Preliminary investigation on biosorption mechanism of 241Am by Rhizopus arrhizus

As an important radioisotope in nuclear industry and other fields, ²⁴¹Am is one of the most serious contamination concerns due to its high radiation toxicity and long half-life. Encouraging biosorption of ²⁴¹Am from aqueous solutions by free or immobilized Rhizopus arrhizus (R. arrhizus) has been observed in our experiments. In this study, the preliminary evaluation on the mechanism was further explored via chemical or biological modification of R. arrhizus using europium as a substitute for americium. The results indicated that in approximately 48 hours R. arrhizus was able for efficient adsorption of ²⁴¹Am. The pH value of solutions decreased gradually with the uptake of ²⁴¹Am by R. arrhizus, implying that H⁺ was released from R. arrhizus via ion-exchange. The biosorption of ²⁴¹Am by the decomposed cell wall of R. arrhizus was as efficient as by the intact fungus. The adsorption ratio for ²⁴¹Am by deacylated R. arrhizus dropped, implying that carboxyl functional groups of R. arrhizus play an important role in the biosorption of ²⁴¹Am. Most of the investigated acidic ions have no significant influence on the adsorption of ²⁴¹Am, while saturated EDTA can strongly inhibit the biosorption of ²⁴¹Am by R. arrhizus. When the concentrations of coexistent Eu³⁺, Nd³⁺ were 300 times more than that of ²⁴¹Am, the adsorption ratios would decrease to about 86% from more than 99%. It could be noted by transmission electron microscope (TEM) analysis that the adsorbed Eu is scattered almost in the whole fungus, while Rutherford backscattering spectrometry (RBS) indicated that Ca in R. arrhizus have been replaced by Eu via ion-exchange. The change of the absorption peak structure in the IR spectra implied that there was complexation between metals and microorganism. The results implied that the adsorption mechanism of ²⁴¹Am by R. arrhizus is very complicated involved ion-exchange, complexation process as well as nonspecific adsorption in the cell wall by static electricity.     

Microbial enhance of chitosan production by Rhizopus arrhizus using agroindustrial substrates

This study investigated the potential of Rhizopus arrhizus UCP 402 for producing chitosan using corn steep liquor and honey as agroindustrial nitrogen and carbon sources. A complete factorial design was used to assess the improved biomass and chitosan production. The results were evaluated using Pareto charts (Statistica 7.0 software). The chitosan obtained was characterized by X-ray diffraction. The cristallinity index (I(C)), and infrared spectroscopy (FTIR) were used to evaluate the degree of deacetylation (DD %). The morphological aspects of the R. arrhizus were evaluated by measuring the diameter of the colonies by light microscopy. The results obtained showed higher biomass and chitosan yields (20.61 g/L and 29.3 mg/g), respectively, in the selected assays. The characterization of the macromolecular arrangement of chitosan showed a crystallinity index compatible with the literature, and the infrared peaks confirmed a degree of 86%. The experimental data obtained suggest that adding honey to corn steep liquor is a promising way to improve microbiological chitosan production.     

Highly efficient bio-sorption of trivalent f-elements using wild type Rhizopus arrhizus dead fungus

Journal of Radioanalytical and Nuclear Chemistry - Wild type Rhizopus arrhizus biomass was demonstrated as highly efficient bio-sorbent for trivalent f-elements. Both Am3+ and Eu3+ were found to...     

Carbohydrate sensing with a metal-based indicator displacement assay

A Pd-based indicator displacement assay for the fluorimetric sensing of carbohydrates has been developed. The assay allows the detection of saccharides in the low millimolar concentration range in water at neutral pH.     

Accuracy and precision of a coulometric titration technique with mercaptans as test compounds

A coulometric determination of mercaptan sulfur, concentrating on the effect of quantity and structure of mercaptans on the accuracy and reproducibility of their quantitative determination, is described. A series of pure mercaptans were used as test compounds. A potentiometric endpoint detection technique was devised consisting of a sulfide-sensitive electrode as the indicator electrode and a calomel electrode as the reference electrode. A silver electrode acted as the generator anode and a platinum electrode as the cathode. The measurements were performed in an ethanolic solution of NH₄OH and NH₄NO₃ as supporting electrolytes. The accuracy of mercaptan determination corresponding to 168.20–15.00 μg of mercaptan sulfur varied from ±1 to ±4% except for sec- and tert-butyl mercaptans at their lowest concentrations. Furthermore, the presence of a branched alkane chain increased the percentage error, while the presence of a phenyl group decreased the error.     

Chelometric titration of calcium using a mixed indicator

A mixed indicator for the chelometric titration of calcium has promise fur the determination of microgram amounts of calcium in the presence of relatively high concentrations of other ions. Potassium cyanide eliminates the interference of certain metals. Addition of methyl alcohol improves the visibility of the end-point in a semimicro titration of calcium, although it does not improve the end-point for macro titrations.This indicator also may be useful in the determination of magnesium after calcium has been removed from the sample.     

A novel titration technique for the analysis of streamed samples — the triangle-programmed titration technique : Part 3. Titrations with Electrically Generated Bromine

The triangle-programmed titration technique brings together the advantages of flow-through techniques and titration methods. Titrations with bromine prepared by current-programmed electrolysis are reported; suitable instrumentation is described for biamperometric end-point indication. The electrode processes and the effects of different parameters of the reagent addition program are discussed. The applicability of the method to organic and inorganic substances is described. The technique is applicable to flowing sample solutions of small volume, and the rate of analysis is similar to that achieved with other semi-automated analyzers.     

Constant-current potentiometric titration of orthophosphate with cetylpyridinium chloride: a feasibility study

The feasibility of constant-current potentiometric titration of orthophosphate with cetylpyridinium chloride has been studied. The phosphate solution is acidified with hydrochloric acid to pH 1.1-1.3 and an excess of molybdate solution added. For l mg of phosphorus (as phosphate) the optimum Mo:P ratio is about 40. Cetylpyridinium chloride reacts stoichiometrically with 12-molybdophosphate, in 3:1 ratio. The optimum cathodic polarizing current is 1.1 muA. The blanks for molybdate are relatively small, constant and non-stoichiometric.     

Direct complexometric titration of thorium with versene using SPADNS

Summary The existing volumetric methods for the determination of thorium are indirect and unsatisfactory. A direct titrimetric method for the estimation of thorium has been developed which involves the adjustment ofph, addition of 1 ml. of 0.02% SPADNS indicator, dilution to volume and titration with versene. It is based on the fact that thorium forms a coloured complex with SPADNS and after the bulk of thorium has reacted with versene, the highly coloured thorium- indicator complex is destroyed, marking the end point. Quantity of thorium as small as 5 mg. can be titrated accurately when present in a volume of 50 ml. Determination of thorium can also be made in presence of large amount of iron by adding ascorbic acid prior to the titration. Interferences of various ions have also been studied. The method proposed for thorium is selective and should be of considerable use in many cases.The author's thanks are due to Dr. A. K. Ghosal, Principal Darjeeling Government College, for providing all laboratory facilities and Dr. A. K. Mukherjee, Indian Association for the Cultivation of Science, Calcutta for his kind help in the work.     

Determination of cationic polyelectrolytes using a photometric titration with crystal violet as a color indicator

The reaction of the cationic dye, crystal violet (CV) with the anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) results in a decrease of the absorbance of CV at the maximum absorption wavelength (590 nm). This change of the absorption spectra of the CV has been already applied to the determination of anionic polyelectrolytes using flow injection analysis method. In this paper, CV was applied to the indicator for the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by photometric titration, using a PVSK solution as a titrant. The end-point of the titration is detected as the break point of the titration curve. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 0 to 5×10⁻⁵ eq. mol dm⁻³ for Cat-floc, glycol chitosan and methylglycol chitosan. The effects of the concentration of CV and coexisting electrolytes in the sample solution and the effect of pH of the sample solution on the degree of the change of absorbance at the end-point were also examined.     

Critical comparison of evaluation methods of potentiometric titration data using a microcomputer-controlled automatic potentiometric titration system

A microcomputer-controlled automatic potentiometric titrator withP controlled intelligent auto-sampler has been built for serial analysis. Controlling and evaluating programs have also been written. In order to use the most powerful evaluating method, a comparison was made between the methods. The data of the titration curves were obtained by the implicit relation characterizing the curve. The different evaluating methods were tested by using these data. The effects of random errors stemming from measurements were also investigated. The methods used were: two point differentiating formula, differentiation of interpolating and smoothing spline functions, the Gran method, and implicit regression with the Gauss-Newton-Marquardt method. Regression is outstanding among the methods, but it needs much more computing time compared with others. The second-best method is the differentiation with smoothing spline function with end point determination based on finding the sign reversal of the second derivative. This method is much faster than regression.     

The titration of clay minerals I. Discontinuous backtitration technique combined with CEC measurements

Evolution of liquid holdup profile in a standing foam formed by whipping and stabilized by sodium caseinate in the presence of xanthan gum when subjected to 16 and 29g centrifugal force fields was measured using magnetic resonance imaging for different pH, ionic strength, protein and xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Foam drainage was slowest at pH 7, lower ionic strength, higher protein and gum concentrations. Foam was found to be most stable at pH 5.1 near the isoelectric point of protein, lower ionic strength and higher protein and xanthan gum concentrations. A predicted equilibrium liquid holdup profile based on a previous model (G. Narsimhan, J. Food Eng. 14 (1991) 139) agreed well with experimental values at sufficiently long times. A proposed model for velocity of drainage of a power law fluid in a Plateau border for two different simplified geometries was incorporated in a previously developed model for foam drainage (G. Narsimhan, J. Food Eng. 14 (1991) 139) to predict the evolution of liquid holdup profiles. The model predictions for simplified circular geometry of Plateau border compared well with the experimental data of liquid holdup profiles at small times. At longer times, however, the predicted liquid holdup profile was larger than the observed, this discrepancy being due to coarsening of bubble size and decrease in foam height not accounted for in the model. A Newtonian model for foam drainage under predicted drainage rates did not agree with the experimental data.     

Spectrophotometric titration of ionisable groups in proteins: a theoretical study

A simple theoretical model is proposed for evaluation of the optical titration behaviour of tyrosyl and carboxyl residues in proteins. The pK values involved in the model are computed using the semi-empirical method. The titration curves are calculated using the values of the molar absorption differences for tyrosyl residues in the ultraviolet (UV) region at 245 and 295 nm, and for carboxyl residues in the infrared (IR) region at 1565 and 1707 cm(-1), respectively. The theoretical tyrosyl titration curves are compared with the experimental data for lysozyme, myoglobin and chymotrypsinogen (available in the literature). This approach provides a good tool for distinguishing between the ionisation and the conformational changes in the alkaline range. The quantitative evaluation of the change of molar extinction coefficients as a function of pH in the case of carboxyl titration for lysozyme, trypsin and cytochrome c shows a good agreement with the experimental titration data.     

Potentiometric titration of tellurium with a fluoride-selective electrode

Tellurium, as tellurite, can be determined with a fluoride-selective electrode by means of an indirect procedure based on precipitation of tellurite with excess of lanthanum(III), followed by back-titration with standard fluoride. The end-point is located by using the Gran method, and the titrations are suitable for tellurite concentrations above 1 mM.     

A dielectric study of poly(vinyl acetate) using a pulse-probe technique

There is considerable literature available that describes our understanding of the viscoelastic properties of polymers subjected to mechanical stresses or deformations. What we refer to here as a pulse-probe technique is one method that is commonly used to study the time-dependent behavior of materials in histories, e.g., temperature-jump or step-deformations, that exhibit fading memory responses. In the linear case the behavior is well understood in the context of Boltzmann superposition ideas. However, there is only limited work available that investigates the dielectric response of materials within this same context. In the present study, we present an investigation of the dielectric behavior of poly(vinyl acetate) (PVAc) using a two-step pulse-probe technique. Time domain dielectric experiments were performed in the vicinity of the glass transition temperature. After establishing the linear response function in single-step experiments, two types of pulse-probe experiments were performed. In one, the time duration t ₁ of the first step in the probe was varied. In the second case, the magnitude of the field E ₁ applied to the sample for the first step was varied. We not only demonstrate the existence of the memory effect in the dielectric response, but also find that the responses are consistent with the linear Boltzmann superposition principle. Evidence of deviations from linear superposition at the highest electric fields is also presented.     

Hydrating peptides using a sprouting technique

A scheme for generating water coordinates, whose proton orientations are random, and simultaneously generating side chain coordinates of peptides, preparatory to studying solvation of peptides using molecular dynamics schemes is presented in an X-PLOR context. Examples from the Integrin and Tropomyosin systems are used to illustrate the procedure. © 1994 by John Wiley & Sons, Inc.     

On the accuracy of micro Winkler titration procedures: a case study

Accuracy data (expressed as precision and trueness) presented by the authors of three different micro modifications of the Winkler titration procedure for dissolved oxygen concentration determination are critically evaluated. Tentative uncertainty estimates are extracted from the data based on the single-laboratory validation approach (originally published in the Nordtest Technical Report 537) and they lead to expanded uncertainty (k = 2) estimates in the range from 0.13 to 0.27 mg l⁻¹ for the three procedures. It is demonstrated that, in all cases, the authors have presented the accuracy and/or precision estimates of the procedures in a way that can lead to too optimistic conclusions about the uncertainty of their procedures. This case study demonstrates the usefulness and flexibility of the single-laboratory validation approach to uncertainty estimation, even in the case of insufficient data, and can be of interest to laboratory workers dealing with measurement procedures from the literature. It is also expected to be of interest to university instructors of analytical chemistry and metrology in chemistry as a real-life example of the critical evaluation of the literature data. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.