Dissolved sample storage

Effect of storage on viscosity. Factors such as the method of storing undissolved nitrocellulose affect the viscosity of its solutions. It has been established (Kanamaru [73]) that nitrocellulose kept in a polar liquid, e.g. water, alcohol, and tested for viscosity at stated periods by dissolving samples in acetone, shows for the first few days a rather rapid increase in viscosity, which gradually becomes slower. If cellulose is stored in a non-polar liquid, such as carbon tetrachloride, or petroleum ether, then the viscosity of solutions remains unchanged or increases only very slightly. 

Kaiser, K., M. Kaupenjohann, and W. Zech. 2001. Sorption of dissolved organic carbon in soils Effects of soil sample storage, soil-to-solution ratio, and temperature. Geoderma 99 317-328. 

Biochemical Oxygen Demand. The biochemical oxygen demand (BOD) test is an empirical determination of the oxygen requirement of a sample. It is most often appHed to wastewaters, industrial effluents, and poHuted waters. The decrease in the dissolved oxygen concentration resulting primarily from biological action is measured after storage for 5 d at 20°C. 

For the storage of a substance dissolved in a volatile solvent, the solution must be placed directly in the flask, not within a vial. During the evacuation, gently sway the flask and adjust the evacuation speed to avoid sample loss due to a sudden boiling of the solution. Replace the inside space of the flask completely with the solvent vapor (typically methanol) by boiling the sample solution for a period of 1-2 minutes before closing the stopcock. In using this method, however,... 

A reference substance can be either the formulated test substance suspended in water or the technical or analytical grade active ingredient of the test substance dissolved in a solvent. The reference substance is normally used to fortify field matrices to develop information on the field storage stability of the active ingredient. Reference substances should be prepared at the analytical facility where the matrix samples are to be analyzed. Methods to prepare reference substances for field use will be discussed later. 

Cranston and Murray [35,36] took samples in polyethylene bottles that had been pre-cleaned at 20 °C for four days with 1% distilled hydrochloric acid. Total chromium Cr(VI) + Cr(III) + Crp (Crp particulate chromium) was coprecipitated with iron (II) hydroxide, and reduced chromium Cr(III) + Crp was co-precipitated with iron (III) hydroxide. These co-precipitation steps were completed within minutes of the sample collection to minimise storage problems. The iron hydroxide precipitates were filtered through 0.4 pm Nu-cleopore filters and stored in polyethylene vials for later analysis in the laboratory. Particulate chromium was also obtained by filtering unaltered samples through 0.4 pm filters. In the laboratory the iron hydroxide co-precipitates were dissolved in 6 N distilled hydrochloric acid and analysed by flameless atomic absorption. The limit of detection of this method is about 0.1 to 0.2 nM. Precision is about 5%. 

Preservation and Storage of Samples for the Determination of Dissolved Organic Carbon... 

From the results it can be concluded that the decrease in dissolved organic carbon with storage time is always lowest when the samples come deep frozen deep freezing in a glass ampoule resulted in the lowest decline. Even under these conditions the storage time should be as low as possible. 

In this case, a likely explanation for the apparent supersaturation is that the chemical analysis included not only dissolved aluminum and iron, but also a certain amount of aluminum and iron suspended in the water as colloids and fine sediments. Analytical error of this type occurs because the standard sampling procedure calls for passing the sample through a rather coarse filter of 0.45 tun p0re size and then adding acid to preserve it during transport and storage. 

Transmission spectra were taken immediately after allowing the pigmented samples to cool down to room temperature. Interpretation of the characteristic 570 nm band shows that at 180°C, all of the pigment crystals are dissolved, provided their concentration is small (0.005 and 0.01%, respectively). At 140°C, however, not all crystals are dissolved. Fig. 25 demonstrates that crystallization, taking place inside a sample rather than on its surface, is not completed even after years of storage [39],... 

According to the modified procedure (602), milk is thoroughly mixed in its storage container immediately before transfer of the 1 ml aliquot in the extraction tube. This is necessary because approximately 50% of phenylbutazone in milk is associated with the cream. The sample is extracted with 2.4 ml diethyl ether and 2.4 ml petroleum ether in presence of 1 ml ethanol and 100 1 25% ammonia solution. The organic layer that contains the milk lipids is discarded. Five ml hexane-tetrahydro furan (4 1) is added to the aqueous layer, which is tiien acidified with hydrochloric acid and the layers are mixed. Under the acidic conditions, phenylbutazone partitions quantitatively into tlie organic layer, which is collected, evaporated, and dissolved in the mobile phase to be analyzed by liquid chromatography. Separation is performed on a reversed-phase column using an isocratic 0.02 M phosphate buffer/methanol mobile phase, and determination is by ultraviolet detection at 264 nm (Fig. 29.18.2). The limit of detection and limit of quantification were 3.0 and 5.4 ppb, respectively (Table 29.17). 

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