Search

Through a detailed optimization process, response surfaces were obtained for micro-HPLC/SCD under various reversed-phase (methanol/water) elution conditions. Linear dynamic range, correlation coefficient, response factor, and limit of detection were found to vary with mobile-phase composition. The lowest sensitivity achieved was a detectivity of 600 fg of S/s at a mobile-phase composition of 40% methanol/60% water. Application of the HPLC/SCD interface to the separation of thiocarbamates extracted from apples is presented

The use of the ozone-based sulfur chemiluminescence detector (SCD) coupled with packed column supercritical fluid chromatography (SFC) was evaluated. Optimization studies performed include the quenching effect of the CO 2 mobile phase and organic species on the chemiluminescence species (SO 2 * ) and the necessary air and hydrogen flow rates to gain maximum SCD sensitivity. Detectivities of 2 pg S/s and 1 pg S/s (S/N=3) were obtained when capillary SFC (60-nL injection) and packed column conditions (500-nL injection) were employed, respectively

The effect of modifier on solid-phase trapping efficiency in off-line supercritical fluid extraction was studied. Two types of traps-solid surface (stainless steel) and sorbent (octadecyl silica)-were studied with pure carbon diocide and 1%, 2%, 4% and 8% methanol-modified carbon dioxide. The trapping efficiency of a polarity test mix consisting of N,N-dimethylanilline, acetophenone, naphthol, decanoic acid, and n-tetracosane was studied at trap temperatures ranging from 5 to 80 o C with each fluid. For low concentrations of methanol and the ODS sorbent, trap temperatures below 20 o C were necessary for volatile (bp

Sulfamethoxazole and trimethoprim have been extracted from a drug formulation, Septra Infusion, with pure supercritical carbon dioxide. Both direct extraction of the aqueous-based matrix and indirect extraction of the formulation immobilized onto Celite were studied. Exhaustive analytical extraction was achieved when active components were less than 1.0 mg. A number of co-extractants were found, but each was blind to the HPLC/UV assay.

Doping polyimides with cobalt ion causes the room temperature direct current electrical resistivity to decrease relative to the polymer alone, the reduction being most pronounced for the air-side of the cobalt modified polyimides. At a constant electrical field, resistivity for the volume, air-side and glass-side modes decreases yet further with an increase in temperature as expected for semiconductors and insulators. X-ray photoelectron spectroscopy indicates the air-side of the cobalt modified polyimides is predominantly Co3O4. The bulk resistivity of the air-side and activation energy of conduction for this surface are comparable to high purity sintered Co3O4. Charging characteristics at room temperature indicate a substantial polymer matrix contribution to both the glass-side and volume mode measurements but a negligible contribution to the air-side electrical properties. Volume electrical resistivity for similar additive levels is reduced by increasing the molecular flexibility of the host polymer.

The development of a simultaneous on-line detector for metal species separated by effective molecular size is described. A new spray chamber to facilitate this analysis in relatively high-volatility organic solvents and to serve as the interface between a liquid chromatography (LC) and an inductively coupled plasma atomic emission spectrometer (ICP-AES) is evaluated. Detection limits in toluence are comparable to those found in aqueous static operation of ICP-AES. The requirements of computer-based data output and examples of the output developed are presented. The LC-ICP interface is demonstrated by size separation of three synthetic mixtures. Two of the mixtures are iron and silicon organometallic species with different ligands attached, while the third mixture consists of approximately 20 different metals in essentially the same ligand environment.

As part of a research program to decrease the electrical resistivity of polyimide films with ionic additives a variable temperature three probe electrical resistivity measurement system has been designed and constructed. Sample temperature, electrification time, atmosphere, and measurement mode are computer controlled. As a data interpretation aid, temperature cycled analysis can be routinely performed. Surface resistivities in the range 103–1015 ohm and volume resistivities in the range 105–1018 ohm-cm are theoretically measurable under well controlled experimental conditions from room temperature to 250°. The electrical resistivity measurement system is useful for the evaluation of polymer films or films in general. Application of the system for analysis of cobalt, lithium and tin ion-modified polyimide films and some experimental considerations are presented. Correlation of the electrical measurements with differential scanning calorimetry, thermomechanical analysis, and thermogravimetric analysis is demonstrated.

Organometallic and metalloorganic compounds have been separated by size exclusion chromatography using pyridine eluent. A directly interfaced inductively coupled plasma atomic emission spectrometer was used for detection of these metal-containing species. Problems relating to the use of pyridine in the chromatography of these species are discussed. Most problems appear to be related to non-carbon-bound metal systems. The application of this technique to solvent-refined coal fractions and process solvent is presented. Evidence of solvent selectivity for some of the organically bound metals in the solvent refined coal is given.

The successful interfacing and utilization of fused silica capability Gas chromatography(GC) columns with Fourier transform infrared spectrometry (FTIR) can introduce difficulties not usually encountered with lower efficiency (higher capacity) GC columns. Recognition of these difficulties, however, can lead to refinement of a GC-FTIR detection system which can analyze complete samples with low nanogram detection limits. Chromatography and spectrometric considerations include lightpipe temperature, choice of same introduction, column concentration dynamic range capability, infrared data acquisition rate and spectral S/N ratio. These parameters as they relate to capability GC-FTIR method development are discussed. GC-FTIR 'identification limits' for sixteen model compounds which represent both polar and non-polar functionalities have been established employing optimized chromatographic-spectrometric parameters for complex mixture analysis.