Classification of plastic eye dropper tips using Harkins and Brown's factor.

In this work, the weights of drops produced by seven commercially available eye drop dispensing systems were investigated using benzalkonium chloride solutions in concentration range of 0-0.02%. The effect of the surface tension, the effective diameter of the dropper tip, and the dropper bottle volume on the drop weights was studied at the vertical position. Based on the principle of Tate's law, the theoretical maximal weights of drops were expressed. In all cases, the lower the surface tension, the lower drop weights were noted. Simultaneously, effect of both the effective diameter of the dropper tip and the dropper bottle volume on the drop weights could be described. A regression equation characterized a significantly negative linear interaction of both variables. Comparing the theoretical drop weights with those measured experimentally, Harkins and Brown's factors, FHB, were received. The mean drop weights obtained for the Traube's stalagmometer were 62% that of the theoretical values. FHB values detected for the plastic dropper tips were significantly greater ranging from 0.66 to 0.76. In contrast to the obvious characterization of dropper tips by geometrical parameters, a classification of dropper tips with Harkins and Brown's factor is proposed.