Electrolytic Tungsten Needle Sharpening

F sharpened tungsten needles are essential tools required for the manipulation of small particles (1, 2, 3). They can be purchased commercially from Fine Science Tools at a cost of roughly $100 for a set of ten needles. Tungsten needles can easily become damaged during routine use, and accidentally bumping the sharpened end of a tungsten needle immediately renders it useless. For laboratories that frequently isolate and manipulate small particles, the costs associated with purchasing tungsten needles from a commercial source can become significant over an extended period of time. It is also useful for any analyst who frequently handles small particles to have a set of tungsten needles with a variety of shapes and various degrees of sharpening, ranging from fine to coarse (1, 2). Many analysts who handle small particles on a regular basis agree that there is a perfect needle — in terms of size and shape — for every particle. It is the author’s experience that using needles of appropriate taper, curvature and fineness for a given particle decreases the time involved in sample preparation and minimizes the risk of losing or damaging the particle. The need for a wide range of needle shapes and fineness, the frequency with which needles get damaged, and the relatively high cost of commercial tungsten needles make it worthwhile to learn how to sharpen your own needles. There are generally two methods used for sharpening tungsten needles: a chemical method, involving sodium nitrite, and an electrolytic method. Both have been previously described by others (1, 2). It is the author’s personal experience that the chemical method, while effective at sharpening tungsten needles, does not provide large degrees of control over the shape and fineness of the needle produced. The chemical method is also somewhat messy, requiring an open flame and producing a spatter of molten sodium nitrite in the work area. Therefore, the electrolytic method is preferred. This method involves an electrochemical reaction between the tungsten wire and a piece of platinum wire immersed in a solution of potassium hydroxide. However, there are few detailed literature descriptions of how to sharpen tungsten needles using the electrolytic method, although there is a brief description in The Particle Atlas (1). This article provides a detailed description of one version of the electrolytic sharpening method, which will enable the reader to reproduce the setup in their own lab.