between determined and certified values at the 95% confidence
level. For each sample, duplication tests were repeated 20 times a
day for intra-assays and repeated for 20 consecutive days in the
same manner (three duplicates per day) for interassays. The
relative standard deviations (RSDs) of intra- and interassays
were 6.15 and 6.62% for Ca, 4.35 and 5.22% for Cu, 4.98 and
6.30% for Fe, 4.81 and 6.49% for Mg, 4.98 and 6.30% for Mn,
and 4.98 and 6.30% for Zn, respectively. These coefficients of
variation (CVs) were acceptable for clinical sample detection
(CV < 7%), although the average interassay CV (6.06%) is slightly
higher than that of the intraassay (5.07%).
Recovery tests were performed by adding diluted stock trace
element solutions for accuracy assessment according to standard
recovery test protocols. In this experiment, diluted singleelement
stock trace element solutions (with 0.5% HNO3) of
low, medium, and high concentrations were added and analyzed
for five replicates. Recovery (%) is calculated as the ratio
of the recovered concentration and added concentration, and
average recovery (%) is the mean of high, medium, and low
concentrations of standard materials. The results in Table 4
indicate recoveries of different added concentrations ranging
between 90.0 and 109.3% and average recoveries of each
element ranging from 96.2 to 103.4%, which are superior to
the ICP-MS results reported by Montesinos et al. (20). Moreover,
the RSDs of recovery, including low, medium, and
high concentrations of each trace element, were sufficiently
low (<2.5%) (see Table 4).
Limits of Detection. The limits of detection (3σ/S) and quantification
(10σ/S) are 1.5 and 5 μg L-1 for Ca, 3 and 9.8 μg L-1 for
Cu, 2.2 and 7.3 μg L-1 for Fe, 1.8 and 6 μg L-1 for Mg, 2.1 and
7 μg L-1 for Mn, and 1.3 and 4.3 μg L-1 for Zn, respectively. The
detection and quantification limits were calculated according to
International Union of Pure and Applied Chemistry (IUPAC)
recommendations, where σ is the standard deviation (SD) of the
calibration blank (n = 10) and S is the slope of the analytical
curve. Although the detection limits are poorer than those of
ET-AAS and ICP-MS in milk sample determination (21), the
limits of detection and quantification for Fe, Cu, and Zn are
higher than those from earlier developed FAAS techniques and
even reached the detection limit levels of ICP-OES (22, 23). The
other two elements had similar sensitivities to traditional FAAS
methods in the milk matrix (5).
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