Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Science

Committee Chair(s)

Gary H. Richardson


Gary H. Richardson


C. A. Ernstrom


D. G. Hendricks


A Wescor Vapor Pressure Osmometer measured the osmolality of a solution by sensing the vapor pressure above the solution in a closed chamber. The instrument sensing element comprised a precision thermocouple which measured the dew point temperature depression, a function of the water vapor pressure in the chamber. It used approximately 5-7 microliter samples to saturate a 0.64 cm filter paper disc. The instrument fixed a milliosmolal digital reading and signaled test completion in 110 seconds. The instrument weighed approximately 3. 62 kilograms, was 26. 7 x 24. 1 x 10. 2 cms in size and had a range of 0 to 1999 milliosmolal. The modular solid state osmometer contained no mechanical moving parts, required no refrigerated components, sample pipetting, sample tube, and no operator attention following sample insertion. Cleaning the sample chamber pocket between tests with an acetone impregnated tissue improved repeatability of the osmometer and reduced the coefficient of variability from O. 76% to 0. 70% on a raw milk sample. Two hundred individual cow milk samples from 20 herds were run in February, 1974, to establish a mean freezing point in Cache Valley herds for that period. The mean and standard deviation was 280±3.0 millisomolal. Results of milk samples containing 0 to 25% added water measured by the osmometer were compared to those obtained from an Advanced thermistor cryoscope. The coefficient of correlation was 0.991. A collaborative study was conducted involving eight hospitals and industry laboratories. When the results of two laboratories were discarded, due to instrument maintenance problems, there were no significant differences among the laboratories in their abilities to quantitate added water. Proper maintenance of the osmometer in order to keep the thermocouple clean and frequent calibration checks are recommended.



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