Moisture analysers

Moisture analyses are important because samples contain water either as chemically combined hydrates or as occluded surface-adsorbed moisture. Water is an inherent part of most biological substances and constitutes >90% of the fresh weight of some plant materials. To afford reproducible analytical results, samples are usually dried before analysis and the percentage composition of the sample is then calculated on a dry basis. 

Current methodologies for use on grains and grain products recognized by the AACC, including moisture analyses based on convection, vacuum, and microwave ovens. 

Though the protocol was written for a dry solid, it should also be mentioned that liquid samples can also be run (Firestone, 1998). Liquid samples can be added directly to the vessel itself or can be treated as a solid with an extraction step in the Karl Fischer solvent as presented in the protocol. The preference for moisture analyses is the gravimetric method (unit aj.i) largely due the higher costs of equipment and the use of chemicals in the Karl Fischer method. Currently one observes very few applications of the Karl Fischer method on food products published by the AOAC for nutritional labeling purposes. In particular, these food products are cocoa, cocoa products, confectionery coatings, and molasses (Sullivan and Carpenter, 1993). 

The infrared moisture analyser may also be used for quick determination of water content although it gives a value that is different than the other two methods (subject of a future unit on NIR). This may be useful if a rapid IR method is used in a production line so one can correlate line moisture with true moisture. 

In contrast to location 1, the profile at location 2 was shallower, contained more sand, and below a depth of 0.60 meters would be considered a loam. The sandy layers at the profile base would tend to accelerate movement of the pesticide associated with the bulk flow of water and perhaps would account for the lack of residues in the deeper layers of the profile and for contaminated well water nearby. Based on texture and moisture analyses, one would expect a longer time required for downward movement of EDB at location 1 compared with location 2. 

Essentially two methods are used in ceramic laboratories to establish the moisture content one is using the moisture analyser and the other the determination of the moisture content in the drying chamber. To ascertain the moisture content with the aid of the moisture analyser, a material sample of approx. 10-20g is taken from the material to be extruded and the moisture content is assessed in the moisture analyser (Fig. 2). 

It is useful to grind the sample before placing it into the moisture analyser. The most popular moisture analysers work on the basis of infrared, and the time required for an analysis of an average-sized sample is between 5 and 15 minutes. The result can be directly read off expressed as a percentage. Working with a moisture analyser is convenient and is recommended in particular for the assessment of the moisture content of raw materials prior to calculation of the batch formula, also for the purpose of checking the incoming material delivered from suppliers of raw materials and ceramic bodies. 

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. 

Water concentration in XLPE film was determined coulometri-cally using a DuPont Model 903, Moisture Evolution Analyzer (MEA). The instrument was isolated in a dry box flushed with dry N to minimize extraneous sources of moisture. Analyses were run for 30 min. at 70 C and the total amount of water evolved from a preweighed sample was read directly from the instrument. 

This test method involves a rapid quantitative determination of the residue in bitumen emulsion using a moisture analyser. It is applicable to all non-solvent-containing emulsion types, anionic, cationic, non-polymer-modified or polymer-modified bitumen emulsions. 

A sample of bitumen emulsion, minimum 1 g and up to 3 g, is placed in a moisture analyser equipped with a heating element and capable of running either isothermally or in a programmable temperature-gradient mode. 

The most important factor characterising the powder was its water content, which was measured using a halogen moisture analyser (HB43-S, Mettler Toledo GmbH, Germany). To account for this, the encapsulation efficiency of the experiments was calculated using (15.2) and the results are presented in Fig. 15.44. 

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