Moisture measurement methods

Chevalier, D., Ossart, F. and Ghommids, C. (2006) Development of a non-destructive salt and moisture measurement method in salmon (Salmo salar) fillets using impedance technology. Food Control, 17, 342-347. 

Moisture measurements are important in the process industries because moisture can foul products, poison reactions, damage equipment, or cause explosions. Moisture measurements include both absolute-moisture methods and relative-humidity methods. The absolute methods are those that provide a primaiy output that can be directly calibrated in terms of dew-point temperature, molar concentration, or weight concentration. Loss of weight on heating is the most familiar of these methods. The relative-humidity methods are those that provide a primaiy output that can be more direc tly calibrated in terms of percentage of saturation of moisture. 

Dew-Point Method For many applications, the dew point is the desired moisture measurement. VHien concentration is desired, the relation between water content and dew point is well-known and available. The dew-point method requires an inert surface whose temperature can be adjusted and measured, a sample gas stream flowing past the surface, a manipulated variable for adjusting the surface temperature to the dew point, and a means of detecting the onset of con-densation. 

Wexi.ER, A. In Humidity and Moisture. Measurements and Control in Science and Industry. Volume 1 Principles and Methods of Humidity Measurement in Gases, (Ed. R. E. Ruskin) (Reinhold. New York,... 

Table 1.15.1 Residual moisture content (RM) of different vaccines measured by four different measurement methods...

As indicated previously, moisture was measured by oven-drying at 103°C for 24 h (8). Three samples from each of the five silages were taken for moisture measurement. Mean particle length (MPL) was measured by the standard separator method using five screens and a pan (11). Three samples of about 2 kg each were taken to measure MPL for each of the five silages. 

In some instances, nonaccessibility, or the so-called average ordered fraction, is measured rather than crystallinity. Values vary depending on the size of the probe molecule and its ability to penetrate and be adsorbed in all the disordered regions. It will be noted that the average ordered fraction is relatively close for the deuteration and moisture regain methods. In addition, the average ordered fraction is decreased about 25% by mercerization. 

The methods for the determination of residual moisture currently used at the Center for Biologies Evaluation and Research at the U.S. FDA are the gravimetric (loss on drying) method, the Karl Fischer method, and the thermogravimetric (TG) and thermogravimetric/mass spectrometric (TG/MS) method. Current work in progress involves the use of vapor pressure moisture measurements to provide additional information about residual moisture content and its interaction with the components of the freeze-dried final container and its contents. 

The current challenges to moisture measurement include devising methods to deal with smaller and smaller sample sizes in single-dose final containers, working with samples that are very sensitive to ambient humidity even in the dry box, and understanding the interaction between water in the freeze-dried cake, the vial head space, and the container closure, and the changes that occur over time. 

In this chapter, we have reviewed some critical aspects of stoppers that are used for packaging of lyophilized biopharmaceuticals. We have listed the desirable attributes for lyophilization closures for use with protein formulations. We have discussed issues relating to preparation of stoppers. Two issues, siliconization and occluded water, have been dealt with in detail. Siliconization can be a cause of particulate generation and aggregation, as shown by our experience with recombinant tumor necrosis factor formulations. We have described methods of measurement of stopper-occluded moisture and discussed their relative merits and demerits. We further studied the kinetics of moisture removal from stoppers under selected conditions. Our approach to validation of moisture removal from stoppers has also been presented. Finally, we have discussed the usefulness of occluded moisture measurement for determination of moisture uptake by protein products under real... 

Bardat, A. Biguet, J. Chatenet, J. Courteille, F. Moisture measurement a new method for monitoring freeze drying cycles. J. Parenter Sci. Technol. 1993, 47, 293-299. 

The EPA Method 6 provides procedures for measuring sulfur dioxide emissions from stationary sources where the gas sample is extracted from the exhaust stack. Ammonia, water-soluble cations, and fluorides cause interferences with SOx measurements. Method 6A concerns sulfur dioxide, moisture, and carbon dioxide measurements from fossil fuel combustion sources by chemically separating the SO2 and CO2 components, where different reagent chemicals are used. Method 6C discusses the use of instrument analyzers to measure... 

Electronic moisture meters usually operate on a dielectric principle and/or kernel surface conductance with compensation for sample temperature and density. Thus, electronic moisture meters measure electrical properties that are calibrated to oven moisture measurements. The typical air-oven reference methods used for whole soybeans are the AOCS Method Ac 2-41, ASABE Standard S352.2, and AACC Method 44-15a. 

In addition to the air-oven methods for moisture measurement, there is also a Karl Fischer titration method. In this method, moisture is considered to be the moisture that is extracted by methyl alcohol in a sealed container with ground soybeans for a specified time period (Paulsen, 1991). This water-alcohol extract is placed in a reaction chamber where the water reacts with iodine. The amount of iodine used in titration is a measure of the amount of water in the soybeans. Soybean samples tested with the Karl Fischer method usually show about 0.2 percentage points lower moisture than those tested with the USDA air-oven method (Paulsen, 1991). The standard deviations of differences from duplicate samples were lower (0.07 percentage points) for the USDA air-oven method than for the Karl Fischer method (0.11 percentage points) (Paulsen, 1991). 

Wang and Johnson (2001) reported on test measurement methods that were major indicators of soybean oil quality. These tests included peroxide value, anisidine value, FFA content, phospholipid content, total tocopherol content, oxidative stability index, color, and moisture content. For soybean meal, they reported on urease activity, protein dispersibility index (PDI), rumen bypass or rumen undegradable protein, trypsin inhibitor activity, moisture content, residual oil content, protein content, fiber content, color, amino acid profiles, and protein solubility under alkaline (KOH) conditions. 

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