Water sorption measurement procedure

Prior to sorption measurements, zeolite samples were activated by evacuation at elevated temperatures. There is frequently some question as to how precisely one can establish the mass of a zeolite sample from which all zeolitic water, but no water arising from collapse of structural hydroxyl groups, has been removed (l f ). In order to establish that the (zeolitic-water-free) masses of the activated zeolite samples used here are well defined, the following stepwise activation procedure was used. Each sample was first heated in vacuo at 300°C. When the pressure had dropped to below about 10 torr, the balance was isolated from the pumps, the rate of pressure increase measured, and evacuation resumed. This process was repeated until the rate of pressure increase fell to below 5 X 10 torr min l, a duration of time which was from 15 to 30 minutes. This is a rate such that were the increase due to water vapor alone, and were the rate to remain constant, the weight loss would still be undetectable after 2h hrs., a duration seldom exceeded in activating zeolites. 

The working group in the COST 90 bis Project has developed a reference material (microcrystaUine cellulose, MCC) and a reference method for measuring water sorption isotherms, and conducted a collaborative study to determine the precision (repeatability and reproducibility) with which the sorption isotherm of the reference material may be determined by the reference method. A detailed procedure for the resulting standardized method was presented, and the factors influencing the results of the method were discussed [158-160]. 

Perkins [18] carried out radium and radiobarium measurements in seawater by sorption and direct multidimensional gamma-ray spectrometry. The procedure described includes the removal of radium and barium from water samples on sorption beds of barium sulfate impregnated alumina (0.5-1 cm thick) and direct counting of these beds on a multidimensional y-ray spectrometer. The radioisotopes can be removed at Unear flow rates of sample of up to 1 m/min. 

The diffusion coefficients of acetaminophen in PNIPAAm gel at different temperatures were measured by a simple sorption experiment. PNIPAAm gel with a 10 x 4 composition (see Fig. 1) was synthesized in cylindrical form by the procedure described in Sect 4.1.1. After equilibration of a gel sample in water at... 

Both Cr111 and Cr concentrations in natural water samples were measured by flame AAS after pre-concentrations of the chromium species on microcolumns packed with activated alumina (acidic form) (Sperling et al., 1992). An FI manifold was used in this work to obtain conditions for species-selective sorption and subsequent elution of the chromium species directly to the nebuliser of the spectrometer. In this procedure, water samples were maintained at a safe pH of 4 prior to analysis. Analytical conditions of pH 2 and 7 were attained by adding buffers on-line only fractions of a second before the corresponding chromium species was sorbed into the column. In this manner, any risk of losses of analytes and/or shifts in equilibria between the species at pH 2 and 7 were minimised. The detection limits were 1.0 and O.Smgdm 3 for Cr111 and Cr, respectively. 

Changes in the structure and hydrophilic properties of the wood cell wall m specimens after the impregnation and ageing procedures samples were studied by the water vapours sorption method. The sorption-desoqjtion isotherms measured on a vacuum sorption balance at 295 K were analysed by the comparative method in combination with the BET method (8). The accessible specific area A (m /g), reflecting swelling capacity, the mass hydrophilicity a (mM/g) and the surface concentration of Ihc hydrophilic centres a (groups/nm ) was determined. 

Any procedure for wood specific gravity or density based on measuring weight and volume can be considered accurate only if the wood sample has been first extracted with suitable organic solvents to remove extraneous resins, oils, fats, gums, etc. (27). These materials bulk cell walls, block potential sites for water adsorption/ab-sorption, alter potential wood swelling/shrinkage, and thereby interfere with the accurate characterization of wood tissue. 

In 200-mL deionized water 0.1 g of humic acid particles were suspended at 298 K, stirred at 430 rpm, 0.02 mmole metal ions added, and the sorption rate measured as described above. At the end of the first experiment, the humic acid particles, (which were now partially saturated with the metal ion) were allowed to settle, the supernatant solution was withdrawn, the particles in the reaction vessel were washed with deionized water, resuspended again in 200 mL water, 0.02 mmole metal ions added as before, and the sorption rate was determined. This procedure was repeated several times for each metal ion. More details of this technique have been given previously (Bunzl et al., 1976b). 

Experimental Procedure. Each sample was first characterized by both mercury intrusion and nitrogen sorption. Mercury intrusion measurements were replicated at least four times, and the solid residues from each analysis were collected and combined after the bulk of the mercury was decanted. These samples were washed free of mercury by using 50% nitric acid (25 mL per 0.5 g of solid) and then washed free of acid by filtering and reslurrying in demineralized water (six times with 50 mL per 0.5 g of solid). The washed samples were then rapidly cooled in liquid nitrogen and freeze-dried (Chemlab SB4). For comparison, samples of material that had not been analyzed with mercury intrusion were washed and dried in a similar manner to test for structural modification caused by the acid-washing technique. 

A procedure is available to determine partitioning organic chemicals between water and soil or sediment. By measuring sorption coefficients for specific solids, a single value is obtained which can be used to predict partitioning under a variety of conditions. The... 

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