bUnequivocal class separations of tissue lipids are important particularly whcn high temperature gas Chromatography is used at the same time for the determination of the long-chain acid composition of major lipid classes. This problem was studied most recently by Hirsch and Ahrens (1) ; their procedurc involves silicic acid column chromatography with clution by ether-petroleum ether mixtures fo...

Gravimetric fat data were obtained for a wide range of dairy products with fat contents ranging from 0.5 to 83% using pressurized solvent extraction at elevated temperatures and pressure (80-120 degrees C; 10.3 MPa). Extraction performance was sensitive to solvent composition, temperature, and sample matrix. By optimizing solvent mixtures, sample-solvent contact times of 8-10 min were sufficien...

A method is described for extracting the petroleum from petroleum-bearing ̄uid inclusions hosted in the diagenetic cements of sedimentary rocks, whilst minimising contamination from petroleum in the pore space. A clean-up technique, involving the addition of extraction standards to the rock prior to analysis, has been developed that allows increased con®dence that the hydrocarbons extracted are...

Determining the complete molecular composition of petroleum and its refined products is not feasible with current analytical techniques because of the astronomical number of molecular components. Modeling the composition and behavior of such complex mixtures in refinery processes has accordingly evolved along a simplifying concept called lumping. Lumping reduces the complexity of the problem to...

This paper reviews major activities outside the United States on human health issues related to chemical mixtures. In Europe an international study group on combination effects has been formed and has started by defining synergism and antagonism. Successful research programs in Europe include the development and application of statistically designed experiments combined with multivariate data a...

Dear Editor, The basis for ecotoxicology is the relationship between dose and response. Hypothesis testing can be indicative of difference, but should never be relied on without considering whether there is a true dose-response relationship. Hypothesis testing cannot inform the researcher regarding causation or uncertainty associated with an observed response, particularly in the case of comple...

INTRODUCTION 180 CHEMISTRY OF PETROLEUM BIODEGRADATION . 180 Degradation of Individual Hydrocarbons ...... 180 Degradation of Hydrocarbons Within Petroleum Mixtures ..... 182 TAXONOMIC RELATIONSHIPS OF HYDROCARBON-UTILIZING MICROORGANISMS .............................. ... .. 184 DISTRIBUTION OF HYDROCARBON-UTILIZING MICROORGANISMS ...... 186 ENVIRONMENTAL FACTORS INFLUENCING BIODEGRADATION OF ...

Mixture toxicity is a topic that has become a matter of concern during the last two decades. One of the major problems with assessing the toxicity of mixtures and the associated human and environmental risk is the large number of possible mixtures, as well as the fact that the actual mixture effect for a given set of constituents might strongly depend on the actual composition of the mixture, i...