Engineering topics

Jarman, Kristin H

Publications and source records attributed to Jarman, Kristin H.

4 records

DOE OSTI2012

Demonstrated Wavelength Portability of Raman Reference Data for Explosives and Chemical Detection

As Raman spectroscopy continues to evolve, questions arise as to the portability of Raman data: dispersive versus Fourier transform, wavelength calibration, intensity calibration, and in particular the frequency of the excitation laser. While concerns about fluorescence arise in the visible or ultraviolet, most modern (portable) systems use near-infrared excitation lasers, and many of these are relatively close in wavelength. We have investigated the possibility of porting reference data sets from one NIR wavelength system to another. We have constructed a reference library consisting of 145 spectra, including 20 explosives, as well as sundry other compounds and materials using a 1064 nm spectrometer. These data were used as a reference library to evaluate the same 145 compounds whose experimental spectra were recorded using a second 785 nm spectrometer. In 128 cases of 145 (or 88.3% including 20/20 for the explosives) the compounds were correctly identified with a mean 'hit score' of 954 of 1000. Adding in criteria for when to declare a correct match versus when to declare uncertainty, the approach was able to correctly categorize 134 out of 145 spectra, giving a 92.4% accuracy. For the few that were incorrectly identified, either the matched spectra were spectroscopically similar to the target or the 785 nm signal was degraded due to fluorescence. The results indicate that imported data recorded at a different NIR wavelength can be successfully used as reference libraries, but key issues must be addressed: The reference data must be of equal or higher resolution, the systems require rigorous wavelength calibration, and wavelength-dependent intensity response should be accounted for in the different systems.

47 OTHER INSTRUMENTATION↗

DOE OSTI2011

Raman Database Considerations for Near-Infrared Systems

For Raman spectroscopy the ability to detect is often limited by the existence and quality of the reference library to which field spectra are compared. Developing such databases is often labor- and resource-intensive; typically the generated data are not transferred to other instruments. Still other considerations may exist for comparing data at visible and ultraviolet excitation wavelengths such as resonance enhancement. However, for the common near-infrared wavelengths of 785, 830, 960, 1047 and 1064 nm where this is normally of a lesser concern, it is logical to consider whether data can be ported from one spectrometer to another so as to obviate the expensive and time-consuming process of generating reference data for each system. The present experiment generated a list of 125 chemical and common substances and formed a database from their corresponding 1064 nm spectra. The same molecules were then measured using a 785 nm system the new spectra were treated as “unknowns” and compared to the 1064 nm database using a commercial search algorithm. We found that at least 108 of the 125 spectra recorded at 785 nm were correctly identified using the search algorithm. For the few that were incorrectly identified, in most cases the spectra were extremely similar or the 785 nm signal was degraded due to fluorescence, as would occur regardless of reference data. Our results indicate that if the spectrometers are properly calibrated on both their wavelength and intensity axes, “foreign” data recorded at a different NIR wavelength can be successfully used as reference libraries

Kunkel, Brenda M↗

DOE OSTI2011

Characterization of Diesel Fuel by Chemical Separation Combined with Capillary Gas Chromatography (GC) Isotope Ratio Mass Spectrometry (IRMS)

The purpose of this study was to perform a preliminary investigation of compound-specific isotope analysis (CSIA) of diesel fuels to evaluate whether the technique could distinguish between the diesel samples from different sources/locations. The ability to differentiate or correlate diesel samples could be valuable for detecting fuel tax evasion schemes. Two fractionation techniques were used to isolate the n-alkanes from the fuel. Both δ13C and δD values for the n-alkanes were then determined by CSIA in each sample. Plots of δD versus δ13C with sample n-alkane points connected in order of increasing carbon number gave well separated clusters with characteristic shapes for each sample. Principal components analysis (PCA) with δ13C, δD, or combined δ13C and δD data on the yielded scores plots that could clearly differentiate the samples, thereby demonstrating the potential of this approach for fingerprinting fuel samples using the δ13C and δD values.

compound specific isotope ratio mass spectrometry↗

DOE OSTI2011

Peptide identification

Peptides are identified from a list of candidates using collision-induced dissociation tandem mass spectrometry data. A probabilistic model for the occurrence of spectral peaks corresponding to frequently observed partial peptide fragment ions is applied. As part of the identification procedure, a probability score is produced that indicates the likelihood of any given candidate being the correct match. The statistical significance of the score is known without necessarily having reference to the actual identity of the peptide. In one form of the invention, a genetic algorithm is applied to candidate peptides using an objective function that takes into account the number of shifted peaks appearing in the candidate spectrum relative to the test spectrum.

59 BASIC BIOLOGICAL SCIENCES↗