3.1.1.3. Elution. Three elution methods were performed:
(1) HCl 1M; (2) HCl/methanol (1/99); and (3) H2SO4 0.1M. The highest recovery rates were obtained with HCl 1M as had been reported by Chinnici et al. (2005) with fruit juice.
3.1.1.4. Recoveries. To establish the efficiency of the organic acids SPE, the method was applied to a mixture of standard solutions. The results are shown in Table 3. This procedure was also performed on a mixture of organic acids added to brewed coffee (spiking). Table 3 shows the recoveries of these carboxylic acids after applying SPE method to brewed coffee.