Antonio Celso Spinola Costa

New Materials for Solid‐Phase Extraction of Trace Elements

Abstract The development of new sorbents and their application in preconcentration methods for determination of trace elements is a subject of great interest. This review summarizes and discusses several analytical methods involving the preparation and use of new solid‐phase materials. The performance and general properties of sorbents such as carbon nanotubes, imprinted ions, biosorbents, nanoparticles, and fullerene are discussed in detail. The perspective and future trends in the use of these materials are also considered.

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.

Pre-concentration procedure for determination of copper and zinc in food samples by sequential multi-element flame atomic absorption spectrometry.

In this paper is proposed a simultaneous pre-concentration procedure using cloud point extraction for the determination of copper and zinc in food samples employing sequential multi-element flame atomic absorption spectrometry (FS-FAAS). The reagent used is 1-(2-pyridylazo)-2-naphthol (PAN) and the micellar phase is obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. The optimization step was performed using Box-Behnken design for three factors: solution pH, reagent concentration and buffer concentration. A multiple response function was established in order to get an experimental condition for simultaneous extraction of copper and zinc. Under the optimized experimental conditions, the method allows the determination of copper with a limit of detection (3sigma(b)/S, LOD) of 0.1 microg L(-1), precision expressed as relative standard deviation (R.S.D.) of 2.1 and 1.3% (N=10), for copper concentrations of 10 and 50 microg L(-1), respectively. Zinc is determined with a LOD of 0.15 microg L(-1) and precision as R.S.D. of 2.7 and 1.7% for concentrations of 10 and 50 microg L(-1), respectively. The enhancement factors obtained were 36 and 32 for copper and zinc, respectively. The accuracy was assessed by analysis of certified reference materials, namely, SRM 1567a - Wheat Flour and SRM 8433 - Corn Bran from National Institute of Standards & Technology and BCR 189-wholemeal flour from Institute of Reference Materials and Measurements. The method was applied to the determination of copper and zinc in oats, powdered chocolate, corn flour and wheat flour samples. The copper content in the samples analyzed varied from 1.14 to 3.28 microg g(-1) and zinc from 8.7 to 22.9 microg g(-1).

Determination of Copper, Iron, Nickel, and Zinc in Ethanol Fuel by Flame Atomic Absorption Spectrometry Using On‐Line Preconcentration System

Abstract In this work, an on‐line system for preconcentration and determination of copper, iron, nickel, and zinc at µg L−1 level by flame atomic absorption spectrometry (FAAS) has been developed. Amberlite XAD‐4 functionalized with 3,4‐dihydroxybenzoic acid packed in a minicolumn was used as metal sorbent. The retained metals can be quickly eluted from sorbent material, with the eluent stream consisting of hydrochloric acid solution, directly to the nebulizer burner system of the FAAS. Analytical parameters were evaluated and the results demonstrated that all studied metals can be determined, using borate buffer to adjust the sample pH at 8.0. The results showed that the proposed method is simple and rapid. The limits of detection were estimated as 2.3, 5.0, 7.8, and 0.1 µg L−1 for copper, iron, nickel, and zinc, respectively, using a preconcentration time of 60 s and a sample flow rate of 5.5 mL min−1. Enrichment factors of 22, 15, 12, and 54 and coefficients of variations of 3.5, 4.4, 4.4, and 3.2% were obtained in the determination of copper, iron, nickel, and zinc, respectively. The system presented an analytical throughput of 10 samples per hour and was successfully applied in the determination of metals in ethanol fuel.

Flow-injection solid-phase spectrophotometry for the determination of zinc in pharmaceutical preparations

A flow system exploiting solid-phase spectrophotometry is proposed for the determination of zinc in pharmaceutical preparations. The chromogenic reagent 1-(2-tiazolylazo)-2-naphthol (TAN) was immobilized on C18 bonded silica loaded into a homemade flow cell with 1 mm optical path and 78 mm 2 cross section. The flow cell was designed in such a way that the sensitivity is enhanced and the attenuation of the radiation beam due to scattering and absorption by the solid material is minimized. The flow cell was placed in the spectrophotometer so that the radiation beam was focused on the overall surface containing the adsorbing material. Reagent immobilization was performed on-line and allowed to work for at least one month. Analyte reaction, retention and detection were performed simultaneously, followed by elution with hydrochloric acid. The apparent molar absorptivity was estimated as 2.0210 5 l mol ˇ1 cm ˇ1 and the procedure allowed the determination of zinc in the 0.04‐4.0 mg l ˇ1 range with a coefficient of variation of 3.3% (na10). A sample throughput of 45 determinations per hour and a detection limit of 10 m gl ˇ1 (99.7% confidence level) were achieved. The results agreed at a 95% confidence level with those found by inductively coupled plasma atomic emission spectrometry. # 1999 Elsevier Science B.V. All rights reserved.

Determination of vitamin B6 in pharmaceutical formulations by flow injection-solid phase spectrophotometry.

In this work, a new solid phase spectrophotometric method in association with flow injection analysis for Vitamin B6 (pyridoxine) determination has been developed with direct measurement of light-absorption in C18 material. In the developed method, successive passage of the complex, previously formed in the flowing stream, and eluent through the flow cell and continuous monitoring of the process provided the analytical information needed to determine pyridoxine. Pharmaceutical samples containing Vitamin B6 were previously dissolved in 0.1 mol l(-1) phosphate buffer solution (pH 7.5) and a sample volume of 235 microl was injected directly into carrier stream consisting of a mixture of methanol and 0.1 mol l(-1) phosphate buffer solution adjusted to pH 7.0 (1+1, v/v). The blue indophenol dye produced from the reaction between pyridoxine and N,N-diethyl-p-phenylenediamine after oxidation by potassium hexacyanoferrate(III) was quantitatively retained on C18 support and the spectrophotometric detection was performed simultaneously at 633 nm. The retained complex was quickly eluted from C18 material with the eluent stream consisting of a mixture of methanol and 0.01 mol l(-1) HCl (6+4, v/v). The results showed that the proposed method is simple, rapid and the analytical response is linear in the concentration range of 0.5-10 and 0.2-4 mg l(-1) using 235 and 860 microl of sample, respectively. The limits of detection are 0.15 and 0.060 mg l(-1) and the R.S.D. are 3.6% (at 2 mg l(-1) level) and 4.0% (at 1 mg l(-1) level) using sample volume of 235 and 860 microl, respectively. The system presented an analytical throughput of 15 determinations per hour when a sample volume of 235 microl was utilized. The procedure was successfully applied to the determination of Vitamin B6 in pharmaceutical formulations containing vitamins of B group and others active principles such as Vitamin C and minerals.

Nickel and zinc determination by flow-injection solid-phase spectrophotometry exploiting different sorption rates

Flow-injection solid-phase spectrophotometry is applied for sequential determination of nickel and zinc, exploiting their different sorption rates on 1-(2-thiazolylazo)-2-naphthol (TAN) immobilized on C(18)-bonded silica. The Zn(II) sorption rate on the solid support is constant for flow rates ranging from 0.70 to 2.2 ml min(-1), but for Ni(II) the sorption rate decreases with increasing flow rate. A flow system was designed to perform sequential measurements at two different flow rates (0.85 and 1.9 ml min(-1)). The absorbance was measured at 595 nm, where both TAN-immobilized complexes showed maximum absorption. The coefficients of variation were estimated (n=10) as 1.1 and 1.7% (at 1.9 ml min(-1)) and 1.2 and 2.1% (at 0.85 ml min(-1)) for zinc and nickel, respectively. This strategy was applied to determine zinc and nickel in copper-based alloys and the results agreed with certified values at the 95% confidence level. The sample throughput was estimated as 36 h(-1).

ICP-AES determination of small amounts of zinc in copper-base alloys after separation by adsorption of the zinc-TAN complex on Sep Pak C18 cartridges.

The use of ICP/AES for the determination of zinc, in low concentration levels, in matrices containing high levels of copper is difficult because copper interferes in the zinc main emission wavelength (213.856 nm). In the present work, a separation of zinc from copper matrices was possible, using the reaction of zinc(II) cation with 1-(2-tiazolylazo)-2-naphthol (TAN), in the pH range of 6.5-8.0, resulting in a stable red complex. Copper also reacts with TAN but its interference was avoided by the addition of ascorbic acid and thiosulphate in the reaction medium. In this way, the aqueous solution was passed through a SEP PAK C18 cartridge, in which the zinc(II)-TAN complex was quantitatively retained, but it did not occur with copper which passes through the cartridge, as [Cu(2)(S(2)O(3))(2)](2-), with the aqueous solution. The cartridge was washed with water and the complex eluted with ethanol. Then, the alcohol was evaporated and the complex decomposed by nitric acid. It results in both zinc pre-concentration and separation from copper. The zinc quantification was carried out by ICP/AES at 213.856 nm. The relative standard deviations, for ten different aliquots, were 5.7% and the average recovery found for zinc was 96%, even when the concentration ratio Cu/Zn was up to 500/1 (mg l(-1):mg l(-1)). Other metals, like nickel, for example, can react with TAN in the same way as zinc but they do not interfere in the emission wavelength 213.856 nm.

2-(2-Thiazolylazo)-p-cresol(TAC) as a Reagent for the Spectrophotometric Determination of Lead(II)

Abstract The reaction between lead(II) and 2-(2-Thiazolylazo)-p-Cresol(TAC) in the presence of TERGITOL NPX (4 mg/ml) at an apparent pH 9.0–10.0 results in an intensely colored complex which is stable for at least 4 hr. The composition of the complex is 1:2 cation: TAC and the log of the formation constant is 11.92 ± 0. 40. Beers law is obeyed up to 6.0μg.ml−1 of lead(II) at 650nm. The apparent molar absorptivity at 650 nm is 2.07 × 104 1. mole−1.cm−1 and the detection limit was obtained as 10.0 ng.ml−1 of lead(II). The method is applied to determination of lead(II) in copper-base alloy.

Comparison of decomposition procedures for analysis of titanium dioxide using inductively coupled plasma optical emission spectrometry

Abstract The determination of impurities in titanium dioxide pigments, such as Al, Cd, Cr, Fe, Mn, P, Zn and Zr, is relevant because trace elements affect pigment properties. The critical step in the analysis of this pigment is the conversion of the solid sample to a representative solution. This study compared four acid decomposition procedures for TiO2 for the determination of Al, P and trace impurities using inductively coupled plasma optical emission spectrometry. The decomposition procedures investigated involved acid digestion with: (i) (NH4)2SO4/H2SO4; (ii) HF/H2SO4; (iii) H3PO4; and (iv) HCl/HNO3/HF. This latter mixture was tested in a microwave-assisted procedure with closed vessels. Comparing the procedures using conventional conductive heating, the procedure using (NH4)2SO4/H2SO4 was the most suitable for complete decomposition of TiO2 samples, requiring approximately 30 min. Applying a paired t-test, it was shown that all strategies led to results in agreement at a 95% confidence level with those obtained using X-ray fluorescence. The accuracy for Cr, Fe, P and Zr was also checked using a certified reference material, and again all results were in agreement at a 95% confidence level. The performance of two ICP-OESs, one based on a mini-torch using a radial view configuration, and the other based on an axial view configuration, were compared. Both plasmas are intensely affected by matrix constituents. The mini-torch plasma is less able to cope with high amounts of solids; however this parameter also negatively affects the background level when using axial-viewed ICP-OES.