Author: Verner LagessonPublisher:
ISBN: 9789170326806
Category :
Languages : en
Pages : 100
Book Description
Micro gas chromatographic separation combined with uv- and ir-sectrophotometric detection/identification
Author: Verner LagessonPublisher:
ISBN: 9789170326806
Category :
Languages : en
Pages : 100
Book Description
Advances in Gas Chromatography and Vacuum UV Spectroscopy
Author: Zackery Ray RobersonPublisher:
ISBN:
Category :
Languages : en
Pages : 200
Book Description
In forensic chemistry, a quicker and more accurate analysis of a sample is always being pursued. Speedy analyses allow the analyst to provide quick turn-around times and potentially decrease back-logs that are known to be a problem in the field. Accurate analyses are paramount with the futures and lives of the accused potentially on the line. One of the most common methods of analysis in forensic chemistry laboratories is gas chromatography, chosen for the relative speed and efficiency afforded by this method. Two major routes were attempted to further improve on gas chromatography applications in forensic chemistry. The first route was to decrease separation times for analysis of ignitable liquid residues by using micro-bore wall coated open-tubular columns. Micro-bore columns are much shorter and have higher separation efficiencies than the standard columns used in forensic chemistry, allowing for faster analysis times while maintaining the expected peak separation. Typical separation times for fire debris samples are between thirty minutes and one hour, the micro-bore columns were able to achieve equivalent performance in three minutes. The reduction in analysis time was demonstrated by analysis of ignitable liquid residues from simulated fire debris exemplars. The second route looked at a relatively new detector for gas chromatography known as a vacuum ultraviolet (VUV) spectrophotometer. The VUV detector uses traditional UV and far-ultraviolet light to probe the pi and sigma bonds of the gas phase analytes as well as Rydberg traditions to produce spectra that are nearly unique to a compound. Thus far, the only spectra that were not discernable were from enantiomers, otherwise even diastereomers have been differentiated. The specificity attained with the VUV detector has achieved differentiation of compounds that mass spectrometry, the most common detection method for chromatography in forensic chemistry labs, has difficulty distinguishing. This specificity has been demonstrated herein by analyzing various classes of drugs of abuse and applicability to "real world" samples has been demonstrated by analysis of de-identified seized samples
Automated Measurements of Infrared Spectra of Chromatographically Separated Fractions
Author: Peter R. GriffithsPublisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 88
Book Description
Selective Detection for Gas Chromatography by Ultraviolet Spectrometry
Author: Debra L. Van EngelenPublisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 502
Book Description
Spectrometric detection systems for gas chromatography (GC) based on gas phase ultraviolet absorbance and fluorescence measurements have been developed and evaluated in this research. Polynuclear aromatic compounds (PNAs) are selectively detected by these systems. Limits of detection for PNAs range from 4 ng to 90 ng for absorbance determinations, and from 3 ng to 400 ng for fluorescence determinations made at a fixed waveband. The spacial design and optical components have been carefully selected to be compatible with hightemperature gas-phase measurements (ca. 250°C) while preserving the resolution of the chromatographic separation and enhancing the sensitivity of the multimode spectrometric determinations. Vapor-phase determinations of GC eluates are made directly as they leave the GC column in specially designed, heated flow-through detector cells with low volume and dead space. A long pathlength cell of 167 mm was used to enhance the sensitivity of the absorbance measurements. High-temperature, quartz fiber optic bundles transmit light to and from the detector cell, thus thermally isolating optical components. There are two configurations for these GC detection systems, each advantageous for either quantitative or qualitative determinations, respectively. In the first, waveband selection is accomplished via optical filters. These simple and compact systems are particularly suited to precise and sensitive determinations of polynuclear aromatic compounds. The sensitivity and selectivity of the absorbance and fluorescence measurements vary with individual compounds. These differences also provide some qualitative information about eluates. The second detection system configuration provides repetitive UV spectral information of GC eluates. This computer-controlled system scans a modified Czerny- Turner monochromator and can acquire up to two 62-nm spectra of eluates per second. Spectral information thus obtained may be used for identification purposes and to locate unresolved GC eluates. After compounds have been separated and identified, fixed waveband spectrometric data acquired at an absorption maximum may be used to determine concentrations.
On-line Measurement of the Infrared Spectra of Gas Chromatographic Eluents
Author: Peter R. GriffithsPublisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 32
Book Description
Encyclopedia of Separation Science
Author: Ian D. WilsonPublisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 556
Book Description
Volume 1 of this resource encyclopedia contains Level 1, which provides a broad overview of the theory of the 12 main categories of separation techniques. Volumes 2-4 (Level 2) expand coverage with detailed theoretical and technical descriptions of particular techniques. The remaining Volumes 5-9 (Level 3) cover applications of these techniques from the micro to the macro, and from the analytical laboratory bench to large-scale industrial processes. The last volume consists mainly of the index.
Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications ...
Author: Instrumentation for Microcolumn Separations
Author: Murray HackettPublisher:
ISBN:
Category : Gas chromatography
Languages : en
Pages : 240
Book Description
Advances in Gas Chromatography, Thermolysis, Mass Spectrometry, and Vacuum Ultraviolet Spectrometry
Author: Ashur RaelPublisher:
ISBN:
Category :
Languages : en
Pages : 262
Book Description
In the area of forensic chemistry, improved or new analysis methods are continually being investigated. One common and powerful technique used in forensic chemistry is wall-coated open-tubular column (WCOT) gas chromatography with electron ionization single quadrupole mass spectrometry (GC-MS). Improvements to and effectiveness of alternatives to this instrumental platform were explored in an array of parallel inquiries. The areas studied included the column for the chromatographic separation, the universal detection method employed, and the fragmentation method used to enhance molecular identification. Superfine-micropacked capillary (SFμPC) columns may provide an alternative to commercial packed GC columns and WCOT GC columns that combines the benefits of the larger sample capacity of packed columns and the benefits of the excellent separation capabilities and mass spectrometry (MS) flow rate compatibility of WCOT columns. SFμPC columns suffer from high inlet pressure requirements and prior reported work has required specialized instrumentation for their use. Fabrication of and chromatography with SFμPC GC columns was successfully achieved with typical GC-MS instrumentation and within the flow rate limit of a MS. Additionally, the use of higher viscosity carrier gasses was demonstrated to reduce the required inlet pressure for SFμPC GC columns. Recently, a new vacuum ultraviolet spectrometer (VUV) universal detector has been commercialized for GC. The ability of VUV detectors to acquire absorbance spectra from 125 nm to 430 nm poses a potential alternative to MS. As such, GC-VUV provides an exciting potential alternative approach to achieving excellent quantitative and qualitative analysis across a wide range of analytes. The performance of VUV and MS detectors for forensic analysis in terms of quantitative and qualitative analysis was compared. Analysis of alkylbenzenes in ignitable liquids was explored, which can be important evidence from suspected arson fires and are difficult to differentiate with MS. The VUV detector was found to have superior specificity and comparable sensitivity to the MS detector in scan mode. Addition of thermolysis (Th) as an orthogonal fragmentation pathway provides the opportunity to increase the differences between MS fragmentation patterns. Fragmentation has been widely established to aid in identification of molecules with MS by providing characteristic fragments at characteristic relative abundances. However, molecules with very similar structures do not result in sizable spectral differences in all cases with typical MS fragmentation techniques. A series of Th units were fabricated and integrated into GC-Th-MS instruments. Th-MS was conducted with the thermally labile nitrate esters across a range of instrumentation and thermal conditions.
Author: