Retention, selenomethionine

Selenomethionine forms optical enantiomers and a chiral column is needed to separate the two forms [160-162], As the presence of salts and organic matter can cause retention times to vary, it is essential that spiking is used to verify them. Also, it should be noted that retention time alone does not allow peaks to be unequivocally assigned. It has been found that the removal of lipid material prior to protein extraction dramatically improves the reproducibility of the chromatographic system and the lifetime of the columns. 

Salbe, A. D., and Levander, O. A. (1990). Comparative toxicity and tissue retention of selenium in methionine-deficient rats fed sodium selenate or L-selenomethionine. /. Nutr. 120, 207-212. 

In humans, whole body retention studies following oral administration of sodium selenite have indicated that selenium elimination is triphasic (Thomson and Stewart 1974). During the initial phase, which lasted about 1 week, elimination of selenium was rapid, with a half-life of approximately 1 day (Thomson and Stewart 1974). In the second phase, which also lasted approximately 1 week, selenium elimination was slower, with a half-life of 8-9 days. In the third phase, selenium elimination was much slower, with a half-life estimated to be 115-116 days. The first two elimination phases correspond to the fecal elimination of nonabsorbed selenium and the urinary excretion of absorbed but unutilized selenium (Thomson and Stewart 1974). Selenomethionine elimination is also triphasic however, its terminal half-life is longer than that of sodium selenite. The average half-lives of selenomethionine for the three phases were measured to be approximately 0.4-2, 5-19, and 207-290 days, respectively (Griffiths et al. 1976). 

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