Water content determination procedure

Determination of the density of solids (grain density) is directly determined either by using a precision balance and a pycnometer or by calculation from bulk density and the water content. The procedure assumes that oven drying has driven all pore fluids from the sample, leaving the precipitated pore water salts with the solid matter. The specific gravity of solids can then be determined as follows ... 

The sample vessel is pierced quickly, placed in the DSC at room temperature and heated at 10°Cmin". An endothermic deviation of the sample baseline due to the vaporization of water is observed. The presence of a very small amount of water can be detected by this procedure. The sample is heated until no deviation of the sample baseline is observed. The dried sample is then quickly reweighed and the intrinsic water content determined. 

The water content of crude oils is determined by a standardized method whose procedure is to cause the water to form an azeotrope with an aromatic (generally industrial xylene). Brought to ambient temperature, this azeotrope separates into two phases water and xylene. The volume of water is then measured and compared with the total volume of treated crude. 

In Table 5.3, is compared with the total hydroxyl concentration (Ni, + N ) of the corresponding fully hydroxylated, sample. The results clearly demonstrate that the physical adsorption is determined by the total hydroxyl content of the surface, showing the adsorption to be localized. It is useful to note that the BET monolayer capacity n JH2O) (= N ) of the water calculated from the water isotherm by the BET procedure corresponds to approximately 1 molecule of water per hydroxyl group, and so provides a convenient means of estimating the hydroxyl concentration on the surface. Since the adsorption is localized, n.(H20) does not, of course, denote a close-packed layer of water molecules. Indeed, the area occupied per molecule of water is determined by the structure of the silica, and is uJH2O) 20A ... 

The analytical procedure is checked by analyses of method blanlcs to assure that secondary contamination by the analytes to be determined is avoided or minimized. Because the water content of the CRM matrix to be analyzed may vary from one laboratory to another (dependent on the local humidity and temperature), the water content has to be determined. Accordingly, at least three independent samples are kept at I05°C for 2 h, then allowed to cool to ambient temperature in a desiccator and the water loss is determined. The certified values are generally reported on a dry mass basis. 

Water Content — 0.20% by wt. This limit insures that the material is miscible without turbidity with 19 volumes of 99% heptane at 20°. Determination is conducted by Karl Fischer Method, as described in ASTM D1364 and here as Spec MIL-E-463B, Procedure 4.3 7 uoder ETHANOL, Analytical Procedures... 

Several manufactured products as well as solvents and raw materials are analysed for their water content (or % humidity). Of all the available methods, the Karl Fischer procedure is the most widely used, accounting for almost 500000 determinations per day world-wide. 

Figure 25 shows a transition through critical conditions of polybutadienes in two solvent pairs. After separation, using substances with known X0 in hexane ( = 0) and a standard procedure 64), one can determine the water content in the column... 

Peroxide Determinations. Bawn and Williamson report two iodometric procedures for determining peracetic acid (Methods I and III below) and one method for determining total peroxide (4) (Method II). Bawn and Jolly report another method for total peroxide (5) (Method IV below). The difference between total peroxide and peracetic acid is assumed to be acetaldehyde monoperacetate (AMP). Each method was tested in our preliminary studies. Method III is preferred for peracetic acid because the results are more reproducible. In Method I a large blank titration was always observed, while in Method III the blank titration was very small. Method IV is preferred for total peroxide because it seems to be more sensitive to total peroxide and less sensitive to water content of the acetic acid solvent. 

Bearing in mind, from the discussion above, that °Brix really only allows estimation of relative water content in a series of related systems, this measure is used sufficiently frequently to require that the procedures be outlined. The sections below describe the use of the refrac-tometer and the hydrometer for determining water concentration. These instruments are readily available from a number of sources including Brannan and ERTCO Precision (for... 

Incomplete pigment extraction may also be due to variable sample moisture content. Maximum pigment extraction is obtained in an extraction solution of 80% acetone and 20% water, including the water content of the sample. The procedure as outlined is for samples with 70% 3% water. Determine the water content of the sample, and then adjust the water content of the extraction solution as needed to obtain a final 80% acetone and 20% water in the extraction (Carpenter and Clark, 1995). 

The distillation method of moisture determination requires collection and determination of the water evolved from the coal when the sample is heated in a boiling solvent that is itself immiscible with water. The solution and extraction methods require either solvent extraction of the water from the coal (followed by subsequent determination of the water content of the solvent) or use of a standard reagent that will exhibit differences in concentration by virtue of the water in the coal. A nonthermal solvent method of determining moisture involves the use of an extraction procedure in which the coal is shaken with a solvent that extracts the water from the coal. The degree of change in some physical property of the solvent, such as density, is then used as a measure of the water extracted. 

Water samples can be acid digested to determine total metal content, using procedures as described above. Trace metals can be determined in this way because the concentrations are brought to a sufficiently high level when the... 

Procedure Transfer about 300 mg of the test article (accurately weighed) to a 150-mL beaker, dissolve in 1.5 mL of anhydrous formic acid, and add 60 mL of glacial acetic acid. Add crystal violet Test Solution, and immediately titrate with 0.1 N HCIO4 to a green endpoint. Perform a blank determination, and make any necessary correction. Each milliliter of 0.1 N HCIO4 is equivalent to 29.43 mg of aspartame. The method description cautions that a blank titration exceeding 0.1 mL may be due to excessive water content, and may cause loss of visual endpoint sensitivity. 

In any case, a strict standard operating procedure (SOP) must be followed to assure at least reproducibility. Figure 27 shows a useful SOP which might require some modifications depending on the characteristic properties of cell suspensions. Wet weight determinations are by far less accurate since a defined water content is not easy to arrange reproducibly. 

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