Static sampling systems

On occasion, we need to collect static samples from pipe systems, water heaters, etc., to determine whether they contribute lead and other contaminants to the water. In this case, our goal is to collect the stagnant water that has been in a system for several days. Prior to static conditions sampling, the system should not be used for a period of time from three days to a week. Sampling may take place after a small volume of water in the pipe immediate to the tap has been flushed. 

Atmosphere The nature of the atmosphere surrounding the sample is important in relation to the transfer of heat and the chemistry of the sample reaction. Common sample atmospheres are shown in Table 36.1. In addition, the flow rate of the gas is important a static system will not remove reaction products from the sample. 

Apparatus. The apparatus and experimental procedure have been described (9). A static system was used with catalyst samples (normally 0.1 gram of hydrated material) in the bottom of the reaction vessel (volume 1 X 10" m ). The reaction was followed by periodically sampling the gas phase above the catalyst and analyzing by GLC techniques. 

To improve the overall amount of analyte that is extracted, a flowing donor is often used i.e., the sample is pumped past the donor side of the membrane in a dynamic flow system. Also static systems with a stagnant donor are common, often with convective mixing by stirring. 

This chapter mainly covers extraction systems with liquid membrane phases and trapping in the acceptor. Two- and three-phase systems are compared, as well as dynamic and static systems and flat versus hoUow-fiber membrane materials. These types of systems have been successfully applied to a number of analyte and sample types and can be important alternatives to more orthodox approaches to sample preparation. 

The carbon content of the poisoned samples (self-poisoning and deliberate poisoning at T>373 K in diene or acetylene) was measured by TPO (1.3 kPa O2, flow and/or static systems, respectively CO2 (m/z=44) and CO (m/z=28) were detected by mass spectrometer (AEI MS 20 and Balzers QMG 511). DSC thermograms (Perkin Elmer DSC-4) were recorded in O2 stream (40 K/min ramp from ambient to 773 K). 

Complete evaluation of the product in terms of physical and mechanical properties could not be made on the small samples produced in a static system of this size. Serious end effects observed and described... 

Square wave voltammetry is always performed using a computer-controlled potentio-static system with functional elements organized essentially as in Figure 7.3.11. The computer provides for operator interaction, synthesizes the waveform, sequences the sampling and logging of data, computes difference currents, and handles reporting of results, either graphically or otherwise. In many systems, the computer also controls the electrode, especially if an SMDE is involved. 

Five per cent metal-pumice catalysts were prepared by reduction with hydrogen of a suitable salt evaporated onto the support deuterium was obtained by the reaction of heavy water with zinc at 400°, and mass-spec-trometric analysis of a typical preparation showed 1.6% HD. Reactions were carried out in a static system, and after the required conversion had occurred, the condensible products were analyzed mass-spectrometrically. Low-energy electrons were used, and the basis of the calculation has been described before (4), but the previously avoidable use of a weighing factor for the probability of C-D fission was made necessary by the very large proportion of propane-ds in many of the samples. For most of the results in this paper, this factor was taken as 0.834, but a recent measurement of the mass-spectrum of pure propane-dg has indicated that the true value is somewhat lower, and as a result propane-dg has been slightly underestimated. The weighing factor was applied only to propanes-dg and -d , which in most cases represent the greater part of the whole. 

It is tempting to assume when a sample is placed in the beam of a spectrometer that this is a static system when compared with a more obvious dynamic system such as a chemical reaction. However, you should consider the insertion of a sample into a spectrometer beam as being a kind of reaction between a photon and a molecule, as shown in Figure 1.3. Here the transition from the lower to the upper level is shown together with the resulting absorption band. 

In a static headspace, the sample is in a closed static system in which conditions are at thermodynamic equilibrium. After establishment of the equilibrium, the... 

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