Daniel C. Lima

Atomic spectrometric methods for the determination of metals and metalloids in automotive fuels - : A review

Gasoline, diesel, ethanol and more recently also biodiesel are the four types of fuel used for automobile, truck and other transportation vehicle. The presence of metallic and metalloid species in automotive fuels is undesirable, except in the form of additives in order to improve specific characteristics of the fuel. Metallic or metalloid elements may derive from the raw product, such as nickel and vanadium in petroleum-based fuel or phosphorus in biodiesel, or they may be introduced during production and storage, such as copper, iron, nickel and zinc in case of petroleum-based fuel and alcohol or sodium and potassium in the case of biodiesel. The most famous additive to fuel is undoubtedly lead, the use of which has been banned or drastically reduced now in many countries of the world. The problems related to the trace element content may be economic, such as fuel degradation and poisoning of automotive catalysts, and/or environmental, such as the emission of metal compounds to the atmosphere. The analytical methods that have been developed for metal and metalloid quantification in automotive fuel are reviewed in this article. The main atomic spectrometric techniques used for trace metal and metalloid determination in fuels, particularly atomic absorption spectrometry with flames, graphite furnaces and with chemical vapor generation, and inductively coupled plasma coupled with optical emission and mass spectrometry are presented, including the different sample preparation procedures proposed for these techniques.

Application of Multivariate Techniques in Optimization of Spectroanalytical Methods

Abstract The present article describes fundamentals and applications of multivariate techniques used for the optimization of analytical procedures and systems involving spectroanalytical methods such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma mass spectrometry (ICP‐MS), considering the main steps of a chemical analysis. This way, applications of experimental designs in optimization of sampling systems, digestion procedures, preconcentration procedures, instrumental parameters of quantification steps of analytical methods, and robustness tests have been summarized in this work.

Multivariate optimization of ultrasound-assisted extraction for determination of Cu, Fe, Ni and Zn in vegetable oils by high-resolution continuum source atomic absorption spectrometry.

An assisted liquid-liquid extraction of copper, iron, nickel and zinc from vegetable oil samples with subsequent determination by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was optimized by applying a full factorial design in two levels and the response surface methodology, Box-Behnken. The effects of the acid concentration and the amplitude, cycle and time of sonication on the extraction of the analytes, as well as their interactions, were assessed. In the selected condition (sonication amplitude = 66%, sonication time = 79 s, sonication cycle = 74%), using 0.5 mol L(-1) HCl as the extractant, the limits of quantification were 0.14, 0.20, 0.21 and 0.04 μg g(-1) for Cu, Fe, Ni and Zn, respectively, with R.S.D. ranging from 1.4% to 3.6%. The proposed method was applied for the determination of the analytes in soybean, canola and sunflower oils.

The chemical generation of NO for the determination of nitrite by high-resolution continuum source molecular absorption spectrometry.

In the present work, we propose a method for the determination of nitrite based on the chemical generation of nitric oxide (NO) and its detection by high-resolution continuum source molecular absorption spectrometry. NO is generated by the reduction of nitrite in acidic media with ascorbic acid as the reducing agent and then transferred into a quartz cell by a stream of argon carrier gas. The conditions under which the NO is generated are as follows: 0.4 mol L(-1) hydrochloric acid, 1.5%(w/v) ascorbic acid, an argon gas pressure of 0.03 MPa and an injection time of the reducing agent of 4s. All measurements of molecular absorption were performed using the NO line at 215.360 nm, and the signal was measured by peak height. Under these conditions, the method described has limits of detection and quantification of 0.045 and 0.150 μg mL(-1) of nitrite, respectively. The calibration curve is linear for nitrite concentrations in the range 0.15-15 μg mL(-1). The precision, estimated as the relative standard deviation (RSD), was 3.5% and 4.4% for solutions with nitrite concentrations of 0.5 and 5.0 μg mL(-1), respectively. This method was applied to the analysis of different water samples (well water, drinking water and river water) collected in Cachoeira City, Bahia State, Brazil. The results were in agreement with those obtained by a spectrophotometric method using the Griess reaction. Addition/recovery tests were also performed to check the validity of the proposed method. Recoveries of 93-106% were achieved.

Methods for vanadium determination in fuel oil by GF AAS with microemulsification and acid digestion sampling

Two methods for vanadium determination in fuel oil are proposed using GF AAS. The first is based on the preparation of a microemulsion followed by direct injection into the graphite tube. The pyrolysis and atomization temperatures, 1500 and 2700 oC, respectively, were chosen from the temperature curves. This procedure allows determination of vanadium with a detection limit of 0.10 µg g-1 and characteristic mass of 87 pg. The other method uses total acid digestion of the sample with sulfuric acid, nitric acid and hydrogen peroxide. In this procedure, the pyrolysis and atomization temperatures recommended were 1000 and 2700 oC, respectively. Among the analytical characteristics for this method are a detection limit of 0.25 µg g-1 and a characteristic mass of 63 pg. The accuracy of both procedures was confirmed by the determination of vanadium in the certified reference material NIST SRM 1634c-trace metals in fuel oil.

Critical study using experimental design of the determination of lead by high-resolution continuum source hydride generation atomic absorption spectrometry

The present study critically evaluates quartz tube (QT) atomisation and high-resolution continuum source hydride generation atomic absorption spectrometry (HR-CS HG-AAS) for the determination of lead. A full two-level factorial design was performed to characterise the effects of the following reagent concentrations on the analytical procedure: sodium tetrahydroborate, potassium hexacyanoferrate(III) and nitric acid. This chemometric tool demonstrated that an increasing acid concentration increases hydrogen production, which dilutes the analyte in the quartz tube during analytical measurements. The experimental conditions established in the final procedure were determined using a Box–Behnken design. The method was used to determine the concentration of lead in water samples, with limits of detection and quantification of 0.13 and 0.40 μg L−1, respectively. Method precision, expressed as relative standard deviation (RSD), was 6.36% and was obtained with a 10.00 μg L−1lead solution. The accuracy was confirmed by determining the lead concentration in the NIST standard reference material, SRM 1643d, for trace elements in natural water. This method was then used to determine the lead concentration in eighteen water samples collected in the Sao Paulo River (Bahia State, Brazil). The lead concentrations varied from 0.62 to 3.73 μg L−1. All samples were also analysed by inductively coupled plasma mass spectrometry (ICP-MS). Statistical tests demonstrated that there was no difference between the results obtained by both procedures.

Multivariate optimization of simple procedure for determination of Fe and Mg in cassava starch employing slurry sampling and FAAS

A slurry sampling procedure has been developed for Fe and Mg determination in cassava starch using flame atomic absorption spectrometry. The optimization step was performed using a univariate methodology for 200mg samples and a multivariate methodology, using the Box-Behnken design, for other variables, such as solvent (HNO3:HCl), final concentration (1.7molL-1) and time (26min). This procedure allowed determination of iron and magnesium with detection limits of 1.01 and 3.36mgkg-1, respectively. Precision, expressed as relative standard deviation (%RSD), was of 5.8 and 4.1% (n=10) for Fe (17.8mgkg-1) and Mg (64.5mgkg-1), respectively. Accuracy was confirmed by analysis of a standard reference material for wheat flour (NIST 1567a), which had certified concentrations of 14.1±0.5mgkg-1 for Fe and 40±2.0mgkg-1 for Mg, and the concentrations found using proposed method were 13.7±0.3mgkg-1 for Fe and 40.8±1.5mgkg-1 for Mg. Comparison with concentrations obtained using closed vessel microwave digestion was also realized. The concentrations obtained varied between 7.85 and 17.8mgkg-1 for Fe and 23.7-64.5mgkg-1, for Mg. The simplicity, easily, speed and satisfactory analytical characteristics indicate that the proposed analytical procedure is a good alternative for the determination of Fe and Mg in cassava starch samples.

Determination of the Mineral Composition of Watercress and Data Evaluation Using Multivariate Analysis

This paper reports the determination of the mineral composition of watercress (Nasturtium officinale Cruciferae, Brassicaceae), grown in soils from three cities in the Bahia State of Brazil, and in a fourth city where plants were grown in a hydroponic system. The sampling was carried out during the summer and winter. Analyses were performed with inductively coupled plasma optical emission spectrometry (ICP OES), and the accuracy was confirmed with a certified reference material of apple leaves. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed different mineral compositions of the samples collected in the summer and winter. Samples collected in the summer had a higher concentration of the nutrients iron, calcium, and magnesium, and the samples collected in the winter had a higher concentration of manganese and copper. The average contents of the samples (expressed as wet weight) were 2.50 and 3.03 mg g−1 for calcium, 0.37 and 0.86 mg g−1 for magnesium, 8.68 and 10.84 µg g−1 for iron, 8.42 and 8.47 µg g−1 for zinc, 0.61 and 0.47 µg g−1 for copper, and 7.78 and 5.03 µg g−1 for manganese for summer and winter, respectively. These results are in agreement with values previously reported in the literature. Samples collected from the hydroponic system in the winter had a lower concentration of all nutrients.

A separation system for lead fractionation in river water using electrothermal atomic absorption spectrometry

This work proposes a separation system that uses the Sep-Pak C-18 cartridge to enable the determination of labile and total lead in natural water samples. This method is composed of two steps. First, the sample is percolated through the cartridge, where the lead that is bound to the organic compounds is retained and the quantification of labile lead is performed using the eluate from this separation. Afterwards, another sample enables the determination of total lead. Lead was determined through electrothermal atomic absorption spectrometry (ET-AAS) using aluminum as a chemical modifier under the following instrumental conditions: pyrolysis temperature of 800 °C and atomization temperature of 1800 °C. This method allows the determination of lead with limits of detection and quantification of 0.14 and 0.47 μg L−1, respectively. The accuracy of this method for the determination of total lead was confirmed by analysing a standard reference material of trace elements in natural water supplied by NIST. Experiments using lead solutions in the presence of humic acid confirmed the efficiency of the Sep-Pak C-18 cartridge for the quantitative extraction of lead ions bound to organic complexing agents. This method was applied for the determination of labile and total lead in river water samples collected in Santo Amaro City, Bahia State, which is a region that is historically contaminated by lead as a result of a lead ore smelter that operated in the area from 1960 to 1993. For the five samples analyzed, the total lead concentrations ranged from 1.18 to 13.57 μg L−1. The fraction of labile lead ranged from 48% to 80% in four samples. The fifth sample had a labile lead content of 11%. The total carbon content was also determined in all the analyzed samples. The obtained concentrations did not present a correlation with the results obtained for lead.

Application of Factorial Design and Desirability Function to Develop a Single Analytical Procedure for the Determination of Metals in Different Tissues of Blue Crab (Callinectes danae)

In this scientific work, it was developed a single analytical procedure for the sample preparation of different tissues of blue crabs using microwave-assisted digestion for the determination of Cu, Mn, Fe and Zn by fast sequential flame atomic absorption spectrometry (FS FAAS). The limits of quatification were 10.5, 1.6, 8.9 and 19.3 μg g for Cu, Mn, Fe and Zn, respectively. The precision was estimated in terms of repeatability using the relative standard deviation (RSD, n = 7) 3.4% for Cu; 4.8% (Mn); 4.7% (Fe) and 4.7% (Zn) and accuracy of the procedure was confirmed by analysis of certified reference material (CRM) of oyster tissue (NIST 1566B) with concentration values of 71.3 for Cu, 18.3 for Mn, 202.5 for Fe and 1415 μg g for Zn. The procedure has been applied for the determination of Cu, Mn, Fe and Zn in several blue crab samples from Cachoeira River estuary, Ilhéus, Bahia, Brazil.