EC was
determined according to the AOAC official method 994.07
with some modifications (AOAC 1997). The d5-EC was
used as the internal standard instead of n-propyl carbamate.
GC/MS conditions were revised to separate the d5-EC peak
from EC peak and shorten a run time. To develop analytical
methods depending on food composition, samples were
classified into four matrices, which include non-fatty liquid
(apple juice), proteinous liquid (milk), alcoholic beverage
(Soju, ~20% ethanol), and non-fatty solid (rice porridge).
Apple juice matrix was firstly neutralized using 1 N
sodium hydroxide solution and then 10 g of neutralized
sample was mixed with 30 mL of distilled water and then
5 g of sodium chloride was dissolved in it. After spiked
with 100 ng of d5-EC, it was loaded into a Chem Elut SPE
column. After 4 min of equilibration, EC was eluted with
160 mL of methylene chloride at a rate of 1 drop per second.
The eluent was concentrated to about 2~3 mL using a
rotary evaporator, transferred into v-vial, and further concentrated
to 1 mL under a gentle stream of nitrogen. Each
sample was extracted and analyzed by GC-MS in triplicate.
The milk and soju were extracted using the above method
with slight modification. Milk was centrifuged to remove
proteins before loaded to the SPE column. Soju was diluted
into 5% alcohol content to improve chromatographic resolution