Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Structural evidence for fast-ion conduction in the silver and copper halides at high temperatures and pressures

The results of recent powder neutron diffraction investigations of the high pressure and high temperature phases within the binary Cu and Ag halides are summarised, with emphasis on the relationship between the observed structural disorder and evidence for fast-ion behaviour provided by other techniques such as ionic conductivity measurements, differential thermal analysis and molecular dynamics simulations. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Accuracy of determination of trace metals in soil and sewage sludge

Errors in the analysis of liquid samples are often large enough to be important. For solid materials, additional potential complications arise in separating the determinand from the sample matrix and in controlling possible interferences from co-extracted species. These considerations have led to the development of a stepwise, co-ordinated approach by which a group of laboratories have achieved predefined standards of accuracy. Sample digestion has been examined. The analysis of digests has then been addressed; the control of analytical precision has been emphasised. Finally, a demonstration of overall comparability has been undertaken. The results are presented.     

The λ-complete multigraphs

Let E₁……E_m be the edges of a hypergraph. Assume each element in the union of the edges occurs in at least two of E₁……E_m. Assume further that every pair of distinct edges, E₁, and E₁, intersect in at most one element and that for each such pair there are exactly λ other edges E_k such that E₁ and E₁ both intersect E_k. We characterize the hypergraphs for which each |E₁| ≤ 2. These are the λ-complete multigraphs.