3.2.5. Calibration of data
Solid-phase extraction py-MCM-48 was performed for a series
of solutions containing of nickel or lead ions at a concentration
of 10–250 ng mL1. The correlation coefficient was 0.9997 for nickel
and 0.9996 for lead ions. To determine the limit of detection
(LOD) of the proposed method for nickel and lead ions, 500 mL aliquots
of a blank solution (n = 10) were passed through the column
under the optimal experimental conditions. The LOD values with
py-MCM-48 were 0.14 and 0.11 ng mL1 for nickel and lead ions,
respectively. These results were obtained according to the equation
CLOD = KbSb/m (ACS Committee on Environment Improvement,
1980) for a numerical factor kb = 3.
3.2.6. Validation of the method
Two certified reference materials (NIST 1571 (Orchard leaves)
and NIST 1572 (Citrus leaves)) were used for the validation of
the proposed method. As Table 2 shows a good correlation was obtained
between the estimated content and the one found by the
present method. The concentration of nickel and lead that obtained
by py-MCM-48 was compared with the standard method. For this
reason, the concentration of nickel and lead was determined at
optimum conditions according to the earlier report (Bezerra, Santos,
Lemosc, Korn, and Ferreira, 2007). Table 3 shows the results
of nickel and lead determination in two selected samples by present
method and reference method. As can be seen, good correlation
was achieved between estimated content by present method and
reference method. Therefore, py-MCM-48 can be used as a confident
solid-phase for extraction and determination of nickel and
lead in food samples. The results indicate that the proposed method
for lead and nickel is not affected by potential interferences
from the major matrix elements of the analysed plant samples.
3.2.7. Determination of nickel and lead in real environmental samples
Since, natural samples have complex matrices, non-specific
background absorption caused by interfering species of the sample
matrix. To reduce this undesirable effect, mesoporous silica was
applied for selective sorbent for nickel and lead extraction in pH