Cathodic adsorptive stripping voltammetric determination of rutin in soybean cultivars

A highly sensitive and selective cathodic adsorptive stripping voltammetric method for determination of rutin is presented. The method relies on the accumulation of a Cu(II)–rutin complex at a hanging mercury drop electrode (HMDE), followed by its reduction during a differential pulse voltammetric scan. The electrochemical behavior of the Cu(II)–rutin complex at HMDE was investigated by cyclic voltammetry. Results show that the electrode process is adsorption-controlled and gradually becomes less reversible at high scan rates where peak separation grows. Under the optimized conditions (phosphate buffer pH 6, ?1.000 V accumulation potential, 180 s accumulation time, 70 mV pulse amplitude, 50 mV s^?1 scan rate and 1.6 × 10^?6 M Cu(II) concentration), the reduction peak current (I_pc) of the Cu(II)–rutin complex is linear (I_pc (nA) = 10.070 + 1.9 × 10⁸ [Rutina]) to rutin concentration in the range from 2.0 × 10^?7 to 1.4 × 10^?6 M, with a correlation coefficient of 0.999. The detection and quantification limits obtained were 7.0 × 10^?9 M and 2.2 × 10^?8 M, respectively. The method was successfully applied to the determination of rutin in soybean cultivars, with recoveries of 94–105%.     

A rapid and sensitive method for the determination of dibutyl phthalate in wine by flow-injection chemiluminescence analysis

A sensitive method for the determination of picogram level dibutyl phthalate (DBP) in wine by flow-injection chemiluminescence (FI–CL) analysis is presented for the first time, which was based on the quenching effect of DBP on the luminol–myoglobin (Mb) CL system. The decrement of CL intensity was linearly proportional to the logarithm of DBP concentration in the range of 0.1–100 pg mL⁻¹ with the detection limit of 0.03 pg mL⁻¹ (3σ). At a flow rate of 2.0 mL min⁻¹, a complete determination of DBP including sampling and washing could be accomplished in 0.5 min, giving the maximum sample throughput of 120 h⁻¹. The proposed method was successfully applied to the determination of DBP in wine, human serum and urine samples with the relative standard deviations (RSDs) of less than 3.0% (n = 5). The molecule docking results showed that DBP interacted with the amino acid residues near the heme moiety of Mb. The possible CL mechanism of luminol–Mb–DBP reaction should be that the binding of Mb with DBP forming a 1:1 complex (binding constant K = 1.55 × 10⁴ L mol⁻¹) led to the conformational change of Mb and resulted in the quenching of CL intensity.     

Determination of clothianidin in food products by using an automated system with photochemically induced fluorescence detection

A flow-through system based on the integration of solid-phase spectroscopic detection implemented with photochemically induced fluorescence (PIF) is proposed for the determination of clothianidin (a non-fluorescent neonicotinoid insecticide) through a multicommutated method. The pesticide is injected into the carrier stream (0.015 mol L⁻¹C₂H₄O₂/NaC₂H₃O₂, pH = 5.0) and flows towards a homemade photoreactor, which consists of a PTFE tubing loosely coiled around a low-pressure mercury lamp (15W). After the photochemical reaction of clothianidin, the generated fluorescent photoproduct is transported to a flow cell packed with Sephadex-SP C-25 where it is retained and monitored (λ_ex = 357 nm/λ_em = 418 nm). The method presents a detection limit of 1.5 ng mL⁻¹, a sample throughput of 23 h⁻¹ and inter-day relative standard deviation lower than 3%. The described system has been satisfactorily applied to the determination of clothianidin in samples of drinking water, rice and honey. Taking into account that the maximum residue limit specified in the Codex Alimentarius Commission for rice grains is 0.5 mg kg⁻¹, recovery experiments have been carried out for clothianidin concentrations in the 0.3-10.0 mg kg⁻¹ range.     

Levels and sources of volatile organic compounds including carbonyls in indoor air of homes of Puertollano,the most industrialized city in central Iberian Peninsula. Estimation of health risk

Twenty nine organic air pollutants including carbonyl compounds, alkanes, aromatic hydrocarbons and terpenes were measured in the indoor environment of different houses together with the corresponding outdoor measurements in Puertollano, the most industrialized city in central Iberian Peninsula. VOCs were sampled during 8 weeks using Radiello^® passive samplers, and a questionnaire on potential VOCs sources was filled out by the occupants. The results show that formaldehyde and hexanal was the most abundant VOCs measured in indoor air, with a median concentration of 55.5 and 46.4 μg m⁻³, respectively followed by butanal (29.1 μg m⁻³), acetone (28.4 μg m⁻³) and acetaldehyde (21.4 μg m⁻³). After carbonyls, n-dodecane (13.1 μg m⁻³) and terpenes (α-pinene, 13.4 μg m⁻³ and limonene, 13.4 μg m⁻³) were the compounds with higher median concentrations. The indoor/outdoor (I/O) ratios demonstrated that sources in the indoor environment are prevailing for most of the investigated VOCs especially for limonene, α-pinene, hexanal, formaldehyde, pentanal, acetaldehyde, o-xylene, n-dodecane and acetone with I/O ratio >6. Multiple linear regressions were applied to investigate the indoor VOC determinants and Spearman correlation coefficients were used to establish common sources between VOCs. Finally, the lifetime cancer risk associated to formaldehyde, acetaldehyde and benzene exposure was estimated and they varied from 7.8 × 10⁻⁵ to 4.1 × 10⁻⁴ for formaldehyde, from 8.6 × 10⁻⁶ to 3.5 × 10⁻⁵ for acetaldehyde and from 2.0 × 10⁻⁶ to 1.5 × 10⁻⁵ for benzene. For formaldehyde, the attributed risk in most sampled homes was two orders of magnitude higher than the one (10⁻⁶) proposed as acceptable by risk management bodies.     

A magnetic ion-imprinted polymer for lead(II) determination: A study on the adsorption of lead(II) by beverages

In this work a variety of beverage samples had been kept in a contaminated area to investigate their lead adsorption. To determine the adsorbed Pb(II), a novel magnetic lead ion-imprinted polymer, grafted onto Fe₃O₄ nanoparticles, was synthesized and used as a selective sorbent for the preconcentration of Pb(II) ions. The sorbent was characterized by different techniques. The synthesized sorbent was applied for highly accurate and selective determination of Pb(II) ions absorbed from polluted air in several beverages and results were compared. To validate the method, three certified reference materials were analyzed by the proposed method and the results showed that pre-concentrating by this sorbent and subsequent determination by flame atomic absorption spectroscopy is an accurate method for lead determination in beverage samples (recoveries higher than 95%). The limits of detection and the relative standard deviations were less than 1.7 μg kg⁻¹ and 4.1%, respectively. The sorption capacity of this new sorbent was 51.8 mg g⁻¹. Finally, this method was used for the determination of Pb(II) ions in polluted beverage samples, and the results revealed that under equal conditions, coffee exhibits more tendency to adsorb Pb(II) ions.     

Investigation of amino acids in wolfberry fruit (Lycium barbarum) by solid-phase extraction and liquid chromatography with precolumn derivatization

The aim of this work is to present a simple and sensitive reverse-phase liquid chromatography method for the determination and investigation of amino acids in wolfberry fruit (Lycium barbarum) after solid-phase extraction-derivatization. The method linearity, calculated for each amino acid, had a correlation coefficient higher than 0.9950, in concentrations ranged from 9.60 to 3.33 × 10³ μmol L⁻¹. The detection limits of amino acids were between 2.42 and 6.51 μmol L⁻¹. The calculated recoveries for amino acids in wolfberry fruit were from 87.3% to 97.1% and relative standard deviations were from 2.62% to 5.22%. The investigation illustrated that each tested wolfberry fruit contained at least 16 amino acids and the main amino acids were glutamic acid, aspartic acid, proline, alanine, serine, glycine, lysine, and tyrosine. The levels of amino acid in wolfberry fruit were varying from different areas.     

Heat-assisted slurry sampling GFAAS method for determination of lead in food standard reference materials

A valid method based on heat-assisted slurry sampling graphic furnace atomic absorption spectrometry (HASS-GFAAS) was developed for the accurate determination of trace Pb in food standard reference materials (SRMs). The HASS technique significantly improved Pb recovery and precision compared to conventional slurry sampling techniques. The optimized HASS procedure was performed as follows: first, the sample (particle size ≤ 150 μm) was diluted with 0.05% (v/v) Triton X-100 containing 2% HNO₃ and 1% H₂O₂ followed by heating for 20 min at 120 °C on a heating block. Next, the obtained slurry was sonicated in an autosampler cup, and finally, the slurry was introduced into a graphite tube and analyzed by the GFAAS with a Pb electrodeless discharge lamp (EDL). Calibration with aqueous standard solutions was used for Pb determination in food samples. The characteristic mass and limit of detection for Pb based on the integrated absorbance for a 2% (m/v) sample were 12 ± 0.6 pg and 0.003 mg kg⁻¹, respectively. The accuracy (95.1–102% recovery) and good precision (0.1–3.6%) of this procedure are illustrated by the results obtained for the 12 food reference materials. The proposed method is suitable for determination of trace Pb in solid food samples.     

Single-run analysis of vitamin D photoproducts in oyster mushroom (Pleurotus ostreatus) after UV-B treatment

A single-run high performance liquid chromatography (HPLC) with diode array detector (DAD) based method was developed for the separation, identification and comprehensive quantification of degradation products of ergosterol formed in oyster mushroom (Pleurotus ostreatus) after UV-B exposure. After 60 min, 10 substances involved in the photoprocess were separated, identified by their characteristic DAD spectrum and distinguished by their molecular weight, in cases where spectra were identical: vitamin D₂, previtamin D₂, tachysterol₂, lumisterol₂ and ergosterol, and, in minor quantity, their structural analogues of the 22,23-dihydroergocalciferol (vitamin D₄) series. Sample preparation protocol affected the total yields and the ratios of previtamin and vitamin D₂/D₄. Hot alkaline hydrolysis resulted in the best digestion of the mushroom matrix and accordingly gave the highest vitamin D yield (D₂: 141.32 μg g⁻¹ dry matter, DM; D₄: 22.72 μg g⁻¹ DM). Limit of detection for vitamin D_2/4 was 0.02 μg g⁻¹ dry matter (DM) and was estimated for previtamin D_2/4 (0.06 μg g⁻¹ DM), tachysterol_2/4 (0.02 μg g⁻¹ DM) and lumisterol_2/4 (0.06 μg g⁻¹ DM). Recovery of spiked vitamin D₂ was 97 ± 0.7%. The study provides an analytical tool to assess the process of vitamin D generation after UV-B treatment for the production of oyster mushrooms with a balanced nutritional profile of vitamin D compounds.     

A fast and effective method of quantitative analysis of VB1, VB2 and VB6 in B-vitamins complex tablets based on three-dimensional fluorescence spectra

Scattering signals and partial overlapping of target peaks usually appear in fluorescence determination. In this study, the improved wavelet moment method was proposed and applied to the quantitative determination of multiple target components in real B-vitamins complex tablets based on three-dimensional (3D) fluorescence spectra. The correlation coefficients (R) were more than 0.9939, and the correlation coefficients of leave-one-out cross-validation (R_LOO-cv) were more than 0.9376. The inter-day and intra-day variations were less than 5.8% and 6.1%, respectively. The recovery ranged from 97.6% to 109.4%. The limits of detection (LODs) and quantification (LOQs) were less than 0.07 μg mL⁻¹ and 0.13 μg mL⁻¹, respectively. All the statistical parameters indicated that the method was stable and reliable. The application to the practical samples confirmed that wavelet moment method effectively extracted the features of target components in 3D spectra and the proposed method could be applied to the analyses of food or other complex samples.     

Spectrophotometric method for determination of aluminium content in water and beverage samples employing flow-batch sequential injection system

A sensitive, precise and reliable flow-batch method for the determination of aluminium (Al) was developed using a sequential injection-monosegmented flow system incorporating a mixing chamber unit. Eriochrome cyanine R (ECR) was used as a chromogenic reagent in the presence of N,N-dodecyltrimethylammonium bromide (DTAB). The Al-ECR complex at pH 6 gave a maximum absorption at 584 nm. In-line single standard calibration and a standard addition procedure were developed employing the monosegmented flow technique. Under the optimum conditions, a linear calibration graph in the range of 0.0075–0.625 mg L⁻¹ Al was obtained with limits of detection and quantitation of 0.0020 and 0.0070 mg L⁻¹, respectively. Relative standard deviations were 0.8 and 1.3% for 0.010 and 0.025 mg L⁻¹ Al (n = 11), respectively. A sample throughput of 24 h⁻¹ using an in-line standard calibration approach and 6 h⁻¹ using four standard addition levels was achieved. The developed system was successfully applied to water samples and beverage samples. The results agreed well with those obtained from the ICP-AES method. Good recoveries between 85 and 104% were obtained.     

Fluorometric method based on molecular recognition solid-phase extraction for determination of riboflavin in milk and infant formula

Riboflavin (vitamin B₂) is involved in several biological processes, particularly in energy production, and it is acquired from food ingestion, principally from supplemented food during the first years of life. Therefore, a simple, fast and cost-effective high-throughput method for determination of riboflavin in milk and infant formula is proposed, based on selective extraction using commercially available molecularly imprinted polymers targeted to riboflavin, followed by direct fluorometric determination. Several aspects were studied, namely microplate assay conditions, the composition of eluting solution and the stability of riboflavin in the eluate. Hence, elution using 1% (v/v) acetic acid in methanol or in acetonitrile is recommended, followed by immediate analysis or solvent evaporation, with reconstitution and analysis within 24 h. The proposed method provided a LOD of 0.03 mg L⁻¹, with working range for undiluted samples between 0.125 and 2 mg L⁻¹, and sample throughput of 24 h⁻¹. It was successfully applied to certified reference material NIST-1846 and also to commercial milk and infant formula samples.     

Exposure assessment of arsenic speciation in different rice types depending on the cooking mode

Total (As_t), inorganic arsenic (As_i = As(III) + As(V)) and dimethylarsonic acid (DMA) were determined in 37 commercial rice samples collected in France. As_t was measured by inductively coupled plasma-mass spectrometry (ICP-MS) whereas anion-exchange chromatography – ICP-MS was used for As_i and DMA determination. As_t in raw rice varied from 0.041 to 0.535 mg kg⁻¹ whereas As_i varied from 0.025 mg kg⁻¹ (polished Basmati rice) up to 0.471 mg kg⁻¹ (organic rice duo). The daily intake and associated health risk for different population groups as a function of age and gender was also assessed. The intake varied between 0.002 and 0.184 μg kg⁻¹ body weight for As_t and 0.002 and 0.153 μg kg⁻¹ body weight for As_i, which do not pose a chronic toxicity risk. Organic wholegrain rice may entail a risk for children in the case of sole consumption at the expense of polished rice. The impact of rice cooking/boiling in terms of the overall toxicological risk related to As species was also investigated. Pre-rinsing and boiling the raw rice by using an excess of water is the most efficient mode to obtain a significant As_i removal and further reduction of the toxicological risk for children, particularly for white rice varieties.     

Cost-effectiveness of rabies post-exposure prophylaxis in the context of very low rabies risk: A decision-tree model based on the experience of France

IntroductionBenefit-risk of different anti-rabies post-exposure prophylaxis (PEP) strategies after scratches or bites from dogs with unknown rabies status is unknown in very low rabies risk settings.Design and settingA cost-effectiveness analysis in metropolitan France using a decision-tree model and input data from 2001 to 2011.PopulationA cohort of 2807 patients, based on the mean annual number of patients exposed to category CII (minor scratches) or CIII (transdermal bite) dog attacks in metropolitan France between 2001 and 2011.InterventionsFive PEP strategies: (A) no PEP for CII and CIII; (B) vaccine only for CIII; (C) vaccine for CII and CIII; (D) vaccine+ rabies immunoglobulin (RIG) only for CIII; and (E) vaccine for CII and vaccine+ RIG for CIII.Main outcomes measuresThe number of deaths related to rabies and to traffic accidents on the way to anti-rabies centers (ARC), effectiveness in terms of years of life gained by reducing rabies cases and avoiding traffic accidents, costs, and incremental cost-effectiveness ratios (ICER) associated with each strategy.ResultsStrategy E led to the fewest rabies cases (3.6 × 10⁻⁸) and the highest costs (€1,606,000) but also to 1.7 × 10⁻³ lethal traffic accidents. Strategy A was associated with the most rabies cases (4.8 × 10⁻⁶), but the risk of traffic accidents and costs were null; therefore, strategy A was the most effective and the least costly. The sensitivity analysis showed that, when the probability that a given dog is rabid a given day (P_A) was >1.4 × 10⁻⁶, strategy D was more effective than strategy A; strategy B became cost-effective (i.e. ICER vs strategy A <3 × French Gross Domestic Product per capita) when P_A was > 1.4 × 10⁻⁴.ConclusionsIn the metropolitan France's very low rabies prevalence context, PEP with rabies vaccine, administered alone or with RIG, is associated with significant and unnecessary costs and unfavourable benefit-risk ratios regardless to exposure category.     

Determination of phytosterols in oenological matrices by liquid chromatography-atmospheric pressure chemical ionization and ion-trap mass spectrometry

The aim of the present study is the identification of plant sterols and the development of an analytical method that allows for the quantification of such family of compounds in oenological matrices. The application of liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry (LC-APCI-ITMS) to sterol characterization is a useful tool and was selected to perform this research. Sterol separation was achieved using a C8 column with a mobile phase consisting of water and acetonitrile under gradient conditions and column temperature of 35 °C, which leads to analyte elution in less than 25 min. Retention times, precursor ions and MRM transitions of analytes allowed for the identification and sensitive quantitative determination of phytosterols in oenological matrices at trace levels. The method showed a dynamic linear range over the concentration ranges from 0.02 to 320 mg kg⁻¹ for the different parts of grapes and from 8 to 100 ng mL⁻¹ in case of wine. The most abundant phytosterol in all samples was β-sitosterol. The seeds are the richest source of phytosterols having a great amount of β-sitosterol, 314 mg kg⁻¹ fresh berry mass, followed by stigmasterol, fucosterol and campesterol at much lower concentrations (ranging from 3 to 10 mg kg⁻¹).     

Modified cerium(IV)-based antioxidant capacity (CERAC) assay with selectivity over citric acid and simple sugars

A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars. The redox potential of the Ce(IV) oxidant was fine-tuned in 0.3 M H₂SO₄ + 0.7 M Na₂SO₄ aqueous medium for selective oxidation. In the classical Ce(IV)-based assay for which the name CERAC was proposed, the presence of citric acid (at 1.5 × 10^?5 M) caused approximately 25% reduction in Ce(IV) (at 2.0 × 10^?4 M) recovery, whereas in the present method, the presence of citric acid (at 1.0 × 10^?4 M) caused negligible error in the TAC measurement of quercetin. The trolox equivalent antioxidant capacity (TEAC) values in the order of quercetin > rutin > gallic acid > catechin > caffeic acid ≥ ferulic acid > naringenin ≥ naringin > trolox ≥ ascorbic acid were established with the proposed method and were found to be compatible with those found with other antioxidant assays. It is noteworthy that naringin and rutin were also hydrolyzed in the acidic medium of the method so as to exert their full antioxidant capacity not measured by other TAC assays. The proposed TAC assay with Ce(IV) is simple, low-cost, rapid, and can be easily applied in modestly equipped conventional laboratories.     

Rapid preparative extraction and determination of major organic acids in honeysuckle (Lonicera japonica Thunb.) tea

In this study, ionic liquid based microwave-assisted extraction (IL-MAE) followed by high-performance liquid chromatography (HPLC) was developed for determination of major organic acids in honeysuckle tea. The results suggest that varying the anion and cation had significant effects on the preparative extraction efficiency; aqueous solution of [C₆mim]Br was selected as solvent. The optimized extraction parameters were obtained as follows: IL concentration 0.5 M, temperature 50 °C, solvent to material ratio 20:1 mL/g and duration 9 min. Moreover, principal component analysis (PCA) was used to analyze the significances of these factors for IL-MAE and their interactions, and IL concentration was proved to be the most significant parameter. Compared with conventional sample preparation method, the content of organic acids in analytical sample was enhanced about 1.5-fold using IL-MAE in a shorter duration. In addition, a kinetic model of the preparative extraction process was established to fit the experimental data (R² > 0.99). The proposed HPLC method was successfully applied for determination of 5 organic acids in honeysuckle tea. The present research supported necessary data for sample preparation and quality analysis of honeysuckle tea.     

Determination of trace amounts of germanium in food and fruit by spectrophotometry with p-methybenzeneazosalicylflurone

A novel spectrophotometric method was developed for determination of germanium in food and fruit using p-methybenzeneazosalicylflurone as a new chromogenic reagent. Under optimum reaction conditions, the reagent reacts with germanium(IV) to form a red complex with a maximum absorption at 502 nm. The apparent molar coefficient of the complex was 2.0×10⁵ L mol⁻¹ cm⁻¹, and a linear absorbance was obtained for 0–7 μg of germanium in 10 mL solution. The reaction completed rapidly and the absorbance of the complex remains stable for at least 24 h at room temperature. The effect of various substances on the determination of germanium was investigated in succession. The results indicated that all studied co-existing substances can be tolerated in considerable amounts, e.g., 4000-fold molybdenum(VI) and tin(II) do not interfere with the determination of germanium; its selectivity is obviously better than other reagents in the literature. The detection limit, calculated using three times the standard error of estimate of the calibration graph, is 0.006 μg g⁻¹of germanium with the pre-concentration of germanium in digested solution using ferric hydroxide as the co-precipitator.     

Optimization of cheese sample preparation methodology for free amino acid analysis by capillary isotachophoresis

The objective of this work was the evaluation of different conditions for the selected free amino acids extraction from cheese samples, followed by capillary isotachophoresis analysis. Parameters of the extraction: concentration and type of extraction reagents (solvents: methanol, ethanol and mineral acids: perchloric acid, trichloroacetic acid, sulphuric acid and hydrochloric acid), time and temperature, and isotachophoretic separation conditions (voltage, time) were studied. Repeatability, reproducibility and stability of this method at different conditions are discussed. The best yield of free amino acids was obtained after triple extraction (30 min each process) with 0.1 M hydrochloric acid at 50 °C. Histidine, lysine, arginine, ornithine, tyrosine, and phenylalanine were determined using calibration curves and the standard additions method in different types of cheeses. The highest level of amino acids was determined in semi-hard cheese (2626.3 mg 100 g⁻¹ – calibration curve, and 2679.2 mg 100 g⁻¹ – standard additions method), whereas the lowest were found in sheep cheese (426.3 mg 100 g⁻¹ and 455.7 mg 100 g⁻¹, respectively), and Gouda type cheese samples (441.5 mg 100 g⁻¹ and 472.8 mg 100 g⁻¹, respectively).     

Fast method for the determination of copper,manganese and iron in seafood samples

A slurry sampling flame atomic absorption spectrometric method is proposed for the determination of copper, manganese and iron in oysters (Crassostrea rhizophora), clams (Anomalocardia brasiliana) and mussels (Mytella guiyanensis; Perna perna). Optimization was carried out using univariate methodology involving the following variables: nature and concentration of the acid solution for slurry preparation, sonication time and sample mass. The optimized conditions were 80 mg of sample ground in a cryogenic mil, dilution using 1.0 mol L⁻¹ nitric /hydrochloric acid solution, sonication time of 30 min and a slurry volume of 10 mL. The calibration curves had been prepared using standards of copper, manganese and iron also in 1.0 mol L⁻¹ nitric/hydrochloric acid solution. This method allowed the determination of copper, manganese and iron by FAAS, with detection limits of 0.17, 0.09 and 0.46 μg g⁻¹, respectively. The precision, expressed as relative standard deviation (RSD), are 3.0%, 2.9% and 3.8% (n=10), for concentrations of copper, manganese and iron of 17, 22 and 719 μg g⁻¹, respectively. The accuracy of the method was confirmed by analysis of the certified oyster tissue (NIST 1566b). The proposed method was applied for the determination of copper, manganese and iron in samples of oyster, clams and mussels, collected in Ubatuba and Todos os Santos Bay, Brazil. The obtained concentrations varied between 17.1 and 143.9 μg g⁻¹, 17.9 and 29.7 μg g⁻¹ and 364 and 1388 μg g⁻¹, respectively, for copper, manganese and iron. These values agree well with other data reported in the literature. The results showed no significant differences (P>0.005) using the proposed method with those obtained after complete digestion and determination by inductively coupled plasma-optical emission spectroscopy (ICP-OES).     

Synthesis and characterization of functionalized silica with 3,6-ditia-1,8-octanediol for the preconcentration and determination of lead in milk employing multicommuted flow system coupled to FAAS

Novel functionalized silica, containing 3,6-dithia-1,8-octanediol (Si-DIO), was synthesized and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) of ¹³C and ²⁹Si. The Si-DIO was used to pre-concentrate and determine the amount of Pb(II) in milk samples employing a multicommuted flow system coupled to flame atomic absorption spectrometry (FAAS). For the adsorption process, a pre-concentration minicolumn with 100 mg of Si-DIO, a solution of 0.005 mg L⁻¹ Pb(II) at pH 9.0 and HNO₃ as the eluent was used, obtaining an enrichment factor of 28 times with retention efficiency higher than 99%. The Pb(II) ion, using the multicommuted flow system coupled to FAAS, showed a linear response between 0.005 and 20.0 mg L⁻¹; a linear coefficient where r = 0.9939 and n = 7; a detection limit estimated at 0.001 mg L⁻¹ and a relative standard deviation of 3.8% (n = 50). Fifty pre-concentrations runs were tested in the minicolumn without significant variation in the analytical signal. The proposal system showed analytical applicability to determine Pb(II) ion in milk samples, presenting recovery of 90.7–102.5%.