Sample archives, techniques

In many cases, sample archives have proven to be very useful. Analytical techniques have been developed, making it possible to determine concentrations of new elements and other parameters and there are often new needs for information... 

The historical data is sampled at user-specified intervals. A typical process plant contains a large number of data points, but it is not feasible to store data for all points at all times. The user determines if a data point should be included in the list of archive points. Most systems provide archive-point menu displays. The operators are able to add or delete data points to the archive point hsts. The samphng periods are normally some multiples of their base scan frequencies. However, some systems allow historical data samphng of arbitraiy intei vals. This is necessaiy when intermediate virtual data points that do not have the scan frequency attribute are involved. The archive point lists are continuously scanned bv the historical database software. On-line databases are polled for data. The times of data retrieval are recorded with the data ootained. To consei ve storage space, different data compression techniques are employed by various manufacturers. 

This section discusses treatment of the water samples in preparation for instrumental analysis after they have been received, archived and stored in the laboratory. Many approaches may be taken in preparation of water samples for final analysis. The techniques employed will depend upon the type of matrix, e.g., groundwater vs surface water (containing organic materials), the instrumental method and the required detection limits. 

There is little doubt on the basis of the above review that speleothems are useful in an extremely wide range of applications and the frequency of publications devoted to speleothem-based archives is increasing rapidly. Fundamental to all applications is a robust and high-precision chronology and uranium-series techniques currently set the standard in this regard for speleothems. Reliable ages can be obtained for most samples where material appears to be well-preserved. However, it will become increasingly important to demonstrate reliability as the spatial resolution of analysis improves further. 

Based on the heat-induced AR principle, DNA/RNA extraction from FFPE tissues can be successfully achieved by a simple heating protocol that allows satisfactory application of molecular analysis using FFPE tissue samples housed in pathology laboratories worldwide. By a combination of improved extraction methods with various innovative techniques of molecular biology, more reliable results of molecular profiling for archival tissue are anticipated. 

In addition to ICP-MS for the multi-element analysis of aqueous solutions, LA-ICP-MS allows the direct determination of trace elements in biological samples and due to this feature it is a well suited analytical technique for microlocal analysis with spatial resolution. In 1995, Outridge el al.lg reported on the performance of an LA-ICP-MS analysis for studying incremental biological structures as archives of trace element accumulation. The use of LA-ICP-MS for several biological (and environmental) applications is reviewed by Durrant and Ward.19 Selected examples for determination of trace elements and species in biological samples are summarized in Table 9.25. 

In 2002, IUPAC initiated work in the development of terminology of a standard for analytical data. The standard format, XML, is intended to be universal for all types of analytical instrumentation, without permutations for different techniques. The XML format is designed to have information content of data defined in several layers. The most generic information is in the first layer, or core. More specific information about the instrumentation, sample details and experimental settings are stored in subsequent layers. The layers are defined as core, sample, technique, vendor, enterprise and user.29 The existence of a universal format will aid in the analysis of data from multiple sources, as well as in the archival and retrieval of data from historical processes. 

The two main techniques commonly discussed in the literature are known as direct observation (or frozen hydrated observation) and the observation of replicas. Both techniques involve the fast freezing of the sample in a cryogen such as liquid nitrogen, propane, or freon. The frozen sample is then fractured to reveal the interior features. This fractured surface can be coated with a metal film or observed directly. Often, the metal film is removed from the sample and observed as a replica. This type of procedure allows the creation of a permanent archive of the samples prepared, and the observation is the same as with any other electron microscope sample with no concern about contamination of the microscope or beam damage to the sample. 

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