A detailed study of the photophysics and photochemistry of polymer-immobilized luminescent transition-metal complex oxygen sensors is presented. Emphasis is on understanding the underlying origin of the nonlinear Stern-Volmer quenching response. Microheterogeneity is important in both photophysical and photochemical behavior, and the nonlinear quenching responses in RTV 118 silicone rubber can be adequately described by a two-site model, although detailed lifetime measurements suggest a more complex Underlying system. Counterion studies with quenching counterions are shown to be useful probes of the structure of the complex in the polymer. While oxygen enhances photochemical instability, singlet oxygen is not directly implicated in sensor decomposition. I n the photochemistry there is at least one reactive and one much less reactive site, although the photochemistry and quenching measurements probably sample different populations of sites. The existence of reactive sites suggests that stability can be enhanced by a preliminary photolysis to eliminate the more reactive sites.

Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Oxygen quenching of the luminescence of the trls(4,7-dl-phenyP 1,10-phensnthrollne )ruthenlum( 11) perchlorate Immobilized In a silicone rubber Is shown to be an accurate and precise method for measuring oxygen concentrations In solutions and In the gas phase. Quenching can be quantitated by either lifetime or Intensity quenching measurements. Aqueous strong acids, bases, complexlng agents, oxidants, and reducíante do not penetrate the hydrophobic polymer and, therefore, do not affect the response. Gaseous Interference, such as H2S, anesthetic gases (e.g., N20, halothane), and fluorocarbons do not affect the response. Chlorine and especially S02 are strong, but fully reversible, Interferents. A system was developed with a response time of less than 0.2 s, which Is adequate for the monitoring of breathing subjects.

This paper provides additional data on a sewage sludge amended soil certified reference material, CRM 483, which was certified in 1997 for its EDTA and acetic acid extractable contents of some trace metals, following standardised extraction procedures. The additional work aimed to test the long-term stability of the material and the applicability of an improved version of the BCR three-step sequential extraction procedure on the sewage sludge amended soil (CRM 483). The paper demonstrates the CRM 483 long-term stability for EDTA and acetic acid extractable contents of Cd, Cr, Cu, Ni, Pb and Zn and gives the results (obtained in the framework of an interlaboratory study) for the extractable contents of the same elements in the CRM 483, following the BCR three-step sequential extraction scheme. The aqua regia extractable contents following the ISO 11466 Standard are also given. The data are given as indicative (not certified) values.

Lead isotope analysis, using high-precision thermal ionization mass spectrometry, of herbage samples collected annually since the 1860s has revealed a steady reduction in the 206Pb/207Pb ratio from about 1.170 in 1880 to about 1.098 in the period 1980−1985. The value of 1.170 is very close to that (1.171) found previously in Scottish lake sediments for anthropogenic lead deposited prior to the introduction of leaded petrol. Analysis of the data suggests two dominant components in the lead deposited from the atmosphere over the period of 130 years studied. Prior to the turn of the century, lead of industrial or coal origin had a typical 206Pb/207Pb ratio of 1.170 following which a nonradiogenic component with a lower 206Pb/207Pb ratio (1.09 or less) made an increasingly more significant contribution. The decline in ratio commenced well before the introduction of tetraethyllead in petrol, indicating either changes in the source of lead-containing ores or coal or changes in the relative contributions of different sources. The generally smooth change in the isotopic character of the deposited lead suggests a slow change in the relative proportions of the dominant sources. The trend appears however to have been reversed following the declining use of lead additives in petrol. The deposition, in particular that with the low ratios associated in Britain with petrol additives, has had relatively little effect on the bulk soil. The 206Pb/207Pb ratio in bulk soil samples (to 23 cm) from the site, which had been undisturbed for at least 200 years, decreased from 1.187 in 1876 to 1.180 in 1984 but at no time reached the ratio found in the deposition on herbage. Analysis of sections taken down a soil core showed a steady increase in the 206Pb/207Pb ratio from 1.159 at the surface to 1.181 at 15 cm depth. Recent deposition with low 206Pb/207Pb ratios had a significant but not dominant contribution to the lead in the surface soil, which also contained a substantial proportion of older deposition with higher ratios. The ratios in the sections did not reach however that measured in bulk soil samples collected in 1876, indicating that lower ratio lead had reached a depth of at least 16 cm in the soil. Up to 50% or more of the lead at a depth of 16 cm could be anthropogenic in origin.