Optimization Of Experimental Variables Research Articles

Hydrogen production via gasification of corn stover: modeling and simulation using Aspen Plus®

The gasification of biomass is one of the most promising technologies for the sustainable production of hydrogen. Although several studies have been conducted on biomass gasification, a detailed numerical investigation of factors affecting hydrogen production and optimization of experimental variables are required. In addition, a comprehensive kinetic model that accounts for specific reactions encountered during biomass gasification is needed to simulate the effect of experimental conditions on hydrogen production. Therefore, in this study, a kinetic model for gasification of corn stover is developed and simulated in Aspen Plus®. Furthermore, the effect of key variables, i.e. gasification temperature, selection of proper gasifying agent, hydrogen production efficiency (HPE), higher heating value (HHV), and lower heating value (LHV), of the produced hydrogen have been investigated in order to select the optimal process conditions. Results indicate that a maximum HPE of 59% is obtained for steam gasification, whereas air gasification yielded an HPE of 26%, implying that steam as a gasifying agent demonstrated increased hydrogen production. Further, the optimized gasifying agent flow rate in both cases is observed to be 1200 kg/h (steam or air) at 900 °C. The energy and economic analysis of this study indicates the viability of the presented approach.

Bioremediation of Neonicotinoid Pesticide, Imidacloprid, Mediated by Bacillus cereus.

Imidacloprid, a toxic pesticide of the chloronicotinyl category, is employed extensively in agricultural fields, and its exposure causes serious health issues. Biodegradation is considered to be a green and economical approach to remediate pesticides. Herein, imidacloprid degradation efficiency of Bacillus sp. is highlighted, among which Bacillus cereus exhibited the greatest degradation; optimization of experimental variables (pH, imidacloprid and agitation time) via Box-Behnken factorial design and analysis of variance (ANOVA) revealed 92% biodegradation at the initial substrate concentration of 0.03 mM, aerobically in 11 days under favorable pH 7. The subsequent metabolites, identified through liquid chromatography-mass spectrometry, were 5-hydroxy imidacloprid, imidacloprid-guanidine and 6-chloronicotinic acid.

A Facile Strategy for Preparation of Yttrium-90 Therapeutic Sources for Radionuclide Therapy.

Background: Mold brachytherapy using high-energy β--emitting radioisotopes is a promising treatment modality for skin cancers and keloids. Simple methodologies for consistent and stable incorporation of radionuclides into the matrix are desired for preparation of therapeutic sources. Methods: The authors report a facile strategy for the stable incorporation of Yttrium-90 (90Y) into amidoxime-functionalized polyacrylonitrile-polyvinylidene fluoride (PAN-PVDF) membranes. The strategy consisted of surface modification of PAN-PVDF membranes by reaction with hydroxylamine, characterization of the functionalized membranes, and optimization of experimental variables for maximum loading of 90Y onto the membranes. Quality control tests essential for confirming the suitability of the 90Y therapeutic sources for human application, such as uniformity of activity distribution, absence of leaching of activity, and estimation of surface contamination, were performed. Theoretical calculations to estimate the dose imparted by the 90Y therapeutic sources at varying depths of tissue were also carried out to predict the possible therapeutic outcome of treatment. Results: A facile method for large-scale preparation of 90Y-based mold brachytherapy sources could be established. Conclusions: The source fabrication methodology standardized in this work could be tailored for fabrication of custom-made 90Y sources for individualized treatment of superficial tumors, Bowen's disease, and keloids.

Preconcentration of nickel in waters by vortex assisted dispersive liquid-liquid microextraction

AbstractThe present work describes the attempt for the preconcentration of nickel ions by using vortex assisted dispersive liquid-liquid microextraction from aqueous samples. In this method, a small amount of chloroform is rapidly injected by syringe into the water sample containing nickel ions complexed by diethyldithiocarbamate (DDTC).This forms a cloudy solution. The cloudy state is the result of chloroform fine droplets formation, which are dispersed in bulk aqueous sample. Therefore, Ni-DDTC complex is extracted into the fine chloroform droplets and vortex agitation takes place during six minutes. After optimization of experimental variables and determination of analytical characteristics, the method is evaluated for application in real samples. HPLC is used as separation and detection system.

Depositing a ZnxCd1−xS Shell around CdSe Core Nanocrystals via a Noninjection Approach in Aqueous Media

A ZnxCd1−xS shell was deposited around CdSe nanocrystal cores via a noninjection approach in aqueous media. The deposition of the ZnxCd1−xS shell around CdSe cores was carried out at 90 °C in a reaction flask consisting of the shell precursor compounds, together with CdSe nanocrystal cores and the capping reagent glutathione. This newly developed depositing approach uses CdCl2, Zn(OAc)2, and thiourea as Cd, Zn, and S sources, respectively. All of these chemicals were loaded at room temperature. The optical features and structure of the obtained CdSe/ZnxCd1−xS core/shell nanocrystals were characterized by UV−visible and photoluminescence spectroscopy, transmission electron microscopy, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. The influences of various experimental variables, including the Cd-to-Zn ratio, amounts of ligand and thiourea, as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. Through the optimization of experimental variables, the obtained water-soluble core/shell nanocrystals possess a maximum emission efficiency of 35% and a spectral width of less than 30 nm.

Determination of ultra trace amount of enrofloxacin by adsorptive cathodic stripping voltammetry using copper(II) as an intermediate

In this work, a simple and sensitive electroanalytical method was developed for the determination of enrofloxacin (ENRO) by adsorptive cathodic stripping voltammetry (ADSV) using Cu(II) as a suitable probe. The complex of copper(II) with ENRO was accumulated at the surface of a hanging mercury drop electrode at −0.10 V for 40 s. Then, the preconcentrated complex was reduced and the peak current was measured using square wave voltammetry (SWV). The optimization of experimental variables was conducted by experimental design and support vector machine (SVM) modeling. The model was used to find optimized values for the factors such as pH, Cu(II) concentration and accumulation potential. Under the optimized conditions, the peak current at −0.30 V is proportional to the concentration of ENRO over the range of 10.0–80.0 nmol L −1 with a detection limit of 0.33 nmol L −1. The influence of potential interfering substances on the determination of ENRO was examined. The method was successfully applied to determination of ENRO in plasma and pharmaceutical samples.

Characterization and optimization of experimental variables within a reproducible bladder encrustation model and in vitro evaluation of the efficacy of urease inhibitors for the prevention of medical device‐related encrustation

This study presents a reproducible, cost-effective in vitro encrustation model and, furthermore, describes the effects of components of the artificial urine and the presence of agents that modify the action of urease on encrustation on commercially available ureteral stents. The encrustation model involved the use of small-volume reactors (700 mL) containing artificial urine and employing an orbital incubator (at 37 degrees C) to ensure controlled stirring. The artificial urine contained sources of calcium and magnesium (both as chlorides), albumin and urease. Alteration of the ratio (% w/w) of calcium salt to magnesium salt affected the mass of encrustation, with the greatest encrustation noted whenever magnesium was excluded from the artificial urine. Increasing the concentration of albumin, designed to mimic the presence of protein in urine, significantly decreased the mass of both calcium and magnesium encrustation until a plateau was observed. Finally, exclusion of urease from the artificial urine significantly reduced encrustation due to the indirect effects of this enzyme on pH. Inclusion of the urease inhibitor, acetohydroxamic acid, or urease substrates (methylurea or ethylurea) into the artificial medium markedly reduced encrustation on ureteral stents. In conclusion, this study has described the design of a reproducible, cost-effective in vitro encrustation model. Encrustation was markedly reduced on biomaterials by the inclusion of agents that modify the action of urease. These agents may, therefore, offer a novel clinical approach to the control of encrustation on urological medical devices.

Por que otimização multivariada?

Normalmente, estudos que objetivam a otimização de variáveis experimentais são realizados através de procedimentos que avaliam o efeito de uma variável por vez, o que, de maneira geral, impede o estabelecimento de ótimos verdadeiros, em razão da freqüência com que as variáveis se apresentam altamente correlacionadas. Neste trabalho, algumas aplicações práticas são apresentadas, visando demonstrar a conveniência dos procedimentos multivariados de otimização, principalmente sistemas de planejamento fatorial de experimentos. A partir de três exemplos práticos relacionados com a otimização de processos de degradação, discutem-se aspectos relacionados com o desenho experimental e a interpretação de resultados.

Determination of Trace of Methyl tert-Butyl Ether in Water Using Liquid Drop Headspace Sampling and GC

The possibility of applying headspace microextraction into a single drop of solvent for the determination of methyl tert -butyl ether in aqueous solutions has been demonstrated. A drop of benzyl alcohol is used for extraction. The analyte is extracted by suspending a 1.8 μL extracting drop directly from the tip of a microsyringe fixed above an extraction vial with a septum such that the needle passes through the septum and the needle tip is positioned above the surface of the solution. After the extraction is finished, the drop is retracted back into the needle and injected directly into a GC column. Optimization of experimental variables (time, temperature, stirring rate and ionic strength of the solution) with respect to the extraction efficiency was investigated. The calibration range for methyl tert-butyl ether was 0.01–10 ppm and the detection limit 7 ppb. The relative standard deviation for 0.1 ppm methyl tert -butyl ether in water was 5.5%.

A biosensor monitoring DNA hybridization based on polyaniline intercalated graphite oxide nanocomposite

Polyaniline intercalated graphite oxide nanocomposite (PAI/GO) was synthesized. The microstructure of PAI/GO were investigated using Fourier transform infrared spectrometer (FT-IR), X-ray diffractometer (XRD), transmission electron microscope (TEM) and atomic force microscope (AFM). The results show that polyaniline intercalated between interlayers of GO, changes the structure of GO greatly forming nanograins in the chain and helix-like form. The resulting nanocomposite enveloped in carbon paste electrode displays electrochemical activity and two sharp peak potentials of square wave voltammometry (SWV) are at 668 and 207 mV. Such characteristics of PAI/GO have been employed to investigate the interaction between DNA and PAI/GO. The results indicate that single-strand DNA (ssDNA) and double-strand DNA (dsDNA) can change redox characteristics of PAI/GO on the PAI/GO modified carbon paste electrode (CPE) and the modified electrode has strong electrochemical effect on the redox of ssDNA and dsDNA. The SWV redox potentials in ssDNA and dsDNA solution are 90.99 and 18 mV, respectively. The PAI/GO-modified electrode immobilized with ssDNA can be utilized to monitor hybridization of complementary ssDNA with hybridization peak at −270 mV. The influence of various experimental parameters on PAI/GO-modified CPE in ssDNA solution (i.e. frequency and amplitude of SWV, pH and incubation time) was investigated. Under optimization of experimental variables, a linear relationship between the peak current ( E p is around 90.99 mV) recorded with the electrode not immobilized by ssDNA and the ssDNA concentration in solution was obtained covering range from 34 to 241 μg/mL. And the modified electrode immobilized by ssDNA can be utilized to monitor the hybridization and detect complementary ssDNA, covering linear range from 275 to 551 μg/mL. The PAI/GO-modified CPE exhibited a good stability and reproducibility for detecting ssDNA.

Optimization of experimental variables in the dabsyl chloride derivatization of biogenic amines for their determination by RP-HPLC

In the last few years special attention has been paid to the pre-column derivatization of biogenic amines with dabsyl chloride because proper experimental conditions for this reaction are very important. In this study, an experimental design (Doehlert design) was used to optimize the variables involved in the dabsylation of the following amines: histamine, tyramine, phenylethylamine, tryptamine, cadaverine, putrescine, spermidine, and spermine. The optimum experimental conditions for forming the dabsyl derivatives are: reagent concentration, 1.75.10−3 M; pH, 8.2; temperature, 70°C; heating time (t h ), 21 min. Under these conditions good chromatographic repeatability is obtained.

The application of Doehlert designs in the optimization of experimental variables in solid phase spectrophotometry

The optimization of experimental variables may be correctly performed by the use of an appropriate experimental design from which the optimum values of such variables are simultaneously obtained. Three level designs allow us to fit experimental data to 2nd grade polynomial functions, and a suitable study of such functions makes it possible to find the optimum region from relatively few iterations. The Doehlert designs possess a suitable structure for this purpose, and thus from a single design one can locate the optimum region with reasonable accuracy, and if greater exactitude is required, it is only necessary to employ a second design in the previously located region. Another consideration is that these designs comprehend a great capacity for displacement across the variables' experimental domain, which means that a substantial quantity of data from one design can be used for the following experiment. With the application of the Doehlert designs in solid phase spectrophotometry, the optimization of variables can be performed simply, quickly and with greater efficiency compared to traditional methodology.

Sealed inductively coupled plasma atomic emission spectrometry. Part 3. Optimization of experimental variables

Experimental variables for a sealed inductively coupled plasma (ICP) argon discharge are investigated and optimized for the emission spectroscopic determination of arsenic and phosphorus introduced as arsine and phosphine. Important parameters include generator power, gas modifier mixture, discharge container geometry, operating pressure and operating procedure. Less important are the total gas flow rate, container preparation and construction and induction coil geometry. The optimum geometry is a 40 mm quartz sphere with a larger induction coil (≈45 mm in diameter). Detection limits for arsenic and phosphorus are in the low ppb range for a 950 W, 27.12 MHz argon–4% hydrogen ICP.