Sensitivity, concentration optimum choice

In respect of potential CN terrorism we believe that the following three critical items should be added to the CDC recommendations. First, before antidotes are stockpiled there should be international agreement on the most appropriate antidote (or combinations) for the treatment of acute CN poisoning. It is our opinion that hydroxocobalamin is the optimum choice. In the context of mass casualty situations with terrorist release of cyanides on the public, the chosen antidote should be readily available, effective, easy to administer (even by responders with limited training), nontoxic, and does not adversely interact with other antidotes (Thompson, 2004). Second, with respect to CN analyses, there is a requirement for a portable equipment that is specific and, at least semiquantitative, that can be used for on-site reliable bioidentification of CN intoxication. There is also a need for a reliable and sensitive environmental method for the instantaneous measurement of HCN concentrations, and ideally continuous monitoring with automatic warning devices for installation in sites with a potential for HCN attack. Third, educational materials should be made immediately available for distribution to the general population so that they can be prepared for what to expect in the event of a CN terrorism event. 

A higher-MHz NMR spectrometer is always a better choice, since the sensitivity of the experiment is proportional to the frequency of measurement. Moreover, with highly concentrated solutions, the presence of some solid particles can cause an increase in T) (FID will be short) and line broadening of the NMR signals will result. Therefore, an optimum concentration (say, 25-50 millimolar solution) is recommended. Of course, H-NMR spectra can be readily measured at much lower concentrations, though higher concentrations are necessary for recording - C-NMR spectra. 

The most convenient and economic techniques of choice for the rapid analysis of starting materials and for the assessment of purity of a crude reaction product are t.l.c. and g.l.c. These techniques may also be used to monitor the progress of a reaction for which optimum conditions are uncertain, as may be the case when an established published procedure is used as the basis for carrying out other preparations of a similar nature. In these cases the reaction is monitored by the periodic removal from the reaction mixture of test portions for suitable chromatographic study. Clearly the chromatographic behaviour of starting materials and, if possible, expected products, needs to be established prior to the commencement of the reaction. For t.l.c. this would include solvent and thin layer selection, a detection method, and an appraisal of sensitivity of detection with respect to the concentration of components in the reaction medium. For g.l.c. preliminary experiments would be required to select a suitable column and the appropriate operating conditions. 

One of the most important decisions that is left to the analyst when operating a liquid chromatograph is the choice of detector sensitivity. In some instruments the output from the sensor is monitored continuously over its entire dynamic range and so sensitivity is not an optional experimental parameter. Nevertheless, in this case, the sample size determines the concentration range over which the eluted solutes are monitored and thus an optimum sample size must be chosen. The detector should never be operated at its maximum sensitivity unless such conditions are enjoined by limited sample size or column geometry. Provided that there is adequate sample available, and the sample concentration when eluted is within the linear dynamic range of the detector, the maximum sample size that the column can tolerate should be used. This ensures that the detector noise is always minimal... 

As a biosensor, by definition, consists of a biological recognition system in intimate physical and functional contact with an artificial transducer, among the possible combinations the most efHcient ones have to be conceived with regard to the demands of the actual analytical problem. The choice will not only be determined by the optimum sensitivity or the response time to be attained, but also by the properties of the matrix and the concentration range of the substance to be monitored. This may be explained by means of an example. 

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