Rapid fluorimetric assay for primary amine groups in water samples

Bond Elut C₁₈ solid-phase extraction cartridges were used for pre-concentration followed by derivatization with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) of primary amines in water. Optimal conditions were: conditioning the cartridges with borate buffer pH 10.4, retention of the primary amines, addition of the OPA-NAC(3.7 mmol L^–1) 1:1 molar ratio and borate buffer pH 8, elution of the isoindol with MeOH-borate buffer (9:1) pH 10.2 and fluorescence measurement. The equations of the calibration graphs for methylamine, ethylamine, propylamine, butylamine, pentylamine, and -phenylethylamine at _excitation=330 nm and _emission=440 nm, in the optimal conditions are presented. The solid-phase extraction procedure improved ten times the detection limits of the solution derivatization. Those values are in the 0.01–0.06 mg L^–1 interval in function of the amine. Also, it is possible to estimate the total primary aliphatic amine concentration in water, expressed as molar concentration of –NH₂ group or –NH₂-N mg L^–1. On the basis of these studies, the method was applied for the determination of primary amino groups in tap, ground, factory and source water samples.     

Detection and colorimetric determination of the cr04-2 ion with o-dianisidine

A new method is described for the colonmetric determination of CrO₄^-2 ; the reagent used is an acetic solution of o-dianisidino, which gives a red coloration upon acidification. The procedure is described, the limit of perceptibility being of 06 γ/ml Down to this concentration, the coloration still obeys Beer's law and permits the determination with a 15% accuracy. Qualitative investigation of the chromate ion with the above mentioned reagent is also reported. Sensitivity is D = 10^-6.3.     

Radiation‐induced graft modification of knitted poly(ethylene terephthalate) fabric for collagen immobilization

Radiation‐induced graft co‐polymerization of methacrylic acid and N‐vinyl‐2‐pyrrolidone mixture from poly(ethylene terephthalate) knitted fabrics were conducted using a preirradiation method. The influence of the graft conditions, such as irradiation dose, reaction time, monomer concentration and temperature on the degree of grafting was determined. It was found that there is a limiting irradiation dose of 40 kGy above which the degree of grafting does not increase. An increase in the monomer concentration from 20 to 40% and an increase in temperature from 60 to 80°C gave a higher initial rate of grafting as well as higher equilibrium graft levels. The characterization of the fabric was carried out by attenuated total reflectance infrared spectroscopy (ATR‐IR), X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The grafted fabric surface, carrying negatively charged carboxylate ions, was shown to attract collagen, being positively charged to provide bioreceptive surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

Reaction-induced secondary photopolymerization in diacetylene—bis(toluenesulfonate) (TS)

Profiles of spatially inhomogeneous photopolymerization of TS crystals upon UV irradiation through a micro-mesh under hydrostatic pressure have been recorded. Spatially isotropic polymer growth into shadow zones provide evidence for secondary chain initiation next to a running chain induced by molecular motion accompanying the monomer addition reaction.     

The ring puckering potential function of trimethylene sulfide and trimethylene selenide

The rotational constants A,B and C are functions of the vibrational quantum numbers for the out-of-plane bending modes of trimethylene sulfide and trimethylene selenide. Infrared and microwave spectroscopy have been used to determine the dependence between these parameters. The height and shape of the barrier arising from combination of the ring bending modes is also determined. CNDO/2 calculations are used to predict the position of the hydrogen atoms of the methylene groups in trimethylene sulfide and trimethylene selenide. The four-membered rings are non-planar for several vibrational states of the ring bending modes.     

Influence of molecular characteristics of nonionic cellulose ethers on their interaction with ionic surfactant investigated by conductometry

The interaction between nonionic derivatives of cellulose, hydroxypropylmethyl cellulose (HPMC) and methyl cellulose (MC), and ionic surfactant, sodium dodecylsulfate (SDS) were investigated by conductometric titration method, at 30°C. Obtained titration curves show two break points: critical aggregation concentration (cac) defined as the concentration of SDS at which interaction starts, and polymer saturation concentration (psp) as the concentration at which interaction finishes. Changes of characteristic concentration breaks were determined in dependence on concentration and molecular characteristics of cellulose derivatives (degree of substitution (DS) and molecular mass, i.e. intrinsic viscosity). It was shown that the first break point, cac, is independent of polymer concentration; while the second break point, psp, increases as polymer concentration increases, as described by a linear correlation. The slopes of linear relationship justify the DS on the intensity of the cellulose derivatives–SDS interaction. Changes in the intrinsic viscosity of cellulose derivatives do not exhibit influence on the interaction with SDS.     

Testing the adequacy of equilibrium models for complex formation Complexation between molybdate and oxalate revisited

In potentiometric studies of metal-ligand equilibria a given model is tested by adjustment of the corresponding stability constants with the purpose of obtaining as good a fit as possible to the experimental data. When judging the goodness-of-fit it is of great importance to be in control of any possible systematic error in concentrations or electrode parameters. The molybdate-oxalate system is used to demonstrate how one crucial parameter influences the evaluations of goodness-of-fit. The system is simple, having only one complex species, MoO(3)oxal(2-), with logarithmic stability constant 13.816 in the pH-range 4-7.     

Characterization via liquid chromatography coupled to diode array detector and tandem mass spectrometry of supercritical fluid antioxidant extracts of Spirulina platensis microalga

Spirulina platensis microalga has been extracted on a pilot scale plant using supercritical fluid extraction (SFE) under various extraction conditions. The extraction yield and the antioxidant activity of the extracts were evaluated in order to select those extracts with both the highest antioxidant capacity and a good extraction yield. These extracts were characterized using LC coupled to diode array detection (DAD) and LC coupled to mass spectrometry (MS) with two different interfaces, atmospheric pressure chemical ionization (APCI) and electrospray (ESI) which allowed us to perform tandem MS by using an ion trap analyzer. The best extraction conditions were as follows: CO2 with 10% of modifier (ethanol) as extraction solvent, 55 degrees C (extraction temperature) and 220 bar (extraction pressure). Fractionation was achieved by cascade depressurization providing two extracts with different activity and chemical composition. Several compounds have been identified in the extracts, corresponding to different carotenoids previously identified in Spirulina platensis microalga along with chlorophyll a and some degradation products. Also, the structure of some phenolic compounds could be tentatively identified. The antioxidant activity of the extracts could be attributed to some of the above mentioned compounds.     

Maximal chains inωω and ultrapowers of the integers

Summary Various questions posed by P. Nyikos concerning ultrafilters on and chains in the partial order (, <^*) are answered. The main tool is the oracle chain condition and variations of it.The first author is partially supported by the basic research fund of the Israeli Academy. The second author is partially supported by NSERC and was a guest of Rutgers University while the research on this paper was being done. The authors would also like to thank P. Nyikos for his valuable comments on early versions of this paper. This is number 465 on the first author's list of publications     

Relatively pseudocomplemented Hilbert algebras

We characterise those Hilbert algebras that are relatively pseudocomplemented posets.