Provenance best” elements

Environmental variables such as temperature, salinity or nutrients cannot be directly measured for the past, but are determined via proxy data (see Fischer Wefer 1999). The minute tests of planktic foraminifera represent one of our best archives of these proxies. Their excellent preservation, global occurrence and high abundance in carbonate rich marine sediments above the lyso-cline are prime reasons for their extensive use in palaeoceanographic and palaeoclimatic studies. Analyses of elemental and isotopic compositions in addition to species abundances (see Fischer Wefer 1999 for review) have proven to be valuable proxies to understand past climate. 

A proposed protocol submitted to the NIST committee for consideration is described below. Most, if not aU, elements of the protocol are expected to become requirements for future certification as a viable CWA detection device. Techniques described in this protocol serve as approaches that laboratories may follow. While suggested methodologies may not be the only or the best that are available, they have been thoroughly employed and have demonstrated highly satisfactory results for many years. Any deviation from these procedures must be thoroughly proven valid before use. That is the procedure must not cause artifacts. The ultimate objective is to evaluate the test item with the following questions in mind ... 

The main classes of catalysts used for heterogeneous WHPCO reaction are clays and anionic clays (hydrotalcites), metal-ion exchanged zeolites and mesoporous silica containing transition metals, and doped metal oxides. Although some other transition metals have been also used (Mn, V), most catalysts contain iron and/or copper as the active elements. Leaching of the active metal is also a significant problem in this case. While different types of catalysts have been reported, only a few of them have been effectively proven to have a stable activity in long-term continuous experiments or at least in several repeated batch tests. Between the stable catalysts, Fe- and Cu-PILC (pillared clays) materials " have the best combination of activity and stability. However, the limited quantity of active elements (around 2% wt. of iron or copper) necessary to achieve stable performances, limits the overall activity. 

Success can best be achieved through application of a process model that merges proven performance management techniques with sound risk management practices. Experience indicates that the following eight process elements are essential for effectively maintaining workplace conditions and practices necessary to sustain incident-free operations. 

---