没食子酸修饰的超高交联吸附树脂对2,4-二氯苯氧乙酸的吸附性能研究

通过后交联反应和化学修饰反应制备了没食子酸修饰的超高交联吸附树脂(GAMR),以大孔吸附树脂XAD-4树脂为对照,研究了GAMR对水中2,4-二氯苯氧乙酸(2,4-D)的吸附性能.实验结果表明:GAMR具有较丰富的微孔,比表面积和微孔面积分别为1 232.3和899.5 m²·g^-1.GAMR对2,4-D的吸附动力学过程符合准一级动力学方程,吸附过程同时存在物理吸附和化学吸附.Freundlich等温方程能较好地拟合GAMR对2,4-D的吸附等温线.GAMR对2,4-D吸附过程的ΔG为负值,ΔH和ΔS均大于0,表明吸附是自发、吸热和熵增加的过程.与XAD-4相比,所制备的GAMR对2,4-D的吸附去除率显著提高.     

Validated high-performance thin-layer chromatographic method for quantification of gallic acid and ellagic acid in fruits of Terminalia chebula,Phyllanthus emblica,and Quercus infectoria

A simple and rapid high-performance thin-layer chromatographic method for quantification of gallic acid and ellagic acid in dried fruits of Terminalia chebula, Phyllanthus emblica, and Quercus infectoria has been developed. The chromatographic development was carried out on precoated silica gel 60 F₂₅₄ plates in a mixture of toluene:ethyl acetate:chloroform:formic acid (4:8:1:3 v/v/v/v). The plate was scanned densitometrically at a wavelength of 280 nm. The retention factor value of gallic acid and ellagic acid was found to be 0.63 ± 0.2 and 0.53 ± 0.1, respectively. The developed method was validated in terms of linearity, precision, accuracy, sensitivity, robustness, specificity and stability as per the international conference of harmonization guidelines. The method showed good linear relationship over a range of 100–600 ng/band (gallic acid) and 100–500 ng/band (ellagic acid) with a regression coefficient (r²) of 0.997 (gallic acid) and 0.996 (ellagic acid). The method showed high accuracy (99.65%–100.85%). The percentage relative standard deviation of intra-day and inter-day precision studies was not more than 2%. The method is highly robust and has displayed high specificity. The developed method is new, simple, and accurate and can be successfully employed in routine analysis of raw materials and formulations containing gallic acid and ellagic acid.     

Exploring the potential of biodiesel derived crude glycerol into high value malic acid: Biosynthesis,process optimization and kinetic assessment

In this study, Zygosaccharomyces rouxii, a sugar tolerant yeast culture was explored for the production of high value malic acid using crude glycerol from biodiesel plant. In addition, the effect of addition of glutamic acid (precursor) (0.25 to 1%), temperature (15 to 30 ​°C) and time (0 to 24 days) of the fermentation process was also investigated by both conventional as well as Response Surface Methodology (RSM). The highest malic acid of 72.1 ​± ​0.05 ​g/L was obtained and RSM predicts the accurate optimized conditions such as 30% crude glycerol concentration in the fermentative media with 0.75% addition of precursor with initial pH 5 ​at 20 ​°C for 20 days. This study reveals that the crude glycerol can be efficiently used and the production of malic acid was raised with 3 folds correspond to no precursor under optimal conditions. The growth and product kinetics were studied by Monod, Logistic, Leudeking Piret as well as Logistic incorporated Leudeking-Piret models with and without precursor and Logistic incorporated Leudeking-Piret model allowed the best fit for the malic acid production.     

Determination of homogentisic acid in urine for diagnosis of alcaptonuria: Capillary electrophoretic method optimization using experimental design

Homogentisic acid (HGA) is a diagnostic metabolite that accumulates in the urine and tissues of patients with alkaptonuria which is a rare autosomal recessive disease. HGA is a specific metabolite in urine and serum, which is used for diagnosis of alkaptonuria. This study presents an inexpensive and easy capillary electrophoretic method for the quantitative determination of HGA in urine samples. The method was optimized using full factorial experimental design. The optimal separation electrolyte and separation voltage were revealed as 45 mmol/L phosphate buffer at pH 7.0 and 22 kV, respectively. Under these conditions the presence of HGA was detected in 6 min. Repeatability of migration times and corrected peak areas of HGA (as RSD) were 0.37 and 1.99, respectively. The detection limit was 0.56 μg/mL, 3 times of the average noise, and the quantification limit was 1.85 μg/mL, 10 times the average noise for HGA. Urine samples were directly injected to the capillary without any pretreatment step.     

Factorial design for optimization of experimental variables in preconcentration of copper by a chromotropic acid loaded Q-Sepharose adsorbent

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5 ml portion of a 0.02 mol l⁻¹ HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18 mol l⁻¹ sodium nitrate in the matrix. A 5 ml portion of a 0.02 mol l⁻¹ CTA was sufficient for loading of a 0.5 ml column prior to preconcentration of copper from a 150 ml sample solution. Matrix ions of Ca²⁺, Mg²⁺, Na⁺ and K⁺ and potentially interfering ions of Pb²⁺, Ni²⁺, Cd²⁺, Co²⁺, Zn²⁺ and Mn²⁺ with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0 μg l⁻¹ was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.     

Chemiluminescence method for the assay of perphenazine in drug formulation using permanganate in sulphuric acid with flow injection technique and a chemometrical optimization approach

An accurate selective flow injection chemiluminescence (CL) method for the assay of perphenazine was explored. In the method 394 ppm permanganate solution was used as a chemiluminogenic reagent in 0.289 mol dm⁻³ sulphuric acid media. A photomultiplier tube was used as a detector at a total flow rate of 4.94 ml/min. Perphenazine was determined by a linear calibration plot of the following equation in the range 50–350 ppm: mV=−4.488+0.1162C, with a correlation coefficient of 0.9989 for five measurements and a relative standard deviation less than 2.33. A sampling frequency not less than 110 samples h⁻¹ was established. Three factors namely, the flow rate, sulphuric acid and permanganate concentrations were found to have an influence on the amount of chemiluminescence intensity produced. Therefore, their interaction effects were thoroughly investigated by employing the 2³ factorial design chemometrical approach and the results obtained revealed a higher interaction between sulphuric acid and permanganate and a less significant interaction for both reagents with the flow rate. The interaction of variables observed necessitated the conduct of the super modified simplex optimization procedure which has resulted in offering the proper optimum conditions as stated above and led to the quantitative assay of perphenazine. An interference study indicated that the method was suitable for application in pharmaceutical preparations.     

Evaluation of optimization techniques for an extractive alcoholic fermentation process

The mathematical optimization of a continuous alcoholic fermentation process combined with a flash column under vacuum was studied. The objective was to maximize % yield and productivity in the fermentor. The results using surface response analysis combined with modeling and simulation were compared withy those obtained when the problem was written as a nonlinear programming problem and was solved with a successive quadratic programming (SQP) technique. Two process models were evaluated when the process was optimized using the SQP technique. The first one is a deterministic model, whose kinetic parameters were experimentally determined as functions of the temperature, and the second is a statistical model obtained using the factorial design technique combined with simulation. Although the best result was the one obtained using the rigorous model, the values for productivity and % yield obtained using the simplified model are acceptable, and these models can be used when the development of a rigorous model is excessively difficult, slow, or expensive.     

Catalytic adsorptive stripping voltammetry determination of ultra trace amount of molybdenum using factorial design for optimization

A highly sensitive procedure is presented for the determination of ultra-trace concentration of molybdenum by catalytic adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the molybdenum (Mo)-pyrocatechol violet (PCV) complex on to a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by chlorate. The influence of variables was completely studied by factorial design analysis. Optimum analytical conditions for the determination of molybdenum were established. Molybdenum can be determined in the range 1.0 × 10⁻³-100.0 ng ml⁻¹ with a limit of detection of 0.2 pg ml⁻¹. The influence of potential interfering ions on the determination of molybdenum was studied. The procedure was applied to the determination of molybdenum in mineral water and some analytical grade substances with satisfactory results.     

Sequential and simultaneous statistical optimization by dynamic design of experiment for peptide overexpression in recombinant Escherichia coli

The production of recombinant anti-HIV peptide, T-20, in Escherichia coli was optimized by statistical experimental designs (successive designs with multifators) such as 2^4–1 fractional factorial, 2³ full factorial, and 2² rotational central composite design in order. The effects of media compositions (glucose, NPK sources, MgSO₄, and trace elements), induction level, induction timing (optical density at induction process), and induction duration (culture time after induction) on T-20 production were studied by using a statistical response surface method. A series of iterative experimental designs was employed to determine optimal fermentation conditions (media and process factors). Optimal ranges characterized by %T-20 (proportion of pepttide to the total cell protein) were observed, narrowed down, and further investigated to determine the optimal combination of culture conditions, which was as follows: 9, 6, 10, and 1 mL of glucose, NPK sources, MgSO₄, and trace elements, respectively, in a total of 100 mL of medium inducted at an OD of 0.55–0.75 with 0.7 mM isopropyl-β-d-thiogalactopyranoside in an induction duration of 4 h. Under these conditions, up to 14% of T-20 was obtained. This statistical optimization allowed, the production of T-20 to be increased more than twofold (from 6 to 14%) within, a shorter induction duration (from 6 to 4 h) at the shake-flask scale. Coauthors.     

Screening of mixed poly(ethylene oxide) solutions for microchip separation of double-stranded DNA using an orthogonal design approach

We describe a quick and systematic optimization of molecular weights (MWs) and concentrations of a series of mixed poly(ethylene oxide) (PEO) matrices for separating specific double-stranded DNA fragments on polymethylmethacrylate-based microchips by using an orthogonal design (ORD) approach. The mixed matrices are composed of PEOs in four MW ranges (M(w) 8 x 10(6), 1 x 10(6), 4 x 10(5), and 1 x 10(5)) with varying concentration ratios. In the mixed solutions, PEO with an intermediate MW of 4 x 10(5) is found to be a dominant factor for separating small DNA fragment pairs (e.g., 82 and 88 bp), while PEO with a high MW of 8 x 10(6) plays an important role in separating intermediate and large fragments (e.g., 271 and 281 bp, 506 and 517 bp, 7 and 10 kbp). High-concentration PEO mixtures give better resolution for short fragments, while dilute PEO mixtures show better resolution for long fragments. The optimized matrices are suitable for high-resolution separation of multiplex polymerase chain reaction-amplified products and restriction digest fragments ranging in size from 20 bp to 40 kbp within 4 min at a constant field strength of 177 V/cm. The experimental results indicate the robustness and speediness of the ORD to screen the contribution of PEO MWs and to tune optimally the PEO concentration ratio of different MWs with reference to the performance of specific DNA fragments separated.     

Stepwise optimization approach for improving LC‐MS/MS analysis of zwitterionic antiepileptic drugs with implementation of experimental design

In this article, a step‐by‐step optimization procedure for improving analyte response with implementation of experimental design is described. Zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, were chosen as model compounds to undergo chloroformate‐mediated derivatization followed by liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS) analysis. Application of a planned stepwise optimization procedure allowed responses of analytes, expressed as areas and signal‐to‐noise ratios, to be improved, enabling achievement of lower limit of detection values. Results from the current study demonstrate that optimization of parameters such as scan time, geometry of ion source, sheath and auxiliary gas pressure, capillary temperature, collision pressure and mobile phase composition can have a positive impact on sensitivity of LC‐MS/MS methods. Optimization of LC and MS parameters led to a total increment of 53.9%, 83.3% and 95.7% in areas of derivatized vigabatrin, pregabalin and gabapentin, respectively, while for signal‐to‐noise values, an improvement of 140.0%, 93.6% and 124.0% was achieved, compared to autotune settings. After defining the final optimal conditions, a time‐segmented method was validated for the determination of mentioned drugs in plasma. The method proved to be accurate and precise with excellent linearity for the tested concentration range (40.0 ng ml^?1–10.0 × 10³ ng ml^?1). Copyright © 2013 John Wiley & Sons, Ltd.     

A mild and efficient reaction for conversion of carboxylic acids into acid bromides with ethyl tribromoacetate/triphenylphosphine under acid-free conditions

Acid bromides were prepared efficiently from carboxylic acids with readily available ethyl tribromoacetate and triphenylphosphine at room temperature under neutral conditions. The present process is applicable to the preparation of various acid bromides from aromatic and aliphatic carboxylic acids. Aromatic carboxylic acids were found to be more reactive than aliphatic carboxylic acids under reaction conditions.     

A new multiresponse optimization approach in combination with a D-Optimal experimental design for the determination of biogenic amines in fish by HPLC-FLD

A new strategy to approach multiresponse optimization in conjunction to a D-optimal design for simultaneously optimizing a large number of experimental factors is proposed. The procedure is applied to the determination of biogenic amines (histamine, putrescine, cadaverine, tyramine, tryptamine, 2-phenylethylamine, spermine and spermidine) in swordfish by HPLC-FLD after extraction with an acid and subsequent derivatization with dansyl chloride. Firstly, the extraction from a solid matrix and the derivatization of the extract are optimized. Ten experimental factors involved in both stages are studied, seven of them at two levels and the remaining at three levels; the use of a D-optimal design leads to optimize the ten experimental variables, significantly reducing by a factor of 67 the experimental effort needed but guaranteeing the quality of the estimates. A model with 19 coefficients, which includes those corresponding to the main effects and two possible interactions, is fitted to the peak area of each amine. Then, the validated models are used to predict the response (peak area) of the 3456 experiments of the complete factorial design. The variability among peak areas ranges from 13.5 for 2-phenylethylamine to 122.5 for spermine, which shows, to a certain extent, the high and different effect of the pretreatment on the responses. Then the percentiles are calculated from the peak areas of each amine. As the experimental conditions are in conflict, the optimal solution for the multiresponse optimization is chosen from among those which have all the responses greater than a certain percentile for all the amines. The developed procedure reaches decision limits down to 2.5 μg L⁻¹ for cadaverine or 497 μg L⁻¹ for histamine in solvent and 0.07 mg kg⁻¹ and 14.81 mg kg⁻¹ in fish (probability of false positive equal to 0.05), respectively.     

A novel homocystine-agarose adsorbent for separation and preconcentration of nickel in table salt and baking soda using factorial design optimization of the experimental conditions

Homocystine was for the first time, chemically linked to a highly cross-linked agarose support (Novarose) to be employed as a chelating adsorbent for preconcentration and AAS determination of nickel in table salt and baking soda. Nickel is quantitatively adsorbed on a small column packed with 0.25 ml of the adsorbent, in a pH range of 5.5–6.5 and simply eluted with 5 ml of a 1 mol l⁻¹ hydrochloric acid solution.

A factorial design was used for optimization of the effects of five different variables on the recovery of nickel. The results indicated that the factors of flow rate and column length, and the interactions between pH and sample volume are significant.

In the optimized conditions, the column could tolerate salt concentrations up to 0.5 mol l⁻¹ and sample volumes beyond 500 ml. Matrix ions of Mg²⁺ and Ca²⁺, with a concentration of 200 mg l⁻¹, and potentially interfering ions of Cd²⁺, Cu²⁺, Zn²⁺ and Mn²⁺, with a concentration of 10 mg l⁻¹, did not have significant effect on the analyte's signal. Preconcentration factors up to 100 and a detection limit of 0.49 μg l⁻¹, corresponding to an enrichment volume of 500 ml, were obtained for the determination of the analyte by flame AAS. Application of the method to the determination of natural and spiked nickel in table salt and baking soda solutions resulted in quantitative recoveries. Direct ETAAS determination of nickel in the same samples was not possible because of a high background observed.     

Use of fractional factorial design for optimization of digestion procedures followed by multi-element determination of essential and non-essential elements in nuts using ICP-OES technique

Two digestion procedures have been tested on nut samples for application in the determination of essential (Cr, Cu, Fe, Mg, Mn, Zn) and non-essential (Al, Ba, Cd, Pb) elements by inductively coupled plasma-optical emission spectrometry (ICP-OES). These included wet digestions with HNO₃/H₂SO₄ and HNO₃/H₂SO₄/H₂O₂. The later one is recommended for better analytes recoveries (relative error < 11%). Two calibrations (aqueous standard and standard addition) procedures were studied and proved that standard addition was preferable for all analytes. Experimental designs for seven factors (HNO₃, H₂SO₄ and H₂O₂ volumes, digestion time, pre-digestion time, temperature of the hot plate and sample weight) were used for optimization of sample digestion procedures. For this purpose Plackett-Burman fractional factorial design, which involve eight experiments was adopted. The factors HNO₃ and H₂O₂ volume, and the digestion time were found to be the most important parameters. The instrumental conditions were also optimized (using peanut matrix rather than aqueous standard solutions) considering radio-frequency (rf) incident power, nebulizer argon gas flow rate and sample uptake flow rate. The analytical performance, such as limits of detection (LOD < 0.74 μg g⁻¹), precision of the overall procedures (relative standard deviation between 2.0 and 8.2%) and accuracy (relative errors between 0.4 and 11%) were assessed statistically to evaluate the developed analytical procedures. The good agreement between measured and certified values for all analytes (relative error <11%) with respect to IAEA-331 (spinach leaves) and IAEA-359 (cabbage) indicates that the developed analytical method is well suited for further studies on the fate of major elements in nuts and possibly similar matrices.     

Temperature program optimization by computer simulation for the capillary GC analysis of fatty acid methyl esters on biscyanopropyl siloxane phases

The selectivity of capillary columns coated with biscyanopropyl siloxane stationary phases for the separation of fatty acid methyl esters has been optimized by means of computer-assisted column temperature optimization software. Temperature programming rates yielding the highest resolution in the shortest analysis time were selected for split, splitless, and on-column injection operated in the constant pressure and pressure programmed modes.     

Experimental design in the optimization of a microwave acid digestion procedure for the determination of metals in biomorphic ceramic samples by inductively coupled plasma mass spectrometry and atomic absorption spectrometry

In the present paper, we have synthesized a biomorphic ceramic material from oak wood as biological template structure and infiltration with zirconia-sol. After the material characterization, we have optimized the sample dissolution by acid attack in an oven under microwave irradiation. Experimental designs were used as a multivariate strategy for the effect's evaluation of varying several variables. This article describes the development by response surface methodology (RSM) of a procedure for zirconium determination, and other ions, such as copper and nickel by inductively coupled plasma mass spectrometry (ICP-MS) and others, such as iron, calcium and magnesium determination by flame atomic absorption spectrometry (FAAS) in the synthesized sample after digestion. A full factorial design (3³) was used to find optimal conditions for the procedure through response surface study. Three variables (time, HNO₃ volume and HF volume) were regarded as factors and as response to the concentration of different metal ions in the optimization study.