Characterization of mesoporous aluminosilicate materials by means of inverse liquid chromatography.

Estimation of the properties of mesoporous aluminosilicates in various environments is important when assessing their sorption capacity. Using inverse liquid chromatography (ILC), Hansen solubility parameters (HSP) and linear free energy relationship (LFER) parameters were calculated to determine the properties of aluminosilicates in a protic and an aprotic system, using water and acetonitrile as the mobile phase, respectively. The calculated Hansen parameters, reflecting the ability of the material under investigation to different types of intermolecular interactions, slightly differ depending on the mobile phase used. It was found that in the presence of water the surface of aluminosilicates shows a weaker ability to interact, as evidenced by negative or near-zero e, s, a, b, v coefficients. Additionally, it was found that the Si/Al ratio in aluminosilicates structure has little effect on the determined parameters.

Surface properties and surface free energy of cellulosic etc mucoadhesive polymers.

The paper presents the sorption and wettability properties for several mucoadhesive polymers (Carbopol 974P NF (carbomer polymer; carboxy polymethylene), Noveon AA-1, (polycarbophil; acrylic acid polymer crosslinked with divinyl glycol) HPMC (hypromellose; cellulose 2-hydroxyethyl methyl ester) and HEC (cellulose 2-hydroxyethyl ether) and a film-forming polymer Kollidon VA 64 (polyvinylpyrrolidone-vinyl acetate copolymer)) commonly used in controlled drug delivery systems. Moreover, the surface energy of powders was determined using the data obtained according to the three types of experimental investigation. The contact angle measurements for powders were performed according to the Washburn method and using the capillary rise technique. Whereas the sessile drop method was performed on the compressed discs of mucoadhesive polymers. For the surface characterization the IGC technique was also applied. The results obtained by different methods, for both: wettability and surface energies, were compared and correlated. The presented study showed significant differences in the morphology and surface properties of mucoadhesion polymers considered. It was confirmed that for the accurate quantification of the free surface energy (and its components), for mucoadhesive polymers considered, not only the IGC in finite concentration, but also the Washburn method should be used.

The solubility parameter for biomedical polymers-Application of inverse gas chromatography.

The solubility parameter seems to be a useful tool for thermodynamic characterisation of different materials. The solubility parameter concept can be used to predict sufficient miscibility or solubility between a solvent and a polymer, as well as components of co-polymer matrix in composite biomaterials. The values of solubility parameter were determined for polycaprolactone (PCL), polylactic acid (PLA) and polyethylene glycol (PEG) by using different procedures and experimental data, collected by means of inverse gas chromatography.

Examination of the chemical changes in cured phenol-formaldehyde resins during storage.

Chemical changes occurring within cured phenol-formaldehyde resins (resite and novolak type) during their storage were investigated by FT-NIR, py-GCMS and inverse gas chromatography. It was shown that a mixture of resite with novolak was less stable than resite or novolak itself as regards bulk properties. This aging phenomenon is mainly due to reaction of ammonia (product of hexa decomposition) with CH2OH groups present in resite. FT-NIR technique seems to be the least sensitive method for assessment chemical changes occurring during cured resins storage. Applications of py-GCMS and IGC method made able to indicate that more significant changes were for bulk samples (py-GCMS results) than on their surface (IGC results).

Assessment of the chemical changes during storage of phenol-formaldehyde resins pyrolysis gas chromatography mass spectrometry, inverse gas chromatography and Fourier transform infra red methods.

The chemical changes occurring in the phenol-formaldehyde resins (resol and novolac type) during their storage were investigated. In this paper the FT-IR, py-GCMS and inverse gas chromatography methods were applied for assessment of the changes occurring during storage of the phenolic resins. We have found that during storage some examined resins occurred partial curing. The results from all techniques applied are consistent. Py-GCMS is useful technique for screening the storage processes but IGC seems to be most sensitive one.

The increase of apatite layer formation by the poly(3-hydroxybutyrate) surface modification of hydroxyapatite and ß-tricalcium phosphate.

The aim of this study was the surface modification of hydroxyapatite and ß-tricalcium phosphate by poly(3-hydroxybutyrate) grafting and characterization of modificates. The bioactivity examination was carried out by the determination to grow an apatite layer on modified materials during incubation in simulated body fluid at 37°C. The additional issue taken up in this paper was to investigate the influence of fluid replacement. The process of the surface modification of biomaterials was evaluated by means of infrared and Raman spectroscopy. Formation of the apatite layer was assessed by means of scanning electron microscopy and confirmed by energy dispersive, Raman and Fourier transformed infrared spectroscopy. During exposure in simulated body fluid, the variation of the zeta potential, pH measurement and relative weight was monitored. Examination of scanning electron microscopy micrographs suggests that modification of hydroxyapatite and ß-tricalcium phosphate by poly(3-hydroxybutyrate) significantly increases apatite layer formation. Raman spectroscopy evaluation revealed that the formation of the apatite layer was more significant in the case of hydroxyapatite modificate, when compared to the ß-tricalcium phosphate modificate. Both modificates were characterized by stable pH, close to the natural pH of human body fluids. Furthermore, we have shown that a weekly changed, simulated body fluid solution increases apatite layer formation.

Effect of impregnating agent and relative humidity on surface characteristics of sorbents determined by inverse gas chromatography.

Sorbents that potentially can be used for separation of the products of biotechnological conversion of glycerol were examined. Properties of Zeolite 5A, resins: Amberlite, Diaion and their samples impregnated with an aqueous solutions of 1,2,3-propanetriol, 1,3-propanediol, 2,3-butanediol, acetic acid, succinic acid and model fermentation broth were investigated. Because surface properties will probably depend on the ambient humidity the IGC experiments were carried out under different conditions of relative humidity RH=0, 40 and 80%. Activity of the sorbents surface was expressed by the value of the dispersive component of the free surface energy. Inverse gas chromatography was also used to express acid-base properties of materials described by KA and KD parameters. The changes in the activity of investigated sorbents significantly varied depending on the type of impregnating agent. Moreover, the obtained results demonstrate that humidity can strongly influence, in some cases, the dispersive component of the free surface energy and the ability to specific interactions (KA and KD).

Quantitative criteria for needle trap device selection.

In this note the quantitative criteria for selection of parameters of the NTD system were derived. The conditions were formulated for the force exerted on syringe, the volume of tested solution, for the time of test and contact time of solution with the sorbent. The last two conditions allowed to establish limits for combinations of fundamental geometrical and macroscopic structural characteristics of the system. The practical reasons of testing and sampling effectiveness of the NTD systems were taken into account.

Role of Hansen solubility parameters in solid phase extraction.

The sorbent-eluent systems combined from eight polymeric sorbents and seven solvents as eluents were used for the extraction of phenol and its oxidation products from water samples. The individual interactions between sorbents, eluents and analytes were characterized by Hansen solubility parameters. Principal components analysis (PCA) was used for revealing the dominant interactions (dispersive, polar, and hydrogen bonding type) in sorbent-analyte-eluent systems. The importance of solubility parameters was also determined by a novel procedure based on sum of ranking differences (SRD). Although PCA and ranking by SRD are based on different principles and calculations, they have provided very similar results. The recovery in a given system has been predicted from the magnitudes of mutual interactions (sorbent-analyte, sorbent-eluent, analyte-eluent) by multiple linear regression.

New procedure for the determination of Hansen solubility parameters by means of inverse gas chromatography.

The Hansen solubility parameter (HSP) seems to be a useful tool for the thermodynamic characterization of different materials. Unfortunately, estimation of the HSP values can cause some problems. In this work different procedures by using inverse gas chromatography have been presented for calculation of pharmaceutical excipients' solubility parameter. The new procedure proposed, based on the Lindvig et al. methodology, where experimental data of Flory-Huggins interaction parameter are used, can be a reasonable alternative for the estimation of HSP values. The advantage of this method is that the values of Flory-Huggins interaction parameter chi for all test solutes are used for further calculation, thus diverse interactions between test solute and material are taken into consideration.

Surface characterization of poly(lactic acid) and polycaprolactone by inverse gas chromatography.

Inverse gas chromatography (IGC) has been used to characterise the surface properties of polycaprolactone (PCL) and poly(lactic acid) (PLA). The dispersive component of the surface free energy (gamma(S)(D)) was found to be very small for both of them--values close to 30 mJ/m(2) in the case of the PLA and ca. 40 mJ/m(2) for the PCL. The retention times of the n-alkanes, necessary to calculate the dispersive component of the surface energy, were obtained from the maximum, the centre at half height and the centre of mass of the chromatographic peak. While the values obtained using the first two parameters appear not to be affected by the peak asymmetry, in spite of having been obtained above the glass transition temperature of the polymer, the values obtained using the latter have been found to be not reliable. The drawbacks of using n-alkanes with a very small retention time have also been discussed, estimating the error it can introduce in the final results. Finally, the acid-base properties of the two biopolymers were determined using the approaches suggested by Schultz et al. and by St. Flour and Papirer. Although both methods describe the surfaces of PLA and PCL as neutral ones, differences between the values of the parameters K(A), K(D) and S(C) were obtained.

Use of topological indices of polychlorinated biphenyls in structure-retention relationships.

Topological parameters (Balaban index and electrotopological index) were used as structural parameters in the structure-retention relationships (SRRs). These relationships were found to be statistically valid and useful in the prediction of retention data of polychlorinated biphenyls (PCBs) despite of the temperature program used in the gas chromatographic experiment.

Ketoimino groups as silica surface modifiers.

The presented work is devoted to Porasil C silica, with organic compounds bonded to its surface and capable of electron-donor-acceptor (EDA) interactions. These packings are a good base for studying interactions among stationary phases and the adsorbate molecules showing electron-donor properties. The presented work concentrates on the phases containing ketoimino groups at their surface. Copper and chromium chlorides were bonded through these to the surface. Physicochemical characteristics of the obtained packings were determined by the use of elemental analysis, differential scanning calorimetry (DSC) and inverse gas chromatography. We examined the influence of the surface modification on the retention parameters of the nucleophilic compounds.

Principal component analysis of polarity and interaction parameters in inverse gas chromatography.

Inverse gas chromatography is used in the characterization of aliphatic-aromatic and aromatic ketones, their oximes, and ketone-oxime or oxime-oxime mixtures. All these organic materials are used as liquid stationary phases in gas chromatographic columns. A series of polarity and Flory-Huggins interaction parameters are determined and used to describe the physicochemical properties of examined materials, metal extractants, and products of their degradation. Principal component analysis (PCA) is performed on a data matrix consisting of polarity and interaction parameters for ketones, their oximes, and mixtures. The calculations are carried out on the correlation matrix. It is found that seven principal components account for more than 95% of the total variance in the data, indicating that the polarity (interaction) parameters are not correlating well. Physical meanings are attributed to the principal components, the most influential ones being that the first and the second principal components account for several Flory-Huggins interaction parameters, whereas the fifth is correlated with criterion "A". The plots of component loadings show characteristic groupings of polarity indicators, whereas that of component scores show several groupings of stationary phases. Cluster analysis provides mainly the same groupings. PCA allows for the grouping of polarity and solubility parameters based on the information carried within those parameters. There is no need to use more than one parameter from each cluster. McReynolds polarity and the partial molar excess Gibbs free energy of solution per methylene group carry the same information. The groups of ketones, oximes, and their mixtures can be distinguished with the use of PCA on the basis of the measured polarity, solubility parameters, or both.

Selectivity of solid-phase extraction phases in the determination of biodegradation products.

The extraction techniques connected with gas chromatography were used to describe quantitatively and qualitatively the biodegradation process. We investigated the biodegradation of hydrocarbons and non-ionic surfactants. Solid-phase extraction (SPE) and liquid-liquid extraction were used for the isolation of the non-degraded compounds and their degradation products. The selectivity of SPE has a significant influence on the isolation and preconcentration of organic compounds from water.

Solubility and polarity parameters of polyoxyethylene glycol dialkyl ethers.

Solubility parameters were estimated for model individual polyoxyethylene glycol dialkyl ethers and correlated with polarity parameters determined by gas chromatography. The effects of the length of the polyoxyethylene chain and of the terminal alkyl groups on the values of the parameters investigated and on the obtained relationships are discussed. It was found that polarity parameters can be estimated from the total solubility parameter with relatively low errors (approximately 1% for the retention index of ethanol and methanol and for the polarity index of ethanol). The polarity index of methanol and the relative retention of alcohols can be estimated with errors of approximately 3-4%. Using the total solubility parameter, polyoxyethylene glycol dialkyl ethers can be arranged in the same order of increasing polarity as in the case of polarity parameters determined by gas chromatography.

Reproducibility of echocardiography. A study evaluating the variability of serial echocardiographic measurements.

In this study, serial reproducibility was determined on standard M-mode (M-mode) and two dimensional guided M-mode (2-D M-mode) records for ten normal volunteers and 20 patients. Overall intraobserver variability in the normal group was 518 +/- 1.8 percent (M-mode) and 3.1 +/- 0.8 percent (2-D M-mode), and in the patient group 3.1 +/- 0.6 percent (M-mode) and 4.7 +/- 0.7 percent (2-D M-mode) (P = NS). Variability on serial examination, however, was twofold to threefold greater. In the normal group, reproducibility varied by 10.8 +/- 1.6 percent (M-mode) and 9.4 +/- 1.2 percent (2-D M-mode), while in the patient group, it was 8.7 +/- 0.9 percent (M-mode) and 9.4 +/- 0.7 percent (2-D M-mode). The lowest serial variability achieved was for the diastolic LV dimension on serial M-mode examination (4 percent); the largest variability pertained to measurement of the interventricular septum (14 percent). Other structures had intermediate variation in reproducibility. This study emphasizes that establishing performance variability for an echocardiographic laboratory is an important part of the interpretation of serial records.

Adrenalectomy prevents hypoxic lung histamine accumulation.

The lung histamine concentration of rats exposed to chronic hypobaric hypoxia was higher than in normoxic sea-level control rats. This hypoxia-induced lung histamine increase was absent in adrenalectomized chronically hypoxic rats. Adrenalectomy, per se, did not influence lung histamine content. The results suggest that the lung histamine content of chronically hypoxic rats is under hormonal control. This control mechanism is not evident under normoxic conditions.

Noninvasive tests to evaluate the severity of aortic stenosis. Limitations and reliability.

Fifty patients were examined with phonocardiograms, carotid pulse tracings, and M-mode echocardiograms to evaluate the ability of noninvasive tests to identify the severity of aortic valvular disease as determined at cardiac catheterization. Linear and multivariate analysis showed these noninvasive approaches to have only fair correlation with the severity of the disease. A binary division of the population under study into severe and nonsevere subgroups based on aortic valvular area (less than or equal to 0.8 sq cm in severe group [n = 25]; greater than 0.8 sq cm in nonsevere group [n = 25]) allowed sensitivity, specificity, and likelihood ratios to be determined. The likelihood ratio increased fourfold as the interval from the ECG Q wave to the murmur's peak (Q-MP) prolonged to 320 msec and increased sevenfold when the rate-corrected left ventricular ejection time (delta LVET) was more than 40 msec beyond values predicted from standard regression equations. Echocardiographic measurements were less helpful. Prolonged values of Q-MP and delta LVET proved to be the best discriminators of severe aortic valvular disease in this population where the prevalence of severe and nonsevere disease was equal.