Ariane V. Zmozinski

Determination of calcium, magnesium and zinc in lubricating oils by flame atomic absorption spectrometry using a three-component solution

Lubricating oils are used to decrease wear and friction of movable parts of engines and turbines, being in that way essential for the performance and the increase of that equipment lifespan. The presence of some metals shows the addition of specific additives such as detergents, dispersals and antioxidants that improve the performance of these lubricants. In this work, a method for determination of calcium, magnesium and zinc in lubricating oil by flame atomic absorption spectrometry (F AAS) was developed. The samples were diluted with a small quantity of aviation kerosene (AVK), n-propanol and water to form a three-component solution before its introduction in the F AAS. Aqueous inorganic standards diluted in the same way have been used for calibration. To assess the accuracy of the new method, it was compared with ABNT NBR 14066 standard method, which consists in diluting the sample with AVK and in quantification by F AAS. Two other validating methods have also been used: the acid digestion and the certified reference material NIST (SRM 1084a). The proposed method provides the following advantages in relation to the standard method: significant reduction of the use of AVK, higher stability of the analytes in the medium and application of aqueous inorganic standards for calibration. The limits of detection for calcium, magnesium and zinc were 1.3 μg g(-1), 0.052 μg g(-1) and 0.41 μg g(-1), respectively. Concentrations of calcium, magnesium and zinc in six different samples obtained by the developed method did not differ significantly from the results obtained by the reference methods at the 95% confidence level (Students t-test and ANOVA). Therefore, the proposed method becomes an efficient alternative for determination of metals in lubricating oil.

Establishment of a method for determination of arsenic species in seafood by LC-ICP-MS

An analytical method for determination of arsenic species (inorganic arsenic (iAs), methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), trimethylarsine oxide (TMAO) and arsenocholine (AC)) in Brazilian and Spanish seafood samples is reported. This study was focused on extraction and quantification of inorganic arsenic (iAs), the most toxic form. Arsenic speciation was carried out via LC with both anionic and cationic exchange with ICP-MS detection (LC-ICP-MS). The detection limits (LODs), quantification limits (LOQs), precision and accuracy for arsenic species were established. The proposed method was evaluated using eight reference materials (RMs). Arsenobetaine was the main species found in all samples. The total and iAs concentration in 22 seafood samples and RMs ranged between 0.27-35.2 and 0.02-0.71 mg As kg(-1), respectively. Recoveries ranging from 100% to 106% for iAs, based on spikes, were achieved. The proposed method provides reliable iAs data for future risk assessment analysis.

Determination of Cd and Cr in tannin samples by high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sample sequential analysis (HR-CS SS-GF AAS)

A fast and reliable analytical method for the sequential determination of Cd and Cr in tannin samples by high-resolution continuum source graphite furnace atomic absorption spectrometry with direct solid sampling from the same sample aliquot (HR-CS SS-GF AAS) is proposed. A pyrolysis temperature of 400 °C and atomisation temperature of 1500 °C were used for the determination of Cd; no losses of Cr were observed at these temperatures. After the atomisation of Cd, the wavelength was changed and Cr was atomised at 2500 °C. Several studies with different modifiers were performed, but no chemical modifier was needed. Calibration was achieved using aqueous standards. The linearity of the response, performed by evaluating the absorbance value relative to the sample mass, was investigated as well. Relative standard deviation (RSD) values lower than 15% were found, which are acceptable for direct analysis. The parameters of merit were: a characteristic mass of 0.3 pg and 2.2 pg for Cd and Cr, respectively; the limit of detection (LOD) of 0.5 μg kg−1 and 17 μg kg−1 for Cd and Cr, respectively; the limit of quantification (LOQ) of 2 μg kg−1 and 57 μg kg−1 for Cd and Cr, respectively. The accuracy was validated by analysing three certified reference materials (tea, pine needles and bush branches). The results were not statistically different from the certified values at a 95% confidence level. Therefore, calibration using aqueous standards is suitable for this application. This method is simple, fast and suitable for routine analysis.

Determination of lead in biomass and products of the pyrolysis process by direct solid or liquid sample analysis using HR-CS GF AAS

A method has been developed for the determination of lead in biomass, bio-oil, pyrolysis aqueous phase, and biomass ashes by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) and direct solid or liquid sample analysis. All measurements were performed without chemical modifier and calibration could be carried out using aqueous standard solutions. A pyrolysis temperature of 800°C and an atomization temperature of 2200°C were applied. The limits of detection and quantification were, respectively, 0.5 µg kg(-1) and 2 µg kg(-1) using the analytical line at 217.001 nm and 6 µg kg(-1) and 19 µg kg(-1) at 283.306 nm. The precision, expressed as relative standard deviation, was between 3% and 10%, which is suitable for direct analysis. The lead concentrations found for the solid samples varied between 0.28 and 1.4 mg kg(-1) for biomass and between 0.25 and 2.3 mg kg(-1) for ashes, these values were much higher than those found for bio-oil (2.2-16.8 µg kg(-1)) and pyrolysis aqueous phase (3.2-18.5 µg kg(-1)). After the determination of lead in the samples, it was possible to estimate the relative distribution of this element in the fractions of the pyrolysis products, and it was observed that most of the lead present in the biomass was eliminated to the environment during the pyrolysis process, with a significant portion retained in the ashes.

Determination of cadmium and lead in fresh fish samples by direct sampling electrothermal atomic absorption spectrometry

The determination of cadmium and lead in fish samples has large analytical interest due to the potential toxicity of these elements. The development of fast and reliable analytical methods is extremely important for an effective control of contamination. In this work, the feasibility of Cd and Pb determination in fresh fish samples using direct sampling by electrothermal atomic absorption spectrometry (DS-ET AAS) was investigated. For optimization of the furnace temperature program, pyrolysis and atomization curves with TORT-2 and DORM-3 certified reference materials were carried out using chemical modifier (0.05% Pd + 0.03% Mg + 0.05% Triton X-100). The figures of merit obtained were: characteristic mass of 1.0 pg and 16 pg and limit of detection (LOD) of 0.2 μg kg−1 and 1.0 μg kg−1 for Cd and Pb, respectively, based on 8 mg of sample mass. The results obtained for certificated references materials were statistically not different from the certified values at 95% confidence level, using the calibration with aqueous standards, showing that this calibration method is suitable for this application. For assessment of the accuracy of the method, fresh fish samples were digested. The results obtained with direct determination of Cd and Pb in fresh fish samples and with microwave assisted acid digestion were statistically accordant. The developed method for analysis of fresh fish samples is accurate, simple, fast and suitable for routine application, avoiding digestion procedures or the drying/lyophilization and grinding procedures, usually used in DS analysis, reducing the preparation time, risk of contamination and costs.

Direct solid sample analysis with graphite furnace atomic absorption spectrometry—A fast and reliable screening procedure for the determination of inorganic arsenic in fish and seafood

Direct solid sample analysis with graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated initially with the intention of developing a method for the determination of total As in fish and other seafood. A mixture of 0.1% Pd+0.06% Mg+0.06% Triton X-100 was used as the chemical modifier, added in solution over the solid samples, making possible the use of pyrolysis and atomization temperatures of 1200 °C and 2400 °C, respectively. The sample mass had to be limited to 0.25 mg, as the integrated absorbance did not increase further with increasing sample mass. Nevertheless, the recovery of As from several certified reference materials was of the order of 50% lower than the certified value. Strong molecular absorption due to the phosphorus monoxide molecule (PO) was observed with high-resolution continuum source AAS (HR CS AAS), which, however, did not cause any spectral interference. A microwave-assisted digestion with HNO3/H2O2 was also investigated to solve the problem; however, the results obtained for several certified reference materials were statistically not different from those found with direct SS-GF AAS. Accurate values were obtained using inductively coupled plasma mass spectrometry (ICP-MS) to analyze the digested samples, which suggested that organic As compounds are responsible for the low recoveries. HPLC-ICP-MS was used to determine the arsenobetaine (AB) concentration. Accurate results that were not different from the certified values were obtained when the AB concentration was added to the As concentration found by SS-GF AAS for most certified reference materials (CRM) and samples, suggesting that SS-GF AAS could be used as a fast screening procedure for inorganic As determination in fish and seafood.

Determination of cadmium and lead in fresh meat by slurry sampling graphite furnace atomic absorption spectrometry

In this work a method for cadmium and lead determination in fresh meat based on slurry sampling graphite furnace atomic absorption spectrometry is proposed. The fresh meat samples were weighed directly into the autosampler cups of the spectrometer using a microbalance and the slurry was prepared using tetramethylammonium hydroxide (TMAH). The use of the response surface method for optimizing the slurry preparation has shown that it was possible to find the optimum zone in the experimental field of the variables under study. Calibration was performed against aqueous standards and a mixture of 0.05% v/v Pd + 0.03% v/v Mg + 0.05% v/v Triton X-100 was used as a modifier. The results obtained for cadmium and lead in two certified reference materials were statistically not different from the certified values on a 95% confidence level, indicating that calibration against aqueous standards is suitable for this application. A comparison of the results obtained by slurry sampling with the digestion method adopted by the Brazilian Ministry of Agriculture showed no significant differences between the results at the 95% confidence level. The positive results obtained in this work suggest that the application of this procedure in other element determinations is worthy of exploration.

Chemical composition of microalgae Heterochlorella luteoviridis and Dunaliella tertiolecta with emphasis on carotenoids

BACKGROUND Microalgae have been used as food supplements owing to their high protein, polyunsaturated fatty acid and carotenoid contents. As different carotenoids have distinct properties and the carotenoid composition of microalgae has been poorly explored in the literature, this study determined the complete carotenoid composition of two microalgae species, Heterochlorella luteoviridis and Dunaliella tertiolecta, using high-performance liquid chromatography coupled with diode array detection and tandem mass spectrometry (HPLC-DAD/MS2 ). Additionally, the proximate composition and major minerals were evaluated. RESULTS The carotenoid composition of the two microalgae was similar, with 13 carotenoids being found in H. luteoviridis and 12 in D. tertiolecta. The major carotenoids were all-trans-lutein (1.18 mg g-1 in H. luteoviridis and 1.59 mg g-1 in D. tertiolecta), all-trans-violaxanthin (0.52 mg g-1 in H. luteoviridis and 0.45 mg g-1 in D. tertiolecta) and all-trans-β-carotene (0.50 mg g-1 in H. luteoviridis and 0.62 mg g-1 in D. tertiolecta). All-trans-lutein was the predominant carotenoid in both microalgae, representing around 40% (mass fraction) of the total carotenoids. The lutein content found in these microalgae was significantly higher (2-40 times) than that in other important food sources of lutein (e.g. parsley, carrot, red pepper and broccoli). CONCLUSION The microalgae H. luteoviridis and D. tertiolecta are excellent sources of lutein that could be commercially exploited by the food and pharmaceutical industries. Moreover, it was confirmed that both microalgae are good sources of protein, lipids and calcium.

Determination of Fe, Cr and Cu in used lubricating oils by ET AAS using a microemulsion process for sample preparation

The analysis of metals in used lubricating oils has been widely reviewed and published in the literature, especially because they provide valuable information about the lubricated system. The determination of metals such as Fe, Cr and Cu may indicate the presence of contaminants in the oil or wear of parts of motors. In this work, a method for the determination of Fe, Cr and Cu by atomic absorption spectrometry with electrothermal atomization (ET AAS) using a microemulsion process for sample preparation has been developed. A pseudo-ternary phase diagram was built in order to investigate the region where a homogeneous and stable system (microemulsion) could be achieved. The optimized conditions for the microemulsion formation were: 2.0% (w/w) of lubricating oil, 31% (w/w) of aviation kerosene, 5% (w/w) of nitric acid 14 mol L−1, 5% (w/w) of Triton X-100 and 57% (w/w) of n-propanol. The developed method is simple and fast, involving few steps and avoiding the use of carcinogenic solvents. Moreover, the increased stability of the microemulsion and of the analytes in a microemulsified medium and the use of aqueous standards for calibration were achieved. The values of the detection limits for Fe, Cr and Cu were 1.9 mg kg−1, 0.04 mg kg−1 and 0.2 mg kg−1, respectively. Good accuracy was attained since the results obtained were not significantly different within 95% level of confidence (Students t-test) from those of an acid-digestion method and the certified value of the NIST certified reference material wear-metals in lubricating oil (SRM 1084a). Therefore, the method developed in this work becomes an efficient alternative for the determination of Fe, Cr and Cu in used lubricating oil.

Influence of pH in the synthesis of ferric tannate pigment for application in antifouling coatings

Ferric tannate was synthesized at pH 4 and pH 7 (FT4 and FT7, respectively) as a new class of environmentally friendly antifouling pigments. The solubility of both pigments was evaluated by gravimetric tests, showing that FT4 is more soluble than FT7. A mixture of rosin/acrylic resin (9:1 w/w) was sufficient to form an antifouling coating due to improved matrix properties. Electrochemical impedance spectroscopy (EIS) measurements were used to determine the apparent water coefficient of diffusion (D) and coating behavior. The D in the coating formulated with FT4 exhibited better values than that obtained with FT7. EIS results showed that both coatings present Fickian behavior at the initial stages of immersion, while flat Nyquist plots revealed penetration of water in the films. The physicochemical characteristics of FT4 pigment were determined by thermogravimetry and Fourier transform infrared. Immersion tests in the Mediterranean Sea demonstrated the excellent efficacy of the FT4-containing coating against marine fouling after six months of immersion.