Doehlert Design Research Articles

Adsorption of uranium by amidoximated chitosan-grafted polyacrylonitrile, using response surface methodology.

The amidoximated chitosan-grafted polyacrylonitrile (CTS-g-PAO) was prepared for the adsorption of uranium from water. The effects of pH, concentration of uranium and the solid-liquid ratio on the adsorption of uranium by CTS-g-PAO were optimized using Doehlert design of response surface methodology (RSM). The adsorption capacity and removal efficiency achieved 312.06 mg/g and 86.02%, respectively. The adsorption process attained equilibrium only in 120 min. More than 80% of the absorbed uranium could be desorbed by 0.1 mol/l HCl or EDTA-Na, and CTS-g-PAO could be reused at least 3 times. The CTS-g-PAO and U(VI) ions formed a chelate complex due to FTIR spectral analysis. The surface morphology of CTS-g-PAO was also investigated by SEM. The adsorption process was better described by Langmuir isotherm and pseudo second order kinetic model. Results obtained indicated that CTS-g-PAO was very promising in adsorption of uranium from water.

Quality by design in the chiral separation strategy for the determination of enantiomeric impurities: Development of a capillary electrophoresis method based on dual cyclodextrin systems for the analysis of levosulpiride

Quality by design (QbD) concepts, in accordance with International Conference on Harmonisation Pharmaceutical Development guideline Q8(R2), represent an innovative strategy for the development of analytical methods. In this paper QbD principles have been comprehensively applied in the set-up of a capillary electrophoresis method aimed to quantify enantiomeric impurities. The test compound was the chiral drug substance levosulpiride (S-SUL) and the developed method was intended to be used for routine analysis of the pharmaceutical product. The target of analytical QbD approach is to establish a design space (DS) of critical process parameters (CPPs) where the critical quality attributes (CQAs) of the method have been assured to fulfil the desired requirements with a selected probability. QbD can improve the understanding of the enantioseparation process, including both the electrophoretic behavior of enantiomers and their separation, therefore enabling its control. The CQAs were represented by enantioresolution and analysis time. The scouting phase made it possible to select a separation system made by sulfated-β-cyclodextrin and a neutral cyclodextrin, operating in reverse polarity mode. The type of neutral cyclodextrin was included among other CPPs, both instrumental and related to background electrolyte composition, which were evaluated in a screening phase by an asymmetric screening matrix. Response surface methodology was carried out by a Doehlert design and allowed the contour plots to be drawn, highlighting significant interactions between some of the CPPs. DS was defined by applying Monte-Carlo simulations, and corresponded to the following intervals: sulfated-β-cyclodextrin concentration, 9–12mM; methyl-β-cyclodextrin concentration, 29–38mM; Britton–Robinson buffer pH, 3.24–3.50; voltage, 12–14kV. Robustness of the method was examined by a Plackett–Burman matrix and the obtained results, together with system repeatability data, led to define a method control strategy. The method was validated and was finally applied to determine the enantiomeric purity of S-SUL in pharmaceutical dosage forms.

Optimization of microwave assisted extraction parameters of neem (Azadirachta indica A. Juss) oil using the Doehlert’s experimental design

Demand for neem oil for use in cosmetics, pharmaceutics and biodiesel formulations has been on a steady increase and is expected to rise even more in the future. In order to meet increasing demand, it is important to define optimum conditions that can increase volumes and quality of oil produced. Parameters for microwave assisted extraction (MAE) of neem oil were optimized using the Doehlert design. Quantity of oil extracted, fatty acid profiles and acid number were used to evaluate the effect of microwave heating time, temperature and solvent/biomass ratio on the MAE process. Second order models were generated and used to establish optimum MAE parameters of heating time (24min), temperature (80°C), solvent/solute ratio (3:1). Under these conditions, close to 80% of the oil was extracted in comparison to 10h required for the Soxhlet process. Scanning electron microscopy revealed that structure degradation of the kernels by microwaves was the main driving force behind the rapid and efficient extraction process, but had no significant effect on the fatty acid profiles and acid numbers, respectively. MAE process can therefore be used to extract high volumes of oil within short intervals without significant degradation of the oil quality. This paper presents for the first time, to the best of our knowledge, a study on the microwave extraction process of neem oil.

Optimization of the 3-Point Bending Failure of Anodized Aluminum Formed in Tartaric/Sulphuric Acid Using Doehlert Design

The bending failure of anodized aluminum in tartaric/sulphuric acid bath was modeled using Doehlert design. Bath temperature, anodic current density, sulphuric acid, and tartaric acid concentrations were retained as variables. Thickness measurements and 3-point bending experiments were conducted. The deflection at failure (D f) and the maximum load (F m) of each sample were, then, deducted from the corresponding flexural responses. The treatment of experimental results has established mathematical models of second degree reflecting the relation of cause and effect between the factors and the studied properties. The optimum path study of thickness, deflection at failure, and maximum load, showed that the three optima were opposite. Multicriteria optimization using the desirability function was achieved in order to maximize simultaneously the three responses. The optimum conditions were: C tar = 18.2 g L−1, T = 17.3 °C, J = 2.37 A dm−2, C sul = 191 g L−1, while the estimated response values were e = 57.7 µm, D f = 5.6 mm, and F m = 835 N. Using the established models, a mathematical correlation was found between deflection at failure and thickness of the anodic oxide layer. Before bending tests, aluminum oxide layer was examined by scanning electron microscopy (SEM) and atomic force microscopy. After tests, the morphology and the composition of the anodic oxide layer were inspected by SEM, optical microscopy, and glow-discharge optical emission spectroscopy.

Multivariate optimization for extraction of pyrethroids in milk and validation for GC-ECD and CG-MS/MS analysis.

A simple and inexpensive method based on solvent extraction followed by low temperature clean-up was applied for determination of seven pyrethroids residues in bovine raw milk using gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) and gas chromatography with electron-capture detector (GC-ECD). Sample extraction procedure was established through the evaluation of seven different extraction protocols, evaluated in terms of analyte recovery and cleanup efficiency. Sample preparation optimization was based on Doehlert design using fifteen runs with three different variables. Response surface methodologies and polynomial analysis were used to define the best extraction conditions. Method validation was carried out based on SANCO guide parameters and assessed by multivariate analysis. Method performance was considered satisfactory since mean recoveries were between 87% and 101% for three distinct concentrations. Accuracy and precision were lower than ±20%, and led to no significant differences (p < 0.05) between results obtained by GC-ECD and GC-MS/MS techniques. The method has been applied to routine analysis for determination of pyrethroid residues in bovine raw milk in the Brazilian National Residue Control Plan since 2013, in which a total of 50 samples were analyzed.

Manganese ore tailing: Optimization of acid leaching conditions and recovery of soluble manganese

Manganese recovery from industrial ore processing waste by means of leaching with sulfuric acid was the objective of this study. Experimental conditions were optimized by multivariate experimental design approaches. In order to study the factors affecting leaching, a screening step was used involving a full factorial design with central point for three variables in two levels (23). The three variables studied were leaching time, concentration of sulfuric acid and sample amount. The three factors screened were shown to be relevant and therefore a Doehlert design was applied to determine the best working conditions for leaching and to build the response surface. By applying the best leaching conditions, the concentrations of 12.80 and 13.64 %w/w of manganese for the global sample and for the fraction −44 + 37 μm, respectively, were found. Microbeads of chitosan were tested for removal of leachate acidity and recovering of soluble manganese. Manganese recovery from the leachate was 95.4%. Upon drying the leachate, a solid containing mostly manganese sulfate was obtained, showing that the proposed optimized method is efficient for manganese recovery from ore tailings.

Application of fractional factorial and Doehlert designs for optimizing the preparation of activated carbons from Argan shells

A high quality activated carbon has been obtained, by physical activation with steam, from a Moroccan agricultural by-product (Argan shells) and their characteristics were investigated. In order to optimize experimental conditions of the preparation, a combination of a fractional factorial design and a Doehlert design was applied. In the first step of this work, a two-level fractional factorial design 2(5–1) was used to study effects and first order interactions of various factors such as atmosphere in carbonization step, carbonization time at 400°C, activation temperature, activation time and steam flow. The results reveal that the most influential factors on the yield and the methylene blue adsorption are activation temperature, activation time, steam flow and the presence of a significant interaction between activation temperature and activation time in both cases. In the second step, activation temperature and activation time were optimized using Response Surface Methodology with a Doehlert design, and Desirability function. The optimal conditions for the preparation of activated carbon have been identified to be an activation temperature of 880°C, an activation time of 96min and steam flow fixed at this positive level of 0.2cm3min−1. The characteristics of prepared activated carbon obtained at the optimal conditions were determined using adsorption capacity of methylene blue, iodine and phenol, BET surface area, pHpzc, and surface functions based on Boehm method. Those characteristics (MB adsorption: 608.9mgg−1, iodine adsorption: 1026.4mgg−1, phenol adsorption: 633.3mgg−1, BET surface area: 1292m2g−1) were shown greater than those of a commercial activated carbon used in water treatment and those reported by other researchers studying activated carbon preparation from various solid wastes by steam activation method.On the other hand, this work showed that Argan shells are a good precursor for the production of activated carbon, by steam physical activation, with high performance to be used in water treatment applications.

Optimization of ultrasound-assisted dispersive liquid–liquid microextraction for ultra performance liquid chromatography determination of benzodiazepines in urine and hospital wastewater

Ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) combined with ultra-performance liquid chromatography (UPLC) was developed for the determination of seven benzodiazepines (alprazolam, bromazepam, clonazepam, diazepam, lorazepam, lormetazepam and tetrazepam) in urine samples and hospital wastewater. Several parameters affecting UA-DLLME efficiency such as type and dispersive solvent volume and ionic strength were investigated. The effects of pH, ultrasonic time and extraction solvent volume on the extraction efficiency were studied simultaneously using a Doehlert design and desirability functions. The optimal conditions were: 0.5 mL of sample; 1.6 mL acetone, as a dispersive solvent; 160 μL of chloroform, as an extraction solvent; pH 9; 4.5 min of ultrasound application; 0.2 g of NaCl and 8 min of centrifugation at 3500 rpm. The chromatographic separation of benzodiazepines was carried out by a UPLC system using a binary mobile phase composed of aqueous phosphate buffer (0.001 M, pH 6) and acetonitrile, ACN in gradient elution mode (4 min total analysis). Under the optimized conditions, the calibration curves showed good linearity in the studied ranges with determination coefficients higher than 0.994. The limits of quantification (LOQs) ranged from 1.8 to 7.4 ng mL−1 and 0.05 to 0.42 ng mL−1 in urine and wastewater, respectively. Intra- and inter-day precision ranged from 3.1 to 14.1% and the recoveries ranged from 81 to 124%. The application of the proposed analytical procedure in human urine samples and wastewater from a hospital and municipal treatment plants revealed the presence of benzodiazepines.

Modelling the recovery of Listeria monocytogenes in high pressure processed simulated cured meat

Abstract Current EC regulations require that ready-to-eat products should not exceed the limit of 100 CFU/g for Listeria monocytogenes throughout their shelf-life. On that basis a quantitative analysis for high hydrostatic pressure to produce safe (regarding L. monocytogenes levels) cured meat products with low salt concentration has been developed. An extended Doehlert design for a range of pressures (450–800 MPa), sodium chloride (0–34.9 g/L) and sodium nitrite (mg/L) concentrations, as well as the resulting a w (0.955–0.987) levels, was generated. Based on the logistic regression analysis, it appears that the recovery of L. monocytogenes is influenced by the applied pressure, the storage time and the synergistic effect of pressure and a w on inhibiting microbial recovery. This means that the sodium chloride and sodium nitrite concentrations tested indirectly affected the recovery of Listeria and consequently the shelf-life of the product by regulating the a w levels. The lower the water activity, the less the inactivation and recovery induced by pressure immediately and during storage, respectively.

Application of Plackett–Burman and Doehlert designs for optimization of selenium analysis in plasma with electrothermal atomic absorption spectrometry

ObjectivesThe aim of this study was the optimization of selenium determination in plasma samples with electrothermal atomic absorption spectrometry using experimental design methodology. Design and methods11 variables being able to influence selenium analysis in human blood plasma by electrothermal atomic absorption spectrometry (ETAAS) were evaluated with Plackett–Burman experimental design. These factors were selected from sample preparation, furnace program and chemical modification steps. Both absorbance and background signals were chosen as responses in the screening approach. Doehlert design was used for method optimization. ResultsResults showed that only ashing temperature has a statistically significant effect on the selected responses. Optimization with Doehlert design allowed the development of a reliable method for selenium analysis with ETAAS. Samples were diluted 1/10 with 0.05% (v/v) TritonX-100+2.5% (v/v) HNO3 solution. Optimized ashing and atomization temperatures for nickel modifier were 1070°C and 2270°C, respectively. A detection limit of 2.1μgL−1 Se was obtained. Accuracy of the method was checked by the analysis of selenium in Seronorm™ Trace element quality control serum level 1. The developed procedure was applied for the analysis of total selenium in fifteen plasma samples with standard addition method. Concentrations ranged between 24.4 and 64.6μgL−1, with a mean of 42.6±4.9μgL−1. ConclusionsThe use of experimental designs allowed the development of a cheap and accurate method for selenium analysis in plasma that could be applied routinely in clinical laboratories.

Multiclass method for the determination of quinolones and β-lactams, in raw cow milk using dispersive liquid–liquid microextraction and ultra high performance liquid chromatography–tandem mass spectrometry

An analytical method based on a sample treatment by dispersive liquid–liquid microextraction (DLLME) followed by ultra high performance liquid chromatography–tandem mass spectrometry analysis (UHPLC–MS/MS) for the determination of 17 quinolones and 14 β-lactams (penicillins and cephalosporins) in raw cow milk, was validated according to the European Commission guidelines as cited in the Decision 2002/657/EC. The extraction efficiency of the DLLME depends on several parameters such as the nature and volumes of extractant and dispersive solvents, pH, concentration of salt, shaking time and time of centrifugation. These variables were accurately optimized using multivariate optimization strategies. A Plackett–Burman design to select the most influential parameters and a Doehlert design to obtain the optimum conditions have been applied. Two different pH values were used for the extraction of compounds (pH 3 for acidic quinolones and β-lactams and pH 8 for amphoteric quinolones). The method was validated using matrix-matched standard calibration followed by a recovery assay with spiked samples. The limits of quantification found ranged from 0.3ngg−1 for amoxicillin to 6.6ngg−1 for ciprofloxacin, and the precision was lower than 15% in all cases as is required by the European Regulation. The decision limits (CCα) ranged between 4.1 and 104.8ngg−1, while detection capabilities (CCβ) from 4.2 to 109.7ngg−1. These values were very close to the corresponding maximum residue limits (MLRs) for the studied antibiotics. Recoveries between 72 and 110% were also obtained. Finally, in order to evaluate the applicability of the method, 28 raw cow milk samples were analysed and it was observed that 28% of the samples were positive. However, only 11% were considered non-compliant with the current EU legislation (Commission Regulation 37/2010), due to some milk samples corresponded to treated cows with these antibiotics.

Assessment of sugars separation from a model carbohydrates solution by nanofiltration using a design of experiments (DoE) methodology

Nanofiltration (NF) of a model solution of different molecular weight carbohydrates (inulin, sucrose, glucose and fructose) has been studied with a pilot cross-flow unit, using a membrane with molecular weight cut off (MWCO) of 600Da. The aim of this work was to screen operational parameters and to determine the most feasible domain in order to separate inulin-type fructans from model solutions containing low molecular weight (LMW) sugars. Firstly, parameters such as transmembrane pressure (TMP), feed concentration (C0) and retentate flow (QR) were screened using a Koshal design for single-component solutions. The results indicated that the most influential parameters were TMP and C0. Then, a Doehlert design was used to improve single-inulin nanofiltration. Indeed, surface response analysis (p<0.05) revealed inulin rejection values over 90%, for high TMP (1400kPa) and low C0 (5g/100mL). In order to test the robustness of these results in presence of sugar, a full factorial design was used to evaluate the separation of a binary solution containing sucrose and inulin. In this case, the permeate flux (Jv) and inulin rejection (Rinulin) results were in agreement with those obtained with single-component solutions. Furthermore, additional experiments on a complex quaternary mixture (sucrose–glucose–fructose–inulin), confirmed that the presence of mono and di-saccharides do not modify significantly Rinulin. Actually, it is possible to obtain even slightly better results for the separation process (Rinulin=93%). All the results were statistically validated using analysis of variance (ANOVA).

Simultaneous determination of macronutrients, micronutrients and trace elements in mineral fertilizers by inductively coupled plasma optical emission spectrometry

An analytical method for simultaneous determination of macronutrients (Ca, Mg, Na and P), micronutrients (Cu, Fe, Mn and Zn) and trace elements (Al, As, Cd, Pb and V) in mineral fertilizers was optimized. Two-level full factorial design was applied to evaluate the optimal proportions of reagents used in the sample digestion on hot plate. A Doehlert design for two variables was used to evaluate the operating conditions of the inductively coupled plasma optical emission spectrometer in order to accomplish the simultaneous determination of the analyte concentrations. The limits of quantification (LOQs) ranged from 2.0mgkg−1 for Mn to 77.3mgkg−1 for P. The accuracy and precision of the proposed method were evaluated by analysis of standard reference materials (SRMs) of Western phosphate rock (NIST 694), Florida phosphate rock (NIST 120C) and Trace elements in multi-nutrient fertilizer (NIST 695), considered to be adequate for simultaneous determination. Twenty-one samples of mineral fertilizers collected in Sergipe State, Brazil, were analyzed. For all samples, the As, Ca, Cd and Pb concentrations were below the LOQ values of the analytical method. For As, Cd and Pb the obtained LOQ values were below the maximum limit allowed by the Brazilian Ministry of Agriculture, Livestock and Food Supply (Ministério da Agricultura, Pecuária e Abastecimento — MAPA). The optimized method presented good accuracy and was effectively applied to quantitative simultaneous determination of the analytes in mineral fertilizers by inductively coupled plasma optical emission spectrometry (ICP OES).

Preparation, characterization and in vitro antiviral activity evaluation of foscarnet-chitosan nanoparticles

A new nanoparticulate system for foscarnet delivery was prepared and evaluated. Nanoparticles were obtained by ionotropic gelation of chitosan induced by foscarnet itself, acting as an ionotropic agent in a manner similar to tripolyphosphate anion. A Doehlert design allowed finding the suitable experimental conditions. Nanoparticles were between 200 and 300nm in diameter (around 450nm after redispersion). Nanoparticle size increased after 5h, but no size increase was observed after 48h when nanoparticles were crosslinked with glutaraldehyde. Zeta potential values of noncrosslinked and crosslinked nanoparticles were between 20 and 25mV, while drug loading of noncrosslinked nanoparticles was about 40% w/w (55% w/w for crosslinked nanoparticles). Nanoparticle yield was around 25% w/w. Crosslinked nanoparticles showed a controlled drug release. Foscarnet released from nanoparticles maintained the antiviral activity of the free drug when tested in vitro against lung fibroblasts (HELF) cells infected with HCMV strain AD-169. Moreover, nanoparticles showed no toxicity on non-infected HELF cells. These nanoparticles may represent a delivery system that could improve the therapeutic effect of foscarnet.

Selective separation of ferric and non-ferric forms of human transferrin by capillary micellar electrokinetic chromatography

The previously published method allowing the separation of non-ferric (iron-free) and ferric (iron-saturated) forms of human serum transferrin via capillary electrophoresis has been further developed. Using a surface response methodology and a three-factorial Doehlert design we have established a new optimized running buffer composition: 50mM Tris–HCl, pH 8.5, 22.5% (v/v) methanol, 17.5mM SDS. As a result, two previously unobserved monoferric forms of protein have been separated and identified, moreover, the loss of ferric ions from transferrin during electrophoretic separation has been considerably reduced by methanol, and the method selectivity has been yet increased resulting in a total separation of proteins exerting only subtle or none difference in mass-to-charge ratio. The new method has allowed us to monitor the gradual iron saturation of transferrin by mixing the iron-free form of protein with the buffers with different concentrations of ferric ions. It revealed continuously changing contribution of monoferric forms, characterized by different affinities of two existing iron binding sites on N- and C-lobes of protein, respectively. Afterwards, the similar experiment has been conducted on-line, i.e. inside the capillary, comparing the effectiveness of two possible modes of the reactant zones mixing: diffusion mediated and electrophoretically mediated ones. Finally, the total time of separation has been decreased down to 4min, taking the advantage from a short-end injection strategy and maintaining excellent selectivity.

Determination of micronutrient minerals in coconut milk by ICP OES after ultrasound-assisted extraction procedure

In this paper, multivariate optimisation was applied to the development of an ultrasound-assisted multi-elemental extraction procedure to measure micronutrient minerals in coconut milk samples by inductively coupled plasma optical emission spectrometry (ICP OES). The factorial and Doehlert designs were applied to optimise the process variables. Using this approach, the optimal experimental condition for 1.0g of coconut milk was determined: 10min sonication time; 20.0mL of HNO3 (1.0molL−1); and 5min centrifugation time at 2000rpm. The extraction percentage was calculated using the analyte concentration obtained by a total digestion procedure as a reference. Accuracy was assessed by analysing a certified reference material (NIST 1549). The proposed procedure was applied to the analysis of commercial samples of coconut milk, and the resulting concentration ranges, in μgg−1, were as follows: 5.8–131 (Ca), <0.27–1.56 (Cu), 0.76–5.52 (Fe), 212–1781 (K), 14.9–201 (Mg), <0.11–3.88 (Mn), 274–625 (Na), 26–341 (P) and <0.74–3.2 (Zn). The method described offers a rapid, easy and efficient sample preparation method for direct determination of micronutrient minerals in coconut milk by ICP OES.

Extraction optimization and antinociceptive activity of (1⟶3)-β-d-glucan from Rhodotorulamucilaginosa

β-d-glucans are polymers of d-glucose monomers found in the cell walls of many bacteria, plants, fungi and yeasts. A variety of β-d-glucans differing in structures have been isolated from various sources and their biological activity to be regulated by various structural factors, such as the primary structure, molecular weight, solubility, and conformation. This study investigated the effect of extraction time and temperature on the yield of β-d-glucan produced by Rhodotorulamucilaginosa. A statistical Doehlert design was applied to determine the important effects and interactions of these independent variables on the yield of β-d-glucan, the dependent variable. Significant models were obtained. The best yield was of 25% obtained after 128min of extraction in a temperature of 72°C. The polysaccharides were characterized as (1⟶3)-β-d-glucan by methods spectroscopic (FT-IR, 1HNMR and 13CNMR). In addition, the antinociceptive effect was evaluated using different experimental tests (acetic acid-induced writhing test, formalin test and tail immersion test). The (1⟶3)-β-d-glucan showed a potent peripheral antinociceptive effect, possibly by the inhibition of inflammatory mediators.

Experimental Design in Analytical Chemistry—Part I: Theory

This paper reviews the main concepts of experimental design applicable to the optimization of analytical chemistry techniques. The critical steps and tools for screening, including Plackett-Burman, factorial and fractional factorial designs, and response surface methodology such as central composite, Box-Behnken, and Doehlert designs, are discussed. Some useful routines are also presented for performing the procedures.

Multivariate Optimization of the QuEChERS-GC-ECD Method and Pesticide Investigation Residues in Apples, Strawberries, and Tomatoes Produced in Brazilian South

Apple, strawberry and tomato are among the foods with higher contamination for pesticide use in Brazil. Thereby, a multivariate optimization of the QuEChERS method coupled to GC-ECD was proposed to investigate the level of pesticides residues clorpyrifos, dimethoate, malathion, mevinphos, pedimentalina, simazine and trifluralin in apple, strawberries and tomatoes produced in Santa Catarina state, South of Brazil. The process involved a two-level full factorial and Doehlert designs followed by validation of the modified method and its application in 91 real samples collected during the years 2010 and 2011. Modifications in the method provided increased detectability and satisfactory values of linearity, accuracy and precision. In real samples, residues of at least one pesticide (> LOQ) were found in 8 (27.6%) apple, 12 (40.0%) strawberry and 17 (53.1%) tomato samples. The results indicated the necessity of continuous monitoring for pesticide use in fruits and vegetables.

Use of Doehlert design in the optimization of extraction conditions in the determination of organochlorine pesticides in bovine milk samples by HS-SPME

The extraction of pesticides lindane, heptachlor, aldrin, dieldrin and endrin from milk by HS-SPME was investigated followed by separation/detection of these compounds by GC-ECD.