An evaluation of osmolality measurement by freezing point depression using micro-amounts of sample.

An evaluation of the Advanced micro-osmometer is presented. This instrument has been shown to have an excellent analytical precision (within-run CV = 0.59%, between-day CV = 0.58%). It is accurate over an analytical range of 0-2000 mmol/kg of osmolality shown by linearity studies and split sample correlations against vapour pressure osmometry, freezing point osmometry and an external quality assurance programme. Analytical errors due to operator technique are almost eliminated because of good instrument design. Preliminary results on whole-blood osmolality are included. The required sample size of 20 mul permits osmolality measurements on most clinical samples. It is concluded that the Advanced micro-osmometer satisfies laboratory requirements.