Direct determination of nickel in petroleum by solid sampling–graphite furnace atomic absorption spectrometry

A procedure for the direct GFAAS determination of Ni in petroleum samples using a solid sampling strategy is proposed. Palladium was used as conventional modifier. Central composite design multivariate optimization defined the optimum temperature program and the Pd mass, allowing calibration using aqueous analytical solution. The limit of detection (LOD) at the optimized conditions was 0.23 ng of Ni, for typical sample masses between of 0.10 and 0.60 mg. Linearity at least up to 11 ng of Ni and a characteristic mass of 45 pg were observed, defining a dynamic range between 0.52 and 110 μg g⁻¹. Typical coefficients of variation (n = 10) in the analysis of oil reference materials were 7%. Method validation was performed both by the analysis of oil certified reference materials and by comparison with an independent method (ASTM 5863-B). No statistically significant difference was observed between obtained and expected values. The total determination cycle lasted 5 min, equivalent to a sample throughput of 6 h⁻¹ for duplicate determinations.     

Simple and selective method for determination of iodide in pharmaceutical products by flow injection analysis using the iodine–starch reaction

This work exploited the well-known iodine–starch reaction for development of a simple flow-injection (FI) method for determination of iodide in pharmaceutical samples. Iodide in an injected zone was oxidized to iodine. A gas diffusion unit enables selective permeation of iodine through a hydrophobic membrane. Detection was made very selective for elemental iodine by employing formation of the I₃ ^––starch complex. The detection limit (3S/N) of the system was 1 mg I L^–1. For a liquid patent medicine used for asthma treatment we suggested modification of the system. Direct injection of this sample, which contains a particularly high concentration level of iodide (ca. 9000 mg I L^–1), can be achieved by coupling a dialysis unit to the FI system. This has increased the working range to 6000–10,000 mg I L^–1 without employing complicated nanoliter injection.     

Investigation of the mechanisms of the action of chemical modifiers for electrothermal atomic absorption spectrometry: what for and how?

Modern trends in the research of the action of chemical modifiers for electrothermal atomic absorption spectrometry (ETAAS) are discussed critically. The most prolific approach is that of investigation of processes occurring during the drying and pyrolysis stages with wide application of data from different fields of chemistry and physics.     

Determination of ultra-trace amounts of nickel in environmental samples by atomic absorption spectrometry with in-situ trapping of volatile species in an iridium–palladium coated graphite furnace

A sensitive and accurate method is described for the determination of ultra-trace nickel in environmental samples with in-situ trapping of volatile species in iridium-palladium coated graphite furnace atomic absorption spectrometry. The effects of the conditions for the generation and collection of volatile nickel species, such as medium acidity, potassium borohydride concentration, enhancement reagent concentration, reaction temperature, as well as graphite tube coating, carrier gas flow rate and trapping time were investigated. Phenanthroline was selected as the enhancement reagent due to its good enhancing effect, and iridium–palladium coating was used for the in-situ trapping of volatile nickel species at 300°C. Under the optimal conditions, the calibration curve was linear from 0.21 up to 30.0 ng mL^?1 with correlation coefficient of 0.9991, the detection limit (S/N = 3) was 0.21 ng mL^?1 for 4 mL sample volumes and the relative standard deviation for 11 determinations of Ni at 10 ng mL^?1 was 3.5%. The results found by the proposed methods are accordant with the certified values of water, soil and tea certified reference materials. The proposed methods have been applied for the determination of ultra-trace Ni in tap, river and wastewater, as well as rice and soil samples, with recoveries ranging from 97.3 to 100.5%.     

Supramolecular dispersive liquid–liquid microextraction-based solidification of floating organic drops combined with electrothermal atomic absorption spectrometry for determination of chromium species

A simple, sensitive and reliable method has been developed for separation and preconcentration of chromium (VI) from aqueous samples before determination by electrothermal atomic absorption spectrometry. The method is based on the extraction of the hydrophobic complex of chromium (VI) with ammonium pyrrolidine dithiocarbamate in the coacervates made up of decanoic acid reverse micelles in the water–tetrahydrofuran mixture. Parameters affecting the extraction efficiency of the analyte were studied and optimised. Under the optimum conditions, the linear range, enhancement factor, the limit of detection and limit of quantification were found to be 0.008–0.4 µg L^?1, 127, and 1.8 ng L^?1 and 6.0 ng L^?1, of Cr(VI), respectively. The relative standard deviation at the concentration level of 0.1 µg L^?1 Cr(VI) (n = 6) was 4.2%. Total chromium was determined after the oxidation of Cr(III) to Cr(VI) with permanganate in acidic medium. The method was successfully applied to the determination of chromium species in water and human serum samples.     

Solidified floating organic drop microextraction–electrothermal atomic absorption spectrometry for ultra trace determination of antimony species in tea, basil and water samples

Solidified floating organic drop microextraction was applied as a separation/preconcentration step prior to the electrothermal atomic absorption spectrometric (ETAAS) determination of ultra trace of antimony species. The method was based on the formation of an extractable complex between Sb(III) and ammonium pyrrolidinedithiocarbamate at pH ~ 5, while Sb(V) was remained in the aqueous phase. The antimony extracted into 1-undecanol was determined by ETAAS. Total antimony was determined after the reduction of Sb(V) to Sb(III) with potassium iodide and ascorbic acid. The amount of Sb(V) was determined from the difference of concentration of total antimony and Sb(III). Under the optimum conditions an enhancement factor of 437.5 and a detection limit of 5.0 ng L^?1for the preconcentration of 25 mL of sample was achieved. The relative standard deviation at 300 ng L^?1 of antimony was found to be 3.5 % (n = 6). The proposed method was successfully applied to the determination of antimony in tea, basil and natural water samples.     

Application of microwave-assisted dispersive liquid–liquid microextraction and graphite furnace atomic absorption spectrometry for ultra-trace determination of lead and cadmium in cereals and agricultural products

This study was designed to determine the ultra-trace amounts of lead (Pb) and cadmium (Cd) in various cereals (rice, wheat, barley, peas, beans, corn and lentil) obtained from the markets in Kermanshah city, West Iran. An efficient microextraction method was applied to separation and preconcentration of metal ions. This method is dispersive liquid–liquid microextraction based on solidification of floating organic drop, which overcomes the most important problems of other microextraction techniques. Some effective parameters on extraction were studied and, under optimised conditions, the enhancement factors were 122 and 115 for Cd and Pb, respectively. The calibration graphs were linear in the range of 0.1–50 µg kg^?1 with correlation coefficient more than 0.992. The detection limit was 0.05 µg kg^?1. The values of intra-day relative standard deviations and inter-day relative standard deviations were in the range of 4.7?5.3% and 6.0?6.8%, respectively. The Pb concentrations in rice and wheat samples were considerably higher than the allowable limits set by World Health Organization. The method was successfully applied to determination of the Pb and Cd in cereals, and application of the proposed method to the analysis of two certified reference materials produced results that were in good agreement with the certified values.     

Scanning electron microscopy studies on surfaces from electrothermal atomic absorption spectrometry—III. The lanthanum modifier and the determination of phosphorus

Morphological studies on graphite surfaces by scanning electron microscopy are presented for platforms made from pyrolytic graphite, and for polycrystalline electrographite tubes with pyrolytic graphite coating in which phosphorus was determined without and with the addition of higher concentrations of lanthanum as the modifier. Lanthanum causes severe pitting and corrosion of the graphite surface already after relatively few determinations, and definite indication was found for the formation of intercalation compounds between lanthanum and graphite. No sign was found, however, for the formation of a dense coating of lanthanum carbide as proposed by several authors. The mechanism for the increase of phosphorus sensitivity is most probably the formation of a thermally stable compound involving lanthanum and phosphorus which leads to vaporization of phosphorus at high enough temperatures to obtain sufficient atomization and useful analytical signals. This is supported by the morphological changes of the graphite surface observed after application of higher lanthanum concentrations, and the resulting increased number of active carbon sites. Phosphorus alone also causes substantial corrosion of graphite, but with a completely different pattern. A very pronounced secondary coating of tube and platform wall is observed in the absence of lanthanum which is most probably supported by the formation and decomposition of compounds between phosphorus and graphite.     

Solvent extraction—atomic absorption determination of chromium(VI) in soils

The extraction of chromium(VI) from aqueous saline solutions (NaNO₃) using a trioctylamine solution in toluene was studied in order to determine chromium(VI) in soil samples by atomic absorption spectrometry. It was found that the quantitative recovery of chromium(VI) was attained after extraction with the 0.1 M extractant solution (pH 1.5) for 15 min followed by-back extraction with 4 M HNO₃. Chromium(III) was not extracted under these conditions     

Speciation of very low amounts of arsenic and antimony in waters using dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

A new procedure for the determination of inorganic arsenic (III,V) and antimony (III,V) in water samples by dispersive liquid–liquid micro extraction separation and electrothermal atomic absorption spectrometry (ETAAS) is presented. At pH 1, As(III) and Sb(III) are complexed with ammonium pyrrolidine dithiocarbamate and extracted into the fine droplets formed when mixing carbon tetrachloride (extraction solvent), methanol (disperser solvent) and the sample solution. After extraction, the phases are separated by centrifugation, and As(III) and Sb(III) are determined in the organic phase. As(V) and Sb(V) remain in the aqueous layer. Total inorganic As and Sb are determined after the reduction of the pentavalent forms with sodium thiosulphate. As(V) and Sb(V) are calculated by difference. The detection limits are 0.01 and 0.05 µg L^− 1 for As(III) and Sb(III), respectively, with an enrichment factor of 115. The relative standard deviation is in the 2.9–4.5% range. The procedure has been applied to the speciation of inorganic As and Sb in bottled, tap and sea water samples with satisfactory results.     

Simultaneous separation and preconcentration of ultra-trace of Cu(II), Pb(II) and Zn(II) in water samples by air-assisted liquid–liquid microextraction prior to determination by graphite furnace atomic absorption spectrometry

A simple, rapid and efficient method has been developed for the extraction, preconcentration and determination of copper, lead and zinc ions in water samples by air-assisted liquid–liquid microextraction coupled with graphite furnace atomic absorption spectrometry (GFAAS). In the proposed method, much less volume of an organic solvent (in the order of some µL) was used as the extraction solvent in the absence of disperser solvent. Fine organic droplets were formed by sucking and injecting of the mixture of aqueous sample solution and extraction solvent with a syringe for several times in a conical test tube. After extraction, phase separation was achieved by centrifugation and the enriched analytes in the sedimented phase were determined by GFAAS. Several variables potentially affecting the extraction efficiency were investigated and optimized. Calibration graphs were linear in the concentration range of 45.0–1100 ng L^?1. Detection limits were in the range of 18.0–26.0 ng L^?1. The accuracy of the developed procedure was checked by analyzing NRCC-SLRS4 Riverine water as a certified reference material. Finally, the proposed method was successfully applied to determine the selected heavy metals in tap, surface and river water samples.     

Determination of chromium,manganese and vanadium in sediments and soils by modifier—free slurry sampling electrothermal atomic absorption spectrometry

Slurried sediment and soil samples of the certified reference materials with a highly elevated level of the metals of interest (Mn, Cr and V) were analysed by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background correction. The method of slurry preparation and time-temperature programmes were optimized and, finally, the use of chemical modifiers was not necessary. The effect of alternate spectral lines and gas mini-flows on characteristic masses of analytes was studied. The homogeneity of samples and the influence of short sample grinding were also discussed. The simple, aqueous standard based calibration graphs (except Mn at the concentration > 1000 mg kg⁻¹) were applied for the quantification of results. The results of determinations obtained by slurry sampling agreed well with the cetified values, and the relative standard deviations (RSDs) for the over-all analytical procedure repeatability (at slurries concentration level about 2 mg/2 ml) were less than 9.5%, except manganese (10.4%).     

Development of a sequential injection analysis system for the potentiometric determination of nitrite in meat products by using a Gran’s plot method

A method was developed for in vitro dissolution and ICP-AES based determination of cadmium (Cd) for evaluating its bioaccessibility in herbal medicines to investigate the utility of this test for toxicological assessments. The bioaccessible Cd content of five commonly consumed and Cd-accumulating herbal medicines was determined by in vitro dissolution test with a biorelevant medium simulating gastric conditions. Cd levels were determined by a validated ICP-AES method. In all 5 herbal medicines, the total amount of Cd in herbal medicines was not proportional to the bioaccessible Cd content, which varied from 23.0% to 54.9%. The Cd tolerance limit was exceeded by four of the five herbal medicines in terms of total Cd content, but by only one of these in terms of bioaccessible Cd content. Assessments based on total content may overestimate the risk of Cd toxicity from herbal medicines. Assessing bioaccessibility by in vitro dissolution test coupled with ICP-AES method may be a more appropriate means of determining the safety of herbal medicines containing Cd.     

Evaluation of tungsten–rhodium coating on an integrated platform as a permanent chemical modifier for cadmium,lead, and selenium determination by electrothermal atomic absorption spectrometry

A tungsten–rhodium coating on the integrated platform of a transversely heated graphite atomizer is proposed as a permanent chemical modifier for the determination of Cd, Pb, and Se by electrothermal atomic absorption spectrometry. It was demonstrated that coating with 250 μg W+200 μg Rh is as efficient as the conventional Mg(NO₃)₂+NH₄H₂PO₄ or Pd+Mg(NO₃)₂ modifiers for avoiding most serious interferences. The permanent W–Rh modifier remains stable for 300–350 firings of the furnace, and increases tube lifetime by 50%–100% when compared to pyrolytic carbon integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis. The characteristic masses and detection limits achieved using the permanent modifier were respectively: Cd 1.1±0.4 pg and 0.020 μgL⁻¹; Pb 30±3 pg and 0.58 μgL⁻¹ and Se 42±5 pg and 0.64μgL⁻¹. Results from the determination of these elements in water reference materials were in agreement with the certified values, since no statistical differences were found by the paired t-test at the 95% level.     

Dissolved carbon dioxide flotation-assisted in-syringe dispersive liquid–liquid microextraction coupled with microsampling flame atomic absorption spectrometry for selective determination of palladium in water samples

Dissolved carbon dioxide flotation-assisted in-syringe dispersive liquid–liquid microextraction (DCF-IS-DLLME) followed by microsampling flame atomic absorption spectrometry was developed as a simple, inexpensive and fast method for extraction and determination of Pd(II). In the proposed approach, N,N′-bis (naphthylideneimino) diethylenetriamine (NAPdien) was utilized as a selective complexing reagent for Pd(II) ion. Several influential factors on the extraction efficiency including types and volumes of extraction and disperser solvents, pH of the sample solution, concentration of NAPdien and interfering ions were studied. By applying the optimal conditions, a preconcentration factor of 28.7 and limit of detection of 2.5 ng mL^?1 were provided by the proposed method. Linearity was in the range of 10–400 ng mL^?1 with a correlation coefficient (R ²) of 0.9968. Intra-day RSD% values for five repetitive measurements of the spiked solutions at the concentrations of 20 and 100 ng mL^?1 were 5.2 and 2.4%, respectively, whereas it was obtained within the range of 3.6–18.6% for the real samples. Inter-day RSD% values of the spiked solutions were found to be 9.6 and 8.7%, respectively. The results demonstrated that except for Fe²⁺ and Fe³⁺, no remarkable interfering effect was created by the other studied ions for determination of Pd(II) so that the tolerance limits (W _Ion/W _Pd(II)) of the major cations and anions were in the range of 1000–10,000. Finally, DCF-IS-DLLME was successfully applied for determination of Pd(II) in different water samples and the obtained relative recoveries in the range of 94.5–105% illustrated favorable accuracies for the proposed method.     

Optimisation of a selective method for the determination of organophosphorous triesters in outdoor particulate samples by pressurised liquid extraction and large-volume injection gas chromatography–positive chemical ionisation–tandem mass spectrometry

A selective analytical method for the determination of nine organophosphate triesters and triphenylphosphine oxide (TPPO) in outdoor particulate matter is presented. It involves a fully automated pressurised liquid extraction (PLE) step, integrating an alumina clean-up process, and subsequent determination by large-volume injection gas chromatography–positive chemical ionisation–tandem mass spectrometry (LVI-GC–PCI–MS/MS). The extraction variables (solvent, amount of adsorbent, temperature, time and number of cycles) were optimised using a multicriteria strategy which implements a desirability function that maximises both extraction and clean-up efficiencies while searching for the best-compromise PLE conditions. The final method affords quantification limits of between 0.01 and 0.3 μg g⁻¹ and recoveries of >80%, with the exceptions of the most polar analytes, TCEP and TPPO (~65%) for both urban dust and PM10 samples. Moreover, the method permitted the levels of these compounds in dust deposited outdoors (between LOD and 0.5 μg g⁻¹ for TEHP) and PM10 samples (between LOD and 2.4 μg m⁻³ for TiBP) to be measured and reported for the first time. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.