Doehlert Design Research Articles

Effect of storage conditions (relative humidity, duration, and temperature) on the germination time of Aspergillus carbonarius and Penicillium chrysogenum

Fungal conidia are disseminated, often in the air, for a certain period of time, prior to contaminating food products. The objective of this study was to examine the effects of the relative humidity, RH (%), time (day), and temperature (°C) during this period of time, called “storage”, on the germination time, τ (h), of Aspergillus carbonarius and Penicillium chrysogenum. A Doehlert design was used in the range, 20–100% RH, 2–28days, and 5–25°C. As compared to un-stored conidia, the germination time of conidia stored at 60% RH, 15days, 5°C was increased by 23 and 28%, for A. carbonarius and P. chrysogenum, respectively. Stored conidia exhibited a minimum τ value at 60% RH, and 100% RH for A. carbonarius and P. chrysogenum, respectively. For these species, τ was minimum for 2days of storage. The effect of temperature was RH dependent for A. carbonarius. The germination time of stored conidia was clearly greater than that of fresh conidia obtained in the laboratory. This result should be taken into account to determine the mould free shelf-life of food products.

Application of Doehlert uniform shell designs for selecting optimal amounts of internal standards in the analysis of prostaglandins and leukotrienes by liquid chromatography–tandem mass spectrometry

A protocol for the analysis of multiple prostaglandins and leukotrienes in cell culture media by using multiple internal standards was validated. A two-factor Doehlert design was used to determine the behaviour of the relationship analyte/internal standard (namely: PGE2/PGE2-d4, PGE3/PGE2-d4, LTB4/LTB4-d4 and LTB5/LTB4-d4) and to select the optimal amounts of deuterated internal standards for quantifying simultaneously the prostaglandins and leukotrienes in cell culture media by LC–MS/MS. The selection of optimal amounts of internal standards was based on mathematical models that allow visualizing concentration regions where the response factors remain constant over a wide range of analytical concentrations. The linearity of the calibration curves for each analyte at the optimal levels suggested by the mathematical models was statistically confirmed by means of the ratio lack-of-fit to pure error. The validated protocol was successfully applied in the simultaneous quantification of pro- and anti-inflammatory eicosanoids in stimulated cod head kidney cell culture media. The two-factor Doehlert design has permitted to estimate the experimental response as a function of six variables (PGE2, PGE3, LTB4, LTB5, PGE2-d4 and LTB4-d4) which represents a substantial reduction of resources, time and experiments of approximately 84% (7×3 experiments) when compared with the full six-factor Doehlert design (43×3 experiments).

Dispersive liquid–liquid microextraction coupled with programmed temperature vaporization-large volume injection-gas chromatography–tandem mass spectrometry for multiclass pesticides in water

A simple solvent-less procedure for the determination of seventeen pesticides and related compounds in environmental water and wastewater using dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–mass spectrometry in tandem (GC–MS/MS) with large-volume injection, having a programmed temperature vaporizer (PTV-LVI), is described. The parameters affecting the extraction efficiency of the target analytes from water samples were systematically investigated. A response surface Doehlert design was used. The best extraction conditions involved a rapid injection of a mixture of 1.9mL of acetonitrile (as a dispersant) and 178μL of trichloroethane (as an extractant) into 10mL of water placed in a conical bottom glass tube. After manually shaken for 3.0min and centrifugation at 3600rpm (5min), 50μL of the sedimented phase was directly injected into the PTV-LVI-GC–MS/MS system. The limits of quantitation (LOQs) ranged from 0.5 to 18ngL−1 for all pesticides, except empentrin (132ngL−1). The relative standard deviations (RSDs) for the analytes ranged between 0.8 and 14.6% for both intraday and interday precision. Accuracy, expressed as the mean extraction recovery, was between 70 and 130%. Using the internal standard method and surrogate deuterated standards, the total concentration of pesticides was in the range from 2.7 to 440ngL−1 in seawater, river water and sewage water.

Optimization of microwave assisted extraction for determination of iron and manganese in cereal flour using FAAS: Doehlert design

The present work describes the development by response surface methodology of a method for manganese and iron determination by flame atomic absorption spectrometry (FAAS) in cereal flours, which is based on microwave assisted extraction. The optimization process was performed using two level fractional factorial designs (24-1) and Doehlert design matrix. Four variables such as irradiation power, time, temperature and concentration of nitric acid were regarded as factors in the optimization. Results of two level fractional factorial designs with 10 runs for manganese and iron extraction, based on the Pareto chart, demonstrated that the factors irradiation power, time and temperature are statistically significant, and concentration of nitric acid is not significant. Then, a Doehlert design was carried out in order to determine the optimum conditions for the procedure through response surface study. The working conditions were established as a compromise between optimum values found for each analyte. These values were 87.0°C, 573.0 W and 40.0 min, for temperature, irradiation power and time, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference material. The procedure proposed was applied for the determination of iron and manganese in cereal flours.

Optimization of tartaric/sulphuric acid anodizing process using Doehlert design

The aim of this study was to investigate the influence of tartaric/sulphuric acid anodizing parameters (bath temperature, anodic current density, sulphuric acid and tartaric acid concentrations) on the anodic oxide layer properties. A Doehlert design was implemented to optimize this process. Four responses were retained, namely: growth rate, microhardness, dissolution rate and weight loss after abrasion of the anodic oxide layer. A multicriteria optimization using desirability function was performed in order to find a compromise between maximization of growth rate and microhardness and minimization of dissolution rate and weight loss after abrasion.Under the determined optimal anodizing conditions (Ctart=23.1gL−1, 8.6°C, 2.1Adm−2, Csul=151gL−1), the estimated response values were 0.59μmmin−1, 3.64gm−2min−1, 446HV and 70gm−2 for growth rate, dissolution rate, microhardness and weight loss after abrasion, respectively. The morphology and the composition of the anodic oxide layer were examined by scanning electron microscopy, atomic force microscopy and glow-discharge optical emission spectroscopy.

On the activation of implanted silicon ions in p-In0.53Ga0.47As

We present a systematic study of Si dopant implantation and activation in p-type In0.53Ga0.47As in an attempt to optimize the source and drain regions of an n-channel III-V metal–oxide–semiconductor field-effect transistor. Test structures based on the transfer length method were fabricated on Si-implanted p-In0.53Ga0.47As/p-InP buffer/semi-insulting InP. A Doehlert design of experiment (DOE) was used to investigate the effect of annealing temperature and time on the electrical properties of the samples. The DOE covered an experimental domain of 625–725 °C and 15–45 s. The current–voltage characteristics of all tested structures exhibited excellent ohmic behavior. The DOE revealed a minimum sheet resistance of (195.6 ± 3.4) Ω/□ for an optimum anneal condition of 715 °C for 32 s. Nonalloyed Au/Ge/Au/Ni/Au contacts, on the sample annealed at 675 °C for 30 s (center point of the experimental domain), exhibited a low specific contact resistance of (7.4 ± 4.5) × 10−7 Ω cm2. The sample annealed at 675 °C for 30 s was further investigated using secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (XTEM) analyses. SIMS revealed that Si ions did not diffuse with annealing, while XTEM showed the formation of characteristic loop defects potentially responsible for the sheet resistance and specific contact resistance degradation.

Selective extraction and preconcentration of chromium using Moringa oleifera husks as biosorbent and flame atomic absorption spectrometry

In this study a new method for selective extraction and preconcentration of chromium in water using Moringa oleifera husks as the solid phase with a flow injection system and detection by flame atomic absorption spectrometry was developed. The behavior of Cr(III) and Cr(VI) adsorption onto Moringa oleifera husks allowed the selective separation of Cr(III) in the pH range of 7–9 and Cr(VI) in the pH range of 1–2. The operational variables of the preconcentration system were optimized through full factorial and Doehlert designs. The limits of detection for Cr(III) and Cr(VI) were 1.92 and 2.45μg L−1 and the precision were below 1.63% and 0.08%, respectively. Results for recovery tests using different water samples were higher than 88% for Cr(III) and 81% for Cr(VI).

Pesticides in seaweed: optimization of pressurized liquid extraction and in-cell clean-up and analysis by liquid chromatography–mass spectrometry

Chemical residues, such as insecticides and anthelmintics, are frequently redistributed from the aquatic environment to marine species. This work reports on a fast validated protocol for the analysis of azamethiphos, three avermectins, two carbamates and two benzoylurea pesticides and chemotherapeutic agents in seaweeds based on pressurized liquid extraction and separation of analytes by liquid chromatography coupled with tandem mass spectrometry. The variables affecting the efficiency of pressurized liquid extraction, including temperature, number of extraction cycles, static extraction time and percent acetonitrile flush volume, were studied using a Doehlert design. The optimum parameters were 100 °C and one cycle of 3 min with 70 % acetonitrile. Adequate in-cell clean-up of the seaweeds was achieved using 0.8 g of Florisil over 0.1 g of graphitized carbon black on the bottom of the cell. The optimized method was validated using an analyte-free seaweed sample fortified at different concentrations. The limits of quantification ranged from 3.6 μg kg(-1) (azamethiphos) to 31.5 μg kg(-1) (abamectin). The recovery was from 87 to 120 % in most cases at different spiking levels. Finally, the reproducibility of the method expressed as the relative standard deviation and evaluated at concentrations of 10 and 50 μg kg(-1) was in the range 9-14.3 % and 6.1-12.3 %, respectively. The applicability of the method was evaluated with five commercial and 12 wild edible seaweeds, and four target compounds were detected in two wild seaweeds at a concentration below the quantification limit.

Rational design of core–shell molecularly imprinted polymer based on computational simulation and Doehlert experimental optimization: application to the separation of tanshinone IIA from Salvia miltiorrhiza Bunge

Computational simulation and Doehlert experimental optimization were done for the rational design of a core-shell molecularly imprinted polymer (CS-MIP) for use in the highly selective separation of Tanshinone IIA (TSIIA) from the crude extracts of Salvia miltiorrhiza Bunge (SMB). The functional monomer layer of the polymer shells directed the selective occurrence of imprinting polymerization at the surface of silica through the copolymerization of vinyl end groups with functional monomers and also drove TSIIA templates into the formed polymer shells through the charge-transfer complex interactions between TSIIA and the functional monomer layer. As a result, the maximum rebinding capacity was achieved with the use of optimal grafting ratio by the Doehlert design. The CS-MIP exhibited high recognition selectivity and binding affinity to TSIIA. When the imprinted particles were used as dispersive solid phase extraction sorbents, the recovery yield of TSIIA reached 93% by a one-step extraction from the crude extracts of SMB, and the purity of TSIIA was larger than 98% by HPLC analysis. These results show the possibility of a highly selective separation and enrichment of TSIIA from the SMB using the TSIIA-imprinted core-shell molecularly imprinted polymers.

Advanced Thermal Hydrolysis: Optimization of a Novel Thermochemical Process to Aid Sewage Sludge Treatment

The aim of this work was to study in depth the behavior and optimization of a novel process, called advanced thermal hydrolysis (ATH), to determine its utility as a pretreatment (sludge solubilization) or postreatment (organic matter removal) for anaerobic digestion (AD) in the sludge line of wastewater treatment plants (WWTPs). ATH is based on a thermal hydrolysis (TH) process plus hydrogen peroxide (H(2)O(2)) addition and takes advantage of a peroxidation/direct steam injection synergistic effect. On the basis of the response surface methodology (RSM) and a modified Doehlert design, an empirical second-order polynomial model was developed for the total yield of: (a) disintegration degree [DD (%)] (solubilization), (b) filtration constant [F(c) (cm(2)/min)] (dewaterability), and (c) organic matter removal (%). The variables considered were operation time (t), temperature reached after initial heating (T), and oxidant coefficient (n = oxygen(supplied)/oxygen(stoichiometric)). As the model predicts, in the case of the ATH process with high levels of oxidant, it is possible to achieve an organic matter removal of up to 92%, but the conditions required are prohibitive on an industrial scale. ATH operated at optimal conditions (oxygen amount 30% of stoichiometric, 115 °C and 24 min) gave promising results as a pretreatment, with similar solubilization and markedly better dewaterability levels in comparison to those obtained with TH at 170 °C. The empirical validation of the model was satisfactory.

Statistical optimization for the production of lichenase by a newly isolated Bacillus licheniformis UEB CF in solid state fermentation using pea pomace as a novel solid support

A newly isolated Bacterium strain UEB CF was selected from southern Tunisia, exhibiting the highest clear zone on agar plates containing barley flour by staining with Congo red. On the basis of 16S rDNA sequence analysis, this strain was identified as Bacillus licheniformis. Its capacity to produce lichenase was assessed under solid-state fermentation (SSF) using pea pomace as an abundant agro-industrial substrate. Cultivation conditions of B. licheniformis UEB CF for lichenase production were optimized using Doehlert design. The impact on enzyme production of four independent variables, namely cultivation time, moisture-to-substrate ratio (L/S), inoculum volume and culture temperature were evaluated by response surface methodology (RSM). A second-order polynomial model was determined by the multiple regression analysis of the experimental data. A statistical analysis showed a satisfactory adjustment of the quadratic model with the experimental data. Contour plots were generated to assess the change in the response surface and to understand the relationship between the enzyme production yield and the culture conditions. A ridge analysis revealed that the optimum values of the tested variables for maximizing enzyme production were as follows cultivation time, 84h; L/S ratio 4ml/gs; inoculum volume, 0.8ml (8×107CFU/ml) and culture temperature, 44°C. The experiment carried out under these conditions led to a lichenase production yield of 280U/g dry substrate, which was in agreement with the predicted value of 293±49U/gds by the model.

Experience plan for controlled-atmosphere cone calorimeter by Doehlert method

Controlled-atmosphere cone calorimeter is an interesting test method to study at the same time the effect of oxygen concentration and radiant heat flux on materials' fire behaviour and gas release. However, measurements in an extended range for these two variables can be tedious. To optimize the experimental measurement, this paper proposes a methodology based on the Doehlert design. The Doehlert method allows significant optimization of the number of tests. The optimization of measurement response is then accomplished using polynomial approximations to establish fire behaviour constitutive. Copyright © 2012 John Wiley & Sons, Ltd.

Factorial and Doehlert designs in the optimization of a separation procedure using polyurethane foam as a solid phase extractant for platinum determination in ferrous matrices using inductively coupled plasma optical emission spectroscopy

A procedure for separation of platinum from ferrous matrices was developed using platinum sorption as chloride complexes on polyurethane foam, with subsequent determination by inductively coupled plasma optical emission spectrometry (ICP OES). The procedure was optimized using a two-level full factorial and Doehlert designs. Four variables (foam mass, shaking time, stannous chloride concentration and hydrochloric acid concentration) were regarded as factors in the extraction optimization. Results of the two-level full factorial design, 24 with 16 runs based on Analysis of Variance (ANOVA) showed that only two factors (foam mass and shaking time) are statistically significant. Doehlert design was applied in order to determine the optimum conditions for platinum separation. The proposed procedure allowed platinum determination with a detection limit of 66 μg L−1 and a precision, calculated as relative standard deviation (RSD), of 1.2% in a set of 10 measurements for a platinum concentration of 10.0 μg L−1. The studied procedure was applied to platinum determination in several ferrous matrices (iron ores, pure iron and catalysts). Spike tests on iron ores and pure iron showed good performance in platinum recovery. The good accuracy of the proposed procedure was confirmed by analysis of an ore platinum standard reference material (SARM-7).

Evaluation of vermicompost as a raw natural adsorbent for adsorption of pesticide methylparathion

The assessment of vermicompost (VC) as a low-cost and alternative adsorbent for the removal of the pesticide methylparathion (MP) from an aqueous medium has been investigated by batch and column experiments. Parameters related to MP adsorption, i.e. equilibrium time (61.5 min) and adsorption pH (6.8) were optimized by using Doehlert design. The initial and final MP concentrations after adsorption assays were determined by square-wave adsorptive cathodic stripping voltammetry using an electrode composed of a multiwalled carbon nanotube dispersed in mineral oil. Batch adsorption experimental data were fitted to the Langmuir and Freundlich isotherm adsorptions, and a very good fit to the Langmuir linear model, giving a maximum adsorption capacity (MAC) of 0.17 mg g−1. This result was very similar to that obtained with the column experiments. In order to evaluate the MP desorption from column packed VC, 100.0 ml of nitric acid solution (pH 3.0) has been percolated through material. No leaching of MP was observed, thus confirming the strong interaction between MP and VC. The satisfactory MAC obtained and low cost makes the VC a reliable natural material for the removal of MP from aqueous effluents.

PREBIOTIC DI‐D‐FRUCTOSE DIANHYDRIDE‐ENRICHED CARAMELS: DEVELOPMENT OF BATCH PROCESS (1 L) AND OPTIMIZATION OF OPERATING CONDITIONS

ABSTRACTAn experimental design was used to scale up the synthesis of caramels enriched in di‐D‐fructose dianhydride. The scale‐up from 100 mL to 1 L is particularly difficult because the mixture is a viscous paste. Using the Doehlert design for three factors, a model of difructose dianhydrides (DFAs) yield in relation to operating conditions was established. By considering only the significant coefficients, a second model was rewritten. The second model was verified and validated. F‐test was calculated (3.3) and was satisfactory (probability of adjustment is 25%). In a 100‐mL flask, the optimum DFAs yield was 30%. The determination of an optimum in a 1‐L reactor was 50% with better rheological conditions (a lower proportion of resin and a higher proportion of water).PRACTICAL APPLICATIONSDFAs have prebiotic properties and are intended to be used as food additives. The possibility of producing them by caramelization allows one to consider the addition of these healthy caramels to different food matrices. The synthesis used at 100‐mL scale presented the advantage of satisfying yields but the inconvenience of strong rheological constraints. This work shows that the passage at the larger scale is possible while increasing performance and decreasing the viscosity of the medium. This step is fundamental in the industrial extrapolation process.

Simultaneous determination of BTX and total hydrocarbons in water employing near infrared spectroscopy and multivariate calibration

A method for the simultaneous determination of benzene, toluene and xylenes (BTX) in water based on the use of a silicone sensing phase, detection by near infrared spectroscopy and multivariate calibration is described. A Doehlert design was employed to define the calibration and external validation sets, which were prepared in the concentration ranges of 2.0–30 mg L −1 for benzene, 4.0–40 mg L −1 for toluene and 1.0–15 mg L −1 for xylenes; these ranges were selected after evaluation of the concentration of these compounds in a water sample contaminated by gasoline. The determinations were performed by inserting a polydimethylsiloxane (PDMS) rod (3.2 mm diameter and 5.0 mm long) into a flask containing the aqueous BTX solution (without headspace), made 3.0 mol L −1 with sodium chloride in order to improve the extraction of the hydrocarbons by the polymer. After extraction, the cylinder was placed in a home-made cell for absorbance measurements from 800 to 2500 nm. The calibration models were constructed using Partial Least Square (PLS) regression and Multiple Linear Regression (MLR), with variables selected by the Successive Projection Algorithm (SPA). PLS models provided relative errors of prediction of 10.9%, 13.3%, 21.9% and 9.6% for benzene, toluene, xylenes and total hydrocarbons, respectively. These values can be considered acceptable for the concentration range studied, indicating that the proposed method can be useful for simultaneous determination of aromatic compounds in water employing NIR.

Quality by design approach for developing chitosan-Ca-alginate microspheres for colon delivery of celecoxib-hydroxypropyl-β-cyclodextrin-PVP complex

The aim of the present work was to develop a new multiparticulate system, designed for colon-specific delivery of celecoxib for both systemic (in chronotherapic treatment of arthritis) and local (in prophylaxis of colon carcinogenesis) therapy. The system simultaneously benefits from ternary complexation with hydroxypropyl-β-cyclodextrin and PVP (polyvinylpyrrolidone), to increase drug solubility, and vectorization in chitosan-Ca-alginate microspheres, to exploit the colon-specific carrier properties of these polymers. Statistical experimental design was employed to investigate the combined effect of four formulation variables, i.e., % of alginate, CaCl 2, and chitosan and time of cross-linking on microsphere entrapment efficiency (EE%) and drug amount released after 4 h in colonic medium, considered as the responses to be optimized. Design of experiment was used in the context of Quality by Design, which requires a multivariate approach for understanding the multifactorial relationships among formulation parameters. Doehlert design allowed for defining a design space, which revealed that variations of the considered factors had in most cases an opposite influence on the responses. Desirability function was used to attain simultaneous optimization of both responses. The desired goals were achieved for both systemic and local use of celecoxib. Experimental values obtained from the optimized formulations were in both cases very close to the predicted values, thus confirming the validity of the generated mathematical model. These results demonstrated the effectiveness of the proposed jointed use of drug cyclodextrin complexation and chitosan-Ca-alginate microsphere vectorization, as well as the usefulness of the multivariate approach for the preparation of colon-targeted celecoxib microspheres with optimized properties.

Combined solid‐phase extraction and gas chromatography–mass spectrometry used for determination of chloropropanols in water

A sensitive and rapid derivatization method for the simultaneous determination of 1,3-dichloro-2-propanol (1,3-DCP) and 3-chloropropane-1,2-diol (3-MCPD) in water samples has been developed. The aim was to research the optimal conditions of the derivatization process for two selected reagents. A central composite design was used to determine the influence of derivatization time, derivatization temperature and reagent volume. A global desirability function was applied for multi-response optimization. The analysis was performed by gas chromatography-mass spectrometry. During the optimization of the extraction procedure, four different types of solid-phase extraction (SPE) columns were tested. It was demonstrated that the Oasis HLB cartridge produced the best recoveries of the target analytes. The pH value and the salinity were investigated using a Doehlert design. The best results for the SPE of both analytes were obtained with 1.5 g of NaCl and pH 6. The proposed method provides high sensitivity, good linearity (R(2)≥0.999) and repeatability (relative standard deviations % between 2.9 and 3.4%). Limits of detection and quantification were in the range of 1.4-11.2 ng/mL and 4.8-34.5 ng/mL, respectively. Recoveries obtained for water samples were ca. 100% for 1,3-DCP and 3-MCPD. The method has been successfully applied to the analysis of different samples including commercially bottled water, an influent and effluent sewage.

Extraction of trans-resveratrol from red wine and optimization by response surface methodology

The optimization of liquid–liquid extraction of resveratrol from wine by organic solvent was investigated using a Doehlert design. Preliminary experiments were conducted to choose the solvent used for the experimental design. Two parameters were analysed: the composition of the binary solvent mixture and the solution/solvent ratio. The best result was obtained by superimposing the isoresponses of selectivity and yield. The optimum operating conditions for extraction were: (i) a solvent mixture of cyclohexane/pentanol with a weight ratio of 40/60 and (ii) a solution/solvent ratio of 30/70. Under these conditions, the yield is above 95% for a selectivity of about 6.6‰.

Multivariate optimization of a spectrophotometric method for copper determination in Brazilian sugar-cane spirits using the Doehlert design

This present work reports a multivariate optimization of a spectrophotometric method for copper determination in sugar-cane spirits, exploring the reaction of Cu(II) with phenylfluorone (PF) in the presence of cetylpyridinium chloride (CPC) and Triton X-100. The optimization strategy was based on the application of a two-level full factorial design for the screening of significant variables followed by a Doehlert design to determine the optimum conditions. The highest sensitivity was achieved when the pH was 8.0 and the PF and TX-100 concentrations were 6.2×10−5 and 1.0×10−2molL−1, respectively. The optimized method presented a limit of detection of 3.4μgL−1 and a limit of quantification of 11μgL−1 and was applied in the determination of Cu in 17 samples. The obtained results were compared with those obtained by ICP OES and no statistical difference between the methods was observed.