Development of a new clean-up method for the determination of 5-methyl-tetrahydrofolate in milk samples using a sol-gel ß-lactoglobulin column

The specific forms of folic acid, a vitamin of the B-group, are generally determined in foods after sample clean-up using affinity columns containing folate binding protein covalently bound to a solid support material. The new approach described in the present paper is to isolate the target analyte by using the less costly milk protein ß-lactoglobulin, entrapped in the pores of a sol-gel glass. Sol-gel ß-lactoglobulin columns were included in a clean-up procedure developed to determine 5-methyl-tetrahydrofolate in milk samples. Concentrations of 5-methyl-tetrahydrofolate in milk samples with different fat contents ranged from 31 to 70 ng/ml. Repeated use of the ß-lactoglobulin columns for sample preparation resulted in a decrease of analyte recovery. However, due to the high column to column reproducibility good results were obtained when the standard addition method was performed with columns which had already been used for the same number of sample clean-ups. Œ 2005 Springer Science + Business Media, Inc.