Reagents, concentration threshold

As the considerations of Section 3.4.1 demonstrate, an important requirement for either pulsed or cw electronic transition chemical laser operation is the achievement of large metal atom or free-radical concentrations. Moreover, these reagent concentrations must be made available in a manner that ensures that the chemical pumping rate of the upper laser level is large enough compared with the rates of the competing processes of collisional quenching and radiative, decay that an upper level population is created sufficient to exceed laser threshold requirements. 

Onc-Factor-at-a-Timc Optimization One approach to optimizing the quantitative method for vanadium described earlier is to select initial concentrations for ITiOz and 1T2S04 and measure the absorbance. We then increase or decrease the concentration of one reagent in steps, while the second reagent s concentration remains constant, until the absorbance decreases in value. The concentration of the second reagent is then adjusted until a decrease in absorbance is again observed. This process can be stopped after one cycle or repeated until the absorbance reaches a maximum value or exceeds an acceptable threshold value. 

This innovation generally involves modifications to the operation of the sampler and random access reagent selection, and can be implemented in both segmented and unsegmented flow analysers. For unsegmented flow analysis, the spectrophotometric determination of zinc and phosphate in soil extracts [368] is a good example. Zinc was determined only when phosphate was present at concentrations above a threshold level. The number of determinations required was reduced by 30%. Analogously, an expert flow system was proposed for the turbidimetric determination of chloride and sulphate in natural waters [369]. Both methods were implemented in the same manifold, and the need for sulphate determination was dependent on the chloride concentration determined. 

The results in Fig. 2 indicate that nucleation began after some time had passed, most likely due to a transient heat-up time and some time required for dissolution of the amorphous gel to achieve some threshold concentration. However, it is most noteworthy that the nucleation event in zeolite crystallization systems always has been determined to have ended when only about 10-15% of the aliunino-sificate material had been consumed. That is, it is remarkable that with 85 - 90% of the aliunino-silicate reagents left in the system, the nucleation process was somehow caused to cease, while crystal growA proceeded for the duration of the synthesis. This must be noted in the context of the amorphous gel dissolving sufficiently fast that the solution phase concentration was essentially constant up to almost 80% conversion in some cases [33-35],... 

A regulation indicating the maximum permissible airborne concentration of a dangerous compound in a place of work over 8 hours a day is enforced on the basis of threshold limiting values (TLVs). These are collected in lists and a selection of TLVs of phosgenation reagents is given in Table 3.4 in Chapter 3. 

Negative ion spectra of flavonoid O- and C- glycosides have been recorded using desorption c.i.-m.s. at a low reagent gas pressure. In laser desorption m.s., cationization of saccharides is best achieved by introduction of cations in the +1 oxidation state rather than other oxidation states, and it was shown that sample preparation and the concentration of salt and saccharide (above a threshold level) had little effect. ... 

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