The methods were validated for this kind of matrix. All validation
parameters are shown in Table 1. Linearity was assessed from
the calibration curves obtained at five concentration levels of each
compound. The correlation coefficient and linearity coefficient
were also evaluated, indicating good linearity in the working range
(r 0.990 and LC 95%). The sensitivity of the method was evaluated
by the limits of detection (LOD) and quantitation (LOQ). The
methods and analytical techniques used were very sensitive for the
compounds studied. Accuracy was measured by spiking a sample
with each of the analytes of interest at three different concentration
levels (low, medium and high in the range calibration) in triplicate.
Reference materials were also used to assess accuracy in the analysis
of mineral elements. The results are the average of all the
measurements. The methods used showed good recoveries, from
89% (lactose) to 109% (L-malic acid). The standard deviation of these
replicates was used to determine repeatability. Reproducibility was
calculated by measuring the same standard sample on three