Mass spectral determinations of the folic acid content of fortified breads from Chile

Sixty-four samples of fortified bread that were collected from 50 bakeries within the vicinity of Santiago, Chile were assayed for their folic acid content using a high-performance liquid chromatography-mass spectrometry (LC-MS) procedure with stable-isotope dilution. A ¹³C₅ analogue of folic acid was spiked into each sample as an internal standard and the analyte was extracted from bread into a phosphate buffer, purified on a solid phase cartridge, and analyzed by LC-MS in the negative ion mode using electrospray ionization. The relative standard error for the precision of the method was 3.8% based on the analyses of five replicate samples. The accuracy of the method was determined using a standard method of addition of the analyte into bread samples and folic acid was quantified over a concentration range that bracketed the fortification levels (100-900 ng g^-1 of bread). A subset of bread samples (n = 14) was also assayed using a microbiological assay (L. casei) and the results of these analyses were compared with the LC-MS determinations. The mean variation in the values as determined by the microbiological assay and the LC-MS method was on the order of 10%. Overall, it was found that in 38% of the bakery samples, the concentrations of folic acid were within the target values as specified by the program (151 and 264 μg g^-1). Nineteen percent of the samples had folic acid concentrations that were below 151 μg g^-1 and 43% of the samples exceeded the upper level.