Athanasios G. Vlessidis

Effect of the degree and type of the dealumination method on the structural, compositional and acidic characteristics of H-ZSM-5 zeolites

Abstract A series of H-ZSM-5 zeolites with different framework Si/Al ratios were prepared by hydrothermal synthesis and post-synthesis dealumination by various methods, i.e., HCl, steaming, steaming/HCl and ammonium hexafluorosilicate (AHFS). The degree of framework dealumination and the amount/type of the extra-framework phases formed were greatly dependent on the method of dealumination and the severity of the experimental conditions. The hydrothermal treatment of a parent ZSM-5 sample with Si/Al∼27 was very effective and produced significant amounts of Si–Al extra-framework phases, while the reaction with HCl in relatively strongly acidic environments resulted in very low dealumination. Treatment with AHFS was proven to be an appropriate method for preparing moderately dealuminated H-ZSM-5 samples which are free from extra-framework Al. The relative crystallinity and the microporosity of all dealuminated H-ZSM-5 zeolites were retained to a high degree (>80%), even for the severely steamed samples (∼96% dealumination). The morphology of the crystals/particles was not changed significantly; however, each dealumination method had a different effect on the partial breakdown of the crystals and on the formation of extra-framework/amorphous phases with a mesoporous character. The number of acid sites that corresponded to the high-temperature desorption peak of the ammomia-temperature programmed desorption spectra was found to be equivalent to the framework Al (FAl) content of all H-ZSM-5 samples, irrespective of the degree of dealumination and the amount of extra-framework phases. Theses phases had a low capability of adsorbing ammonia compared to the FAl atoms and were the main source of acidity for the severely steamed samples which had almost no FAl.

Ultratrace Determination of Silver, Gold, and Iron Oxide Nanoparticles by Micelle Mediated Preconcentration/Selective Back-Extraction Coupled with Flow Injection Chemiluminescence Detection

A new method has been developed for the ultrasensitive determination of silver, gold, and iron oxide nanoparticles in environmental samples. Cloud point extraction was optimized and used as a means to extract and preconcentrate all nanoparticle species simultaneously from the same sample. The extracted nanoparticles were sequentially isolated from the surfactant-rich phase by a new selective back-extraction procedure and dissociated into their precursor metal ions. Each ion solution was injected in a flow injection analysis (FIA) manifold, accommodating the chemiluminogenic oxidation of luminol, in order to amplify chemiluminescence (CL) emission in a manner proportional to its concentration. Under the optimum experimental conditions, the detection limits were brought down to the picomolar and femtomolar concentration levels with satisfactory analytical features in terms of precision (2.0-13.0%), selectivity against dissolved ions, and recoveries (74-114%). The method was successfully applied to the determination of iron oxide, silver, and gold nanoparticles in environmental samples of different complexity, ranging from unpolluted river water to raw sewage. The developed method could also serve as a basis for future deployment of molecular spectrometry detectors for the selective determination and speciation analysis of nanoparticles in environmental applications.

Programming Fluid Transport in Paper-Based Microfluidic Devices Using Razor-Crafted Open Channels

Manipulating fluid transport in microfluidic, paper-based analytical devices (μPADs) is an essential prerequisite to enable multiple timed analytical steps on the same device. Current methods to control fluid distribution mainly rely on controlling how slowly the fluid moves within a device or by activating an on/off switch to flow. In this Article, we present an easy approach for programming fluid transport within paper-based devices that enables both acceleration as well as delay of fluid transport without active pumping. Both operations are programmed by carving open channels either longitudinally or perpendicularly to the flow path using a craft-cutting tool equipped with a knife blade. Channels are crafted after μPADs fabrication enabling the end user to generate patterns of open-channels on demand by carving the porous material of the paper without cutting or removing the paper substrate altogether. Parameters to control the acceleration or delay of flow include the orientation, length, and number of open channels. Using this method, accelerated as well as reduced fluid transport rates were achieved on the same device. This methodology was applied to μPADs for multiple and time-programmable assays for metal ion determination.

Monitoring reactive oxygen species in vivo using microdialysis sampling and chemiluminescence detection as an alternative global method for determination of total antioxidant capacity

Abstract A microdialysis sampling system coupled to chemiluminescence (CL) detection was developed to monitor the variation of lucigenin (Luc) CL emission in vivo in real time. The Luc CL emission is linearly correlated to the d-ROM test, thus providing evidence of equivalence to total antioxidant capacity (TAC). Furthermore, the system is simple, low cost, rapid and sensitive enough for real time monitoring of TAC variation in vivo under different physiological and pathological conditions. It is accurate and far more precise than the traditional methods since it overcomes uncontrolled conditions of handling samples. The production capacity of reactive oxygen species (proROS capacity) of individual antioxidant compounds mostly found in biological fluids was investigated using luminol CL emission. The implications of the proROS capacity of antioxidant compounds in biological fluids is further discussed under the perspective of explaining the appearance of certain pathological diseases, and on the basis of establishing a healthy diet for human beings. Further investigation showed that ascorbic acid (AA) plays a protective role in living organisms, so a diet rich in AA is important for health. Furthermore, it was found that lower physiological level of AA or higher physiological level of uric acid (UA) or glucose (GLU) may reduce O 2 into reactive oxygen species (ROS, e.g. H 2 O 2 , O 2 − ) in the presence of Fe(III). This may explain some syndromes in the cases of AA deficiency (e.g. scurvy) and related diseases, e.g. diabetes or gout. From the data obtained, there is a strong indication that the damage or pathological alternation is probably due to the higher level of ROS, which are generated from the reduced oxygen in the presence of pathological level of related reductants.

Dehydrogenation of propane over natural clinoptilolite zeolites

Abstract Clinoptilolite is one of the most commonly used natural zeolites in environmental and industrial applications. In this study, the activity and selectivity of two different clinoptilolite tuffs from Thrace region of Greece were investigated using the model reaction of propane dehydrogenation and were compared to those of synthetic proton and metal-modified ZSM-5 zeolite catalysts. The clinoptilolite bearing tuff from Metaxades (MCH) showed appreciable activity for propane dehydrogenation, similar to that of a steamed Cr-modified ZSM-5 zeolite and considerably higher compared to the second natural clinoptilolite tuff (SF) from the area of Pentalofos and to the H-ZSM-5 zeolite. The total propylene yield for the MCH sample at 540 °C was 8.4%, compared to 3.4% for SF, 5.3% for steamed H-ZSM-5 and 8.3% for steamed Cr-modified ZSM-5. The proton-exchanged forms of both natural zeolites showed improved conversion of propane but resulted in lower propylene selectivity due to subsequent hydrogen transfer, cracking and cyclo-oligomerization reactions induced by the higher number of framework Bronsted acid sites.

Chemiluminescence (CL) emission generated during oxidation of pyrogallol and its application in analytical chemistry. I. Effect of oxidant compound

An investigation of chemiluminescence (CL)-emission generated by the oxidation of pyrogallol using various inorganic oxidant compounds is reported in this F.I.A.-merging zone application. The oxidant compounds that showed measurable CL-emission were permanganate, periodate, hypochlorite anions, cerium(IV) and hydrogen peroxide. The different oxidant compounds showed CL-emissions at different pH-ranges. The CL-emission was limited by the inner filter effect and this was more intense for oxidants of selective oxidation. Kinetic effects were also found in the case of oxidation by permanganate. Plots of CL-emission against pH give evidence of speciation and or deactivation mechanism effects. The analytical parameters for the determination of the oxidants are given. Sensitivities of 895 600, 19 500, 33 723, 10 680 and 56 703 mV M(-1) were found for the determination of permanganate, cerium(IV), periodate, hypochlorite and hydrogen peroxide, respectively. The calibration curves of the oxidant determination were generally S-shaped; the S-shaped calibration curve of periodate was closer to a straight line relationship while that of hypochlorite was almost a straight line; detection limits in the range of 10(-4) M oxidant concentration were found for nearly all oxidants. The analytical parameters for determination of pyrogallol by the CL-emission generated through oxidation by the different oxidants at optimum conditions were 1.16x10(6) mV M(-1) for permanganate; 0.086x10(6) mV M(-1) for cerium(IV); 0.91x10(6) mV M(-1) for periodate; 0.012x10(6) mV M(-1) for hypochlorite; and 0.25x10(6) mV M(-1) for hydrogen peroxide. The detection limit was 1.0x10(-4) M. The nearly straight-line relationship (initial part of the plot) for CL-emission with oxidant concentration gives an indication that the CL-reaction of pyrogallol oxidation by hypochlorite proceeds through a process that involves energy transfer while the pronounced S-shaped curve produced by permanganate gives the indication that the reaction proceeds through a process that does not involve energy transfer according to the mathematical model of CL-emission that controls the F.I.A.-merging zone technique of the flow apparatus used in this work. The sequence of completeness of the oxidation process by each oxidant was MnO(4)(-)>H(2)O(2)>IO(4)(-)>OCl(-); the stoichiometric quantity of the oxidant per pyrogallol molecule for the rapid part of the overall oxidation by each different oxidant was attempted; this is an index-value of the oxidation state of the fluorescent excited molecule. Finally, the impact of the above findings for further analytical applications is discussed.

Graphite furnace and hydride generation atomic absorption spectrometric determination of cadmium, lead, and tin traces in natural surface waters: Study of preconcentration technique performance

In this study three major types of preconcentration methods based upon different principles (cation exchange, physical absorption and hydrophobic extraction) were evaluated and optimized for the extraction and determination of three highly toxic heavy metals namely Cd, Pb and Sn by graphite furnace and hybrid generation atomic absorption spectrometry in real samples. The optimum analytical conditions were examined and the analytical features of each method were revealed and compared. Detection limits as low as 0.003-0.025 microg L(-1) for Cd(2+), 0.05-0.10 microg L(-1) for Pb(2+) and 0.1-0.25 microg L(-1) for Sn(4+) depending on the extraction method were obtained with RSD values between 3.08% and 6.11%. A preliminary assessment of the pollution status of three important natural ecosystems in Epirus region (NW Greece) was performed and some early conclusions were drawn and discussed.

Dialysis membrane sampler for on-line flow injection analysis/chemiluminescence-detection of peroxynitrite in biological samples.

Peroxynitrite, as a derivative of nitric oxide, is a potent oxidant. It reacts with several biological molecules, makes cellular and tissue damages, and is related with many diseases; therefore, it is of major concern in current medical research works. In this work, a special perm-selective cellulose acetate membrane sampler is used to implement flow injection analysis (FIA)/chemiluminscence (CL)-detection method for the detection of peroxynitrite with Luminol CL-reagent. Optimum detection conditions were established, and the permeability of peroxynitrite through cellulose acetate (CA) membrane, as well as the interference from matrix constituents were studied. The proposed method has the high sensitivity of the CL-detection and the selectivity of perm-selective membrane sampler. The obtained detection limit of 1x10(-11) M (without dialysis membrane) and 1x10(-10) M (with dialysis membrane), makes it possible to monitor the elusive peroxynitrite in biological samples. The mechanism of luminol CL-emission generated during oxidation by peroxynitrite and the kinetics of peroxynitrite decomposition were also studied using FIA/CL-detection set-up.

Indirect chemiluminescence-based detection of mefenamic acid in pharmaceutical formulations by flow injection analysis and effect of gold nanocatalysts.

A highly sensitive flow injection-chemiluminescence detection (FI-CL) method based on periodate oxidation of two popular luminescent compounds for the determination of mefenamic acid (MFA) is presented. The method is an indirect CL detection method based on the CL emission generated during the oxidation of Pyrogallol (Pg) or Luminol (Lu) with the excess of periodate that remains after oxidation of MFA within the time period of 15 min. The MFA calibration curves obtained with either luminescent compounds were linear over a wide concentration range, depending on the system employed, offering detection limits in the range of low to ultra-low microg L(-1) levels. Gold nanoparticles (Au-NPs) were also assessed as means for enhancing the CL signal. Pg-periodate was not affected by the presence of gold nanocatalysts as opposed to Lu-periodate CL signal which exhibited a significant increase in the presence of citrate synthesized Au-NPs. The reproducibility of the method, expressed by the relative standard deviation (R.S.D.), was very satisfactory and always below 5% as evidenced by repeated measurements (n>or=10) of standard solutions at two concentration levels (2 and 20 microg L(-1)).

The use of surfactant-based separation techniques for monitoring of orthophosphate in natural waters and wastewater

In an effort to monitor orthophosphate in natural waters and wastewater in the Ipirous region (Greece), an analytical methodology was established owing to the need for interference-free determination at the low mg/l levels. The method applied for the determination of orthophosphate is based on its reaction with molybdate towards a yellow heteropoly acid complex, which is electrically balanced with a cationic surfactant (cetylatrimethylammonium bromide) towards a complex non-polar derivative. This derivative is conveniently solubilized in the micelles of a non-ionic surfactant under mild conditions and measured spectrophotometrically at 370 nm after its uptake with a sulfuric acid-methanol solution. By simply preconcentrating 10 ml of sample volume a detection limit of 2.6 microM was obtained. Due to the required dilution step and signal enhancement caused by the presence of surfactant, interference from the presence of anionic species (mostly silicate and arsenate) was minor and could be conveniently alleviated by the use of tartaric acid and Na(2)SO(3), respectively. The method was successfully applied to real samples obtained for the natural sites subject to the monitoring survey ranging in their matrix complexity from clean river water to wastewater.