Conductivity Detectors for Column or Paper Chromatography

SUMMARY

A conductivity detector, employing inexpensive operational amplifiers, has been constructed for chromatographic use. The detector is capable of observing conductance changes as small as 1 part in 10⁵ with bridge signals of 100 mV. Detector linearity is good over a wide dynamic range. When used in conjunction with a cell employing mercury strip electrodes, the detector can monitor the elution of ions in paper chromatography. The alkali metals were separated and detected on Whatman No. 1 paper with a sensitivity of less than 10 nmoles. This sensitivity limit was not determined by noise in the detector electronics, but by ionic impurities in the paper. The same detector, and a cell employing platinum electrodes separated from the effluent by ion-exchange membranes, was tested and found suitable for use in column chromatography. Again the sensitivity was not limited by the detector electronics.     

Opto-Mechanical and Electronic Design of a Tunnel-Trap Si Radiometer

A transmission-type light-trap silicon radiometer has been developed to hold the NIST spectral power and irradiance responsivity scales between 406 nm and 920 nm. The device is built from replaceable input apertures and tightly packed different-size silicon photodiodes. The photodiodes are positioned in a triangular shape tunnel such that beam clipping is entirely eliminated within an 8 field-of-view (FOV). A light trap is attached to the output of the radiometer to collect the transmitted radiation and to minimize the effect of ambient light. The photodiodes, selected for equal shunt resistance, are connected in parallel. The capacitance and the resultant shunt resistance of the device were measured and frequency compensations were applied in the feedback network of the photocurrent-to-voltage converter to optimize signal-, voltage-, and loop-gain characteristics. The trap radiometer can measure either dc or ac optical radiation with high sensitivity. The noise-equivalent-power of the optimized device is 47 fW in dc mode and 5.2 fW at 10 Hz chopping. The relative deviation from the cosine responsivity in irradiance mode was measured to be equal to or less than 0.02 % within 5° FOV and 0.05 % at 8° FOV. The trap-radiometer can transfer irradiance responsivities with uncertainties comparable to those of primary standard radiometers. Illuminance and irradiance meters, holding the SI units (candela, color- and radiance-temperature), will be calibrated directly against the transfer standard trap-radiometer to obtain improved accuracy in the base-units.     

Nanophase Glass-Ceramics

Future applications for glass-ceramics are likely to capitalize on designed-in, highly specialized properties for the transmission, display, and storage of information. Glass-ceramics with microstructures comprised of uniformly dispersed crystals <100 nm in size offer promise for many potential new applications as well as provide unique attributes for many current products. This paper focuses on two types of nanocrystalline glass-ceramics: transparent glass-ceramics and tough, high-modulus glass-ceramics with precisely engineered surfaces. Transparent glass-ceramics are formed from certain aluminosilicate glasses capable of efficient crystal nucleation and slow growth. The key crystalline phases include β-quartz solid solutions, characterized by low-thermal-expansion behavior; spinel, with high hardness and elastic modulus; and mullite, which shows unique chromium-luminescence behavior.     

THE DEVITRIFICATION OF “PYREX” GLASSES1

A study has been made of the devitrification phenomena of three “Pyrex” glasses, which were found to have liquidus temperatures lower than any other known mixtures containing 50 high a silica content. “Pyrex” glass 774 (702EJ), refractive index 1.471, has a liquidus temperature of 1077°, 772 (702P), index 1.486, 1042° and 776 (720GO), index 1.473, 1036°. In all cases tridymite is the primary phase and cristobalite was never observed.     

Cognitive–behavioral group therapy for bereaved adults and children following an air disaster.

On September 8, 1994, USAir Flight 427 from Chicago crashed on its descent to the Pittsburgh International Airport. All 132 passengers and crew were killed. This crash was unique in that more than 80% of the victims were residents of the greater Pittsburgh area. In this regard, the need for professional intervention became vital. Group intervention allowed the professionals to promptly serve a large number of affected families. It was hypothesized that the group experience would lead to bonding and support that would persist beyond the time limits of the group. A group-based intervention program for adult and child survivors is described, including its administrative structure, therapeutic objectives and interventions, and group process. A direct outcome of this group was the establishment of The USAir Flight 427 Disaster Support League and, subsequently, the development of the National Air Disaster Alliance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Study of the thermal behaviour of alipharomatic polyesters around the glass–rubber transition region by thermomechanical analysis: the mobile and rigid amorphous fraction

The objective of this work was the study using thermomechanical analysis (TMA) of a peculiar behaviour, which was observed some years ago, around the glass–rubber transition region in some thermoplastic alipharomatic polyesters. For this purpose a series of nine alipharomatic polyesters was prepared by the two‐stage melt polycondensation method in a glass batch reactor and subjected to TMA in both penetration and expansion mode. Differential scanning calorimetry (DSC) was additionally used and the results are discussed focusing mainly on the first derivative curve of TMA thermograms in the penetration mode. From this curve, which shows two distinct peaks, the first peak could be attributed to the glass transition temperature (T_g) of the mobile amorphous fraction, since the value coincides with that obtained from DSC and is due to the abrupt shrinkage of the amorphous part of the sample. The second peak (up to 40 °C higher than T_g) is due most probably to the softening of the rigid amorphous fraction and the passage of the polymeric sample from the glass region to the cold crystallization region. When the sample is more crystalline than amorphous then the first peak is smaller or is completely absent. Copyright © 2006 Society of Chemical Industry