2.2. Nitrite and nitrate determination
The nitrite and nitrate contents of edible bird’s nests were
determined using the ion chromatography system. This
method was based on Malaysian Standard MS 2509:2012 (P),
Dionex application note 133 and Dionex application update
131 [16]. The edible bird’s nest extracts were prepared by mixing
of 0.5 g of powder with 20 ml of ultrapure water (1:40 w/v).
The mixture was immersed in a water bath at 80 C for 30
min, followed by centrifugation with a centrifuge (accuSpinTM
1, Fisher Scientific, Germany) at 3500 rpm for 15 min. The
supernatant was filtered through a 0.45 lm filter. A 20
ll of filtrate or extract was injected into an ion chromatography
(ICS-90, Dionex Corporation, USA) for analysis. All analyses
were performed in duplicates. A five point external
calibration curves for seven standard anions were constructed
with high linearity (R2 = 0.999–1.0). Standard curves were
used for nitrite and nitrate identification and quantification
of edible bird’s nests. The instrument detection limit was at
0.1 ppm. The Chromeleon 6 chromatography software was
used to compare the data from edible bird’s nests to standard
and automatically converted each peak area in a chromatogram
to concentration following Eq. (1):
A ¼ C V F 1000
W 1000 ð1Þ
where A = amount of nitrite or nitrate in the sample, lg/g;
C = amount of nitrite or nitrate in the sample obtained from
the calibrated curve, mg/l; V = volume of sample solution, ml;
F = dilution factor of sample solution; W = weight of sample, g.
2.3