SPECTROPHOTOMETRIC DETERMINATIONS ON DROPLETS SHRUNK IN OIL

In modern biochemical reseach there is an increasing demand for quantitative analysis in the submicrogram range. Glick (1,2) has surveyed the analytical micro methods utilizing spectrophotometric techniques. To obtain sufficient optical density with small volumes, these methods often require a cuvet consisting of a thin capillary giving a long optical path. Another approach was taken by Ornstein and Lehrer (3), who introduced the so-called shrinking droplet cuvet. By imbibing a spherical drop with a water-absorbing transparent gel they were able to reduce the volume of the drop up to 1000 times, giving a 10 times reductuin of diameter. In this way the optical density was increased about 100 times. Hellman, Ulfendahl, and Wallin (4) presented a method of shrinking droplets in air on nowetting Teflon film. The diameter of the drops couls easily be reduced to about 150 μ (≈2 nl) but a futher reduction was difficul owing to the increasing speed of diameter reduction. If the avaliable initial sample volume is of the order of nanoliters, the increase in optical density will be insignficant and the applicablity of the method thus confined to rather large samples. To over come this limitation the method has been modified; this paper describes the results obtained when using oil instead of air as the imbibing medium. The modification allows drops with an initial wolume of a few nanoliters to be shrunk in a controlled way down to about 0.004nl. © 1969.