Poisons trace analysis

Podbielniak analysis See POD analysis. pad bel ne.ak a.nal a sos poison CHEM A substance that exerts inhibitive effects on catalysts, even when present only In small amounts for example, traces of sulfur or lead will poison platinum-based catalysts. poiz an )... 

The use of activation analysis in criminal investigations (forensic activation analysis) is also well established. The basic idea here is to match the trace-element distributions found in bullets, paint, oil, and so on found at the scene of a crime with the trace-element distributions in objects found with criminal suspects. Such identification is rapid and nondestructive (allowing the actual evidence to be presented in court). Moreover, the probability of its correctness can be ascertained quantitatively. Other prominent examples of the use of forensic activation analysis involve confirmation of the notion that Napoleon was poisoned (by finding significant amounts of arsenic in hair from his head) and the finding that the activation analysis of the wipe samples taken from a suspect s hand can reveal not only if he or she has fired a gun recently but also the type of gun and ammunition used. 

Gas chromatographic (GC) methods also provide possibilities to detect the irreversibly held amounts of a poison (51), although these techniques are less accurate than the gravimetric methods. The number of irreversibly adsorbed molecules can be calculated from the material balance for successively injected pulses of the poison and the eluted amounts. Alternatively, adsorption equilibrium can be attained at low temperature, the adsorbed amount being determined by frontal analysis (51). Desorption may then be carried out at the same temperature and the irreversibly held amount can be calculated either from the difference between adsorbed and desorbed amounts of a first cycle or from the difference of the adsorbed amounts of a first and a second adsorption (52). Desorption temperatures can then be raised stepwise after the first desorption and the dependence of the irreversibly adsorbed amounts on desorption temperature determined from the corresponding desorbed amounts. The accuracy of these GC measurements is limited because of the usually very pronounced tailing of the desorption trace for the systems of interest. 

Previous studies (Zheng, 1993) have identified a range of Permian coal environments and geochemistry. The samples studied represent these variations. We have collected 50 samples from three areas, Haizi Township, Jiaole Township, and the Xingyi—Dadi area (Fig. 17.2). Some of the mines are small dog holes (Fig. 17.3D), and collection of kilogram samples in all localities was not possible. Selected samples were analyzed for proximate and ultimate analysis and all were analyzed for trace elements. In this report, we discuss only the trace-element results as they bear direedy on chronic arsenic poisoning. 

The forensic scientist employed in the analysis of specimens for metal concentrations is involved generally in two main areas of investigation. The first is in the determination of toxic metals in biological tissue in order to ascertain the cause of death or injury (homicidal or suicidal) in suspected poisoning cases. The second is to compare certain characteristic trace element concentrations in materials found at the scene of the crime with the same type of material found in the possession of the accused. A special case of this second approach is in the analysis of the elements barium,... 

If it is considered that the deceased had been poisoned over an extended period prior to death, it is important to collect hair (plucked from the roots with the ends tied with thread at the scalp end) and nail specimens. The growing hair and nail can absorb many trace elements from the blood stream and these elements are permanently bound to the keratin. Knowing that the average rate of growth of human hair is approximately 1cm per month, sectional analysis of the hair from the root to the tip will produce a calendar of exposure to the element. 

The choice of the selective poisons which can label the growing chain is not limited to CO and COz. Allene could be used alternatively, if a sensitive method for the determination of C=C bonds in polymer is available. Other candidates are COS and CS2 provided that their insertion into the propagative center is confirmed 99). The trace sulfur analysis can be used to monitor the labelled chains. 

For Fe, Zn and Pb that may cause chemical poisoning, model poisoned catalysts were prepared by dipping catalysts into aqueous solutions of metal nitrates at various concentrations, and the catalyst carrying the nearest amount of each element was selected for the selectivity measurement. The uniform distribution of the loaded metals in the catalyst layer was confirmed by EPMA line analysis. While B. E. T. surface areas of the model poisoned catalysts differ little, the amoimt of CO adsorption decreases with the increase in the concentration of the poisonous metal, and it is noteworthy that the amount greatly decreases by loading a trace amount of Zn or Pb. 

Many techniques have been used to detect the presence of poisons on metal surfaces, particularly by chemical analysis, but the effectiveness decreases with the poison content and special techniques become necessary for traces. For instance, special analytical (gas chromatography) capabilities to measure S concentrations below 5 ppb and CH4 below 1 ppm must be on-line (253). The sensitivity of spectroscopic methods becomes in those cases an important advantage. IR has often been employed to detect surface and/or bulk species by means of their character-... 

The most suitable technique for chemically active and reactive trace components is the introduction of a more reactive compound into the carrier gas. This protects the trace components against moisture and trace amounts of oxygen, improves the shape of the chromatographic zones and prevents losses of the substance in the column and other units because the reactive and adsorptive component of the carrier gas poisons the adsorbing sites in the units and on the sohd support and reacts with contaminants in the carrier gas. To the best of our knowledge, one of the first applications of this method was the addition of 1% of boron trichloride to the carrier gas in the analysis of readily hydrolysable compounds. 

The detection limits of the old methods for the determination of arsenic (10) were too high to determine arsenic in uncontaminated biological samples. With the invention of instrumental techniques, such as flame atomic absorption (emission) spectrometry, graphite furnace atomic absorption spectrometry, neutron activation analysis, inductively coupled plasma atomic emission spectrometry, and inductively coupled plasma mass spectrometry, the ubiquity of arsenic in our environment was proven. The improvement of the analytical techniques has changed the reputation of arsenic from a poisonous substance to an essential trace element at least for warm-blooded animals (11). An arsenic requirement for humans cannot be deduced from these animal experiments. In recent literature, there are certainly more hints that arsenic might be an essential trace element for humans, but there is still a lot of future research work necessary to prove this. 

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