Humidity measurement gravimetric method

The gravimetric method is accepted as the most accurate humidity-measuring technique. In this method a known quantity of gas is passed over a moisture-absorbing chemical such as phosphorus pent-oxide, and the increase in weight is determined. 

A gravimetric method is often used for the measurement of water vapor permeability. The water vapor transmission rate (WVTR) according to this method is the amount of water vapor in g that permeates in 24 hours under standard test conditions (temperature, air relative humidity, water vapor sorbant) through aim2 sample surface area. The method measure a flux and not a permeability coefficient. 

They are usually measured by gravimetric methods, where a known amount of solid of known initial moisture content is exposed to a gas of specified relative humidity. After sufficient time, the new weight of the sample is measured, which allows one to calculate the actual moisture content. 

The gravimetric method measures surface moisture and loosely bound water of hydration [17]. The gravimetric method was described in the U.S. Code of Federal Regulations [15] before 1990. In the CBER/FDA laboratory the gravimetric (loss on drying) test [2,44] is performed in a humidity- and... 

One very common method of measuring the rate of water permeation through a film is cup method which is the gravimetric method described by Fu et al. [22]. The membrane to be tested is placed and fixed over a standard cup, at least half filled with water. The cup is placed in a chamber in which air at constant relative humidity is circulated at a constant temperature. This method measures water permeation rate at a high water activity on the feed side of the membrane since the atmosphere is saturated with water vapour. The VPS described above provides more flexibility in the feed water vapour composition and allows for the measurement of water transport in a mixture. 

Hageman et al. [3.13] calculated the absorption isotherms for recombinant bovine somatotropin (rbSt) and found 5-8 g of water in 100 g of protein, which was not only on the surface but also inside the protein molecule. Costantino et al. [3.72] estimated the water monolayer M0 (g/100 g dry protein) for various pharmaceutical proteins and for their combination with 50 wt% trehalose or mannitol as excipient. They compared three methods of calculating MQ (1) theoretical (th) from the strongly water binding residues, (2) from conventional adsorption isotherm measurements (ai) and (3) from gravimetric sorption analysis (gsa) performed with a microbalance in a humidity-controlled atmosphere. Table 3.5 summarizes the results for three proteins. The methods described can be helpful for evaluating RM data in protein formulations. 

Measurement of moisture uptake is typically done by either of two general methods. The classical approach involves equilibration of solid at several different humidities and the subsequent determination of water content either by gravimetric or analytical methods such as Karl Fischer titration or loss on drying. Moisture adsorption or desorption may be measured by use of this method and the pro-... 

Water absorbing capacity was determined gravimetrically using a modification of the method described by Elizalde et al (//), with some modification. Briefly, all samples were equilibrated in a 10% relative humidity (RH) chamber for 48 hours. Then, samples were transferred into a 98% RH chamber and exposed to moisture for 5 min. The dry matter and the absolute amount of absorbed water were determined. All measurements were made in triplicate. The results were expressed as the mean SD in mg water absorbed by per gram of psyllium per minute. 

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