Furthermore,
the extracts prior to the clean up step are various mixtures containing
different substances coming from animal and vegetable
tissues. Polyamide resin used in SPE cartridges adsorbs polar
compounds containing groups that can be protonated. Since the
sample extract is at pH 2 before the SPE step, the dyes are adsorbed
to the polyamide stationary phase by Van der Waals’ interactions.
Other hydrophilic substances can mask SPE interaction sites by
reducing their binding power for the dyes and consequently
reducing the capacity of the cartridges. Furthermore, some substances,
as amaranth, are strongly restrained by SPE cartridges and
the ammonia solution used for elution could be insufficient for its
release (low recoveries). For solid food matrices, LOQ values
calculated as 10 the standard deviations of blank noise were
10 mg kg1 for groups AeC and 5 mg kg1 for group B.