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Electrical resistance measurement system successful during recent field experiments Using an electrical resistance measurement system to detect interfaces between adjacent refined petroleum products transported through a petroleum pipe line has [...]

This paper compares static (i.e., temporally unchanging) thermal gradient gas chromatography (GC) to isothermal GC using a stochastic transport model to simulate peak characteristics for the separation of C12–C14 hydrocarbons resulting from variations in injection bandwidth. All comparisons are made using chromatographic conditions that give approximately equal analyte retention times so that the resolution and number of theoretical plates can be clearly compared between simulations. Simulations show that resolution can be significantly improved using a linear thermal gradient along the entire column length. This is mainly achieved by partially compensating for loss in resolution from the increase in mobile phase velocity, which approximates an ideal, basic separation. The slope of the linear thermal gradient required to maximize resolution is a function of the retention parameters, which are specific to each analyte pair; a single static, thermal gradient will not affect all analytes equally. A static, non-linear thermal gradient that creates constant analyte velocities at all column locations provides the largest observed gains in resolution. From the simulations performed in this study, optimized linear thermal gradient conditions are shown to improve the resolution by as much as 8.8% over comparative isothermal conditions, even with a perfect injection (i.e., zero initial bandwidth).

'Veterans of the Wars' Edgar Lee Masters (1869-1950) Edwin, your father has never ceased to be My admiration, and I can close my eyes And see his soldier shape arise [...]

I am a life member of the DAV and served in the U.S. Army. It disappoints me that the DAV opposes H.R. 23 authorizing the payment of a $1,000 monthly [...]

In a terrorist event or industrial accident, environmental toxins will be inhomogeneously distributed on surfaces. A field vacuum extractor (FVE) can be used to sample contamination on fixed surfaces in a non-destructive fashion, but application to heterogeneously contaminated environments tends to be limited by the sampling time and time required for analysis, which is ∼15 to 30 min for a laboratory gas chromatograph/mass spectrometer (GC/MS). In the present study, FVE surface sampling was combined with a portable, fast-duty cycle GC/MS that enables analysis of a surface sample approximately every 3 minutes. Employing multiple FVE devices enables rapid measurement of many samples as might be required for characterizing contamination that is inhomogeneously distributed in a release environment. The FVE utilizes solid phase microextraction (SPME) fibers to sorb volatilized compounds from an evacuated headspace enclosed over the surface to be sampled (vinyl floor tile in the present study), over the course of a 30 min sampling time. Recovery of organophosphonate compounds in quantities sufficient to enable identification was achieved sampling floor tile exposed to as little as 30 ng. The amount detected was found to increase in a linear fashion with quantity applied to the floor tile, over three orders of magnitude. Carboxen–polydimethylsiloxane (PDMS) was used as the SPME sorbent phase and was sufficiently robust for multiple sampling and analysis cycles. The carboxen–PDMS retained 2–5% of the organophosphonate compounds after the initial GC/MS analysis, and this fraction could be readily measured in a subsequent re-analysis of the same sample. The re-analysis showed identifiable quantities of the organophosphonate compounds in all experiments except those with the lowest exposure quantities. Thus, once-analyzed carboxen–PDMS fibers may be archived for re-analysis at a later date if desired.

The rapid and accurate detection and identification of chemical warfare agents and toxic industrial chemicals can be critical to the protection of military and civilian personnel. The use of gas chromatography (GC) - mass spectrometry (MS) can provide both the sensitivity and selectivity required to identify unknown chemicals in complex (i.e. real-world) environments. While most widely used as a laboratory-based technique, recent advances in GC, MS, and sampling technologies have led to the development of a hand-portable GC/MS system that is more practical for field-based analyses. The unique toroidal ion trap mass spectrometer (TMS) used in this instrument has multiple benefits related to size, weight, start-up time, ruggedness, and power consumption. Sample separation is achieved in record time (~ 3 minutes) and with high resolution using a state-of-the-art high-performance low-thermal-mass GC column. In addition to providing a system overview highlighting its most important features, the presentation will focus on the chromatographic and mass spectral performance of the system. Results from exhaustive performance testing of the new instrument will be introduced to validate its unique robustness and ability to identify targeted and unknown chemicals.

Type II diabetes, in its late stages, is often associated with the formation of extracellular islet amyloid deposits composed of islet amyloid polypeptide (IAPP or amylin). IAPP is stored before secretion at millimolar concentrations within secretory granules inside the β-cells. Of interest, at these same concentrations in vitro, IAPP rapidly aggregates and forms fibrils, yet within secretory granules of healthy individuals, IAPP does not fibrillize. Insulin is also stored within the secretory granules before secretion, and has been shown in vitro to inhibit IAPP fibril formation. Because of insulin's inhibitory effect on IAPP fibrillization, it has been suggested that insulin may also inhibit IAPP-mediated permeabilization of the β-cell plasma membrane in vivo. We show that although insulin is effective at preventing fiber-dependent membrane disruption, it is not effective at stopping the initial phase of membrane disruption before fibrillogenesis, and does not prevent the formation of small IAPP oligomers on the membrane. These results suggest that insulin has a more complicated role in inhibiting IAPP fibrillogenesis, and that other factors, such as the low pH of the secretory granule, may also play a role.

Amyloid diseases are traditionally characterized by the appearance of inter- and intracellular fibrillar protein deposits, termed amyloid. Historically, these deposits have been thought to be the etiology of the disease. However, recent evidence suggests that small oligomers of the amyloidogenic protein/peptide are the origin of neurotoxicity. Although the importance of identifying the toxic oligomeric species is widely recognized, such identification is challenging because these oligomers are metastable, occur at low concentration, and are characterized by a high degree of heterogeneity. In this work, a fluorescently labeled β-amyloid(1–40) is used as a model amyloidogenic peptide to test the effectiveness of what we believe is a novel approach based on single-molecule spectroscopy. We find that by directly counting the photobleaching steps in the fluorescence, we can determine the number of subunits in individual β-amyloid(1–40) oligomers, which allows us to easily distinguish among different species in the mixtures. The results are further analyzed by comparison with Monte Carlo simulations to show that the variability seen in the size of photobleaching steps can be explained by assuming random dipole orientations for the chromophores in a given oligomer. In addition, by accounting for bias in the oligomer size distribution due to the need to subtract background noise, we can make the results more quantitative. Although the oligomer size determined in this work is limited to only small species, our single-molecule results are in good quantitative agreement with high-performance liquid chromatography gel filtration data and demonstrate that single-molecule spectroscopy can provide useful insights into the issues of heterogeneity and ultimately cellular toxicity in the study of amyloid diseases.

The challenge of organizing a history of medical education is not unlike the challenge of medical education itself. Which way and how thick does one slice the vast loaf to provide nourishing, palatable, and attractive substance for further growth? What should be included and what must be trimmed away? This requires a good understanding of the subject, sound judgment, and a set of values, which give overall shape and character to the whole. Professor Numbers and his colleagues have demonstrated these qualities admirably in putting together this fine collection of historical essays.Martin Kaufman's excellent overview at the beginning provides a sensitive, integrative framework for the individual parts as represented by 12 significant disciplines. The subjects are well balanced between the basic sciences, the clinical specialties, and broader sociomedical fields, including public health and medical ethics. All are interesting as well as informative, with an index and appropriate footnotes, which

Micro-HPLC has a legitimate role when combined on-line with a mass spectrometer (micro-LC/MS) because the latter is a mass-flow sensitive detector. Thus, the more concentrated micro-HPLC peaks provide better detection limits for micro-LC/MS than those obtained from conventional HPLC flow rates. Most of the LC/MS interfaces developed so far benefit from micro-HPLC. This review briefly highlights the developments in micro-LC/MS from early reports, and then focuses on recent developments in direct liquid introduction (DLI) micro-LC/MS. A variety of examples taken from the authors work is shown to provide the chromatographer some insight as to what the limitations and capabilities are of the DLI micro-LC/MS technique.