Determination of hydrocarbons in water – interlaboratory method validation before routine monitoring

The clarification of hydrocarbon input into the Baltic sea via rivers is one of the priority issues of the 4th Pollution Load Compilation (PLC-4) within the framework of international Baltic Sea marine monitoring. An interlaboratory comparison was conducted to check the applicability of a new method for the determination of hydrocarbons by solvent extraction and gas chromatography. Surrogate oil solutions with known hydrocarbon content were distributed among the participants for preparation of water samples of different hydrocarbon concentration. In using these concentrations as assigned values and by setting target values for precision, the proficiency of participating laboratories could be tested as a qualifying step before involvement in PLC-4 routine monitoring. The results of the exercise indicate that hydrocarbons in water samples can be monitored as a mandatory test item within the framework of PLC-4. Received: 31 October 2000 Accepted: 3 January 2001     

Conjugate natural convection from an array of discrete heat sources: part 1 — two- and three-dimensional model validation

Two- and three-dimensional (2- and 3-D) numerical models have been developed for conjugate natural convection in a discretely heated cavity. Experimental results obtained for the same geometry, using water and FC-77 as the coolants, were in excellent agreement with the 3-D numerical predictions. In contrast, because of the inability to account for thermal spreading in the lateral direction, the 2-D model overpredicted measured average surface temperatures of the discrete heat sources. However, the 2-D model still predicted general trends and flow patterns that were experimentally obtained. The nature and extent of 3-D effects on the flow and heat transfer have been delineated.     

Some generalizations of the T-method in simultaneous inference

Two extensions of the T-method for multiple comparisons on a set of parameters are discussed, which are easily applied to cases where the allied random variables do not satisfy the usual conditions imposed by the T-method. The two generalized T-procedures are compared with the S and the Bonferroni methods and illustrated by various examples.     

Determination (monitoring) of PAHs in surface waters: why an operationally defined procedure is needed

The results of interlaboratory studies on the determination of selected PAHs in samples of pure water and water containing suspended matter are presented and discussed in this study. Determinations were performed by independent analytical laboratories which used different sample-preparation procedures, i.e. liquid-liquid extraction and solid-phase extraction with columns and speedisks. The study indicates that the results of PAHs determination depend on the type of isolation technique and the final determination procedure used by a given laboratory. Differences among the determined concentrations of specific PAHs reached 700%. In this work it has been shown that modern analysis does not offer isolation techniques for PAHs which would secure their speciation in the aquatic environment.     

Development and implementation of the CCME Reference Method for the Canada-Wide Standard for Petroleum Hydrocarbons (PHC) in soil: a case study

Petroleum hydrocarbons have historically been analyzed by a wide variety of test methods. Interlaboratory studies have shown that standardization of both extraction and gas chromatographic analysis improved interlaboratory variability in hydrocarbon analysis. The Canadian Council of Ministers of the Environment has required a reference method for use with the Canada-wide standard for petroleum hydrocarbons. The process for developing and validating this method is described. This method requires the determination of 4 hydrocarbon fractions, namely, F1 (nC6 to nC10), F2 (>nC10 to nC16), F3 (>nC16 to nC34) and, F4 (nC35+), using GC-FID or gravimetry. The Tier 1 method was validated in a single laboratory study. This validated method was subjected to interlaboratory studies to determine its applicability and precision.     

Interlaboratory studies on wastewater toxicity using Daphnia magna

In order to verify the quality of biological measurements, the National Institute of Chemistry in Slovenia is regularly organizing interlaboratory comparisons to estimate the analytical precision of different laboratories using the same test and to determine if statistically significant differences exist between results. Several interlaboratory trials named “ILC-Waste Water” (ILC-WW) were organized in the last 7 years. Acute toxicity testing with Daphnia magna mobility inhibition assay (ISO 6341) was included in eight successive rounds and about 20 laboratories from Slovenia and a few adjacent countries took part in each study with two samples (T1 and T2) at two different concentration levels. Variation coefficients of the mean 24 h EC50s were determined for each exercise and the evaluation of the interlaboratory variability was analysed. Comparisons were also made of the results and the variability laboratories using organisms taken from laboratory cultures versus those who used daphnias hatched from dormant eggs (Daphtoxkits).     

有序处理连续比较的置信区间

为有序均值的连续比较提出了一个新的检验过程.他们的过程对满足简单序的均值有重要的应用价值,例如在研究增长剂量对药物效用的影响. 与其它检验过程相比(例:Hayter\ucite{4}中的检验), 其优点在于产生了更短的连续比较的置信限,从而能够提供更多机会发现在何药剂量处有不同的效用.但作为有序均值的齐性检验, 它的势表现远劣于其它检验.本文的目的是提出一检验过程在尽量保持Lee andSpurrier\ucite{8}检验的优点的同时大大地提高其势表现.     

Counterexamples for comparisons of queues with finite waiting rooms

We constructG/G/1/k queueing models that fail to have anticipated monotonicity properties with respect to the capacityk. In one model the long-run average number of customers in the system is arbitrarily close to the capacityk, but it decreases to an arbitrarily small value when the capacity is increased. In another model the throughput is arbitrarily close to the arrival rate when the capacity isk, but the throughput decreases to an arbitrarily small value when the capacity is increased. These examples involving non i.i.d. service times, which are associated with external arrivals instead of being assigned when service begins, show that stochastic assumptions and arguments involving more than direct sample-path comparisons are essential for obtaining useful bounds and positive comparison results.