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71.
Lazarus EA Navratil GA Greenfield CM Strait EJ Austin ME Burrell KH Casper TA Baker DR DeBoo JC Doyle EJ Durst R Ferron JR Forest CB Gohil P Groebner RJ Heidbrink WW Hong R Houlberg WA Howald AW Hsieh C Hyatt AW Jackson GL Kim J Lao LL Lasnier CJ Leonard AW Lohr J La Haye RJ Maingi R Miller RL Murakami M Osborne TH Perkins LJ Petty CC Rettig CL Rhodes TL Rice BW Sabbagh SA Schissel DP Scoville JT Snider RT Staebler GM Stallard BW Stambaugh RD St John HE Stockdale RE Taylor PL Thomas DM 《Physical review letters》1996,77(13):2714-2717
72.
73.
A 20-year-old conjecture about the mod 2 Steenrod algebra The method of Walker and Wood is used to completely determine the nilpotence height of the elements in the Steenrod algebra at the prime 2. In particular, it is shown that for all , . In addition, several interesting relations in are developed in order to carry out the proof.
74.
A novel interface between high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS) is described. The eluent from the HPLC is nebulised into a heated cyclone spray-chamber and the solvent removed using a Nafion membrane drier, held at 75 degrees C, and a cryogenic condenser. The condenser consists of 6 Peltier heat pumps connected to liquid cooled aluminium blocks. At a nebuliser gas flow rate of 0.6 l min(-1), the membrane drier removes 58% of the vapour and the Peltier condenser 75% of the remaining vapour, i.e. a total desolvation efficiency of 89%. This enables the use of HPLC solvents which otherwise would destabilise the ICP, e.g. 100% acetonitrile or methanol, and permits the use of solvent gradients with minimal baseline drift. The system has been applied to the determination of platinum species in an organoplatinum drug used for chemotherapy in human plasma ultrafiltrate of patients treated with this new drug (JM-216). The limit of detection for platinum species has been 0.6 ng nl(-1) (i.e. 120 pg of Pt) and several species have been separated with good resolution. 相似文献
75.
Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Ross WR Skubic P Snow J Wang PL Wood M Bortoletto D Brown DN Fast J McIlwain RL Miao T Miller DH Modesitt M Schaffner SF Shibata EI Shipsey IP Wang PN Battle M Ernst J Kroha H Roberts S Sparks K Thorndike EH Wang CH Dominick J Sanghera S Skwarnicki T Stoynowski R Artuso M He D Goldberg M Horwitz N Kennett R 《Physical review letters》1993,71(20):3259-3262
76.
Cinabro D Henderson S Kinoshita K Liu T Saulnier M Wilson R Yamamoto H Sadoff AJ Ammar R Ball S Baringer P Coppage D Copty N Davis R Hancock N Kelly M Kwak N Lam H Kubota Y Lattery M Nelson JK Patton S Perticone D Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Zoeller MM Crawford G Fulton R Fujino D Gan KK Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Ross WR 《Physical review letters》1993,70(24):3700-3704
77.
78.
Jacques E. Desnoyers Gérald Perron Sylvain Léger Byron Y. Okamoto Terrence H. Lilley Robert H. Wood 《Journal of solution chemistry》1978,7(3):165-178
The freezing-point depression of the ternary systems tetraalkylammonium bromides-t-butanol-water for the first five homologs of R4NBr was measured. In the case of Bu4NBr, the effect of size of the alcohol (methahol ton-butanol) was also investigated. From the corresponding freezing-point data for the binary systems the apparent salting constants
were calculated. The true salting constantsk
s were obtained by extrapolation to infinite dilution. These are all very close to zero at the freezing temperature. From the
corresponding thermochemical data the temperature dependence ofk
s was calculated, and above 5°C all the R4NBr salts int-butanol; the salting-in increases with temperature and with the size of the hydrophobic cations. The scaled-particle theory
is at present the only one which can account semiquantitatively for the temperature dependence of the salting-in effect.
On leave of absence from Chemistry Department, The University, Sheffield S3 7HF, England
To whom correspondence should be addressed. 相似文献
79.
Two methods of determining trace levels of platinum and gold in aqueous solutions with high concents of total dissolved solids were investigated. The first involves preconcentration and separation of the precious metals from the interfering matrix by solvent extraction, followed by graphite furnace atomic absorption spectrometry (GFAAS) with Zeeman effect background correction. The direct determination of Pt and Au in solutions of high ionic strength by GFAAS is not desirable because of interference between elements in the matrix and the analyte, increased imprecision of analysis, greatly increased background absorbance leading to increased detection limits and rapid deterioration of the graphite tube. All the extraction methods for gold examined in this study resulted in decreased imprecision, increased sensitivity and lower background absorbance compared with direct measurements on the aqueous solution. All techniques also exhibited good recoveries (> 8%) and reproducibilities (relative standard deviation < 10%). The highest sensitivities for gold extraction from distilled water were obtained for dibutyl sulfide (DBS)—toluene and the lowest for cyanide—dibutyl ketone. The degree of extraction of Au was, however, dependent on the composition of the solution, indicating that standard and sample matrices should be closely matched even when employing solvent extraction. Solvent extraction was generally less successful for Pt. In order to obtain an acceptable imprecision in the Pt extractions, it was found that the use of SnCl2 as a labilizing agent is essential for most of the techniques investigated.The second method was direct measurement by inductively coupled plasma mass spectrometry (ICP—MS). ICP—MS offers the advantages of a very low detection limit (100 ng l?1 or better) without preconcentration and a large dynamic range. However, severe matrix effects can occur in concentrated solutions. Whereas high concentrations in solution of both sodium perchlorate and sodium chloride decrease the sensitivity, the presence of sulfide and natural organic (fulvic) acid increase the sensitivity for Pt and Au by a factor of up to 4. Sulfate, on the other hand, decreases the sensitivity of ICP-MS for Pt. The method of standard additions or isotope dilution is recommended for routine use to circumvent this problem, especially when the nature of the matrix is unknown or cannot be easily matched in the standards. 相似文献
80.
Acylation of phosphine oxide anions with derivatives of cyclic anhydrides or oxidative cleavage of cyclic allyl phosphine oxides gives Ph2PO-ketoacids: reduction, separation of diastereoisomers, and completion of the Horner-Wittig reaction gives single isomers () or () of unsaturated acids. 相似文献