|Which side of the membrane should I use, the shiny or dull side?||Most researchers may not even notice that there is a "sidedness" to filters, and, for most applications, orientation will not affect filter performance. However, membranes do have a slightly asymmetric pore structure: the shiny side of the membrane is the "tighter" side. In some applications, you can take advantage of this difference by selecting a specific filter orientation. ultrafiltration membranes should always be used shiny side up, regardless of application for drop dialysis ( a buffer exchange technique in which a few drops of DNA or protein are placed in a 0.05 or 0.025 um filter and floated on a buffer solution), apply the sample to the shiny side of the filter and float the filter dull side to the buffer. This measure will enhance buffer exchange and discourage sample loss. The Millipore Express and Express Plus membranees are also sided - these membranes should be used shiny side facing down.
|What is the difference between pore size and pore size distribution?||Whereas pore size is a measure of the diameter of the largest pore, pore size distribution is a measure of the range of pore sizes. The range of pore sizes can be normally distributed, and the spread can be quite narrow (e.g. the ratio of largest to smallest may be less than 2). On the other hand, pore size distribution can be very heterogeneous. In the case of large spreads and heterogeneity, the pore size will be far less predictive of flow rate (either filtration or capillary) than it will be for a membrane with a narrow pore size distribution. It is important to note that the pore size corresponding to the bubble point is not at the middle of the distribution, but is the largest pore.