However, when analyzing B12 at low concentrations, an additional standard curve using breast milk as matrix for the expected low B12 range below the recommended calibration range should be analyzed with the samples to ensure accuracy of the results. The B12 recovery of NIST SRM 1849 formula of 91.6% again demonstrates some interference possible due to the milk based matrix. The relative standard variation of ±3.3% shows high precision of the measurement..