Sergio Luis Costa Ferreira

Cloud Point Extraction as a Procedure of Separation and Pre‐Concentration for Metal Determination Using Spectroanalytical Techniques: A Review

Abstract Cloud point extraction is a separation and preconcentration procedure that has been extensively applied for trace metal determination in several different matrices. Its major advantages are simple experimental procedures, low cost, high preconcentration factors, and environmental safety. These aspects include it in a set of analytical methods in agreement with the “green chemistry” principles. The surfactants characteristics and the process of micelle formation are outlined for a better understanding of the technique. After general considerations about the cloud point extraction basis and its extraction mechanism for metal chelates are considered, selected spectroanalytical techniques and their application for analysis of the micellar phase are discussed. The micellar extraction in metal speciation analysis, the on‐line incorporation of cloud point extraction to flow injection analysis, and coupling with capillary electrophoresis are described.

Biodiesel: parâmetros de qualidade e métodos analíticos

The establishment of quality standards for biodiesel was a key step to win the confidence of the market and the automotive industry, thus ensuring the success of the new fuel. In this review are presented standard methods and other analytical methods suggested for analysis of biodiesel. The methods of analysis were divided into groups according to information that may be provided on the contaminants from the raw material of the production process, the molecular structures of biodiesel and its degradation during storage.

Separation and preconcentration procedures for the determination of lead using spectrometric techniques: A review

Lead is recognized worldwide as a poisonous metal. Thus, the determination of this element is often required in environmental, biological, food and geological samples. However, these analyses are difficult because such samples contain relatively low concentrations of lead, which fall below the detection limit of conventional analytical techniques such as flame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry. Several preconcentration procedures to determine lead have therefore been devised, involving separation techniques such as liquid-liquid extraction, solid phase extraction, coprecipitation and cloud point extraction. Citing 160 references, this paper offers a critical review of preconcentration procedures for determining lead using spectroanalytical techniques.

Determination of phosphorus, sulfur and the halogens using high-temperature molecular absorption spectrometry in flames and furnaces--A review.

The literature about the investigation of molecular spectra of phosphorus, sulfur and the halogens in flames and furnaces, and the use of these spectra for the determination of these non-metals has been reviewed. Most of the investigations were carried out using conventional atomic absorption spectrometers, and there were in essence two different approaches. In the first one, dual-channel spectrometers with a hydrogen or deuterium lamp were used, applying the two-line method for background correction; in the second one, a line source was used that emitted an atomic line, which overlapped with the molecular spectrum. The first approach had the advantage that any spectral interval could be accessed, but it was susceptible to spectral interference; the second one had the advantage that the conventional background correction systems could be used to minimize spectral interferences, but had the problem that an atomic line had to be found, which was overlapping sufficiently well with the maximum of the molecular absorption spectrum. More recently a variety of molecular absorption spectra were investigated using a low-resolution polychromator with a CCD array detector, but no attempt was made to use this approach for quantitative determination of non-metals. The recent introduction and commercial availability of high-resolution continuum source atomic absorption spectrometers is offering completely new possibilities for molecular absorption spectrometry and its use for the determination of non-metals. The use of a high-intensity continuum source together with a high-resolution spectrometer and a CCD array detector makes possible selecting the optimum wavelength for the determination and to exclude most spectral interferences.

Nickel determination in saline matrices by ICP-AES after sorption on Amberlite XAD-2 loaded with PAN.

In the present paper, a solid phase extraction system for separation and preconcentration of nickel (ng g(-1)) in saline matrices is proposed. It is based on the adsorption of nickel(II) ions onto an Amberlite XAD-2 resin loaded with 1-(2-pyridylazo)-2-naphthol (PAN) reagent. Parameters such as the pH effect on the nickel extraction, the effect of flow rate and sample volume on the extraction, the sorption capacity of the loaded resin, the nickel desorption from the resin and the analytical characteristics of the procedure were studied. The results demonstrate that nickel(II) ions, in the concentration range 0.10-275 microg l(-1), and pH 6.0-11.5, contained in a sample volume of 25-250 ml, can be extracted by using 1 g Amberlite XAD-2 resin loaded with PAN reagent. The adsorbed nickel was eluted from the resin by using 5 ml 1 M hydrochloric acid solution. The extractor system has a sorption capacity of 1.87 mumol nickel per g of Amberlite XAD-2 resin loaded with PAN. The precision of the method, evaluated as the R.S.D. obtained after analyzing a series of seven replicates, was 3.9% for nickel in a concentration of 0.20 microg ml(-1). The proposed procedure was used for nickel determination in alkaline salts of analytical grade and table salt, using an inductively coupled plasma atomic emission spectroscopy technique (ICP-AES). The standard addition technique was used and the recoveries obtained revealed that the proposed procedure shows good accuracy.

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.

Determination of vanadium in petroleum and petroleum products using atomic spectrometric techniques

Vanadium is recognized worldwide as the most abundant metallic constituent in petroleum. It is causing undesired side effects in the refining process, and corrosion in oil-fired power plants. Consequently, it is the most widely determined metal in petroleum and its derivatives. This paper offers a critical review of analytical methods based on atomic spectrometric techniques, particularly flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET AAS), inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS). In addition an overview is provided of the sample pretreatment and preparation procedures for vanadium determination in petroleum and petroleum products. Also included are the most recent studies about speciation and fractionation analysis using atomic spectrometric techniques.

Application of factorial designs and Doehlert matrix in optimization of experimental variables associated with the preconcentration and determination of vanadium and copper in seawater by inductively coupled plasma optical emission spectrometry

In the present paper a procedure for preconcentration and determination of vanadium and copper in seawater using inductively coupled plasma optical emission spectrometry (ICP OES) is proposed, which is based on solid-phase extraction of vanadium (IV), vanadium (V) and copper (II) ions as 1-(2-pyridylazo)-2-naphthol (PAN) complexes by active carbon. The optimization process was carried out using two-level full factorials and Doehlert matrix designs. Four variables (PAN mass, pH, active carbon mass and shaking time) were regarded as factors in the optimization. Results of the two-level full factorial design 24 with 16 runs for vanadium extraction, based on the variance analysis (ANOVA), demonstrated that the factors pH and active carbon mass, besides the interaction (pH×active carbon mass), are statistically significant. For copper, the ANOVA revealed that the factors PAN mass, pH and active carbon mass and the interactions (PAN mass×pH) and (pH×active carbon mass) are statistically significant. Doehlert designs were applied in order to determine the optimum conditions for extraction. The procedure proposed allowed the determination of vanadium and copper with detection limits (3σ/S) of 73 and 94 ng l−1, respectively. The precision, calculated as relative standard deviation (R.S.D.), was 1.22 and 1.37% for 12.50 μg l−1 of vanadium and copper, respectively. The preconcentration factor was 80. The recovery achieved for determination of vanadium and copper in the presence of several cations demonstrated that this procedure improved the selectivity required for seawater analysis. The procedure was applied to the determination of vanadium and copper in seawater samples collected in Salvador City, Brazil. Results showed good agreement with other data reported in the literature.

Factorial design in the optimization of preconcentration procedure for lead determination by FAAS

The present paper proposes a preconcentration procedure for lead determination using flame atomic absorption spectrometry (FAAS). It is based on lead(II) ions extraction as brilliant cresyl blue (BCB) complex and its sorption onto Diaion HP-2MG, a methacrylic ester copolymer. The optimization step was carried out using factorial design and the variables studied were pH, shaking time and reagent concentration. In the established experimental conditions, lead can be determinate with a limit of detection of 3.7mugL(-1) lead (N = 20) and a relative standard deviation of 7% for a lead concentration of 100mugL(-1). The accuracy was confirmed by analysis of a certified reference material, the stream sediment furnished by National Research Centre for Certified Reference Materials (NRCCRM), China (GBW 07310). Effect of other ions in the procedure proposed was also studied. The method was applied for lead determination in real samples of water, tea, soil and dust. Tests of addition/recovery in the experiments for lead determination in water samples revealed that the proposed procedure could be applied satisfactorily for analysis of these samples.

Copper determination in natural water samples by using FAAS after preconcentration onto amberlite XAD-2 loaded with calmagite.

A procedure for separation and preconcentration of trace amounts of copper in natural water samples, has been proposed. It is based on the adsorption of copper(II) ions onto a column of Amberlite XAD-2 resin loaded with calmagite reagent. This way amounts of copper within the range from 0.0125 to 25.0 microg, in a sample volume of 25 to 250 ml, and pH from 3.7 to 10.0 was concentrated as calmagite complex in a column of 0.50 g of Amberlite XAD-2 resin. Copper (II) ion was desorpted by using 5.0 ml of 2 mol l(-1) hydrochloric acid. Detection and determination limits of the proposed procedure for 250 ml sample volume were 0.15 and 0.50 microg l(-1), respectively. Selectivity test showed that (in the indicated concentration), calcium(II) (500 mg l(-1)), magnesium(II) (500 mg l(-1)), strontium(II) (50 mg l(-1)), iron(III) (10 mg l(-1)), nickel(II) (10 mg l(-1)), cobalt(II) (10 mg l(-1)), cadmium(II) (10 mg l(-1)) and lead(II) (10 mg l(-1)) did not interfere in copper determination by this procedure. Precision of the method, evaluated as the relative standard deviation by analyzing a series of seven replicates, was 2.42% for a copper mass of 1.0 microg in a sample volume of 100 ml. The accuracy of the proposed procedure was evaluated by means of copper determination in reference biological samples. The achieved results were in good agreement with certified values. The extractor system had a sorption capacity of 1.59 mumol of copper per gram of resin loaded with calmagite. The proposed procedure was applied for copper determination by FAAS in natural water samples. Samples were collected from different places of Salvador city, Bahia, Brazil. The achieved recovery, measured by the standard addition technique, showed that the proposed procedure had good accuracy. A good enrichment factor (50x) and simplicity are the main advantages in this analytical procedure.