用GC-三级四极杆MS/MS一次进样筛选鱼和飞灰样品基质中四至八氯代PCDD/Fs的方法

用高分离能力的气相色谱-高分辨质谱(HRGC-HRMS)核实二噁英/呋喃是一项昂贵又费时的分析工作,需要高素质的仪器操作人员,而在认证分析前采用筛选法检查样品是检测不出还是浓度超出HRGC-HRMS方法定量范围,可以大大地减少HRGC-HRMS实验室的工作负荷.最新提供的信息表明约10%筛选过的样品需用HRGC-HRMS认证/核实.有些GC/MS/MS方法需要多次进样以获得有毒和无毒的PCDD/Fs,或用功能变换法[1-4]可以确保检测出所有的有毒的2,3,7,8-氯代PCDD/Fs,但损失某些无毒的PCDD/Fs(2,3,7,8氯代PCDD/Fs除外).     

用PTV和(或)无分流进样的薄层毛细管GC分析三文鱼和菠菜中PCDD/Fs的HRGC-HRMS方法优化

降低二噁英(PCDD/Fs)的检出限(LOD)可以更好地估计这类有毒化合物在食品中的含量.通常的分析方法用无分流进样注入内径0.25 mm长60m的色谱柱.     

MULTIPLE CRITERIA SCREENING OF A LARGE WATER POLICY SUBSET SELECTION PROBLEM1

ABSTRACT: A new screening approach is applied to a large‐scale multiple criteria water management problem to remove actions that cannot possibly be in the best subset. An inherent advantage of the approach is its ability to identify inferior actions by examining them individually, rather than within subsets. In a case study involving the selection of actions to address high water levels in the Great Lakes‐St. Lawrence Basin, two statistical indicators, the mode and the mean, are used to aggregate the opinions of experts and representatives of interest groups on the impacts of actions according to various criteria. Application of the screening approach shows that some of the proposed actions can be removed as they can never be in the optimal subset, thereby reducing the size of the problem.     

THE IMPACT OF FLOODPLAIN REGULATIONS ON RESIDENTIAL LAND VALUES IN OREGON1

ABSTRACT: The impact of floodplain regulations on mean appreciation rates of residential land values was tested at six study areas in five counties in western Oregon. The study hypothesis that such regulations significantly depress appreciation rates of regulated lands relative to those of similar unregulated lands was in most cases rejected. When the hypothesis was accepted circumstances would render conclusions tenuous. The problems and issues facing this type of research are presented in case studies of two of the research study areas. The following factors challenge investigators seeking to resolve questions about the relationship between land use regulations and land values: varying degrees of stringency with which regulations are enforced; unequal assessment procedures between counties; influences external to floodplain regulations that may affect appreciation rates, including denial of permits for septic tanks, flood damages, and amenity values associated with waterfront locations; and the uncertain effect that the availability of flood insurance, which accompanies floodplain regulations, has on land values.     

Forest-user attitudes toward alternative fire management policies

The formulation and implementation of new fire policies in the national forests depend upon public acceptance. A national survey of organized groups of forest users indicates that, contrary to the concern of many forest managers, considerable support exists for flexible fire suppression policies. Forest users are also willing to accept the risk associated with the manager's use of prescribed fire. However, important intergroup differences do exist. Such variation is discussed in relation to a number of socioeconomic variables, general fire knowledge, specific knowledge about the effects of low-intensity fires, and risk preference levels.