Ignitable Liquid Classification and Identification Using the Summed-Ion Mass Spectrum

Abstract

The mass spectra calculated by summing the intensities of each nominal mass over all chromatographic times, the summed ion spectra, were calculated for a set of 440 commercially available ignitable liquids that had been analyzed by gas chromatography–mass spectrometry. Each ignitable liquid is generally comprised of a mixture of chemicals, and the mixtures may be very complex in some cases, e.g., petroleum distillates, gasoline, etc. The summed ion spectra were evaluated to determine if they contained sufficient information content to allow their use for rapid and accurate identification of the ignitable liquid in a database or library. The summed ion nominal mass spectra were encoded in one bit per channel at 1% transition intensity and a set of 96,580 unique pairwise comparisons were made between spectra, resulting in an average of approximately 50 differing channels per comparison. A subset of 62 summed ion spectra were further compared by a similarity metric and found by cluster analysis to group closely along the ASTM ignitable liquid classification scheme. Receiver operator characteristic analysis of the use of the similarity index in combination with the summed ion spectra was shown to provide 99% probability of correct liquid identification and 95% probability of correct ASTM classification by primary and sub-class. Interlaboratory tests found 95% probability of correct liquid identification and 85% probability of correct ASTM classification at the primary class level. These results demonstrate the use of the summed ion spectrum as a first step in the rapid identification of an ignitable liquid by database or library searching.     

Involvement of surface cysteines in activity and multimer formation of thimet oligopeptidase

Thimet oligopeptidase is a metalloenzyme involved in regulatingneuropeptide processing. Three cysteine residues (246, 248,253) are known to be involved in thiol activation of the enzyme.In contrast to the wild-type enzyme, the triple mutant (C246S/C248S/C253S)displays increased activity in the absence of dithiothreitol.Dimers, purportedly formed through cysteines 246, 248 and 253,have been thought to be inactive. However, analysis of the triplemutant by native gel electrophoresis reveals the existence ofdimers and multimers, implying that oligomer formation is mediatedby other cysteines, probably on the surface, and that some ofthese forms are enzymatically active. Isolation and characterizationof iodoacetate-modified monomers and dimers of the triple mutantrevealed that, indeed, certain dimeric forms of the enzyme arestill fully active, whereas others show reduced activity. Cysteineresidues potentially involved in dimerization were identifiedby modeling of thimet oliogopeptidase to its homolog, neurolysin.Five mutants were constructed; all contained the triple mutationC246S/C248S/C253S and additional substitutions. Substitutionsat C46 or C682 and C687 prevented multimer formation and inhibiteddimer formation. The C46S mutant had enzymatic activity comparableto the parent triple mutant, whereas that of C682S/C687S wasreduced. Thus, the location of intermolecular disulfide bonds,rather than their existence per se, is relevant to activity.Dimerization close to the N-terminus is detrimental to activity,whereas dimerization near the C-terminus has little effect.Altering disulfide bond formation is a potential regulatoryfactor in the cell owing to the varying oxidation states insubcellular compartments and the different compartmental locationsand functions of the enzyme. Received March 1, 2003; revised June 17, 2003; accepted June 23, 2003.     

Intravenous immunoglobulin inhibits IgE production in human B lymphocytes

This study sought to determine the prevalence of spontaneous reperfusion of an infarct-related artery (IRA) and associated myocardial salvage in the absence of thrombolysis or angioplasty. Twenty-one patients with acute myocardial infarction received only heparin and aspirin. At a median of 18 hours after presentation, 12 patients (57%) had angiographic patency of the IRA. Technetium-99m sestamibi was injected acutely on presentation and again at hospital discharge. Acute and final perfusion defect sizes were measured. Their difference, myocardial salvage, was calculated along with salvage index (myocardial salvage/acute defect). Comparing patients with a patent versus occluded IRA, myocardium at risk was similar (16% +/- 12% vs 12% +/- 9% left ventricle, p = NS); however, myocardial salvage (9% +/- 9% vs -2% +/- 7% left ventricle, p = 0.01), and salvage index (0.62 +/- 0.37 vs 0.19 +/- 0.33, p = 0.01) were greater in patients with spontaneous reperfusion. Resolution of chest pain was greater in patients with a patent IRA (100% vs 55%, p = 0.003). Spontaneous reperfusion of the IRA occurs frequently in patients with acute myocardial infarction and is associated with significant myocardial salvage.     

The utility of parotid gland and level I and II neck fine-needle aspiration

OBJECTIVE: Although fine-needle aspiration (FNA) commonly is used in the diagnostic workup of parotid gland and level I and II neck lesions, the effect of an FNA service on patient care has not been definitively established. METHODS: Follow-up was obtained in 158 patients who underwent FNA. The value of FNA was analyzed by determining the proportions of cases in which management was altered by the information obtained. RESULT: The percentage of lesions classified by FNA as benign, nonneoplastic; benign, neoplastic; atypical or suspicious; malignant; and insufficient was 42%, 28%, 16%, 41%, and 7%, respectively. By using FNA, an operation was avoided in 70% and 79% of patients with a nonneoplastic lesion and a metastasis, respectively. CONCLUSIONS: Although definitive subclassification of some lesion types was poor, FNA was useful in patient triage.     

A longitudinal study of AIDS conversations between mothers and adolescents

This paper presents the results of a study on the introduced, free-ranging patas monkey population of Southwestern Puerto Rico (SWPR). It describes information on the population size, social group composition, diet, daily ranging patterns, and patas home range during a 3 year period. The patas monkey population in the study area consisted of approximately 120 individuals in four heterosexual groups and several all-male bands. Within their home ranges (26.8 km2), the population density was 4.47 individuals/km2. Home range size among the population's four heterosexual groups varied from 3.72 km2 to 15.39 km2, and minimum daily distance traveled ranged from 0.8-2.0 km. In general, the social structure and mating system of this population parallels what has been described for African populations. However, habitat use, ranging behavior, and the quality of intergroup interactions suggests that patas of this population exhibit territorial behavior.     

Combustion of Propellants with Ammonium Dinitramide

This paper reports a series of experiments involving ammonium dinitramide (ADN), a new energetic oxidizer of potential use in composite solid propellants. The experiments include (a) self‐deflagration of pressed pellets of ADN; (b) combustion of sandwiches with ADN laminae on both sides of a binder lamina that is either “pure” or filled with particulate oxidizer and other additives; and, (c) combustion of propellants with a bimodal oxidizer size distribution, wherein, combustion of coarse ADN and fine AP (ammonium perchlorate) and vice versa were used, in addition to mixtures of coarse ADN and AP, fine ADN and AP, and all‐ADN or all‐AP formulations.     

Characterization of automobile float glass with laser-induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry

A comparative analysis of the discriminating power of laser-induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), each coupled with refractive index (RI) measurements, is presented for a study of 23 samples of automobile float glass. Elemental emission intensity ratios (LIBS) and elemental concentration ratios (LA-ICP-MS) and their associated confidence intervals were calculated for each float glass sample. The ratios and confidence intervals were used to determine the discrimination power of each analytical method. It was possible to discriminate 83% of the glass samples with 99% confidence based on LIBS spectra alone, and 96-99% of the samples could be discriminated based on LIBS spectra taken in conjunction with RI data at the same confidence level. LA-ICP-MS data allowed for 100% discrimination of the samples without the need for RI data. The results provide evidence to support the use of LIBS combined with RI for forensic analysis of float glass in laboratories that do not have access to LA-ICP-MS.     

Columnar self-assembly of colloidal nanodisks

The self-assembly of sterically stabilized colloidal copper sulfide nanodisks, 14-20 nm in diameter and 5-7 nm thick, was studied. The nanodisks were observed by electron microscopy and small-angle X-ray scattering to form columnar arrays when evaporated as thin films from concentrated dispersions. These superstructured nanomaterials might give rise to technologically useful properties, such as anisotropic electrical transport and electrorheological and optical properties.