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd was used as the modifier. The effectiveness of the ETV sample introduction technique and dynamic reaction cell in alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine Fe, Co, Ni, Cu, and Zn in NIST SRM 1573a tomato leaves reference material and NRCC DORM-2 dogfish muscle reference material and also real samples such as a tea and a swordfish sample purchased locally. Since the sensitivities of the elements studied in slurry and aqueous solution were different, an analyte addition technique was used for the determinations. The analytical results of the reference materials agreed with the certified values. The precision between sample replicates was better than 6% for all determinations. The method detection limit estimated from analyte addition curves was 0.01, 0.006, 0.007, 0.004, and 0.006 μg g⁻¹ for Fe, Co, Ni, Cu, and Zn, respectively, in the original biological samples.     

Fractionation of metals and metalloids by chemical bonding from particles accumulated by electrostatic precipitation in an Argentine thermal power plant

A study was undertaken to evaluate the distribution of Al, As, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in San Nicolás (Argentina). Five samples were collected during one week of operation. For the fractionation, the scheme applied consisted in extracting the elements in four fractions namely (i) soluble and exchangeable elements; (ii) carbonates, oxides and reducible elements; (iii) bound to sulfidic metals; and (iv) residual elements. Metals and metalloids at μg g^− 1 level were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). For validation, a standard reference material (SRM 1633 coal fly ash) from NIST was subjected to the same chemical sequential extraction procedure that the samples. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. Total analyte concentration (in μg g^− 1) varied from 10.6 for Pb to 17,622 for Al. Minimum and maximum concentrations (in μg g^− 1) found in individual samples in the four fractions were: Al, 92.7–9668; As, < 0.3–143; Cr, 2.0–10.4; Cu, < 0.2–35.6; Fe, < 0.3–4992; Mn, < 0.1–128; Ni, < 0.3–139; Pb, < 0.5–9.1; Ti, < 0.3–2243; V, 17.0–112.9; and Zn, < 0.1–68.2. The leachability of the 11 elements under study proved to be different. Low percentages of Al (1%), V (7%) and Cr (8%) were detected in the most bioavailable fraction. Arsenic was found to be most abundant in the non-silicate phase, represented by the second and third fractions, while Cr, Fe, Ni, Pb and Zn were mostly associated to the residual fraction.     

Electrothermal atomic absorption spectrometric method for the determination of vanadium in diesel and asphaltene prepared as detergentless microemulsions

A method based on electrothermal atomic absorption spectrometry for the determination of vanadium in diesel and asphalthene fractions is proposed. In order to avoid analyte losses observed at the microgram per liter range for metal traces in organic solutions, diesel samples were stabilized as detergentless microemulsions by mixing with propan-1-ol and nitric acid solution. The solid asphaltene oil fraction was separated and dissolved in dichloromethane before mixing these solution with propan-1-ol and nitric acid solution. Wall atomization as well as no modifier was used. For diesel, aqueous analytical solutions could be used for calibration. For asphaltene, calibration was performed with analytical solutions prepared at the dichloromethane+propan-1-ol+nitric acid medium, spiked with inorganic standard solution. Linear ranges up to 200 μg l⁻¹ were observed, as well as limit of detection of 5 μg l⁻¹ and 4 μg g⁻¹ for diesel and asphaltene, respectively. Good recoveries were obtained for V-cyclohexanebutyrates spiked diesel samples, as well as coherent results for the asphaltene fraction of the NIST 1634c (trace elements in fuel oil) certified reference material.     

Microhomogeneity assessments using ultrasonic slurry sampling coupled with electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) is a very powerful technique for the direct analysis of solid materials prepared as slurries. The use of isotope dilution USS-ETV-ICP-MS (USS-ETV-ID-ICP-MS) for micro-homogeneity characterization studies of powdered reference materials based on elemental analyses, was investigated. Slurry analysis conditions were optimized taking into consideration density, particle size, analyte extraction, slurry mixing, analyte transport and sampling depth. Slurries were prepared using 1–20 mg of material and adding 1.0 ml of 5% nitric acid diluent containing 0.005% Triton X-100®. Three reference materials were analyzed (RM 8431a Mixed Diet, SRM 1548a Typical Diet and SRM 2709 San Joaquin Soil). Cu and Ni were determined in each material and Fe was also determined in RM 8431a Mixed Diet. ETV conditions were optimized and the benefit of using Pd as a carrier to enhance transport, combined with oxygen ashing was demonstrated. The accuracy of the method was verified by comparing analytical results with certified values. The precision of the method was demonstrated by comparing R.S.D.'s for slurry samples and aqueous standards and elemental ‘homogeneity’ was quantified based on the slurry sampling variability. The representative sample mass analyzed was calculated taking into consideration extraction of analyte into the liquid phase of the slurry. Representative sample masses of approximately 4 mg of RM 8431a provided slurry sampling variabilities of 10% or less for Cu, Fe and Ni. Representative sample masses of approximately 10 mg of SRM 1548a provided slurry sampling variabilities of approximately 10% for Cu and Ni. Representative sample masses of approximately 0.3 mg of SRM 2709 resulted in total analytical variabilities of less than 7%, highlighting the fact that the San Joaquin Soil is clearly the most homogeneous of the materials characterized.     

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of As and Se in soil and sludge

Slurry sampling electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry (ICP-MS) has been applied to determine As and Se in soil and sludge samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd and ascorbic acid were used as mixed modifiers to enhance the ion signals. The effectiveness of ETV sample introduction technique for alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine As and Se in NIST SRM 2709 San Joaquin soil reference material and NIST SRM 2781 domestic sludge reference material and a farmland soil sample collected locally. Since the sensitivities of As and Se in slurry solution and aqueous solution were different, analyte addition technique was used to determine As and Se in these samples. The As and Se analysis results of the reference materials agreed with the certified values. The precision between sample replicates was better than 5% for all determinations. The method detection limit estimated from analyte addition curves was about 0.03 and 0.02 μg g⁻¹ for As and Se, respectively, in original soil and sludge samples.     

Investigations on the use of chemical modifiers for the direct determination of trace impurities in Al2O3 ceramic powders by slurry electrothermal evaporation coupled with inductively-coupled plasma mass spectrometry (ETV-ICP-MS)

The direct determination of trace impurities in Al2O3 ceramic basic powders by ICP-MS using electrothermal evaporation (ETV) with slurry sampling has been investigated. To increase interference-free analyte volatilization, the use of the palladium-group modifiers (PGM) IrCl3, Pd(NO3)2, and PdCl2 for the determination of Ca, Fe, Ga, Mg, Mn, Na, Ni, and V in Al2O3 powders was studied. Their role, which in ETV-ICP-MS and ETV-ICP-OES is to stabilize the investigated analyte during the ashing phase, to increase vaporization of the matrix, and to reduce transport losses was investigated. Optimum analysis results were obtained with PdCl2 modifier when 500 ng Pd was used for a sample weight of 100 microg Al2O3 injected into the ETV. Calibration was performed by standard addition with aqueous solutions of the analytes. The RSDs calculated from triplicate analysis ranged form 5 to 10%. Detection limits between 0.07 microg g(-1) (Ga) and 1.1 microg g(-1) (Na) were achieved. The accuracy was proven for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V by analyzing an NIST standard reference Al2O3 material (SRM 699) with a middle grain size of 16.4 microm. The analytical method was used for the analysis of Al2O3 powder (AKP 30, Sumitomo, Japan) with impurities in the low microg g(-1) range and a middle grain size of 1.1 microm. The results obtained for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V were comparable with those obtained by ICP-MS subsequent to conventional decomposition with hydrochloric acid at high pressure.     

Development of an ultrasound-assisted extraction method for biomonitoring of vanadium and nickel in the coastal environment under the influence of the Prestige fuel spill (North east Atlantic Ocean)

As a consequence of the Prestige shipwreck occurred in the Northeast Atlantic Ocean in November 2002, the need for establishing the environmental impact caused by metals has been of primary concern. Among the different metals contained in the fuel spill, V and Ni are particularly of interest since they appear at relatively high concentration in the original fuel. Biomonitoring of V and Ni using wild mussels (Mytilus edulis) collected along the Galician Coast (NW Iberian Peninsula) has been performed. Ultrasound-assisted extraction of V and Ni from dried mussel tissues using probe sonication allowed a fast solid-liquid extraction thus facilitating sample preparation from large sample batches used for biomonitoring. V and Ni were determined in shellfish caught in the Galician littoral and tar balls from the Prestige spill by electrothermal-atomic absorption spectrometry and inductively coupled plasma-optical emission spectrometry, respectively. A Plackett-Burman saturated design was applied for screening optimization of variables influencing the ultrasound-assisted extraction of V and Ni from shellfish. Efficient extraction of both metals was obtained from slurries prepared in 2 mL capacity sample vials (10 mg sample with a particle size less than 100 μm) using a 3% (v/v) HNO₃ diluent and subjected to probe sonication (3 min; 30% vibrational amplitude of the probe). The method was successfully validated by means of three certified reference materials: NRCC-TORT-2 Lobster hepatopancreas, NIST-SRM 1566b Oyster tissue and NIST-SRM 2977 Mussel tissue. The detection limit (LOD) of V and Ni in the marine biological tissues, calculated according to the 3σ criterion, were 0.24 μg g⁻¹ and 0.15 μg g⁻¹ for V and Ni, respectively. V and Ni concentrations in M. edulis were in the range 1.7-4.8 and 0.8-2.8 μg g⁻¹, respectively. Whilst no significant variations in Ni contents were observed in regard to reference values, an important increase in V concentration is observed at some sampling points, thereby indicating bioaccumulation.     

Feasibility of using solid sampling graphite furnace atomic absorption spectrometry for speciation analysis of volatile and non-volatile compounds of nickel and vanadium in crude oil

A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L⁻¹ Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g⁻¹, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Near‐field laser ablation inductively coupled plasma mass spectrometry: a novel elemental analytical technique at the nanometer scale

An analytical technique utilizing a near‐field effect (to enhance the incident light energy on the thin tip of an Ag needle) in a laser ablation inductively coupled plasma mass spectrometry (NF‐LA‐ICP‐MS) procedure was developed. To produce the thin needles with a tip diameter in the hundreds of nm range a robust needle etching procedure was established. The ‘sample‐to‐tip’ distance was controlled via the measurement of a tunnel current between the needle and sample surface. The NF‐LA‐ICP‐MS technique thus developed was applied for the analysis of copper isotopic standard reference material NIST SRM 976 and tungsten‐molybdenum alloy NIST SRM 480 in the nm resolution range. The observed craters ranged from 200 nm to about 2 µm in diameter and were dependent on the needle used as well as on the ‘sample‐to‐tip’ distance. The mass spectrometric measurements of ⁶³Cu⁺ ion intensity on NIST SRM 976 showed that using near‐field enhancement in laser ablation allowed a roughly 6‐fold increase in the ion intensity of the analyte when the needle was about 100 nm (and below) from the surface, in contrast to when it was far away (e.g. 10 µm) from the sample. The relative standard deviation (RSD) of the ⁶⁵Cu⁺/⁶³Cu⁺ isotopic ratio measurements by NF‐LA‐ICP‐MS was 3.9% (n = 9). The detection efficiencies obtained for the compared LA‐ICP‐MS and NF‐LA‐ICP‐MS methods were found to be 4.6 * 10^?3 counts per second (cps)/ablated atom and 2.7 * 10^?5 cps/ablated atom, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of metals and metalloids in light and heavy crude oil by ICP-MS after digestion by microwave-induced combustion

A method for light and heavy crude oil digestion using microwave-induced combustion (MIC) in closed vessels is described for further determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V, and Zn by inductively coupled plasma mass spectrometry (ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels and analyte determination by inductively coupled plasma optical emission spectrometry (ICP OES) were also used for results comparison. For MIC procedure, samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 µl of 6 mol l^− 1 ammonium nitrate as aid for ignition. The concentration of nitric acid used as absorbing solution was evaluated (1, 2, 4, 7, 10 and 14 mol l^− 1) using an additional reflux step after combustion. Accuracy was evaluated for As, Ba, Ni, Se V, and Zn using certified reference material (CRM) with similar matrix composition and for Cr, Fe, K, Mg, Mn, and Mo by neutron activation analysis (NAA). Recovery tests were also performed for all the analytes by MIC and they were better than 97% using 2 mol l^− 1 nitric acid as absorbing solution (with reflux step). Agreement with certified values and NAA results was better than 95%. Using MIC it was possible to obtain lower limits of detection (LODs) by ICP-MS and also by ICP OES in comparison with those obtained by MW-AD. In spite of both sample preparation techniques were apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using diluted nitric acid as absorbing solution that is an important aspect to minimize interferences by ICP-MS and ICP OES. In order to avoid polyatomic interferences on ⁵²Cr and ⁵⁶Fe determinations by ICP-MS, a dynamic reaction cell with ammonia gas was used. Residual carbon content in digests obtained by MW-AD and MIC was 15% and < 1%, respectively. Using MIC the simultaneous digestion of 8 samples was possible in less than 30 min.     

Aqueous two-phase extraction of nickel dimethylglyoximato complex and its application to spectrophotometric determination of nickel in stainless steel

A polyethylene glycol (PEG)-based aqueous two-phase system has been established for the extraction of Ni-dimethylglyoximato complex. Appropriate amounts of PEG solution and solid (NH₄)₂SO₄ were added to the Ni-dimethylglyoximato complex which had been formed in the presence of sodium tartrate and K₂S₂O₈ at pH 12 in a separatory funnel and shaken vigorously for about 1 min. The mixture was allowed to stand for 10 min and then the absorbance of the extracted complex in the upper PEG-rich phase was measured at 470 nm. Beer's law was obeyed over the range of 0.26-2.1 ppm Ni. The proposed extraction method has been applied to the determination of Ni in steel. A steel sample was decomposed with an appropriate acid mixture. An aliquot of the sample solution was taken, treated with H₃PO₄ and most of the iron and copper were removed by hydroxide precipitation using solid BaCO₃ to control the pH of the sample solution in advance of the extraction of Ni. The analytical results obtained for Ni in steel certified reference material JSS 650-10 (The Japan Iron and Steel Federation), BCS 323 (Bureau of Analysed Samples Ltd.) and NIST SRM 361 and 362 (National Institute of Standards and Technology) were in good agreement with certified values.     

Synthesis of amberlite XAD-2-PC resin for preconcentration and determination of trace elements in food samples by flame atomic absorption spectrometry

A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through –N=C– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as packing for the minicolumn in an on-line system preconcentration system for cadmium, cobalt, copper and nickel determination. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer–burner system of the flame atomic absorption spectrometer (FAAS). Elution of all metals from minicolumn can be made with 0.50 mol L^− 1 HCl or HNO₃. The enrichment factors obtained were 16 (Cd), 24 (Co), 15 (Cu) and 19 (Ni), for 60 s preconcentration time, and 39 (Cd), 69 (Co), 36 (Cu) and 41 (Ni), if used 180 s preconcentration time. Under the optimum conditions, the proposed procedure allowed the determination of cadmium, cobalt, copper and nickel with detection limits of 0.31, 0.32, 0.39 and 1.64 μg L^− 1, respectively, when used preconcentration periods of 180 s. The accuracy of the developed procedure was sufficient and evaluated by the analysis of the certified reference materials NIST 1515 apple leaves and NIST 1570a spinach leaves. The method was applied to the analysis of food samples (spinach, black tea and rice flour).     

Determination of Arsenic and Vanadium in Airborne Related Reference Materials By ICP-MS

This study investigated sample digestion techniques and instrumental interference in determining As and V in airborne related reference materials using inductively coupled plasma mass spectrometry (ICP-MS). Four reference materials, NIST SRM 1648 urban particulate matter,BCR Reference Material No. 176 city waste incineration ash, NIST SRM 2709 San Joaquin soil, and NIST SRM 1633b coal fly ash were dissolved through acid mixture high-pressure bomb digestion.     

Biomonitoring of essential and toxic metals in single hair using on-line solution-based calibration in laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful and sensitive surface analytical technique for the determination of concentration and distribution of trace metals within biological systems at micrometer spatial resolution. LA-ICP-MS allows easy quantification procedures if suitable standard references materials (SRM) are available. In this work a new SRM-free approach of solution-based calibration method in LA-ICP-MS for element quantification in hair is described. A dual argon flow of the carrier gas and nebulizer gas is used. A dry aerosol produced by laser ablation (LA) of biological sample and a desolvated aerosol generated by pneumatic nebulization (PN) of standard solutions are carried by two different flows of argon as carrier or nebulizer gas, respectively and introduced separately in the injector tube of a special ICP torch, through two separated apertures. Both argon flows are mixed directly in the ICP torch. External calibration via defined standard solutions before analysis of single hair was employed as calibration strategy. A correction factor, calculated using hair with known analyte concentration (measured by ICP-MS), is applied to correct the different elemental sensitivities of ICP-MS and LA-ICP-MS. Calibration curves are obtained by plotting the ratio of analyte ion M⁺/³⁴S⁺ ion intensities measured using LA-ICP-MS in dependence of analyte concentration in calibration solutions. Matrix-matched on-line calibration in LA-ICP-MS is carried out by ablating of human hair strands (mounted on a sticky tape in the LA chamber) using a focused laser beam in parallel with conventional nebulization of calibration solutions. Calibrations curves of Li, Na, Mg, Al, K, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Mo, Ag, Cd, I, Hg, Pb, Tl, Bi and U are presented. The linear correlation coefficients (R) of calibration curves for analytes were typically between 0.97 and 0.999. The limits of detection (LODs) of Li, V, Mn, Ni, Co, Cu, Sr, Mo, Ag, Ba, Cd, I, Hg, Pb, Bi and U in a single hair strand were in the range of 0.001-0.90 μg g⁻¹, whereas those of Cr and Zn were 3.4 and 5.1 μg g⁻¹, respectively. The proposed quantification strategy using on-line solution-based calibration in LA-ICP-MS was applied for biomonitoring (the spatial resolved distribution analysis) of essential and toxic metals and iodine in human hair and mouse hair.     

Direct solid sampling electrothermal vaporization of alumina for analysis by inductively coupled plasma optical emission spectrometry

A procedure based on electrothermal evaporation (ETV) and inductively coupled plasma atomic emission spectrometry (ICP-OES) for the determination of trace impurities in Al₂O₃ powders without any sample pretreatment is presented. With the aid of matrix modifier the transport and the evaporation efficiency for refractory compounds could be increased by forming halides with a lower boiling point. As calibration is still a problem in direct solid sample analysis, different calibration approaches including the use of certified reference materials from NIST and standard addition of aqueous solutions of analytes were discussed. The accuracy obtained with calibration and with the standard addition method was shown up for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V for the case of Al₂O₃ NIST standard reference material (SRM 699). The ETV–ICP-OES method was used for the analysis of Al₂O₃ powders with impurities in the low μg/g range and the results for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V obtained with evaporation of discrete powder amounts with ETV–ICP-OES and slurry evaporation under the use of ultrasonic homogenization during the sampling and ETV–ICP-MS were shown to be in a good agreement.