2.7. Analytical quality control
Recoveries were measured by adding pure standards
to strawberry and black currant samples prior to
S. HaÈkkinen et al. / Food Research International 32 (1999) 345±353 347
extraction and hydrolysis. The recoveries were good or
tolerable (70±96%) for most of the compounds studied
(for details, see HaÈ kkinen et al., 1998). In the calcula-
tion of the ®nal results, the recoveries of the pure stan-
dards were not taken into account.
To study repeatability (within-day precision) of the
HPLC method, a hydrolyzed black currant sample was
analyzed 6 times within 1 day. The coecients of varia-
tion (CV) were between 5.4 and 7.3% (HaÈ kkinen et al.,
1998). Within-laboratory reproducibility (day-to-day
precision) of the whole method (including sample
extraction and hydrolysis plus HPLC analysis) was stu-
died by duplicate analyses of a freeze-dried black cur-
rant sample on 6 days during a period of 6 weeks. The
CVs were between 7.7 and 19.5% for the main phenolics
present in black currant (HaÈ kkinen et al.).