Moisture determination desiccator method

Methods for determination of the total moisture in coal have been placed into the following categories (1) thermal methods that often include distillation methods (2) a desiccator method (3) distillation methods, which often include extraction and/or solution methods (5) chemical methods and (6) electrical methods. 

There appears really to be no method by which true external moisture may be determined, that is, no method by which only the surface moisture is removed in such fashion that the residual solvent in the powder is found to be the same both before and after the powder has been allowed to take up moisture. Samples of powder were taken and residual solvent was determined by the several methods indicated in the next table. The samples were exposed 2 weeks to an atmosphere practically saturated with water vapor, and residual solvent was again determined as before. The surprising result was secured in every case, as indicated, that the amount of residual solvent was less after the powder had been exposed to the moist atmosphere than it was before it had been exposed. Yet the powder had taken up large quantities of moisture during the exposure. It is clear that the exposure to the moist atmosphere had made the volatile matter of the interior of the grains more accessible to desiccating influ-... 

Water is quantitatively distilled from many materials by heating. In direct determination, water vapor is collected on any of several solid desiccants, and its mass is determined from the mass gain of the desiccant. The indirect method, in which the amount of water is determined by the loss of mass of the sample during heating, is less satisfactory because it must be assumed that water is the only component volatilized. This assumption is frequently unjustified, however, because heating of many substances results in their decomposition and a consequent change in mass, irrespective of the presence of water. Nevertheless, the indirect method has found wide use for the determination of water in items of commerce. For example, a semiautomated instrument for the determination of moisture in cereal grains can be purchased. It consists of a platform balance on which a 10-g sample is heated with an infrared lamp. The percent moisture is read directly. 

Adsorption and desorption isotherms may be determined by monitoring equilibrium moisture uptake or loss in samples stored in desiccators with different relative humidities (saturated salt solution yielding different percentage relative humidity). The amount of water present is determined by loss of drying (LOD), TGA, Karl Fischer titration, the coulometric method, or near-IR spectroscopy. 

Analytical results compare best when the moisture content of milk samples is accurately determined. Water determination in fi eeze dried whole milk powder can be performed using either direct or indirect methods. The most common direct techniques are based either on desiccation or on oven drying. In this research work, freeze drying followed by the oven drying method was used. 

ASABE Standard S352.2 (2006) provides an unground method of measuring moisture for soybeans. Here 15.0 g of soybeans are weighed into tared moisture dishes and are dried in an air oven at 103 1°C for 72 h. Dried samples are placed into a desiccator to cool before weighing. Replicate determinations should check within 0.2% moisture. 

As an option, the moisture content can be determined in the drying cabinet by drying of the material to the point of reaching mass constancy. The amount of material to be used for this purpose is between 10 and 30g. The weight of the sample is determined in the wet state and it should also be ground for this method. After the sample has been dried at a temperature of 110°C, it has to be cooled down in the desiccator. 

A common method for determining moisture content of grains and oilseeds is to dry samples in triplicate in a convection air oven at a specified temperature for a specified duration (Table 27.7 ASAE [12]). About 10-15 g samples are weighed in covered aluminum dishes. The dishes are uncovered and placed with their covers in the oven at the set temperature. At the end of the drying period, dishes are covered and placed in a desiccator for cooling to the room temperature. The dishes with dried sample are weighed again. Moisture content of samples is calculated as the ratio of the... 

The elemental composition of the raw peat and solid product was determined using an elemental analyzer (Yanaco CHN Corder MT-5 and MT-6). Additionally, proximate analysis (based on JIS M 8812) total sulfur analysis (based on JIS M 8819) and calorific analysis (based on JIS M 8814) were conducted separately. The gross calorific value (CV) was measured using the bomb calorimetric method and the effective calorific value (ECV) of the sample at a constant pressure was determined based on JIS M 8814, which is followed by ISO 1928. The equilibrium moisture content of the dried solid product was further analyzed while maintaining their moisture contents according to JIS M 8811. Briefly, an aliquot of the sample was placed inside a desiccator containing saturated salt solution and then measured rapidly using a moisture content analyzer (Sartorius MA 150). 

To conduct a water sorption study, the product was stored in desiccators with solid salt or saturated salt solutions for 48 h of equilibration at an ambient temperature (Figure 8). The salts included phosphorus pentoxide, lithium chloride, potassium acetate, magnesium chloride, potassium carbonate, and sodium chloride, which generated relative humidities of, approximately, 0, 11, 23, 33, 43, and 75%, respectively. The vials were sealed immediately after equilibration. The moisture in the lyophilized product was determined by the Karl Fischer method. 

A minimum of six of the ampoules/vials used for check weighing are marked and numbered at intervals throughout the fill to determine the dry weight (by weighing before filling and after freeze drying and/or further desiccation) of the final material. These samples are used to determine the percentage residual moisture content of the freeze-dried material by the Karl Fischer method. 

Moisture content determination of an essential oil can be carried out by Karl-Fischer titration, GC, spectroscopy, or electrometric methods. Drying of an essential oil is realized by the addition or filtering through a desiccating agent (e.g., anhydrous sodium sulfate). A simple test to check the presence of moisture in an essential oil is carried out by mixing 0.5-mL essential oil with 1-mL carbondisulfide. A clear solution indicates the absence of moisture. 

---