Synthesis and application of imprinted polyvinylimidazole-silica hybrid copolymer for Pb determination by flow-injection thermospray flame furnace atomic absorption spectrometry

A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb²⁺ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb²⁺ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L⁻¹), eluent (HNO₃) concentration (0.5 mol L⁻¹) and preconcentration flow rate (4.0 mL min⁻¹), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L⁻¹ (r = 0.999) with limit of detection of 0.75 μg L⁻¹; the precision (repeatability) calculated as relative standard deviation (n = 10) was 5.0 and 3.6% for Pb²⁺ concentration of 10.0 and 60.0 μg L⁻¹, respectively. From on-line breakthrough curve, column capacity was 3.5 mg g⁻¹. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min⁻¹, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb²⁺/Cd²⁺, Pb²⁺/Cu²⁺ and Pb²⁺/Zn²⁺. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb²⁺ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb²⁺ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results.     

Improvements in thermospray flame furnace atomic absorption spectrometry

In thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) a nickel atomization tube is placed in the acetylene/air flame on a holder built onto a standard AAS burner head. The liquid to be analyzed is transported by a low or high-pressure pump through a very hot, simple, inexpensive ceramic capillary tip acting as a flame-heated thermospray into the flame furnace. This results in complete sample introduction and increases the residence time of the sample in the absorption volume. This leads for 17 elements to a 3-110-fold improvement in the power of detection compared to conventional flame AAS. The absolute detection limits (3s values, N=25) lie between 0.2 μg l⁻¹ (Zn) and 310 μg l⁻¹ (Se) according to the element. The R.S.D. (N=15) is 1.4-5.5% according to the element and applied concentration. TS-FF-AAS can easily be incorporated on any standard flame AAS instrument and can be automated with a standard autosampler.     

Direct determination of Cd, Cu and Pb in wines and grape juices by thermospray flame furnace atomic absorption spectrometry

The applicability of thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was evaluated for direct determination of Cu, Cd and Pb in wines and grape juices. The developed procedure does not require preliminary acid digestion of the samples. The optimum conditions for determination of Cu, Cd and Pb in wines were studied and the performance was compared to those typically obtained by flame atomic absorption spectrometry (FAAS). A sample volume of 150 microL was introduced into a heated nickel tube at a flow rate of 0.54 mLmin(-1) and 0.14 molL(-1) HNO(3) was used as sample carrier flowing at 2.5 mLmin(-1) for determining all analytes. The effect of ethanol concentrations on Cu, Cd and Pb absorbance signals were studied. All determinations were carried out by adopting optimized conditions and quantification was based on the standard additions method. Limits of detection (LOD) of 12.9, 1.8 and 5.3 microgL(-1) (n=14) for Cu, Cd and Pb, respectively, were obtained for wine samples (3sigma(blank)/slope, n=14). Relative standard deviations (R.S.D., %) of 2.7, 2.1 and 2.6 for Cu, Cd and Pb, were obtained (n=6) for wine samples. The values determined for grape juice samples were similar to these ones. The analytical throughput was 45 determinations h(-1) and accuracy was checked by addition-recovery experiments.     

Direct determination of Cu,Mn, Pb,and Zn in beer by thermospray flame furnace atomic absorption spectrometry

In this work, thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was employed for Cu, Mn, Pb, and Zn determination in beer without any sample digestion. The system was optimized and calibration was based on the analyte addition technique. A sample volume of 300 μl was introduced into the hot Ni tube at a flow-rate of 0.4 ml min⁻¹ using 0.14 mol l⁻¹ nitric acid solution or air as carrier. Different Brazilian beers were directly analyzed after ultrasonic degasification. Results were compared with those obtained by graphite furnace atomic absorption spectrometry (GFAAS). The detection limits obtained for Cu, Mn, Pb, and Zn in aqueous solution were 2.2, 18, 1.6, and 0.9 μg l⁻¹, respectively. The relative standard deviations varied from 2.7% to 7.3% (n=8) for solutions containing the analytes in the 25–50 μg l⁻¹ range. The concentration ranges obtained for analytes in beer samples were: Cu: 38.0–155 μg l⁻¹; Mn: 110–348 μg l⁻¹, Pb: 13.0–32.9 μg l⁻¹, and Zn: 52.7–226 μg l⁻¹. Results obtained by TS-FF-AAS and GFAAS were in agreement at a 95% confidence level. The proposed method is fast and simple, since sample digestion is not required and sensitivity can be improved without using expensive devices. The TS-FF-AAS presented suitable sensitivity for determination of Cu, Mn, Pb, and Zn in the quality control of a brewery.     

Cloud point extraction for determination of cadmium in soft drinks by thermospray flame furnace atomic absorption spectrometry

Cloud point extraction (CPE) is proposed as a preconcentration procedure for the determination of Cd in soft drinks by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The cadmium reacted with pyridyl-azo-naphthol (PAN) to form hydrophobic chelates, which were extracted into the micelles of Triton X-114 in a solution buffered at pH 9. NaCl was used for the phase separation. The variables which affect the preconcentration were optimized using a 2³ factorial design and central composite design (CCD). A response surface maximum point was obtained, and the critical values were a concentration of 0.13 mmol L^? 1 PAN, 0.03% m/v Triton X-114 and 2.3% m/v NaCl. Under the optimized conditions, after the extraction and preconcentration steps, a sample volume of 100 μL was introduced into the hot Ni tube using water as the carrier at a flow rate of 0.4 mL min^? 1. The values obtained for the detection limit, relative standard deviation and preconcentration factor were 0.0178 μg L^? 1, 4.1% (n = 8) and 55.5, respectively. The accuracy of the proposed method was demonstrated by performing addition-recovery experiments. Recoveries varied from 88 to 104%.     

Evaluation of selenium behavior in thermospray flame furnace atomic absorption spectrometry

The behavior of selenium in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was studied and the developed procedure was applied for selenium determination in biological materials after microwave-assisted sample digestion. A sample volume of 600 μL was introduced into the hot metallic Ni tube at a flow rate of 0.4 mL min⁻¹ using water as carrier. The limit of detection obtained for Se was 8.7 μg L⁻¹ (3s_blank/slope, n = 10), which is 95-fold better than that typically obtained using FAAS. The applicability of the TS-FF-AAS procedure was evaluated for selenium determination in biological materials. Certified reference materials of pig kidney (BCR 186) and mussel (GBW 08571) were analyzed and a t-test had not shown any statistically significant difference at a 95% confidence level between determined and certified values for both materials. The procedure was successfully applied for determination of Se in pig kidney and shellfish. It was demonstrated that TS-FF-AAS improved the performance of FAAS (flame atomic absorption spectrometry) for determination of Se.     

Improvements in cobalt determination by thermospray flame furnace atomic absorption spectrometry using an on-line derivatization strategy

An on-line derivatization strategy was developed for improving cobalt sensitivity using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) as the analytical technique. This strategy involves the generation of a volatile cobalt compound, providing better sample vaporization efficiency. The effect of sodium diethyldithiocarbamate (DDTC) as complexing agent on the integrated absorbance signal was evaluated. Parameters including the pH of complex formation, complex concentration and volume, sample volume, flame gas composition and tube atomization configuration were optimized. A wide linear range (from 23 microg L(-1) to 3 mg L(-1); r(2)=0.9786) was obtained, with the best one (r(2)=0.9992) attained from 23 to 400 microg L(-1) with a sample throughput of 30 h(-1). The improvement in the detection power was 17-fold when compared to FAAS, which provides 7 microg L(-1) as the limit of detection when considered TS-FF-AAS technique. A relative standard deviation (n=10) of 4% for a cobalt solution containing 50 microg L(-1) was attained, and the accuracy of the procedure was evaluated through certified reference materials (IAEA-SL-1, lake sediment; and ISS-MURST-A1, Antarctic marine sediment). Good agreement between the results at the 95% confidence level was observed.     

Indirect flow-injection determination of ascorbic acid by flame atomic absorption spectrometry

A continuous-flow procedure is proposed for the indirect determination of ascorbic acid, based on its reducing properties because of the oxidation of its 1,2-enediol group. Iron(III) was injected into a 1,10-phenanthroline stream, which was mixed with a sample carrier and then with a sodium picrate solution stream. In these conditions the iron(III) was reduced to iron(II) by the ascorbic acid. Thus, the iron(II) formed reacts with 1,10-phenanthroline to form a charged red complex, which with picrate ion forms a stable red-orange uncharged ion-association complex that is adsorbed on-line on a non-ionic polymeric adsorbent (Amberlite XAD-4), proportionally to the ascorbic acid in the sample. The unadsorbed iron was determined by flame atomic absorption spectrometry. The proposed method allows the determination of ascorbic acid in the range 0.5–25 g ml^–1 with a relative standard deviation of 2.9% at a rate of ca. 90 samples h^–1. This method has been applied to the determination of ascorbic acid in pharmaceutical preparations, fruit juices and sweets. The results obtained in the analysis are compared with those provided by the 2,6-dichloroindophenol method.     

Analysis of submicroliter samples using micro thermospray flame furnace atomic absorption spectrometry

A recently described thermospray flame furnace atomic absorption spectrometric (TS-FF-AAS) system has been modified in order to extend the applicability of the method for the determination of elemental traces in very small sample volumes (microliter or submicroliter). As an easily available, effective thermospray vaporizer, a fused silica capillary was used and the liquid sample was transported by 1 MPa (10 bar) gas pressure delivered by a standard gas cylinder. A 0.3 microL sample volume can be analyzed with a higher power of detection than using 3 orders of magnitude larger sample volumes with conventional flame atomic absorption spectrometry. The relative standard deviations (N=12) for 0.3 microL volumes and 5 microg/mL Pb samples amount to 3.1% and 3.8% in signal height and signal area, respectively. The detection limit was found to be 69 ng/mL. Initial experiments with other elements (Cd, Hg, Tl, Zn) led to similar results.     

Direct determination of Cu and Zn in fruit juices and bovine milk by thermospray flame furnace atomic absorption spectrometry

In the present work, thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was employed for Cu and Zn determination in bovine milk and fruit juice samples without any pretreatment. TS-FF-AAS system was optimized and a sample volume of 300 μl was injected into the carrier stream (0.014 mol l⁻¹ HNO₃ at a flow rate of 0.4 ml min⁻¹), and it was introduced into a hot Ni tube. The detection limits obtained for Cu and Zn in aqueous solution were 2.2 and 0.91 μg l⁻¹, respectively, and 3.2 μg l⁻¹ for Cu in a medium containing water-soluble tertiary amines. The relative standard deviations varied from 2.7 to 4.2% (n=12). Sample preparation was carried out by simple dilution in water or in water-soluble tertiary amines medium. Accuracy was checked by performing addition-recovery experiments as well as by using reference materials (whole milk powder, non-fat milk powder, and infant formula). Recoveries varied from 97.7 to 105.3% for Cu and Zn. All results obtained for reference materials were in agreement with certified values at a 95% confidence level.     

Comparison of tungsten coil electrothermal vaporization and thermospray sample introduction methods for flame furnace atomic absorption spectrometry

Flame furnace atomic absorption spectrometry (FF-AAS) is a newly developed flame atomic absorption spectrometric technique based on arranging a flame furnace onto the top of the flame burner head. In this fundamental investigation, 25 elements were carefully tested by using either thermospray FF-AAS or tungsten coil electrothermal vaporization FF-AAS, of which 15 volatile and semi-volatile elements (Cd, Tl, Ag, Pb, Zn, Hg, Cu, Sb, Bi, Te, In, As, Se, Sn and Au) exhibited better limits of detection compared to those by conventional FAAS; however, non-volatile or refractory elements (Fe, Co, Ni, Cr, Mn, Pd, Pt, Al, Be and V) showed inferior sensitivities by the proposed methods.     

Cloud point extraction–thermospray flame quartz furnace atomic absorption spectrometry for determination of ultratrace cadmium in water and urine

A simple, low cost and highly sensitive method based on cloud point extraction (CPE) for separation/preconcentration and thermospray flame quartz furnace atomic absorption spectrometry was proposed for the determination of ultratrace cadmium in water and urine samples. The analytical procedure involved the formation of analyte-entrapped surfactant micelles by mixing the analyte solution with an ammonium pyrrolidinedithiocarbamate (APDC) solution and a Triton X-114 solution. When the temperature of the system was higher than the cloud point of Triton X-114, the complex of cadmium-PDC entered the surfactant-rich phase and thus separation of the analyte from the matrix was achieved. Under optimal chemical and instrumental conditions, the limit of detection was 0.04 μg/L for cadmium with a sample volume of 10 mL. The analytical results of cadmium in water and urine samples agreed well with those by ICP-MS.     

The coupling of rapidly synergistic cloud point extraction with thermospray flame furnace atomic absorption spectrometry

Rapidly synergistic cloud point extraction (RS-CPE) was coupled with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) to result in new CPE patterns and accelerated (1?min) protocols. It is demonstrated, for the case of copper (II) ion, that TS-FF-AAS improves the sampling efficiency and the sensitivity of FAAS determinations. Problems of nebulization associated with previous methods based on the coupling of FAAS and RS-CPE are overcome. TS-FF-AAS also improves sensitivity and gives a limit of detection for copper of 0.20?μg?L^-1, which is better by a factor of 32. Compared to direct FAAS, the factor is 114.

A sensitive method for cadmium determination using an on-line polyurethane foam preconcentration system and thermospray flame furnace atomic absorption spectrometry.

A new sensitive and low cost method for cadmium determination at microg l(-1) levels that combines an on-line preconcentration system with the thermospray flame furnace atomic absorption spectrometry technique (TS-FF-AAS) is described in this work. Cadmium is preconcentrated from an acidic medium (pH 2.0) by forming a complex with ammonium O,O-diethyldithiophosphate (DDTP), which is then adsorbed onto polyurethane foam (PUF). The elution step is performed by using 80% (v/v) ethanol. The effects of the chemical and flow variables associated with the preconcentration were studied, such as the pH of formation of the Cd-DDTP complex, the DDTP concentration, the preconcentration and elution flow rate and the mass of adsorbent. The present method was operated in volume-mode (2 ml) and provided a linear range from 0.4 to 15.0 microg l(-1) with a sample throughput of 16 h(-1). The increase of power detection related to TS-FF-AAS by coupling the preconcentration system was confirmed by the enhancement of sensitivity (ca. 5 times), when compared to the value for TS-FF-AAS alone, thus achieving a low detection limit (0.12 microg l(-1)). The accuracy of the method was confirmed from analyses of spiked water samples and by the use of a reference technique (ETAAS). Certified biological materials were also used for the same purpose.     

Acid extraction and cloud point preconcentration as sample preparation strategies for cobalt determination in biological materials by thermospray flame furnace atomic absorption spectrometry

A thermospray flame furnace atomic absorption spectrometer (TS-FF-AAS) was employed for Co determination in biological materials. Cobalt presents a high atomization temperature and consequently poor sensitivity is obtained without changing its thermochemical behavior. The effect of different complexing agents on sensitivity was evaluated based on the formation of Co volatile compounds. A cloud point procedure was optimized for Co preconcentration for further improvement of sensitivity. Samples were treated with 1 mol l^− 1 hydrochloric acid solution for quantitative extraction of Co without simultaneous extraction of Fe, since it is a strong interferent. After the extraction and preconcentration steps, a sample volume of 150 μl was introduced into the hot Ni tube using air as carrier at a flow-rate of 0.4 ml min^− 1. The best sensitivity was attained using ammonium pyrrolidinedithiocarbamate (APDC) and Triton X-114 was employed for implementation of the cloud point procedure. The detection limit obtained for Co was 2.1 μg l^− 1 and the standard deviation was 5.8% for a solution containing 100 μg l^− 1 (n = 10). Accuracy was checked using two certified reference materials (tomato leaves and bovine liver) and results were in agreement with certified values at a 95% confidence level. Employing the developed procedure, Co were quantified in different biological materials (plant and animal tissues). The proposed method presents suitable sensitivity for cobalt determination in the quality control of foods.     

Indirect flow-injection determination of methadone by atomic absorption spectrometry

A simple continuous redox flow system coupled on-line with an atomic absorption spectrometer for the determination of methadone at the ng ml^?1 level is described. It is based on the reduction of the keto group of the analyte in a camium or zinc microcolumn and determination of the metal ions formed. The drug can be determined in the range 5–50 ng ml^?1 with a relative standard deviation between 1.8 and 2.5% at a sampling frequency of 150 h^?1. The selectivity of the method allows the analyte to be determined in the presence of other drugs.     

Ti and Ni tubes combined in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the determination of copper in biological samples

This study presents an evaluation of Cu determination in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) using Ni and Ti metal tube atomizers. The TS-FF-AAS system was equipped with Ti tubes inserted inside Ni tubes (called Ni/Ti), and also different configurations of Ti tube atomizers placed on an oxidizing air/acetylene flame. This new arrangement combining both tubes permitted an increased sensitivity (approximately 4 times) when it was compared with single Ni or Ti tubes. This high sensitivity is due to the formation of TiO₂ inside the Ti tubes (shown by X-ray diffractometry and microanalyses), improving the Cu atomization through the corresponding oxide. The estimated gaseous phase temperatures for the tubes (Ni, Ti and Ni/Ti) were of the same magnitude (varied from 1400 to 1800 °C). Tests with concomitants (Na, K, Ca and Mg) showed similar behavior of Ni and Ni/Ti tubes. The differences between Ni and Ni/Ti tube atomizers for Cu sensitivity were not related to differences between the tube atomizers' internal volumes. The method accuracy was verified using certified reference materials (CRM's) of biological samples prepared with a closed-vessel microwave system using diluted HNO₃. A 2 µg L^− 1 Cu detection limit was obtained using a Ni/Ti tube atomizer. The recoveries for Cu from the CRM's were about 100%. Finally, the use of a Ti tube inside a Ni tube increased the Ti tube lifetime.     

Online preconcentration system for determining ultratrace amounts of Cd in vegetal samples using thermospray flame furnace atomic absorption spectrometry

A system has been developed for online preconcentration and determination of Cd using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). It is based on the solid-phase extraction of Cd in an Amberlite XAD-2 minicolumn loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM), and the metal ion is eluted with 1 mol L⁻¹ hydrochloridric acid, followed by its determination. The online system allows determining Cd with a detection limit of 8.0 ng L⁻¹ and a quantification limit of 25.0 ng L⁻¹. The precision (repeatability), calculated as the relative standard deviation (% RSD) in sample solutions containing 0.5 and 3.0 μg L⁻¹ of Cd, was 6.1 and 4.5%, respectively. The preconcentration factor obtained was 24. The system’s accuracy was confirmed by analyzing the following certified reference materials (CRMs): Rice flour NIES 10b, Apple leaves NIST 1515 and Orchard leaves NBS 1571. This procedure was applied to the determination of Cd in cabbage and powdered guarana samples.     

Assessment of cadmium and iron adsorption in sediment,employing a flow injection analysis system with on line filtration and detection by flame atomic absorption spectrometry and thermospray flame furnace atomic absorption spectrometry

This work presents an evaluation of iron and cadmium adsorption in sediment of the Furnas Hydroelectric Plant Reservatory located in Alfenas, Minas Gerais (Brazil). The metal determination was done employing a flow injection analysis (FIA) with an on-line filtering system. As detection techniques, flame atomic absorption spectrometry (FAAS) for iron and thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for cadmium determinations were used. The developed methodology presented good limits of detection, being 190 μg L⁻¹ for iron and 1.36 μg L⁻¹ for cadmium, and high sampling frequency for both metals 144 and 60 readings h⁻¹ for iron and cadmium, respectively. Both metals obey the Langmuir model, with maximum adsorptive capacity of 0⋅169 mg g⁻¹ for iron and 7⋅991 mg g⁻¹ for cadmium. For iron, a pseudo-first-order kinetic model was obtained with a theoretical Q_e = 9⋅8355 mg g⁻¹ (experimental Q_e = 9⋅5432 mg  g⁻¹), while for cadmium, a pseudo-second-order kinetic model was obtained, with a theoretical Q_e = 0.3123 mg g⁻¹ (experimental Q_e = 0⋅3052 mg g⁻¹).     

Determination of cadmium and lead at low levels by using preconcentration at fullerene coupled to thermospray flame furnace atomic absorption spectrometry

A new and sensitive method for Cd and Pb determinations, based on the coupling of thermospray flame furnace atomic absorption spectrometry and a preconcentrator system, was developed. The procedure comprised the chelating of Cd and Pb with ammonium pyrrolidinedithiocarbamate with posterior adsorption of the chelates on a mixture (40 mg) of C₆₀ and C₇₀ at a flow rate of 2.0 ml min⁻¹. These chelates were eluted from the adsorbent by passing a continuous flow of ethanol (80% v/v) at 0.9 ml min⁻¹ to a nickel tube placed in an air/acetylene flame. After sample introduction into the tube by using a ceramic capillary (0.5 mm i.d.), the analytical signals were registered as peak height. Under these conditions, improvement factors in detectability of 675 and 200 were obtained for Cd and Pb, respectively, when compared to conventional flame atomic absorption spectrometry. Spiked samples (mineral and tap waters) and drinking water containing natural concentrations of Cd were employed for evaluating accuracy by comparing the results obtained from the proposed methodology with those using electrothermal atomic absorption spectrometry. In addition, certified reference materials (rye grass, CRM 281 and pig kidney, CRM 186) were also adopted for the accuracy tests. Due to the good linearity ranges for Cd (0.5–5.0 μg l⁻¹) and Pb (10–250 μg l⁻¹), samples with different concentrations could be analyzed. Detection limits of 0.1 and 2.4 μg l⁻¹ were obtained for Cd and Pb, respectively, and RSD values <4.5% were observed (n=10). Finally, a sample throughput of 24 determinations per hour was possible.