Moisture analyzer

The water content of an 875.4-mg sample of cheese was determined with a moisture analyzer. What is the %w/w H2O in the cheese if the final mass was found to be 545.8 mg ... 

Moisture. In relatively pure sugar solutions, moisture is deterrnined as the difference between 100 and Brix. In crystalline products, it is usually deterrnined by loss-on-drying under specified conditions in an oven or by commercial moisture analyzers that have built-in balances. Moisture in molasses and heavy symps is deterrnined by a special loss-on-drying technique, which involves coating the sample onto sand to provide a greater surface area for oven drying. The result of this test is usually considered dry substance rather than moisture. 

Most adsorbers operate on a fixed drying cycle time and, frequently, the cycle lime is set for the worst conditions. However, the adsorbent capacity is not a fixed value it declines with usage. For the first few months of operation, a new desiccant has a very high capacity for water removal. If a moisture analyzer is used on the effluent gas, a much longer initial drying cycle can be achieved. As the desiccant ages, the cycle time will be automatically shortened. This will save regeneration fuel costs and improve the desiccant life. 

Abbott, M. Roth R.J. Henry, Automated Process Control of Moisture II — Optical Moisture Analyzer , PATR 4298 (1971)... 

Solids moisture analyzer (Consolidated Electrodynamics Corp, 360 Sierra Madre Villa, Pasadena, Cal, or equivalent) (See Fig Et 9)... 

MEASURING MOISTURE USING A MICROWAVE MOISTURE ANALYZER... 

The microwave moisture analyzer allows one to dry a sample by two modes. Mode 1 dries a sample at a specific power setting for a given time period. Mode 2 dries a sample at a specific power setting using a time period that is determined by the analyzer itself, ending the ran when no weight change is achieved within a preset time interval criterion. This protocol looks only at Mode 1 operation. 

Microwave moisture analyzers are the next step in gravimetric analyses by focusing on much shorter drying times. Currently there are only a few matrices recognized by the AOAC for use in the microwave drying method (Sullivan and Carpenter, 1993). Although there hasn t been a collaborative study for AOAC approval to support other matrices, the micro-wave moisture analyzer has been used successfully in such matrices as grains (Okabe et al., 1973) and flours (Davis and Lai, 1984). 

Air drying at 105°C or vacuum drying at 70°C for > 18 hr is usually used to determine the solid mass in the sample. The Karl Fisher technique is generally recommended, due to temperature abuse in the oven method. However, the oven method is widely used due to its simplicity and availability in most laboratories. The infrared moisture analyzer may also be used for quick determination of water content although it gives a different value from that obtained by the other two methods. 

Microwave moisture analyzer, gravimetric measurement of water, 9-11 Milk... 

Berthold 1992. Microwave Moisture Analyzer LB 354 MICROMOIST. EGG Berthold, 101 Corporation Drive, Aliquippa, PA 15001-4863. 

The dry weight was determined by using an MA-40 moisture analyzer (Sartorius AG, Geottingen, Germany). h DVB, divinylbenzene. 

During the past 40 years there have been numerous exciting extensions of electrochemistry to the field of analytical chemistry. A series of selective-ion potentiometric electrodes have been developed, such that most of the common ionic species can be quantitatively monitored in aqueous solution. A highly effective electrolytic moisture analyzer provides continuous online assays for water in gases. Another practical development has been the voltammetric membrane electrode for dioxygen (02), which responds linearly to the partial pressure of 02, either in the gas phase or in solution. The use of an immobilized enzyme (glucose oxidase) on an electrode sensor to assay glucose in blood is another extension of electrochemistry to practical analysis. 

Another example of the application of the principles of coulometric titrations to a continuous on-stream analyzer is the moisture analyzer developed by Kei-del.18 It illustrates one of the outstanding advantages of the coulometric generation of a titrant namely, an intermediate is produced as a titrant that would not be available in standard solutions. The principle of the moisture analyzer is to place a phosphoric acid solution between two closely spaced platinum electrodes (helically wound in a glass tube). When current is passed between the two electrodes, the water in the phosphoric acid is electrolyzed... 

Figure 6.9 Keidel coulometric moisture analyzer for the determination of water in gases. At a flow rate of 100 mL min-1 a moisture content of 1 ppm gives a current of 13.2 A.

Moisture analyzers include a large variety of designs listed here. The list includes their inaccuracies (1) electrolytic hygrometer (2-5% FS), (2) capacitance (3% FS), (3) impedance (3% FS), (4) piezoelectric (10% AR or 2 ppm by volume), (5) heat of adsorption, (6) infrared (0.5-1% FS), (7) microwave (for a 1-15% moisture range, error is within 0.5%, less if corrected for density), (8) Karl Fischer titrator (0.5-1% FS), (9) drying oven (0.5-1% FS), (10) dipole, (11) cavity ring down, (12) fast neutron (0.2% in solid s density corrected), and (13) radio-frequency absorption (5 ppm). 

Some of the industrial process analyzers are of the probe type (capacitance, fiber-optic IR probes), others can look through the process stream in the pipe (microwave), and the majority require some form of a sampling system. Table 3.27 provides a summary of the ranges and other features of many of the process moisture analyzers. 

The noncontacting moisture analyzer can be provided with gamma radiation densitometer to compensate for variations in process density. (Courtesy of Berthold Technologies.)... 

The microwave absorption hygrometer operates similarly to the IR absorption hygrometer, but in the microwave frequency band of 20-22 GHz (K band), the wavelength is about 13-15 mm. The unit senses the mass of moisture in the beam path, so the readout is normally in terms of the mass of moisture per unit volume. When using microwave moisture analyzers to measure the moisture content of moving webs or other materials that are thinner than 0.5 mm, multiple transmission is required. Because the absorption of microwaves is affected by both bulk density and solids temperature, both of these variables must be measured and compensated for if precise readings are desired (Figure 3.29). 

It is a fundamental requirement that liquefied petroleum gas should not contain free water (ASTM D-2713). Dissolved water may give trouble by forming hydrates and giving moisture vapor in the gas phase. Both of these will lead to blockages. Therefore, test methods are available to determine the presence of water using electronic moisture analyzers (ASTM D-5454), dew-point temperature (ASTM D-1142), and length-of-stain detector tubes (ASTM D-4888). 

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