Analytical curves for aqueous standards at pH
3.0 containing between 2 and 1000 ng ml−1 of the
five PUHs, prepared according to the procedure
described in Section 2.4, were obtained by plotting
the analyte peak area of their parent forms
against the analyte concentration. The analytical
figures of merit for a sample volume of 10 ml and
the m/z values used for identification/quantitation
are summarized in Table 2. The linear range was
similar for all herbicides (2–750 ng ml−1),
fluometuron excepted (20–1000 ng ml−1). Detection
limits were calculated as the minimum concentration
providing a chromatographic signal
three times higher than background noise. The
precision of the method (as R.S.D.) was checked
using 11 standards containing all herbicides at a
concentration of 50 ng ml−1, always lower than
8.5%.