Novel approach for mono-segmented flow micro-titration with sequential injection using a lab-on-valve system: a model study for the assay of acidity in fruit juices

A new concept for micro-titration using a "lab-on-valve"(LOV) system with sequential injection of mono-segmented flow is proposed. The performance of the system was demonstrated by the assay of acidity in fruit juices which is based on acid-base neutralization. A standard/sample solution containing citric acid, indicator, sodium hydroxide, were sandwiched between air segments and were aspirated in microliter volumes through a selection valve into a holding coil. The acid, indicator, and base were mixed by flow reversal. After removing air segments, the solution was pushed to the detector for monitoring of the change in absorbance of the indicator color, which depended on the concentration of the remaining base. With LOV, microliter volumes of the solution can be detected without dispersion of the color zone. A calibration graph (plot of absorbance vs. acidity value) in the range of 0.2-1.2% (w/v) as citric acid was established. Sample throughput of 30 sample h(-1) and good reproducibility (RSD = 1.2%, n= 11 for 0.6% acidity) were achieved. The procedure has been applied to determine acidity in fruit juices.     

Thiol‐Directed Synthesis of Highly Fluorescent Gold Clusters and Their Conversion into Stable Imaging Nanoprobes

Fluorescent gold clusters (FGCs) with tunable emission from blue to red and quantum yields in the range of 6–17 % have been synthesized by simple modification of the conditions used for the synthesis of gold nanoparticles, namely by replacing the stronger reducing agent with a controlled amount of thiol. Various functional FGCs with hydrodynamic diameters of 5–12 nm have been successfully synthesized and used as cell labels. The results of our investigations strongly indicate that FGCs composed of Au⁰ are more stable imaging probes than commonly reported red/NIR‐emitting FGCs with a composition of Au⁰/Au^I, as this combination rapidly transforms into nonfluorescent large clusters on exposure to light. The FGC‐based nanoprobes reported herein exhibit stable fluorescence upon continuous light exposure and can be used as imaging probes with low cytotoxicity.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

Simple lab-on-chip approach with time-based detection

A simple lab-on-chip approach with time-based detection is proposed. A platform is made from a piece of acrylic differently shaped channels for introducing sample and reagent(s) using flow manipulation. Time-based changes involving migration of the reaction zone are monitored. The changes can be visually monitored by using a stop-watch with naked eyes observation. Some applications for the determination of ascorbic acid, acetic acid and iron in real samples with different chemistries were demonstrated.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

Gamma-ray spectrometry combined with acceptable knowledge (GSAK): A technique for characterization of certain remote-handled transuranic (RH-TRU) wastes

Gamma-ray spectrometry combined with acceptable knowledge (GSAK) is a technique for the characterization of certain remote-handled transuranic (RH-TRU) wastes. GSAK uses gamma-ray spectrometry to quantify a portion of the fission product inventory of RH-TRU wastes. These fission product results are then coupled with calculated inventories derived from acceptable process knowledge to characterize the radionuclide content of the assayed wastes. GSAK has been evaluated and tested through several test exercises. This paper describes the GSAK approach, while Part II presents the test results.