Measurement of attogram quantities of 231Pa in dissolved and particulate fractions of seawater by isotope dilution thermal ionization mass spectroscopy

A technique has been developed to quantify ultratrace 231Pa (50-2000 ag; 1 ag = 10(-18) g) concentrations in seawater using isotope-dilution thermal ionization mass spectrometry (TIMS). The method is a modification of a process developed by Pickett et al. (Pickett, D. A.; Murrell, M. T.; Williams, R. W. Anal. Chem. 1994, 66, 1044-1049) and extends the technique to very low levels of protactinium. The procedural blank is 16 +/- 15 ag (2sigma), and the ionization efficiency (ions generated/atom loaded) approaches 0.5%. Measurement time is <1 h. The amount of 231Pa needed to produce 231Pa data with an uncertainty of +/-4-12% is 100-1000 ag (approximately 3 x 10(5) to 3 x 10(6) atoms). Replicate measurements made on known standards and seawater samples demonstrate that the analytical precision approximates that expected from counting statistics and that, based on detection limits of 38 and 49 ag, protactinium can be detected in a minimum sample size of surface seawater of approximately 2 L for suspended particulate matter and <0.1 L for filtered (<0.4 microm) seawater, respectively. The concentration of 231Pa (tens of attograms per liter) can be determined with an uncertainty of +/-5-10% (2sigma) for suspended particulate matter filtered from 5 to 10 L of seawater. For the dissolved fraction, 0.5-1 L of seawater yields 231Pa measurements with a precision of 1-10%. Sample size requirements are orders of magnitude less than traditional decay-counting techniques and significantly less than previously reported ICP-MS techniques. Our technique can also be applied to other environmental samples, including cave waters, rivers, and igneous rocks.     

Surface plasmon resonance detection for capillary electrophoresis separations

A miniaturized surface plasmon resonance sensor has been used as an on-line detector for capillary electrophoresis separations. The capillary was modified slightly to shield the sensor electronics from the high voltages applied during the separation. A three-component mixture of high refractive index materials was separated and detected at the millimolar level by an untreated gold-sensing surface. A simple protein immobilization procedure was used to functionalize the surface for selective protein detection. A hybrid buffer system was developed, in which both the deposition of immobilized protein layers and the electrophoretic delivery of protein analytes were optimized. The detection system has a reproducibility of 15%, a dynamic range of 3 orders of magnitude, and a detection limit for IgG of 2 fmol.     

Analysis of endocrine disruptors, pharmaceuticals, and personal care products in water using liquid chromatography/tandem mass spectrometry

A method has been developed for the trace analysis of 27 compounds from a diverse group of pharmaceuticals, steroids, pesticides, and personal care products. The method employs solid-phase extraction (SPE) and liquid chromatography/tandem mass spectrometry (LC/MS/MS), using electrospray ionization (ESI) in both positive and negative modes and atmospheric pressure chemical ionization in positive mode. Unlike many previous methods, a single SPE procedure using 1 L of water coupled to a simple LC method is used for all ionization modes. Instrument detection limits for most compounds were below 1.0 pg on column with reporting limits of 1.0 ng/L in water. Recoveries for most compounds in deionized water were greater than 80%. Sulfuric acid was found to be the preferred sample preservative, and structures of all MS/MS product ions are proposed. Matrix effects from waters with a high content of treated municipal effluent were observed in both ESI modes and are discussed in the paper.     

A hybrid reality environment and its application to the study of earthquake engineering

Visualization can provide the much needed computer-assisted design and analysis environment to foster problem-based learning, while Virtual Reality (VR) can provide the environment for hands-on manipulation, stimulating interactive learning in engineering and the sciences. In this paper, an interactive 2D and 3D (hybrid) environment is described, which facilitates collaborative learning and research and utilizes techniques in visualization and VR, therefore enhancing the interpretation of physical problems within these fields. The environment described, termed VizClass, incorporates a specially designed lecture room and laboratory integrating both 2-D and 3-D spatial activities by coupling a series of interactive projection display boards (touch-sensitive whiteboards) and a semi-immersive 3D wall display. The environment is particularly appealing for studying critical, complex engineering problems, for example, where time-varying feature modifications and coupling between multiple modes of movement are occurring. This paper describes the hardware architecture designed for this new hybrid environment as well as an initial application within the environment to the study of a real case history building subjected to a variety of earthquakes. The example simulation uses field measured seismic data sources, and illustrations of simple visual paradigms to provide an enhanced understanding of the physical model, the damage accumulated by the model, and the association between the measured and observed data. A detailed evaluation survey was also conducted to determine the merits of the presented environment and the techniques implemented. Results substantiate the plausibility of using these techniques for more general, everyday users. Over 70% of the survey participants believed that the techniques implemented were valuable for engineers.

Words about Images: Coordinating Community in Amateur Photography

This paper describes how the adoption of digital technologies by two amateur photography communities created coordination challenges. Digital technologies disrupted the classification schemes used not just to sort images into groups for competition, but also served to coordinate the community itself. In opening up the classification scheme, members were able to see and reflect on the sources used to establish the definitions that sorted images and organised their practices not just locally but more widely across various boundaries. Without having words about images, both amateur photography communities would have struggled to coordinate.