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181.
When diatomaceous earth and glass columns are acylated prior to coating with a silicone liquid phase, then subjected to heat treatment in an atmosphere of nitrogen, gas chromatographic columns can be prepared that show a marked reduction in adsorption. These columns can be used with a nitrogen-specific detector to chromatograph unmodified polar compounds such as morphine and cyclobarbital in nanogram amounts. Virtually no alteration of peak shape and no variation of retention time are observed over the range 10(-6)-10(-9) g of polar drugs. This represents, for these polar drugs, an "improvement" in chromatographic capability of the order of about 1000-fold in comparison with the best conventional commercial columns. Application to toxicological analysis of morphine in urine is described. 相似文献
182.
183.
Anne Penfold Street Earl Glen Whitehead 《Journal of Combinatorial Theory, Series A》1974,17(2):219-226
A subset S of a group G is said to be a sum-free set if . Such a set is maximal if for every sum-free set T ? G, we have |T| ? |S|. Here, we generalize this concept, defining a sum-free set S to be locally maximal if for every sum free set T such that S ? T ? G, we have S = T. Properties of locally maximal sum-free sets are studied and the sets are determined (up to isomorphism) for groups of small order. 相似文献
184.
T. C. Clarke K. K. Kanazawa V. Y. Lee J. F. Rabolt J. R. Reynolds G. B. Street 《Journal of Polymer Science.Polymer Physics》1982,20(1):117-130
Poly(p-phenylene sulfide) (PPS) is a melt- and solution-processible polymer which on treatment with AsF5 forms a blue-black material with a conductivity of 1–10 Ω?1 cm?1. Thermopower measurements indicate that the resulting polymer is p type, consistent with partial oxidation of the PPS by the AsF5. The rate and extent of this doping process prove to be particularly sensitive to the degree of crystallinity of the starting polymer. There is also evidence of crosslinking of the polymer chains during the reaction with AsF5. The details of both the chemistry and physics of the doping of PPS and several of its derivatives are presented. 相似文献