Provided are certain polyolefinic membranes which are useful as components of filters for liquid purification. Advantageously, the filter membranes of the disclosure possess greatly reduced concentrations of certain trace metals, thus making them particularly useful in the filtration of liquids used in the fabrication of microelectronic devices. In one aspect, the disclosure provides a filter membrane comprising a polyolefin, wherein said polyolefin has less than about 4 ppm total of metals chosen from titanium, aluminum, iron, zinc, and magnesium.