Progress in direct solid sampling analysis using line source and high-resolution continuum source electrothermal atomic absorption spectrometry

Determination of cadmium in lichens by solid sampling graphite furnace atomic absorption spectrometry (SS-GF-AAS)

The determination of trace metal contents directly from a solid sample is a trend in modern atomic spectrometry. The aim of this study was to develop an analytical method for the routine determination of Cd in lichens using solid sampling graphite furnace atomic absorption spectrometry (SS-GF-AAS). For the determination of Cd, the temperature program of the graphite furnace was optimized using a mixed matrix modifier (Pd + Mg (NO₃)₂ + Triton X-100). The limit of detection and the limit of quantification were 0.9 μg/kg and 3 μg/kg, respectively. The analytical method for Cd determination in the plant matrix was verified by the analysis of certified reference materials of lichens, seaweed, and rye grass. The developed procedure was applied to the study of Cd distribution in thalli of Usnea antarctica lichen from James Ross Island, Antarctica. The SS-GF-AAS analytical method is particularly suited for use in environmental studies and plant physiology (the microanalysis of anatomical structures).

A handling-free methodology for rapid determination of Cu species in seawater based on direct solid micro-samplers analysis by high-resolution continuum source graphite furnace atomic absorption spectrometry

A very simple, sensible and advanced new methodology for the determination of copper species in seawater has been developed. The method consisted of two steps: first a separation/preconcentration of copper species by using liquid phase microextraction-based solvent bars followed by the direct analysis of these solid polymeric micro-samplers in an atomic absorption spectrometer provided with a device for direct analysis. For liquid microextraction, di-2-pyridylketone benzoylhydrazone (dPKBH) dissolved in octan-1-ol was selected as the extracting agent due to its ability to transport inorganic Cu species from seawater samples. The optimum chemical and physical conditions for copper micro-extraction were sample pH 8, a dPKBH concentration of 0.010 mol L^-1, a stirring speed of 800 rpm and an extraction time of 10 min. A graphite furnace temperature program was optimised to assure the complete elimination of the solvent bar matrix, and the atomisation step took place at 2200 °C. The method exhibited a limit of detection of 0.026 μg L^-1 of copper and a linear range up to 1.50 μg L^-1, showing great repeatability and reproducibility (4.07% and 4.43%, respectively). Suitability of the method was confirmed by analysing a certified reference material (CASS-4) under optimum conditions, being the first time ever that a direct solid analysis-based method has been used for the determination of total dissolved copper concentration in seawater. Furthermore, the method was applied to the determination of the operationally defined transportable Cu fraction in seawater samples at natural conditions and the results were compared with theoretical data provided by Visual MINTEQ® 3.1 software. A mathematical model that permits to estimate total dissolved copper concentration was obtained, and the non-transportable copper fraction was calculated by difference.

On the spectroscopic investigation of lipstick stains: Forensic trace evidence

In forensic science, lipsticks are considered as crucial trace evidence because it helps in the linking of the criminal with the crime scene. In the present work, twenty-five lipstick samples are characterized and discriminated by using ATR-FTIR spectroscopy coupled with multivariate statistical methods. The utilized approach is non-destructive, fast, and provides reproducible results. It is observed from the FTIR spectra that lipstick contains various aliphatic and aromatic compounds e.g. Propyl ester of Hexanoic acid, Silicates, etc. Further, the discrimination power is calculated by using three approaches i.e. visual examination, cluster analysis (HCA and k-means) and factor analysis method. The multivariate method combined with t-statistics delivered a higher value of discriminating power i.e. 100% which is an improvement on the 99.00% discrimination power of visual comparison method. The developed method is validated by analyzing five duplicate samples and predicted them to their respective brands significantly. This study establishes a method which provides proof of concept discrimination of the lipstick samples. In the future, it can be quite possible to create an FTIR database of more lipstick samples for the identification of unknown/suspected lipstick samples.

Micro-sampling method based on high-resolution continuum source graphite furnace atomic absorption spectrometry for calcium determination in blood and mitochondrial suspensions

A micro-sampling and straightforward method based on high resolution continuum source atomic absorption spectrometry (HR-CS AAS) was developed to determine extracellular and intracellular Ca in samples of interest in clinical and biomedical analysis. Solid sampling platforms were used to introduce the micro-samples into the graphite furnace atomizer. The secondary absorption line for Ca, located at 239.856nm, was selected to carry out the measurements. Experimental parameters such as pyrolysis and atomization temperatures and the amount of sample introduced for the measurements were optimized. Calibration was performed using aqueous standards and the approach to measure at the wings of the absorption lines was employed for the expansion of the linear response range. The limit of detection was of 0.02mgL^-1 Ca (0.39ng Ca) and the upper limit of linear range was increased up to 8.0mgL^-1 Ca (160ng Ca). The proposed method was used to determine Ca in mitochondrial suspensions and whole blood samples with successful results. Adequate recoveries (within 91-107%) were obtained in the tests performed for validation purposes.

Direct determination of chromium in infant formulas employing high-resolution continuum source electrothermal atomic absorption spectrometry and solid sample analysis

The present work proposed an analytical method for the direct determination of chromium in infant formulas employing the high-resolution continuum source electrothermal atomic absorption spectrometry combined with the solid sample analysis (SS-HR-CS ET AAS). Sample masses up to 2.0mg were directly weighted on a solid sampling platform and introduced into the graphite tube. In order to minimize the formation of carbonaceous residues and to improve the contact of the modifier solution with the solid sample, a volume of 10 µL of a solution containing 6% (v/v) H2O2, 20% (v/v) ethanol and 1% (v/v) HNO3 was added. The pyrolysis and atomization temperatures established were 1600 and 2400 °C, respectively, using magnesium as chemical modifier. The calibration technique was evaluated by comparing the slopes of calibration curves established using aqueous and solid standards. This test revealed that chromium can be determined employing the external calibration technique using aqueous standards. Under these conditions, the method developed allows the direct determination of chromium with limit of quantification of 11.5 ng g(-1), precision expressed as relative standard deviation (RSD) in the range of 4.0-17.9% (n=3) and a characteristic mass of 1.2 pg of chromium. The accuracy was confirmed by analysis of a certified reference material of tomato leaves furnished by National Institute of Standards and Technology. The method proposed was applied for the determination of chromium in five different infant formula samples. The chromium content found varied in the range of 33.9-58.1 ng g(-1) (n=3). These samples were also analyzed employing ICP-MS. A statistical test demonstrated that there is no significant difference between the results found by two methods. The chromium concentrations achieved are lower than the maximum limit permissible for chromium in foods by Brazilian Legislation.

Determination of total sulfur in food samples by solid sampling high-resolution continuum source graphite furnace molecular absorption spectrometry

The determination of sulfur in food samples via the rotational molecular absorption of carbon monosulfide (CS) was performed using a solid sampling high-resolution continuum source electrothermal atomic absorption spectrophotometer (SS-HR-CS-ETAAS). In the presence of plenty of carbon in the graphite furnace as well as in food samples, CS was formed in the gas phase without the addition of any molecule forming element externally. The effects of the wavelength selected to detect CS, graphite furnace program, amount of sample, coating of the graphite tube and platform with Ir, and the use of a Pd modifier on the accuracy, precision, and sensitivity were investigated and optimized. Sulfur was determined in an iridium-coated graphite tube/platform at 258.056 nm by applying a pyrolysis temperature of 1000 °C and a molecule forming temperature of 2400 °C. The calibration curve prepared from Na2S was linear between 0.01 μg (LOQ) and 10 μg of S. The accuracy of the method was tested by analyzing certified reference spinach and milk powder samples by applying a linear calibration technique prepared from aqueous standard. The results were in good agreement with certified values. The limit of detection and characteristic mass of the method were 3.5 and 8.1 ng of S, respectively. By applying the optimized parameters, the concentrations of S in onion and garlic samples were determined.

On-line sample processing involving microextraction techniques as a front-end to atomic spectrometric detection for trace metal assays: a review

Within the last decade, liquid-phase microextraction (LPME) and micro-solid phase extraction (μSPE) approaches have emerged as substitutes for conventional sample processing procedures for trace metal assays within the framework of green chemistry. This review surveys the progress of the state of the art in simplification and automation of microextraction approaches by harnessing to the various generations of flow injection (FI) as a front end to atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) or inductively coupled plasma atomic emission spectrometry or mass spectrometry (ICP-AES/MS). It highlights the evolution of flow injection analysis and related techniques as vehicles for appropriate sample presentation to the detector and expedient on-line matrix separation and pre-concentration of trace levels of metals in troublesome matrices. Rather than being comprehensive this review is aimed at outlining the pros and cons via representative examples of recent attempts in automating green sample preparation procedures in an FI or sequential injection (SI) mode capitalizing on single-drop microextraction, dispersive liquid-phase microextraction and advanced sorptive materials including carbon and metal oxide nanoparticles, ion imprinted polymers, superparamagnetic nanomaterials and biological/biomass sorbents. Current challenges in the field are identified and the synergetic combination of flow analysis, nanotechnology and metal-tagged biomolecule detection is envisaged.

Liposomes as an alternative delivery system for investigating dietary metal toxicity to Daphnia magna

Dietary metal toxicity studies with invertebrates such as Daphnia magna are often performed using metal-contaminated algae as a food source. A drawback of this approach is that it is difficult to distinguish between the direct toxicity of the metal and indirect effects caused by a reduced essential nutrient content in the metal-contaminated diet, due to prior exposure of the algae to the metal. This hampers the study of the mechanisms of dietary metal toxicity in filter-feeding freshwater invertebrates. The aim of the present study was to develop a technique for producing metal-contaminated liposomes as an alternative delivery system of dietary metals. These liposomes are not vulnerable to metal-induced shifts in nutrient quality. Liposomes were prepared by the hydration of phosphatidylcholine in media containing either 0 (control) or 50mg Ni/L. The liposomes had average diameters of 19.31 (control) and 10.48 μm (Ni-laden), i.e., a size appropriate for ingestion by D. magna. The liposome particles were then mixed with uncontaminated green algae in a 1/10 ratio (on a dry wt. basis) to make up two diets that differed in Ni content (i.e., 2.0 μg Ni/g dry wt. in the control and 144.2 μg Ni/g dry wt. in the Ni-contaminated diet, respectively). This diet was then fed to D. magna during a 21-day chronic bioassay. The experiment showed that the Ni content and the size distribution of the liposomes were stable for at least 7 days. Also the use of phosphatidylcholine as a liposome component did not affect the reproduction of the daphnids. Exposure to increased level of dietary Ni resulted in 100% mortality after 14 days of exposure and in an increased whole-body Ni concentration in D. magna of 14.9 and 20.4 μg Ni/g dry wt. after 7 and 14 days of exposure, respectively. The Ni-exposed daphnids also exhibited a reduced size (i.e., 30% smaller than the control) after 7 days and a completely halted growth between day 7 and day 14. In terms of reproduction, the size of the first brood (number of juveniles) of the Ni-exposed daphnids was significantly reduced (by 85%) compared to the control. None of the Ni-exposed individuals were able to produce a second brood before dying. The algal ingestion rate - after correction for the indirect effect of a reduced size - was increased (by 68%) by dietary Ni after 6 days of exposure compared to the control, but was severely reduced (by 80% compared to the control) after 13 days. These data suggest that an inhibition of the ingestion process may have contributed to the observed effects of dietary Ni on growth and reproduction beyond 6 days of exposure, although the involvement of other mechanisms cannot be excluded. The mechanism(s) which led to the reduced growth during the first week of exposure remain unclear, although inhibition of the ingestion process can likely be excluded here as an explanation. Overall, this paper demonstrates, using this new method of delivering dietary Ni via liposome carriers and thus excluding potential diet quality shifts, that dietary Ni can indeed induce toxic effects in D. magna. This method may therefore be a promising tool to help further elucidate the mechanisms of dietary metal toxicity to filter-feeding invertebrates.