Response Surface Experimental Design Research Articles

Experimental design optimization of the tetralin hydrogenation over Ir–Pt-SBA-15

Experiment design-response surface methodology (RSM) is used in this work to model and optimize two responses in the hydrogenation of tetralin to decalin using bimetallic Ir–Pt-SBA-15 catalyst. In this study, we analyze the influence of the nature of the catalyst (metal molar fraction and metal loading), the catalyst/substrate ratio and the temperature of the reaction as factors for the design. The responses analyzed were conversion at 3h and at 5h of reaction time. The response surfaces were obtained with the Box–Behnken design, finding the best combination between the reaction parameters that allowed optimizing the process. By applying the statistic methodology, the higher levels of the two objective functions were obtained employing the catalyst with 1wt.% of iridium and 0.7–0.8wt.% of platinum; the optimal ratio between mass of catalyst and mole of tetralin was 17–19g/mol and temperature between 200 and 220°C.

Effects of extrusion parameters on tensile strength of polybenzimidazole fiber-reinforced high density polyethylene composites

Abstract The objectives of this study were to examine the effects of fiber content and extrusion parameters on polybenzimidazole (PBI) fiber-reinforced polyethylene composites and to determine the optimum values for the tensile strength. The PBI fiber was physically mixed with high density polyethylene (HDPE) and then extruded through a twin screw extruder. The extrusion parameters were studied at different levels, barrel temperatures at 240°C, 250°C and 260°C and screw speeds at 12 rpm, 15 rpm and 18 rpm. The tensile strength was measured using a universal testing machine. A response surface experimental design using Design-Expert was applied to investigate the effect of fiber loading and extrusion parameters (barrel temperature, screw speed) on tensile properties of the resulting composite and consequently analyzing the optimized value for these parameters to yield maximum tensile strength. The analysis predicted a linear model which suggests that in order to achieve maximum tensile strength the screw speed should be 18 rpm, the barrel temperature at 240°C and at a fiber loading of 2%.

Comparison of in-cell lipid removal efficiency of adsorbent mixtures for extraction of polybrominated diphenyl ethers in fish.

Polybrominated diphenyl ethers (PBDEs) have become ubiquitous environmental contaminants due to their incorporation into many consumer products. Their ability to bioaccumulate to alarming levels in fat-rich matrices such as fish demands fast and efficient methods to monitor these contaminants. We present an analytical method for selective-pressurised liquid extraction (S-PLE) of PBDEs from fish tissue. Fat removal performance of different mixtures of Florisil, silica gel and sulphuric acid-impregnated silica gel were evaluated using a response surface experimental design approach for determining the optimal fat-retaining mixture for S-PLE. Acid-silica gel had the greatest individual effect on fat retention; with a two-thirds acid-silica one-third Florisil mixture found to be the most efficient (>97%). Method validation was performed using recovery experiments at three spiked concentration levels (0.05, 0.5 and 5ngg(-1) ww). Mean recoveries of target analytes in spiked samples ranged from 70 to 124%, with relative standard deviations <27%. The S-PLE lipid removal efficiency combined with the sensitivity of triple quadrupole mass spectrometers provides a fast and comparatively inexpensive analytical method for analysis of PBDEs in fish samples.

Isocline analysis of competition predicts stable coexistence of two amphibians.

We investigated the interaction between larvae of two anuran amphibian species (Rana temporaria and Bufo bufo) to test models of two-species competition. The study had a response surface experimental design with four replicates, each consisting of 24 density combinations. Larval performance-and, by assumption, change in population size-was defined by a linear combination of survival, growth, and development. We fit six competition models from the literature and discovered that density dependence was strongly non-linear, with the highest support for the Hassel-Comins model. Rana temporaria was competitively superior to B. bufo; the impacts of both species on growth and development were about five- to tenfold greater than those on survival. Isocline analysis predicted a stable configuration, which agrees with the observation that these two species are syntopic in nature. The results of this study confirm competition theory by identifying a model structure that agrees with data and making predictions that are broadly supportive of the observations.

Multivariate DoE Optimization of Asymmetric Flow Field Flow Fractionation Coupled to Quantitative LC-MS/MS for Analysis of Lipoprotein Subclasses

In this report we demonstrate a practical multivariate design of experiment (DoE) approach for asymmetric flow field-flow fractionation (AF4) method optimization using separation of lipoprotein subclasses as an example. First, with the aid of commercially available software, we built a full factorial screening design where the theoretical outcomes were calculated by applying established formulas that govern AF4 channel performance for a 5–35 nm particle size range of interest for lipid particles. Second, using the desirable ranges of instrumental parameters established from theoretical optimization, we performed fractional factorial DoE for AF4 separation of pure albumin and ferritin with UV detection to narrow the range of instrumental parameters and allow optimum size resolution while minimizing losses from membrane immobilization. Third, the optimal range of conditions were tested using response surface DoE for sub-fractionation of high and low density lipoproteins (HDL and LDL) in human serum, where the recovery of the analytes were monitored by fraction collection and isotope-dilution LC-MS/MS analysis of each individual fraction for cholesterol and apolipoproteins (ApoA-1 and ApoB-100). Our results show that DoE is an effective tool in combining AF4 theoretical knowledge and experimental data in finding the most optimal set of AF4 instrumental parameters for quantitative coupling with LC-MS/MS measurements.

Application of Response Surface Method as an Experimental Design to Optimize Clarification Process Parameters for Sugarcane Juice

In this study, the response surface method and experimental design were applied for optimization of independent variables for clarification of sugarcane juice. A central composite design, with 6 axial points, 8 factorial points and 6 replicates at the centre point were used to build a model for predicting and optimizing clarification process parameters. The independent parameters viz Temperature (73.59, 77, 82, 87 and 90.41°C), Activated charcoal thickness (0.83, 1.0, and 1.25, 1.5 and 1.67 mm) and deola (0.063, 0.2, 0.4, 0.6 and 0.74 g/l) were selected and analyzed. Statistical checks (ANOVA table, R2 value, model lack of fit test and F-value) indicating that the model was adequate for representing the experimental data. The dependent parameters measured were viscosity, °Brix, and total solids values. Optimum values of process parameters obtained by using simultaneous optimization of dependent parameters were: 77.55°C temperature, 1.5 mm activated charcoal thickness and 0.48 g/lit deola.

Application of a computational neural network to optimize the fluorescence signal from a receptor-ligand interaction on a microfluidic chip.

We describe the use of a computational neural network platform to optimize the fluorescence upon binding 5-carboxyfluorescein-d-Ala-d-Ala-d-Ala (5-FAM(DA)3 ) (1) to the antibiotic teicoplanin covalently attached to a glass slide. A three-level response surface experimental design was used as the first stage of investigation. Subsequently, three defined experimental parameters were examined by the neural network approach: (i) the concentration of teicoplanin used to derivatize a glass platform on the microfluidic device, (ii) the time required for the immobilization of teicoplanin on the platform, and (iii) the length of time 1 is allowed to equilibrate with teicoplanin in the microfluidic channel. Optimal neural structure provided a best fit model, both for the training set (r(2) = 0.961) and test set (r(2) = 0.934) data. Model simulated results were experimentally validated with excellent agreement (% difference) between experimental and predicted fluorescence shown, thus demonstrating efficiency of the neural network approach.

Preparation and optimization of N-trimethyl-O-carboxymethyl chitosan nanoparticles for delivery of low-molecular-weight heparin

The aim of this study was preparation, optimization and in vitro characterization of nanoparticles composed of 6-[O-carboxymethyl]-[N,N,N-trimethyl] (TMCMC) for oral delivery of low-molecular-weight heparin. The chitosan derivative was synthesized. Nanoparticles were prepared using the polyelectrolyte complexation method. Box–Behnken response surface experimental design methodology was used for optimization of nanoparticles. The morphology of nanoparticles was studied using transmission electron microscopy. In vitro release of enoxaparin from nanoparticles was determined under simulated intestinal fluid. The cytotoxicity of nanoparticles on a Caco-2 cell line was determined, and finally the transport of prepared nanoparticles across Caco-2 cell monolayer was defined. Optimized nanoparticles with proper physico-chemical properties were obtained. The size, zeta potential, poly-dispersity index, entrapment efficiency and loading efficiency of nanoparticles were reported as 235 ± 24.3 nm, +18.6 ± 2.57 mV, 0.230 ± 0.03, 76.4 ± 5.43% and 12.6 ± 1.37%, respectively. Morphological studies revealed spherical nanoparticles with no sign of aggregation. In vitro release studies demonstrated that 93.6 ± 1.17% of enoxaparin released from nanoparticles after 600 min of incubation. MTT cell cytotoxicity studies showed no cytotoxicity at 3 h post-incubation, while the study demonstrated concentration-dependent cytotoxicity after 24 h of exposure. The obtained data had shown that the nanoparticles prepared from trimethylcarboxymethyl chitosan may be considered as a good candidate for oral delivery of enoxaparin.

Rheological behavior of avocado (Persea americana Mill, cv. Hass) oleogels considering the combined effect of structuring agents

The onset temperatures (Tonset) and crystallization temperatures (Tc) of oleogels prepared from avocado oil were determined by thermorheological testing. Crystallization studies were established by formulating oleogels with the following structuring agents: beeswax, monodiglycerides of fatty acids, and sorbitan monostearate (Span 60). Using a response surface experimental design, the effects of the concentration of each structuring agent, their mixtures, and the cooling rate on the variable temperature of crystallization were evaluated. The results showed that structuring agents have a significant effect on the crystallization temperatures (Tc). Additionally, the cooling rate was inversely related to the crystallization temperature, namely, lower rates of cooling led to higher crystallization temperatures. The crystallization temperature (Tc) varied from 29.5 to 53.6 °C, and Tonset varied between 33.8 and 58.7 °C.

Modeling fouling of hollow fiber membrane using response surface methodology

Hollow fiber membranes have been widely employed for potable water treatment, wastewater treatment and reclamation, and desalination pretreatment. They have advantages such as small footprint, ease of operation, and high removal of particles and pathogens. Nevertheless, membrane fouling is one of the most serious issues in operating hollow fiber membrane systems. Although there have been numerous researches for understanding and forecasting fouling, it is still challenging to predict fouling based on explicit mathematical models. A more practical approach is to apply statistical models, which allows more accurate fouling prediction. In this context, this study attempts the development of a statistical model to analyze fouling of hollow fiber membranes. A response surface experimental design was used to optimize and investigate the influence of process variables such as foulant types (kaolin, colloidal silica, NOM, and alginate), foulant concentration, and imposed flux on the fouling rate. The results obtained from the experiments were evaluated by multiple regression analysis method and empirical relationship between the response and independent variables. Empirical models were developed to understand the interactive correlation between the responses and process variables.

Production of hexaoligochitin from colloidal chitin using a chitinase from Aeromonas schubertii

Chitin derivatives, such as those with modified main saccharide chains and deacetylated side chains, exhibit versatile biological functions. The biomedical properties of chitin oligosaccharides depend on their degree of oligomerization. Of the chitin oligosaccharides, chitin hexamers are generally the most potent. In our recent study, N-acetylchitohexaose was obtained by digesting chitin with ASCHI61, a chitinase from Aeromonas schubertii. In this work, the factors involved in the production of chitin hexasaccharide were evaluated experimentally. Using steep map analysis and cross-analysis, the substrate concentration and reaction pH were identified as the key factors in this reaction, and the interactions between these parameters were observed. Using a response surface experimental design, we predicted that a colloidal chitin concentration of 3.4mgmL−1 and a pH of 6.54 were the optimal conditions for producing hexaoligochitin. These conditions were verified in separate experiments, in which 38.73mmolL−1 of N-acetylchitohexaose was obtained. The maximum amount of hexamer produced was 42.175mgL−1, an increase of only 0.27% from the predicted value.

Enhancement of the antimicrobial properties of bacteriophage‐K via stabilization using oil‐in‐water nano‐emulsions

Bacteriophage therapy is a promising new treatment that may help overcome the threat posed by antibiotic-resistant pathogenic bacteria, which are increasingly identified in hospitalized patients. The development of biocompatible and sustainable vehicles for incorporation of viable bacterial viruses into a wound dressing is a promising alternative. This article evaluates the antimicrobial efficacy of Bacteriophage K against Staphylococcus aureus over time, when stabilized and delivered via an oil-in-water nano-emulsion. Nano-emulsions were formulated via thermal phase inversion emulsification, and then bacterial growth was challenged with either native emulsion, or emulsion combined with Bacteriophage K. Bacteriophage infectivity, and the influence of storage time of the preparation, were assessed by turbidity measurements of bacterial samples. Newly prepared Bacteriophage K/nano-emulsion formulations have greater antimicrobial activity than freely suspended bacteriophage. The phage-loaded emulsions caused rapid and complete bacterial death of three different strains of S. aureus. The same effect was observed for preparations that were either stored at room temperature (18-20°C), or chilled at 4°C, for up to 10 days of storage. A response surface design of experiments was used to gain insight on the relative effects of the emulsion formulation on bacterial growth and phage lytic activity. More diluted emulsions had a less significant effect on bacterial growth, and diluted bacteriophage-emulsion preparations yielded greater antibacterial activity. The enhancement of bacteriophage activity when delivered via nano-emulsions is yet to be reported. This prompts further investigation into the use of these formulations for the development of novel anti-microbial wound management strategies.

Transfer of retention patterns in gas chromatography by means of response surface methodology

Accurate transfer of retention patterns in temperature-programmed gas chromatography is challenging because minor variations in column properties and experimental conditions may have significant impact on the elution patterns. An experimental method for accurate transfer of retention indices is proposed and validated. The methodology is based on response surface methodology and experimental design. The temperature rate and the start temperature of the rate are varied systematically in the region where the optimal conditions are expected to be found. Response surfaces that explain the absolute deviation to the target retention indices are calculated for each compound. These response surfaces are thereafter averaged and the minimum in the average surface is regarded as optimal conditions for reproduction of the retention pattern. The methodology was applied on fatty acid methyl esters using equivalent chain lengths as the retention index system. Two different target patterns were tested on two BPX-70 columns with different dimensions. Validation of the proposed conditions showed that the retention patterns could be reproduced with an error that was only fractions of a peak width.

NO Fluorescence Quantification by Chitosan CdSe Quantum Dots Nanocomposites

The quantification of nitric oxide (NO) based on the quenching of the fluorescence of a nanocomposites sensor constituted by cadmium/selenium quantum dots (CdSe) stabilized by chitosan (CS) and mercaptosuccinic acid (MSA) is assessed. The optimization of the response of the CS-CdSe-MSA nanocomposites to NO was done by multivariate response surface experimental design methodologies. The highest fluorescence quenching was obtained at pH5.5 and at room temperature. The NO quantification capability of CS-CdSe-MSA was evaluated using standard solutions and a NO donor reagent. A large linear working range from 5 to 200μM and a limit of detection of 1.86μM were obtained. Better quantification results were obtained using the NO donor reagent. Besides NO, the response of the fluorescence of CS-CdSe-MSA to the main reactive oxygen and nitrogen species and similar NO compounds was also assessed.

Multivariate optimisation of an ultrasound assisted-matrix solid-phase dispersion method combined with LC-fluorescence detection for simultaneous extraction and determination of aflatoxins in pistachio nut samples

This paper describes the application of ultrasound-assisted matrix solid-phase dispersion as an extraction and clean-up procedure for aflatoxins (B1, B2, G1 and G2) and subsequent determination by LC-fluorescence detection. A Box–Behnken design was used to determine the parameters influencing the extraction procedure through response surface methodology and experimental design. The influence of different variables including type of dispersing phase, sample-to-dispersing phase ratio, type and quantity of clean-up phase, ultrasonication time, ultrasonication temperature, nature and volume of the elution solvent were investigated in the optimisation study. C18, graphitic carbon black and acetonitrile were selected as dispersing phase, clean-up phase and elution solvent, respectively. The optimised values were sample-to-dispersing phase ratio of 1:1, 50 mg of graphitic carbon black, 11 min ultrasonication time, 30°C ultrasonication temperature and 3 ml acetonitrile. Under the optimal conditions the limits of detection (LODs) were ranged from 0.04–0.11 µg kg−1 and the relative standard deviations (RSDs) of the extraction method were less than 8.6%. The recoveries of the matrix solid-phase dispersion process ranged from 74% to 78% with relative standard deviation lower than 9% in all cases. Finally, the matrix solid-phase dispersion was successfully applied to extraction of trace amounts of aflatoxins in pistachio samples.

Toluene chemiresistor sensor based on nano-porous toluene-imprinted polymer

In this work, the application of molecularly imprinted polymer (MIP) as the recognition element of a chemiresistor sensor was introduced. Toluene-imprinted polymer and non-imprinted polymer (NIP) were synthesized and then mixed with carbon black powder in the presence of melted n-eicosane as the binder agent. The obtained composites were applied for the construction of chemiresistor sensors. The sensor, fabricated with toluene-imprinted polymer, showed a significant response towards toluene. Moreover, the response of the NIP-based (polymer synthesized without solvent) chemiresistor sensor was very small and negligible. The components of the MIP-based sensing composite were found to strongly influence the sensor sensitivity. Response surface experimental design methodology was applied to optimize the important parameters of the proposed sensor. Cross-sensitivity of the MIP-based chemiresistor sensor for different vapours was investigated and a satisfactory result was found for toluene vapour recognition. It was shown that the sensor response to toluene concentration in air was linear in the concentration range of 3.8 to 46.4 ppm. The detection limit and relative standard deviation (for five separate determinations) of the designed sensor were calculated equal to 0.8 ppm and 5.6%, respectively.

Correlation Between Reactive Modification Conditions and Degree of Long‐Chain Branching in Chemically Modified Linear Low Density Polyethylene Using Response Surface Experimental Design

Changes induced in the molecular architecture of linear low‐density polyethylene during early stages of peroxide modification in a microcompounder are monitored by means of size exclusion chromatography and dynamic shear oscillatory measurements as a function of peroxide concentration, mixing temperature and resident time. By the use of a response surface method and according to a box Behnken statistical design, various contour plots are constructed to establish correlations between the processing parameters and degree of long‐chain branching. All investigated process parameters are shown to have a significant effect on the degree of long‐chain branching, the order of significance being concentration &gt; temperature &gt; mixing time. The interactive effects of these factors are determined.

An efficient chemical analysis of phenolic acids and flavonoids in raw propolis by microwave-assisted extraction combined with high-performance liquid chromatography using the fused-core technology

A closed-vessel microwave-assisted extraction (MAE) technique was optimized for the first time for the extraction of polyphenols from raw propolis. The results obtained by means of response surface experimental design methodology showed that the best global response was reached when the extraction temperature was set at 106°C, the solvent composition close to EtOH–H2O 80:20 (v/v), with an extraction time of 15min. In comparison with other techniques, such as maceration, heat reflux extraction (HRE) and ultrasound-assisted extraction (UAE), the extraction with MAE was improved by shorter extraction time and lower volume of solvent needed.The HPLC analyses of propolis extracts were carried out on a fused-core Ascentis Express C18 column (150mm×3.0mm I.D., 2.7μm), with a gradient mobile phase composed by 0.1% formic acid in water and acetonitrile. Detection was performed by DAD and MS.The method validation indicated that the correlation coefficients were >0.999; the limit of detection was in the range 0.5–0.8μg/ml for phenolic acids and 1.2–3.0μg/ml for flavonoids; the recovery range was 95.3–98.1% for phenolic acids and 94.1–101.3% for flavonoids; the intra- and inter-day %RSD values for retention times and peak areas were ≤0.3 and 2.2%, respectively.The quali- and quantitative analysis of polyphenols in Italian samples of raw propolis was performed with the validated method. Total phenolic acids ranged from 5.0 to 120.8mg/g and total flavonoids from 2.5 to 168.0mg/g.The proposed MAE procedure and HPLC method can be considered reliable and useful tools for the comprehensive multi-component analysis of polyphenols in propolis extracts to be used in apitherapy.

Chara can outcompete Myriophyllum under low phosphorus supply

In the course of re-oligotrophication in Lower Lake Constance, Germany, the tall-growing angiosperm Myriophyllum spicatum has been almost replaced by dense and lower-growing charophytes. We hypothesise that Chara globularis negatively affects the performance of M. spicatum due to density competition and nutrient interference. Intra- and interspecific competition was assessed using a response surface experimental design with different densities of both species in mono and mixed stands in an outdoor mesocosm experiment. After 8 weeks, we measured the growth and various functional traits of both species, including stoichiometry, ash-free dry mass and dry-matter content, and for M. spicatum, additionally chlorophyll content, leaf-mass fraction, formation of autofragments, and root/shoot ratio. With increasing density, C. globularis reduced the growth of M. spicatum much more strongly than that of conspecifics. Increasing density of C. globularis led to a lower chlorophyll a to b ratio and lower nitrogen content based on ash-free dry mass in M. spicatum as well as reduced autofragmentation. Established C. globularis meadows can negatively affect tall-growing angiosperms such as M. spicatum when the environmental conditions, such as low phosphorus availability and high water-clarity, are appropriate. These findings have implications for the management of lakes, specifically those where a nuisance growth of tall macrophytes occurs, e.g. in systems where M. spicatum is invasive.

Optimization of microwave‐assisted extraction of analgesic and anti‐inflammatory drugs from human plasma and urine using response surface experimental designs†

The performance of microwave-assisted extraction and HPLC with photodiode array detection method for determination of six analgesic and anti-inflammatory drugs from plasma and urine, is described, optimized, and validated. Several parameters affecting the extraction technique were optimized using experimental designs. A four-factor (temperature, phosphate buffer pH 4.0 volume, extraction solvent volume, and time) hybrid experimental design was used for extraction optimization in plasma, and three-factor (temperature, extraction solvent volume, and time) Doehlert design was chosen to extraction optimization in urine. The use of desirability functions revealed the optimal extraction conditions as follows: 67°C, 4 mL phosphate buffer pH 4.0, 12 mL of ethyl acetate and 9 min, for plasma and the same volume of buffer and ethyl acetate, 115°C and 4 min for urine. Limits of detection ranged from 4 to 45 ng/mL in plasma and from 8 to 85 ng/mL in urine. The reproducibility evaluated at two concentration levels was less than 6.5% for both specimens. The recoveries were from 89 to 99% for plasma and from 83 to 99% for urine. The proposed method was successfully applied in plasma and urine samples obtained from analgesic users.