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The isothermal retention times of seven cyclic (D 4 to D 10 ) and nine linear (L 5 to L 13 ) dimethylsiloxane oligomers on a nonpolar gas chromatographic column were determined at temperatures between (308.15 and 438.15) K. Using normal alkanes as standard reference and calibration compounds, these retention times were used to derive liquid state vapor pressures at 298.15 K as well as enthalpies of vaporization that allow for the estimation of vapor pressures over a wide range of temperatures. The data agree within 0.25 log units with vapor pressure values previously reported by Flaningam (1986) but extend those values to lower temperatures and larger oligomers. Cyclic dimethylsiloxanes are more volatile than linear dimethylsiloxanes of a similar size. Oligomers with 10 and more dimethylsiloxane units are expected to sorb appreciably to aerosol at environmentally relevant temperatures.

An undergraduate experiment for the analysis of potential water pollutants is described. Students are exposed to two complementary techniques, ELISA and GC-MS, for the analysis of a water sample containing atrazine, desethylatrazine, and simazine. Atrazine was chosen as the target analyte because of its wide usage in North America and its utility for students to predict environmental degradation products. The water sample is concentrated using solid-phase extraction for GC-MS, or diluted and analyzed using a competitive ELISA test kit for atrazine. The nature of the water sample is such that students generally find that ELISA gives an artificially high value for the concentration of atrazine. Students gain an appreciation for problems associated with measuring pollutants in the aqueous environment: sensitivity, accuracy, precision, and ease of analysis. This undergraduate laboratory provides an opportunity for students to learn several new analysis and sample preparation techniques and to critically evaluate these methods in terms of when they are most useful.

In this experiment students applied advanced instrumental methods of metals analysis to investigate the imprint of anthropogenic activities as observed in aquatic sediments. Sediments from a mid-latitude varved meromictic lake were collected using a cold finger corer and were sectioned by year; the core covered the time frame 1300 to the present. Metals were extracted by microwave digestion and analyzed by ICP-AES and GFAAS. Quality control spike and recovery, replicate, and blank analyses were all within acceptable limits. Target metal concentrations remained relatively constant until the late 19th century, when lead, manganese, and cadmium increased significantly. The concentrations of these metals then undergo a marked reduction toward the end of the 20th century, indicating a possible change in anthropogenic behavior.

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