Moisture samples

Sample quantity to estimate moisture for specific material is influenced to various levels of significance by properties such as particle-size range as well as relative amounts or moisture distributed among denoted forms of retention. Practical sample size estimates require background knowledge of parameters derived from experience for specific materials. More detailed examination of moisture-sampling aspects is provided in reference texts (Pitard). 

Example 4 Calculation of Sample Weight for Surface Moisture Content An example is given with reference to material with minimal internal or pore-retained moisture such as mineral concentrates wherein physically adhering moisture is the sole consideration. With this simphfication, a moisture coefficient K is employed as miiltipher of nominal top-size particle size d taken to the third power to account for surface area. Adapting fundamental sampling theory to moisture sampling, variance is of a minimum sample quantity is expressed as... 

The instrumental analyzer procedure, EPA Method 3A, is commonly used for the determination of oxygen and carbon dioxide concentrations in emissions from stationary sources. An integrated continuous gas sample is extracted from the test location and a portion of the sample is conveyed to one or more instrumental analyzers for determination of O9 and CO9 gas concentrations (see Fig. 25-30). The sample gas is conditioned prior to introduction to the gas analyzer by removing particulate matter and moisture. Sampling is conducted at a constant rate for the entire test run. Performance specifications and test procedures are provided in the method to ensure reliable data. 

Despite its advantages, SFE is employed routinely in only a few pesticide laboratories, for the extraction of low-moisture samples such as grains, pulses, dried fruit and tea. The technique requires specialized equipment because the extractions are performed at high pressure (45 psi) and elevated temperatures (around 60 °C) to maintain aC02 density ofO.85 gmL The analyte(s) may be trapped on Cig solid-phase material and eluted with a small volume (around 5 mL) of a polar solvent, such as acetonitrile. 

Weichbrodt et reported on the use of focused open-vessel microwave-assisted extraction (EOV-MAE) for the determination of organochlorine pesticides in high-moisture samples such as fish. The results were comparable to those with closed-vessel microwave-assisted extraction (CV-MAE) and ASE. The main advantage of FOV-MAE is that the use of Hydromatrix is unnecessary as the solvent mixture of ethyl acetate and cyclohexane allows the removal of water from the sample matrix via azeotropic distillation. 

The utilization of IR spectroscopy is very important in the characterization of pseudopolymorphic systems, especially hydrates. It has been used to study the pseudopolymorphic systems SQ-33600 [36], mefloquine hydrochloride [37], ranitidine HC1 [38], carbovir [39], and paroxetine hydrochloride [40]. In the case of SQ-33600 [36], humidity-dependent changes in the crystal properties of the disodium salt of this new HMG-CoA reductase inhibitor were characterized by a combination of physical analytical techniques. Three crystalline solid hydrates were identified, each having a definite stability over a range of humidity. Diffuse reflectance IR spectra were acquired on SQ-33600 material exposed to different relative humidity (RH) conditions. A sharp absorption band at 3640 cm-1 was indicative of the OH stretching mode associated with either strongly bound or crystalline water (Fig. 5A). The sharpness of the band is evidence of a bound species even at the lowest levels of moisture content. The bound nature of this water contained in low-moisture samples was confirmed by variable-temperature (VT) diffuse reflectance studies. As shown in Fig. 5B, the 3640 cm-1 peak progressively decreased in intensity upon thermal... 

J.B. Reeves, Near- versns mid-infrared spectroscopy Relationships between spectral changes indnced by water and relative information content of the two spectral regions in regard to high-moisture samples, Appl. Spectra sc., 49, 295-903 (1995). 

Use larger syringe to inject larger volumes for low moisture samples. Duplicates are recommended. 

For extraction, water content is considered an important factor. It has been found that working with low-moisture samples simplifies the extraction process. Industrial extraction normally is done with dry material, which reduces complications arising from the solvents used for processing and their recovery. 

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-... 

To determine the total moisture, either an analysis sample can be prepared from the moisture sample, or the regular analysis sample can be used for this purpose, provided that the moisture analysis is performed on the analysis sample within a prescribed time after the air-dry sample is prepared. When separate analysis samples are used for moisture and for the other determinations that are... 

Gross moisture sample sample representing one lot of coal and composed of a number of increments on which neither reduction nor division has been performed or a subsample for moisture testing taken. 

A Perkin-Elmer thermogravimetric analyzer (TGA) was used to determine the hydrogen desorption kinetics at atmospheric pressure. This instruntent was located in another glove box under nitrogen atmosphere to prevent any exposure of the samples to air and moisture. Samples were heated to 2S0°C at a ramping rate of S°C/min under 1 atm of He, using an initial 1 minute delay to ensure an environment of pure He. Approximately 10 mg of sample were used in the TGA. 

It is noted that the temperature of the drying plateaus tend to increase towards the centre of the 14% moisture samples which is not the case for the 44% moisture samples. The simulated mass is in agreement with measured data as shown in Figure 4b. 

Sorption isotherms quantify how tightly water is bound to a sohd. The goal of obtaining a sorption isotherm for a given solid is to measure the equilibrium relationship between the percentage of water in the sample and the vapor pressure of the mixture. The sorption isotherm describes how dry a product can get if contacted with humid air for an infinite amount of time. An example of a sorption isotherm is shown in Fig. 12-11. In the sample isotherm, a feed material dried with 50 percent relative humidity air a , = 0.5) will approach a moisture content of 10 percent on a dry basis. Likewise, a material kept in a sealed container will create a headspace humidity according to the isotherm a 7 percent moisture sample in the example below will create a 20 percent relative humidity a ,= 0.2) headspace in a sample jar or package. 

Complex (LMe, Pr2)ScCl2(THF) is an off-white solid that is soluble in most organic solvents, such as diethyl ether, THF, hexanes (slightly), toluene, and bromoben-zene however, prolonged exposure to chlorinated solvents such as dichloro-methane or chloroform results in decomposition. Although (LMe l>,2)ScCI2(THF) rapidly decomposes upon exposure to even trace air or moisture, samples can be stored indefinitely under an inert atmosphere. 

EPA Method 4 moisture sampling train reference method. (From U.S. EPA, 40 CFR 60 Standards of Performance for New Stationary Sources, Washington, DC U.S. Environmental Protection Agency, 2001.)... 

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