Doehlert Experimental Design Research Articles

Removal of sulfadiazine from simulated industrial wastewater by a membrane bioreactor and ozonation

Ozonation can be used as a polishing treatment for degrading low-concentration pharmaceutical compounds recalcitrant to biological treatment, when large amounts of biodegradable organics have been previously removed by biological processes. Nevertheless, a systematic investigation has not yet been carried out for the coupled MBR + O3 process through an experimental design approach. Thereby, the purpose of this study is to evaluate the performance of different processes (membrane bioreactor-MBR, ozonation; and integrated MBR + O3) for removing the antibiotic sulfadiazine (SDZ) from a synthetic wastewater matrix of industrial interest. The MBR behavior was monitored over seven months for different parameters (pH, temperature, permeate flow, transmembrane pressure, biological oxygen demand-BOD5, chemical oxygen demand-COD, total organic carbon-TOC, solids, and SDZ concentration). Additionally, the amount of SDZ sorbed onto the sludge was characterized, an issue which is scarcely addressed in most research works. Ozonation experiments were conducted in batch mode in a 2-L glass reactor provided with openings for gas flow. For the MBR + O3 process, the effects of gas flow rate (0.1–1.5 L min−1) and inlet ozone concentration (4–12 mg L−1) on SDZ removal from the MBR permeate were systematically assessed using a Doehlert experimental design and response surface methodology. The results indicated that the MBR system showed good performance regarding organic matter removal efficiency, evaluated in terms of BOD5 (91.5%), COD (93.1%) and TOC (96.3%). In contrast, SDZ was partially removed (33%) by the MBR; in that case, the results indicated that the antibiotic was moderately removed with the sludge and partially biodegraded. In turn, the MBR + O3 system showed excellent performance for removing SDZ (100%), TOC (97%), BOD5 (94%) and COD (97%). The statistical analysis confirmed that the influence of ozone gas flow rate upon the SDZ removal rate was more important than that exhibited by inlet ozone concentration. Therefore, coupling MBR and ozone can be considered a promising alternative for point source treatment of antibiotic production wastewater.

UVA/persulfate-driven nonylphenol polyethoxylate degradation: effect of process conditions

ABSTRACT UV/persulfate (UV/PS) technologies have gained increased attention as efficient alternatives for removing pollutants from different classes, although processes based on the UVA-driven (PS) activation have not yet been discussed in the literature for the removal of the nonionic surfactant nonylphenol polyethoxylate (NPEO). The present study investigated the simultaneous effect of the initial persulfate concentration ([PS]0) and specific photon emission rate (E P,0) on NPEO degradation by UVA/PS following a Doehlert experimental design. The results for [NPEO]0 = (4.65 ± 0.15) mg L−1 indicated more than 97.8% NPEO removal after 2 h, with pseudo first-order specific degradation rate (k obs) of 0.0320 min−1, for [PS]0 = 7.75 mmol L−1 and E P,0 = 0.437 μmol photons L−1 s−1. Under these conditions, NPEO half-life time was about 22 min, and the EC50-48 h (% v/v) values for Daphnia similis before and after treatment did not differ significantly. Higher values of E P,0 would influence NPEO removal for [PS]0 not higher than 8–10 mmol L−1, although lower degradation efficiencies were obtained with higher [NPEO]0 or real wastewater, except for longer reaction times. Additionally, UVA/PS showed to be efficient for tensoactivity removal, despite the negligible total organic carbon (TOC) removal achieved. Finally, UVC and UVA resulted in NPEO degradation higher than 96% and similar tensoactivity removals when UVA/PS was conducted under optimal conditions ([PS]0 = 10 mmol L−1; E P,0 = 0.324 μmol photons L−1 s−1), suggesting that UVA radiation available in solar light could be advantageously employed for NPEO removal at concentrations usually found in wastewater.

Pigment production by Fusarium solani BRM054066 and determination of antioxidant and anti-inflammatory properties

The fungal kingdom has been widely studied as a source of bioactive compounds of interest to the pharmaceutical and food industry. This paper studies the production of natural red pigments by Fusarium solani BRM054066 in the submerged fermentation system, using Doehlert experimental design to determine optimal cultivation conditions. The chemical composition of the red pigment was determined by Nuclear Magnetic Resonance spectroscopy (NMR) and Ultra-Performance Liquid Chromatography coupled to Mass Spectrometry (UPLC-MS). Antioxidant activity was assessed by the ability to sequester of free radical DPPH. In the analysis of anti-inflammatory activity, murine peritoneal macrophages activated by LPS were used, and the gene expression of TNF-α, IL-1β, IL-6, IL-10 and IL-17 was determined using qPCR. As a result, it was found that agitation at 200 rpm and glucose concentration ≥ 20 g/L promote the best results in the production of red pigment. The chemical compounds identified were two naphthoquinones, fusarubin and dihydrofusarubin, and an anthraquinone, a bostrycoidin, being fusarubin the majority compound. The red pigment showed antioxidant activity by scavenge 50% of the DPPH radical, in a concentration of 24 µg/mL. The pigment also showed an effective anti-inflammatory capacity by reducing the overexpression of the pro-inflammatory cytokines TNF-α, IL-1β and IL-6 and promoting the production of anti-inflammatory IL-10 and IL-17, in murine macrophages activated by LPS (p < 0.05). According to the results, the fungus F. solani BRM054066, under optimized conditions of cultivation, proved to be a promising source of biologically active natural pigments with wide industrial applicability.

Clarification of tangerine juice using cellulases from Pseudoyma sp.

Tangerine juice was treated with crude extract containing cellulase from Pseudozyma sp. obtained by liquid fermentation. The thermal stability of cellulase was investigated by incubating crude extract at different temperatures and times. The pulp, obtained from tangerine, was pasteurized at 85°C for 5min and then used in a clarification process with a Doehlert experimental design. The results showed that the cellulase obtained from Pseudozyma sp. is thermostable at temperatures of 60, 70 and 90°C and retained 98%, 88% and 80% of activity, respectively, after a 1-h incubation time. The optimum conditions for clarification were verified by varying the enzyme extract concentration (%, v v-1) and the time (minutes) in a shaker at 150rpm, at 50°C. The optimum condition for clarification was obtained in the 80th min with a 1.25% enzymatic extract concentration (v v-1), resulting in a reduction of tangerine juice viscosity by 65%. The analysis of physical and chemical parameters of tangerine juice after clarification showed that the enzyme extract improved the process responsible for the clarification of tangerine juice. The results are promising since this is a methodology that can be used in the citrus juice industry.

A new strategy for the synthesis of monomethylhydrazine using the Raschig process. 2: Continuous synthesis of stoichiometric monochloramine using the microreactor technology

After having established in a previous paper that the synthesis of stoichiometric monochloramine is hazardous due to the high exothermicity of the reaction and the risk of decomposition of the solution from 36 °C, it appeared that the best solution for this synthesis is to use microreactor technology. A series of experiments carried out using a Doehlert experimental design provided access to a mathematical model describing, for an initial fixed composition ratio [NH4+]0/[OCl−]0, the evolution of the yield as a function of temperature, the flow rate of the reagents and the number of sodium hydroxide equivalent. Thus, the optimal conditions for the synthesis of stoichiometric chloramine using microreactor technology were established.

Valorization of an Abundant Slaughterhouse By-product as a Source of Highly Technofunctional and Antioxidant Protein Hydrolysates

Chicken blood meal (CBM) is a slaughterhouse by-product of great environmental concern, rich in protein and iron, mainly used as animal feed and fertilizer. In this work, the valorization of CBM as a source of protein hydrolysates (CBMH) is proposed. The hydrolysis reaction conditions were assessed using a Doehlert experimental design. Samples of CBMH were thus prepared at optimal conditions: T = 54 °C, pH 8.5 and enzyme-to-substrate ratio (E/S) = 6.5% with different reaction durations in order to study the impact of the degree of hydrolysis (DH) on the properties of the product. The characteristics studied in the hydrolysates were among others: chemical structure, technofunctional properties [compared to those from soy protein isolate (SPI)] and antioxidant activity. CBMH samples displayed MW < 14.4 kDa, increasing heme content correlated with their color parameters, formation of hygroscope aggregates and enhanced thermal stability. UV-spectroscopy, infrared spectroscopy and circular dichroism confirmed the conformational changes in CBMH to be dependent on the DH. Compared to CBM, CBMH had improved oil holding capacity that decreased with the DH. CBMH foams exhibited better behavior at neutral pH than those from SPI. Moreover, CBMH emulsions displayed lower emulsifying activity and higher but decreasing emulsifying stability. CBMH samples displayed antioxidant activity (FRAP, DPPH and ABTS), whereas only the FRAP values suffered a negative impact due to the extended hydrolysis. The results suggest that the valorization of CBM can be achieved via hydrolysis, resulting in potential ingredients for the food, cosmetic and pharmaceutical industries.

Comparison between UVA- and zero-valent iron-activated persulfate processes for degrading propylparaben.

Conventional wastewater treatments are not efficient in removing parabens, which may thus end up in surface waters, posing a threat to aquatic biota and human health. As an alternative treatment, persulfate (PS)-driven advanced oxidation technologies have gained growing attention for removing these pollutants. In this study, the degradation of propylparaben (PrP) by UVA- and zero-valent iron (ZVI)-activated persulfate was investigated. The effects of initial PS concentration ([PS]0) and irradiance or ZVI concentration were explored using the Doehlert experimental design. For the UVA-activated system, the specific PrP degradation rate (k) and percent removal were consistently higher for increasing [PS]0 and irradiance, varying in the ranges 0.0053-0.0192min-1 and 37.9-77.3%, respectively. In contrast, extremely fast PrP degradation was achieved through the ZVI/PS process (0.3304 < k < 0.9212min-1), with removal percentages above 97.5%; in this case, paraben degradation was hindered for a ZVI dosage beyond 40mgL-1. Regarding toxicity, ECOSAR predictions suggest that the degradation products elucidated by LC-MS/MS are less toxic than PrP toward fish, daphnid, and green algae. In addition, both processes showed to be strongly dependent on the water matrix, being ZVI/PS more impacted for a MBR effluent, although its performance was much better than that exhibited by the UVA-driven process (t1/2 of 65.4 and 276.1min, respectively).

Intensification of the ozone-water mass transfer in an oscillatory flow reactor with innovative design of periodic constrictions: Optimization and application in ozonation water treatment

Ozone-water mass transfer was investigated in continuous mode using a macroscale oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC). The effects of oscillation amplitude (x0) and frequency (f) on the mass transfer coefficient (kLa) were assessed through a Doehlert experimental design. Different gas and liquid flow rates were also studied. The results show that kLa increases with f (up to 4 Hz), x0 (up to 15 mm), and the gas flow rate (up to 150 Ncm3 min−1). No significant changes in kLa were observed over a wide range of liquid flow rates (up to 180 mL min−1) and for Re0 < 1000. In all conditions studied, and among different reactor configurations tested, the higher kLa values were observed with the OFR-SPC, achieving kLa values up to 35 times higher than those obtained in a conventional bubble column. Moreover, the enhancement on the mass transfer efficiency (MTE) promoted by the oscillatory movement was more pronounced as the gas (ozone) flow rate decreases and liquid (water) flow rate increases, which is another advantage of this system when looking for large-scale implementation of the ozonation process in water treatment. Ozonation experiments using a mixture of fluoroquinolones in different matrices (distilled water, surface water and urban wastewater) were also performed, the results demonstrating that OFR-SPC is an interesting reactor alternative for ozone-driven water treatment.

Core-shell microparticles formed by the metal-organic framework CIM-80(Al) (Silica@CIM-80(Al)) as sorbent material in miniaturized dispersive solid-phase extraction

Core-shell SiO2@CIM-80(Al) microspheres were synthesized, characterized, and used as novel sorbent in a dispersive miniaturized solid-phase extraction (D-μSPE) method for the determination of fourteen polycyclic aromatic hydrocarbons (PAHs) in wastewaters by ultra-high performance liquid chromatography coupled to a fluorescence detector (UHPLC-FD). A Doehlert experimental design permitted to optimize the main parameters affecting the microextraction procedure, intending the obtaining of a simple approach. Optimized extraction conditions include 13 mg of SiO2@CIM-80(Al) microparticles (~2 mg CIM-80(Al)), 2.5 min of extraction time, 0.125 mL of acetonitrile (ACN) as desorption solvent and 0.5 min of desorption time. The entire method showed adequate analytical performance with limits of detection down to 5 ng L−1, and inter-day precision lower than 14.1% for a concentration level of 0.5 μg L−1. The extraction capability of SiO2@CIM-80(Al) microspheres was compared to that obtained with commercially available silica microspheres and the neat MOF CIM-80(Al), demonstrating the advantages of the use of MOF core-shell sorbents in D-μSPE.

Optimization Scale Pasteurization of Baobab Juice Using Response Surface Methodology (RSM)

The Adansonia digitate L. known as Baobab is the only species present in West Africa and grows wild. All parts of the plant are used by humans. In Senegal, baobab pulp is widely consumed; it is used as raw material in small and medium enterprises (SMEs) for making juices, concentrates, jams, powder. Drinks or juices from baobab are highly appreciated by consumers; however rapid fermentation can happen even after pasteurization that can shorten their shelf-life. A Doehlert experimental design was used to find a good scale of heat treatment ensuring a proper conservation of baobab juice. Results of the experimental design showed that a heat treatment of 80°C for 10 min gives a baobab juice with good sanitary quality that meets the international standards.

Application of Doehlert experimental design for the removal of radium from aqueous solution by cross-linked phenoxycalix[4]pyrrole-polymer using Ba(II) as a model.

Ra-226 is a naturally occurring radionuclide that is derived from uranium-238 series, and it is present at low concentrations in rocks, soil, and groundwater. Many efforts have been exerted for the decontamination of radium from aqueous media in order to meet the increasing water demand of the population. To this aim, a new polymer based on cross-linked phenoxycalix[4]pyrrole was designed and employed in solid/liquid extractions in order to remove radium from aqueous solutions. Preliminary experiments have highlighted the capability of this polymer to extract 22% of Ra-226 from aqueous acidic solution. The optimization of the extraction experimental factors in the direction to attend the maximum removal of Ra-226 from water was carried out employing Ba2+ due to its similar chemical behavior as radium, in order to minimize the consumption of Ra-226 solutions and the risk of radioactive contamination. Doehlert experimental plan was then applied to determine the optimal conditions (pH, time, temperature) for the removal of Ba2+ from aqueous solutions.

Grape Berry Flavonoid Responses to High Bunch Temperatures Post Véraison: Effect of Intensity and Duration of Exposure.

Climate models predict an increase in the frequency and duration of heatwaves with an increase in intensity already strongly evident worldwide. The aim of this work was to evaluate the effect of two heatwave-related parameters (intensity and duration) during berry ripening and identify a threshold for berry survival and flavonoid accumulation. A Doehlert experimental design was used to test three temperature intensities (maxima of 35, 46, and 54 °C) and five durations (3 to 39 h), with treatments applied at the bunch level shortly after véraison. Berry skin and seeds were analysed by liquid chromatography-triple quadrupole-mass spectrometry (LC-QqQ-MS) for flavonoids (flavonols, anthocyanins, free flavan-3-ols, and tannins). Berries exposed to 46 °C showed little difference compared to 35 °C. However, berries reaching temperatures around 54 °C were completely desiccated, and all flavonoids were significantly decreased except for skin flavonols on a per berry basis and seed tannins in most cases. Some compounds, such as dihydroxylated flavonoids and galloylated flavan-3-ols (free and polymerised), were in higher proportion in damaged berries suggesting they were less degraded or more synthesised upon heating. Overall, irreversible berry damages and substantial compositional changes were observed and the berry survival threshold was estimated at around 50–53 °C for mid-ripe Shiraz berries, regardless of the duration of exposure.

Fluorescent sensing of Pb2+ by microwave-assisted synthesized N-doped carbon dots: application of response surface methodology and Doehlert design

In this work, a cheap, simple, selective and sensitive turnoff fluorescent sensor was presented for Pb2+ determination. N-doped carbon dots (N-CDs) were synthesized by microwave-assisted method. Characterization of N-CDs was performed by transmission electron microscopy, dynamic light scattering and Fourier transform infrared spectroscopy. The important parameter (pH, concentration of carbon dots: CCDs and time) was optimized with Doehlert experimental design and response surface methodology. Optimum condition for maximum turnoff was pH 3, CCDs 8 mg mL−1 and 5 min. Limit of detection and linear range was 0.02 µM and 0.05–25 µM.

A catalyst-free process for gas ozonation of reduced sulfur compounds

The feasibility of homogenous gas ozonation process was investigated in order to reduce the negative environmental impact caused by reduced sulfur compounds (RSCs). Emitted from a variety of industrial plants, this class of compounds are known by their odor properties. Selecting hydrogen sulfide (H2S), methyl ethyl sulfide (MES) and dimethyl disulfide (DMDS) as representative odorous RSCs, the influence of four gas ozonation process parameters (ozone concentration, humidity level, reactor temperature and residence time) on their removal efficiencies was evaluated using a Doehlert experimental design in an experimental domain compatible with industrial constraints. Ozone concentration was the only process parameter that has resulted in a positive – but limited – effect on the removal efficiency of the mix of RSCs. However, even if ozone was present in large excess (20 times the RSCs concentration), MES and DMDS were slightly consumed (around 30%). Only H2S has shown interesting removal efficiencies (up to 80%). In addition to the measurement of reagent concentrations, Selected Ion Flow Tube coupled with Mass Spectrometry (SIFT/MS) was applied to identify and quantify the potential products of RSCs-ozone reaction. Methyl ethyl sulfone (MESO2) was found to be the primary product of MES, whereas methyl methanethiosulfinate (DMSOS) and sulfur dioxide (SO2) for DMDS, suggesting that the organic monosulfide and disulfides would not follow the same reaction mechanism with ozone in gas phase. In addition, SO2 and H2O may not be the only end products for H2S ozonation, since additional peaks were detected in SIFT/MS spectra.

Chemometric Optimisation of a Copper Sulphide Tailings Flocculation Process in the Presence of Clays

The presence of fine and ultra-fine gangue minerals in flotation plants can contribute to sub-optimal valuable ore recovery and incomplete water recycling from thickeners, with the performance of the latter equipment relying on adequate flocculation. In order to study the dependence of the flocculation process on the suspension-flocculant mixing conditions, a series of experiments—chosen using chemometric analysis—were carried out by varying mixing conditions, solid concentration, water salinity and flocculant dosage. To this purpose, two different tailings (both featuring coarse and fine content) were considered and a response surface methodology based on a Doehlert experimental design was used. The results suggest that the operational conditions to optimise the flocculated tailings settling rate and the suspended solids that report to a thickener overflow are not necessarily the same. This is a reasonable outcome, given that the settling rate depends on the coarse aggregates generated in the slurry, while the overflow solids content is governed both by either fine particle content (and its characteristics) or small aggregates. It is inferred that to maximise dewatering performance two stages should be involved—a separate treatment of the thickener overflow to remove fine content and thickening at optimal flocculant dosage to enhance this process.

Cellulose cone tip as a sorbent material for multiphase electrical field-assisted extraction of cocaine from saliva and determination by LC-MS/MS

A porous and hydrophilic sorbent material was used in an extraction system, assisted by electric fields, for the extraction of cocaine in saliva and subsequent determination by ultra-high-performance liquid chromatography associated with sequential triple quadrupole mass spectrometry (UHPLC-MS/MS). The cellulose-based material was characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. The time and voltage variables applied in the extraction process were investigated through a Doehlert experimental design, and with the best conditions found (35min and 300 V) some validation parameters were evaluated. The established working range was 1–100 μg L−1 (R2 > 0.99), and the detection and quantification limits determined were 0.3 and 0.8 μg L−1, respectively. Recoveries from 80 to 115% and coefficient of variation ≤15 and 16% for intra-day and inter-day assays, respectively, were obtained for sample concentrations of LOQ, 5, 25, and 75 μg L−1, indicating satisfactory accuracy and precision for the proposed method. In addition, the method presented no matrix effect, and the extraction efficiency was between 56 and 70%. The results showed that the material used has adequate physicochemical characteristics and can be applied as a sorbent and electrolyte support in multiphase extractions using electric fields.

Method development for simultaneous determination of polar and nonpolar pesticides in surface water by low-temperature partitioning extraction (LTPE) followed by HPLC-ESI-MS/MS.

During this research, chemometric approaches were applied for optimization of the low-temperature partitioning extraction (LTPE) for the simultaneous analysis of the pesticides: acephate, difenoconazole, fenamidone, fluazifop, fluazinam, methamidophos, and thiamethoxam from surface water samples and determination by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. It was used the 23 full factorial and the Doehlert experimental designs. The extraction technique was optimized by evaluating the effects of the three variables: sample pH, ionic strength (addition of Na2HPO4), and organic solvent volume. Considering the interest to find an optimal condition for all analytes simultaneously, the best extraction parameters found were as follows: pH = 5.33, concentration of Na2HPO4 = 0.0088 mol L-1 and organic phase volume = 4.5 mL. The optimized methodology showed LOD and LOQ levels from 0.33 to 8.13 ng L-1 and from 1.09 to 26.84 ng L-1, respectively. The recovery values ranged from 38.37 and 99.83% and the RSD values varied from 2.33 to 18.92%. The method was applied to surface water analysis sampled in areas with intensive agricultural practices in Ouro Branco City, Minas Gerais, Brazil. The difenoconazole was detected in concentrations between 12.53 and 94.76 ng L-1.

Development of a sensitive and fast method for detection of catecholamines and metabolites by HRMS

Variations in endogenous levels of catecholamines may be caused by changes in the organism, which are associated with the development of certain diseases by exogenous sources that are related to the intentional administration of some catecholamine. This study presents the development, validation and application of an analytical method to detect and to analyze the catecholamines and its metabolites simultaneously. The sample extraction consisted basically in hydrolysis and solid-phase extraction using a weak cation exchange functionalized polymeric sorbent cartridges. The catecholamines analysis was performed on orbitrap high resolution mass spectrometry HRMS-orbitrap equipped with electrospray. Modifications in different electrospray variables (S-lens, sheath gas flow and capillary temperature) were performed following the Doehlert experimental design (DOI). The validation parameters evaluated were repeatability, intermediate precision, matrix interference, limit of quantification, linearity, carryover and robustness. The most favorable conditions found according to the DOI for all analytes were S-lens fixed at 80 rf, sheath gas flow at 20 au and capillary temperature at 300 °C. The repeatability obtained from 100%, intermediate precision was 70%, matrix interference was observed, limit of quantification of the 5 ng·mL−1, linearity was 80%, robustness was 80% and carryover was not observed. DOI showed the most favorable conditions for the analysis of all the target compounds, contributing to the establishment of the method parameters. When applied in real samples, the method proved to be rapid, sensitive and selective even in the presence of urine interferents.

Electrochemical mineralization of uric acid with boron-doped diamond electrode: Factor analysis and degradation mechanism

In the present study, the mineralization performance and pathway of uric acid (UA) on boron-doped diamond (BDD) anodes were investigated. The oxidation behavior of UA on BDD surface was firstly tested through cyclic voltammetry measurements. The individual and joint effects of four quantitative parameters (applied current density, NaHCO3 concentration, NaCl concentration and flow rate) on UA mineralization were then examined with Doehlert experimental design. The results acquired by statistical analysis revealed that NaCl concentration and applied current density displayed the most dominant roles on UA degradation, while the influences of NaHCO3 concentration and flow rate were statistically insignificant. As a result, the following optimal conditions were reached: applied current density of 7.80 mA cm−2, NaHCO3 concentration of 6.0 mM, NaCl concentration of 9.0 mM and flow rate of 600 mL min−1, which gave a TOC decay of 89.4%, a specific energy consumption of 125.36 KWh kg−1 TOC, a combustion current efficiency of 15.0% and an electrical energy per order of 35.79 KWh m−3 order−1 within 30 min of electrolysis. Further results from LC/MS analysis confirmed the ring rupture of UA during the electrolysis, due to the attack of hydroxyl radicals and active chlorine species. Accordingly, two plausible degradation pathways of UA in bicarbonate and chloride media on BDD anode were proposed respectively.

Microwave-assisted digestion using dilute nitric acid solution and investigation of calibration strategies for determination of As, Cd, Hg and Pb in dietary supplements using ICP-MS

This study proposes an analytical procedure for microwave-assisted sample preparation of dietary supplements for athletes using dilute nitric acid solution followed by determination of elemental impurities (As, Cd, Hg and Pb) by inductively coupled plasma mass spectrometry (ICP-MS) according to the United States Pharmacopeia Chapters 2232 and 233. Calibration strategies as internal standardization (IS), multi-isotope calibration (MICal), and one-point standard addition (OP SA) were applied for correction of matrix effects. The optimization of the sample preparation procedure was performed using Doehlert experimental design based on overall desirability results (residual acidity, dissolved organic carbon and recoveries reached for certified reference material of Typical Diet) for each calibration method evaluated. Accuracy was also evaluated by recovery experiments according to the permissible daily exposure specific for each element and samples were spiked with element concentrations of 0.5J and 1.5J in order to check accuracies for As, Cd, Hg and Pb. Recoveries ranged from 82 to 120% using IS, 90 to 125% using MICal, 88 to 120% using OP SA and the repeatability was demonstrated by a precision lower than 10% RSD. Ten samples of dietary sport supplements were analyzed using the three calibration methods evaluated and the concentrations of As, Cd and Pb determined in eight samples were lower than the limits established by the Chapter 2232.