GAS FACTS published periodically for analytical chemists
To remedy this situation, Scott has begun an experimental program to evaluate several systems of interest to chromatographers. First to be Miscibilities in examined was methanol/ supercritical carbon dioxide. A few of the experimental curves are fluids shown. It can be seen that In supercritical fluid chromasolubility of methanol in C02 tography, the use of a mobile is not significantly influenced phase containing a polar by either temperature or compound, ie, CH3OH in C02, pressure changes in the region can change separation propbelow 100atmospheres-and erties without altering that in this pressure range, critical temperature, viscosity mole fraction of the alcohol or density of the fluid. Such must be kept below 0.15 to additions can greatly extend maintain a homogeneous the applications of this system. Above about 120 analytical method. However, atmospheres, pressure and it is necessary to know the temperature both exert miscibility of the two comsignificant effects. During ponents under operating conthe experiments, it was also ditions. Unfortunately, observed that after temperaexperimental data do not ture changes, several hours exist and sufficient data are were required before the not available for use in system reached a new 1 Peng-Robinson or other equilibrium. theoretical models. If you are interested in learning more of this pioneering work, get in touch with Scott. We'll be happy to discuss with you our efforts to generate solubility information so essential for chemists involved in supercritical fluid chromatography and extraction. You can also learn about mixtures at conditions near and below the critical point.
BRIEFS Accuracy of Selective Extraction Procedures for Metal Speciation in Model Aquatic Sediments
1417
As currently practiced, chemical extractions of model aquatic sediments demonstrate insufficient selectivity to permit sensible interpretation. A primary problem is redistribution of trace elements among sediment phases during extraction. Carolyn Kheboian and Christopher F. Bauer*, Department of Chemistry, University of New Hampshire, Durham, N.H. 03824 Anal. Chem., 59 (1987)
Integrated Solid State Probe for Determination of Activity of Sodium Chloride 1423 A dual ISFET probe is prepared by applying Na + - and Cl~selective membranes to adjacent gates of the same transistor chip. The probe has lower drift and better temperature stability than individual ISFETs and is suitable for measuring physiological levels of NaCl activity. Klâra Bezegh, Danuta Petelenz, Andres Bezegh, and Jiri Janata*, Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112 Anal. Chem., 59 (1987)
Microelectrochemical Transistors Based on Electrostatic Binding of Electroactive Metal Complexes in Protonated Poly(4-vinylpyridine): Devices That Respond to Two Chemical Stimuli 1426 Modification of an interdigitated array of eight microelectrodes with Fe(CN) 6 3 ~-loaded protonated poly(4-vinylpyridine) allows a new kind of chemically responsive microelectrochemical transistor to be demonstrated. Daniel Bélanger and Mark S. Wrighton*, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass. 02139 Anal. Chem., 59 (1987)
Moderate-Power Argon Microwave-Induced Plasma for the Detection of Metal Ions in Aqueous Samples of Complex Matrix 1433 The effect of the matrix on solution nebulization is examined. With high salt solutions, atom lines provide better levels of detection than ion lines. Peter G. Brown, David L. Haas, John M. Workman, and Joseph A. Caruso*, Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, and Fred L. Fricke, U.S.F.D.A. Elemental Analysis Laboratory, 1141 Central Parkway, Cincinnati, Ohio 45202 Anal. Chem., 59 (1987)
'Ffeng. DY and Robinson. DB. IndEng ChemFundam. 1976. I 59-64.
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666 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 10, MAY 15, 1987
Laser Ablation of Solids for Elemental Analysis by Inductively Coupled Plasma Mass Spectrometry 1437 Direct elemental analysis of NBS microprobe steel standards by laser ablation-ICP/MS yields linear analytical curves with precision and accuracy of approximately ±5%. Detection limits are 0.2-2 μg/g for Cr, Cu, As, Nb, Zr, Mo, and Sb. Peter Arrowsmith, SCIEX, 55 Glen Cameron Road, Thornhill, Ontario, Canada L3T 1P2 Anal. Chem., 59 (1987)
