Sample attack methods

The results obtained on zinc indicated that all methods were reasonably good. Unfortunately, the high acidity of the sample attacked the stopper of the JEB tube and leached zinc from the rubber. Because of the many variables involved, such as the position in which the tube was stored and the length of time that the solution was in contact with the rubber, the amount of contamination was indeterminate. The accuracy and precision of the zinc data were, therefore, questionable and are not reported here. 

Since ozone attack on rubber is essentially a surface phenomenon, the test methods involve exposure of the rubber samples under static and/or dynamic strain, in a closed chamber at a constant temperature, to an atmosphere containing a given concentration of ozone. Cured test pieces are examined periodically for cracking. 

The main features of PC are low cost, need for small sample amount, high level of resolution, ease of detection and quantitation, simplicity of apparatus and use, difficult reproducibility (because of variation in fibres) and susceptibility to chemical attack. Identification of the separated components is facilitated by the reproducible Rj values. Detection methods in PC have been reviewed [368]. Fluorescence has been used for many years as a means of locating the components of a mixture separated by PC or TLC. However, also ATR-IR and SERS are useful. Preparative PC is unsuitable for trace analysis because filter paper inevitably contains contaminants (e.g. phthalate esters, plasticisers) [369]. For that purpose an acceptable substitute is glass-fibre paper [28]. 

Recently, Noort et al developed a procedure that is based on straightforward isolation of adducted BuChE from plasma by means of affinity chromatography with a procainamide column, followed by pepsin digestion and LC/electrospray tandem MS analysis of a specific nonapeptide containing the phosphonylated active site serine-198 residue (5). This method surpasses the limitations of the fluoride-reactivation method, since it can also deal with dealkylated ( aged ) phosphonylated BuChE. The method allowed the positive analysis of several serum samples of Japanese victims of the terrorist attack in the Tokyo subway in 1995. Furthermore, the method could be applied for detection of ChE modifications induced by, e.g., diethyl paraoxon and pyridostigmine bromide, illustrating the broad scope of this approach. This new approach... 

If these methods do prove inconclusive, biomedical sample analysis may provide a unique method for establishing exposure. Due to both the complex technical requirements and the strict forensic approach used it is unlikely that this information will be available in the early phases of response to such an incident. Biomedical sample analysis does however offer another method by which proof of the use of chemical agents can be provided, and thus has a potentially significant role in the overall preparation of a capability for the response to a terrorist chemical agent attack. 

Gather important information the agent used was it aerosol, liquid, gas, powder or vapor location method of delivery do you have the necessary personal protective equipment (PPE) to deal with the hazard, or have you called for assistance by a specialized team are you sure that anyone who enters a contaminated area has the proper PPE and is trained in its use be sure to establish control — keep all victims, non-victims and bystanders at the crime scene (if there is any suspicion of an attack) until it is determined who among them may be a terrorist or a witness perform decontamination, triage if necessary, isolation, quarantine, search and locate evidence, maintain chain of control, and collect samples. 

As mentioned previously, introducing the sample to the flowing mobile phase at the head of the column is a special problem in HPLC due to the high pressure of the system and the fact that the liquid mobile phase may chemically attack a rubber septum. For these reasons, the use of the so-called loop injector is the most common method for sample introduction. 

There are limited data on the chemical resistance of various oxide materials in the literature (Samsonov 1982, Ryshkewitch and Richerson 1985). Furthermore, many of the studies are concerned with solid, nonporous materials. Nevertheless, these may provide an indication of the general trends. Until a definitive and quantitative database of chemical stability of various inorganic membranes becomes available, some simple dissolution-type test methods using membrane samples may be employed on a comparative basis to estimate the extent of attack by a chemical under the application conditions. An example of such a simple test is given below. 

Continuous analysis requires flexible tubes which are not attacked by the materials under examination, and this places certain limitations on the scope of the method. Certain reactive and corrosive materials cannot he satisfactorily pumped, although advances have been made in the development of inert plastics and other synthetic materials. Displacement pumping with the aid of a liquid compatible with sample and reagents provides an alternative, though generally inconvenient, approach. No such limitations arise in discrete analysers because there is no restriction on the choice of materials for sample and reagent containment. 

The classic test for chemical resistance (ASTM D-543) measures the percentage weight change of test samples after immersion in different liquid systems. Tests for chemical resistance have been extended to include changes in mechanical properties after immersion. Since chemical attack involves changes in chemical structure, it can be readily observed by many instrumental methods that measure chemical structure, in particular, surface structure. 

The use of such methods for electrochemical quantitation in conservation and restoration, however, should involve the attack of the sample by an adequate reagent and the subsequent determination of selected analytes in solution. This methodology involves handling of micro- or submicrosamples, and further treatment of highly diluted solutions with concomitant opportunities for sample loss and/or sample contamination. 

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