The leftover blood samples were obtained from the local
hospital. The whole blood samples (1 mL) were added to 4mL of
the mixture solution of concentrated nitric acid and concentrated
perchloric acid (3:1 v/v) [30] and heated to near dryness. The
sample solution was then filtered using a 0.45mm member
filter.
Forall cases, thefilteredsolutionwas dilutedwith 0.1Mammonia
buffer at pH 11 before measurement. Fortunately, after preparation
of the real samples, the solution obtained was colorless. Therefore,
there was no interference effect from color of sample.