Total-Pure™ Centrifuge Tubes are produced from a proprietary purified polypropylene blend that is certified to be free of trace metal content. Tested via ICP-MS, these tubes are certified to contain less than 1ppm of common trace metals including: Calcium, Magnesium, Zinc, Iron, Manganese, Copper, Aluminum, Silicon, Nickel, Vanadium, Sodium, Phosphorous, Cobalt, Chromium, Potassium, Lithium, Lead, Selenium, Cadmium, Mercury, and Arsenic.In addition to a superior level of purity, TotalPure™ Tubes include a wide array of premium features. These tubes also feature Hi-Viz™ graduations that are easily identified at any angle and the printed max-freeze line indicates the maximum allowable volume to be frozen inside the tubes. TotalPure's natural color caps offer a smooth seal that is easy to open/close with one hand without compromising the integrity of the 95kPA leak-proof seal.• Ultra-Pure Polypropylene Blend Certified Free of Trace Metals