Moisture content, of samples

Residual moisture content of samples can play a major role in reproducible sampling of the matrix, as well as in the interaction of the microwave energy with the sample. 

Determine moisture content of sample (see Support Protocol 1)... 

The moisture content of samples, in equilibrium, in the ESEM is varied at constant temperature (10°C), while lowering the pressure in the ESEM chamber from 9 torr to 2 torr. At the same time, relative humidity varies from 100% to 20%. The created chamber climate induces evaporation of the unbound (free) water in the cement paste (CP) samples without or with an embedded aggregate (to model simple concrete). It has been observed that curing conditions, sample age, water/cement (w/c) ratio, the presence of an aggregate, as well as the value of the RH, gives rise to different drying behaviour of the... 

Because water provides the greatest extinction coefficient in the NIR for pharmaceutically relevant materials, it stands to reason that this is one of the most measured substances by the NIR technique. A recent application involves noninvasive measurement of water in freeze-dried samples. Derksen et al. [56], for instance, used NIR to determine water through the moisture content of samples with varying active content. Ka-met et al. applied NIR to moisture determination of lyophi-lized pharmaceutical products [57]. 

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... 

Moisture content of samples was evaluated with a Sartorius MA 30 Moisture Analyser by heating about 1 g of substance at 130 up to constant weight (about IS min.). Percent of weight loss was recorded. 

Chemical noise arises from a host of uncontrollable variables that affect die chemistry of the system being analyzed. Exampks include undetected variations in temperature or pressure that affect the position of chemical equilibria, flnetuations in relative humidity that cause changes in the moisture content of samples, vibrations that lead to stratification of powdered solids, changes in light intend that affect photosensitive materials, and laboratory fumes that interact with samples or reagents. Details on the effects of chemical noise appear in later chapters lliat deal with specific instrumental methods. In this eha >ter we focus exclusively on instrumental noise. 

Noncontact NIR analyzers were known and widely used since the early 1970s. The first use of these analyzers was in measuring moisture content of samples moving on conveyers. Several two- or three-color interference filter-based instruments are still manufactured and sold for applications in the inorganic, tobacco, food, chemical, plastic, and other industries. 

The moisture content of cmde sulfur is determined by the differential weight of a known sample before and after drying at about 110°C. Acid content is determined by volumetric titration with a standard base. Nonvolatile impurities or ash are determined by burning the sulfur from a known sample and igniting the residue to remove the residual carbon and other volatiles. 

Equilibrium moisture content of a hygroscopic material may be determined in a number of ways, the only requirement being a source of constant-temperature and constant-humidity air. Determination may be made under static or dynamic conditions, although the latter case is preferred. A simple static procedure is to place a number of samples in ordinaiy laboratoiy desiccators containing sulfuric acid solutions of known concentrations which produce atmospheres of known relative humidity. The sample in each desiccator is weighed periodically until a constant weight is obtained. Moisture content at this final weight represents the equilibrium moisture content for the particular conditions. 

A samphng probe is placed at any location in the stack, and a grab sample is collected in an evacuated flask. This flask contains a solution of siilfiiric acid and hydrogen peroxide, which reacts with the NO. The volume and moisture content of the exhaust-gas stream must be determined for calculation of the total mass-emission rate. The sample is sent to a laboratoiy, where the concentration of nitrogen oxides, except nitrons oxide, is determined colorimetrically. 

Moisture content. The moisture content of solid wastes usually is expressed as the mass of moisture per unit mass of wet or diy material. In the wet-mass method of measurement, the moisture in a sample is expressed as a percentage of the wet mass of the material in the diy-mass method, it is expressed as a percentage of the diy mass of the material. In equation Form, the wet-mass moisture content is expressed as follows ... 

The data presented in Figure 19.7 were obtained on a Sonntag-Universal machine which flexes a beam in tension and compression. Whereas the acetal resin was subjected to stresses at 1800 cycles per minute at 75°F and at 100% RH, the nylons were cycled at only 1200 cycles per minute and had a moisture content of 2.5%. The polyethylene sample was also flexed at 1200 cycles per minute. Whilst the moisture content has not been found to be a significant factor it has been observed that the geometry of the test piece and, in particular, the presence of notches has a profound effect on the fatigue endurance limit. 

The temperature to which a sample of air has to be reduced to bring it to saturation. The moisture content of the air sample fixes it. 

NOTE The moisture content of steam can be measured by means of a throttling calorimeter or by analysis of the sodium content in a sample of condensed steam, using perhaps a specific ion electrode or flame photometer. 

The reduction of the sample was made at 2250 K In a flowing stream of hydrogen carrier gas ( SO cm /mln). The total pressure of the carrier gas was approximately 1 atm. The water vapor produced during the reduction was swept by the carrier gas Into an electrolytic-type (P2O5) moisture monitor and a continuous recorder trace of the water concentration as a function of time was obtained. A typical plot of the moisture content of the carrier gas as a function of time Is shown In Figure 3. The region on the left side of this figure where the moisture content... 

Figure 3 shows the UV-vis DRS spectra of the three groups of catalysts In all cases, a prominent Au plasmon peak around 525 run was observed. This peak was sharper for catalysts of both groups A and B, and broader for catalysts of group C. That is, catalysts of lower C.F. s had broader peaks. In addition, there were three peaks at 270, 230, and 200 nm. These bands were related to the hydroxyls on AljOj, since they were observed on pure AljO, also, and their intensities changed with the moisture content of the sample. 

The sampling of a suction lysimeter is initiated by applying a vacuum (approximately 40-50 cm of mercury) through the vacuum/pressure line with a hand pump or electric pump. The valve on the sampling line must be closed. A constant vacuum may be maintained on the lysimeter using an electric pump. The time required before collecting a sample from a lysimeter will depend on the method of vacuum application, the moisture content of the soil, and the soil type. 

Dry column chromatography [528] provides several improvements over traditional column chromatography, such as better resolution and high speed. Another important characteristic is the near-quantitative applicability of TLC results in dry column analysis. Knowledge of the TLC characteristics of a sample is useful before column chromatography is employed. Careful control of the moisture content of the adsorbent is crucial to the dry column as well as other types of chromatography. 

Soil samples are handled by shaking 2 pounds of soil, the moisture content of which has been determined for subsequent correction to dry weight, with 1.5 ml. of benzene per gram of soil for 1 hour in the metal cans on the mechanical stripper. 

Before measuring conductivity, carbon materials and their mixtures were dried to residual moisture content of less than 5wt%. A sample of the investigated material was put into a measuring cell, representing a dielectric cylinder closed at both ends by the measuring electrodes. 

In Table I results of Rn-226 activity measurements cn geological samples are shewn together with measurements cn Rn exhalation rates from the sanples. The exhalation rates varies considerably with the moisture content of material. The exhalation rate is lew for dry samples and when the moisture content increases, the exhalation rate increases until it reaches a plateau. When the moisture content increases further, a rapid increase in radon exhalation occur. When the saturation level of moisture is reached, the exhalation rate drops dramatically. The exhalation rates given in Table I are obtained by assuming that the most probable moisture content is whithin the plateau of exhalation rate/moisture curve. (Stranden et al, 1984, Stranden et al, 1984a). 

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