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.     

Detection of silver nanoparticles in parsley by solid sampling high-resolution–continuum source atomic absorption spectrometry

In this work, we present a fast and simple approach for detection of silver nanoparticles (AgNPs) in biological material (parsley) by solid sampling high-resolution–continuum source atomic absorption spectrometry (HR-CS AAS). A novel evaluation strategy was developed in order to distinguish AgNPs from ionic silver and for sizing of AgNPs. For this purpose, atomisation delay was introduced as significant indication of AgNPs, whereas atomisation rates allow distinction of 20-, 60-, and 80-nm AgNPs. Atomisation delays were found to be higher for samples containing silver ions than for samples containing silver nanoparticles. A maximum difference in atomisation delay normalised by the sample weight of 6.27?±?0.96 s mg^?1 was obtained after optimisation of the furnace program of the AAS. For this purpose, a multivariate experimental design was used varying atomisation temperature, atomisation heating rate and pyrolysis temperature. Atomisation rates were calculated as the slope of the first inflection point of the absorbance signals and correlated with the size of the AgNPs in the biological sample. Hence, solid sampling HR-CS AAS was proved to be a promising tool for identifying and distinguishing silver nanoparticles from ionic silver directly in solid biological samples.

Evaluation of a generalized regression artificial neural network for extending cadmium’s working calibration range in graphite furnace atomic absorption spectrometry

A generalized regression artificial neural network (GRANN) was developed and evaluated for modeling cadmiums nonlinear calibration curve in order to extend its upper concentration limit from 4.0 g L^–1 up to 22.0 g L^–1. This type of neural network presents important advantages over the more popular backpropagation counterpart which are worth exploiting in analytical applications, namely, (1) a smaller number of variables have to be optimized, with the subsequent reduction in development hassle; and, (2) shorter development times, thanks to the fact that the adjustment of the weights (the artificial synapses) is a non-iterative, one-pass process. A backpropagation artificial neural network (BPANN), a second-order polynomial, and some less frequently employed polynomial and exponential functions (e.g., Gaussian, Lorentzian, and Boltzmann), were also evaluated for comparison purposes. The quality of the fit of the various models, assessed by calculating the root mean square of the percentage deviations, was as follows: GRANN > Boltzmann > second-order polynomial > BPANN > Gauss > Lorentz. The accuracy and precision of the models were further estimated through the determination of cadmium in the certified reference material Trace Metals in Drinking Water (High Purity Standards, Lot No. 490915), which has a cadmium certified concentration (12.00±0.06 g L^–1) that lies in the nonlinear regime of the calibration curve. Only the models generated by the GRANN and BPANN accurately predicted the concentrations of a series of solutions, prepared by serial dilution of the CRM, with cadmium concentrations below and above the maximum linear calibration limit (4.0 g L^–1). Extension of the working range by using the proposed methodology represents an attractive alternative from the analytical point of view, since it results in less specimen manipulation and consequently reduced contamination risks without compromising either the accuracy or the precision of the analyses. The implementation of artificial neural networks also helps to reduce the trial-and-error task of looking for the right mathematical model from among the many possibilities currently available in the various scientific and statistic software packages.     

Speciation of Cr(III) and Cr(VI) ions using a β-cyclodextrin-crosslinked polymer micro-column and graphite furnace atomic absorption spectrometry

A sensitive and selective method for the speciation of Cr(III) and Cr(VI) in water samples was developed. It is based on the selective binding of the complex formed between Cr(III) and 4-(2-pyridylazo)resorcinol adsorbed on a cross-linked polymer modified with β-cyclodextrin and placed in a micro-column. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify chromium. Cr(VI) ion is not adsorbed but remains in the aqueous sample phase. Thus, an in-situ separation of Cr(VI) and Cr(III) is accomplished. The concentration of Cr (VI) was calculated by subtracting the value for Cr(III) from that for total chromium. Under optimum conditions, the limit of detection of Cr(III) is 0.056 μg L^?1, and the linear range is from 2.0 to 160.0 μg L^?1. The relative standard deviation is 2.5% (n?=?3, at 30.0 μg L^?1). The preconcentration factor is 25. The method was applied to the speciation of chromium in water samples, and recoveries in spiked real samples range from 101.9% to 104.5%. A reference water sample (GBW(E)080642) also was analyzed, and the results were in good agreement with the certified values.

Determination of ultra traces of lead in water samples after combined solid-phase extraction–dispersive liquid–liquid microextraction by graphite furnace atomic absorption spectrometry

A solid-phase extraction coupled with dispersive liquid–liquid microextraction (DLLME) method followed by graphite furnace atomic absorption spectrometry (GFAAS) was developed for the extraction, preconcentration, and determination of ultra trace amounts of lead in water samples. Variables affecting the performance of both steps were thoroughly investigated. Under optimized conditions, 100 mL of lead solution were first concentrated using a solid phase sorbent. The extracts were collected in 1.50 mL of THF and 18 μL of carbon tetrachloride was dissolved in the collecting solvent. Then 5.0 mL pure water was injected rapidly into the mixture of THF and carbon tetrachloride for DLLME, followed by GFAAS determination of lead. The analytical figures of merit of method developed were determined. With an enrichment factor of 1,800, a linear calibration of 3–60 ng L^?1 and a limit of detection of 1.0 ng L^?1 were obtained. The relative standard deviation for seven replicate measurements of 30 ng L^?1 of lead was 5.2 %. The relative recoveries of lead in mineral, tap, well, and river water samples at spiking level of 10 and 20 ng L^?1 are in the range 94–106 %.     

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.     

Slurry sampling for the determination of arsenic, cadmium, and lead in mainstream cigarette smoke condensate by graphite furnace–atomic absorption spectrometry and inductively coupled plasma–mass spectrometry

The slurry sampling technique has been applied for the determination of As, Cd, and Pb in mainstream cigarette smoke condensate (MS CSC) by graphite furnace-atomic absorption spectrometry (GF-AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). The MS CSC of the 1R4F Reference Cigarette was collected by electrostatic precipitation and was subsequently prepared as two slurry samples with and without the dispersing agent Triton X-100. Comparison of results determined by ICP-MS analyses of the 1R4F MS CSC slurry samples with those from the conventional microwave digestion method revealed good agreement. The precision of Triton X-100 slurry sampling and of microwave-assisted digestion was better than 10% RSD, and both were superior to slurry sampling without use of Triton X-100. The accuracy of the analytical results for the Triton X-100 slurry sample was further verified by graphite furnace-atomic absorption spectrometry (GF-AAS). For GF-AAS, the method limits of detection are 1.6, 0.04, and 0.5 microg x L(-1) for As, Cd, and Pb, respectively. For ICP-MS, the method limits of detection are 0.06, 0.01, and 0.38 microg x L(-1) for As, Cd, and Pb, respectively. The MS CSC of the 1R4F Reference Cigarette was collected in accordance with the Federal Trade Commission (FTC) smoking regime (35 mL puff volume of 2-s puff duration at an interval of 60 s) and the concentrations of As, Cd and Pb were 6.0+/-0.5, 69.3+/-2.8, and 42.0+/-2.1 ng/cigarette, respectively.     

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%.     

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.     

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.     

Freon (CHF<Subscript>3</Subscript>)-assisted atomization for the determination of titanium using ultrasonic slurry sampling–graphite furnace atomic absorption spectrometry (USS–GFAAS): a simple and advantageous method for solid samples

A simple and advantageous method for the determination of titanium using graphite furnace atomic absorption spectrometry with slurry sampling has been developed. Titanium is one of the refractory elements that form thermally stable carbides in the graphite tube, which leads to severe memory effects. Trifluoromethane (Freon-23) was applied in the purge gas during the atomization step or alternatively just prior to the atomization to successfully eliminate the problems of carbide formation and increase the lifetime of the furnace tube which could be used for more than 600 heating cycles. A flow rate of 40 mL min^–1 (5% of Freon in argon) was used to obtain symmetrical peaks with no tailing. However, when the gas flow rate was too high (250 mL min^–1) the peak-tailing and memory effects reappeared. Ti was determined in various materials covering a wide range of concentrations, from 2.8 g g^–1 to 12% (m/m) Ti. The accuracy of the method was confirmed by analyzing certified reference materials (CRMs) or by comparing the results with those obtained using inductively coupled plasma–atomic emission spectrometry (ICP–AES) after decomposition of the samples. The materials analyzed were soil, plant, human hair, coal, urban particulate matters, toothpaste, and powdered paint.     

Silica supported Br?nsted acids as catalyst in organic transformations:A comprehensive review

Br?nsted acid catalysts have been used in a number of organic transformations. To overcome limi‐tations, such as toxicity, volatility, high price and hazardous nature of the conventional methods, the c...     

How long does it take to melt a gold nanorod?: A femtosecond pump–probe absorption spectroscopic study

Using pump–probe femtosecond transient absorption spectroscopy, we determined the rate of the bleach of absorption around 700–800 nm due to the longitudinal surface plasmon band of gold nanorods. Using TEM of the spotted, completely irradiated solutions suggest that the dominant products of the photothermal conformation of the rods are spheres of comparable volume. This lead to the conclusion that the melting of the rods is at least 30–35 ps, independent of the power used (5–20 μJ) or the nanorod aspect ratio (1.9–3.7).     

ChemInform Abstract: Is it Possible to Synthesize a Neutral Noble Gas Compound Containing a Ng—Ng Bond? A Theoretical Study of H—Ng—Ng—F (Ng: Ar,Kr, Xe).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.