Agitation of Sample

Precipitation and Purification. During the hydrolysis, control tests are made by turbidimetric titration of samples taken intermittently. When the desired degree of hydrolysis is reached, the ester is precipitated from the reaction solution into water. It is important for the precipitate to have the proper texture for subsequent washing to remove acid and salts for thermal stabilization. Before precipitation, the reaction solution is usually diluted with additional aqueous acetic acid to reduce the viscosity. If a flake texture is desired, the solution is poured into a vigorously stirred, 10—15% aqueous acetic acid. To precipitate the acetate in powder form, dilute acetic acid is added to the stirred reaction solution. In both cases, the precipitated ester is suspended in 25—30% aqueous acid solutions and finally washed with deionized water. The dilution, precipitation temperature, agitation, and strength of the acid media must be controlled to ensure uniform texture. 

As mentioned above, two experimental methods were examined as a source of kinetic samples Method A Agitated Glass Ampoule and Method B Static Mixer. These are described in turn in the following paragraphs. Analysis of samples was done using high temperature size exclusion chromatography (SEC) under conditions previously described (9.101. 

Boylan and Tripp [76] determined hydrocarbons in seawater extracts of crude oil and crude oil fractions. Samples of polluted seawater and the aqueous phases of simulated samples (prepared by agitation of oil-kerosene mixtures and unpolluted seawater to various degrees) were extracted with pentane. Each extract was subjected to gas chromatography on a column (8 ft x 0.06 in) packed with 0.2% of Apiezon L on glass beads (80-100 mesh) and temperatures programmed from 60 °C to 220 °C at 4°C per minute. The components were identified by means of ultraviolet and mass spectra. Polar aromatic compounds in the samples were extracted with methanol-dichlorome-thane (1 3). 

All drains in a toxic laboratory with exception of those from the toilets should lead to a toxic sump. The toxic sump should be fitted with the wherewithal to permit addition of reagents, agitation, and sampling, as well as adequate indicators and alarms to highlight malfunctions. Valving should be convenient to operate and the system should feature parallel tanks so one batch can be treated while the lab continues to discharge to the other tank. Provision should be provided to pump out contents when untreatable. 

These activities may introduce many hazards, such as contaminants, materials of repair corrodible, combustible or catalytic in the given environment, blocked vents, open valves etc. into the restarted plant, while shutdown and startup are, in any event, the most dangerous periods. Many examples of reactive hazards thus introduced are to be found in [1], Mutatis mutandis, this is also true of the laboratory this Handbook contains many incidents consequent upon stopping a reaction and/or its agitation to sample, change cooling bath, etc. 

Preparation and analysis of SDS extracts from digester sludge. The particulates from a 30-ml sample were removed by centrifugation (15,00Qg) at 4 C for 20 min. The particulates were washed three times with 100 mM Tris buffer pH 7.0 and resuspended in 15 ml of buffer. The extraction procedure consisted of agitating the sample with a Fisher model 346 rotator at 25 C in the presence of 0.1% SDS for 1 h. The particulate material was then removed by centrifugation at 15,000 g at 4 C for 20 min, and the supernatant was used to perform the enzyme assays. 

As can be seen in Figures 2 and 3, the agitation of the sample was the most important factor for almost all the analytes. In all cases, this factor has a positive effect, and it appears to be of increasing importance as the degree of chlorination of the PCBs increases. Also, the extraction time was a significant factor for all the compounds, as might be expected. 

The samples were placed in headspace vials. When saponification was performed, a few milliliters of NaOH solution were added to the sample. The vial was sealed with a headspace aluminum cap furnished with a Teflon-faced septum, immersed in a water bath maintained at 100 °C, and let equilibrate for 6 min before HSSPME. Afterward, the fiber was exposed to the headspace over the sample for 5-240 min, depending on the experiment. The sample was magnetically agitated during sampling. Once the exposition period was finished, the fiber was immediately inserted into the GC injector and the chromatographic analysis was carried out. Desorption time was set at 5 min. 

The simplest method of sampling is to put the sample into a sealed vial and heat it as shown in Figure 11.23. The sample, either in solution or slurried with a relatively involatile solvent with little potential for interference, e.g. water, is put into a sealed vial fitted with a rubber septum and heated and agitated until equilibrium is achieved. Then a fixed volume of head space, e.g. 1 ml is withdrawn. The sample is then injected into a GC in the usual way. If capillary column GC is used a split injection has to be used to facilitate sample injection a flow of 10 1 out of the split vent would ensure that a 1 ml sample could be injected in about 5 s with the flow through the column being 1 ml/min. Several points are important to note ... 

Test 1. DPhA Nitration Method Cut a sample of proplnt into small pieces, as described in Vol 2 of Encycl, p C131-L, under "Preparation of Sample", and weigh ca 5g, within 0.2mg, in a tared 250ml lipped beaker. Add a mixture of 10ml glac AcOH and 20ml nitric acid of density 1.42 and heat the beaker on a steam bath at 95° for 1 lA hours Cool the beaker with contents but do not agitate. Pout... 

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