Abstract
A novel analytical method was applied for identification of isoprenoid quinones in Escherichia coli by liquid chromatography atmospheric press chemical ionization mass spectrometry in negative mode (LC‐NI‐APCI‐MS). Extraction and clean‐up of sample were carried out on Sep‐Pak Plus Silica solid‐phase extraction cartridges. Ubiquinone‐7 (UQ‐7), Ubiquinone‐8 (UQ‐8) and Mequinone‐8 (MK‐8) were determined directly using combined information on retention time, molecular ion mass, fragment ion masses and UV characteristic spectrometry without any standard reagent. It was found that UQ‐8 was the major component of isoprenoid quinones in Escherichia coli under aerobic condition. Compared with UQ‐8, the relative abundance of UQ‐7 and MK‐8 is only 15% and 14%, respectively. The average recoveries of UQ‐6, UQ‐10 and vitamin K~1~ in Escherichia coli were investigated by standard spiking experiment. The recoveries were achieved in the range from 94 to 106%, and the relative standard deviations (RSD) of the triplicate analysis of the spiked samples (UQ‐6, UQ‐10 and vitamin K~1~) ranged from 3 to 8%. The detection limits of LC‐NI‐APCI‐MS were estimated to be 5, 40 and 0.8 μg/g dry cell for UQ‐6, UQ‐10 and vitamin K~1~, respectively. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)