Marco Aurélio Zezzi Arruda

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.

Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration

A new micelle-mediated phase separation of metal ions, applied for preconcentrating trace levels of cobalt as a prior step to its determination by flame atomic spectroscopy, has been developed. Two methods were proposed employing both Triton X-100 and sodium dodecyl sulfate (SDS) as a mixed micellar system while the phase separation was induced by HCl or NaCl addition. Cobalt was complexed with pyridylazo compounds (PAN, PAR, 5-Br-PADAP) in an aqueous surfactant medium and it was concentrated in the surfactant rich phase after phase separation. The chemical variables affecting the cloud point extraction were evaluated, optimized and successfully applied to cobalt determination in pharmaceutical samples. Under the optimized conditions, the preconcentration system permitted limits of detection as 1.1 and 1.6 mug l(-1) cobalt, respectively, when HCl and NaCl were used. Both proposed methods showed linear calibration within a 25-200 mug l(-1) cobalt range. The extraction efficiency was investigated at different cobalt concentrations (40-185 mug l(-1)) and good recoveries (98-102%) were obtained by using NaCl as electrolyte. The results obtained were compared with those observed with ET AAS.

Trends in metal-binding and metalloprotein analysis

This review describes recent tendencies for metal-binding and metalloprotein analysis, emphasizing metal quantification in proteins through X-ray, atomic absorption, mass spectrometric techniques, and others. Hyphenated techniques such as capillary electrophoresis-synchrotron radiation X-ray fluorescence (CE-SRXRF), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), matrix-assisted laser desorption/ionisation-time-of-flight mass spectrometry (MALDI-TOF-MS), etc. are also presented. As protein separation techniques electrophoresis (mainly sodium dodecyl sulphate-polyacrylamide gel electrophoresis, SDS-PAGE), capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) are indicated, due to their inherent sensitivity, resolution and/or easy implementation. Latest challenges in metallomics are also commented.

A fast ultrasound-assisted extraction of Ca, Mg, Mn and Zn from vegetables

A fast and accurate method for the extraction of Ca, Mg, Mn and Zn from vegetables is proposed. Ultrasonic energy and dilute acid are used for the extraction. Optimisation conditions for the ultrasonic bath were established: 1 l of water; 25°C; 2% v/v detergent concentration; horizontal and vertical positions in the bath for sonicating samples: central and bottom, respectively. Using these conditions, the nitric acid concentration (0–1.4 mol l−1), sonication time (0–30 min) and particle size (150–63 μm) were optimised. The best conditions for extraction were: 0.14 mol l−1 HNO3, 10 min of sonication time and a particle size <75 μm. The accuracy of the proposed ultrasound-assisted extraction method was assessed by using certified reference materials, as well as wet digestion. Recoveries ranging from 96 to 102% were obtained under the extraction conditions mentioned above with different kinds of plant samples for the majority of the metals studied.

Molecularly imprinted polymer as a solid phase extractor in flow analysis

Molecularly imprinted polymers (MIPs) are novel alternative materials for solid phase extraction. Applications in flow analysis are recent and enhanced in-line separation/concentration procedures have been proposed. Use of flow systems is very important in the context. The aim of this review is then to highlight the implementation of MIP as solid phase extractor in flow analysis, emphasizing potentialities, limitations and applications.

Vermicompost as a natural adsorbent material: characterization and potentialities for cadmium adsorption

Vermicompost (humic material) samples were submitted to characterization by infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, electron microscopy etc. In addition, its cation exchange capacity (CEC) was determined. Factorial experiments were designed in order to elucidate the interaction mechanisms between Cd2+ and the adsorptive sites of vermicompost. The maximum adsorptive capacity for cadmium was evaluated by a Langmuir isotherm. The characterization revealed that vermicompost exhibits high CEC values (ca. 72.9 meq per 100 g), high surface area (porous material), chelating groups and a maximum adsorptive capacity for Cd (38.6 mg g-1) at pH 5.0. This potential application was exploited in the analysis of synthetic and real (mineral water) samples with Cd concentrations of ca 5 mg L-1, requiring a preconcentration step. An enrichment factor of 100 was attained.

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 300mul was injected into the carrier stream (0.014moll(-1) HNO(3) at a flow rate of 0.4mlmin(-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 0.91mugl(-1), respectively, and 3.2mugl(-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.

Use of ultrasonic baths for analytical applications: a new approach for optimisation conditions

Optimisation conditions for obtaining maximum cavitation intensity in ultrasonic baths are proposed using a simple and fast method. Parameters such as water volume, temperature, detergent concentration, horizontal and vertical positions, number of tubes in the bath, sonication time and bath water substitution were studied. The results obtained for both baths studied (Neytech and Cole-Parmer) lead to the following conditions for maximum cavitation intensity: 1 L of water at room temperature, 0.2 % (v/v) of detergent, central position on the bottom of the tank. Only one tube at a time should be used inside the bath during the ultrasound application. The cavitation intensity was linear with the sonication time up to 10 minutes and the water substitution during the sonication improved reproducibility. This system using continuous water change makes possible the sonication of 6 consecutive samples, without changes in the water volume.

Simultaneous sample digestion and determination of Cd, Cu and Pb in biological samples using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) with slurry sample introduction

In a Ni tube placed in an oxidizing air/acetylene AAS flame simultaneous digestion/oxidation of biological samples and powerful trace determinations were performed. A ceramic capillary was used for sample introduction. This capillary acted as a flame-heated thermospray nozzle (TS-FF-AAS). Slurry samples, prepared in 0.3 mol L−1 HNO3, were transported by a new 0.6 MPa (84 psi) flow injection system through the hot capillary into the flame tube furnace. A nitric acid vapour environment exists inside the tube at temperatures above 1000 °C oxidising the samples. The element traces could then be measured by AAS. For these investigations, 300 µL slurry samples (0.1 to 1.0% w/v) from various biological materials, such as pig kidney (CRM 186), bovine liver (SRM 1577), spinach (SRM 1570), orchard leaves (SRM 1571) citrus leaves (SRM 1572), tomato leaves (SRM 1573) and tomato puree were used. Reference values were additionally obtained by electrothermal atomic absorption spectrometry (ETAAS). The standard deviation (n = 10) was between 3 and 5% using the same slurry and about 10% when the whole process was repeated on subsequent days. The detection limits for Cd, Cu and Pb were found to be 0.5, 4.3 and 3.5 µg g−1, respectively. A t-test showed no differences between the found and certified values at a 95% confidence level. In all experiments the calibration could be performed with aqueous standard solutions.

On-line molecularly imprinted solid-phase extraction for the selective spectrophotometric determination of nicotine in the urine of smokers

This work describes an on-line molecularly imprinted solid-phase extraction (MISPE) method for spectrophotometric determination of nicotine in urine samples of smokers. This method is based on manganese (VII) to manganese (VI) reduction in an alkaline medium, promoted by nicotine. Two wash solutions (1:4 (v/v) acetonitrile:sodium hydroxide--pH 11.4, and nitric acid--pH 2.5) were employed to circumvent interferences. Aqueous solutions containing nicotine plus different possible concomitants (cotinine, anabasine, norcotinine and caffeine) were tested individually. The analytical calibration curve was prepared in urine samples collected from non-smokers and spiked with nicotine standard from 1.1 to 60 micromol L(-1) (r(2)>0.998). The limit of quantification and the analytical frequency were 1.1 micromol L(-1) and 11 h(-1), respectively. The precision, evaluated using 3, 10 and 30 micromol L(-1) nicotine in urine, was 10, 10 and 4% (intra-day precision) and 12, 13 and 5% (inter-day precision), respectively. Accuracy was checked through high performance liquid chromatography and the results did not present significant differences at the 95% confidence level according to the Students t-test.