Drop weight variation in an automated collection procedure and its relationship to apparent surface tension.

A drop counter-regulated fraction collector yields samples containing equal numbers of drops. Such fractions vary slightly in weight depending on experimental conditions such as surface tension. Provided that variables such as flow rate and eluate density remain constant, apparent surface tension may be estimated directly from the weights of eluate fractions obtained from gel filtration experiments. The detergents sodium cholate and sodium lauryl sulphate significantly decreased drop weights in this system. Following gel filtration on Sepharose 4B, sodium cholate eluted in the fractions containing low molecular weight material. It eluted in the same position when pre-mixed with human plasma. Normal plasma was found to contain two surface tension-reducing components with apparent molecular weights of 3-10(6) and 1-10(5). The apparent surface tension of whole human plasma was found to be time dependent and decreased as the flow rate was reduced.