Use of polyurethane foam and 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline for determination of nitrite by diffuse reflectance spectroscopy and colorimetry

Polyurethane foam (PUF) has been suggested as a solid polymeric reagent for determination of nitrite. The determination is based on the diazotization of end toluidine groups of PUF with nitrite in acidic medium followed by coupling of polymeric diazonium cation with 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline. The intensely colored polymeric azodye formed in this reaction can be used as a convenient analytic form for the determination of nitrite by diffuse reflectance spectroscopy (c _min = 0.7 ng mL⁻¹). The possibility of using a desktop scanner, digital camera, and computer data processing for the numerical evaluation of the color intensity of the polymeric azodye has been investigated. A scanner and digital camera can be used for determination of nitrite with the same sensitivity and reproducibility as with diffuse reflectance spectroscopy. The approach developed was applied for determination of nitrite in river water and human exhaled breath condensate.     

Using a digital camera and computer data processing for the determination of organic substances with diazotized polyurethane foams

The possibility of using a digital camera and computer software for the estimation of the color intensity of polymeric azo compounds synthesized by the reaction of the azo coupling of diazotized polyurethane foams (PUFs) with different organic substances was studied. The method is based on photographing colored polyurethane foams with a digital camera followed by the computer processing of the color images. It was found that calibration equations are described by a descending exponent of the first order. The advantages of the proposed method are its high sensitivity due to the chemisorption concentration of substances, simplicity, and low cost. In combination with a high efficiency, compactness, and the availability of digital cameras, this allows us to recommend it for field analysis. It is shown by the example azo coupling reactions involving diazotized PUF that, using digital cameras as detectors and computer data processing, one can determine substances with a sensitivity equal to that of diffuse reflection spectroscopy.     

Analytical possibilities of digital colorimetry: Determination of nitrite using polyurethane foam

Using the example of the determination of nitrite as polymeric azodye, the possibility of using office scanners, digital cameras, and computer data processing in different colorimetric coordinate systems (RGB, CMYK, LAB, and HSV) has been studied. Polymeric azodye was obtained by an azocoupling reaction between diazotized polyurethane foam (PUF) with 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline. The analytically important colorimetric coordinates in these systems were revealed and compared and the coordinates that result in the maximum sensitivity of nitrite determination were chosen. It was shown that calibration curves of the colorimetric coordinates versus concentration of nitrite in aqueous solution can be described by a first-order exponent. The detection limits of nitrite (1–3 ng/ml) were achieved in the RGB and CMYK colorimetric systems.     

A novel dot-blot DNAzyme-linked aptamer assay for protein detection

In this work, a novel dot-blot DNAzyme-linked aptamer assay (DLAA) for protein detection is developed with thrombin as a model protein. A peroxidase-like DNAzyme which serves as the catalytic label is tethered to a 15-mer thrombin-binding aptamer to form a label-free DNAzyme-linked aptamer probe. Based on specific interaction of the aptamer with target protein immobilized on nitrocellulose membrane, a DNAzyme layer is introduced onto the membrane. The DNAzyme can catalyze the H₂O₂-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine to produce a colored insoluble product that is apt to be adsorbed onto the nitrocellulose membrane. As a result, blue dots appear on the membrane, in contrast to the colorless background. As the concentration of thrombin increases, the color of dots gets deep. Such a protein concentration-dependent color change can be quantified via an image-processing software, with a detection limit of 0.6 μM. Furthermore, this assay has been applied successfully to the detection of thrombin in biological samples (e.g., human serum), indicating its practicality for bioanalysis.     

Strategies in lipase production by immobilizedCandida rugosa cells

Growing cells ofCandida rugosa immobilized in polymethacrylamide-hydrazide and polyurethane foam were employed in fluidized and packed bed reactors, for discontinuous and continuous fermentations to obtain extracellular lipase. In spite of hydrodynamic problems, fermentation cultures using polyurethane foam showed higher lipolytic activity than cultures employing polymethacrylamide-hydrazide beads, which was probably owing to the high immobilized biomass concentration in polyurethane observed by direct microscopy enumeration. Different oleic acid concentrations were assayed. The maximum level of lipase was achieved at 4 g/L of oleic acid. These results reaffirm that lipase production is a direct function of cell-substrate contact and that the organic substrate dispersion is important in this system.     

Microdetermination of mercury using silver and copper ion selective electrodes with silver-dithiooxamide and copper-diethyldithiocarbamate loaded polyurethane foams

Summary Microdetermination of Mercury Using Silver and Copper Ion Selective Electrodes with Silver-Dithiooxamide and Copper-Diethyldithiocarbamate Loaded Polyurethane Foams Low levels of mercury(II) are determined by passing their aqueous solutions at pH 1–3 through a column containing silver-dithiooxamide or copper-diethyldithiocarbamate loaded polyurethane foam, followed by monitoring the silver(I) and copper(II) ions released in the effluent with the solid state silver and copper ion selective electrodes, respectively. The rate of the exchange reactions is fast (<3 min) and the efficiency of displacing silver(I) and copper(II) ions is high (>98%). The calibration plots show slopes of 59 and 29 mV/concentration decade of mercury on using the silver and copper sensors, respectively. Determination of 20 ng/ml to 200/ml of mercury(II) in aqueous solutions shows an average recovery of 98.4% and a mean standard deviation of 2%. Many cations and anions do not interfere. Some organomercury compounds are similarly determined after a prior decomposition in an oxygen-filled flask. Results with an average recovery of 98.4% (mean standard deviation 1.9%) are obtained with 10 structurally different mercury compounds.     

Competitive adsorption of -α-lysophosphatidylcholine/β-lactoglobulin mixtures at the interfaces of foams and foam lamellae

The stability of foams formed with the protein β-lactoglobulin as a function of increasing concentration of the lipid analogue -α-lysophosphatidylcholine were investigated using a microconductivity technique. The drainage, surface diffusion and thickness properties of thin liquid films (foam lamallae) were also studied using optical microscopy including epi-illumination, fluorescence recovery after photobleaching and film interferometry techniques. In addition, the surfactant binding properties of the protein were examined. The addition of small quantities of -α-lysophosphatidylcholine to β-lactoglobulin (molar ratio, R < 7:1) increased the foam stability, whereas a slightly higher concentration of surfactant in the mixture (R = 10) caused foam destabilisation. The explanation of these observations is based on changes in the composition and structure of the adsorbed interfacial layers of the thin films caused by competitive displacement of the protein by the surfactant.     

Analytical application of polyurethane foam functionalized with quinolin-8-ol for preconcentration and determination of trace metal ions in wastewater

Quinolin-8-ol-bonded polyurethane foam (Ox-PUF) was synthesized by coupling the polyurethane foam matrix with oxine through an azo (-N=N-) group. The chromatographic retention behavior of Ag⁺, Pb²⁺, and Al³⁺ onto the Ox-PUF was studied. The extraction of Ag⁺, Pb²⁺, and Al³⁺ was accomplished within 15–20 min at pH ranges of 1–4, 4–6, and 6–12, respectively. The kinetics and thermodynamics of the sorption of tested metal ions onto Ox-PUF have been studied. The average values of ΔH, ΔS, ΔG; k ₁, k ₋₁, k′, and t _1/2 at 298 K were −28.7 kJ/mol, 210.1 J/(mol K), −6.74 kJ/mol, 0.095, 0.01, 0.113, and 7.184 min, respectively. The sorption capacities of the Ox-PUF were 0.16, 0.07, and 0.59 mmol/g for Ag⁺, Pb²⁺, and Al³⁺, correspondingly. The proposed method has been successfully applied to the preconcentration and removal of tested metal ions from wastewater. Recoveries between 80 and 99% were obtained (RSD ∼ 7). The text was submitted by the authors in English.     

Use of the Software Processing of Scanned Chromatogram Images in Quantitative Planar Chromatography

The results of quantitative TLC analysis using the software processing of scanned chromatogram images are demonstrated by the example of the separation and determination of food dyes. The chromatograms obtained were digitized by scanning with a flatbed scanner. Quantitative analysis was performed using special-purpose software. The use of the software processing of scanned images does not require expensive analytical instruments and provides an unbiased quantitative evaluation of substances in a chromatographic peak with a minimum of time expenditure.     

Characterization of some essential oils and their key components: Thermoanalytical techniques

The present study was aimed at determining the kinetics of evaporation and establishing vapor pressure curves for both single and multi-component systems by thermogravimetry (TG) and differential scanning calorimetry (DSC). Essential oils (e.g. lavender oil, orange oil, clove oil and eucalyptus oil, etc.) are typically multi-component systems consisting of various volatile pure components (e.g. linalyl acetate, limonene, cinnamaldehyde, etc.) which resemble single component systems. In this study linalyl acetate was taken as the calibration compound for TG. The vapor pressure curves for the pure substances were plotted using TG and vapor pressure plots for clove oil and eucalyptus oil were constructed using DSC. The thermodynamic and kinetic parameters of the pure compounds were compared to that of the multi-component systems to quantitatively and qualitatively measure the influence of different compounds on each other. The k-value from the vapor pressure data for linalyl acetate was calculated as 112006 Pa kg^0.5mol^0.5s^-1 m^-2 K^-0.5. The vapor pressure values were used to determine the Antoine constants using the SPSS 10.0 software.This revised version was published online in November 2005 with corrections to the Cover Date.     

X-ray fluorescence and atomic emission determination of cobalt in water using polyurethane foam sorbents

The conditions of analytical signal formation during direct X-ray fluorescence and arc atomic emission determination of metals using polyurethane foam sorbents were studied. A sorption spectroscopic technique of cobalt determination in water with preconcentration in the form of thiocyanate complexes based on simple ethers using polyurethane foam sorbents was developed. The linear calibration range was two orders of magnitude. With a cobalt concentration from 25 ml of water in the static mode, the lower limit of the metal content was 3 and 9 μg/l for X-ray fluorescence and atomic emission methods, respectively.     

Thermal properties of polyurethanes synthesized using waste polyurethane foam glycolysates

In this work thermal transitions and thermal stability of polyurethane intermediates and polyurethanes were investigated. The intermediates were obtained by glycolysis of waste polyurethane (PUR) in the reaction with hexamethylene glycol (HDO). The excess of HDO was not separated from the product after the glycolysis process was finished. The effects of different mass ratio of HDO to PUR foam on selected physicochemical properties (hydroxyl number, Brookfield viscosity and density) were also determined. The polyurethanes were synthesized from the obtained intermediates by the prepolymer method using diisocyanate (MDI) and glycolysis product of molecular mass in range 700/1000 g mol^–1. Hexamethylene glycol, 1,4-butanediol and ethylene glycol were used as chain extender agents. Influence of NCO groups concentration in prepolymer on glass transition temperature (T _g) and storage and loss modulus (E’, E’’) of polyurethanes were investigated by the DMTA method. Thermal decomposition of obtained glycolysates and polyurethanes was followed by thermogravimetry coupled with Fourier transform infrared spectroscopy. Main products of thermal decomposition were identified.     

Preconcentration and separation of some organic water pollutants with polyurethane foam and activated carbon

Summary Although pesticides and phenols, cause reproductive failure in many areas of the world, there is a no effective means of treating waste water containing these compounds. This work deals with the adsorption of insecticides and phenols from aqueous solution by untreated porous polyurethane foam and activated carbon. Static experiments showed that in comparison with activated carbon a reasonable percentage of the compounds was adsorbed by the foam. Attempts were therefore made to extract these species from aqueous solution by foam column chromatography.The results showed that the adsorption of the compounds was brought about by a mechanism similar to that of solvent extraction. The effect of various experimental conditions such as temperature, extracting medium, pH, contact time, volume of sample flow rate, compound concentration, and eluting solvents on the retention and separation of the compounds has been determined. The height equivalent to a theoretical plate (HETP) was calculated from breakthrough capacity curves and from chromatograms obtained from polyurethane foam columns for the insecticide Dyfonate; values were in the range 2.1–2.3 mm at 10–15 ml min^–1. Extraction of the compounds from natural water, and subsequent recovery, were both found to be complete. The high capacity of polyurethane provides advantages over activated carbon; in particular, large sample volumes can be analyzed at high flow rates.     

Application of halo polyhydroxy polyurethane foam for the extraction of cobalt from cobalamin drugs and urine

Polyhydroxy polyurethane sorbent was modified by the addition of halogen atoms to its matrix to produce a new sorbent distinguished by high surface polarity, enhanced capacity, and improved stability in both acidic and alkaline media. Halo polyhydroxy polyurethane foam (X-PPF) was characterized by NMR, FTIR, UV–Vis, Raman spectroscopy, pH_ZCP values, and scanning electron microscopy images. Experimental studies have proven that X-PPFs have a great potential for the extraction and recovery of cobalt ions and this was attributed to the presence of halogen, phenolic, and urethane groups. The pH_ZCP value of X-PPFs was determined to be 0.91 and the maximum metal recovery was achieved at a pH range of 6–7. The kinetics of the process was best described by pseudo-second-order model (R²?=?1). ΔH, ΔS, and ΔG values were calculated to be ?57.2?kJ?mol^?1, ?172.6?J?K^?1?mol^?1, and ?5.8?kJ?mol^?1, respectively. A perfect isotherm curve with zero intercept (0.002), good correlation (R²?=?0.999), and capacity of 246.8?mg?g^?1 was obtained.     

Characterization of the Surface Redox Process of Adsorbed Cercosporin (CER) at Glassy Carbon Electrodes by Anodic Stripping Square‐Wave Voltammetry

The adsorptive accumulation of cercosporin (CER) at glassy carbon electrodes is studied by square‐wave voltammetry (SWV). The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of CER with glassy carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the CER bulk concentration (c*_CER). SWV was also used to generate Q vs. c*_CER and I_{p, n}. vs. c*_CER calibration plots from pure commercial reagent solutions. Theoretical detection limits of 1.8×10^?7 and 9.7×10^?8 M were calculated from Q. vs. c*_CER and I_{p, n} vs. c*_CER plots, respectively. The lowest concentration value measured experimentally from calibration plots performed at a f =40 Hz for a signal to noise ratio of 2 : 1 was 3.7×10^?8 M, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled CER reduction peak. I_{p, n}./f vs. f plots from SW voltammograms performed at different c*_CER as well as different accumulation times showed the so‐called “quasi‐reversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (?0.260±0.011) V was determined for the formal potential of the adsorbed redox couple from the split voltammetric peak. A full characterization of the surface redox process was obtained by applying the methods of the “quasi‐reversible maximum” and the “split SW peak”. In 1 M HClO₄ aqueous solution, the formal rate constant and the anodic transfer coefficient were (3.5±0.5)×10² s^?1 and (0.50±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1.     

GC-MS Analysis of Organic Vapours Emitted from Polyurethane Foam Insulation

Abstract

The vapours emitted by rigid polyurethane foam at 40° and 80° in dry and in humid (90% RH) air were trapped with a Tenax TA sampling tube and, after thermal desorption, analyzed by high resolution gas chromatography – mass spectrometry. The chromatograms obtained demonstrate a certain characteristic pattern. The qualitative composition of the effluent mixture is basically independent of both temperature and humidity of the foam. Over seventy compounds were identified as polyurethane foam off-gases. Among them the most numerous are hydrocarbons. The most abundant is the blowing agent, trichlorofluoromethane. The most interesting are cyclic acetals, aldehydes, cyclic ethers, alcohols, chloroform and chlorobenzene. The headspace concentration of the majority of them is below 10mg/m³, there are, however, several compounds with the concentration exceeding 100mg/m³.     

Adsorption syntax of Au(III) on unloaded polyurethane foam

The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10⁻⁵M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10⁻² mol·g⁻¹, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10⁻⁴mol·g⁻¹ and 40294±2947 l·g⁻¹, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol⁻¹ reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol⁻¹. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantK _c have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.     

Preparation,characterization and applications of polyurethane foam functionalized with resorcinol for quantitative separation and determination of silver(I) and mercury(II) from tap and wastewater

A stable chelating resin matrix was prepared by covalently linking resorcinol with polyurethane foam matrix through a –N=N– group. Preconcentration and determination of trace Ag⁺ and Hg²⁺ ions from samples of different origin, using Res-PUF, were studied. Various conditions influencing the sorption of these metal ions onto Res-PUF were optimized. The kinetics of sorption of the Ag⁺ and Hg²⁺ by Res-PUF were found to be fast, reached equilibrium in few minutes (5–10?min) and followed a first-order rate equation with an overall rate constant k in 0.102 and 0.267/min, respectively. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for ΔG, ΔH and ΔS of ?3.94, ?22.02 and ?58.37, respectively. The mean free sorption energy (E) computed from the Dubinin–Radushkevich (D–R) isotherm was found to be equal to 8.91 kJ/mol, which reflects the chelation sorption process. The capacities of the foam material were 0.15 and 0.07?mmol/g for Ag⁺ and Hg²⁺, respectively. Preconcentration factors of?>?50 were achieved (RSD?≈?5.99). The proposed preconcentration procedure was applied successfully to the determination of trace metal ions in natural and wastewater samples.     

Extractable organic compounds in polyurethane foam with special reference to aromatic amines and derivatives thereof

Methods for determination of aromatic amines and related compounds in flexible toluene diisocyanate (TDI)-based polyurethane (PUR) foam were investigated. The foam was extracted using 0.1% (w/v) aqueous acetic acid (HAc). Extraction solutions were analysed and aromatic amines were determined as ethyl chloroformate (Et) and pentafluoropropionic acid anhydride (PFPA) derivatives. The determinations were performed using liquid chromatography (LC) and mass spectrometry (MS) detection with electrospray ionisation (ESI) or gas chromatography (GC)-MS with chemical ionisation monitoring negative ions (NCI). The Et derivatives were determined using LC-ESI⁺-MS with detection limit of 2 pg of toluenediamine (TDA). The PFPA derivatives were determined using LC-ESI⁻-MS or GC-NCI-MS with detection limits of 0.1 and 0.02 pg of TDA, respectively. Using trideuterium labelled TDA as internal standard, linear calibration curves were obtained in the range of 0.01-0.50 μg ml⁻¹ (n=7), with correlation coefficients >0.999. When plotting calibration curves for TDA-PFPA derivatives determined using LC-MS against TDA-PFPA using GC-MS and TDA-Et using LC-MS, linear curves were obtained. The relative standard deviation (R.S.D.) for determination of TDA in foam extraction solutions were 13%. LC-MS determination of PFPA derivatives was more selective, as compared to LC-MS of Et derivatives.In foam extraction solutions, 2,4- and 2,6-TDA, several isomers of methylenedianiline (MDA) and dimers of TDA/TDI were observed. 2,4-TDA and 4,4′-MDA are possible human carcinogens. Hydrolysis of the extraction solution revealed a large pool of TDA/TDI compounds and oligomers. The concentration of TDA in foam was affected by the extraction media, temperature and duration. The choice of derivatisation procedure also affected the determination of TDA. In extraction solutions from six different commercially available flexible foam qualities 2,4- and 2,6-TDA were found in the range of 0-7 and 0-6 μg g⁻¹ foam, respectively. When flexible foam was heated, considerable higher concentrations of TDA were observed.     

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

The photo‐degradation of polymer coating systems due to irradiation by UV and Xenon light sources is studied using positron annihilation spectroscopy and electron spin resonance (ESR). Doppler broadened spectra of positron annihilation, as a function of slow positron implantation energy and ESR spectra, are measured in two types of polyurethane which were exposed, ex situ, to UV irradiation for up to 800 h. The UV irradiation systematically decreases the S parameter as a function of exposure duration and increases the ESR signals. Thus, significant S parameter decrease is correlated with the ESR signal increase resulting from photo‐degradation of polymers due to UV irradiation. Parallel in situ positron annihilation and ESR experiments are performed as a function of Xenon light exposure for up to 100 min. These results show that the photo‐degradation of the polyurethane coatings involves initial free‐radical formation, which is correlated with the subnanometer defects detected by positron annihilation spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1289–1305, 1999