Simple rate monitoring methods

A more precise group of methods measure the beam equivalent pressure in molecular beams near the substrate or the atom fraction of interest in the gas phase. There are several ways of doing this including electron impact emission spectroscopy (EIES), conventional ionization gauges, mass spectrometers, glow-discharge optical spectroscopy, and other methods. We will briefly consider these four in turn. 

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Indirect measures of lead absorption include the rate at which lead is excreted from the body and a range of measurements associated with the haonatological system. Lead excretion occurs mainly in urine consequently, levels of lead in urine (PbU) provide a more simple monitoring method. However, various factors can affect PbU so it is not a sufficiently predictable measure for use as a primary control. The small amounts of lead which are excreted in sweat, hair and nails do not provide a practical means of monitoring. 

The rate of a reaction and its dependency on the concentrations of the reactants can be measured in several ways. A simple method involves the measurement of the rate at zero to low conversion at different concentrations of one of the substrates, keeping the concentration of other substrates constant. The latter can be done by using an excess of the other substrates (e.g. tenfold excess), which means that we can assume that the concentrations of the latter ones are constant under so-called pseudo-first-order conditions. Secondly we can monitor the reaction rate over a longer period of time taking into account the change in concentration for this one substrate. Alternatively, one can monitor the concentrations of all species and analyse the results numerically. 

The study and control of a chemical process may be accomplished by measuring the concentrations of the reactants and the properties of the end-products. Another way is to measure certain quantities that characterize the conversion process, such as the quantity of heat output in a reaction vessel, the mass of a reactant sample, etc. Taking into consideration the special features of the chemical molding process (transition from liquid to solid and sometimes to an insoluble state), the calorimetric method has obvious advantages both for controlling the process variables and for obtaining quantitative data. Calorimetric measurements give a direct correlation between the transformation rates and heat release. This allows to monitor the reaction rate by observation of the heat release rate. For these purposes, both isothermal and non-isothermal calorimetry may be used. In the first case, the heat output is effectively removed, and isothermal conditions are maintained for the reaction. This method is especially successful when applied to a sample in the form of a thin film of the reactant. The temperature increase under these conditions does not exceed IK, and treatment of the experimental results obtained is simple the experimental data are compared with solutions of the differential kinetic equation. 

Sivasubramanian and Anilkumar [81] described a simple reversed-phase HPLC method for the determination of omeprazole and domperi-done from tablet formulations. The analysis was carried out on a Hypersil ODS Ci8 (15 cm x 4.6 mm, 5 /jm) column using a mobile phase of methanol- 0.1 M ammonium acetate, pH 4.9 (60 40). The flow-rate and rim time were 1 ml/min and 10 min, respectively. The eluent was monitored at 280 nm. The method was reproducible, with good resolution between omeprazole and domperidone. The detector response was linear in the concentration range of 10-60 /[Pg.222]

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