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No. AD-0232
Table 1: Microwave digestion program
.
Quantitative analysis of fruit juice samples
The analytical results of 15 elemental contents in
different fruit juices were listed and compared to WHO
and US EPA guidelines for drinking water in Table 3.
Six elements (As, Ba, Cd, Cr, Cu and Pb) are regulated
by both authorities. Fe, Mn and Tl are only regulated by
EPA, while Ni is only regulated by WHO.
Barium, Chromium and Copper are regulated by WHO
and US EPA but with different guideline values. All
three elements were detected in the four fruit juice
samples. The concentrations determined were much
lower than the control limits.
Arsenic, especially in its inorganic form, is known to be
one of the most toxic trace elements present in the
environment. The As concentrations in the fruit juices
measured were below the limit of 10 µg/L set by both
WHO and US EPA. The results showed that the Apple
juice contained highest As content of 1.49 µg/L,
followed by mango juice and guava juice of 0.96 µg/L
and 0.393 µg/L, respectively. As was not detected in
yuzu juice.
Cadmium is a human carcinogen and it is toxic to
kidneys, skeletal and respiratory system. According to
the WHO and EPA guidelines, Cd concentration in
drinking water must be lower than 3 and 5 µg/L,
respectively. About 0.1 mg/L of Cd was detected in
apple, mango and guava juices, which is well below the
guideline values set by WHO and US EPA.
Lead is a well known toxic heavy metal which could
affect body systems such as gastrointestinal and
cardiovascular systems through cumulative exposure.
Pb was not detected in the fruit juice samples, except
for guava juice. The measured level was 2.45 µg/L,
which was below the guideline values of 10 and 15 µg/L
from WHO and EPA, respectively. The Pb detected in
the guava juice may indicate that there could be
possible contamination during the production or
processing.
Calibration linearity and detection limits
Calibrations of all targeted analytes show good
linearities with r > 0.9995 as shown in Table 4. LODs
and LOQs were calculated by 3 and 10 times the
standard deviation of calibration blank.
Results and Discussion
Table 2: Analytical conditions and ICP-MS parameters
Recovery and precision
Method recovery and precision were assessed by
spiking 5 µg/L of each element into all four fruit juices
before sample digestion. Recovery rates of 89-117% in
apple juice, 88-105% in yuzu juice, 91-112% in mango
juice and 89-110% in guava juice were obtained,
indicating the robustness of the ICP-MS method to
handle a variety of fruit juices shown in Table 5. Good
analysis precisions were achieved with %RSD less than
2.5 for three replicates.
Analysis stability and reproducibility
Analysis stability of the method was assessed by
analyzing a mixed standard of 5 µg/L continuously. The
measurement was taken at every 30-minute interval
and recovery was calculated. Figure 2 shows the
stability of the 15 targeted elements over 5 hours, with
all normalized recovery values within the range of 80%
- 120%.
The internal standards (Ho, Rh and Y) intensity were
plotted in Figure 3 to monitor the overall instrument drift
normalized to t=0. Throughout the 5 hours, the
intensities drift was less than 6%, demonstrating the
excellent system stability.
Furthermore, day-to-day reproducibility of measured
concentrations was checked using apple juice and
mango juice samples on two consecutive days under
the same analytical conditions. The percentage
variation of the elements measured on different days
were all within 20%, with majority of the analytes below
10%, indicating good reproducibility and robustness of
the method.
Step Time (min)
Ramp to 180
o
C 15
Hold at 180
o
C 10
Cool down 15
Parameter Setting
RF Power 1.20 kW
Sampling Depth 5.0 mm
Plasma Gas Ar 8.0 L/min
Auxiliary Gas Ar 1.10 L/min
Carrier Gas Ar 0.70 L/min
Torch Mini-Torch
Chamber Cyclone Chamber
Chamber Temp. 5
o
C
No. of Scans 10 times
Cell Gas (He) 6.0 mL/min
