A rapid LC-MS/MS method for lutein quantification in spinach (Spinacia oleracea)

Abstract There are very few studies that have reported on the validation of methods used to determine the lutein content in spinach using liquid chromatography–tandem mass spectrometry (LC-MS/MS), and thus the influence of various factors on accurate quantification, including matrix effects, remains unclear. To address this deficiency in methodology, we developed a rapid LC-MS/MS-based method and simple extraction procedure for the quantification of lutein in spinach. Under optimized gradient elution conditions, the separation of all-trans lutein was achieved within 2 min. The matrix effect evaluated using slope values of the regression lines was found to be negligible. The mean recovery of lutein spiked into spinach samples was acceptable. Sample homogeneity achieved by grinding was compatible with the international criteria. We observed no significant differences in the mean lutein content in the two spinach samples determined using the newly developed method compared with those determined using a conventional method. Intermediate precision relative standard deviations for an intra-laboratory test were below 8%. An inter-laboratory validation study conducted to analyze the lutein contents of the two different spinach samples yielded Horwitz ratio values of 0.72 and 1.62. The accuracy and reproducibility of the proposed method were verified in accordance with the internationally accepted Association of Official Analytical Chemists criteria.