About Nu-Chek Prep.:   http://www.nu-chekprep.com/p.htm

Nu-Chek-Prep reference standards are prepared from individual chromatographically pure lipid esters. Each component used in making up our reference mixture is carefully checked by GLC using large overloads. Only those fractions which meet our rigid requirements go into the final make-up. After being weighed to the nearest tenth of a milligram, the combined material is again analyzed as a total mixture. They are then flushed with nitrogen, sealed in glass ampules under vacuum, and finally stored at -30°C. until ready for shipment.