Sensitive and selective ion chromatographic method for the determination of trace beryllium in water samples

A selective and sensitive ion chromatographic method has been developed for the determination of beryllium in a number of water samples at low-μg/l concentrations. The separation was performed on a 250×4.0 mm I.D. iminodiacetic acid functionalised silica gel column. Chromatographed Be(II) was detected using visible detection at 590 nm following post-column reaction with chrome azurol S (CAS). The optimum separation and derivatisation conditions were studied in detail. The optimum eluent conditions were found to be 0.4 M KNO₃, adjusted to pH 2.5 using HNO₃, with optimum post-column detection being achieved using a solution containing 0.26 mM CAS, 2% Triton X-100, 50 mM 2-(N-morpholino)ethanesulfonic acid, pH 6.0. Under the above conditions, the concentration detection limit for Be(II) was found to be 3 μg/l in a standard solution and 4 μg/l in a typical tap water sample, using a 250 μl injection. The method was linear over the investigated range of 10 μg/l to 10 mg/l and highly reproducible. The method was successfully applied to a number of water samples of varying matrix complexity, including simulated seawater, and also to a natural freshwater certified reference material NIST 1640.     

PCR-based detection in a micro-fabricated platform

We present a novel, on-chip system for the electrokinetic capture of bacterial cells and their identification using the polymerase chain reaction (PCR). The system comprises a glass-silicon platform with a set of micro-channels, -chambers, and -electrodes. A platinum thin film resistor, placed in the proximity of the chambers, is used for temperature monitoring. The whole chip assembly is mounted on a Printed Circuit Board (PCB) and wire-bonded to it. The PCB has an embedded heater that is utilized for PCR thermal cycle and is controlled by a Lab-View program. Similar to our previous work, one set of electrodes on the chip inside the bigger chamber (0.6 microl volume) is used for diverting bacterial cells from a flowing stream into to a smaller chamber (0.4 nl volume). A second set of interdigitated electrodes (in smaller chamber) is used to actively trap and concentrate the bacterial cells using dielectrophoresis (DEP). In the presence of the DEP force, with the cells still entrapped in the micro-chamber, PCR mix is injected into the chamber. Subsequently, PCR amplification with SYBR Green detection is used for genetic identification of Listeria monocytogenes V7 cells. The increase in fluorescence is recorded with a photomultiplier tube module mounted over an epifluorescence microscope. This integrated micro-system is capable of genetic amplification and identification of as few as 60 cells of L. monocytogenes V7 in less than 90 min, in 600 nl volume collected from a sample of 10(4) cfu ml(-1). Specificity trials using various concentrations of L. monocytogenes V7, Listeria innocua F4248, and Escherichia coli O157:H7 were carried out successfully using two different primer sets specific for a regulatory gene of L. monocytogenes, prfA and 16S rRNA primer specific for the Listeria spp., and no cross-reactivity was observed.     

Electrical detection of germination of viable model Bacillus anthracis spores in microfluidic biochips

In this paper, we present a new impedance-based method to detect viable spores by electrically detecting their germination in real time within microfluidic biochips. We used Bacillus anthracis Sterne spores as the model organism. During germination, the spores release polar and ionic chemicals, such as dipicolinic acid (DPA), calcium ions, phosphate ions, and amino acids, which correspondingly increase the electrical conductivity of the medium in which the spores are suspended. We first present macro-scale measurements demonstrating that the germination of spores can be electrically detected at a concentration of 10(9) spores ml(-1) in sample volumes of 5 ml, by monitoring changes in the solution conductivity. Germination was induced by introducing an optimized germinant solution consisting of 10 mM L-alanine and 2 mM inosine. We then translated these results to a micro-fluidic biochip, which was a three-layer device: one layer of polydimethylsiloxane (PDMS) with valves, a second layer of PDMS with micro-fluidic channels and chambers, and the third layer with metal electrodes deposited on a pyrex substrate. Dielectrophoresis (DEP) was used to trap and concentrate the spores at the electrodes with greater than 90% efficiency, at a solution flow rate of 0.2 microl min(-1) with concentration factors between 107-109 spores ml(-1), from sample volumes of 1-5 microl. The spores were captured by DEP in deionized water within 1 min (total volume used ranged from 0.02 microl to 0.2 microl), and then germinant solution was introduced to the flow stream. The detection sensitivity was demonstrated to be as low as about a hundred spores in 0.1 nl, which is equivalent to a macroscale detection limit of approximately 10(9) spores ml(-1). We believe that this is the first demonstration of this application in microfluidic and BioMEMS devices.     

Characterization of trace elements in medicinal herbs by instrumental neutron activation analysis

Medicinal herbs are often used as alternative medicines for healing and controlling some diseases in the world. This study focuses on the content of heavy and trace elements of some widely consumed herbs in Libya. Nine most popular herbs were analyzed by k ₀-instrumental neutron activation analysis. All the samples, SRM and flux monitors were irradiated for 7 and 10 hours under thermal neutron flux of 1.3·10¹³ cm⁻²·s⁻¹ at Tajoura nuclear reactor. In total, 33 elements were analyzed in different herbs. The variations in the concentration of the elements are attributed to soil composition and the climate in which the plant grows. The study showed that the toxic elements found in the samples were below the levels prescribed by health regulations. The precision and the accuracy of the results were evaluated by analyzing the reference materials Pine Needles SRM 1575 and Citrus Leaves SRM1572.     

A Coupled System of Caputo-Type Sequential Fractional Differential Equations with Coupled (Periodic/Anti-periodic Type) Boundary Conditions

In this paper, we introduce the concept of coupled (periodic/anti-periodic type) boundary conditions and solve a coupled system of nonlinear sequential fractional differential equations equipped with these conditions. Sufficient criteria ensuring the existence and uniqueness of solutions for the given problem are presented. Our results are new in the given configuration and are well illustrated with the aid of examples.     

Maximum Modulus of Polynomials

Let P(z) =n∑j=0 a_jz~j be a polynomial of degree n and let M(P, r) = max|z|=r|P(z)|. If P(z) ≠ 0 in |z| 1, then M( P, r) ≥ ((1 + r)/ (1 + ρ))~ n M( P, ρ).The result is best possible. In this paper we shall present a refinement of this result and some other related results.     

Surface Functionalization of g‐C3N4: Molecular‐Level Design of Noble‐Metal‐Free Hydrogen Evolution Photocatalysts

A stable noble‐metal‐free hydrogen evolution photocatalyst based on graphite carbon nitride (g‐C₃N₄) was developed by a molecular‐level design strategy. Surface functionalization was successfully conducted to introduce a single nickel active site onto the surface of the semiconducting g‐C₃N₄. This catalyst family (with less than 0.1 wt % of Ni) has been found to produce hydrogen with a rate near to the value obtained by using 3 wt % platinum as co‐catalyst. This new catalyst also exhibits very good stability under hydrogen evolution conditions, without any evidence of deactivation after 24 h.