Development of a flow system for the determination of low concentrations of silver using Moringa oleifera seeds as biosorbent and flame atomic absorption spectrometry

Surfactant modified coconut husk fiber as a green alternative sorbent for micro-solid phase extraction of triazole fungicides at trace level in environmental water, soybean milk, fruit juice and alcoholic beverage samples

In this work, micro-solid phase extraction using surfactant modified biosorbent was investigated for trace level determination of triazole fungicides prior to their analysis by high performance liquid chromatography. Coconut husk fiber (CHF) was selected as an effective biosorbent in the extraction process. Fourier transform infrared spectrometry, scanning electron microscopy and transmission electron microscopy methods were used to characterize the modified biosorbent. Various factors affecting the extraction efficiency of the proposed method were studied including the amount of coconut husk fiber biosorbent (0.1 g), kind and concentration of surfactant as a modifier (sodium dodecyl sulfate, 10 mmol L-1), kind and volume of desorption solvent (methanol, 150 μL), and extraction period (including vortex adsorption time, centrifugation adsorption time, vortex desorption time and centrifugation adsorption time approximately 10 min). Under the selected conditions, the calibration plot was found to be linear in the range of 9-300 μg L-1 with a coefficient for determination of greater than 0.99. The limits of detection and limits of quantification for the studied triazole fungicides were 3.00 and 9.00 μg L-1, respectively. Finally, the proposed method was successfully applied to determine triazole fungicides in environmental water, soybean milk, fruit juice and alcoholic beverage samples with acceptable recoveries obtained in the range of 67.0% to 105.0%.

Selective Extraction and Determination of Chromium Concentration Using Luffa cylindrica Fibers as Sorbent and Detection by FAAS

In this approach, a nonchromatographic method was developed for selective extraction and determination of Cr(III) concentration in isotonic and energy drinks by FAAS. This new method uses Luffa cylindrica fibers as the solid phase extraction and an off-line flow injection system. Cr(III) and Cr(VI) adsorption behavior onto Luffa fibers allowed the selective separation of Cr(III) in the pH range of 4 to 5. The system variables were optimized through full factorial and Doehlert designs. Under optimal conditions, the detection and quantification limit for Cr(III) was 19.2 µg·L−1 and 63.9 µg·L−1, respectively, with precision below 0.19%. A high tolerance toward interfering ions was observed for the proposed method. Recovery test results obtained for different isotonic and energy drinks samples were higher than 87.6%. The method’s accuracy was confirmed through analysis of certified reference materials, water and sediment river samples (APS-1071 and APS-1066).

Ultrasensitive electrochemiluminescence determination of trace Ag ions based on the signal amplification caused by its catalytic effect on Mn(II) oxidation using graphite catheter as electrode

In this work, an ultrasensitive electrochemiluminescence (ECL) method was established for the detection of trace amount of Ag ions (Ag⁺). In sulfuric acid medium, Ag(II), the electro-oxidized product of Ag(I), oxidizes manganese ions (Mn²⁺) to produce permanganate (MnO₄^-) by using a pair of graphite catheters as electrodes. While permanganate and luminol can produce strong chemiluminescence, based on the catalytic effect of Ag(II) on Mn²⁺ oxidation, there is a good linear relationship between the concentration of Ag⁺ and luminescence intensity. Under optimized conditions, the linear range of this method for Ag⁺ is from 0.2 to 150 nM with a detection limit of 0.06 nM. The method was applied for determination of Ag⁺ in various water samples with satisfactory results.

Effect of bioflocculants on the coagulation activity of alum for removal of trihalomethane precursors from low turbid water

Reactivity of chlorine towards hydrophobic groups present in natural organic matter (NOM) provokes the formation of carcinogenic disinfection byproducts such as trihalomethanes in chlorinated water. The present study aimed to investigate the variations in coagulant activity of alum using two different bioflocculants (coagulant aid) namely, Moringa oleifera and Cyamopsistetragonoloba for the removal of hydrophobic fractions of NOM and subsequent chlorine consumption by treated water. Effect of dual coagulants on trihalomethane surrogate parameters such as total organic carbon, dissolved organic carbon, UV absorbing materials and prominent hydrophobic species such as phenolic groups along with aromatic chromophores, polyhydroxy aromatic moiety have also been studied. The concept of differential spectroscopy and absorbance slope index has been employed to understand the combined effects of alum-bioflocculants on the reactivity of NOM with chlorine. Our result shows that the combination of alum and C. tetragonoloba is more efficient for reducing trihalomethane surrogates from chlorinated water as compared to M. oleifera. C. tetragonoloba elicited synchronized effects of sweep coagulation and particle bridging-adsorption which eventually facilitated efficient removal of hydrophobic fractions of NOM. The variation in the mechanistic approach of bioflocculants was due to the presence of cationic charge on M. oleifera and adhesive property of C. tetragonoloba.

A low-cost biosorbent-based coating for the highly sensitive determination of organochlorine pesticides by solid-phase microextraction and gas chromatography-electron capture detection

In this study, an environmentally friendly and low-cost biosorbent coating was evaluated, for the first time, as the extraction phase for solid-phase microextraction (SPME) supported on a nitinol alloy. The characterization of the new fiber was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The applicability of the biosorbent-based fiber in the determination of δ-hexachlorocyclohexane, aldrin, heptachlor epoxide, α-endosulfan, endrin and 4,4'-DDD in water samples was verified, with separation/detection by gas chromatography coupled to electron capture detection (GC-ECD). The influencing parameters (temperature, extraction time and ionic strength) were optimized simultaneously using a central composite design. The optimum conditions were: extraction time of 80min at 80°C and sodium chloride concentration of 15% (w/v). Satisfactory analytical performance was achieved with limits of detection (LOD) between 0.19 and 0.71ngL^-1 and limits of quantification (LOQ) between 0.65 and 2.38ngL^-1. The relative recoveries for the analytes were determined using river and lake water samples spiked at different concentrations and ranged from 60% for α-endosulfan to 113% for δ-hexachlorocyclohexane, with relative standard deviations (RSD) lower than 21%. The fiber-to-fiber reproducibility (n=3) was also evaluated and the RSD was lower than 14%. The extraction efficiency obtained for the proposed biosorbent coating was compared to a commercially available DVB/Car/PDMS coating. The proposed fiber provided very promising results, including LODs at the level of parts per trillion and highly satisfactory thermal and mechanical stability.

Flow analysis in Brazil: contributions over the last four decades

Timeline with the main contributions of Brazilian researchers to flow analysis.

Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Silver after Solid-Phase Extraction with 2-Mercaptobenzothiazole Immobilized on Microcrystalline Naphthalene

A simple and sensitive solid-phase extraction (SPE) procedure combined with flame atomic absorption spectrometry (FAAS) was designed for the extraction and determination of trace amounts of silver. A column of immobilized 2-mercaptobenzothiazole (MBT) on microcrystalline naphthalene was used as the sorbent. Silver was quantitatively retained on the column in the pH range of 0.5–6.0. After extraction, the solid mass consisting of silver complex and naphthalene was dissolved out of the column with 5.0 mL of dimethylformamide, and the analyte was determined by flame atomic absorption spectrometry (FAAS). Under the optimum experimental conditions, the adsorption capacity was found to be 1.18 mg of silver per gram of the sorbent. A sample volume of 800 mL resulted in a preconcentration factor of 160. The relative standard deviation obtained for ten replicate determinations at a concentration of 0.8 µg L−1was 1.4%, and the limit of detection was 0.02 µg L−1. The method was successfully applied to the determination of silver in radiology film, waste water, and natural water samples. The accuracy was examined by recovery experiments, independent analysis by electrothermal atomic absorption spectrometry, and analysis of two certified reference materials.

Preconcentration and determination of copper in tobacco leaves samples by using a minicolumn of sisal fiber (Agave sisalana) loaded with Alizarin fluorine blue by FAAS

In the present study, a minicolumn of sisal fiber loaded with alizarin fluorine blue is proposed as a preconcentration system for copper determination in tobacco leaf samples by flame atomic absorption spectrometry. During the optimization procedure, a two level full factorial design (2(4)) was used at the preliminary evaluation of four factors, involving the following variables: sampling flow rate, elution flow rate, buffer concentration and pH. Regarding the studied levels, this design has shown that buffer concentration and pH were significant factors. The experimental conditions established in the optimization step were: pH=4.75, buffer concentration of 0.005 mol L(-1) for elution with HCl 1.0 mol L(-1) this system allows the determination of copper content with a detection limit (LD) of 0.018 μg L(-1) and a quantification limit (LQ) of 0.061 μg L(-1) precision expressed as relative standard deviation (R.S.D.) of 4.65 and 5.07%, utilizing concentration of 10 and 2.0 μg L(-1), respectively, and a preconcentration factor of 75, for a sample volume of 50.0 mL. Accuracy was confirmed by copper determination in the standard reference material, NIST SRM 1570 a trace element units in Spinach Leaves and by spike tests with recovery levels ranging from 93 to 100%; the procedure was applied for copper determination in tobacco leaf samples collected in Cruz das Almas City, Bahia, Brazil. The achieved concentrations of the three samples analyzed varied from 0.15 to 0.52 μg g(-1).

Determination of low levels of lead in beer using solid-phase extraction and detection by flame atomic absorption spectrometry

In this study, a method for the determination of low concentrations of lead in beer samples using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry (FAAS) was developed. Moringa oleifera seeds were used as a biosorbent material. Chemical and flow variables of the online preconcentration system, such as sample pH, preconcentration flow rate, eluent flow rate, eluent concentration, particle size, and sorbent mass, were studied. The optimum extraction conditions were obtained using a sample pH of 6.0, sample flow rate of 6.0 mL min(-1), 63.0 mg of sorbent mass, and 2.0 mol L(-1) HNO(3) at a flow rate of 2.0 mL min(-1) as the eluent. With the optimized conditions, the preconcentration factor, precision, detection limit, consumption index, and sample throughput were estimated as 93, 0.3% (10.0 μg L(-1), n = 7), 7.5 μg L(-1), 0.11 mL, and 23 samples per hour, respectively. The method developed was successfully applied to beer samples and recovery tests, with recovery ranging from 80% to 100%.

Determination of trace silver in water samples by online column preconcentration flame atomic absorption spectrometry using termite digestion product

A new method for Ag determination in water samples using solid phase extraction (SPE) coupled to a flow injection system and flame atomic absorption spectrometry was developed. The sorbent used for Ag preconcentration and extraction was the termite digestion product. Flow and chemical variables of the system were optimized through a multivariate procedure. The factors selected were adsorbent mass, buffer type and concentration, sample pH, and sample flow rate. The detection limit and precision were 3.4 μg L(-1) and 3.8% (n = 6, 15 μg L(-1)), respectively. The enrichment factor and the linear working range were, respectively, 21 and 10-50 μg L(-1). Results for recovery tests using different water samples were between 96 and 107%. The proposed methodology was applied with success for the determination of Ag in water used to wash clothes impregnated with silver nanoparticles, supplied by a factory located in Santa Catarina, Brazil.