I don’t have the time to fully understand zeta potential, so of course I go to Wikipedia, according to which: “Zeta potential is an abbreviation for electrokineticpotential in colloidal systems. In the colloidal chemistry literature, it is usually denoted using the Greek letter zeta, hence ζ-potential. From a theoretical viewpoint, zeta potential is electric potential in the interfacial double layer (DL) at the location of the slipping plane versus a point in the bulk fluid away from the interface. In other words, zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.”
Okay, that makes my head ache. And thank goodness, Steven Trainoff, director of engineering at Wyatt Technology assures me that even if I don’t exactly know what zeta potential is, I could still appreciate the importance of an instrument they are introducing at Pittcon 2010, the Möbiuζ, which Wyatt claims can more precisely and easily measure the electrophoretic mobility of proteins than other methods.
Accurate measurement of protein electrophoretic mobility—which is related to the zeta potential—is especially important in formulating protein drugs. That’s because protein drugs must be charged in a formulation. The charge must be high enough to ensure that proteins are stable—individual molecules repel each other—but not so high that not enough molecules can be crammed in the formulation. It’s therefore critical to know the charge on the molecule, which can be inferred from the electrophoretic mobility.
Now, many instruments out there can measure electrophoretic mobility, Trainoff says, but they are not good with small proteins, such as the 14.4-kilodalton lysozyme, in the high concentration that they exist in a formulation. That’s because as proteins become smaller, the noise from diffusion becomes too much. Wyatt’s new optical instrument solves this problem by using an array of 30 photodiode detectors instead of the usual single detector. The massively parallel detection system means faster detection and higher sensitivity than is possible with other instruments. For example, Wyatt’s Möbiu? can determine the electrophoretic mobility of a 1-mg/mL sample of immunoglobulin G in about 30 seconds.
Watch out for the March 29 issue for C&EN’s official coverage of Pittcon 2010. Senior Correspondent Stu Borman will summarize the highlights and trends, Senior Correspondent Steve Ritter will compile the most noteworthy instruments on display, and Senior Editors Celia Henry and Mitch Jacoby will report from the technical sessions.